GCIP LSA-NW EAOP 2000 Hourly Precipitation Composite 1.0 General Description The Hourly Precipitation Composite is one of several precipitation datasets provided in the GEWEX Continental-Scale International Project (GCIP) Large Scale Area-North West (LSA-NW) Enhanced Annual Observing Period (EAOP) 2000. This precipitation composite was formed from several data sources (i.e., National Climatic Data Center (NCDC) hourly precipitation dataset (TD 3240), National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC) hourly precipitation data, and the hourly precipitation extracted from the GCIP LSA-NW EAOP-00 Hourly Surface Composite). Data from these sources were quality controlled and merged to form this precipitation composite. This composite contains data for the GCIP LSA-NW EAOP-00 domain and time period (01 April 2000 through 31 March 2001). The GCIP LSA-NW EAOP-00 domain is approximately 90W to 115W longitude and 36N to 51N latitude. 2.0 Detailed Data Description 2.0.1 NCDC Hourly Precipitation Algorithms The NCDC Hourly Precipitation dataset (TD 3240) is formed by retaining both incremental and accumulative precipitation values from the raw precipitation data. Both incremental and accumulative values are contained in the GCIP LSA-NW EAOP-00 Hourly Precipitation Composite. If an accumulation period began prior to but continued into the beginning of the GCIP LSA-NW EAOP-00 time period, the precipitation values in that accumulation period were reset to missing values. An accumulation period that began near the end of the GCIP LSA-NW EAOP-00 time period, but continued after the end of the GCIP LSA-NWE EAOP-00 time period would also have its precipitation values reset to missing. For more information on the NCDC Hourly Precipitation dataset, TD 3240, see NCDC, 1986. 2.0.2 National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC) Algorithms The Climate Prediction Center (CPC) is a component of the National Centers for Environmental Prediction (NCEP). The NCEP/CPC Hourly Precipitation dataset was formed by extracting incremental precipitation values that fell on the hour. The value reported for any hourly observation represents data collected during the previous 60 minutes. All raw precipitation data, including data that do not fall on the hour, can be found on codiac in the GCIP/EOP Surface: Precipitation NCEP/CPC Gage Only Hourly Dataset. Data from cooperators networks such as NCEP/CPC has hundreds of reporting locations change from incremental to accumulator and back to incremental. Others, especially NCEP/CPC stations in West Virgina and Western portions of Pennsylvania changed a couple of times and have now settled on accumulators. Anyone using this data must be aware of the dynamic changes in the network of sites that are processed by HADS...and be aware of the potential lag time from when a change is implemted to when we become aware of the change. This is far, far from a stable environment. To help users in identifying these changes, UCAR/JOSS checks the NCEP/CPC hourly precipitation data for possible accumulated values and resets the UCAR/JOSS Quality Control flags for all "unchecked", "good", and "trace" accumulated precipitation values in the NCEP/CPC network to "questionable". For this purpose, UCAR/JOSS defines accumulated precipitation to be six identical, sequential hourly precipitation values potentially followed by additional identical values or values that increase over time. 2.0.3 Hourly Precipitation Extract from GCIP LSA-NW EAOP-00 Hourly Surface Composite This dataset is formed by extracting both incremental and accumulative precipitation data from the GCIP LSA-NW EAOP-00 Hourly Surface Composite. Both incremental and accumulative values are contained in the GCIP LSA-NW EAOP-00 Hourly Precipitation Composite. Refer to the GCIP LSA-NW EAOP-00 Hourly Surface Composite description document for more information. Due to a coding error in the conversion of the LDMSFCMETR data to QCF format, the record for the last hour of the last day an LDMSFCMETR station reported during the GCIP LSA-NW EAOP 2000 time of interest was inadvertently deleted. As most LDMSFCMETR stations report for the entire GCIP LSA-NW EAOP 2000 time of interest, most of these missing records occur on Mar 31, 2000. A total of 392 records were deleted (one for each LDMSFCMETR station). As the LDMSFCMETR hourly precipitation was extracted from the hourly surface data, the last hourly precipitation value for each LDMSFCMETR station is missing from this GCIP LSA-NW EAOP 2000 Surface Hourly Precipitation Composite. This bug affects the GCIP LSA-NW EAOP 2000 Hourly Surface Composite (but NOT the GCIP LSA-NW EAOP 2000 Surface Specials Composite), and thus the GCIP LSA-NW EAOP 2000 hourly and daily precipitation composites as well. 2.1 Detailed Format Description The GCIP LSA-NW EAOP-00 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 University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) 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 Units ---------------------- ---------------------------------- Date of Observation UTC Time of Observation UTC Network Identifier Abbreviation of platform name Station Identifier Network Dependent Latitude Decimal degrees, South is negative Longitude Decimal degrees, West is negative Station Occurrence Unitless Hourly Precip Value Millimeters Quality Flag See list of Definitions QC Code See list of Definitions 2.2 Data Remarks UCAR/JOSS checks the NCEP/CPC hourly precipitation data for possible accumulated values and resets the UCAR/JOSS Quality Control flags for all "unchecked", "good", and "trace" accumulated precipitation values in the NCEP/CPC network to "questionable". For more information on the quality control performed on this network by UCAR/JOSS, please see section 3.0 below. Due to a coding error in the conversion of the LDMSFCMETR data to QCF format, the record for the last hour of the last day an LDMSFCMETR station reported during the GCIP LSA-NW EAOP 2000 time of interest was inadvertently deleted. As most LDMSFCMETR stations report for the entire GCIP LSA-NW EAOP 2000 time of interest, most of these missing records occur on Mar 31, 2000. A total of 392 records were deleted (one for each LDMSFCMETR station). As the LDMSFCMETR hourly precipitation was extracted from the hourly surface data, the last hourly precipitation value for each LDMSFCMETR station is missing from this GCIP LSA-NW EAOP 2000 Surface Hourly Precipitation Composite. This bug affects the GCIP LSA-NW EAOP 2000 Hourly Surface Composite (but NOT the GCIP LSA-NW EAOP 2000 Surface Specials Composite), and thus the GCIP LSA-NW EAOP 2000 hourly and daily precipitation composites as well. 3.0 Quality Control Processing This precipitation composite was formed from several data sources (i.e., National Climatic Data Center (NCDC) hourly precipitation dataset (TD 3240), National Centers for Environmental Prediction/Climate Prediction Center (NCEP/CPC) hourly precipitation data, and the hourly precipitation extracted from the GCIP LSA-NW EAOP-00 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 GCIP LSA-NW EAOP-00 Hourly Precipitation Composite. Data values less than 20 millimeters were flagged as good. Any data value greater than or equal to 20 millimeters but less than 50 millimeters was flagged as questionable. Any data value greater than or equal to 50 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 based on an isohyet analysis. UCAR/JOSS checks the NCEP/CPC hourly precipitation data for possible accumulated values and resets the UCAR/JOSS Quality Control flags for all "unchecked", "good", and "trace" accumulated precipitation values in the NCEP/CPC network to "questionable". For this purpose, UCAR/JOSS defines accumulated precipitation to be six identical, sequential hourly precipitation values potentially followed by additional identical values or values that increase over time. 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 GCIP LSA-NW EAOP-00 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 Trace of precipitation. 5 Probable amount as a result of melting frozen precipitation. 6 Suspect amount relative to time or period of occurrence. 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 value exceeds output format field size or was negative precipitation. T Trace precipitation amount recorded. I Derived parameter can not be computed due to insufficient data. 4.0 References National Climatic Data Center, 1986: Hourly Precipitation Data, TD 3240. National Climatic Data Center, Asheville, NC, 20 pp.