John Janowiak Climate Prediction Center/NCEP/NWS

Jianyin Liang China Meteorological Agency

Pingping Xie Climate Prediction Center/NCEP/NWS

Robert Joyce CPC / RS Information Systems

IPWG-3 -- Melbourne, Australia October 24, 2006

*CPC Morphing Technique

Rain Gauge Data Merged with CMORPH* Yields: RMORPH

(microwave)

? ?

1.5 hours apart

GPM offers 3-hr sampling … to get finer temporal sampling …take advantage of 30-minute sampling afforded by Geo-IR data

Premise: Error in using IR to interpolate precip. features identified by PMW <

Error in deriving precip. directly from IR

So avoid deriving precipitation estimates directly from IR …

(microwave)

? ?

Derive motion vectors from ½ hourly IR

Apply motion to PMW-derived precipitation

“Morph”

(Joyce et al., J. Hydromet, 2004)

1.5 hours apart

mailto:john.janowiak@noaa.gov

mailto:john.janowiak@noaa.gov

Biases in Satellite Estimates

Gauge-CMORPH Merging AlgorithmGauge-CMORPH Merging AlgorithmStep 1: Bias CorrectionStep 1: Bias Correction

• AssumptionsAssumptions

- Biases relatively stable over a region and time - Biases relatively stable over a region and time

- Biases can be approximated as ratios between the estimates & - Biases can be approximated as ratios between the estimates & gauges gauges

• ProceduresProcedures

- Performed once a day using data for all 24 hourly slots- Performed once a day using data for all 24 hourly slots

- Each day: - Each day: RATIO = GAUGE / CMORPHRATIO = GAUGE / CMORPH (last 30 days; each gauge) (last 30 days; each gauge)

- Optimal Interpolation (OI) technique (Gandin 1965) applied to ratios- Optimal Interpolation (OI) technique (Gandin 1965) applied to ratios

- “Un”biased CMORPH: - “Un”biased CMORPH: CMORPH x RATIOCMORPH x RATIOanalyzedanalyzed

Gauge-CMORPH Merging AlgorithmGauge-CMORPH Merging AlgorithmStep 2: Combining Gauge & Satellite DataStep 2: Combining Gauge & Satellite Data

Bias-corrected satellite estimates and gauge data combined via Bias-corrected satellite estimates and gauge data combined via Optimum Interpolation Technique (“OI”) Optimum Interpolation Technique (“OI”)

--Bias-corrected satellite estimates used as first-guessBias-corrected satellite estimates used as first-guess

- Gauge data are incorporated- Gauge data are incorporated

- Relative weighting at a grid box is a function of:- Relative weighting at a grid box is a function of:

- quality of satellite estimates at the grid box;- quality of satellite estimates at the grid box;

- density of local gauge - density of local gauge network densitynetwork density

Proof-of-Concept:Proof-of-Concept:Guang-Dong Province over Southern ChinaGuang-Dong Province over Southern China

South China Sea

Tibet plateau

Topography

Guang-Dong

Hourly precipitation reports from 394 stations over ~150,000 km2

(~380km2/gauge)

An Example for 03Z, May 5, 2005An Example for 03Z, May 5, 2005

GAUGE ONLY ORIGINAL CMORPH

BIAS CORRECTED MERGED

An Example for 03Z, May 5, 2005An Example for 03Z, May 5, 2005

GAUGE ONLY ORIGINAL CMORPH

BIAS CORRECTED MERGED

Mean Precipitation Mean Precipitation from April 1 – June 30, 2005from April 1 – June 30, 2005GAUGE ONLY ORIGINAL CMORPH

BIAS CORRECTED MERGED

Hourly Gauge-Satellite Merged

PDF of Hourly Precipitation PDF of Hourly Precipitation for April - June, 2005for April - June, 2005

• Frequency of No-Rain EventsFrequency of No-Rain Events

• Gauge Station: Gauge Station: 83.9%83.9%

• Gauge Analysis:Gauge Analysis: 81.5%81.5%

• Original CMORPH:Original CMORPH: 77.3%77.3%

• Gauge-CMORPH Merged:Gauge-CMORPH Merged: 83.3%83.3%

• Frequency of Events with RainFrequency of Events with RainHistogram of precipitation frequency Apr-Jun

0

0.01

0.02

0.03

0.04

0.05

0.06

0-1 1-3 3-5 5-9 9-17 17-33 33-65 65-129 >129Precipitation range(0.1mm/h)

Fre

qu

ency

GaugeOI Gauge+CMORPHOI GaugeCMORPH

Dense Gauge Locations: Disaggregate Gauge Data

Use hourly CMORPH to partition daily gauge amounts into hourly amounts (i.e. “disaggregate”)

- United States

- Australia

- China?

Valid for 24 hrs ending 12z August 8, 2006

-Daily RMORPH constrained to daily gauge amount

- Gauge data partitioned into hourly amounts

-Spurious coverage of light gauge amounts reduced

Valid for 24 hrs ending 12z August 8, 2006

Daily sum of hourly amounts

Where to from Here?

1. Transition regional prototype to global

2. Experiment with OI tuning parameters

3. Cross-validation testing

4. Explore bias-adjustment for oceanic precip

- Normalize estimates to TRMM “2B31”(TMI/PR)

- ATLAS buoys?- Radar?

Thanks for listening

An Example for 03Z, May 5, 2005An Example for 03Z, May 5, 2005

GAUGE ONLY ORIGINAL CMORPH

BIAS CORRECTED MERGED

An Example for 03Z, May 5, 2005An Example for 03Z, May 5, 2005

GAUGE ONLY ORIGINAL CMORPH

BIAS CORRECTED MERGED

(microwave)

(in time)

(in time)

Observed

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