The last two years have seen significant progress in investigating trends in the mesosphere, thermosphere and ionosphere but also some new puzzles have been created. Important part of the progress is finding that the CO2 trend in the lower thermosphere is remarkably higher than expected. Also new information on some other experimental trends helped to improve the global trend scenario and our understanding of long-term trends in the upper atmosphere. Significant progress have been reached in modeling the long-term trends; in some parameters the agreement with observed trend sis now not only quantitative but also qualitative. All that will briefly be reviewed.

The German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF) has
launched a research initiative in 2013/2014 called ROMIC (Role of the Middle Atmosphere in Climate). The aim of ROMIC is to improve our understanding of long term variations in the stratosphere, mesosphere, and lower thermosphere and to investigate their potential role for climate changes in the troposphere. This includes to study coupling mechanisms between various layers and the relative importance of anthropogenic and natural forcing, e.\ g., by the Sun. Scientists at a total of 15 research institutes in Germany are involved and cover a large range of experimental and theoretical topics relevant for ROMIC. Some scientific highlights from the research projects within ROMIC will be presented.The German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF) has launched a research initiative in 2013/2014 called ROMIC (Role of the Middle Atmosphere in Climate). The aim of ROMIC is to improve our understanding of long term variations in the stratosphere, mesosphere, and lower thermosphere and to investigate their potential role for climate changes in the troposphere. This includes to study coupling mechanisms between various layers and the relative importance of anthropogenic and natural forcing, e.\ g., by the Sun. Scientists at a total of 15 research institutes in Germany are involved and cover a large range of experimental and theoretical topics relevant for ROMIC. Some scientific highlights from the research projects within ROMIC will be presented.

We present observations of the energy budget and composition of the mesosphere and lower thermosphere (MLT) over the past 15 years observed by the SABER instrument on the TIMED satellite. Natural variability is evident on timescales ranging from days (e.g., harmonics of the solar rotation period) to decades (e.g., the 11-year solar cycle). Trends in MLT carbon dioxide have been observed in the SABER data record, illustrating the truly “global” nature of global atmospheric change. A reconstruction of the infrared energy budget in the thermosphere extending back 70 years has also been developed. From this reconstruction we further evaluate the magnitude of solar variability from one solar cycle to the next. We have the remarkable result that the total infrared energy radiated by the thermosphere varies by only a small amount from one solar cycle to the next. For solar cycles 19 to 23, solar cycle 23 was in fact the strongest in terms of radiated infrared energy. Lastly, we look to the future and discuss the prospects and priorities for continuing the space-based data record of MLT temperature, composition, and energetics. The SABER-II instrument will be presented and a discussion of a new mission to explore the “heat sink” region of the thermosphere will be given.

During the past two decade, significant advancement has been made to understand the long term trends caused due to anthropogenic activities and that of natural variability in the whole atmosphere from ground to thermosphere. A global picture of the temperature response to GHGs increase and solar activity in the mesosphere and lower thermospheric regoin is presented with respect to geography, period of analysis and seasons. The discrepancy in the solar signal of temperature obtained by experimental data and the model results over the equatorial regions is still unresolved.    In this talk, an update of the long-term trend and solar signal in temperature of the MLT-region has been made based. The question of break in trend as a result of ozone recovery is briefly touched upon. However, now the major challenge is in the interpretation of the various reported results which are diverse and even indicates latitudinal variability. 

Ozone has significant contribution in changing the radiative forcing and temperature in the lower and middle atmosphere by trapping outgoing long wave radiation at 9.6 μm. Thus, it is very important to study the ozone vertical variability and transport mechanism in both stratosphere and troposphere. It has been shown that ozone loss leading to stratospheric cooling and hence changes in the circulation. However, recent studies revealed that the ozone recovery started and is expected to be at the same levels as that of 1980’s by 2050. In the present context we have given special emphasise to investigate ozone, water vapour and temperature long-long trends in a changing climate in the upper troposphere and lower stratosphere (UTLS) region over Indian sub-continent For this we have used multi satellite (Upper Atmosphere Research Satellite (UARS, 1992 – 2005)), (Aura Microwave Limb Sounder (MLS, 2004-2015), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER, 2002-2015) on board TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) observations. The long-term trends observed from these satellite observations has been further confirmed using the long-term ground based ozonesonde observations available from the three Indian stations (Delhi, Pune, and Trivandrum) for a period of 1969 – 2015. In general, ozone minimum and maximum is observed in the upper troposphere and lower stratosphere, respectively. Initial results revealed a significant raise in the altitude of ozone minima when compared to that observed during 1980’s in the upper troposphere. The altitude of ozone maximum also show increasing trend in recent decade compared to 1980’s.

                                                                                              ABSTRACT

               “Mesopause” is the altitude of absolute temperature minimum in the MLT (Mesosphere and Lower Thermosphere) region of terrestrial atmosphere. In the present study, the long term (2002-2012) data of monthly averaged zonal mean temperature and ozone volume mixing ratio (O3 vmr) obtained from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite are used to investigate the influence of solar cycle (during 23-24 solar cycles) and chemistry on tropical (10°N-15°N) mesopause variabilities. It is evident that the mesopause temperature and O3 vmr are positively correlated with 11 year solar cycle (F10.7 solar radio flux) due to the corresponding changes in CO2 and O. It is found that the tropical mesopause temperature is higher in September (~190 K), slightly lower in May and July (~185 K), and lowest (~175–178 K) in other months during 2002-2012. Also the mesopause height is varying between ~95 km (November-April) and ~99-100 km (May-October). The mesopause ozone is larger (~10-12 ppmv) during equinoxes and smaller (~4 ppmv) during solstices for all these years. Further it is clearly evident that the CO2 causes cooling (the only cooling mechanism) and O3 causes heating at 15 μm infrared emission (IR) in the mesopause region. In addition, the net heating rates due to (i) solar heating by O2 and O3, (ii) chemical heating due to seven major exothermic reactions, (iii) O3 long wave (IR) radiative heating and (iv) CO2 cooling rates are being used in the present study. 

In the vertical coupling of the different regions of the Earth’s atmosphere, whole atmospheric science community unanimously concurs the profound role played by gravity waves. Divergence/convergence of the energy and momentum fluxes carried by the gravity waves accelerate/ decelerate the mean flow which in turn partly responsible for the maintenance of QBO and SAO in the stratospheric and mesospheric region, which are the characteristic features of the equatorial middle atmosphere. To quantify the role of short period gravity waves in controlling the dynamics of the MLT region, more than ten years of continuous meteor radar observations during June 2004- Dec 2013 are extensively used. The gravity wave momentum fluxes in the Mesosphere Lower Thermosphere (MLT) region are estimated over Trivandrum (8.5°N, 78°E), a low-latitude station in India during aforementioned period. The radial velocity variances in the 82-98 km height region, which are mainly caused by the gravity waves, measured by the meteor radar are used to determine the gravity wave momentum fluxes. Using the estimated gravity wave momentum fluxes their contribution in driving the mesosphere semiannual oscillation (MSAO) during June 2004 to Dec 2013 is quantified. The results will be discussed in detail in the conference.

The Leibniz-Institute of Atmospheric Physics operates medium frequency (MF) radars for more than one solar cycle to monitor the middle atmosphere at polar and mid-latitude regions. MF-radars allow continuous observations of this atmospheric region by partial reflections due to the presence of sufficient electron density and its fluctuations for the given radar frequency. The actual altitude coverage generally depends on the current state of the atmosphere controlled by the sun, dynamics as well as high natural variability of the mesosphere like e.g. particle precipitation events. At times, the latter are exceptionally frequent in the polar latitudes, partially reaching up to 50 percent occurrence rate with the tendency of appearing in single or multiple distinct layers. We will present examples of such layered mesospheric perturbation events observed with MF radars, their influence to the measurements and further analysis results. Furthermore we will present the statistical analysis of these events for the mentioned period and their relationship to other radar phenomena.

Significant progress has been made on the NCAR Whole Atmosphere Community Climate Model - eXtended (WACCM-X) during the past two years.  WACCM-X is the thermosphere-ionosphere extension of WACCM, which in turn is the whole atmosphere version of the Community Atmosphere Model (CAM), a major component of the Community Earth System Model (CESM).  Thus, WACCM-X not only couples the entire atmosphere-ionosphere system, but can be coupled to ocean, ice, and land models as well.  Recent additions and improvements include completion of ion-neutral chemical processes, updated heating and cooling rates, adjustments to atmospheric dynamics to account for variations in mean molecular mass, equatorial and auroral electrodynamics, and fully 3D ionospheric transport.

We have conducted simulations of anthropogenic change by comparing pre-industrial, present day, and future scenarios for carbon dioxide, methane, ozone, sea surface temperatures, and atmospheric response.  These largely confirm past work with thermosphere-ionosphere modeling and observation, showing that the upper thermosphere cools at a rate of several degrees per decade under present rates of carbon dioxide change, and that this change is largely driven by the effect of lower thermospheric cooling on scale heights.  Changes in middle atmosphere temperature, methane, and ozone, have much smaller effects on the thermosphere.  Thermospheric cooling causes the ionosphere to also contract to lower altitude, but with small changes induced in F-region density, and complex effects on ion temperature.  Whole atmosphere modeling has great power to fully explicate the coupling of these mechanisms, and, ultimately, the effect of dynamical changes throughout the system.

