1. Combining GOES-R and GPM to improve GOES-R rainrate product
Nai-Yu Wang, University of Maryland, ESSIC/CICS
Kaushik Gopalan, ISRO, India
Rachel Albrecht, CPTEC, Brazil
Weixin Xu, University of Maryland, ESSIC/CICS
Rober Adler, University of Maryland, ESSIC/CICS

2. Motivation
GOES-R QPE algorithm uses microwave rain estimates as a calibration
To enhance microwave-based convective and stratiform precipitation partition using lightning by connecting the ice-phased microphysics commonly observed by lightning sensors and microwave radiometers

3. Relating lightning to microwave convective properties
TRMM October 10, 2004 over Brazil (TRMM #39346)
LIS event rate
(events/min)
TMI 85 GHz V-pol TBs
Ice, mixed -phase
Microwave + Lightning
Radar convective/stratiforn type
Delineate
Convective/Stratiform
Rain Rate
LIS flash rate
(flashes/min)

4. TRMM LIS/TMI/PR Database (proxy for GOES-R and GPM)
Four years ( ) of TRMM radar/radiometer/lightning data in 0.1° grid resolution over land
PR convective fraction estimates, near surface rain rates, reflectivity profiles
TMI TBs, convective fraction estimate (from 10/37/85 GHz), rain-rates (from 85 GHz)
LIS radiances, event rates, group rates and flash rates
14 millions raining pixels are used to investigate relationships between lightning frequency/occurrence and convective/statirom partition in the precipitation system observed by microwave

5. Interesting lightning-precipitation Statistics
Four years, 14M TRMM TMI/PR/LIS over land precipitation data (in 0.1o grid resolution) reveal that
6% of rain data has lightning flash rate > 0 fl/min
13.5% of the lightning occur in stratiform, 86.5% in convective
convective rain probability increases with increasing lightning frequency. For example, 34% of rainfall is convective for low flash rates (0-1 fl/min), whereas the convective probability increases to 99.7% for high flash rates (>= 2 fl/min).

6. Raining pixels from Jan 2002 – Dec 2004
Lightning relationships with radar reflectivity and passive microwave 85 GHz Tb
Raining pixels from Jan 2002 – Dec 2004
Lightning occurrence and flash rates increase with decreasing 85 GHz TB and increasing reflectivity!

7. Lightning information in separating convection and straiform precipitation
Lightning info is definitely very useful in
discriminating radar features of convective and
stratiform precipitation
Colder Tb generally increases
with increasing lightning rates

8. TRMM PR/TMI/LIS Database stratified by lighting flash rates
Category
Criterion
Number of pixels (Percentage)
Rain Type Distribution
Convective/Stratiform/other (%)
Category 0 (CAT0)
Pixels where LIS detects
no flashes
~13 million (94%)
6% / 61% / 33%
Category 1 (CAT1)
0-1 flashes
~470,000 (3.4%)
34% / 21% / 45%
Category 2 (CAT2)
1-2 flashes
~221,000 (1.6%)
47% / 11% / 42%
Category 3 (CAT3)
> 2 flashes
~89,000 (0.6%)
99.7% / 0.25% / 0%

9. Using Lightning flash rates in microwave convective and stratiform partitioning
Lightning flash rates are used to classify convective areal fraction by pre-classifying microwave TBs into 4 groups of increasing convective probability, before rain-rate retrievals
RR = RRconv P(C) +RRstrat (1 - P(C))
P(C) : convective fraction
P(C) = a1 TB10V + a2 (TB37V+TB85V)/2
+ a3 NPOL + a4 STDEV + a5 MINIMA +k

10. Effect of Lightning in the microwave convective-stratiform paritioning
TMI P(C)
TMI-LIS P(C)
5 PCTILE
MEDIAN
95 PCTILE
CAT0
no flash
0.10
0.51
0.09
0.47
CAT1
0-1 fl/min
0.11
0.41
0.71
0.29
0.54
0.75
CAT2
1-2 fl/min
0.16
0.50
0.76
0.45
0.68
0.84
CAT3
>2 fl/min
0.24
0.59
0.83
0.98
0.996 1

