GIST Fifteen Minute Precipitation Composite 1.0 General Description The Fifteen Minute Precipitation Composite is one of four precipitation datasets provided in the GEWEX Continental-scale International Project (GCIP) Integrated Systems Test (GIST). This precipitation composite was formed from four data sources (i.e., Arkansas- Red Basin River Forecast Center (ABRFC) Fifteen Minute Precipitation data, NCDC Fifteen Minute Precipitation data, Oklahoma Mesonet (OKMESO) Precipitation data, and the precipitation extracted from the GIST Five Minute Surface Composite). Data from the four sources (over 600 stations) 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 Precipitation Algorithms The ABRFC 15-minute Precipitation dataset was formed by extracting accumulative precipitation values that fell on each 15-minute time (i.e., 00, 15, 30, and 45-minute) within each hour. Incremental values were computed by differencing consecutive pairs of these accumulated values. The incremental value reported at any 15-minute observation represents data collected during the previous 15 minutes. Only incremental values are included in the GIST 15-minute precipitation composite. 2.0.2 NCDC Fifteen Minute Precipitation Algorithms The NCDC Fifteen Minute Precipitation dataset is formed by retaining both incremental and accumulative precipitation values from the raw precipitation data. Both incremental and accumulative values are contained in the GIST 15-minute precipitation composite. If an accumulation period began prior to but continued into the beginning of the GIST time period, the precipitation values in that accumulation period were reset to missing values. An accumulation period that began near the end of the GIST time period, but continued after the end of the GIST time period would also have its precipitation values reset to missing. 2.0.3 OKMESO Precipitation Algorithms The OKMESO Precipitation was formed by extracting accumulative precipitation values that fell on each 15-minute time (i.e., 00, 15, 30, and 45-minute) within each hour and then differencing consecutive pairs of these accumulated values to obtain incremental values. The value reported at any 15-minute observation represents data collected during the previous 15 minutes. Only incremental values are included in the GIST 15-minute precipitation composite. 2.0.4 15-Minute Precip extracted from GIST 5-Minute Surface Composite Each 15-minute precipitation incremental value in this dataset was formed by summing the 5-minute precipitation values extracted from the GIST 5-Minute Surface Composite. For example, the incremental value at 0015, is the sum of the 0005, 0010, and 0015 values from the GIST 5- Minute Surface Composite. The value reported at any 15-minute observation represents data collected during the previous 15 minutes. 2.1 Detailed Format Description The GIST Fifteen Minute Precipitation Composite contains seven metadata parameters and three data parameters. The metadata parameters describe the date/time, network, station and location at which the data were collected. The three data parameters repeat once for each fifteen minutes from UTC 0000 through UTC hour 2345. Data reported for a designated 15-minute observation represents data collected during the previous 15-minutes. All times are reported in UTC, and precipitation data values are reported in millimeters. A Quality Flag and a QC Code are assigned to each data value during the UCAR/Office of Field Project Support (UCAR/OFPS) 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 Time of Observation UTC Network Identifier Abbreviation of platform name Station Identifier Network Dependent Latitude South is negative Longitude West is negative Station Occurrence Unitless 15-Minute Precip Value Millimeters Quality Flag See list of Definitions QC Code See list of Definitions 2.2 Data Remarks The following errors were found in the 1994 GCIP Integrated Systems Test (GIST) Fifteen Minute 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 Improperly Shifted Data In the 1994 GIST Fifteen Minute Precipitation Composite every ABRFC precipitation value was erroneously shifted to the left (earlier) by one record position (fifteen minutes). Correction: To correct the data, all precipitation values must be shifted to the right by one record position. The first ABFRC precipitation value in the April record should be reset to missing or "-999.99 7 M", as that value was collected prior to GIST and is unknown. Once the data are shifted to the right, a bogus value will fall of the end of the last record in the GIST period for each station. This affected all ABRFC stations and records in the GIST Fifteen Minute Precipitation Composite. 2.2.2 Improperly Flagged Missing Values In GIST ABRFC precipitation records where raw ABRFC values exceeded 9999.99 millimeters or were negative, the data values were improperly assigned a Quality Control (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. 2.2.3 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 affected 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, then 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 four datasets (i.e., ABRFC Fifteen Minute Precipitation data, NCDC Fifteen Minute Precipitation data, OKMESO Precipitation data, and the precipitation extracted from the GIST Five Minute Surface Composite). Each of these datasets was Quality Controlled independently. All datasets, except for the precipitation extracted from the GIST Five Minute Surface Composite, were Quality Controlled using the gross limit check method. Further details regarding quality control of the extracted precipitation data are provided in the GIST 5-Minute Surface Composite description document. Gross limit checks were used to determine the quality of the data in the GIST Fifteen Minute Precipitation Composite. Data values less than 15 millimeters were flagged as good. Any data value greater than or equal to 15 millimeters but less than 40 millimeters was flagged as questionable. Any data value greater than or equal to 40 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. The data were never changed, only flagged. Tables 1 and 2 contain the quality control codes and flags, respectively. When the precipitation was extracted from the GIST Five Minute Surface Composite, a hierarchical method was used to determine the final precipitation quality control (QC) flag. Gross limit checks were previously applied to the precipitation in the GIST Five Minute Surface Composite, and the "worst" QC flag was retained as the final 15-minute precipitation QC flag. In order from "worst" to "best", the precipitation QC flags are: M, N, C, I, X, B, E, D, U, G, T where the definitions of these flags are listed in Table 2 below. After the three datasets were merged to form the GIST Fifteen Minute 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.