1.  TITLE

1.1  Data Set Identification.

     Total and convective precipitation

     (6-hourly ; NOAA/NMC, GPCP Hybrid)

1.2  Data Base Table Name.

     Not Applicable.

1.3  CD-ROM File Name.


     Where nnnn_nnn is the parameter name (The NOAA/NMC, GPCP Precipitation 
     data have 2 types of parameters, see table below). Note:  capital letters 
     indicate fixed values that appear on the CD-ROM exactly as shown here, 
     lower case indicates characters (values) that change for each path and 

     The format used for the filenames is: nymmddhh.Z, where n is the 
     parameter descriptor (see table below), y is the last digit of the year 
     (e.g., 7=1987), mm is the month of the year (e.g., 12=December), dd is 
     the day (i.e 01 to 31), and hh is the first two digits in the hour (e.g., 
     12=1200 Greenwich Mean Time (GMT)).  The filename extension (.Z), 
     indicates that the files are compressed and must be decompressed before 
     use (see section 8.4).  Below is the list of the parameters, directory 
     names and descriptors:

     Parameter Description              Parameter Directory Name   Descriptor
     Total Precipitation                TOTL_PRC                            O
     Convective Precipitation           CNVT_PRC                            C

1.4  Revision Date Of This Document.

     April 5, 1995.

                           2.  INVESTIGATOR(S) 

2.1  Investigator(s) Name And Title.

     Dr. Kenneth E. Mitchell 
     Research Meteorologist
     Development Division
     National Meteorological Center (NMC)

     Dr. Ying Lin
     UCAR Visiting Scientist
     Development Division
     National Meteorological Center

2.2  Title Of Investigation.

     Application of NMC Reanalysis precipitation to 
     temporal partitioning of GPCP monthly precipitation
     for ISLSCP Initiative I CD-ROM data sets.

2.3  Contacts (For Data Production Information).

               |         Contact 1       |       Contact 2        |
  2.3.1 Name   |Dr. Ken Mitchell         |Dr. Ying Lin            |
  2.3.2 Address|Development Division     |Development Division    |
               |DOC, NOAA                |DOC, NOAA               |
               |W/NMC22, WWB, Rm 204     |W/NMC22, WWB, Rm 204    |
       City/St.|Wasington DC, USA        |Washington DC, USA      |
       Zip Code|20233                    |20233                   |
 2.3.3 Tel.    |301-763-8161             |301-763-8056            |
 2.3.4 Email   |wd22km@sgi74.wwb.noaa.gov|wd22yl@sun1.wwb.noaa.gov|

2.4  Requested Form of Acknowledgement.

     Mitchell, K.E., and Y. Lin, 1994: Production of 6-hourly 
     continental precipitation data sets for 1987 and 1988 for ISLSCP
     Initiative I, Development Division, National Meteorological 
     Center, Washington, DC.

                       3.  INTRODUCTION

3.1  Objective/Purpose.

     The objective of this data set is to provide a global continental 
     precipitation time series of relatively high temporal frequency.
     Its purpose is to fulfill the precipitation forcing needs of the 
     various land-surface/hydrology initiatives of the Global Energy 
     and Water Cycle Experiment (GEWEX), including ISLSCP, GCIP, GNEP, 
     and PILPS.  

     One chief application is in the initiative of the GEWEX Global Soil 
     Wetness Workshop (4-6 Oct 1994, Longmont, Colorado), which enlisted 
     a number of international land-surface modeling groups to utilize 
     the same global, continental atmosperic forcing data as input to 
     various land-surface process models to generate a set of global 
     soil wetness estimates for use in global climate models and other 
     applications.  A good discussion of the need for and approach to 
     a global soil wetness initiative is given by Dirmeyer (1995) in 
     his summary of a related forerunner meeting on soil wetness 
     (COLA, 19 Aug 94, Calverton, MD).

3.2  Summary of Parameters.

     The data set provides global gridded 1-degree fields of 6-hourly
     total and convective precipitation for 1987/88.  Over a given
     month, the 6-hourly total precipitation sums up to the original
     monthly total of the GPCP data set.  As in the GPCP data set,
     all values over sea points (non-land mass) are set to zero.  
     The convective precipitation is always less than or equal to the 
     total precipitation for each 6-hour (and hence monthly) period.  