11. Improvement of Passive Microwave Retrievals (Used as Calibrator for IR Baseline Algorithm) An Example: Lightning Impact on Rain Rate Retrievals
radar
microwave
microwave + lightning
P(C)
rain
rate
Overall impact of of lightning on rainrate is 5-10%, but focused on highest rainrates

12. IR Rain Estimation Issues and Motivation of incorporating Lightning
Limitations of infrared-based rain estimates:
-- Only “see” the top of precipitating cloud;
(though cloud growth or structure can be considered)
-- May treat cold cirrus clouds as intense convection;
-- May misrepresent convective rain: location, area
and rain intensity (especially under relatively uniform cold cloud shields in mature MCSs);
But geostationary rain estimation still very important because of temporal resolution and rapid access
How would lightning information help?
-- Provide information associated with convection location and intensity (~ rainfall rate)

13. IR (and IR + Lightning) Rain Estimation Applied to TRMM Data
 Initial IR technique is variation of Convective Stratiform Technique (CST, Adler and Negri, 1988)
 Refine initial CST technique
 Lightning information are used to define convective cores “unseen” by IR and eliminate IR cloud top minima incorrectly identified as “convective”

14. IR-based C/S Technique (CST)
STEPS: 1.Find local minima (Tmin); 2. Slope test
3. Assign conv. area; 4. Define strat. Area (T mode) IR
Lightning +
Radar (Conv/Strat)
CST (and most IR techniques) does a GOOD job in catching young convective cells.
CST (from IR)
Conv. Area by PR

15. IR-Lighting-Combined C/S Technique (CSTL)
Conv. cores w/o lightning in mature systems are removed
Conv. areas (with flash) missed by CST are added;
Lightning + IR
Radar (Conv/Strat)
CST (from IR+L)
CST (from IR)
CST does a relatively POOR
job for mature convective systems.

16. CST combined with Lighting (CSTL)
1. CST defined convective cores w/o any lightning
flashes are removed;
2. Convective areas with flashes but missed by CST
are added;
3. Convective rainrate is retrieved as a function of both
IR Tb and lightning flash density.
Rain Rate Assignment
Stratiform area: 2.5 mm/hr;
Conv. without lightning: as a function of Tmin;
Conv. with lightning: as a function of lightning FD;

17. Values of Lightning to IR CST
* CST and CSTL evaluated by PR on convective areas;
* 2000 cases (> 20 lightning flashes) are selected;
Lightning improves the convective detection (POD), lowers the false alarm (FAR); and improve CSI by 30%.

18. CST Issues and Use of Lightning Rainfall Rate (20 km resolution)
IR Tb
TMI
CST
CSTL

19. Summary and Future Work
Relationships between total lightning and precipitation measurements from TRMM radar/radiometer/lightning are analyzed.
A new algorithm to use lightning information to delineate microwave convective areal fraction is developed; Results reveal that lightning flash rates primarily improves the identification of deep convection and heavy convective rainfall ; Bias error reduction of 6% and RMS error increase of 4.5% (JGR paper in press)
Initial work completed in developing framework for testing IR (and IR + lightning) rain estimation with TRMM data and for comparing results with GOES-R baseline algorithm
Preliminary results indicate obvious value of lightning information to establish location of convective cores “unseen” by IR and eliminate incorrect core identification by IR. Preliminary statistics indicate significant improvement in rain estimation with use of lightning data
Next steps include:
full analysis of TRMM IR and IR+L rain estimation to carefully quantify lightning impact and its potential and limitations in comparison/ combination with Baseline algorithm
use of CHUVA and other data sets to evaluate IR+L with Baseline and test with time resolution/evolution