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TRMM Precipitation Radar (PR) Level 3 Monthly 5° x 5° Surface Rainfall (3A26)
Data Access for 3A26: http://mirador.gsfc.nasa.gov/cgibin/mirador/presentNavigation.pl?tree=project&dataset=3A26%20%28Version%20007%29:%20Monthly%205%20x%205%20degree%20Surface%20Rain%20Total&project=TRMM&dataGroup=Gridded&version=007 Contents: This document provides basic information on 3A26, PR Monthly 5° x 5° Surface Rainfall. The primary objective of the 3A26 is to compute the rain rate statistics over 5 degree (latitude) x 5 degree (longitude) x 1 month spacetime regions. The output products include the estimated values of the probability distribution function of the spacetime rain rates at 4 'levels' (2 km, 4 km, 6 km, and pathaveraged) and the mean, standard deviation, and probability of rain derived from these distributions. Three different rain rate estimates are used for the high resolution rain rate inputs to the algorithm: (1) the standard ZR (or 0thorder estimate having no attenuation correction); (2) the HitschfeldBordan (HB); and (3) the rain rates taken from 2A25. (Fits based on the high resolution inputs from the surface reference technique are output to the diagnostic file for evaluation). This algorithm is based on a statistical procedure. Although the radar team believes that a statistical method of this type should be implemented for TRMM, the method is relatively new and the testing has been carried out only on simulated data and on preliminary TRMM data. Caution on the use of the results is well warranted. The data flow of all products are shown in Satellite Algorithm Flow Diagram. Data Characteristics Temporal Coverage  Start Date: 19971208; Stop Date:   Geographic Coverage  Latitude: 40°S  40°N; Longitude:180°W  180°E  Temporal Resolution  Monthly  Horizontal Resolution  5° x 5°; nlat = 16, nlon = 72  Average File Size  Compressed: ~6 MB  File Type  HDF  Data Format Structure The following table summarizes the contents and structure of the PR monthly surface rainfall (3A26) product. Further information can be found in File Specifications for TRMM Products  Version 7.00 Data Format Structure for 3A26, PR Monthly Surface Rainfall  Name  Type  Record Size (byte)  Dim Size (# of Records)  Scaled by  Range  Unit  Description  ECS Core Metadata  Char Attribute  10,000          ECS Core Metadata  PS Metadata  Char Attribute  10,000          Product Specific Metadata  GridStructure  Char Attribute  5,000          GridStructure gives the specification of the geometry of the grids.  Total Counts  Integer SDS  4  nlat*nlon    0 ~ 2,147,483,647    Total number of counts (measurements) per month at each 5° x 5° boxes.  Rain Counts  Integer SDS  4  nlat*nlon*nh2    0 ~ 2,147,483,647    Total number of rain counts (measurements) per month at each 5° x 5° boxes. This is computed at 2km, 4km, 6km, and for the pathaverage.  Zero Order pDf  Integer SDS  4  nlat*nlon*ncat3*nh2*nthrsh    1 ~ 2,147,483,647    Probability distribution function (cumulative) in counts of the zeroth order rain rate estimate at each 5° x 5° boxes. The pDf is computed at 2km, 4km, 6km, and for the pathaverage.  HB pDf  Integer SDS  4  nlat*nlon*ncat3*nh2*nthrsh    1 ~ 2,147,483,647    Probability distribution function (cumulative) in counts of the HitschfieldBordan (HB) rain rate estimate at each 5° x 5° boxes. The pDf is computed at 2km, 4km, 6km, and for the pathaverage.  pDf2A25  Integer SDS  4  nlat*nlon*ncat3*nh2*nthrsh    1 ~ 2,147,483,647    Probability distribution function (cumulative) in counts of the Surface Reference Technique (SRT) rain rate estimate at each 5° x 5° boxes. The pDf is computed at 2km, 4km, 6km, and for the pathaverage.  Zero Order Fit  Float SDS  4  nlat*nlon*nh2*3*nthrsh    TBD    The mean, variance, and probability of rain parameters for the lognormal model obtained from the zeroth order pDf. Fitting parameters are given at 2km, 4km, 6km, and for the pathaverage. In addition, 5 thresholds are used.  HB Fit  Float SDS  4  nlat*nlon*nh2*3*nthrsh    TBD    The 3 fitting parameters for the lognormal model obtained from the HB pDf. Fitting parameters are given at 2km, 4km, 6km, and for the pathaverage. In addition, 5 thresholds are used.  fit2A25  Float SDS  4  nlat*nlon*nh2*3*nthrsh    TBD    The 3 fitting parameters for the lognormal model obtained from the SRT pDf. Fitting parameters are given at 2km, 4km, 6km, and for the pathaverage.  Reliability 0th Order Fit  Float SDS  4  nlat*nlon*nh2*nthrsh    TBD  TBD  Reliability parameter for the 0th order fit.  Reliability HB Fit  Float SDS  4  nlat*nlon*nh2*nthrsh    TBD  TBD  Reliability parameter for the HB fit.  Reliability 2A25 Fit  Float SDS  4  nlat*nlon*nh2*nthrsh    TBD  TBD  Reliability parameter for the SRT fit.  rainMeanTH  Float SDS  4  nlat*nlon*nh3    0.0 ~ 3000.0  mm h^{1}  The mean monthly unconditioned rain rate (mm/h) as determined from the threshold method (in particular, it is determined from the fitting parameters fro the 'thorder method' using a single 'Q' threshold for each height level).  Note: Missing data are given the value of 999, and 777 indicates that too few data points were available to make the fit.  Parameters used in above table: Name  Value  Definition  nlat  16  the number of 5° grid intervals of latitude from 40° S to 40° N  nlon  72  the number of 5° grid intervals of longitude from 180° W to 180° E  nh3  4  the number of fixed heights above the earth ellipsoid, at 2, 4, 6 km plus one for pathaverage, in that order  ncat3  25  the number of categories for probability distribution functions. Rain rate thresholds (mm/hr) are: 12., 14.,..., 60.  nthrsh  6  the number of thresholds used for probability distribution functions. Qthresholds for Zero order: 0.1, 0.2, 0.3, 0.5, 0.75, 50. Qthresholds for HB: 0.1, 0.2, 0.3, 0.5, 0.75, 0.9999. piathresholds for SRT: 1.5, 1., 0.8, 0.6, 0.4, 0.1.  TRMM 3A26 can be accessed and ordered from Mirador at, http://mirador.gsfc.nasa.gov/cgibin/mirador/presentNavigation.pl?tree=project&dataset=3A26%20%28Version%20007%29:%20Monthly%205%20x%205%20degree%20Surface%20Rain%20Total&project=TRMM&dataGroup=Gridded&version=007 Appendix 

