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TOVS/AIRS. OPI. Emission Microwave. Scattering Microwave. Merged IR GPI. Microwave/Other Fusion. Microwave/IR Calibration. Matched 3-hr Geo-IR GPI. Gauge-Adjusted Satellite. AGPI. Low-Orbit AGPI. Multi-Satellite. Gauge. Satellite/Gauge.

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TOVS/AIRS

OPI

Emission

Microwave

Scattering

Microwave

Merged IR

GPI

Microwave/Other

Fusion

Microwave/IR

Calibration

Matched

3-hr

Geo-IR GPI

Gauge-Adjusted

Satellite

AGPI

Low-Orbit

AGPI

Multi-Satellite

Gauge

Satellite/Gauge

Updating the GPCP Global Precipitation Datasets

P5.9

G.J. Huffman1,2, R.F. Adler1,3, D.T. Bolvin1,2, EJ. Nelkin1,2

1: NASA/GSFC Laboratory for Atmospheres

2: Science Systems and Applications, Inc.

3: Univ. of Maryland College Park/ESSIC

http://precip.gsfc.nasa.gov

MOVING TO VERSION 2.1

THE GPCP DATASETS

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

  • 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

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

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%.

1986-87

1987-present

Geo

1979-85

Low-Orbit

1986-present

V2.1 – V2 (mm/d)

‘88-’07 Linear Trend

(mm/d/decade)

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

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

S high lat

Globe

S mid-lat

Tropics

N mid-lat

N high lat

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

PLANS FOR VERSION 3 GPCP

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

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

GPCP V3 SG

AGPI

SGM

GPCP V1

GPCP V2,2.1 SG

GPCP 3-hourly

GPCP V1,1.1 1DD

GPCP Daily

GPCP V1,1.1 Pentad

GPCP Pentad

thin arrows

denote

heritage

High-resolution precipitation products

[CMORPH, PERSIANN, TMPA]

Time

(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

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