Status and Future of The Global Precipitation Climatology Project (GPCP) CDR

Abstract:

The Global Precipitation Climatology Project (GPCP) monthly analysis is a frequently used, standard research product providing a globally complete precipitation analysis based on satellite and gauge information for the period 1979 to the near-present. As a Climate Data Record (CDR) product the current version (Version 2.2) is being transferred to operational production at NOAA NCDC.

The current monthly (1979-present), pentad (1979-present) and daily products (1997-present) are composed of a range of datasets with estimates based on gauges, polar-orbiting passive microwave and geostationary infra-red estimates. Over time, the changes in the available observations that comprise GPCP are inevitable, due to changes in the available satellites, instruments available and algorithms used to estimate precipitation. Several such recent changes have necessitated production of an upgrade to the GPCP Version 2 system and these are described in this paper. This update from V2.2 to V2.3 includes a new bias correction for the SSMIS ocean algorithm, a new correction for the transition from TOVS to AIRS and an update to the gauge dataset used over land.

We will also describe the development and production of a near-real time version of the CDR. The GPCP CDR is usually produced a few months after real-time due to time lags of input data sets and time necessary for data quality control and the merging process. This time lag has limited its use in the month-by-month (real-time) climate monitoring of global precipitation. Recently, however, based on a significant amount of effort by a number of groups and people associated with the GPCP, the process for producing an Interim CDR product (ICDR, available within 10 days of the end of the month) has been developed and implemented for distribution to the research and operational communities. This allows for a rapid end-of-month analysis, comparison with the GPCP monthly climatology, and the potential for using the data for additional monitoring calculations. This GPCP ICDR uses the same analysis techniques, but not all the input data sets are identical. Comparison between the final CDR product and the ICDR indicate small, but occasionally significant differences. The ICDR will be discussed along with some potential applications for monitoring climate including drought and ENSO.