GIST Hourly Surface Composite 1.0 General Description The GEWEX Continental-Scale International Project (GCIP) Integrated Systems Test (GIST) Hourly Surface Composite is composed of meteorological data from several sources (i.e., Automated Surface Observation System (ASOS), Oklahoma Mesonet (OKMESO), Automated Weather Observing System (AWOS), Atmospheric Radiation Measurement Surface (ARMSFC), Wind Profiler Demonstration Network Surface (WPDN), High Plains Climate Network Surface (HPCN), and National Climate Data Center Surface Aviation Observation (NCDC SAO) data for the GIST domain). Data from these sources (343 stations) were merged and quality controlled to form this Surface Composite. This Surface Composite contains data for the GIST time period (01 April 1994 through 31 August 1994) and for the GIST domain, only. The GIST area is approximately 91W to 107W longitude and 31N to 40N latitude. 2.0 Detailed Data Description The GIST Hourly Surface Composite is composed of data from seven different data sources which record meteorological data on-site. The following are descriptions of the various data sources contained in this composite. 2.0.1 ASOS Algorithms The ASOS hourly values were produced from ASOS 5-minute data by extracting all parameters (except precipitation) from the 55-minute observation of the previous hour and assigning those values to the current hourly observation. The precipitation is the sum of the precipitation values during the current hour. The descriptions of the algorithms used by ASOS to produce five minute surface data is located in the GIST Five Minute Surface Composite documentation. 2.0.2 ARMSFC Algorithms The ARMSFC hourly values were produced from ARMSFC 5-minute data by extracting all parameters (except precipitation) from the 55- minute observation of the previous hour and assigning those values to the current hourly observation. The precipitation is the sum of the precipitation values during the current hour. The ARMSFC 5-minute values were derived from ARMSFC 1- minute data. The description of these algorithms is located in the description document for the GIST Five Minute Surface Composite. 2.0.3 OKMESO Algorithms The OKMESO hourly values were produced from OKMESO 5-minute data by extracting all parameters (except precipitation) from the 55- minute observation of the previous hour and assigning those values to the current hourly observation. The precipitation is the sum of the precipitation values during the current hour. A detailed description of the algorithms used to produce OKMESO 5-minute data can be located in the description document for the GIST Five Minute Surface Composite. 2.0.4 AWOS Algorithms AWOS data was collected from Handar, Qualimetrics, and Artais AWOS stations. The AWOS hourly values were produced from AWOS 20-minute and 5-minute data by extracting all parameters (except precipitation) from the 55-minute observation of the previous hour and assigning those values to the current hourly observation. The precipitation is the sum of the precipitation values during the current hour. A detailed description of the algorithms used to produce AWOS 20- minute and 5-minute data can be located in the description document for the GIST Twenty Minute Surface Composite and the GIST Five Minute Surface Composite. 2.0.5 WPDN Algorithms The algorithms used to produce Wind Profiler Demonstration Network hourly surface data are not currently available. 2.0.6 HPCN Algorithms The algorithms used to produce High Plains Climate Network hourly surface data are not currently available. 2.0.7 NCDC SAO Algorithms The NCDC SAO data consists of principle reporting stations which are usually fully instrumented and therefore record a complete range of meteorological parameters. Most of these stations reside at airports and provide aviation support, but with the increasing installation of automated observing instrumentation, more SAO observations are obtained from remote locations. SAO observations vary from hourly and 3-hourly at major stations to reduced observations from "part-time" stations. The majority of observations in this composite come from the NCDC SAO data. The majority of SAO reports consist of manual observations that are taken at 55-minutes of the previous hour. For