3.3  Discussion.

     The starting point for the generation of the 6-hour precipitation
     analyses here was the global 1-degree monthly land mass precipit-
     ation analyses of the GPCP, available as separate, independent 
     data sets in the ISLSCP Initiative I CD-ROM SET.  Briefly summarizing 
     the latter, the GPCP a) collects monthly precipitation totals 
     received in CLIMATE reports via the World Weather Watch GTS (Global 
     Telecommunication System), b) calculates monthly totals from 
     synoptic reports, and c) acquires monthly precipitation data 
     from international/national meteorological and hydrological 
     services/institutions. On the basis of these precipitation-gauge 
     measurements, 1-degree gridded analyses over land areas are 
     carried out using a spatial objective analysis method.  For 
     further documentation, refer to the documentation in this CD-ROM
     collection accompanying the GPCP monthly analyses.  Note that the
     GPCP analyses on this CD-ROM set and applied below are 1-degree,
     land-mass only, and based on surface gauge measurements only.  

     But the GPCP data sets provide only monthly total precipitation.
     To satisfy the GEWEX modeling needs discussed in Sec. 3.1,
     NMC agreed to partition the above GPCP monthly precipitation
     analyses into estimates of 6-hourly total and convective 
     precipitation time series, using the 6-hourly precipitation time 
     series of the global 4DDA-based NMC Reanalysis Project (Kalnay 
     and Jenne, 1991; Kalnay et al. 1993, Kalnay et al., 1995).  The NMC
     Reanalysis 6-hourly precipitation time-series are the source of the 
     derivation of temporal partitioning coefficients or weights applied to 
     the GPCP monthly precipitation totals.  Note that the NMC Reanalysis 
     precipitation is used only to derive weights for temporal partitioning, 
     so that the derived time series sum up over one month to the original 
     monthly GPCP amounts.

     The NMC Reanalysis provides an opportunity to estimate not only
     the 6-hourly time series of total precipitation, but also the
     time series of convective precipitation, since both total and
     convective precipitation amounts at 6-hourly intervals are
     routine products of the Reanalysis.  Here we embrace this 
     opportunity and derive a time series of 6-hourly convective
     precipitation from the 6-hourly total precipitation by applying 
     in each 6-hour period the Reanalysis ratio of convective to total 
     precipitation.  The user must bear in mind that the above ratio
     is a product of the physical parameterizations for stable and
     convective precipitation in the GCM of the NMC Reanalysis.  

                    4.  THEORY OF MEASUREMENTS

The derivation of this data set begins with the GPCP gauge-based monthly 
precipitation analyses.  See the GPCP documentation (GPCP_PRC.DOC), for a 
description of the gauge measurements.

                     5.  EQUIPMENT

See comment in Sec. 4.

5.1  Instrument Description.

     Not applicable.

     5.1.1  Platform.

            Not applicable.

     5.1.2  Mission Objectives.

            Not applicable.  

     5.1.3  Key Variables.

            Not applicable. 

     5.1.4  Principles of Operation.

            Not applicable.  

     5.1.5  Instrument Measurement Geometry.

            Not applicable.  

     5.1.6  Manufacturer of Instrument.

            Not applicable. 

5.2  Calibration.

     5.2.1  Specifications.

            Not applicable.


                     Not applicable. 

     5.2.2  Frequency of Calibration. 

            Not applicable.

     5.2.3  Other Calibration Information.

            Not applicable.  

                      6.  PROCEDURE

6.1  Data Acquisition Methods.

     Four input data sets were acquired to derive the final dataset described 
     in this document.  See Sec. 9 for a description of how these input data 
     sets were processed to derive the final data set.  

     The four input sets are:

     1)  The GPCP global 1-degree gauge-based monthly precipitation 
         analyses for 1987 & 1988 (available and documented on this CD-ROM 

     2)  The NMC Reanalysis global 1.875-degree 4DDA-based 6-hourly 
         total precipitation analyses for 1987 & 1988, available from NMC,
         (Kalnay et al., 1993, Kalnay et al., 1995).