Thermospheric neutral winds are a key driver of the coupled thermosphere-ionosphere system and can be the most important driver when modeling ionospheric densities and temperatures. We present a climatology of thermospheric neutral wind components (meridional and zonal) measured with the 630.0 nm nightglow Fabry-Perot interferometer at Arecibo Observatory from 1980 to 2010. With these data set an empirical climatological model was developed that accounted for the dependencies of time and season as well as solar and geomagnetic activities. This also provides a means to extract the associated long-term trend simultaneously. These dependencies of the model are important for the understanding of any long-term changes related to geomagnetic and solar activity.

The main finding of this study was the detection of a seasonal and local time dependence of the response of the thermospheric neutral winds to solar and geomagnetic activity. In addition, there is a long-term trend in the thermospheric neutral wind, which can be of a larger magnitude than the variation found in the seasonal, solar cycle, and geomagnetic activity effects. A major signature of this trend over the last 30 years was an increase in the meridional northward component up to 1.4 m/s/year before midnight local time during the summer.

Gravity waves (GWs) play a key role for the dynamics of the middle atmosphere. Recent modeling studies have demonstrated that their dynamical and thermal effects extend well into the upper atmosphere above the turbopause (>105 km). Using general circulation modeling techniques incorporating the whole atmosphere GW parameterization of Yiğit et al. (2008) we show that GWs not only influence the general circulation of the upper atmosphere but they impact the spatiotemporal variability of the thermosphere. Currently, these GW effects are not included in long-term trend studies. Therefore, GW effects and the induced atmospheric variability should be taken into account as an important physical mechanism in the studies of the long-term trends in the middle and upper atmosphere. 

Upper thermosphere is a tenuous region compared with the lower atmosphere, yet its interaction with the outer space and its drastic variability have made it a very challenging domain for atmospheric modelers. Although increasing number of dedicated ground-based, aerial and space-borne missions to study this region is a promising sign for the improvement of current models at these altitudes, yet limited spatiotemporal coverage of related missions ties scientist’s hands with very limited observations, in particular at high solar/geomagnetic activity periods.

To compensate for this shortcoming we use ephemerides of NORAD-indexed objects observed over the past five solar cycles to study how the Earth’s space-atmosphere interaction region (SAIR) responds to solar activity. We present a computationally simplified technique that simultaneously solves the motion equations for Daily Decay Rate (DDR) and cross‐sectional area to mass ratio (A/m) of orbiters from consecutive two line element (TLE) records.

With this technique we evaluate more than 50 million TLE records to estimate (for the first time) A/m of more than 15,000 orbiters (including non-functional satellites and debris) and determine how DDR varies. We develop two models based on two widely used density models, i.e. NRLMSISE‐00 and DTM-2013, and compare the observed DDRs with them. Our results show consistency with previous studies in terms of general thermospheric behavior such as the thermospheric “Natural Thermostat”. We discuss possible sources of uncertainties in the results and provide some suggestions for the improvement of current models with the data that are already in hand.
 

The upper atmosphere carries weakly ionised plasma that is sensitive to influences from solar radiation and from interactions with the troposphere and stratosphere due to vertical coupling within the whole atmosphere. These signatures are visible in variations of electric currents flowing in the upper atmosphere. Electric currents have clear signatures in magnetic field observations both, on ground and in space. Therefore, geomagnetic observations reveal new insight into detecting effects from vertical atmospheric coupling monitored in the thermosphere.

One example is the detection of stratospheric warming events that are believed to create enhanced lunar tidal signatures, e.g., in the equatorial electrojet flowing at about 100 km altitude. These signatures, however, vary in longitude. We will present results from a study that investigates the effect of lunar tides and of stratospheric warming in the upper atmosphere based on magnetic data from ground and satellite observations.

Gravity waves (GWs) and solar tides (STs) are main constituents of the dynamical coupling between the atmospheric layers. To the largest part they are generated in the lower atmosphere. STs are large-scale waves that modulate all dynamical fields in the mesosphere and thus leave a strong imprint on the dynamics of the latter. Predominantly via momentum deposition GWs to a large extent control the mesospheric mean circulation. GWs and STs interact strongly with each other: STs modulate the propagation of GWs, while the momentum deposition by breaking GWs influences the amplitude and phase structure of STs in the mesosphere. So far general circulation models (GCMs) have described this interaction process with insufficient accuracy. Conventional GW parameterizations, although indispensable for capturing the effect of mesoscale GWs, neglect both the impact of the transience of the ST fields and that of horizontal gradients in the large-scale wind fields in the atmosphere. Recent work has investigated the GW-ST interaction in a coupled model for linear STs and nonlinear GWs, the latter described using fully interactive ray tracing. Corresponding results will be presented, showing the importance of wave transience and lateral propagation.

The Brewer-Dobson circulation is often quantified by the integrated transport measure age of air (AoA). AoA is affected by all transport processes, including transport along the residual mean mass circulation and two-way mixing. In global models, two-way mixing results from stirring by resolved winds and from unresolved parametrized and/or numerical diffusion.

We present a method to disentangle the effects of residual circulation transport, resolved two-way mixing and unresolved diffusion on AoA. The method is applied to global model data, and it is shown that the large spread in the simulation of AoA between models can in large parts be attributed to differences in the relative strength of mixing (i.e. the ratio of mixing mass flux to net mass flux between tropics and extratropics, which we define as the “mixing efficiency”).

Furthermore, we explore whether (resolved) two-way mixing and the residual circulation are coupled. This would be expected in a steady-state climate as the residual meridional velocity is then proportional to PV eddy mixing (in the absence of unresolved wave driving). A constant mixing efficiency is found for different climate states in equilibrium simulations with the ECHAM model. We use an idealized version of the ECHAM5/MESSy model system to further explore the relationship between residual circulation transport and mixing under different scenarios (e.g. different climate states, with or without additional parametrized wave forcing, steady versus transient forcing).

A better understanding of the processes that control AoA will help to reconcile current discrepancies between simulated and observed AoA and its long-term changes.

The upper branch of the Brewer-Dobson circulation (BDC) is only partly represented in state-of-the-art chemical climate models which mostly do not include the mesopause region, similar to chemical transport models which depend on the vertical domain of the applied analyses. As the atmospheric lifetime of some long-lived trace gases as for example CH4 or N2O is influenced by mesospheric processes, the representation of the upper branch in the model may have an impact on derived trends of such gases. The thermal and wind structure of this height region in the model strongly depends on the gravity wave drag parameterization and the chosen tuning parameters. Here we study the upper branch of the BDC with the KASIMA model which includes the mesopause region up to the lower thermosphere, when nudged to ERA-Interim analyses in the stratosphere. We adapt our Holton-Lindzen type GW drag parameterization in order to improve cross mesopause transport which is often observed after strong mid-winter sudden stratospheric warmings and analyze its impact on trends of mean age of air and long-lived tracers in the middle atmosphere.

The global stratospheric Brewer-Dobson circulation (BDC), with upwelling in the tropics and sinking motion above the poles, is expected to change with rising Greenhouse gas concentrations. A changing BDC, in turn, changes the stratospheric trace gas composition providing an important feedback via radiation and dynamics on climate change. However, trends in the BDC are largely uncertain, hitherto. Current climate models simulate a strengthening residual mean mass circulation throughout the stratosphere, resulting in decreasing mean age of air, the average transit time for an air parcel since entering the stratosphere across the tropical tropopause. Balloon-borne measurements collected over the last decades and satellite measurements with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) show show an inhomogeneous and  more complicated picture of mean age trends.

We present mean age and its trends from updated balloon- and satellite-based datasets and from recent model simulation with the Lagrangian transport model CLaMS driven reanalysis meteorology. Comparison between CLaMS simulated and observed age of air shows good agreement from a climatological point of view, as well as regarding inter-annual variability related to the QBO, decadal changes and long-term trends. We discuss the trends in mean age based on the combination of satellite and balloon measurements and the CLaMS model results, and particularly relate these age trends to trends in residual circulation and mixing.

We investigate the annual cycle of the radiation at the top of the atmosphere (RTOA) and of the surface energy budget on the basis of a general circulation model with intermediate complexity. The model is based on a standard spectral dynamical core and includes an idealized radiation scheme with continuous computation of energy fluxes. The surface energy budget is taken into account by means of a slab ocean with prescribed lateral oceanic heat flux convergence. The moisture budget is based on a new transport scheme and simple parameterizations of condensation and convection. Subgrid-scale parameterizations include gravity waves and turbulent diffusion. Each parameterized process is formulated in an energy conserving fashion such that the resulting numerical error of the mean RTOA is about 0.1 W/m/m. On the seasonal timescale, the annual variation of the RTOA is synchronous with an equally strong imbalance of the surface energy budget. We run the model either with or without orbital eccentricity. Either case exhibits a pronounced annual cycle of the outgoing long-wave radiation (OLR) of a few W/m/m, with the minimum occurring in the northern hemispheric winter. This variation results from the hemispheric differences in the distribution of land and ocean surfaces, which are characterized by different heat capacities and albedos. It is synchronous with an annual variation of the global-mean surface temperature of a few K. The implication of this finding is that long-term changes of the RTOA due to internal variability of the climate system are well possible. In particular, if the ocean absorbs heat while the global-mean surface temperature decreases, the RTOA is positive.
 

