The relationship between polar mesospheric clouds and their background atmosphere as observed by Odin-SMR and Odin-OSIRIS
In this study the properties of polar mesospheric clouds (PMCs) and the background atmosphere in which they exist are studied using measurements from two instruments, OSIRIS and SMR, on board the Odin satellite. The data comes from a set of tomographic measurements conducted by the satellite dur...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/12587/2016/acp-16-12587-2016.pdf |
| Summary: | In this study the properties of polar mesospheric clouds (PMCs)
and the background atmosphere in which they exist are studied using
measurements from two instruments, OSIRIS and SMR, on board the Odin
satellite. The data comes from a set of tomographic measurements conducted by
the satellite during 2010 and 2011. The expected ice mass density and cloud
frequency for conditions of thermodynamic equilibrium, calculated using the
temperature and water vapour as measured by SMR, are compared to the ice mass
density and cloud frequency as measured by OSIRIS. We find that assuming
thermodynamic equilibrium reproduces the seasonal, latitudinal and vertical
variations in ice mass density and cloud frequency, but with a high bias of a
factor of 2 in ice mass density.
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To investigate this bias, we use a simple ice particle growth model to
estimate the time it would take for the observed clouds to sublimate
completely and the time it takes for these clouds to reform. We find a
difference in the median sublimation time (1.8 h) and the reformation time
(3.2 h) at peak cloud altitudes (82–84 km). This difference implies that
temperature variations on these timescales have a tendency to reduce the ice
content of the clouds, possibly explaining the high bias of the equilibrium
model.
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Finally, we detect and are, for the first time, able to positively identify
cloud features with horizontal scales of 100 to 300 km extending far below
the region of supersaturation ( > 2 km). Using the growth model, we conclude
these features cannot be explained by sedimentation alone and suggest that
these events may be an indication of strong vertical transport. |
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| ISSN: | 1680-7316 1680-7324 |