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TRMM Precipitation Radar (PR) Level 3 Monthly 5° x 5° Surface Rainfall (3A26)
Data Access for 3A26: http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/02_Gridded/03_Monthly_Surf_Rain_Total_3A_26/
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 space-time regions. The output products include the estimated values of the probability distribution function of the space-time rain rates at 4 'levels' (2 km, 4 km, 6 km, and path-averaged) 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 Z-R (or 0th-order estimate having no attenuation correction); (2) the Hitschfeld-Bordan (H-B); 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: 1997-12-08; 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: 5.6 KB; Original: ~16.0 KB | | 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 Volume 4 of the "File Specifications for TSDIS Products - Level 2 and Level 3" .
| 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 path-average. | | 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 path-average. | | HB pDf | Integer SDS | 4 | nlat*nlon*ncat3*nh2*nthrsh | - | 1 ~ 2,147,483,647 | - | Probability distribution function (cumulative) in counts of the Hitschfield-Bordan (HB) rain rate estimate at each 5° x 5° boxes. The pDf is computed at 2km, 4km, 6km, and for the path-average. | | 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 path-average. | | Zero Order Fit | Float SDS | 4 | nlat*nlon*nh2*3*nthrsh | - | TBD | - | The mean, variance, and probability of rain parameters for the log-normal model obtained from the zeroth order pDf. Fitting parameters are given at 2km, 4km, 6km, and for the path-average. In addition, 5 thresholds are used. | | HB Fit | Float SDS | 4 | nlat*nlon*nh2*3*nthrsh | - | TBD | - | The 3 fitting parameters for the log-normal model obtained from the HB pDf. Fitting parameters are given at 2km, 4km, 6km, and for the path-average. In addition, 5 thresholds are used. | | fit2A25 | Float SDS | 4 | nlat*nlon*nh2*3*nthrsh | - | TBD | - | The 3 fitting parameters for the log-normal model obtained from the SRT pDf. Fitting parameters are given at 2km, 4km, 6km, and for the path-average. | | 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*nh2 | - | 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 '-th-order 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 | | nh2 | 4 | the number of fixed heights above the earth ellipsoid, at 2, 4, 6 km plus one for path-average, 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.
Q-thresholds for Zero order: 0.1, 0.2, 0.3, 0.5, 0.75, 50.
Q-thresholds for HB: 0.1, 0.2, 0.3, 0.5, 0.75, 0.9999.
pia-thresholds for SRT: 1.5, 1., 0.8, 0.6, 0.4, 0.1. | TRMM 3A26 can be accessed and ordered from the Goddard DAAC's TRMM Data Search and Order System at http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/02_Gridded/03_Monthly_Surf_Rain_Total_3A_26/ .
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Atmos Composition
