Local time dependence of polar mesospheric clouds: a model study
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...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/8893/2018/acp-18-8893-2018.pdf |
| Summary: | 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<sup>−3</sup> 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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| ISSN: | 1680-7316 1680-7324 |