[1] The spatiotemporal behavior of the ozone mixing ratio in the upper mesosphere/ mesopause region under nearly polar night conditions is one of the phenomena not completely understood and reproduced by models thus far. We examine this issue using an advanced three-dimensional model of the dynamics and chemistry of the middle atmosphere (0-150 km) particularly designed to investigate the spatiotemporal structure of this phenomenon in the extended mesopause region. The most marked features of the modeling results are a pronounced ozone maximum around 72 km occurring close to the polar night terminator and a strong drop of the mixing ratio above $80 km. These features were also found by means of ground-based microwave measurements in high latitude at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR, 69.29°N, 16.03°E) and even at the moderate latitude of Lindau (51.66°N, 10.13°E) during the night in the winter season but less marked there. They were absent at both stations during the daytime hours. The calculations suggest that the stronger enhanced ozone values occur in a latitudinal band of approximately 15°in the vicinity of the polar night terminator. During nighttime, enhanced values reach into midlatitudes. The effect is confined both to a height interval approximately between 66 and 76 km and to a certain latitudinal range which alters with season according to the change of the polar night terminator. We discuss the model results in terms of chemistry for nearly grazing incidence conditions of the solar insolation and in context with advective transport.

No abstract

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 + O 3 , deactivation by O, O 2 , and N 2 , 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 CH 4 , CO 2 , O 3 , and N 2 O 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 CO 2 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~À300 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.

[1] Microwave water vapor measurements between 40 and 80 km altitude over a solar cycle (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) were carried out in high latitudes at Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) (69.29°N, 16.03°E), Norway. Some smaller gaps and three interruptions of monitoring in the winters 1996/1997 and 2005/2006 and from spring 2001 to spring 2002 occurred during this period. The observations show a distinct year-to-year variability not directly related to solar Lyman-a radiation. In winter the water vapor mixing ratios in the upper domain were anticorrelated to the solar activity, whereas in summer, minima occurred in the years after the solar maximum in 2000/2001. In winter, sudden stratospheric warmings (SSWs) modulated the water vapor mixing ratios. Within the stratopause region a middle atmospheric water vapor maximum was observed, which results from the methane oxidation and is a regular feature there. The altitude of the maximum increased by approximately 5 km as summer approached. The largest mixing ratios were monitored in autumn. During the summer season a secondary water vapor maximum also occurred above 65 km most pronounced in late summer. The solar Lyman-a radiation impacts the water vapor mixing ratio particularly in winter above 65 km. In summer the correlation is positive below 70 km. The correlation is also positive in the lower mesosphere/stratopause region in winter due to the action of sudden stratospheric warmings, which occur more frequently under the condition of high solar activity and the enhancing the humidity. A strong day-to-day variability connected with planetary wave activity was found throughout the entire year. Model calculations by means of Leibniz-Institute Middle Atmosphere model (LIMA) reflect the essential patterns of the water vapor variation, but the results also show differences from the observations, indicating that exchange processes between the troposphere and stratosphere not modeled by LIMA could have influenced the long-term variability. We show results of measurements, compare these with calculations, and discuss the chemical and dynamical backgrounds of the variation of water vapor in the middle atmosphere.