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Cirrus cloud formation and evolution from the microscale to the synoptic scale
NCAR Advanced Study Program (ASP)
Earth Observing Laboratory
Cirrus clouds, covering ~30% of the Earth’s surface, play important roles in Earth’s climate, weather and atmospheric chemistry. As a major uncertainty in climate models, the magnitude and sign of cirrus clouds’ radiative forcing (cooling or warming) are influenced by both their microphysical properties (such as ice crystal number density and size distribution) and the larger scale characteristics (such as horizontal and vertical extent). However, it is challenging to understand these multi-scale processes due to the limited spatial and temporal coverage of in-situ observations.
In this work, we link in-situ observations with the meteorological background using reanalysis data. Two formation mechanisms are found for cirrus clouds’ initial conditions - ice supersaturation. These two mechanisms show different dynamical conditions (large scale uplifting versus small scale waves/turbulences), as well as mixing of different air masses (tropospheric mixing versus stratospheric-troposphere mixing). Jet stream and the extratropical tropopause are found to play important roles in setting these dynamical conditions.
Besides the regional analyses, we conduct a hemispheric comparison on cirrus cloud formation and evolution (Diao et al. 2013, 2014). Our work is motivated by the question of “are there any differences in cirrus cloud formation and evolution, given that the Northern Hemisphere has ~10 times higher aerosol loading than the Southern Hemisphere?” Comparisons of relative humidity, ice crystal number density and mean diameter, as well as the relative lifetime of cirrus will be shown.
Tuesday, 5 August 2014, 3:30PM
NCAR - Foothills Laboratory
3450 Mitchell Lane
Bldg 2 Small Seminar Room (Rm1001)