1. Updating the GPCP Global Precipitation Datasets G.J. Huffman 1,2, R.F. Adler 1,3, D.T. Bolvin 1,2, EJ. Nelkin 1,2 1: NASA/GSFC Laboratory for Atmospheres 2: Science Systems and Applications, Inc. 3: Univ. of Maryland College Park/ESSIC http://precip.gsfc.nasa.gov Global Precipitation Climatology Project (GPCP) part of World Meteorological Organization / World Climate Research Programme / Global Energy and Water Experiment (GEWEX) Goal is global long-term records of precipitation for international community Presently >1300 citations Focus is long-term, following Climate Data Record paradigm  consistent inputs  careful inter-sensor calibration  consistent processing over a long period Input precipitation datasets SSMI over ocean – Chiu (CUHK/GMU) SSMI over land – Ferraro (NOAA/NESDIS) Geosynchronous and low-orbit IR – Xie (NOAA/NCEP/CPC) OPI – Xie (NOAA/NCEP/CPC) TOVS/AIRS – Susskind (NASA/GSFC) Precipitation gauge analysis – Becker (Global Precipitation Climatology Centre, or GPCC; Deutscher Wetterdienst) Three datasets computed Monthly  2.5°x2.5°, 1979-present  Huffman/Adler algorithm  Microwave calibrator is the single 6 a.m./6 p.m. satellite to ensure consistent diurnal bias behavior  stepwise bias removal before combination  satellite/gauge merger using weighting by estimated inverse error variance Pentad (5-day)  2.5°x2.5°, 1979-present  CMAP pentad estimates rescaled to sum to the GPCP Monthly Daily  1°x1°, October 1996-present  Daily satellite estimates rescaled to sum to the GPCP Monthly Accessing the GPCP Data Official repository is at World Data Center A at National Climatic Data Center WDC-A Home Page:http://lwf.ncdc.noaa.gov/oa/wmo/wdcamet-ncdc.html Developers’ home page contains additional information and graphics MAPB Precipitation Page:http://precip.gsfc.nasa.gov THE GPCP DATASETS P5.9 Emission Microwave Satellite/Gauge Scattering Microwave TOVS/AIR S Microwave/IR Calibration Gauge Gauge-Adjusted Satellite Multi-Satellite Geo Low-Orbit OPI Matched 3-hr Geo-IR GPI Merged IR GPI 1979-85 1986-87 1986-present 1987-present Microwave/Other Fusion AGPI Low-Orbit AGPI An important upgrade to the GPCC gauge analysis required a reprocessing The GPCC introduced a new climatology/anomaly scheme, with many more gauges  high-resolution climatology  Monthly analysis of station anomalies  Final monthly field composed of anomaly analysis added to climatology The new GPCC analysis provides a longer record  Version 2 used GHCN+CAMS prior to start of old GPCC analysis in 1986  Version 2.1 uses new GPCC throughout Alternative OPI datasets were tested, but not used in the Version 2.1 monthly The OPI calibration against the SSMI era was extended to 20 years of data GPCP Version 2.1 released in July 2009 MOVING TO VERSION 2.1 Comparison of Versions 2 and 2.1 The Version 2 and Version 2.1 GPCP climatologies are very similar (map) new GPCC gauge analysis is generally higher  GPCP Land average is higher (table; 6% globally)  Increases are larger in the tropics – total and by percentage (table)  Differences tend to be larger where Version 2 used GHCN+CAMS gauge analysis, before 1986 (time series)  Greatest contribution is in high-precip areas (map)  Some coastal ocean regions also increase (map) open-ocean differences are small  Tend to occur during the OPI era, before SSMI in 1987 (time series) Total is area-weighted sum of Land and Ocean (table; time series)  V2.1 – V2 differences dominated by Land RESULTS – GPCP V2.1 Time Series 1979-2009 To first order, Ocean and Land are anti-correlated variations in Total are relatively small ENSO is the dominant interannual variation Total, Ocean have weak positive correlations Land has a strong negative leading correlation  details sensitive to definition of “Land” Note interdecadal variations on a nearly flat trend line RESULTS – ENSO Signal One of the original GPCP goals was to map the precipitation variations due to ENSO events the composite El Niño – La Niña shows the expected structure across the tropical Pacific also, coherent bands of anomalies angle out from the tropics to mid- latitudes RESULTS – Linear Trends in GPCP Compute the linear trend in V2.1GPCP for 1988-2007, without assuming that this represents a secular trend Precip in the data set (and atmosphere??) shows >0.7mm/d/decade locally resemblance to composite ENSO patterns in Pacific Contribution to the global trend by