Chemistry and Minor Chemical Constituents in Mesosphere

Scope

The minor chemical constituents play a significant role in the middle atmosphere. These constituents determine the radiation budget and influence the dynamics through heat, which calorificate in the chemical reactions. Very few constituents can be measured by the various ground based or rocket- and satellite-borne techniques available. For certain time periods or geographical regions other constituents are unmeasurable. The mesosphere is still a region characterized by different unexplained phenomena. There is a permanent lack of data required for different investigations to employ model data. Moreover, not all phenomena in the atmosphere can be studied by measurements. Two reasons for this are a lack of precision and the absence of ability (for example, the water vapor measurements above 85 km). It is not easy to measure all chemical constituents together in the same place and time, however this is sometimes necessary in order to understand a phenomenon. Consequently, this situation also requires the development of sophisticated models. Both the monitoring of the atmosphere and its modeling are necessary to investigate its physical and chemical state.

On the other hand, three-dimensional dynamical models need global distributions of chemical constituents for calculations of radiation and heat budgets. The solution to the problem is made possible by the development of models which calculate the distribution of the chemical constituents and which also feed the dynamic part of the model. Moreover, three-dimensional models of dynamics and chemistry could be applied to study the influence of anthropogenic activity on Earth’s atmosphere, response of the atmosphere to different impacts and predictions of future states. Furthermore, three-dimensional models of the dynamics and chemistry, verified with data from measurements and examined for the Earth’s atmosphere, can be generalized by changing the orbit and atmospheric parameters for the atmospheres of other planets. This modeling is very important, especially on these other planets where the ability to gain measurements is limited.

The focus of our researches is an attempt to study some of the features of the behavior and distribution of important minor chemical constituents such as ozone, water vapor, hydroxyl etc. in the middle atmosphere using a sophisticated chemistry-transport model (CTM). A time-dependent three-dimensional numerical chemisty-transport model was developed and used to study the distribution of chemical minor constituents in the mesosphere - lower thermosphere (MLT) region. All physical processes believed to be important are simulated in the model, including chemical interaction, photochemical dissociation, eddy and molecular diffusion, and advection. The model was used to investigate multiple phenomena. Examples of these phenomenon are the photochemical Doppler effect, solar influence by Lyman-alpha radiation on mesospheric water vapor, autocatalytic water vapor production as a source of relatively large mixing ratios within the middle to upper mesosphere in high latitudes during the summer, tertiary ozone maximum formation, and trends of mesospheric water vapor due to increase of methane and other minor constituents.