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CPC Unified Precipitation Project
Pingping Xie, Wei Shi, Mingyue Chen and Sid KatzNOAA’s Climate Prediction Center
2011.11.09.
Background
Multiple precipitation analyses generated at CPC over the past ~20 years to satisfy various requirements
Inconsistencies exist among the various CPC precipitation products due to:
• Differences in input data sources; and • Differing objective algorithms
Overall Goal of The Project
To consolidate and unify the various CPC precipitation products
by creating a suite of unified products of global / regional precipitation
The new products will • have better quality• present close quantitative consistency• replace the existing products
Components of the Unified Products
Station reports
• Unified, quality controlled
Satellite estimates
• Multiple satellites / multiple instruments
Analyses
• Global / regional ; Daily / Pentad / Monthly / hourly;
Retrospective / Real-time
A Database of Gauge Reports
Monthly and daily reports from over 32,000
stations
• GTS, NCDC archives (GHCN/GDCN..), COOP, RFC,
Mexico, Brazil, Australia, China…;
Quality Control
• with historical records, buddy check, satellite data and
model forecasts
Distribution of Reporting Stations
for July 1, 2003
Data Source for the US
• HistoricalNCDC COOP; SNOTEL; HADS; GTS
• (near) Realtime24-hr "first order" WMO GTS sites;
24-hr SHEF-encoded precipitation reports received via AWIP from the River Forecast Centers (NWS data stream).
* No MADIS data stream or CoCoRaHS data
* We tend to only use data with stable and long history in the analysis
QC of Daily Reports over the U.S. [1] Overall[1] Overall
Developed ~15 years ago at CPC;
Performed on an operational basis for daily reports from the US;
QC’ed station data used to create analyzed fields of daily precipitation over the CONUS.
QC of Daily Reports over the US[2] Procedures[2] Procedures
Four types:
1. Duplicate Station Check (eliminates duplicates; key punch errors)
2. Buddy Check (check for extreme values)
Examine the absolute value of the difference between the current station and all other stations within a one-degree box centered on the current station. If all of the stations exceed a specified threshold, then the current station is flagged and removed from the analysis.
QC of Daily Reports over the US [3] QC procedures (continued)[3] QC procedures (continued)
3. Standard Deviation Check
Apply a daily climatology (gridded) obtained from the unified gauge data base for the base period 1971 – 2000 (WMO standard). Compare each station observation to the nearest grid point value (from the climatology). The station value must be within 5 standard deviations of the daily climatology. During hurricane days, this check is turned off for affected areas.
4. Radar QC (Eliminate spurious zeros from the rain gauge data)
Systematically compare all daily rain-gauge reports against the nearest grid points in the 24-hr radar estimate of precipitation (Similar to procedures in standard deviation check). Flag and eliminate rain gauge zero reports if the radar estimates ≥ 1.0 mm/day.
Gauge-Based Analysisof Global Daily Precipitation
• >30K station reports
• Optimal Interpolation (OI) with orographic consideration
• 0.5olat/lon grid over global land
• 0.25olat/lon grid over the CONUS
• Daily fields from 1979 (1948 for CONUS) to present
• Real-time operations
Example of Gauge-based Analysis for July 1, 2003