ESOP 1995 Hourly Surface Composite 1.0 General Description The GEWEX Continental-Scale International Project (GCIP) Enhanced Seasonal Observing Period (ESOP) 1995 Hourly Surface Composite is composed of data from several sources (i.e., Artais Automated Weather Observation System (AWOS), Handar AWOS, Qualimetrics AWOS, Oklahoma Mesonet (OKMESO), Department of Energy (DOE) Atmospheric Radiation Measurement Surface (ARMSFC), High Plains Climate Network (HPCN), Automated Surface Observing System (ASOS), Wind Profiler Network (WPN), National Climatic Data Center (NCDC) Surface Airways Observations (SAO), and Colorado Agricultural Meteorological data) for the ESOP 1995 domain. Data from these sources (371 stations) were merged and quality controlled to form this Surface Composite. This Surface Composite contains data for the ESOP 1995 time period (01 April 1995 through 30 September 1995) and for the ESOP 1995 domain only. The ESOP 1995 domain is approximately 31N to 40N latitude and 91W to 107W longitude. 2.0 Detailed Data Description The ESOP 1995 Hourly Surface Composite is composed of data from several different sources which report data at hourly frequencies. The AWOS data are from three different instrumentation vendors which record data on-site at an hourly frequency. * Data were collected from 4 AWOS stations manufactured by Handar Inc., Sunnyvale, CA. * Data were collected from 22 AWOS stations manufactured by Qualimetrics Inc., Sacramento, CA. * Data were collected from 6 AWOS stations manufactured by Artais of Columbus, OH. 2.0.1 AWOS Algorithms The following are descriptions of the various types of AWOS station data. Further details can be found in the AWOS Operations Manual (1988). The algorithms used in the 5 and 20-Minute data can be found in the ESOP 1995 5-Minute and 20-Minute Surface Composite description documents. Handar Hourly AWOS data Handar Hourly AWOS data were based upon 20-Minute data. A complete description of the 20-Minute AWOS data conversion can be found in the ESOP 1995 20-Minute Surface Composite description document. There are no present weather or sea level pressures reported for Handar data. Precipitation is the accumulated precipitation for the hourly period. All other parameters are the values reported for the hourly observation. Qualimetrics Hourly AWOS data Qualimetrics Hourly AWOS data are based upon 20-Minute data. A complete description of the 20-Minute AWOS data conversion can be found in the ESOP 1995 20-Minute Surface Composite description document. Precipitation is the accumulated precipitation for the hourly period. All other parameters are the values reported for the hourly observation. Station pressure is calculated from altimeter setting. Sea level pressure is not reported for the Qualimetrics AWOS data. Present weather is not reported for Qualimetrics AWOS data. Artais Hourly AWOS data Artais Hourly AWOS data are based upon 20-Minute data. A complete description of the 20-Minute AWOS data conversion can be found in the ESOP 1995 20-Minute Surface Composite description document. Precipitation is the accumulated precipitation for the hourly period. All other parameters are the values reported for the hourly observation. Present weather and sea level pressure are not reported for the Artais AWOS data. 2.0.2 Oklahoma Mesonet (OKMESO) Algorithms The following is a brief description of the OKMESO algorithms. Complete details can be found in The Oklahoma Mesonet User's Guide (1995). 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 from the 05-minute of the previous hour through the 00-minute of 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 ESOP 1995 Five Minute Surface Composite. 2.0.3 DOE ARM Surface (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 from the 05-minute of the previous hour through the 00-minute of 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 ESOP 1995 Five Minute Surface Composite. 2.0.4 High Plains Climate Network (HPCN) Algorithms The algorithms used to produce the High Plains Climate Network hourly surface data are not currently available. The High Plains Climate Network reports only the moisture measurement of relative humidity, and does not report any pressure parameter. This hourly composite includes dewpoint as the moisture parameter. To convert relative humidity to dewpoint, the station elevation and the standard atmosphere were used to generate an estimate of the station pressure, which was then used in the relative humidity to dewpoint conversion. 