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Quasi-‐Global Precipita2on as Depicted in the GPCP V2.2 and TMPA V7 G.J. Huffman1, D.T. Bolvin1,2, EJ. Nelkin1,2, R.F. Adler3
1: NASA/GSFC Laboratory for Atmospheres 2: Science Systems and Applications, Inc. 3: Univ. of Maryland College Park/ESSIC
http://precip.gsfc.nasa.gov
How best to use precipita2on es2mates from a diverse, changing, uncoordinated set of satellites with various • Periods of record • Regions of coverage • Sensor-‐specific strengths and weaknesses? We seek the longest-‐possible rela2vely homogeneous record of “global” precipita2on • Global Precipita2on Climatology Project (GPCP)
• Climate Data Record (CDR) standards • emphasize homogeneity over fine-‐scale accuracy
• TRMM Mul2-‐satellite Precipita2on Analysis (TMPA) • High-‐Resolu2on Precipita2on Product (HRPP) approach • emphasize fine-‐scale accuracy over homogeneity
• Less-‐emphasized goal in each is also important, of course Each dataset was upgraded this year • GPCP changes are rela2vely modest, although important
• introduc2on of SSMIS (F17) • next upgrade of GPCC product (par2cularly China)
• TMPA is more substan2al • addi2onal periods of data (boxes on diagram below) • improved IR record for 1998 – February 2000 • updated algorithms (GPROF, in par2cular) • consistently reprocessed data records • single source of gauge analysis • publica2on of addi2onal intermediate data fields
BACKGROUND
GPCP monthly Mul2-‐Satellite (MS) • 1979 – July 1987
• OLR Precipita2on Index calibrated from overlap with GPCP in the later period
• August 1987 – present • lower lat.: IR calibrated by single 6 a.m./p.m. microwave product • higher lat.: GPCP-‐adjusted cloud volume proxy
“Produc2on” TMPA monthly MS • All microwave products calibrated to TRMM Combined Instrument • 3-‐hour holes filled by microwave-‐calibrated IR • 3-‐hour fields accumulated for month For both, MS and GPCC gauge analysis combined to Satellite-‐Gauge (SG) product with weigh2ng by es2mated inverse error variance Each SG tends to follow the calibrators • Over land – the GPCC gauge analysis • Over ocean – satellite calibrator
QUICK COMPARISON OF GPCP AND TMPA ALGORITHMS AND INPUTS
TMPA V.7 (blue) follows calibrator (TRMM Combined Instrument, TCI; green) • 3-‐5% offset results from unresolved issues with the calibra2on
scheme TMPA V.7 exceeds TMPA V.6 (black) • “Sag” in V.6 resulted from using a series of early AMSU precipita2on data sets in 2000-‐2007 (even despite calibra2on!) • V.7 uses a consistently processed AMSU (and MHS) algorithm
throughout The GPCP V2.2 (red) is generally consistent with TMPA V.7 • Overall average is lower • Rela2vely strong correla2on in month-‐to-‐month varia2on • Interannual varia2on
• also well-‐correlated • GPCP has a larger range • GPCP tends to lag by a few months • presumably calibrators have a major role in determining these characteris2cs
TIME SERIES COMPARISON FOR TROPICAL OCEAN
COMPARISON TO MONTHLY ATOLL GAUGES
SUMMARY
The (quasi-‐)global 2me series and paierns of precipita2on agree rather well between GPCP V2.2. and TMPA V.7 Large-‐scale quan2ta2ve differences tend to stem from the calibrators – a “trusted” satellite over ocean, gauge over land • This puts a lot of focus on the calibrators • Modelers see these differences as a huge issue
Data issues: • Atolls specifically selected for lack of orography
• presumably representa2ve of “open ocean” • Atolls are not included in the GPCC gauge analysis
• therefore, these are independent data for both plots • All these are single gauges
• there is an issue comparing point gauge measurements to satellite grid box es2mates
Period of record is longer for GPCP TMPA rela2vely unbiased across most rain rates • Even if TMPA V.7 is 3-‐5% high (see Time Series), the bias
is beier than for GPCP V2.2 • By eye, both seem to show a break in slope around 10
mm/d
1998 2000 2004
TMI,PR,TMI/PR combo.
2002
SSM/I F14
SSM/I F13
SSM/I F15
AMSU N16 AMSU N15
AMSU N17
AMSR-‐E
CPC Merged IR
NCDC GriSat-‐B1 IR
2006
SSMIS F16
MHS N18 MHS N19
SSMIS F17
2008 2010
MHS MetOp
SSMIS F18
GPCP Monitoring Analysis (gauge)
GPCC Full Analysis (gauge)
2012
1980 1990 1985
SSM/I F11
SSM/I F08
SSM/I F13
AIRS soundings
TOVS soundings
1995
SSMIS F17
2000 2005
GPCC Monitoring Analysis (gauge)
GPCC Full Analysis (gauge)
2010
OPI leo-‐, geo-‐IR GPI
Graphs show data records used in TMPA (top) and GPCP SG (right)
Periods of record not used in the datasetS are shown in lighter color
Addi2onal data records used in TMPA V.7 are boxed
TMPA V.7!
GPCP V2.2!
COMPARISONS OF CLIMATOLOGIES
Monthly (and long-‐term) difference governed by: • Land: precipita2on gauge analysis
• significant upgrades in the GPCC version used • changes mostly posi2ve • mostly in complex terrain
• Ocean: calibra2ng satellite es2mator • modest upgrades in TCI • but, V.6 had low bias over much of this period due to AMSU algorithm issues • V.7 has small posi2ve offset from (new, higher) TCI
V.7 – V.6 (mm/d)
Version 7 (mm/d)
Version 6 (mm/d)
GPCP V2.2 (mm/d)
TMPA V.7 (mm/d)
TMPA V.7 – GPCP V2.2 (mm/d)
TMPA V.7 – V.6 (1998-‐2010)
TMPA V.7 – GPCP V2.2 (1998-‐2010)
TMPA averaged to GPCP’s 2.5° grid Monthly (and long-‐term) difference governed by: • Land: precipita2on gauge analysis
• both use the latest GPCC analysis • results very similar • some differences due to interpola2ng gauge analysis to TMPA scale, and to satellite differences in gauge-‐sparse regions
• Ocean: calibra2ng satellite es2mator • GPCP uses • Microwave Emission Brightness Temperature Histogram (METH) log-‐normal fiied histogram approach • TOVS/AIRS cloud volume proxy at higher la2tudes • TMPA uses • TCI calibra2on, extended past orbital band (35°N-‐S)
TMPA has less land-‐sea contrast in Mari2me Con2nent, Southeast Asia • Coastal zones have the biggest difference, but it’s not just the
problema2c “coast” area TMPA (both V.6 and V.7) has secondary maximum running from Hawaii to the Philippines GPCP is higher at higher la2tudes because • METH tends to be higher than TCI and GPROF-‐based esimates • The TOVS/AIRS es2mates tend to be higher and kick in at
la2tude 45°-‐55°, depending on season
FUTURE
The real-‐2me TMPA (TMPA-‐RT) Version 7 has been retrospec2vely processed from March 2000 through May 2012 • Using TMPA-‐RT V.7 code, but en2re archived record of input • Data are posted, but not officially announced • Quality control is under way; seeking “early users” TMPA will be superseded by IMERG in 1-‐2 years GPCP development is ac2ve • Version 2 is being reworked as an official NOAA CDR • Version 3 development has just been funded by NASA
TMPA V.7!
GPCP V2.2!