Documentation for GPCP Satellite-Derived (IR) Monthly Rainfall Estimates To get the file via anonymous ftp, do the following: 1. ftp ftp.ncep.noaa.gov 2. login with userid anonymous (use your e-mail ID as the password) 3. cd pub/precip/gpi/monthly/ 4. set ftp to binary mode (ie bin) 5. get data gpi_mth_2.5_mmday_198601-yyyymm ( yyyymm - the year and month of last available data) ********************************************************************************** * NOTE!! An inter-satellite calibration correction for geostationary satellite * * data has been applied to remove calibration disparities between * * geostationary satellites. * * * * NOTE!! A reduction correction has also been applied to GPI estimates * * produced from geostionary IR coverage at zenith angles(ie >25 deg). * * A systematic bias was found by comparisons of GPI estimates computed * * separately from each geostationary satellite's IR data in overlap regions. * * The satellite with the larger zenith angle yielded a larger amount of * * cloud colder than GPI's temperature threshold of 235K relative to the * * other satellite. This correction removes (partially at least) this bias. * ********************************************************************************** The data are IR-based rainfall estimates which are an intermediate product of the Global Precipitation Climatology Project which is a WMO/WCRP effort. An appropriate reference for these estimates is: "Rainfall variations in the tropics during 1986-89, as estimated from observations of cloud-top temperature", J.E. Janowiak and P. A. Arkin, J. Geophs. Res., Vol. 96, Supplement, pgs. 3359-3373. The data are monthly accumulations (units are mm/day) of estimated rainfall on a 2.5 deg. lat/lon grid. The data are stored in 144 X 32 arrays, and each value represents the estimated areal average rainfall for a 2.5 X 2.5 deg "box". The array orientation is: --->>>>>>> Missing values are identified as "-9999". <<<<<<<<------ 40N ---------------------------- ----------------- | | | | | | | | (1,1) | (2,1) | (3,1) | . . . |(143,1)| (144,1) | | | | | | | 37.5N ---------------------------- ----------------- | | | | | | | | (1,2) | (2,2) | (3,2) | . . . |(143,2)| (144,2) | | | | | | | . . 37.5S ---------------------------- ----------------- | | | | | | | | (1,32)| (2,32)| (3,32)| . . . |(143,32) (144,32) | | | | | | | 40S ---------------------------- ----------------- | | | | | | | 0 2.5E 5E 7.5E 5W 2.5W 0 The dataset is a series of: 144 X 32 arrays of monthly rainfall estimates in mm/day from January 1986 to the last available month. As usual this dataset is updated once a month. The data can be read in FORTRAN as follows: real prec(144,32) open(unit=20,access='direct',file=input_file, 2 status='old',form='unformatted',recl=144*32*4) do 200 irec=1,wrec c wrec - number of all months in this dataset c wrec = yy(number of full years)*12(number of months in a year)+ c mm(number of month in the last year) 200 read(20,rec=irec) prec ************************************************** * ---------> PLEASE NOTE <------------- * * The estimates are valid for the tropics and * * warm season extratropics, and will indicate * * rainfall in regions of persistant thick * * cirrus. This is because temperature is the * * only parameter used in the estimation scheme,* * so, except for the cases noted above, when * * limited to regions where the background temps* * are relatively warm, the estimation technique* * is able to identify regions of deep convec- * * tion. * ************************************************** ************************************************************ IMPORTANT!!! From the April of 1998 monthly data for 2.5x2.5 are derived from 1x1 degree daily data. ************************************************************