A microphysics guide to cirrus clouds – Part 1: Cirrus types
The microphysical and radiative properties of cirrus clouds continue to be beyond understanding and thus still represent one of the largest uncertainties in the prediction of the Earth's climate (IPCC, 2013). Our study aims to provide a guide to cirrus microphysics, which is compiled from...
| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/3463/2016/acp-16-3463-2016.pdf |
| Summary: | The microphysical and radiative properties of cirrus clouds continue
to be beyond understanding and thus still represent one of the
largest uncertainties in the prediction of the Earth's climate
(IPCC, 2013). Our study aims to provide a guide to cirrus
microphysics, which is compiled from an extensive set of model
simulations, covering the broad range of atmospheric conditions for
cirrus formation and evolution. The model results are portrayed in
the same parameter space as field measurements, i.e., in the Ice
Water Content-Temperature (IWC-T) parameter space. We validate
this cirrus analysis approach by evaluating cirrus data sets from
17 aircraft campaigns, conducted in the last 15 years,
spending about 94 h in cirrus over Europe, Australia, Brazil
as well as South and North America. Altogether, the approach
of this study is to track cirrus IWC development with temperature by
means of model simulations, compare with observations and then
assign, to a certain degree, cirrus microphysics to the
observations. Indeed, the field observations show characteristics
expected from the simulated Cirrus Guide. For example, high (low) IWCs
are found together with high (low) ice crystal concentrations
<i>N</i><sub>ice</sub>.
<br><br>
An important finding from our study is the classification of two
types of cirrus with differing formation mechanisms and
microphysical properties: the first cirrus type forms directly as
ice (in situ origin cirrus) and splits in two subclasses, depending
on the prevailing strength of the updraft: in slow updrafts these
cirrus are rather thin with lower IWCs, while in fast updrafts
thicker cirrus with higher IWCs can form. The second type consists
predominantly of thick cirrus originating from mixed phase clouds
(i.e., via freezing of liquid droplets – liquid origin cirrus),
which are completely glaciated while lifting to the cirrus formation
temperature region (< 235 K). In the European field
campaigns, slow updraft in situ origin cirrus occur frequently in
low- and high-pressure systems, while fast updraft in situ cirrus
appear in conjunction with jet streams or gravity waves. Also,
liquid origin cirrus mostly related to warm conveyor belts are
found. In the US and tropical campaigns, thick liquid origin cirrus
which are formed in large convective systems are detected more
frequently. |
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| ISSN: | 1680-7316 1680-7324 |