Comparison of Oceanic Warm Rain from AMSR-E and CloudSat

1. Comparison of Oceanic Warm Rain from AMSR-E and CloudSat Matt Lebsock Chris Kummerow

2. Motivation • Radiosonde data [Ohtake, 1963] • Warm rain falls in all tropical ocean basins in all seasons more frequently than expected • Shipboard Weather Reports [Petty, 1995] • Drizzle and isolated showers are the preferred form of precipitation in many regions • DYCOMS-II [VanZanten et al., 2005] • ‘on roughly a third of the flights mean surface rates approached or exceeded 0.5 mmd-1’’ • RICO [Snodgrass et al., 2009] • in situ: 2.23 mmd-1 • PR: 1.05 mmd-1 • GPCP: 1.25 mmd-1 • VOCALS [Wood et al., 2011] • POC boundary: 10-20 mmd-1 • Open Cells: several mmd-1 • Closed cell: 90% evaporation of drizzle • And many more….

3. Motivation from CloudSat • Areas in the subtropical eastern ocean basins where rain fraction exceeds 5%. • Dominated by warm rain. • Small spatial scales (~5km) • This rain poses a significant challenge to AMSR-E. • Spatial scale • Moderate emmsission signature • No ice scattering • Is it important?

4. CloudSat Algorithm Sensitivity:Reflectivity vs. Attenuation Observations • Challenges • Attenuation • Multiple-scattering • Limited sensitivity at high rates • Opportunities • Extreme sensitivity to light/moderate rain • ~1km Spatial resolution • Useful for quantifying rain from shallow isolated moist convection that other sensors may miss Rain Rates Attenuation Solution Reflectivity Solution

5. CloudSat vs. AMSR-E • AMSR-E version GPROF-2004. • AMSR-E subset to CloudSat ground track (2007-2008). • Common data screening methodology has been employed to both datasets. Key Points Regions of under-catch by the CloudSat algorithm in the deep tropics can be related to saturation of the CloudSat signal in the heaviest rain. CloudSat observes more rain than AMSR-E in regions that have been historically difficult for the passive microwave sensors: The storm tracks The subtropical ocean basins (1) (3) (2)

6. Climatological Validation of CloudSat:Southeast Pacific • New CloudSat rain rates perform better than initial estimates. • Reflectivity based solution • Evaporation modeled Daily Average Precipitation (2006-2009) Courtesy of Anita Rapp (TAMU)

7. Distribution of Warm Rain • Accumulation dominated by frequency of occurrence, not intensity • Accumulation maxima: • East-Pac ITCZ • Trade Cumulus regions.

8. Dependence on Cloud Depth

9. Regime Dependence Ice phase prevalent • Warm rain rates are maximized at moderate boundary layer depths and moisture contents Suppressed

10. Conceptual Model Total Rain Rate Warm Rain Rate Inversion West East

11. CloudSat vs. AMSR-E:Warm Rain • AMSR-E subset to CloudSat ground Track • Common Data screening: • 1 degree boxes in which CloudSat observes no clouds colder than 273 K retained. • Warm rain near deep convection or cirrus screened. • AMSR-Ewarm= f* CloudSatwarm • f= 11%

12. How much warm rain does GPROF miss? Screened Scenes All Scenes ~ 5 W/m2

13. GPROF 2010? • AMSR-E (GPROF-2010) produces more light rain. • Designed to reproduce Precipitation Radar results. PR still misses most warm rain. GPROF 2010 GPROF 2004 Courtesy of Wes Berg (CSU)

14. Summary • CloudSat rain rates suggest that GPROF-2004 may miss up to 0.2 mmd-1 globally. • Small spatial extent (~5km) • Light/moderate rates • Warm tops • GPROF-2010 will increase light rain rates however regional differences will most likely leave room for further improvement. • The dominant mode of missed rain is shallow cumulus in the trades and the ITCZ (Not drizzle) in regimes with moderate boundary layer depths and moisture contents. Difficult to distinguish from cloud emission No scattering signal