Stratospheric and solar cycle effects on long-term variability of mesospheric ice clouds

Details Stratospheric and solar cycle effects on long-term variability of mesospheric ice clouds Stratospheric and solar cycle effects on long-term variability of mesospheric ice clouds

Nov 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgra..11400i06l&link_type=abstract

Journal of Geophysical Research, Volume 114, Issue A11, CiteID D00I06

Physics

12

Atmospheric Composition And Structure: Aerosols And Particles (0345, 4801, 4906), Atmospheric Processes: Mesospheric Dynamics, Atmospheric Composition And Structure: Middle Atmosphere: Composition And Chemistry, Space Weather: Solar Effects, Atmospheric Processes: Climate Change And Variability (1616, 1635, 3309, 4215, 4513)

Scientific paper

Model results of mesospheric ice layers and background conditions at 69°N from 1961 to 2008 are analyzed. The model nudges to European Centre for Medium-Range Weather Forecasts data below ˜45 km. Greenhouse gas concentrations in the mesosphere are kept constant. At polar mesospheric cloud (PMC) altitudes (83 km) temperatures decrease until the mid 1990s by -0.08 K/yr resulting in trends of PMC brightness, occurrence rates, and, to a lesser extent, in PMC altitudes (-0.0166 km/yr). Ice layer trends are consistent with observations by ground-based and satellite instruments. Water vapor increases at PMC heights and decreases above due to increased freeze-drying caused by the temperature trend. Temperature trends in the mesosphere mainly come from shrinking of the stratosphere and from dynamical effects. A solar cycle modulation of H2O is observed in the model consistent with satellite observations. The effect on ice layers is reduced because of redistribution of H2O by freeze-drying. The accidental coincidence of low temperatures and solar cycle minimum in the mid 1990s leads to an overestimation of solar effects on ice layers. A strong correlation between temperatures and PMC altitudes is observed. Applied to historical measurements this gives negligible temperature trends at PMC altitudes (˜0.01-0.02 K/yr). Strong correlations between PMC parameters and background conditions deduced from the model confirm the standard scenario of PMC formation. The PMC sensitivity on temperatures, water vapor, and Ly-α is investigated. PMC heights show little variation with background parameters whereas brightness and occurrence rates show large variations. None of the background parameters can be ignored regarding its influence on ice layers.

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