# Presentation: 889897

## Leveraging TRMM Results for GPM Validation Planning

***David B. Wolff***
*NASA GSFC, Code 912.1, SSAI*
*wolff@radar.gsfc.nasa.gov*

## Acknowledgements

***Richard Lawrence: ****Head NASA TRMM Satellite Validation Office*
***D. Marks, D. Silberstein, J. L. Pippitt: ****Radar data processing and analysis*
***R. Adler, E. A. Smith, E. Amitai, A. Tokay: ****Scientific input and collaboration*
***Univ. of Washington: ****Development of UWASH GV products*

## TRMM GV Sites & Data Processing Status

- Four principal TRMM GV Sites
- Instrumentation: Radar, rain gauges and disdrometers
- NASA GSFC processes several science data products for validation
- Other sites of interest are Key West, FL and the Virginia/Maryland area near Wallops Island.

## Keys Area Precipitation Project

- Ongoing precipitation observations in the Florida Keys.
- Have performed Intensive Operations Program (IOP) for last three summers (2001-2003).

## Wallops Area GV Site

- Gauge Network

- Wakefield WSR-88D

## TRMM GV Products

***Level 1: Quality-controlled reflectivity data in original (polar) coordinates***
*Semi-automated QC program used to remove non-precipitating echo from radar observations*
***Level 2: Rain intensity (gauge and radar), stratiform/convective rain type, gridded (3-d) reflectivity***
*One-minute gauge rain intensities produced by spline interpolation of discrete ‘tips’*
*Radar estimated rain rates: Rosenfeld et al.*
*Stratiform/Convective rain type: Steiner et al.*
***Level 3: Pentad and monthly rainfall maps, reflectivity statistics and distributions***
*Integrated rain intensity maps using forward integration. Quantify errors due to missing radar observations (gaps)*

## GSFC Rain Intensities

***GSFC radar-estimated rain intensities from probability matched gauge and radar observations***
*Current (V5) relationship derived from radar/gauge data in 2002*
*Applied to all other available data *
***Window Probability Matching Method (WPMM) forces match between the probability distributions of gauge rain rates and radar reflectivity (Rosenfeld et al. 1996)***

## Importance of Stable Radar Calibration

## Comparing GSFC & UWASH Results

- Both UWASH and NASA GSFC provide rain estimates at Kwajalein.
- UWASH uses a DSD-based Z-R relationship, independent of rain gauges.
- GSFC uses radar/gauge based WPMM
- Approximately 26% difference between UWASH and GSFC when calibrations offsets are the same (1999 & 2001)

## GSFC/UWASH  Comparison (2001)

-  Both GSFC & UWASH agree with gauges in 2001
-  Given the same radar calibration correction, GSFC rain rates ~ 26% higher than UWASH
-  Differences are understood as algorithmic and based on different philosophies
-  No conclusions possible yet as to which are “correct”

## Comparing GV and TRMM Rain Intensities

**Results from ITE104 (Version 6a) over Kwajalein 01/2001 - 04/2002.**
- Rain intensity estimates with TRMM performed using 0.5° x 0.5° gridded data with similarly gridded GV data
- Shows convergence of TRMM and GV estimates to within ~ 10% over ocean.
- Similar results for MELB and HSTN
- Complications arise in coastal areas and over land

## TRMM/GV Comparisons over Ocean

## Probability Distributions

- Probability distributions of rain rate were derived from TRMM (PR, TMI and COM) and GV estimates
- TRMM -->  global (land or ocean) for Feb 1998 (ITE110 - official V6)
- GV -->  KWAJ (Ocean) and MELB (Land) for period 07-12/1999
- Over ocean all PDFs nearly log-normal with some exceptions.
- Over land, there remains work to be done, especially for 2A12 (TMI).

## Convergence of TRMM & GV Estimates 

## Conclusions and Recommendations

***GV has progressed well over the last year***
*Several year data set to work with from 3/4 sites*
*Will continue to eliminate backlog and improve rain estimates*
***GV vs. GV (KWAJ)***
*If you believe in gauges you get one answer, if you believe in DSD-based Z-R you get another.*
*Difference = 25%*
*No conclusions as to who is right or wrong, we don't know yet.*
*Unfinished business that must be resolved.*
*Quality of estimates is forced by measurements available*
***Importance of ******STABLE****** calibration***
*1 dB adjustment to GSFC estimates resulted in a 13% increase in rain accumulations*
*Must attempt to get radar calibration errors to 1 dB or less (is this possible?)*
*Extremely high priority for TRMM and GPM*
***Convergence statistics***
*Convergence of TRMM and GV are currently within 10-20%. TRMM and then GPM should endeavor to increase this convergence (5% or better).*
*TRMM data can and is being used to prepare for GPM GV *