low, middle, high latitudes for 1988-2008: change expressed as fraction of global-avg precip per decade increases in the tropics neutral or decreasing in all other areas decreased global trend due to downturn in the last 3 years S high lat S mid-latTropicsN mid-latN high latGlobe ‘88-’07 Linear Trend (mm/d/decade) MORE CHANGES COMING TO GPCP The Switch to SSMIS The GPCP is designed to use the 6 a.m. / 6 p.m. microwave sensor on DMSP as the calibrator The consistent observation time avoids changing diurnal bias as other satellites enter and leave the constellation The current record uses SSMI on F08, F11, F13 (heavy red, orange, magenta) SSMI on F13 failed in September 2009, so we need to switch to SSMIS  F17 is closest in time  We plan to start F17 with January 2009 to avoid end-of-lifetime faults in F13 data Early SSMIS data had calibration problems that required years of analysis and algorithm development to mitigate ECMWF, FNMOC, NOAA developed the Universal Pre-Processor (UPP) code for assimilation-oriented dataset production  NCDC and JPL are adapting the UPP to UPP-Climate and Precipitation (UPP-CP) for climate and precipitation work RSS is releasing calibrated SSMIS data NESDIS has developed in-house SSMIS calibrations GPCP is working to use the RSS and NESDIS developments to continue computations of Version 2.1 look for a general announcement when updates are computed PLANS FOR VERSION 3 GPCP V2.1 – V2 (mm/d) Climatological averages by region for Versions 2 and 2.1 in mm/d. Note: “Ocean” is 100% water on 2.5° grid; land is <100%. Version 2.2 The GPCC expects to release its next precipitation gauge analysis “soon” the next version will again  Extend the record  Add more gauges We expect the changes to be large enough that reprocessing will be necessary once again In a reprocess we would also expect to include a reprocessed scattering-based microwave precipitation dataset from NESDIS that has improved quality control determine the need to again recalibrate the OPI estimates for the pre-SSMI era Driving Motivations Other GEWEX observational datasets need finer-scale precipitation data for consistent study of the global water and energy cycle SRB, surface vapor flux, ISCCP The NCDC GridSat-B1 dataset now provides higher resolution IR data GPCP is currently computed with  pentad-accumulated 3-hourly 2.5°x2.5° histograms of IR Tb for 1986-present, latitudes 40°N-S (for the monthly and pentad)  3-hourly 1°x1°histograms of IR Tb for 1997-present, latitudes 40°N-S (for the daily) GridSat-B1 is a superset of the ISCCP B1 data  Original geo-satellite VIS, water vapor, IR subsampled (not averaged) to 10 km, 3-hourly  “all” useful geo-satellite data from the present back to 1981, latitudes 60°N-S  Navigated, calibrated  IR is also intercalibrated, zenith-angle-corrected Algorithms have advanced since the GPCP was developed 10-15 years ago look for a general announcement when updates are computed Design Concepts The monthly product must follow Climate Data Record standards homogeneous record (to the extent possible)  Emphasize continuity over “best’” short-term answer current algorithm seems like a good template The relatively fine-scale IR data now available before the SSMI era requires testing of algorithm concepts what is the best approach in the absence of microwave calibration? Modern “high-resolution precipitation products” provide examples of fine-resolution datasets no need to reinvent the wheel – strong consideration to adopting an existing dataset and recalibrating for consistency with the monthly product no HRPP covers the entire globe  Development work required at high latitudes  Likely that the initial Version 3 fine-resolution product will lack complete high-latitude coverage Time thin arrows denote heritage GPCP V1 SGMAGPI GPCP V2,2.1 SG GPCP V1,1.1 1DD GPCP V1,1.1 Pentad High-resolution precipitation products [CMORPH, PERSIANN, TMPA] GPCP 3-hourly GPCP Daily GPCP Pentad GPCP V3 SG (planned) Timeline Development is on-going, addressing the issues raised in “Design Concepts” It is hoped to have prototypes available in late 2011, with first datasets available thereafter Version 2 will continue to be maintained, upgraded to new sensors as needed, and computed for several years to provide a stable, globally complete product for the community provide the necessary comparative dataset for Version 3 development and validation