     3)  The NMC Reanalysis global 1.875-degree 4DDA-based 6-hourly 
         convective precipitation analyses for 1987 & 1988, available from 
         NMC, (Kalnay et al., 1993, Kalnay et al., 1995).

     4)  The NASA/GSFC global 4x5 degree gauge-based daily precip
         analyses for Dec 1978 through Nov 1979, available from NASA/GSFC,
         (G. Walker, private communication, NASA/GSFC, 
         greg@rootboy.gsfc.nasa.gov; see also Liston et al., 1993,
         specifically Sec. 2.c, page 13).  Sec. 9.2.1 below provides
         more details on this data set.

6.2  Spatial Characteristics.

     For each of the four input data sets listed in Sec. 6.1, 
     the spatial characteristics are as follows:

     1) GPCP Monthly Precipitation: global 1-degree latitude by 
     2) NMC Reanalysis 6-Hourly Total Precipitation: global 
        1.875-degree latitude by longitude.  

        (Specifically a 192 x 94 Gaussian grid, commonly used in 
        global spectral models; the longitude increment is 1.875 
        degree, the latitude increment is slightly variable, but 
        nearly 1.915 degree.)

     3) NMC Reanalysis 6-Hourly Convective Precipitation:  
        same as 2) above.

     4) NASA/GSFC Daily Precipitation: global 4x5 degree latitude 
        by longitude (Dec 1978 - Nov 1979 only) 

     Again, we emphasize that the final derived data set is derived 
     from the above four input data sets as described in Sec. 9.

     The spatial characteristics of the final derived data set is 
     global 1-degree latitude by longitude.  This is described in
     more detail next in Secs. 6.2.1 and 6.2.2.      

     6.2.1  Spatial Coverage.

            The coverage is global.  Data in each file are ordered from North 
            to South and from West to East beginning at 180 degrees West and 
            90 degrees North.  Point (1,1) represents the grid cell centered 
            at 89.5 N and 179.5 W (see section 8.4).

            Only land-mass grid points have non-zero values.  All values over 
            water are zero (as in GPCP).  The 1-degree land/water mask is 
            available in this CD-ROM collection.

     6.2.2  Spatial Resolution.

            The final data set is given on an equal-angle grid that has 
            a spatial resolution of 1 X 1 degree lat/long.

6.3  Temporal Characteristics.

     6.3.1  Temporal Coverage.

            The final data set covers the period Jan 1987 through Dec 1988.

     6.3.2  Temporal Resolution.

            The final data set is 6-hourly. 

                   7.  OBSERVATIONS

7.1  Field Notes.

     See Sec. 3.3.

                   8.  DATA DESCRIPTION

8.1  Table Definition With Comments.

     Not applicable.

8.2  Type of Data.

|                 8.2.1               |               |       |              |
|Parameter/Variable Name              |               |       |              |
|    |          8.2.2                 |     8.2.3     |  8.2.4 |    8.2.5    |
|    |Parameter/Variable Description  |Range          |Units   |Source       |
|TOTAL PRECIP                         |               |        |GPCP gauge   |
|    |The total amount of             |min = 0.,      |[MM]    |analysis and |
|    |precipitation over a six hour   |max = 1000.,   |        |NMC 4DDA     |
|    |period.                         |over sea = 0.  |        |Reanalysis   |
|    |                                |               |        |             |
|CONVECTIVE PRECIP                    |               |        |GPCP gauge   |
|    |The convective precipitation    |min = 0.,      |[MM]    |analysis and |
|    |over a six hourly period.       |max = 1000.,   |        |NMC 4DDA     |
|    |                                |over sea = 0.  |        |Reanalysis   |
|    |                                |               |        |             |

8.3  Sample Data Base Data Record.

     Not applicable.

8.4  Data Format.

     Compressed format:

     The ECMWF data has been compressed using Unix Compress.  Compress uses 
     the modified Lempel-Ziv algorithm popularized in "A Technique for High 
     Performance Data Compression", Terry A. Welch, IEEE Computer, vol. 17, 
     no. 6 (June 1984), pp. 8-19.  Common substrings in the file are first 
     replaced by 9-bit codes 257 and up.  When code 512 is reached, the 
     algorithm switches to 10-bit codes and continues to use more bits until 
     the limit specified by the -b flag is reached (default 16).  Bits must be 
     between 9 and 16.  The default can be changed in the source to allow 
     compress to be run on a smaller machine.