The SBUV series of instruments, although designed to measure stratospheric profile and total column ozone, have also been able to detect and characterize the global distribution of polar mesospheric clouds (PMCs) since 1978.  While the last SBUV/2 instrument was launched in 2009, NASA and NOAA are continuing the long-term monitoring of stratospheric ozone with the Ozone Mapping and Profiling Suite (OMPS) series of instruments.  OMPS carries two instruments that can detect PMCs.  The Nadir Profiler (NP) is similar to SBUV/2 in design, with a hyperspectral CCD detector.  Current operations use a 250 km x 250 km footprint, but future measurements will report 50 km x 50 km pixels within this field of view.  OMPS NP measurements can be processed with the current SBUV PMC detection algorithm.  Results based on 4 years of OMPS NP data from the Suomi NPP satellite will be shown.  The OMPS Limb Profiler (LP) makes limb scattering measurements looking backwards along the orbit using three parallel slits.  The hyperspectral data cover 290-1000 nm spectrally, and from 0 km to 85-100 km in altitude.  Individual bright clouds can be detected over 15-20 degrees in latitude due to the LP viewing geometry, which offers exciting possibilities for tomographic analysis.  The LP center slit measurements observe the same location as the NP measurements 7 minutes later, so that OMPS has the capability to perform “common volume” PMC analysis along every orbit.  Future OMPS measurements during the next 20 years will also be discussed.

The mesosphere is an interesting region for investigation of atmospheric trends, which are expected to be larger there compared to the troposphere. Mesospheric ice layers, observed as noctilucent clouds (NLC) from ground, are the visible manifestation of an extreme temperature state in the polar summer mesopause region. Temperature measurements in the middle atmosphere are very limited in time coverage and accuracy. Hence, indirect information, as provided by mesospheric ice particles, is valuable as it is known that they are very sensitive to background temperature as well as water vapor content.

Ground-based lidar instruments provide NLC occurrence frequency, brightness and altitude. The longest continuous NLC data set is acquired with our lidar at the Arctic station ALOMAR (69°N). The time series covers 22 years and contains about 2860 hours of NLC detections. NLC properties are impacted differently by solar and atmospheric parameters. In general, Lyman-alpha and stratospheric ozone impact all NLC properties, temperature at 83 km impacts mainly the NLC altitude. Strong NLC show increasing occurrence frequency and brightness from 1998 to 2015. Amongst the ice particle parameters, altitude is the longest measured property, first determined by optical triangulation in 1890. Since the early days of such investigations, the accuracy and data basis of NLC altitude measurements has been substantially improved. The overall mean altitude determined from our lidar observations is 83.3 km, which is surprisingly close to the historic values, and differs by less than the geophysical variability of 1.3 km. Since 1994 the altitude of strong clouds increased by only few meters per year.

Polar mesosphere summer echoes (PMSE) are strong enhancements of received signal power at very high radar frequencies occurring at altitudes between about 80 and 95km at polar latitudes during summer. PMSE are caused by inhomogeneities in the electron density of the radar Bragg scale within the plasma of the cold summer mesopause region in the presence of negatively charged ice particles. Thus the occurrence of PMSE contains information about mesospheric temperature and water vapour content but also depends on the ionisation due to solar wave radiation and precipitating high energetic particles. Continuous observations of PMSE have been carried out on the North-Norwegian island Andya (69.3°N, 16.0°E) since 1994. Seasonal mean values of PMSE occurrence for the time period June/July from 20 years of observations have been analysed for long term variations. The PMSE occurrence rate is positively correlated with the solar Lyman α radiation (however low significance level) and the geomagnetic Ap index.  After elimination of the solar and geomagnetically induced parts the PMSE data show a significant positive trend during the time interval from 1994 until 2015. This positive PMSE trend could be caused by an increasing trend of the mesospheric water vapor and/or a decreasing temperature trend.

Long-term changes of water vapour in the lower stratosphere inevitably affect the surface climate. Thus understanding such changes is of primary importance. The longest continuous data set is based on balloon-borne frost point hygrometer observations at Boulder. Overall this data set shows an increase in water vapour since the 1980s accompanied by large variability on short time scales (Hurst et al., 2011). Recently a merged satellite data set, covering the time period between 1988 and 2010, has been analysed showing a decrease of water vapour in the lower stratosphere (Hegglin et al., 2014). This discrepancy is difficult to reconcile. There might be problems with one data set or even with both. Also the local behaviour at Boulder might not be representative for the zonal mean behaviour, which is represented by the satellite observations. So far this has been assumed and the Boulder changes have even been considered to be globally representative. Here I present investigations of this aspect using both model simulations and observations.

References:

Hegglin et al. (2014), “Vertical structure of stratospheric water vapour trends derived from merged satellite data”, Nature Geoscience, 7, 768 – 776, doi:10.1038/ngeo2236. 

Hurst et al. (2011), “Stratospheric water vapor trends over Boulder, Colorado: Analysis of the 30 year Boulder record”, Journal of Geophysical Research, 116, D02,306, doi:10.1029/2010JD015065. 

The medium frequency radar deployed at Tirunelveli (8.7°N, 77.8°E) have been providing continuous data from the year 1993 to the year 2012 that helped to study the long term tendencies in the tidal variabilities in the MLT region. In the present paper we present the results of seasonal, interannual and long-term variabilities of lunar semi-diurnal tides in the upper mesosphere over Tirunelveli. The present study also included comparison with model values. The study shows that the tidal amplitudes are larger in the meridional components of the mesospheric winds than the zonal winds. The seasonal tendencies are similar in both the components. There are unusual amplitude enhancements in the lunar tide in meridional winds during the winters of 2006 and 2009, when major sudden stratospheric warmings (SSW) occurred at high latitude northern hemisphere, whereas zonal lunar tide does not show any clear association with SSW.  Vertical wavelengths of lunar tides in zonal and meridional wind are in the range of 20-90 km. Both zonal and meridional component attains a minimum vertical wavelength in the month of June while maximum in November and December. The monthly mean  zonal and meridional winds are subjected to regression analysis to study the tidal response to long-period oscillations, namely, quasi-biennial oscillation (QBO), solar cycle variation and El-nino southern oscillation (ENSO).  It is found the lunar tide in both zonal and meridional winds show significant QBO response, whereas zonal tide only shows significant negative response to solar cycle and positive response to ENSO. 

We have performed trend studies in the mesosphere in the period 1961–2013 with Leibniz-Institute Middle Atmosphere (LIMA) model driven by European Centre for Medium-Range Weather Forecasts reanalysis (ERA-interim) below approximately 45 km. LIMA adapts temporal variations of CO2 and O3 according to observations, and observed daily Lyman alpha fluxes.

The simulation of the thermal state at the summer upper mesosphere allows to investigate the impact on the morphology of ice particle related phenomena such as polar mesosphere clouds (PMC). The PMC characteristics deduced from LIMA are validated with various data sets from satellite (NOAA-SBUV, AIM-SOFIE) observations. Generally good agreement is found between the modeled long-term PMC variations and that derived from SBUV observations.

We investigate the role of trends in mesospheric water vapor and temperature that mainly force PMC trends. We show that water vapor and temperatures in the stratosphere/meso-  sphere/lower thermosphere vary none-uniformly with time. Especially, we analyze the contribution of varying concentrations of CO2 and O3 to the temperature trend in the mesosphere. It is important to distinguish between trends on pressure altitudes and geometrical altitudes, where the latter includes the effect of shrinking due to cooling at lower heights. As a highlight, we will present first results in analyzing the very first appearance of NLC in 1885 observed after the volcanic eruption of Krakatao in August 1883 that injected a tremendous mass of water vapor into the stratosphere.

Very short lived halocarbons, as bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I) are naturally produced in the oceans and are involved in ozone depletion in the stratosphere. Their global oceanic emissions, based on the projected input parameters of three different CMIP5 models (MPI-ESM-LR, CESM1-CAM5 and HadGEM2-ES) show an increase from 2006-2100 for the RCP 2.6 and 8.5 scenarios, which is most pronounced at high latitudes due to increasing temperature and wind speed. The predicted emission increases are up to 30 % for the RCP 8.5 scenario. We show that the projected emission increases will lead to enhanced stratospheric bromine and ozone depletion by the combination of increased halocarbon emissions and the increase of vertical transport into the tropical stratosphere.

