Clouds and Radiative Fluxes Associated with the 200203 El Nino Event

1
Evaluation of Passive Microwave Rainfall
Estimates Using TRMM PR and Ground Measurements
as References
Xin Lin and Arthur Y. Hou NASA Goddard Space
Flight Center
Accumulated 5-day surface rainfall (mm) from
satellite retrievals, and from single forecasts
by the ECMWF IFS and the NASA GEOS-5
high-resolution global models. The official NOAA
observed best track (black line) and the
forecast tracks (blue line) for Katrina are
superimposed. The ECMWF and NASA forecasts are
initialized at 12z and 06z, 25 August 2005,
respectively. (Lin et al. 2006)
2

• The Global Precipitation Measurement Mission is
  trying to create a multi-member satellite
  constellation to measure precipitation over the
  globe at a 3-hourly interval or shorter.
• It is expected that GPM will consist of a PR for
  calibration purpose, and a number of passive
  microwave sensors to enhance temporal and spatial
  sampling.
• Assess the quality of rainfall estimations from
  cross-track microwave sounders relative to those
  from conically-scanning microwave radiometers
• There are no truth rainfall observations.

3

• Limitations by using ground measurements alone
• Evaluations are only performed over a few sites
  over open oceans and some well-instrumented land
  areas. The error statistics maybe highly
  rain-regime-dependent, and may not be applied to
  other parts of the globe.
• A careful calibration of gauges and operational
  radars at different locations onto a unified
  reference framework is very expensive.
• Satellite rainfall retrieval algorithms have
  different sensitivities on the rain/no rain
  detection, and rain estimations at different rain
  intensities.

4
Why using TRMM PR as a reference?

• One of the TRMM science objectives TRMM PR
  serves as a flying rain gauge to calibrate
  other rainfall retrieval algorithms
• Active microwave sensor
• Theoretical superiority to overland PMW technique
• A number of validation studies have shown the
  high quality of PR data (e.g., Schumacher and
  Houze 2000, Liao et al. 2002)

5
Objectives

• Using both TRMM PR data and ground measurements
  as references to evaluate coincident PMW rain
  retrievals
• Better understand the rainfall error statistics
  of PMW radiometer and sounder data over land and
  ocean
• Better understand the error statistics of
  convective, stratiform, and warm rain estimations

6
Sensors and Rainfall Retrievals

• Active microwave sensor TRMM Precipitation Radar
  (PR)
• Passive microwave radiometers TRMM TMI, SSM/I
  from DMSP F13, F14, and F15, AMSR-E on AQUA,
  GPROF Version 6.
• Passive microwave sounders AMSU-B from NOAA-15,
  -16 and -17 satellites.
• All the rainfall data (January 2005-August 2006)
  are grided onto a 0.25º x 0.25º grid at 10-minute
  intervals.

7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
Over TRMM ocean For instantaneous rain rates
below 5 mm/h, the GPROF6 algorithm tends to do a
better job than AMSU-B.
11
Over TRMM land Rain estimates from PMW sounders
are comparable in quality to those from PMW
radiometers.
12
Using Ground Measurements as A Reference to
Evaluate Passive Microwave Rainfall Retrievals

• NCEP National Hourly Precipitation Analysis
• Hourly radar rainfall estimates from about 140
  WSR-88D radars
• About 3,000 gauge reports
• 4-km resolution
• Data are preliminarily quality controlled.

13
The HSTN and MELB profiles are courtesy of Dave
Wolff,
14
Warm Rain Detection
Warm rain precipitation that is not associated
with ice during its formation Lau and Wu (2003)
suggested that warm rain could account for 31 of
the total rain amount and 72 of the total rain
area in the Tropics
15
Summary

• For instantaneous rain rates between 1 and 10
  mm/h, AMSU-B rainfall estimates are comparable in
  quality to those derived from conically-scanning
  radiometers over land, even though they are some
  what worse over oceans.
• Cross-track microwave sounders with
  high-frequency channels on operational satellites
  can play a significant role in augmenting
  conically-scanning microwave radiometers to
  achieve better sampling and coverage over land.

16
Current and Future Work

• The variation of rainfall error statistics at
  different temporal and spatial resolutions
• The variation of rainfall error statistics over
  different raining regimes
• Simulating GPM satellites in global
  high-resolution model forecasts and global cloud
  model output