     The amount of compression obtained depends on the size of the input, the
     number of bits per code, and the distribution of common substrings.  The 
     ECMWF data has been reduced by approximately 85%.  So watch out!!!

     The data described here can be de-compressed using the platform specific 
     programs listed below. 

     DOS       MAC               UNIX         VMS        
     u16.zip   MacGzip0.3b2      gzip1-2-3    gzip-1-2-3

     These programs are located in the SOFTWARE directory on this CD-ROM.  The 
     programs are also available via FTP from many archival data bases on the 
     Internet.  Information on anonymous FTP sites which supply these software 
     can be obtained via anonymous FTP at ftp.cso.uiuc.edu in the directory 
     /doc/pcnet in the file compression.

     Uncompressed format:

     The CD-ROM file format is ASCII, and consists of numerical fields of 
     varying length, which are space delimited and arranged in columns and 
     rows.  Each column contains 180 numerical values and each row contain 360 
     numerical values.  

          Grid arrangement

             I  = 1 IS CENTERED AT 179.5W
             J  = 1 IS CENTERED AT 89.5N

             90N - | - - - | - - - | - - - | - -
                   | (1,1) | (2,1) | (3,1) |
             89N - | - - - | - - - | - - - | - -
                   | (1,2) | (2,2) | (3,2) |
             88N - | - - - | - - - | - - - | - -
                   | (1,3) | (2,3) | (3,3) |
             87N - | - - - | - - - | - - - |
                  180W   179W    178W   177W


8.5  Related Data Sets.

     1)  The ECMWF data on ISLSCP Initiative I CD-ROMs 2, 3, and 4,
     2)  The GPCP global 1-degree gauge-based monthly precipitation 
         analyses for 1987 & 1988 (available and documented on the ISLSCP 
         Initiative I, Volume 1 CD-ROM).
     3)  The NMC Reanalysis global 1.875-degree 4DDA-based 6-hourly 
         total precipitation analyses for 1987 & 1988, available from NMC,
         (Kalnay et al., 1993, Kalnay et al. 1995).
     4)  The NMC Reanalysis global 1.875-degree 4DDA-based 6-hourly 
         convective precipitation analyses for 1987 & 1988, available from 
         NMC, (Kalnay et al., 1993, Kalnay et al. 1995).
     4)  The NASA/GSFC global 4x5 degree gauge-based daily precip
         analyses for Dec 1978 through Nov 1979, available from NASA/GSFC,
         (G. Walker, private communication, NASA/GSFC, 
         greg@rootboy.gsfc.nasa.gov; see also Liston et al., 1993,
         specifically Sec. 2.c, page 13).  Sec. 9.2.1 below provides
         more details on this data set.

                        9.  DATA MANIPULATIONS

9.1  Formulas.

     9.1.1  Derivation. 

            See Sec. 9.2.1. 

     9.1.2  Techniques/Algorithms.

            See Sec. 9.2.1. 

9.2  Data Processing Sequence.

     9.2.1  Processing Steps and Data Sets.

            For a given month in 1987 & 1988, and for a given global 1-degree 
            grid land mass point denoted (i,j), we denote the following 
            relative to the first three input data sets in Sec. 6.2:

              GP(i,j) - original monthly GPCP precipitation amount
            NMC Reanalysis total precip amount for day k of month for

              RPT06(i,j,k,1) -  first 6-hour period 
              RPT06(i,j,k,2) - second 6-hour period  
              RPT06(i,j,k,3) -  third 6-hour period
              RPT06(i,j,k,4) - fourth 6-hour period

              RPT24(i,j,k)   - summation of above four 6-hour amounts

              RPTMM(i,j)     - monthly total from summation of RPT24(i,j,k)
                               over all days k of given month