The future emissions were calculated with fixed oceanic and atmospheric concentrations over a period of 120 years, which imply increasing oceanic halocarbon production. While the influence of future ocean productivity changes on the oceanic halocarbon production rates and concentrations are currently unclear, additionally, other halocarbon sources in the ocean due to anthropogenic influences need to be taken into account, further increasing the sources. The future emission estimates are needed as input for chemistry climate models to better evaluate the future entrainment of oceanic halogens into the stratosphere and their influence on the chemistry and the recovery of the ozone layer.

This presentation consists of two parts. The first examines whether the meteoric metal layers are sensitive indicators of long-term changes in the upper mesosphere. Output from the Whole Atmosphere Community Climate Model (WACCM) is used to assess the response of the Na, K and Fe layers across a 50-year period (1955-2005), while both model and observational data is used to assess the response of the Na and K layers to the 11-year solar cycle. K displays a much more pronounced response to atmospheric changes on a 50-yr time scale than either Na or Fe, with a predicted increase in column density of 3.5±0.4% decade^-1, mostly arising from the modelled cooling trend of -0.2 to -0.5 K decade^-1 between 80 and 100 km.

The second part examines the removal of the potent greenhouse gases SF₆, NF₃ and CFC-115 in the middle atmosphere. The D region electron concentration is determined using a new version of WACCM with over 300 ion-molecule reactions from the Sodankylä Ion and Neutral Chemistry model. Electron attachment is the major route for SF₆ removal, while photolysis and reaction with O(¹D) largely remove NF₃ and CFC-115. The SF₆ lifetime is (1305 ± 143) years, much shorter than the currently recommended value of 3200 years. The lifetime of NF₃ is (616 ± 34) years, and that of CFC-115 is (492 ± 22) years. Their 100-year global warming potentials are then 22,800, 20,100 and 7630, respectively.

The UVES echelle spectrograph of the Very Large Telescope at Cerro Paranal in Chile provides high-resolution spectra in the wavelength regime from 300 to 1100 nm with a maximum simultaneous wavelength coverage of about 400 nm. Since UVES has been regularly operated since April 2000, thousands of spectra originally taken for astronomical projects are available to study airglow variations on a time scale longer than a solar cycle. Taking data from two set-ups centred on 760 and 860 nm, we measured line intensities for several OH bands in order to derive band intensities and rotational temperatures for different upper vibrational levels v' as a function of solar activity and observing date. The results are compared with those derived from emission and temperature profile data of the radiometer SABER on the TIMED satellite taken since 2002. The discussion will also include an estimation of the contribution of non-thermal effects to the observed trends in the rotational temperatures. The OH intensities can be compared with UVES measurements of atomic oxygen and sodium lines. In agreement with the SABER data, the long-term variations in OH intensity and temperature derived from UVES data are dominated by the solar cycle, whereas secular trends are weak or even absent.

Causes of the difference in absolute values of the foF2 and hmF2 negative trends obtained by different groups are analyzed. Three causes are considered in detail: wrong choice of the initial data used to reveal trends and the absence of the allowance for seasonal and diurnal variations in the trends. The influence of the years of a deep solar activity minimum of 2008-2009 on the foF2 trends is studied. It is shown that the years of the minimum cause some distortion in the curves used to derive the trends. In general, the trends for the period till 2014 are slightly lower than for the period till 2006-2008 analyzed in the previous publications. However, after 2009 a well pronounced negative trend is seen. The time behavior of the slope k of the foF2 dependence on hmF2 is analyzed. Since foF2 depends strongly on the atomic oxygen concentration (roughly speaking it is proportional to [O]) and hmF2 depends on [O] weakly, the slope k of the foF2(hmF2) dependence should decrease with time if there is a decrease in the atomic oxygen concentration. The analysis of the foF2(hmF2) dependence on time for several inospheric stations and various seasons shows that the value of k systematically decreases from the “etalon” period (1958-1980) to later periods. That confirms the hypothesis proposed by the author earlier that the negative trends in foF2 are caused mainly by the decrease in the atomic oxygen concentration in the thermosphere. 

Calculations of long-term trends in the ionosphere are critically dependent on solar activity (solar cycle) correction of ionospheric input data. The standard technique is to compute the dependence on solar activity from the whole analyzed data set and analyze trend of deviations from solar activity dependence. However, if the solar activity dependence changes with time, the solar correction calculated from the whole data set may result in miscalculating the ionospheric trends.

As an ionospheric parameter we consider foE, which is equivalent to electron density maximum in the ionospheric E region. Here we use data of two European stations with the best long data series of parameters of the ionospheric E layer, Slough/Chilton and Juliusruh over 1975-2014 (40 years). Noon-time medians (10-14 LT) are analyzed. The trend pattern after removing solar influence with one correction for the whole period is complex. For yearly average values for both stations first foE is slightly decreasing in 1975-1990, then the trend levels off or a very little increase occurs in 1990-2005, and finally in 2006-2014 a remarkable decrease is observed. However, when the solar correction is calculated separately for the three above periods, we obtain a smooth slightly negative trend. While solar corrections for the first two periods are similar (even though not equal), the solar activity dependence of foE in th third period is clearly weaker.

Thus the stability of solar correction should be carefully tested when calculating ionospheric trends. This could also explain some changes of trends in time.

A simple method has been applied to extract 11-year running mean weighted δfoF211y and δfoF111y variations from June foF2 and foF1 monthly medians at Slough/Chilton and Juliusruh including observations in 2015. The geomagnetic control was shown to be valid. The dependence on geomagnetic activity has become more pronounced and explicit after 1990. The retrieved from routine foF1 ionosonde observations thermospheric parameters over the period of » 5 solar cycles were used for the first time to analyze the mechanism of foF1 and foF2 long-term variations. It was shown that the control was provided via two channels: [O] and [O]/[N2] variations. Geomagnetic activity controls the (O/N2 )11y ratio, while solar activity presented by (F10.7)11y controls [O]11y variations. Atomic oxygen manifests solar cycle and long-term (for some solar cycles) variations with the rising phase in (1965-1982) and the falling phase in (1982-2003). The empirical model MSIS-86 driven by Ap and F10.7 manifests [O]11y and (O/N2 )11y variations similar the retrieved ones including the period of deep solar minimum with a very low [O] in 2008. This confirms the basic idea that daytime mid-latitude foF1 and foF2 long-term variations had a natural (not anthropogenic) origin related to long-term variations in solar and geomagnetic activity.

Until about a decade ago the earth’s upper atmosphere was conventionally treated to be influenced by solar radiation.  Owing to primarily the very low solar activity of cycle 24, several new insights have emerged in the recent past on the upper atmospheric influence with respect to both solar and lower atmospheric forcings owing to continuous and systematic measurements of optical daytime airglow emission measurements at multiple wavelengths carried out during 2000 – 2006 and from 2010 – present.  It is seen that during high solar activity the daytime airglow emission intensities vary with the variation in the solar flux indicating an unambiguous signature of solar forcing on the upper atmosphere.  With reduction in the solar activity, large scale (planetary-size) waves from the lower atmosphere show their influence in the upper atmospheric parameters such as the optical emission intensities and GPS-TEC. Whereas, in the smaller scale (e.g., gravity wave) regime number of waves in the upper atmosphere increase with the increase in solar activity.  With regard to the diurnal variability of the optical emissions, there seems to be a reasonable symmetric behaviour with respect to noon during low solar activity period, whereas their behaviour seems asymmetric during high solar activity, which is attributed to be due to the greater electrodynamical influence of the equatorial processes in the low-latitude ionosphere thermosphere system. These new results obtained recently reveal greater insights into the fundamental nature of coupling between the thermospheric regions in the daytime and their solar activity dependence.

This study used extensive GNSS-derived Total Electron Content of the ionosphere data during the period 2001 - 2012 to examine the isolated and un-explained earlier observations of equinoctial asymmetry and longitudinal variation of ionospheric irregularities over the African low latitude  region. The data were obtained from Libreville, Gabon (0.35 deg. North, 9.68 deg. East, geographic, 8.05 deg. South, magnetic), Mbarara, Uganda (0.60 deg. South, 30.74 deg. East, geographic, 10.22 deg. South, magnetic), and Malindi, Kenya (2.99 deg. South, 40.19 deg. East, geographic, 12.42 deg. South, magnetic). The rate of change of total electron content index greater than 0.5 TECU/Min were considered as severe ionospheric irregularities.  For most of the times, the strength of ionospheric irregularities in March equinox were greater than those during September equinox over East Africa and an opposite observation was made over West Africa.  
These asymmetries might be due to the direction of 
the meridional winds during equinoxes over the different stations. 
Severity of ionospheric irregularity reduced from west towards the east. This might have been related to the decreasing geomagnetic field strength from east towards the west. This is the first study that reveals, the equinoctial asymmetry is different in the West and East African sectors.

