BAMEX 2003 Hourly Precipitation Composite

1.0 General Description

This Hourly Precipitation Composite is one of several precipitation datasets provided for the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) 2003. This precipitation composite was formed from several data sources: Data from these sources were quality controlled and merged to form this precipitation composite. This composite contains data for the BAMEX 2003 domain (30N to 48N latitude and 80W to 104W longitude) and time period (20 May 2003 through 6 July 2003). This BAMEX 2003 Hourly Precipitation Composite dataset contains data from 4113 stations.

Section 2.0 contains a detailed description of the instrumentation, siting, and algorithms used by the source network to collect the data. Section 2.1 contains a detailed description of the format of the composite dataset. Please review Section 2.2 for information on data processing, and for specific issues that affect the data. See Section 3.0 below for the quality control processing performed by the University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) on this dataset. Section 4.0 contains references.

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 BAMEX 2003 Hourly Precipitation Composite. If an accumulation period began prior to but continued into the beginning of the BAMEX 2003 time period, the precipitation values in that accumulation period were reset to missing values. An accumulation period that began near the end of the BAMEX 2003 time period, but continued after the end of the BAMEX 2003 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/Environmental Modeling Center (NCEP/EMC) Algorithms

The Environmental Modeling Center (EMC), previously the Climate Prediction Center (CPC), is a component of the National Centers for Environmental Prediction (NCEP). The NCEP/EMC 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/EMC Gage Only Hourly Dataset.

Data from cooperators networks such as NCEP/EMC has hundreds of reporting locations which change from incremental to accumulator and back to incremental. Others 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 implemented to when NCEP/EMC becomes aware of the change. This is far, far from a stable environment.

To help users in identifying these changes, UCAR/JOSS checks the NCEP/EMC 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/EMC 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 extracted from the BAMEX 2003 Mesonet: Hourly Surface Composite

This dataset is formed by extracting precipitation data from the BAMEX 2003 Mesonet: Hourly Surface Meteorological Composite. Refer to the BAMEX 2003 Mesonet: Hourly Surface meteorological 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 BAMEX time of interest was inadvertently deleted. As most LDMSFCMETR stations report for the entire BAMEX TOI, most of these missing records occur on July 6, 2003. A total of 783 records were deleted (one for each LDMSFCMETR station). As the LDMSFCMETR hourly precipitation was extracted from the LDMSFCMETR hourly surface data, the last hourly precipitation value for each LDMSFCMETR station is missing from this BAMEX 2003 Precipitation (Hourly) Multi-Network Composite. This bug affects the BAMEX 2003 Surface Meteorological (Hourly) Multi-Network Composite (but NOT the BAMEX 2003 Surface Meteorological (Miscellaneous) Multi-Network Composite), and thus the BAMEX 2003 Precipitation (Hourly) Multi-Network Composite and BAMEX 2003 Precipitation (Daily) Multi-Network Composite as well.

2.1 Detailed Format Description

The BAMEX 2003 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

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.

UCAR/JOSS checks the NCEP/EMC 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/EMC 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 BAMEX time of interest was inadvertently deleted. As most LDMSFCMETR stations report for the entire BAMEX TOI, most of these missing records occur on July 6, 2003. A total of 783 records were deleted (one for each LDMSFCMETR station). As the LDMSFCMETR hourly precipitation was extracted from the LDMSFCMETR hourly surface data, the last hourly precipitation value for each LDMSFCMETR station is missing from this BAMEX 2003 Precipitation (Hourly) Multi-Network Composite. This bug affects the BAMEX 2003 Surface Meteorological (Hourly) Multi-Network Composite (but NOT the BAMEX 2003 Surface Meteorological (Miscellaneous) Multi-Network Composite), and thus the BAMEX 2003 Precipitation (Hourly) Multi-Network Composite and BAMEX 2003 Precipitation (Daily) Multi-Network Composite as well.

3.0 Quality Control Processing

This precipitation composite was formed from several data sources. Each of these datasets was Quality Controlled independently.

Gross limit checks were used to determine the quality of the data in the BAMEX 2003 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/EMC 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/EMC 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 flags and codes, respectively. After the datasets were merged to form the BAMEX 2003 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.