Temperatures at 69°N

Thermal structure at polar latitudes (69°N) between 30 km and 90 km altitude

Scope

The polar middle atmosphere (30–90 km) is characterized by large differences in the thermal structure between winter and summer. In summer despite the midnight sun the polar mesopause regions cools down to below 130 K and hence is the coldest region of the entire atmosphere. These low temperature lead to the formation of noctilucent clouds in the summer months. In winter despite the polar night the mesopause region is up to 90 K warmer than in summer.

The reason for these temperature changes which seem paradox at first view are gravity waves. These wave transport energy and momentum in the atmosphere and thereby have a large influence on the atmospheric dynamics and hence cause adiabatic warming and cooling which influences the thermal structure. To better understand these processes and be able to include them correctly in climate models, it is necessary to investigate on the one hand the seasonal changes of the thermal structure which are shown here. On the other hand the short-periodic temperature fluctuations caused by gravity waves and tides have to be investigated.

Methods

To investigate the thermal structure we use the ALOMAR Rayleigh/Mie/Raman (RMR) lidar, meteorological rockets (falling spheres) and radiosonde measurements. From the measurements with the ALOMAR RMR lidar and the meteorological rockets air density profiles are derived which are used to calculate temperature profiles assuming hydrostatic equilibrium. The required start temperature at the upper end is taken from reference atmospheres like CIRA86 or NRLMSISE-00.

More details about this procedure are found in the description of the derivation of temperatures from RMR lidar measurements. The temperature climatology above ALOMAR was assembled using all measurements longer than two hours from the years 1997–2005.

Thermal structure above ALOMAR

Thermal structure from the surface up to 90 km altitude above ALOMAR from measurements with the RMR lidar and falling spheres (in the sommer months) as well as operational analyses of the ECMWF model (below 30 km) for the years 1997–2005.