Nitric Oxide (NO) has been observed by the Solar Occultation For Ice Experiment (SOFIE) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite for 9 continuous years throughout the thermosphere, mesosphere and stratosphere. In this contribution we explore the long term changes of NO, both in volume mixing ratio and number density, and relate them to the responsible physical mechanisms, such as solar radiation and energetic particles. We further investigated the dynamical downward transport of NO from the lower thermosphere into the middle atmosphere during winter time conditions. These results are compared to the modelled NO output of the Whole Atmosphere Community Climate Model (WACCM) and plausible reasons for differences are discussed. 

We applied atmosphere-ocean chemistry-climate model (AOCCM) SOCOL to simulate the changes in ozone layer and surface climate during the first half of 20^th century, which is characterized by steady increase of the solar activity. The performed ensemble simulations are driven by anthropogenic and natural forcing taken in different combinations. The forcing from energetic precipitating particles includes NO_x and HO_x production by auroral and radiation belts electrons, solar protons and galactic cosmic rays. The ionization rates inside the model domain (below 80 km) and influx of NO_x from the thermospheric source were taken from the dataset prepared for IPCC CMIP-6 project. The comparison of the ozone and climate evolution obtained from the performed model experiments allows estimating the contribution of energetic particles to the observed warming during earlier 20^th century.  Preliminary results showed that the contribution of radiation belt electrons to the surface climate is rather small. The analysis of the influence from auroral electrons is ongoing.

Carbon dioxide measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument between 2002 and 2014 were analyzed to reveal the rate of increase of CO2 in the mesosphere and lower thermosphere. The CO2 data show a trend of ~5% per decade at ~80 km and below, in good agreement with the tropospheric trend observed at Mauna Loa. Above 80 km, the SABER CO2 trend is larger than in the lower atmosphere, reaching ~12% per decade at 110 km. The large relative trend in the upper atmosphere is consistent with results from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). On the other hand, the CO2 trend deduced from the Whole Atmosphere Community Climate Model remains close to 5% everywhere. The spatial coverage of the SABER instrument allows us to analyze the CO2 trend as a function of latitude for the first time. The trend is larger in the Northern Hemisphere than in the Southern Hemisphere mesopause above 80 km. The agreement between SABER and ACE-FTS suggests that the rate of increase of CO2 in the upper atmosphere over the past 13 years is considerably larger than can be explained by chemistry-climate models. I will introduce the newly derived gravity wave trend from the v2 SABER temperature profiles till 2015. Significant gravity wave trend of 20%/per decade is observed at southern high latitudes.

In the present study, we focus on low latitude middle atmospheric dynamics over Thumba (8.5⁰ N, 77⁰ E), a low-latitude rocket launching station in India. Several campaigns were carried out at this site to investigate the middle atmospheric dynamical phenomena using balloon, rockets and radar observations. Many of the investigations focused on vertical coupling of the lower and middle atmosphere through spectrum of propagating waves. Climatology and long-term trends of winds and temperature using 45 years of radiosonde observations in the troposphere, 26 years of rocket observations in the stratosphere and lower mesosphere and 11 years of meteor radar observations in the mesosphere and lower thermosphere is discussed. The long period oscillations and their variability in the middle atmospheric winds viz., quasi biennial oscillation (QBO), stratospheric semi-annual oscillations (SSAO) and mesospheric semi-annual oscillations (MSAO) are discussed. The general features and propagation characteristics of tides, gravity and planetary waves (including equatorial waves) are investigated including their role in driving the QBO, SSAO and MSAO through wave-mean flow interactions. A detailed depiction on how these waves couples the different layers of the atmosphere and how they interact among themselves through wave-wave interactions is also presented.   The significance of the present study lies in synthesizing the middle atmospheric research carried out for last four decades at Thumba using host of experiments and campaigns and its contributions towards understanding the middle atmospheric processes.

The South Atlantic Magnetic Anomaly (SAMA), where the total field intensity is low, is one of the most outstanding features of the geomagnetic field, presently occupying the area between South America and South Africa. SAMA is dynamic and its strength, shape and size vary in different time scales. The SAMA center has a westward drift may be related to the westward drift of the geomagnetic axis of the Earth. The low magnetic field on SAMA zone facilitates the entrance of high energy particles from the magnetosphere which may affect ozone content through its effect on NO compounds. In order to analyze this possible effect,  the monthly mean of  total ozone content  (TOC) and of ozone content in three different layers of the middle atmosphere of Cachoeira Paulista station (22.68°S,  315.00 °E)  included in the network of TOMS,  is used, covering the period between 1980 to 2015.

The mechanisms of solar influence on Earth's climate are not yet entirely understood. Direct measurements of the solar irradiance exist only since 1978, which is too short for Sun-climate studies. Models assuming the irradiance changes to be due to the changes in the spatial coverage by the solar surface magnetic features have been successful in reproducing the measured irradiance variations. However, suitable high-resolution magnetograms required for this modelling are only available for about four decades, and the sunspot number usually employed to reconstruct solar irradiance on centennial time scales does not accurately describe the evolution of the bright magnetic features (faculae and the network). A potential source of this information over the last century is provided by the historical Ca II K spectroheliograms. Their employment is not straightforward, however, as they suffer from numerous problems and lack photometric calibration. We have developed a technique to process and photometrically calibrate these images and will present preliminary results from selected historical datasets.

Indirect phase height measurements of low frequency radio waves from 1959 to 2009 are analyzed in order to examine the long-term variability of the mesosphere (D layer, about 82 km altitude) above Europe. The concept of standard phase heights (SPH) guaranties the continuity of the series even in the case of slight frequency changes. Over 50 years field strength measurements of the broadcasting station Allouis (Central France) have been maintained at Kühlungsborn (54° N, 12° E, Mecklenburg, Northern Germany). A homogenized daily series was generated with coverage of 98 % of time for SPH and for plasma scale heights (PSH). Both are used to derive the thickness temperature change between stratopause and 82 km altitude, and in addition the temperature change at 82 km is estimated by the use PSH series alone. Due to enhanced downward transport of NO and subsequent photo-ionization the winter anomaly for SPH and PSH was found. The SPH-series are partially anti-correlated to the solar cycle because stronger photo-ionization is linked with higher number of electrons, which reduces the SPH. Further the statistical analysis of the SPH-series shows a significant overall trend with a decrease of 114 m per decade induced by a shrinking stratosphere due to global warming and mesospheric processes, but with strong intra-decadal variability in winter. Furthermore the PSH-series embraces no significant overall trend but a strong coherence with the 22 year-Hale cycle of the sun. The indicated temperature trends are discussed.

The analysis of the MERRA data performed for years with different ENSO phases shows that development of Sudden Stratospheric Warming (SSW) events under El-Nino and La-Nina conditions proceeds in various ways. For instance, the zonal mean flow averaged over mid-winter months is stronger and polar temperature in the lower stratosphere is colder in years with La-Nina. To consider the ENSO influence on the dynamical processes in the extra-tropical middle atmosphere, the semi-empirical parameterization of the atmosphere heating due to latent heat release that takes into account diurnal and longitudinal variations has been developed and implemented into the Middle and Upper Atmosphere Model (MUAM). The latent heat composites for Northern Hemisphere winter months under El-Nino and La-Nina conditions have been calculated using MERRA precipitation data. The corresponding composites of geopotential height and temperature at lower boundary have been constructed using the JRA-55 reanalysis. The ensemble runs consisting of 10 members for the El-Nino and La-Nina events have been carried out. The comparison of the results demonstrates that the stratospheric polar vortex tends to be weaker and polar region in lower stratosphere is warmer during El Nino winters. The composite amplitudes of Stationary Planetary Wave with wave number 1 (SPW1) are weaker at higher latitudes in the stratosphere under La-Nina conditions while the SPW2 behaves opposite way and has stronger amplitudes. The influence of the noted distinctions on the efficiency of stratosphere-troposphere coupling and possible manifestation of the precipitation efficiency trend observed in the recent decades on the upper atmosphere are discussed.

The middle atmosphere in winter shows a high interannual variability in polar latitudes. To investigate the coupling between stratosphere and troposphere, the annual variation of Northern Annular Modes (NAMs) and the variability of Polar night Jet Oscillations (PJOs) are examined in ERA-Interim reanalysis. 20 major sudden stratospheric warmings are found by using a NAM threshold of -2.3 at the 10 hPa layer in agreement with former studies. With an extended definition of PJO events we identified 9 strong PJOs and 7 no PJO events. Strong PJOs show a strong downward propagating signal into the middle troposphere after the central day (CD). Significant differences between strong PJOs and no PJOs occur: (i) in the upper troposphere about 20 days before CD, (ii) in the stratosphere and troposphere after CD. In the lower stratosphere the zonal mean zonal wind anomalies are significantly reduced for strong PJOs about 20 days and about 45 days after CD. The zonal mean wind reductions are in coherence with pulses of enhanced eddy heat transport by planetary waves and their induced convergence of EP fluxes. For strong PJOs, the reestablishment of a strong polar vortex with strong zonal mean zonal wind anomalies in the upper stratosphere about 10 days after CD is caused mainly by radiative cooling and reduced upward transport of angular momentum by planetary waves. We show that strong PJOs are odds-on favorite for enhanced coupling between stratosphere and troposphere with potential for seasonal forecasts.