            NMC Reanalysis convective precip for day k of month for 

              RPC06(i,j,k,1) -  first 6-hour period 
              RPC06(i,j,k,2) - second 6-hour period 
              RPC06(i,j,k,3) -  third 6-hour period
              RPC06(i,j,k,4) - fourth 6-hour period
              RPC24(i,j,k)   - summation of above four 6-hour amounts
            We note that RPCtt convective precip amount is always less 
            than or equal to the corresponding RPTtt total precip amount.
            The desired partitioned 6-hourly GPCP total precipitation amount
              GPT06(i,j,k,1) -  first 6-hour period
              GPT06(i,j,k,2) - second 6-hour period
              GPT06(i,j,k,3) -  third 6-hour period
              GPT06(i,j,k,4) - fourth 6-hour period  
            The desired partitioned 6-hourly GPCP convective precipitation 

              GPC06(i,j,k,1) -  first 6-hour period
              GPC06(i,j,k,2) - second 6-hour period
              GPC06(i,j,k,3) -  third 6-hour period
              GPC06(i,j,k,4) - fourth 6-hour period  
            In Section 6.2, we noted that the original NMC Reanalysis fields
            are provided on a 192 x 94 global Gaussian grid at 1.875 by
            1.915 degree.  Our first operation is to bilinearly interpolate
            these horizontally to the 1-degree grid of the GPCP fields.  
            The above notation of RPTtt or RPCtt denotes 1-degree Reanalysis 
            fields after this interpolation.   

            Before applying the above 1-degree Reanalysis precipitation 
            fields, we first filtered the fields, as described next, to 
            eliminate an identified tendency for the Reanalysis to generate 
            too many days of measurable daily rainfall in the warm months over 
            the southeast portions of both the North American and Asian 
            continents.  This tendency is a product of the convective 
            parameterization scheme in the GCM of the Reanalysis system.  The 
            hydrological modelers who expect to apply the final 6-hourly 
            precipitation data set firmly urged us to take care in reproducing 
            observed frequencies of measurable daily precipitation.  
            To accomplish the filter, we needed a gauge-based, global,
            land-mass analysis of DAILY rainfall.  Such fields are not
            easily available on a global basis.  (Indeed it is the lack of 
            such gauge-based global daily precipitation analyses that led 
            to this very project to apply Reanalysis to monthly GPCP.)  One 
            exception is the data set 4) in Section 6.1 and Section 6.2, 
            namely the NASA/GSFC gauge-based global 4x5 degree daily 
            precipitation analysis spanning the FGGE months of Dec 1978 
            through Nov 1979 (used in Liston et al., 1993).  Even though the 
            above analysis is for 1979, we decided its frequency of measurable 
            daily rainfall was more representative than that of Reanalysis.  
            Note that we apply below only the FREQUENCY in 1979 as a filter 
            threshold.  We do NOT use the order of precipitation events in the 
            1979 daily series as a source for the order of events in the final 
            1987 & 1988 data set here.  Rather the Reanalysis time series 
            (filtered below) will determine the order of 6-hourly precip 
            Thus for the same FGGE calendar month as the given month
            in 1987 & 1988 assumed above, we denote the daily, 24-hour 
            precipitation amount from the NASA/GSFC gauge-based global 
            analysis as
              NP24(i,j,k) - 24-hour precipitation amount for day k
            Following earlier practice, the above denotes the NASA/GSFC
            analysis after bilinear interpolation from 4x5 degree to the
            GPCP 1-degree grid.

            To accomplish the frequency filter, for each (i,j) land 
            mass point, we compute for the given month a) the number of 
            days, NR(i,j), in which RPT24(i,j,k) exceeded 1 mm and 
            b) the number of days, NF(i,j), in which NP24(i,j,k) exceeded
            1 mm.  If NF(i,j) > 10 (in order to target convective regions
            for the most part) and NR(i,j) > NF(i,j) then we iterated
            to determine a threshold daily precipitation amount, E(i,j), such
            that if RPT24(i,j,k) < E(i,j), then we set RPT24(i,j,k)=0
            and RPC24(i,j,k)=0 and hence also we set 



            for each such day k of the month satisfying the threshold, 
            with the result that after such filtering (month by month) 
            then NR(i,j)=NF(i,j) whenever NF(i,j) > 10.  Thus, at a given 
            grid point (i,j), if RPT24(i,j,k) is less than the threshold 
            E(i,j), then ALL Reanalysis precipitation amounts for that day 
            were set to zero.  Note that the threshold field E(i,j) was 
            determined separately for each of the 48 months in 1987 & 1988.  
            With few exceptions, the values of E(i,j) were less than several 

            We denote all such filtered Reanalysis fields as follows
            (for tt=06 and tt=24):

              RPTttF = filtered counterpart to RPTtt
              RPCttF = filtered counterpart to RPCtt
              RPTMMF = filtered counterpart to RPTMM

            At last, it is straightforward to derive the desired 
            temporally partitioned GPCP analyses.