example, the 0100 UTC hourly observation is taken at 0055 UTC. The precipitation is the sum of the precipitation which occurred during the previous hour. For details on the observer procedures see the Federal Meteorological Handbook No. 1 (1988). The data are transmitted hourly from the reporting stations and archived at NCDC. Automated SAO reports that are closest to the hour are extracted and included in this composite. Only nominal time observations have been included in this composite. The NCDC SAO "Special" observations can be found in the GIST NCDC SAO "Specials" Dataset. Again, see the Federal Meteorological Handbook No. 1 for details on the differences between "nominal" and "special" observations. 2.1 Detailed Format Description The GIST Hourly Surface Composite contains ten metadata parameters and 38 data parameters and flags. The metadata parameters describe the station location and time at which the data were collected. The time of observation is reported both in Universal Time Coordinated (UTC) Nominal and UTC actual time. Days begin at UTC hour 0100 and end at UTC hour 0000 the following day. The data parameters are valid for the reported times. The table below details the data parameters. Several data parameters have an associated Quality Control (QC) Flag Code which is assigned during the OFPS quality control processing. For a list of possible QC Flag values see the Quality Control Section 3.0. Units shown below in Table 1 are only valid for OFPS QC Format (QCF). Table 1. Parameters Units ---------- ----- Date of Observation UTC Nominal Time of Observation UTC Nominal Date of Observation UTC actual Time of Observation UTC actual 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 Station Elevation Meters Station Pressure, QC flag Hectopascals (mb) Reported Sea Level Pressure, QC flag Hectopascals (mb) Computed Sea Level Pressure, QC flag Hectopascals (mb) Dry Bulb Temperature, QC flag Celsius Dew Point, QC flag Celsius Wind Speed, QC flag m/s Wind Direction, QC flag Degrees Total Precipitation, QC flag mm Squall/Gust Indicator Code Value Squall/Gust Value, QC flag m/s Present Weather, QC flag Code Value Visibility, QC flag Meters Ceiling Height (first layer) Hundreds of feet Ceiling Flag (first layer), QC flag Code Value Cloud Amount (first layer), QC flag Code Value Ceiling Height (second layer) Hundreds of feet Ceiling Flag (second layer), QC flag Code Value Cloud Amount (second layer), QC flag Code Value Ceiling Height (third layer) Hundreds of feet Ceiling Flag (third layer), QC flag Code Value Cloud Amount (third layer), QC flag Code Value The list of code values for the Present Weather is too large to reproduce in this document. Refer to WMO, 1988 for a complete list of Present Weather codes. The code values for the Squall/Gust Indicator are: Code Definition ---- ---------- blank No Squall or Gust S Squall G Gust The code values for the ceiling flag Indicator are: Code Definition ---- ---------- 0 None 1 Thin 2 Clear below 12,000 feet 3 Estimated 4 Measured 5 Indefinite 6 Balloon 7 Aircraft 8 Measured/Variable 9 Clear below 6,000 feet (AUTOB) 10 Estimated / Variable 11 Indefinite / Variable 12 12-14 reserved 15 Missing The code values for the Cloud Amount Indicator are: Code Definition ---- ---------- 0 0 ( or clear) 1 1 okta or less, but not zero or 1/10 or less, but not zero 2 2 oktas or 2/10-3/10 3 3 oktas or 4/10 4 4 oktas or 5/10 5 5 oktas or 6/10 6 6 oktas or 7/10-8/10 7 7 oktas or more, but no 8 oktas or 9/10 or more, but not 10/10 8 8 oktas or 10/10 (or overcast) 9 Sky obscured by fog and/or other meteorological phenomena 10 Sky partially obscured by fog and/or other meteorological phenomena 11 Scattered 12 Broken 13 13-14 Reserved 15 Cloud cover is indiscernible for reasons other than fog or other meteorological phenomena, or observation is not made. 2.2 Data Remarks This dataset contains only the NCDC SAO "nominal" observation surface data. The GIST NCDC SAO "specials" observations are located in the GIST NCDC SAO "Specials" Dataset. A value of 999.00 in the ceiling height field of the NCDC SAO data means the sky condition was either clear or a height was not reported. There were 5 AWOS Artais stations that reported surface 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. 