The association between short-term variability in the North Atlantic Oscillation (NAO) and intense geomagnetic storms is analyzed taking into account the solar activity level. The NAO is the dominant pattern of variation in atmospheric circulation in the North Atlantic basin. This oscillation results in a large-scale modulation of the normal patterns of heat and moisture transport, especially in winter, which determines changes in temperature and precipitation in a great area from eastern North America to Central Europe. A positive correlation between long-term variations in the NAO and geomagnetic activity has already been shown in several studies. However, at daily timescales, from the study of more than 200 geomagnetic storms we observe a decrease in the NAO index coincident with the maximum intensity of the geomagnetic storm. An explanation of our result could be given through the upper atmosphere processes induced by geomagnetic storms followed by coupling mechanisms among the different atmosphere regions, reaching finally the troposphere, in the context of an overall increasing trend which may be due to anthropogenic activity. A possible process would be that the NAO decrease due to geomagnetic storms is highly localized in time at daily scales and the high positive correlation between geomagnetic activity indices and NAO, specially after 1970, is due merely to a coincidence of increasing trends in both parameters.

Carbon dioxide (CO₂) is increasing throughout the atmosphere, but recent findings indicate that it is increasing faster near and above the mesopause than in the lower and middle atmosphere, and the mechanism behind this differential trend is unknown. We review this differential CO₂ trend measured by ACE-FTS onboard the SCISAT-1 satellite, and SABER onboard the NASA TIMED satellite. Increases in CO₂ cause the thermosphere to cool and contract, reducing its density, so faster increases should lead to greater cooling. Therefore, if CO₂ is actually increasing more rapidly in the lower thermosphere than in the fully mixed atmosphere, it could revise the conceptual basis for our understanding of global change in the thermosphere-ionosphere. We examine CO₂ trends in the lower and upper atmosphere using a combination of data analysis and model simulations, to understand whether this differential CO₂ trend is responsible for the observed changes in thermosphere and ionosphere climate, how the solar cycle and CO₂ trends contribute to those changes, how they vary with solar time, latitude, and season, and whether the differential CO­₂ trend could explain the larger changes reported in ion temperature.

The long-term trend of different atmospheric parameters has been studied separately during previous years in many papers. This study is focused on the temperature, wind (u and v component), geopotential height and water vapour trends during 1979-2015. We present the trend for winter (October-March), summer (April- September) season or each month with respect to ozone turnaround during mid 1990s. The different reanalyses (MERRA, ERA-Interim, JRA-55 and NCEP-NOE) are used for comparison. We analyzed every grid point to reduce the problem with zonal averages in different pressure levels. The results will show the complex view on the trend in the middle atmosphere (troposphere, stratosphere and lower mesosphere).

The Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) instrument is a UV-Visible-NearIR spectrometer operated on board the European Environmental Satellite (ENVISAT) from August 2002 to April 2012. In its limb viewing mode the instrument observed the Earth's atmosphere tangentially to the surface measuring the scattered solar light. At the University of Bremen, limb-scatter measurements from SCIAMACHY are currently used to retrieve stratospheric vertical distributions of several trace gases (O3, NO2, BrO, H2O) and aerosol optical parameters. In this presentation we analyse changes in the stratospheric composition as observed by the SCIAMACHY instrument during the ten years of its operation. 

Lidar is a very good tool for lower and middle atmospheric explorations. A Nd:YAG laser based Rayleigh Lidar was set up, at a high altitude observatory, Mt. Abu (24.5^o N, 72.7^o E, MSL height 1.7 km), in the Indian sub-tropical region. Temperature climatology and long term trends in the middle atmosphere has been studied using about 19 years (November 1997 to May 2016, with some data gaps) lidar observations. A multivariable analysis is used to consider natural variability (Solar Cycle and QBO) and similarly the changes in stratospheric ozone concentration due to anthropogenic activity have also been taken into account in trends estimations. We have selected different height regions 30-40, 40-50 and 50-60 km for trends analysis. Linear Regression analysis is applied to calculate temperature trend in different altitude regions. Considering the signature of seasonal, QBO and solar cycle variability, a linear decreasing temperature (cooling) has been found. Observed temperature trend is the strongest (-0.38 ± 0.15 K/year) at stratopause level (45 km) and the weakest (-0.14 ± 0.28 K/year) at 55 km during April. Seasonally, stronger temperature trends are found during winter -5.4 ± 2.8, -5.1 ± 2.1 and -2.1 ± 1.9 K/decade at 35, 45 and 55 km, respectively. The temperature trends during summer months are -2.2 ± 1.8, -2.8 ± 1.4 and -2.5 ± 1.6 K/decade at 35, 45 and 55 km, respectively. Lidar observed temperature trends over Mt. Abu are also compared with HALOE (onboard UARS) and SABER (onboard TIMED) temperature observations.

Long-term variations of the equatorial quasi-biennial oscillation (QBO) in the stratosphere are investigated using the reanalysis data and Singapore radiosonde data. A wavelet analysis with a Molret mother wavelet is used to obtain the QBO amplitude defined as 20-40 months period. The QBO components are also calculated with a Lanczos band-pass filter and the QBO amplitudes are defined as √2σ (σ: a root mean square of monthly time series) over consecutive three cycles assuming a monochromatic wave. Long-term trend and decadal variations are evidently analyzed in the QBO amplitude evolution. Composite picture, which is the difference between maximum and minimum phases in the QBO decadal variations reveal that the QBO decadal variations is not symmetric with respect to the equator but have significant interhemispheric differences depending on altitudes.

In a recent study carried out with the Kühlungsborn Mechanistic general Circulation Model (KMCM), it was shown that the interhemispheric coupling mechanism has a net cooling effect on the summer polar mesospheres. Here the comprehensive Whole Atmosphere Community Climate Model (WACCM) is used to reconfirm the hypothesis that the summer polar mesosphere will be much warmer without a gravity wave driven residual circulation in the winter.  It is also seen that the northern hemisphere summer polar mesosphere is most affected by the winter hemisphere.  A parameterization of noctilucent clouds is made in WACCM. It is seen that without a residual circulation southern winter mesosphere, there are less clouds in the northern hemisphere summer mesopause. For noctilucent clouds in the southern hemisphere the effect is less clear, as expected.

Using 13 (April 2002 –December 2014) years of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER/TIMED) 1.6µm OH airglow emission data, we have studied the long-term variation of OH peak emission altitude and volume emission rate (VER) for 0-10 N latitude and 70-90 E longitude grid. We have noted that, during day time the OH peak emission altitude is varying from 80 to 87 km with mean value of 83.5 km and from 82 to 88 km with mean value of 85 km during night time. The signature of semi-annual oscillation (SAO), annual oscillation (AO) and quasi-biennial oscillation (QBO) in the OH peak emission altitude as well as the VER is evident. Our analysis reveals that the SAO and QBO signatures but not the AO signature are very strong in the equatorial region during night time. Apart from the SAO, AO and QBO signatures, the presence of oscillation related to the El Niño oscillation (ENSO) is also noted. After the removal of these oscillations, we find the evidence of the influence of solar activity and a long term trend in the OH emission layer.  It is also found good correlation between the mesospheric and stratospheric variations (ECMWF data). These results are detailed in this present study.

We present the analysis of annual average OH* temperatures in the mesopause region derived from measurements of the GRound based Infrared P-branch Spectrometer (GRIPS) at Wuppertal (51° N, 7° E) in the time interval 1988 to 2015. The temperature time series shows a clear correlation with the solar radio flux F10.7cm (11-year cycle of solar activity) with a sensitivity of about 4 – 5 K/(100 SFU) . Beside this correlation we find a clear trend break in the temperature time series in middle of 2006.

This apparent trend break can be described as long periodic oscillation. A multiple linear regression using the solar radio flux and a 24-year oscillation as parameters leads to a sensitivity to the solar activity of (4.3 ±0.7) K/(100 SFU) and an amplitude of the 24-year oscillation A = (1.95 ±0.43) K. The most important finding here is that using these parameters for the multiple linear regression an additional linear trend is no longer needed. Moreover, with the knowledge of this 24-year oscillation the linear trends derived in this and in a former study of the Wuppertal data series can be reproduced by just fitting a line to the corresponding time interval of the oscillation. This actually means that depending on the analysed time interval completely different linear trends with respect to magnitude and sign can be observed. This fact is of essential importance for any comparison between different observations and model simulations.

Radar observations of mesosphere/lower thermosphere (MLT) monthly mean winds are analysed with respect to long-term trends and their changes between 1980 and 2015. Zonal prevailing winds are generally increasing with time, but there is a tendency for a change in trend in the 1990s. This is also visible in the meridional wind, which increases in the 1980s but decreases in more recent years.   Numerical experiments with a mechanistic global circulation model with nudged tropospheric and lower stratospheric temperatures are performed that show the respective effect of continuous CO₂ increase and stratospheric ozone decrease, and the turnaround of ozone changes in the 1990s. It is also shown that the MLT dynamics and trends in the model strongly depend on the assimilated lower atmosphere data, while the summer trends are more determined by middle atmosphere trace gas changes.

