1. Matt Lebsock Chris Kummerow Graeme Stephens Tristan L’Ecuyer
Comparison of warm rain detection and quantification from spaceborne passive microwave and radar sensors
Matt Lebsock
Chris Kummerow
Graeme Stephens
Tristan L’Ecuyer

2. Questions What does CloudSat tell us about warm rain?
How does this compare with AMSR/E and PR?
Can this inform our understanding of the capabilities of GPM?

3. The Roll of Various Satellite Rainfall Sensors
Passive Microwave (e.g. AMSR/E)
Long term climate record & Frequent global sampling
Imprecise, Cloud/Rain separation
TRMM-Precipitation Radar (PR)
The standard
Minimum detectable signal (0.5 – 1.0 mmh-1)
CloudSat-Cloud Profiling Radar (CPR)
Extreme sensitivity to light rain
Signal saturates in heavy rain
Complementary role (light rain)

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
Lebsock & L’Ecuyer, 2011 JGR

5. Precipitation Occurrence from CloudSat

6. Warm Rain Distribution
Global annual average intensity = 0.23 mmd-1
~7% of global precipitation
Areas of largest accumulation:
East-Pacific ITCZ
Subtropical cumulus regimes (not Scu)
Liu & Zipser, 2009 J. Clim.

7. CloudSat-AMSR/E GPROF Comparison
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.
Missed Accumulation (89%)
Missed Accumulation (11%)
Large regional bias remains

8. GPROF database bias
GPROF database is stratified in terms of SST and CWV
GPROF database is built from TRMM-PR/TMI observations
Bias inherent in the PR will manifest itself in AMSR/E product.
Regime dependent biases separate sharply
Extended Database

9. CloudSat-TRMM/PR Comparison
Hit
Miss
TRMM-PR
429
133
4204
77139
Colocation mismatch:
Requires bias adjustment
Year: 2006, DOY: 227, 2oS, 95oE, CloudSat Granual: 01594
PR Probability of warm rain detection = (11.8%)
(unadjusted = 9.3%)
PR/CloudSat warm rain accumulation (46.6%)
Weighted by area
Oceanic TRMM region

10. PR probability of detection: resolution vs. sensitivity
limited
Sensitivity
limited

11. Implication for GPM: Sensitivity ~88% ~42% GPM
These figures show global means integrated over all areas (land&ocean)

12. Implication for GPM: Resolution Occurrence Accumulation 14%
Rough estimate of spatial resolution effects on PR/DPR accumulation
Occurrence dominated (60%) by events with horizontal dimensions < 5 km

13. Summary
CloudSat provides a unique view of warm rain that complements the TRMM-PR and passive microwave sensors.
Global mean warm rain rate ~ 0.23 mm/day (~7% of the global rainfall)
AMSR/E captures ~89% of warm rain accumulation
Huge improvement in new GPROF2010 product
Significant regional biases remain
TRMM-PR captures ~45% of warm rain accumulation.
Outlook for GPM-DPR is positive
Can reasonably expect this ‘observed accumulation’ to be greater than 88% based on increased sensitivity and 86% based on resolution (>74%).
98-99% of total rain accumulation