M. Grygalashvyly

Hydroxyl layer: Mean state and trends at midlatitudes

Based on an advanced model of excited hydroxyl relaxation we calculate trends of number densities and altitudes of the OH*-layer during the period 1961–2009. The OH*-model takes into account all major chemical processes such as the production by H + O3, deactivation by O, O2, and N2, spontaneous emission, and removal by chemical reactions. The OH*-model is coupled with a chemistry-transport model (CTM). The dynamical part (Leibniz Institute Model of the Atmosphere, LIMA) adapts ECMWF/ERA-40 data in the troposphere-stratosphere. The change of greenhouse gases (GHGs) such as CH4, CO2, O3, and N2O is parameterized in LIMA/CTM. The downward shift of the OH*-layer in geometrical altitudes occurs entirely due to shrinking (mainly in the mesosphere) as a result of cooling by increasing CO2 concentrations. In order to identify the direct chemical effect of GHG changes on OH*-trends under variable solar cycle conditions, we consider three cases: (a) variable GHG and Lyman-α fluxes, (b) variable GHG and constant Lyman-α fluxes, and (c) constant GHG and Lyman-α. At midlatitudes, shrinking of the middle atmosphere descends the OH*-layer by ~ −300 m/decade in all seasons. The direct chemical impact of GHG emission lifts up the OH*-layer by ~15–25 m/decade depending on season. Trends of the thermal and dynamical state within the layer lead to a trend of OH* height by ~ ±100 m/decade, depending on latitude and season. Trends in layer altitudes lead to differences between temperature trends within the layer, at constant pressure, and at constant altitude, respectively, of typically 0.5 to 1 K/decade.

The zonal wind effect on the photochemistry within the mesosphere/mesopause region

Abstract The solar radiation periodically excites the chemistry of the earths atmosphere diurnally. The photochemical system of the mesosphere represents a driven chemical oscillator which shows a resonance-like response to the radiative forcing if the characteristic chemical system time ranges in the order of 1 day. This is the case in the upper mesosphere and mesopause region. An air parcel moves along a parallel according to the direction and velocity of the zonal wind. In compliance with the wind direction this air parcel is subjected to an insolation period longer or shorter than 1 day. The changed period can be described by a modified Doppler formula. For real zonal wind speeds in the domain under investigation, the shift of the Doppler period amounts to more than +4 and −7 hours. As a consequence the diurnal variation of the acting minor constituents and some important parameters, such as the diurnal amplitude or the occurring time of the maximum concentration, change with the zonal wind. We investigate this behavior on the basis of a realistic 3D-model of the dynamics and chemistry of the middle atmosphere. We briefly discuss some results.

Atmospheric Band Fitting Coefficients Derived from Self-Consistent Rocket-Borne Experiment

16 Based on self-consistent rocket-borne measurements of temperature, densities of atomic 17 oxygen and neutral air, and volume emission of the Atmospheric Band (762 nm) we 18 examined the one-step and two-step excitation mechanism of OO2�bbΣgg� for night-time 19 conditions. Following McDade et al. (1986), we derived the empirical fitting coefficients, 20 which parameterize the Atmospheric Band emission OO2�bbΣgg − XXΣgg�(0,0). This allows to 21 derive atomic oxygen concentration from night-time observations of Atmospheric Band 22 emission OO2�bbΣgg − XXΣgg�(0,0). The derived empirical parameters can also be utilised for 23 Atmospheric Band modelling. Additionally, we derived fit function and corresponding 24 coefficients for combined (oneand two-step) mechanism. Simultaneous common volume 25