            First, the 6-hourly partitioned GPCP total precipitation
            is derived for each day k of given month from

              GPT06(i,j,k,m)  = [RPT06F(i,j,k,m)/RPTMMF(i,j)] * GP(i,j)

            for each 6-hourly period m=1,2,3,4.  In the above we see that 
            the Reanalysis 6-hourly amount, scaled by the Reanalysis 
            monthly total, acts as the temporal partitioning or weighting 
            coefficient.  (Note: If GP(i,j)=0, then we set GPT06(i,j,k,m)=0.
            If GP(i,j) is nonzero and RPTMMF(i,j) is zero, we search for
            and substitute for RPT06F and RPTMMF from the nearest land 
            mass (i,j) at which RPTMMF is nonzero.)
            Secondly, the 6-hourly partitioned GPCP convective precipitation
            is derived for each day k of given month from

            for each 6-hourly period m=1,2,3,4.  In the above we see that 
            the Reanalysis 6-hourly convective amount, scaled by the 
            Reanalysis 6-hourly total amount, acts as the convective 
            partitioning or weighting coefficient.  (Note:  If 
            GPT06(i,j,k,m) is zero, then we set GPC06(i,j,k,m)=0.
            If GPT06(i,j,k,m) is nonzero, then RPT06F(i,j,k,m) is 
            nonzero and hence GPC06(i,j,k,m) is well defined.) 

     9.2.2  Processing Changes.

            None at the time of this first revision.

9.3  Calculations.

     9.3.1  Special Corrections/Adjustments.

            See Sec. 9.2.1 above.

9.4  Graphs and Plots.

     See Mo et al. (1995), Kalnay et al. (1993), and Kalnay et al. (1995).

                          10.  ERRORS

10.1  Sources of Error.

      The final data set inherits errors from the four input data
      sets of Section 6.1.

      First, the monthly totals obtained by summing the derived 
      6-hourly time series agree with the input GPCP monthly 
      precipitation.  Hence these monthly totals reflect the 
      accuracy of the GPCP analyses.

      In particular, the procedures of Section 9 were specifically 
      designed to avoid having the monthly totals of this 6-hourly 
      data set reflect any of the biases in monthly totals in the 
      NMC Reanalysis.

      The sources of error in the input GPCP monthly precipitation
      analyses are discussed in Section 10 of the GPCP documentation
      in this CD-ROM set.  The reader should review all of that 

      Within a given month, the temporal character of the 
      precipitation time series is dependent on the temporal character 
      of the NMC Reanalysis precipitation.  

      In the NMC Reanalysis, stringent care was given to quality 
      control (see Kalnay et al., 1993, and Kalnay et al., 1995).
      Nevertheless, as in any modern state-of-the-art multi-variant
      four-dimensional data assimilation system (4DDA), the NMC 
      Reanalysis inevitably embodies some systematic errors.

      The precipitation fields from the NMC Reanalysis have been 
      examined by external researchers and presented at the recent 
      Nineteenth Annual Climate Diagnostics Workshop, sponsored
      during 14-18 Nov 94 at College Park, MD by the Cooperative 
      Institute for Climate Studies at the University of Maryland.
      The results showed, for example, that the diurnal character 
      of the precipitation fields from the NMC Reanalysis compared
      favorably with observations in the spring season over the
      central U.S. and that this diurnal character was significantly
      better than an alternative non-NMC reanalysis product.

      On the other hand, in the NMC Reanalysis, researchers have found 
      that the frequency of measurable daily precipitation is too high 
      over the southeast portions of the North American and Asian
      continents.  Hence the frequency filter described in Section 9.2
      was applied.

