GIST Hourly Precipitation Composite 1.0 General Description The Hourly 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 ), Hourly Precipitation data, NCDC Hourly Precipitation data, Oklahoma Mesonet (OKMESO) precipitation data, and the precipitation extracted from the GIST Hourly Surface Composite). Data from the four sources (over 1000 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 Hourly Precipitation dataset was formed by extracting accumulative precipitation values that fell on the hour and then differencing consecutive pairs of these accumulated values to produce incremental values. The value reported for any hourly observation represents data collected during the previous 60 minutes. Only incremental values are included in the GIST hourly precipitation composite. 2.0.2 NCDC Hourly Precipitation Algorithms The NCDC Hourly 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 Hourly Precip 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 differencing consecutive, hourly, accumulative precipitation observations. The value reported for any hourly observation represents data collected during the previous 60 minutes. Only incremental values are included in the GIST Hourly Precipitation Composite. 2.0.4 Hourly Precipitation Extract from GIST Hourly Surface Composite This dataset is formed by extracting both incremental and accumulative precipitation data from the GIST Hourly Surface Composite. Both incremental and accumulative values are contained in the GIST Hourly Precipitation Composite. Refer to the GIST Hourly Surface Composite description document for more information. 2.1 Detailed Format Description The GIST Hourly 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 was collected. The three data parameters repeat once for each UTC hour from 0000 through UTC hour 2300. Data reported for a designated hour represents data collected during the previous hour. 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 (QC) 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 Hourly Precip Value Hourly Precipitation Value Quality Flag See list of Definitions QC Code See list of Definitions 2.2 Data Remarks 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) Hourly 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 Hourly Precipitation Composite every ABRFC precipitation value was erroneously shifted to the left (earlier) by one record position (one hour). 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 Hourly Precipitation Composite. 2.2.2 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. 2.2.3 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., Arkansas-Red Basin River Forecast Center (ABRFC), Hourly Precipitation data, NCDC Hourly Precipitation data, OKMESO precipitation data, and the precipitation extracted from the GIST Hourly Surface Composite). Each of these datasets was Quality Controlled independently. Gross limit checks were used to determine the quality of the data in the GIST Hourly Precipitation Composite. Data values less than 25 millimeters were flagged as good. Any data value greater than or equal to 25 millimeters but less than 75 millimeters was flagged as questionable. Any data value greater than or equal to 75 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. After the datasets were merged to form the GIST Hourly 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.