1. CPC Unified Gauge – Satellite Merged Precipitation Analysis for Improved Monitoring and Assessments of Global Climate Pingping Xie, Soo-Hyun Yoo, Robert Joyce, and Yelena Yarosh

2. CPC’s Unified Precipitation Project
Multiple precipitation analyses generated at CPC over the past ~20 years to satisfy various requirements
Inconsistencies due to different input data and analysis procedures used
A project is underway at CPC
To create a single suite of unified precipitation products for global / regional applications;
To increase the accuracy, reliability and quantitative consistency of the new products.

3. Components of the Unified Products
Station reports
Unified, quality controlled
Satellite estimates
Multiple satellites / multiple instruments / integrated
Analyses
Gauge-based; gauge-satellite merged
Global / Regional ;

4. Gauge Analysis of Global Daily Precipitation
Interpolation of gauge reports from ~30K stations
Optimal Interpolation (OI) with orographic correction (Xie et al. 2007)
Interpolated on 0.125olat/lon, then averaged on 0.5olat/lon grid over global land for release
Global fields from1979 to present updated daily on a real-time basis
CONUS analysis
from 1948 on
0.25olat/lon
Example
for July 1, 2003

5. High-Resolution Satellite Estimates
CMORPH : CPC Morphing technique (Joyce et al. 2004)
Combined use of satellite PMW and IR data
8kmx8km / 60oS-60oN;
30-min interval / from September 2000 / Real-time
Project on the way to back-extend the CMORPH to 1998
Sample for August 18, 2003

6. Merging Gauge and Satellite Data [ 1 ]
Combining the strength of gauge and satellite data to produce a merged analysis with improved quality
Gauge: accurate point measurements but sparse distribution
Satellite: complete coverage but with bias and random error
Bias-corrected Satellite Estimates over the Globe
Correcting the bias and discontinuities in the CMORPH estimates
over land
through matching the PDF of CMORPH against that of the gauge-based analysis
Over ocean
Adjusting the CMORPH to a long-term data set (pentad GPCP) to facilitate the definition of anomaly

7. Merging Gauge and Satellite Data [ 2 ]
Sample bias-corrected Satellite Estimates

8. Merging Gauge and satellite data [3]
Daily Gauge
Comparison of satellite estimates with gauge data for Apr. – Sep., 2009
Bias is corrected almost completely over the global land;
Correlation for daily precipitation over 0.25olat/lon grid boxes is improved by ~0.05
CMORPH
How is the correlation computed? Is there a certain percentage of gauges withheld from the bias correction process and then used to perform the correlation?
Why is 7 months of KF-CMORPH needed for 6 months of bias correction? Do you need at least two gauges in a grid box?
Only grid boxes with at least one gauge are included in computing the bias and the correlation
Gauge-Adjusted CMORPH

9. Merging Gauge and Satellite Data [ 4 ]
July 2005 Monthly Mean Precip at T382

10. Merging Gauge and Satellite Data [ 5 ]
July 2005 Diurnal Standard Deviation of Hourly Precip.

11. Merging Gauge and Satellite Data [6]
Combining Bias-corrected Satellite Estimates with Daily gauge over the Several Regions
This is only possible for several regions due to different daily ending time in the gauge reports
Africa (06Z)
CONUS/MEX (12Z)
S. America (12Z)
Australia (00Z)
China (00Z)
Combining the bias-corrected CMORPH with gauge observations through the Optimal Interpolation (OI) over selected regions where gauge observations have the same daily ending time
in which the CMORPH and gauge data are used as the first guess and observations, respectively

12. Merging Gauge and Satellite Data [ 7 ] Example over China

13. Merging Gauge with Satellite Data [ 8 ] Example over CONUS

14. Merging Gauge with Satellite Data [ 89] Example over Africa

15. Summary
Prototype algorithm is developed and test products are constructed for the gauge-satellite merged global precipitation analyses
Two sets of gauge-satellite precipitation analyses
Bias-corrected Satellite Estimates
Global
8kmx8km; 30-min
1998 to the present
Gauge-satellite combined analyses
Regional
0.25olat/lon; daily
Unified gauge – satellite precipitation analyses useful for climate monitoring, model verifications, hydrological studies, et al.