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