      The resultant temporal character of the 6-hourly time series, 
      though having some of the limitations of a global 4DDA system,
      are nevertheless superior in our view for many applications to 
      the alternative of a researcher having to take the GPCP monthly 
      amounts and arbitrarily distributing these amounts across the
      monthly period (e.g., a constant mean 6-hourly amount for
      the whole month).  Furthermore, the Reanalysis-based time
      series are strongly linked to the regular progression of
      synoptic weather systems and convective triggers that
      characterize the real atmosphere.

      As cited earlier, the data set includes the 6-hourly time
      series for both total and convective precipitation.  Of
      the two, the total precipitation time series is more
      reliable, as the temporal character and relative magnitude
      of the convective time series is heavily tied to the
      convective parameterization scheme in the GCM of the 
      NMC Reanalysis system.  Some sensitivities of the Reanalysis
      precipitation to choice of convective parameterization scheme
      are presented in Kalnay et al. (1993).  Despite some NMC 
      reluctance to provide the convective time series, GEWEX modelers 
      strongly urged this present attempt, because their land surface 
      process models often require a partitioning between non-convective
      and convective precipitation, and once again 4DDA, or its
      Reanalysis equivalent, was viewed as the best reasonably 
      available means for providing this separation.

10.2   Quality Assessment.

       10.2.1  Data Validation by Source.

               See Section 10.2.1 of the GPCP documentation for
               information on that source.

               The NMC Reanalysis precipitation has been compared
               on a global monthly basis with GPCP monthly analyses,
               with other precipitation climatologies, and with
               other Reanalysis products from other centers.  Regional,
               diurnal, and water budget characteristics have been
               studied by both internal and external NMC researchers.
               Since the Reanalysis products are very new, much of the 
               above research is not yet available in the commonly 
               available literature.  One exception is the study by
               Mo et al. (1995), who examined the sensitivity of the
               Reanalysis, including global precipitation analyses, to
               the use or omission of satellite data in the Reanalysis.
               Other very recent examples of Reanalysis fields are given 
               in Kalnay et al. (1995).

       10.2.2  Confidence Level/Accuracy. 

               See previous Sec. 10 subsections above. 

       10.2.3  Measurement Error for Parameters and Variables.

               Not applicable.

       10.2.4  Additional Quality Assessment Applied.

               In the final data set, the following checks were applied.

               1 - No negative values.

               2 - The summation over one month of the 6-hourly time
                   series of total precipitation agrees at every 
                   grid point with the original GPCP monthly amount.

               3 - The convective precipitation amount is always less
                   than or equal to the total precipitation amount.

               4 - All over water values (sea) are zero.

               5 - No missing flags (-99999.99) are present in either
                   the input GPCP monthly analyses or the final output
                   6-hourly time series.

                                 11.  NOTES

11.1  Known Problems With The Data.

      See Section 10 above and Section 11.1 in the companion documentation 
      for the GPCP monthly precipitation analyses. 

11.2  Usage Guidance.

      In data void or sparse continental areas, the quality of the 
      analysis results will be less reliable. 

11.3  Other Relevant Information.

      Not available.

                         12.  REFERENCES

12.1  Satellite/Instrument/Data Processing Documentation.

      WCRP, 1990.  The Global Precipitation Climatology Project - 
          Implementation and Data Management Plan. WMO/TD-No. 367, Geneva, 
          June 1990, 47 pp. and appendices. 
      Kalnay, E., M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, 
          S. Saha, G. White, J. Woollen, M. Chelliah, J. Janowiak, K.C. Mo, J. 
          Wang, A. Leetmaa, R. Reynolds, R. Jenne, E. Kung, and D. Salstein, 
          1993.  The NMC/NCAR CDAS/Reanalysis Project, NMC Office Note 401, 
          Washington, DC, October 1993, 42 pp. and figures.

