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Volume 18, issue 12
Atmos. Chem. Phys., 18, 8893–8908, 2018
https://doi.org/10.5194/acp-18-8893-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue: Sources, propagation, dissipation and impact of gravity waves...

Atmos. Chem. Phys., 18, 8893–8908, 2018
https://doi.org/10.5194/acp-18-8893-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Jun 2018

Research article | 26 Jun 2018

Local time dependence of polar mesospheric clouds: a model study

Francie Schmidt, Gerd Baumgarten, Uwe Berger, Jens Fiedler, and Franz-Josef Lübken Francie Schmidt et al.
  • Leibniz-Institute of Atmospheric Physics, Rostock University, Kühlungsborn, Germany

Abstract. The Mesospheric Ice Microphysics And tranSport model (MIMAS) is used to study local time (LT) variations of polar mesospheric clouds (PMCs) in the Northern Hemisphere during the period from 1979 to 2013. We investigate the tidal behavior of brightness, altitude, and occurrence frequency and find a good agreement between model and lidar observations. At the peak of the PMC layer the mean ice radius varies from 35 to 45 nm and the mean number density varies from 80 to 150 cm−3 throughout the day. We also analyze PMCs in terms of ice water content (IWC) and show that only amplitudes of local time variations in IWC are sensitive to threshold conditions, whereas phases are conserved. In particular, relative local time variations decrease with larger thresholds. Local time variations also depend on latitude. In particular, absolute local time variations increase towards the pole. Furthermore, a phase shift exists towards the pole which is independent of the threshold value. In particular, the IWC maximum moves backward in time from 08:00 LT at midlatitudes to 02:00 LT at high latitudes. The persistent features of strong local time modulations in ice parameters are caused by local time structures in background temperature and water vapor. For a single year local time variations of temperature at 69° N are in a range of ±3 K near 83 km altitude. At sublimation altitudes the water vapor variation is about ±3.5 ppmv, leading to a change in the saturation ratio by a factor of about 2 throughout the day.

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Local time variations of polar mesospheric clouds (PMCs) in the Northern Hemisphere are studied using a combination of a global circulation model and a microphysical model. We investigate the brightness, altitude, and occurrence of the clouds and find a good agreement between model and observations. The variations are caused by tidal structures in background parameters. The temperature varies by about 2 K and water vapor by about 3 ppmv at the altitude of ice particle sublimation near 81.5 km.
Local time variations of polar mesospheric clouds (PMCs) in the Northern Hemisphere are studied...
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