Trends of mean winds and waves are studied on the basis of continuous wind measurements in the mesosphere and lower thermosphere (MLT) using MF and Meteor radars since 1998 at Andenes (69°N, 16°E), and since 1990 at Juliusruh (55°N, 13°E). At middle latitudes, trends of zonal winds between1990 – 2015 show a significant increase of westward directed winds in summer below 83 km. In winter, the trends are nearly opposite, however, the results are only partly significant due to the higher variability of planetary waves. At polar latitudes, the seasonal variation of the zonal wind is dominated by a stable, but in comparison to middle latitudes weaker westward directed jet below about 88 km in summer. The trends are only partly significant and show an increase of westward directed winds at all heights. Possible differences caused by both used radar techniques will be discussed. The long term wind measurements are also used to estimate trends of the activity of gravity waves (GW) with different periods. We will update our previous results indicating that the observed zonal wind trend at about 75 km during summer at mid latitudes goes along with an enhanced GW activity with periods of 3 - 6 h thus illuminating the contribution of the selective GW filtering by the background winds. These studies are extended for other periods and seasons at both latitudes. In contrast to trends at mid latitudes, the filtering effect seems to be of less importance at polar latitudes during the summer months.

Temperature trends in the middle atmosphere depend primarily on the trends in the radiatively active constituents (primarily CO2, ozone and H2O). Effects such as vertical coupling of radiative transfer (non-locality) and secondary absorption bands, however, have enough influence to render most regression analyses of temperature trends as a function of local constituent variations misleading. The role of these processes is demonstrated through an analysis of the factors affecting the modelled temperature response during the periods 1975 to 1995 and 2010 to 2040. These periods are characterized by differing rates of change in ozone and CO2 so that the various roles of the important radiative processes can be distinguished. The models used include the Canadian Middle Atmosphere Model (CMAM) simulation REF-B2 undertaken in support of the Chemistry Climate Model Evaluation effort and a one-dimensional radiative transfer model forced using appropriate globally averaged quantities from the CMAM run. In this paper, the processes of interest are introduced, the motivation for using the two time periods for this analysis outlined and the impact of the various processes on the temperature trend presented.

A dedicated empirical model of the lower ionosphere (50 to 150 km) is built on rocket borne radio wave propagation data. The data are from non-auroral latitudes and "normal" conditions otherwise. Below 70 km in addition Langmuir probe data extend the altitude coverage. Each measured electron density value is compared to its corresponding model value and the deviation (factor) is plotted against time ranging from 1947 to 2004. In the large scatter an increase of about 1% per year can be seen between 75 and 95 km, whereas above 95 km a decrease of similar order seems to prevail. Above 125 km the electron densities increase again appreciably.

Compelling evidence from direct measurements of thermospheric density and ionospheric temperature indicates that the terrestrial upper atmosphere is experiencing long-term cooling over the last few solar cycles. Such cooling seems consistent qualitatively with speculation of upper atmospheric changes associated with anthropogenic increase of greenhouse gases as first suggested by Roble and Dickson (1989). However, quantitative differences among observations and between simulations and observations of the long-term cooling still exist, raising important questions regarding the most significant driver(s) of climate change at ionosphere and thermosphere altitudes. In this presentation, we will review ionospheric long-term trend observations based on incoherent scatter radars. In particular, we will present new observations from two high latitude sites at Sondrestrom (Invariant latitude 73.2°N) from 1990-2015, and Chatanika/Poker Flat (Invariant latitude 65.9°N) over the span of 1976-2015 (with a gap from 1983-2006).  Results are compared to conditions at the mid-latitude Millstone Hill site (Invariant latitude 52.8°N) from 1968-2015. The aggregate radar observations have very comparable and consistent altitude dependence of long-term cooling trends. The trends below 275 km are significantly higher (-3 ~ -1K/year at 250km) than anticipated from model predictions given the anthropogenic increase of greenhouse gases. The cooling trends above 275 km continue to increase in magnitude but values are strongly dependent on magnetic latitude. Our results indicate that drivers, from above of below, other than those directly associated with greenhouse gas increases can play an important role in determining the strong long-term cooling in the upper atmosphere.

As the EISCAT UHF radar system in Northern Scandinavia started its operations in the early 1980s, the collected data covers several solar cycles.  The long time-series of collected data provides us the opportunity to study long-term variations and trends of ionospheric parameters in the auroral zone.

In the present study we have used the EISCAT Tromsø UHF data to investigate variations of the Hall conductivity and ion temperatures in the E-region around noon.  Both the ion temperature and the peak altitude of the Hall conductivity are confirmed to depend strongly on solar zenith angle. However, the dependence on solar activity seems to be weak.

In order to search for trends in these parameters,  the ion temperature and peak altitude of the Hall conductivity data were adjusted for their seasonal and solar cycle dependence. A very weak descent (~0.2 km/ decade) was seen in the peak altitude of the Hall conductivity. The ion temperature shows a significant cooling trend (~10 K/ decade).  This trend seems to be affected by a trend in the MSIS neutral temperature.

In this paper, we discuss what causes the characteristics of the variations in the electric conductivities and ion temperatures.

Over 30 years of EISCAT radar measurements at Tromso are analyzed to determine various ionospheric and thermospheric parameters at high latitude. Plasma momentum equations are used to derive field-aligned electric fields and currents, as well as thermospheric density, from the observations. The results will be presented focusing on solar-cycle variations and long-term trends. The validity of the techniques will be also discussed.

The response other ionized chemical species in the lower ionosphere (D-region) to solar cycle in UV have been simulated with 3D global photochemical transport model CHARM-I (CHemical Atmospheric Research Model with Ions), developed at the Laboratory for Atmospheric Chemistry and Dynamics at Central Aerological Observatory [1]. Model describes the interaction between 70 neutral and ionized chemical species involved in 200 photochemical reactions. “Family” technique was used for solving kinetic part of equations for neutrals and the algorithm which controls total electroneutrality was realized for ions. Prather’s scheme was used to describe advection. 3D global temperature wind components fields (daily averaged) calculated by GCM ARM (Atmospheric Research Model [2]) were used in simulations. Solar cycle signal in UV solar irradiance measured from space (SIM and other instruments) has been introduced in the model. Ionization was induced by Lα and GCRs. The results obtained by simulations revealed global changes in electron density and of other ions (no more than 20%) in phase with solar cycle in the mesosphere. Limited response induced by GCRs was found also in the lower stratosphere. This work was supported by Russian Science Foundation for Basic Research (grant N 13-05-0105213). [1] A.A. Krivolutsky, L.A. Cherepanova, T. Yu. V’yushkova, A.I. Repnev, The Three-dimensional global numerical model CHARM-I: The Incorporation of Processes of Ionospheric D-region, vol. 55, N 4, 483-503, 2015. [2] A.A. Krivolutsky, L.A. Cherepanova, A.V. Dement’eva, A.I. Repnev, and A.V. Klyuchnikova. Global circulation of the Earth’s atmosphere between 0-135 km calculated with the ARM model. Consideration of the solar activity contribution. Geomagnetism and Aeronomy, vol. 55, N 6, 808-828, 2015.

Simultaneous measurements of the Total Electron Content (TEC) and the peak electron density NmF2 at vertical sounding sites enable the estimation of the equivalent slab thickness of the ionosphere. This shape parameter, defined as the ratio of variables TEC and NmF2 of the vertical electron density profile, is closely related to the neutral gas scale height under undisturbed conditions. Under disturbed conditions the equivalent slab thickness is very sensitive to the competition of plasma driving forces lifting up or moving down the plasma.

To get near real time information on these perturbation processes, the equivalent slab thickness is continuously monitored by combining vertical sounding and corresponding TEC data over Juliusruh/Germany, Pruhonice/Czech Republic and Tromsoe/Norway via the space weather service of DLR (http://swaciweb.dlr.de).

In this paper we discuss long-term trends of the equivalent slab thickness over several European ionosonde stations within the entire solar cycle 23 and beyond. The long-term trend of the equivalent slab thickness indicates a cooling process in the thermosphere during solar cycle 23. To get reliable conclusions on these long-term trends a discussion of the diurnal behaviour of the slab thickness is required. Ionospheric storms may change the equivalent slab thickness dramatically.