3.0 Quality Control Processing The GIST Hourly Surface Composite was formed from several sub- datasets (i.e., Automated Surface Observation System (ASOS), Oklahoma Mesonet (OKMESO), Automated Weather Observing System (AWOS), Atmospheric Radiation Measurement Surface (ARMSFC), Wind Profiler Demonstration Network Surface (WPDN), High Plains Climate Network Surface (HPCN), and National Climate Data Center Surface Aviation Observation (NCDC SAO) data for the GIST domain). Each dataset was quality controlled by comparing the station observations with the MAPS (Mesoscale Analysis and Predictions System) hourly gridded surface analyses. MAPS was developed and the analyses were produced by the Forecast Systems Laboratory of the NOAA Environmental Research Laboratories (Miller and Benjamin, 1992). The same method which was used to quality control the STORM- FEST data (Scully and McGuirk, 1993) was used to quality control the GIST Hourly Surface Composite. Hourly MAPS gridded values were interpolated to a station's latitude, longitude, elevation and observation time and were then compared to the observed values. Observed values were then flagged "good", "questionable" or "unlikely" based upon the comparison with MAPS. Data were not changed, only flagged. Only the station pressure, sea level pressure, temperature, dew point, wind speed and wind direction were quality controlled this way. The following table shows the allowed variance from MAPS values for each parameter. Parameters Good Questionable Unlikely Station Pressure <2.00mb >=2.00mb >=5.00 mb Sea Level Pressure <2.00mb >=2.00 mb >=5.00 mb Calculated Sea Pressure <4.00mb >=4.00mb >=10.00 mb Dry Bulb Temp <2.50 C >=2.50 C >=5.00 C Dew Point Temp <2.50 C >=2.50 C >=5.00 C Wind Speed <5.00 m/s >=5.00 m/s >=10.00 m/s Wind Dir (Ws<10m/s) <=90.00 deg >90.00 deg >=180.00deg Wind Dir (Ws>=10m/s) <=50.00 deg >50.00 deg >=90.00 deg Precipitation <25.00 mm >=25.00 mm >=75.00 mm The squall/gust wind speed data were not quality controlled. Gross limit checks were also used to determine the quality of the precipitation values. Several "questionable" and "unlikely" data values were also manually inspected. After inspection, the quality control flag may have been manually updated to better reflect the likelihood of the actual occurrence of the precipitation value. Data were never modified, only flagged. Negative precipitation was also coded "unlikely". A table of the possible quality control flags and their meanings is listed below. 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. General consistency checks were applied to the dry bulb temperature, wind direction, and the relationship between precipitation and cloud amount/cloud cover. If the dew point temperature was greater than the dry bulb temperature both values were coded "questionable". Also, wind direction for observed "calm" winds was given the same QC code as the wind speed. If precipitation was reported, but the cloud amount was "none" or "clear", then both the cloud amount and precipitation values were coded "questionable". Several impossible values were also checked. Negative wind speeds were coded "unlikely". Wind directions of less than zero or greater than 360 degrees were coded "unlikely". 4.0 References ASOS User's Guide, ASOS Project Office, NOAA, National Weather Service, Washington D.C., June 1992. Miller, P.L. and Benjamin S.G., 1992: A System for the Hourly Assimilation of Surface Observations in Mountainous and Flat Terrain., Mon. Wea. Rev., 120, 2342-2359. Scully, K.W. and McGuirk, D.E., 1993: The Use of MAPS Analyses for Quality Control of Surface Observations from STORM-FEST. Preprints, Eight Symposium on Meteorological Observations and Instrumentation, Anaheim, California, 17-22. The Oklahoma Mesonet User's Guide, Oklahoma Climatological Survey, The University of Oklahoma, May, 1995 United States Department of Commerce, 1988: Federal Meteorological Handbook Number 1, Surface Observations. National Oceanic and Atmospheric Administration, Washington, D.C., April 1988. United States Department of Transportation (USDOT), 1988. AWOS Operations Manual, Federal Aviation Administration. World Meteorological Organization (WMO), 1988: Manual on Codes Volume I, Part B - Binary Codes. WMO, Geneva, Switzerland.