Cloudsat and Drizzle: What can we learn Cloudsat and Drizzle: What can we learn? Robert Wood, University of Washington, Seattle contributions from Chris Bretherton, Kim Comstock, Sandra Yuter, Peter Caldwell and Bjorn Stevens CLOUDSAT Science Team Meeting, Laguna Beach, May 2004

Fraction of precipitation reports indicating “drizzle” Drizzle is prevalent form of precip. in MBL cloud regions 0% 10% 20% 30% 40% 50% >50%

Precipitation rates by dynamical regime

Light precipitation constitutes sizeable fraction of the areal mean rain amount in the tropics and subtropics

IMET Buoy (85W, 20S) measurements (data courtesy of Robert Weller, WHOI)

Scanning C-band radar (EPIC 2001) drizzle is intermittent with cellular structure max reflectivity of 20-30 dBZ 0 90 180 270 15 km 30 km -24 -12 0 12 24 dBZ

Can drizzle affect MBL dynamics?

Cloud macrostructure Pockets Of Open Cells (POCs) are frequently observed in otherwise unbroken Sc. These may be formed as a cloud response to drizzle-induced decoupling POCs

Microphysical-macrophysical links Figure courtesy Bjorn Stevens, UCLA 0 Tb 5 Low Tb indicative of large drops 11 - 3.75 m brightness temperature difference

More drizzle in heterogeneous clouds MODIS brightness temperature difference, GOES thermal IR, scanning C-band radar

What we know Drizzle is common in the subtropical MBL Drizzle has the potential to influence cloud dynamics and possibly macro-structure

What we don’t know Climatological distribution of drizzle What factors control the production of drizzle (cloud thickness, LWP, cloud microphysics) Quantitative assessment of the role of drizzle in modifying cloud dynamics/structure

How Cloudsat/A-Train can help Cloudsat will provide seasonal maps of drizzle in the subtropical MBL Aqua (MODIS, AMSR-E) and CALIPSO will provide estimates of MBL forcing terms (cloud cover, LWP, microphysics, SST, MBL-depth)

Fraction of areal mean precipitation observed

How long do we need to average?

Cloudsat Validation plans IMET buoys in regions of light precipitation (SE Pacific, Atlantic trade-winds) – “surface drizzle indicator” VOCALS 2007 – Ship/aircraft/island-based field campaign in SE Pacific stratus

Suggested outline of approach (a) Produce quantitative seasonal mean maps of drizzle properties in the subtropical MBL using Cloudsat (b) Use Aqua/Calypso measurements and NCEP/ECMWF reanalysis to constrain MBL forcing terms (c) Begin holistic synthesis of satellite measurements using new Park/Leovy/Rozendaal MBL model as framework (d) Make quantitative assessment of the importance of precipitation in forcing the subtropical MBL

Mean entrainment rates Entrainment rate [mm/s] ◄ NE Pacific SE Pacific ► Subsidence rate [mm/s]

Can precipitation affect MBL dynamics? Mixed layer budget analysis using observationally-derived forcings (EPIC 2001) and entrainment, shows subcloud negative buoyancy fluxes ( decoupling) only when drizzle is included

Frequency of precipitation occurrence (from Petty 1995) Fraction of reports indicating some form of precipitation (JJA 1958-1991) Regions dominated by MBL cloud do precipitate 0% 2% 4% 8% 16% 32%