GIST Daily Precipitation Composite 1.0 General Description The GIST Daily Precipitation Composite is one of four precipitation datasets provided in the GEWEX Continental-scale International Project (GCIP) Integrated Systems Test (GIST). This precipitation composite is composed of data from approximately 2400 stations from several sources (i.e., Oklahoma Mesonet (OKMESO) Daily Precipitation data, Arkansas- Red River Basin River Forecast Center (ABRFC) Daily Precipitation data, National Weather Service (NWS) Cooperative Observer Daily Precipitation data, and the Daily Precipitation extracted from the GIST Hourly Precipitation Composite). Data from these sources were quality controlled and merged to form this precipitation composite. This composite contains data for the GIST domain and time period (01 April 1994 through 31 August 1994). The GIST domain is approximately 91W to 107W longitude and 31N to 40N latitude. 2.0 Detailed Data Description 2.0.1 ABRFC Daily Precipitation Algorithms The ABRFC Daily Precipitation dataset was formed by extracting accumulative precipitation values that fell on the 0000 hour of each day. Incremental values were computed by differencing consecutive pairs of these accumulated values. The incremental value reported for any daily observation represents data collected during the previous 24 hours. Only incremental values are included in the GIST Daily Precipitation Composite. 2.0.2 NWS Cooperative Observer Daily Precipitation Algorithms The NWS Cooperative Observer Daily Precipitation was formed by extracting the daily incremental precipitation values provided in the raw data. The incremental value reported for any daily observation represents data collected during the previous 24 hours. Only incremental values are included in the GIST Daily Precipitation Composite. 2.0.3 OKMESO Daily Precipitation Algorithms The OKMESO Daily Precipitation was formed by extracting the daily incremental precipitation values provided in the raw data. The incremental value reported for any daily observation represents data collected during the previous 24 hours. Only incremental values are included in the GIST Daily Precipitation Composite. 2.0.4 Daily Precip Extracted from GIST Hourly Precipitation Composite Each daily precipitation incremental value in this dataset was formed by summing the 24 hourly precipitation values extracted from each GIST Hourly Surface Composite record. The hourly values are summed from hour 0000 through hour 2300. The value reported for any daily observation represents data collected during the previous 24 hours. 2.1 Detailed Format Description The Daily Precipitation Composite contains six metadata parameters and four data parameters. The metadata parameters describe the station location and time at which the data were collected. The four data parameters repeat once for each day in the monthly record. Every record has 31 days reported, regardless of the actual number of days in the month. For months with less than 31 days, the extra days are reported as missing (i.e., '-999.99 7 M'). Each 24 hour precipitation value has an associated observation hour. The observation hour is the ending UTC hour for the 24 hour period for which the precipitation value is valid. Data values are valid for the 24 hours preceding the observation hour given for the day. A Quality Flag and a Quality Control (QC) Code are assigned to each data value during quality control processing. For a list of possible Quality Flag and QC Code values see the Quality Control section 3.0. The table below details each parameter. Parameters Description ---------- ----------- Date of Observation UTC Network Identifier Abbreviation of platform name Station Identifier Network Dependent Latitude South is negative Longitude West is negative Station Occurrence Unitless Daily Precip Value Daily Precipitation Value Quality Flag See list of Definitions QC Code See list of Definitions Observation hour Beginning UTC hour for 24 hour period for which value is valid. 2.2 Data Remarks Negative precipitation and values too large to be represented in the output format were changed to missing ('-999.99') and were assigned the 'C' QC code. The NCDC Summary of Day Co-operative data have observation hours that vary by station. Data values are valid for the 24 hours preceding the observation hour given for the day. There were 5 AWOS Artais stations that reported precipitation data for GIST (i.e., ALM, ATS, 1f0, WWR, and OUN). The AWOS Artais precipitation value reported on each hour is the sum of all precipitation values reported during that hour. If precipHHMM is the AWOS Artais precipitation value reported at hour HH and minute MM, then the hourly value precip0000 equals the sum of the twenty minute precip0000, precip0020, and precip0040 values. The calculation should have been the total for the preceeding hour (data at time 23:20 + data at time 23:40 + data at time 00:00 should equal the hourly total for 00:00). This error impacts data from the five Artais stations that operated during the GCIP/GIST period only. All other precipitation values in the dataset are correct. The following errors have been found in the 1994 GCIP Integrated Systems Test (GIST) Daily Precipitation Composite. These data are available on CODIAC and the GIST CD-ROM 1. Only the GIST ABRFC precipitation data are affected. If you require assistance or need more detail concerning any of the corrections described below, please contact jossgcip@joss.ucar.edu. 2.2.1 Incorrectly Shifted Daily ABRFC Precipitation Data. In the 1994 GIST Daily Precipitation Composite, during April only, the first station (alphabetically) in each ABRFC subnetwork had each precipitation value erroneously shifted to the left (earlier) by one record position (one day). Since each daily precipitation record contains one month's worth of data per station, only five April daily records were affected. Table 1 contains a list of affected months and stations. Table 1 - Affected Stations Sub-network