2.0.5 Automated Surface Observing System (ASOS) Algorithms The following are descriptions of the algorithms used by ASOS to produce hourly surface data. Complete details may be found in the ASOS User's Guide (1992). 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 from the 05-minute of the previous hour through the 00-minute of the current hour. The descriptions of the algorithms used by ASOS to produce five minute surface data are located in the ESOP 1995 Five Minute Surface Composite documentation. 2.0.6 Wind Profiler Network (WPN) Algorithms The algorithms used to produce Wind Profiler Network hourly surface data are not currently available. 2.0.7 National Climatic Data Center (NCDC) SAO's 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 ESOP 1995 NCDC SAO "Specials" Dataset. Again, see the Federal Meteorological Handbook No. 1 for details on the differences between "nominal" and "special" observations. 2.0.8 Colorado Agricultural Meteorological Network Algorithms The algorithms used to produce Colorado Agricultural Meteorological Network hourly surface data are not currently available. 2.1 Detailed Format Description The ESOP 1995 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. Missing values are reported as 9's in the data field. The table below details the data parameters in each record. Several data parameters have an associated Quality Control (QC) Flag Code which is assigned during the Joint Office for Science Support (JOSS) quality control processing. For a list of possible QC Flag values see the Quality Control Section 3.0. 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 When not present in the raw data, the dewpoint is computed using the formula from Bolton (1980). Calculated Sea Level pressure is computed from station pressure, temperature, dewpoint, and station elevation using the formula of Wallace and Hobbs (1977). 3.0 Quality Control Processing The ESOP 1995 Hourly Surface Composite was formed from several datasets (i.e., Hourly Artais AWOS, Hourly Handar AWOS, Hourly Qualimetrics AWOS, Hourly Oklahoma Mesonet (OKMESO), Hourly DOE ARM Surface (ARMSFC), High Plains Climate Network (HPCN), Hourly Automated Surface Observing System (ASOS), Wind Profiler Network (WPN), National Climatic Data Center (NCDC) SAO's and Colorado Agricultural Meteorological data) for the ESOP 1995 domain. These datasets were collected over the ESOP 1995 domain (i.e., 31N to 40N and 91W to 107W) and were combined to form a surface composite. The composite was quality controlled to form the final ESOP 1995 Hourly Surface Composite. During the JOSS Horizontal Quality Control (JOSS HQC) processing, station observations of pressure, temperature, dew point, wind speed and wind direction were compared to "expected values" computed using an objective analysis method adapted from that developed by Cressman (1959) and Barnes (1964). The JOSS HQC method allowed for short term (>/= 30 day) variations by using 30 day standard deviations computed for each parameter when determining the acceptable limits for "good", "questionable", or "unlikely" flags. "Expected values" were computed from inverse distance weighted station observations within a 300 km Radius Of Influence (ROI) centered about the station being quality controlled (the station being quality controlled was excluded); i.e.; theta_e = / Where theta_e is the "expected value" of the parameter at the site in question, theta(i) is the observed value of the parameter at site i, w(i) is the weighting factor for site i (here the inverse of the distance between site i and the station being quality controlled), and <...