Weather and Climate Systems

Characterizing Cirrus Cloud RHICE at the ARM SGP Site For Different Synoptic Classifications

Andrew Dzambo
OU School of Meteorology

01 April 2015, 3:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Cirrus clouds have long been known to impact the earth’s radiation budget. Characterizing cirrus clouds in climate models has also proven challenging over the years. Climatologies of cirrus clouds have been created in the past based on their inherent microphysics, relative occurrence through the year, and dynamics driving their formation. Our understanding of cirrus clouds is very good overall, however, little is known about how RH, specifically RH with respect to ice (RHICE¬), varies in cirrus clouds under different synoptic regimes. This study attempts to bridge this gap in our understanding by incorporating a sophisticated synoptic climatology with collocated radiosonde and millimeter wavelength cloud radar (MMCR) data at the ARM program’s Southern Great Plains site.
The synoptic climatology is according to Marchand et al. (Journal of Climate; 2009) and includes 21 classifications under 5 parent classifications; each classification was derived from a neural-network algorithm that utilized ARM Ka-band radar data and ECMWF ERA-Interim reanalysis data over a span of 13 years. Key results found in cirrus cloud RHICE include variations of ice saturation according to parent classification, the dependence of integrated water vapor in the cloud with sedimentation, and cloud-relative altitude of maximum RHICE and minimum (negative) Doppler velocity. Implications regarding ice nucleation mechanism (heterogeneous vs. homogeneous), ambient dynamics driving cirrus cloud formation (e.g. gravity waves, turbulence) and radiative impacts with respect to how they affect/are affected by cirrus cloud RHICE are also discussed.

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