Station Month ----------- ------- ----- ABRFC/DCP ACDO2 04 ABRFC/GOES ALMK1 04 ABRFC/NNET ACMN5 04 ABRFC/OBS AMAT2 04 ABRFC/WSR CMXK1 04 Correction: To correct this problem, each precipitation value for the records indicated in Table 1 must be shifted to the right by one record position (one day). The first precipitation value in the record should then be reset to missing or "-999.99 7 M" as that value was collected prior to GIST and is unknown. Shifting the data will cause a bogus value to fall off the end of the corrected record. See the example below for the affects of this shifting. A complete description of the data record can be found in the GIST Daily Precipitation description document available on CODIAC. Note that unlike these examples there are no carriage returns in the data. Example of Incorrectly Shifted Record ------------------------------------- 1994/04 ABRFC/DCP ACDO2 35.65000 -97.36667 0 -999.99 7 M 0 7.11 0 G 0 4.06 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 7.11 0 G 0 3.81 0 G 0 17.27 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 -999.99 7 M 0 -999.99 7 M 0 3.05 0 G 0 0.00 0 G 0 4.32 0 G 0 7.11 0 G 0 22.61 0 G 0 -999.99 7 M 0 -999.99 7 M 0 -999.99 7 M 0 Example of Correctly Shifted Record ----------------------------------- 1994/04 ABRFC/DCP ACDO2 35.65000 -97.36667 0 -999.99 7 M 0 -999.99 7 M 0 7.11 0 G 0 4.06 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 7.11 0 G 0 3.81 0 G 0 17.27 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 0.00 0 G 0 -999.99 7 M 0 -999.99 7 M 0 3.05 0 G 0 0.00 0 G 0 4.32 0 G 0 7.11 0 G 0 22.61 0 G 0 -999.99 7 M 0 2.2.2 Improperly Handled Missing Days In the 1994 GIST Daily Precipitation Composite, whenever a complete day's worth of data were missing from the raw ABRFC files, all subsequent daily values in that record were erroneously shifted left (earlier) by record position (one day). For example, if the raw ABRFC data were missing for day 5, days 1-4 were not affected, but the data for day 6 was put into day 5's record position, the data for day 7 was put into day 6's position and so forth. Multiple days of missing raw data could result in multiple shifts to the left. This error affected an undetermined number of ABRFC Daily Precipitation records in the GIST Daily Precipitation Composite. Correction: To correct this problem, the user must obtain the GIST ABRFC Miscellaneous Precipitation dataset which contains all the GIST ABRFC precipitation data, determine omitted values, then properly convert and insert the missing data values/records. The GIST ABRFC Miscellaneous Precipitation dataset is available on CODIAC. 2.2.3 Improperly flagged Missing Values In all GIST ABRFC precipitation records where raw ABRFC values exceeded 9999.99 millimeters or were negative, the data values were improperly assigned a QC flag of 'M' instead of 'C'. This affected an undetermined number of ABRFC precipitation records. Correction: To correct this problem, the user must obtain the GIST ABRFC Miscellaneous Precipitation dataset which contains all the GIST ABRFC precipitation data and determine which values exceed 9999.99 or are negative, and then switch the QC flags for these values to 'C'. The GIST ABRFC Miscellaneous Precipitation dataset is available on CODIAC. 2.2.4 Inadvertently Omitted Data Occasionally records were inadvertently omitted from the final GIST ABRFC precipitation (e.g., station FLTA4 is missing from the GIST ABRFC daily precipitation). This affects an undetermined number of GIST ABRFC precipitation records. Correction: To correct this problem, the user must obtain the GIST ABRFC Miscellaneous Precipitation dataset which contains all the GIST ABRFC precipitation data, determine omitted records, and properly convert and insert the missing data values/records. The GIST ABRFC Miscellaneous Precipitation dataset is available on CODIAC. 3.0 Quality Control Processing This precipitation composite was formed from several datasets (i.e., Oklahoma Mesonet (OKMESO) Daily Precipitation data, Arkansas-Red River Basin River Forecast Center (ABRFC) Daily Precipitation data, NWS Cooperative Observer Daily Precipitation data, and the Daily Precipitation extracted from the GIST Hourly Precipitation Composite). Each of these datasets was independently Quality Controlled. Gross limit checks were used to determine the quality of the data in this composite. Data values less than 101.6 millimeters (4 inches) were flagged as good. Any data value greater than or equal to 101.6 millimeters but less than 127 millimeters (5 inches) was flagged as questionable. Any data value greater than or equal to 127 millimeters was flagged as unlikely. Several questionable and unlikely data values were also manually inspected. After inspection, the quality control code and flag may have been manually updated to better reflect the likelihood of the actual occurrence of the precipitation value. Data were never modified, unless the precipitation value was negative or too large to be represented in the output format. In these cases the data value was flagged with a QC code of 'C' and changed to a missing value (i.e., '-999.99'). Table 1 and 2 list the quality control flags and codes plus their meanings. After the datasets were merged to form the GIST Daily Precipitation Composite, a statistics program was executed to ensure that the quality of the individual datasets had been retained. Table 1 Quality Control Flag Description -------------------- ----------- 0 No qualifier required 1 Accumulation period 2 End of Accumulation period 3 Deleted value. Original data was unreadable. 4-6 Reserved 7 Missing value Table 2 QC Code Description ------- ----------- U Unchecked G Good M Normally recorded but missing D Questionable B Unlikely N Not available or Not observed. X Glitch E Estimated C Reported precipitation value exceeds 9999.99 millimeters or was negative. T Trace precipitation amount recorded. I Derived parameter can not be computed due to insufficient data. 4.0 References None.