> is the sum over all stations "i" in the current ROI that have valid observations of the parameter at the time in question. Data were always compared at like solar times. To determine an observation's HQC flag setting, the difference between the actual observation and its "expected value" was compared to that parameter's normalized standard deviation. Normalizing factors (also called the sensitivity coefficients) were chosen to control the "good", "questionable", and "unlikely" flag limits for each parameter. See Table 3-1 for ESOP 1995 normalizing factors. Table 3-2 contains the HQC flag limit ranges derived from the normalizing factors given in Table 3-1 and estimated standard deviations for each parameter so that 95% of the QC limits applied to the ESOP 1995 data fell within these ranges. For example, 95% of the observed station pressure values that were flagged as "good" were within 1.5 mb of the expected value. The significant overlap of the ranges seen in Table 3-2 was partially due to seasonal and station differences in standard deviations. The actual HQC limits applied at any particular time depended upon the dynamic nature of the particular station's parameter values over time. Data were never changed, only flagged. HQC was only applied to station pressure, sea level pressure, calculated sea level pressure, temperature, dew point, wind speed and wind direction. If the calculated sea level pressure quality control information was available, its flag was applied to the station and sea level pressures. If the calculated sea level pressure could not be quality controlled, the sea level pressure quality control flag was applied to the station pressure. If the sea level pressure could not be quality controlled, the station pressure quality control flag was not overridden. Table 3-1 Normalizing factors used for ESOP 1995 Hourly Surface Composite Parameter Good Questionable Unlikely --------- ---- ------------ -------- Station Pressure 0.2 0.2 0.5 Sea Level Pressure (SLP) 0.2 0.2 0.5 Calculated SLP 0.4 0.4 1.0 Dry Bulb Temperature 0.5 0.5 1.0 Dew Point Temperature 0.5 0.5 1.0 Wind Speed 2.25 2.25 4.0 Wind Direction 1.22 1.22 2.2 Table 3-2 Ranges of HQC flag limit values for ESOP 1995 Hourly Surface Composite Parameter Good Questionable Unlikely --------- ---- ------------ -------- Station Pressure (mb) < 1.5 [0.7-3.9] > 1.7 Sea Level Pressure (mb) < 1.7 [0.5-4.3] > 1.2 Calculated SLP (mb) < 3.9 [0.9-9.8] > 2.2 Dry Bulb Temperature (deg.C) < 2.9 [1.2-5.8] > 2.4 Dew Point Temperature (deg.C) < 3.2 [1.2-6.3] > 2.4 Wind Speed (m/s) < 7.4 [3.2-13.2] > 5.6 Wind Direction(degrees) < 156.8 [94.6-180.] > 170.5 The squall/gust wind speed data were not quality controlled. General consistency checks were also 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". Negative squall/gust wind speeds were coded "unlikely". Wind directions of less than 0 degrees or greater than 360 degrees were coded "unlikely". If these consistency checks would have upgraded the quality control flags previously set by HQC or gross limit checks, then they were not applied. However, if these consistency checks would have degraded the previously set QC flags, they were applied. The JOSS HQC scheme relied on spatial and temporal continuity to flag the data. It has been shown that this method works very well for temperature, dew point, pressure, and wind speed, but is not a very good scheme for the wind direction. The flags appear to be overly lax and perhaps could be tightened. Gross limit checks were also used to determine the quality of the precipitation values. The gross limits are shown in Table 3-3. Certain "questionable" and "unlikely" data values were also manually inspected. After inspection, the quality control flag may have been manually modified to better reflect the physical reasonableness of the data. Data were never modified, only flagged. Negative precipitation was also coded "unlikely". The meanings of the possible quality control flags are listed in Table 3-4. Table 3-3 - Precipitation Gross Limit Values Parameter Good Questionable Unlikely --------- ---- ------------ -------- Hourly Precipitation < 20.0 mm >= 20.0 mm >= 50.0 mm Table 3-4 - Quality Control Flags 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 ASOS User's Guide, ASOS Project Office, NOAA, National Weather Service, Washington D.C., June 1992. AWOS Operations Manual, Federal Aviation Administration, United States Department of Transportation (USDOT), 1988. Barnes, S. L., 1964: A technique for maximizing details in numerical weather map analysis. J. Appl. Meteor., 3, 396-409. Bolton, D., 1980: The computation of equivalent potential temperature., Mon. Wea. Rev., 108, pp 1046-1053. Cressman, G. P., 1959: An operational objective analysis system. Mon. Wea. Rev., 87, 367-374. 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. Wallace, J.M., P.V. Hobbs, 1977: Atmospheric Science, Academic Press, 467 pp. World Meteorological Organization (WMO), 1988: Manual on Codes Volume I, Part B - Binary Codes. WMO, Geneva, Switzerland.