Knowledge of the upper atmosphere state, and in particular of the ionosphere, is essential in several applications such as systems used in radio frequency communications, satellite positioning and navigation. In general, these systems depend on the ionosphere, involving it as part of the system or as an interference source. In all the cases an essential task is determining the path and modifications of ray propagation through the ionospheric plasma. The ionospheric refractive index and the maximum usable frequency MUF that can be received over a given distance, are key parameters which in general are simplified neglecting the Earth’s magnetic field effect. The value of M(3000)F2, related to the MUF that can be received over 3000 km is routinely scaled from ionograms using a technique which also neglects the geomagnetic field effect assuming a standard simplified propagation model. M(3000)F2 should be affected then by a systematic trend linked to the Earth’s magnetic field secular variation. On the other hand, among the upper atmosphere effects expected from increasing greenhouse gases concentration is the lowering of the F2-layer peak density height, hmF2. This ionospheric parameter is usually estimated using the M(3000)F2 factor, so it would also carry this “systematic trend”. The magnitude of the geomagnetic field effect on MUF estimations is assessed as well as the consequences of this effect on hmF2 long-term trend estimations, which, at some locations, can be significant in comparison to the few kilometers decrease expected from greenhouse gases effect.

for the CMIP6 solar forcing team:

K. Matthes, B Funke, M. E. Andersson, L. Barnard, J. Beer, P. Charbonneau, M. A. Clilverd, T. Dudok de Wit, M. Haberreiter, A. Hendry , C. H. Jackman, M. Kretzschmar, T. Kruschke, M. Kunze, U. Langematz, D. R. Marsh, A. Maycock, S. Misios, C. J. Rodger, A. A. Scaife, A.  Seppälä, M. Shangguan, M.  Sinnhuber, K. Tourpali, I. Usoskin,  M. van de Kamp, P. T. Verronen, and S. Versick

We describe the recently generated solar forcing dataset for CMIP6 and highlight in particular changes with respect to the CMIP5 recommendation. The solar forcing is provided for radiative properties, i.e., total solar irradiance (TSI) and solar spectral irradiance (SSI), and F10.7cm radio flux, as well as particle forcing, i.e., geomagnetic indices Ap and Kp, and ionisation rates to account for effects of solar protons, electrons and galactic cosmic rays. This is the first time that a recommendation for solar-driven particle forcing is provided for a CMIP exercise. The solar forcing dataset is provided at daily and monthly resolution separately for the CMIP6 Historical Simulation (1850–2014), for the future (2015–2300), including an additional extreme Maunder Minimum-like sensitivity scenario, as well as for a constant and a time-varying forcing for the preindustrial control simulation. This paper provides an overview on the forcing dataset and how it was created, and discusses implications for climate modeling.

We model solar irradiance variations over a broad range of timescales. 3D MHD simulations with MURAM are used to simulate Total Solar Irradiance changes on timescales of minutes to days due to convection. Changes due to surface magnetism are modelled with SATIRE-S relying on the high-cadence solar imagery from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory. A comparison to observations shows that  such a combination of SATIRE and MURAM is remarkably successful in reproducing available records of Total Solar Irradiance on timescales of minutes to decades. This demonstrates that solar magnetism and convection can account for TSI variability at all timescale it has ever been measured (with the exception of  5-minute oscillations from p-modes). We also present a comparison of our model to empirical models of solar irradiance variations.

Although state-of-the-art reconstructions based on proxies and (semi-) empirical models converge in terms of the total solar irradiance, they still significantly differ in terms of SSI with respect to the mean spectral distribution of energy input and temporal variability. This study aims at quantifying the related uncertainties for the Earth’s climate by forcing two complex chemistry-climate models with four different SSI reconstructions and the reference spectrum RSSV1-ATLAS3, derived from observations. This study represents the work performed within the ROMIC-SOLIC project which contributes directly to the CMIP6 solar forcing recommendation by the SPARC/SOLARIS-HEPPA initiative.

We use two state-of-the-art chemistry climate models - CESM1(WACCM) and EMAC - to conduct a number of timeslice experiments. External forcings and boundary conditions are fixed and identical for all experiments, except for the solar forcing. A first set of simulations employing absolute solar minimum forcing according to the four SSI-reconstructions is analyzed to assess the impact of differing spectral energy distribution. The second set of simulations for analyzing effects of differing solar cycle variability consists of one solar minimum simulation, employing the reference spectrum RSSV1-ATLAS3 and four solar maximum experiments. The latter are a result of adding the 11 year solar cycle amplitude according to the four reconstructions to RSSV1-ATLAS3.

The results of this study show significant differences in temperature and ozone concentrations for the stratosphere and partly for the troposphere originating from a combination of photolytic and radiative effects. The impact of the differences in spectral energy distribution is significantly larger than that of solar cycle uncertainty.

UV SSI has been monitored from space since 1978. This is accompanied by the development of models aimed at reconstructing UV SSI variability by relating it to solar magnetism. There is controversy between the various measurements and models in terms of the wavelength-dependence of the variation over the solar cycle. This sees the application of the various data sets to climate models yield qualitatively different results. Here, we highlight the main discrepancies between available records and reconstructions. More importantly, we discuss the likely causes.

Observations indicate that a signature of the quasi-biennial oscillation (QBO) in the tropical lower stratosphere can be seen in the mean temperature, mean zonal wind, ozone concentration, and tidal amplitudes in the MLT. The QBO is expected to vary with increasing greenhouse gases through changes in tropospheric wave sources and speeding up of the stratospheric circulation. The QBO also responds to perturbations in stratospheric aerosols from volcanic eruptions. This presentation will discuss the processes that lead to the QBO signal in the MLT and the potential impact of stratospheric QBO trends on the MLT.

Long-term changes in the middle atmosphere due to anthropogenic greenhouse gas emissions are examined in relation to the effect of the equatorial Quasibiennal Oscillation (QBO) on the northern winter circulation. The examinations are based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations 1979-2100 of the Earth-System-Model MPI-ESM that generates the QBO internally. A remarkable result is that the trends in temperature, zonal wind and residual circulation are much stronger during the westerly (QBO-West) than the easterly (QBO-East) phase of the QBO (factor 2-4). An in-depth-analysis based on recent formulations of the three-dimensional (3D) residual circulation, which represents the 3D Brewer-Dobson circulation (BDC), shows that this trend behavior is related to both the radiative cooling of the middle atmosphere and the changes in the 3D BDC and associated dynamical heating rates, where both affect the strength and position of the polar vortex. In particular, the change in transient eddy fluxes over North America affects the excitation and propagation of planetary Rossby waves due to the Rocky Mountains and, subsequently, the QBO-signal in the stationary planetary wave one (usually pronounced during QBO-East) and wave two (usually pronounced during QBO-West) in temperature, zonal wind and 3D BDC. Effects of changes in the frequency of sudden stratospheric warmings and possible impacts on surface climate are discussed. For verification of the model dynamics, reanalysis data (ERA-Interim), daily-mean wind fields derived from Aura/MLS satellite data and simulations with the general circulation and chemistry model HAMMONIA are also examined.

A Near Infrared Imaging Spectrograph (NIRIS) has been developed in-house which measures O₂(0-1) and OH(6-2) band nightglow emissions using which the rotational temperatures are derived. NIRIS is being operated from a low-latitude location, Mount Abu (24.6⁰N, 72.8⁰E), in India. NIRIS data revealed significant enhancements in mesospheric temperatures over low-latitudes during the major sudden stratospheric warming (SSW) event of January 2013. This motivated us to carry out detailed investigations to understand the mesospheric temperature distribution over different latitudes during SSW events. In order to do that, we have used satellite-based mesospheric temperature measurements that were obtained from three different instruments namely, Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), Optical Spectrograph and InfraRed Imaging System (OSIRIS) and Solar Occultation For Ice Experiment (SOFIE). The variations in the mesospheric temperatures at different latitudes have been characterized based on northern hemispheric stratospheric temperature enhancements at high-latitudes during SSW periods. Using the long term (2004-2013) analysis of satellite-based measurements, new features, such as the formation of “double-humped” structure in the mesospheric to stratospheric temperature ratios with respect to latitude during major SSW events with two crests over tropical- to mid-latitudes and a trough over the geographic equator has been revealed. In this study a hitherto unknown aspect of the relationship between stratospheric temperatures at high-latitude and mesospheric temperatures at different latitudes has been brought to light. These results strongly support the interactions in stratospheric-mesospheric coupling and high- to low-latitude coupling of mesosphere lower thermosphere regions, especially during SSW events.

Climatology of zonal-mean zonal wind, deviations of temperature from its winter-mean values, and amplitudes and vertical component of Eliassen-Palm fluxes created by large-scale planetary waves (PWs) at high northern latitudes at altitudes from ground up to 60 km is studied using 35-years (1980-2014) databases of meteorological reanalysis MERRA (years 1980 -2014) and UK Met Office (1994 2014). Climatological temperature deviations averaged over 70-90 latitudinal band reveal cooler and warmer layers descending due to seasonal changes during polar night. PW amplitudes and upward Eliassen-Palm fluxes averaged over 35 years have periodical maxima with the  main maximum in the beginning of January at altitudes 40 – 50 km. During the intervals of more frequent occurrence of sudden stratospheric warmings, maxima of PW amplitudes and Eliassen-Palm fluxes, also minima of eastward winds in the high-latitude northern stratosphere have been found. Climatological intra-seasonal irregularities of sudden stratospheric warming dates could indicate the existence of stratospheric vacillation phases repeating in different years.  There are differences between atmospheric characteristics averaged over years 1981 – 1994 and 1995 – 2014 including lower multiyear average eastward winds and warmer polar stratosphere during the last interval.