12.2  Journal Articles and Study Reports.

      Dirmeyer, P.A., 1995. Summary of Meeting on Problems in Initializing 
          Soil Wetness, submitted to Bull. Amer. Meteor. Soc. (also available 
          as COLA Report No. 9, January 1995, COLA, Calverton, MD).
      Kalnay, E., M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, 
          M. Iredell, S. Saha, G. White, J. Woollen, Y. Zhu, M. Chelliah, W. 
          Ebisuzaki, W. Higgins, J. Janowiak, K.C. Mo, C. Ropelewski, A. 
          Leetmaa, R. Reynolds, R. Jenne, 1995. The NMC/NCAR Reanalysis 
          Project.  Submitted to the Bull. Amer. Meteor. Soc.
      Kalnay, E., and R. Jenne, 1991. Summary of the NMC/NCAR reanalysis. 
          Bull. Amer. Meteor. Soc., 72:1897-1904.
      Liston, G.E., Y.C. Sud, and G.K. Walker, 1993.  Design of a Global Soil 
          Moisture Initialization Procedure for the Simple Biosphere Model, 
          NASA Tech Memo 104590, NASA Goddard Space Flight Center, Greenbelt, 
          MD, 130 pp.
      Mo, K.C., X.L. Wang, R. Kistler, M. Kanamitsu, and E. Kalnay, 1995. 
          Impact of satellite data on the CDAS-Reanalysis System, Mon. Wea. 
          Rev., 123:124-139.

12.3  Archive/DBMS Usage Documentation.

      Contact the EOS Distributed Active Archive Center (DAAC) at NASA Goddard 
      Space Flight Center (GSFC), Greenbelt Maryland (see Section 13 below).
      Documentation about using the archive or information about access to the 
      on-line information system is available through the GSFC DAAC User 
      Services Office.

                             13.  DATA ACCESS

13.1  Contacts for Archive/Data Access Information.

      GSFC DAAC User Services
      NASA/Goddard Space Flight Center
      Code 902.2
      Greenbelt, MD 20771

      Phone:     (301) 286-3209
      Fax:       (301) 286-1775
      Internet:  daacuso@eosdata.gsfc.nasa.gov

13.2  Archive Identification.

      Goddard Distributed Active Archive Center
      NASA Goddard Space Flight Center
      Code 902.2
      Greenbelt, MD 20771

      Telephone:  (301) 286-3209
      FAX:        (301) 286-1775
      Internet:   daacuso@eosdata.gsfc.nasa.gov

13.3  Procedures for Obtaining Data.

      Users may place requests by accessing the on-line system, by sending 
      letters, electronic mail, FAX, telephone, or personal visit.

      Accessing the GSFC DAAC Online System:

      The GSFC DAAC Information Management System (IMS) allows users to 
      ordering data sets stored on-line.  The system is open to the public.

      Access Instructions:

      Node name:  daac.gsfc.nasa.gov
      Node number:
      Login example: telnet daac.gsfc.nasa.gov
      Username:  daacims
      password:  gsfcdaac

      You will be asked to register your name and address during your first

      Ordering CD-ROMs:

      To order CD-ROMs (available through the Goddard DAAC) users should 
      contact the Goddard DAAC User Support Office (see section 13.2).

13.4  GSFC DAAC Status/Plans.

      The ISLSCP Initiative I CD-ROM is available from the Goddard DAAC.

                        14.  OUTPUT PRODUCTS AND AVAILABILITY 

14.1  Tape Products.


14.2  Film Products. 


14.3  Other Products. 


                             15.  GLOSSARY OF ACRONYMS

4DDA           four dimensional data assimilation
COLA           Center for Ocean-Land-Atmosphere Studies
DAAC           Destributed Active Archive Center
DOC            Department of Commerce
EOS            Earth Observation System
EOS-DIS        EOS data and Information System
GCIP           GEWEX Continental Scale Project
GCM            General Circulation Model
GEWEX          Global Energy and Water Cycle Experiment
GNEP           GEWEX Numerical Experimentation Project
GPCP           Global Precipitation Climatology Project
GSFC           Goddard Space Flight Center
GTS            Global Telecommunications System
ISLSCP         International Satellite Land Surface Climatology Project
NASA           National Aeronautics and Space Administration
NMC            National Meteorological Center
NOAA           National Oceanic and Atmospheric Administration
PILPS          Project for Intercomparison of Land-Surface Process Schemes
UCAR           University Corporation for Atmospheric Research