SGP97 ARM-CART CLASS Format Upper Air Sounding Data Set 1.0 General Description This is one of the upper air sounding datasets developed for the Southern Great Plains 1997 (SGP97). Included in this data set are five Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) sounding stations; Lamont (Central Facility), Morris (B5), Purcell (B6), and Vici (B4), OK and Hillsboro (B1), KS. This data set covers the period from 1 June through 31 July 1997. The SGP97 domain is approximately 97W to 99W longitude and 34.5N to 37N latitude 2.0 Detailed Data Description All upper air soundings were converted to University Corporation for Atmospheric Science/Joint Office for Science Support (UCAR/JOSS) Cross Chain LORAN Atmospheric Sounding System (CLASS) Format (JCF). JCF is a version of the National Center for Atmospheric Research (NCAR) CLASS format and is an ASCII format consisting of 15 header records for each sounding followed by the data records with associated Quality Control (QC) information. At each of the boundary facilities (B1, B4, B5, and B6) soundings were typically released once per weekday at 1800 UTC and at the central facility five times per weekday at 06, 12, 15, 18, and 21 UTC. However, during Intensive Observing Periods (IOPs) the sounding frequency increased to up to 8 per day (3-hourly; including weekends) at each of the sites. 2.1 Detailed Format Description All upper air soundings were converted to University Corporation for Atmospheric Science/Joint Office for Science Support (UCAR/JOSS) Cross Chain LORAN Atmospheric Sounding System (CLASS) Format (JCF). JCF is a version of the National Center for Atmospheric Research (NCAR) CLASS format and is an ASCII format consisting of 15 header records for each sounding followed by the data records with associated Quality Control (QC) information. Header Records The header records (15 total records) contain data type, project ID, site ID, site location, release time, sonde type, meteorological and wind data processors, and the operator's name and comments. The first five header lines contain information identifying the sounding, and have a rigidly defined form. The following 7 header lines are used for auxiliary information and comments about the sounding, and may vary from data set to dataset. The last 3 header records contain header information for the data columns. Line 13 holds the field names, line 14 the field units, and line 15 contains dashes ('-' characters) delineating the extent of the field. The five standard header lines are as follows: Line Label (padded to 35 char) Contents 1 Data Type: Description of type and resolution of data. 2 Project ID: ID of weather project. 3 Launch Site Type/Site ID: Description of launch site. 4 Launch Location (lon,lat,alt): Position of launch site, in format described below. 5 GMT Launch Time (y,m,d,h,m,s): Time of release, in format: yyyy, mm, dd, hh:mm:ss The release location is given as: lon (deg min), lat (deg min), lon (dec. deg), lat (dec. deg), alt (m) Longitude in deg min is in the format: ddd mm.mm'W where ddd is the number of degrees from True North (with leading zeros if necessary), mm.mm is the decimal number of minutes, and W represents W or E for west or east longitude, respectively. Latitude has the same format as longitude, except there are only two digits for degrees and N or S for north/south latitude. The decimal equivalent of longitude and latitude and station elevation follow. The seven non-standard header lines may contain any label and contents. The label is padded to 35 characters to match the standard header lines. Data Records The data records each contain time from release, pressure, temperature, dewpoint, relative humidity, U and V wind components, wind speed and direction, ascent rate, balloon position data, altitude, and quality control flags (see the QC code description). Each data line contains 21 fields, separated by spaces, with a total width of 130 characters. The data are right-justified within the fields. All fields have one decimal place of precision, with the exception of latitude and longitude, which have three decimal places of precision. The contents and sizes of the 21 fields that appear in each data record are as follows: Field Format No. Width Parameter Units Missing Value ----------------------------------------------------------------------- 1 6 F6.1 Time Seconds 9999.0 2 6 F6.1 Pressure Millibars 9999.0 3 5 F5.1 Dry-bulb Temperature Degrees C 999.0 4 5 F5.1 Dew Point Temperature Degrees C 999.0 5 5 F5.1 Relative Humidity Percent 999.0 6 6 F6.1 U Wind Component Meters / Second 9999.0 7 6 F6.1 V Wind Component Meters / Second 9999.0 8 5 F5.1 Wind Speed Meters / Second 999.0 9 5 F5.1 Wind Direction Degrees 999.0 10 5 F5.1 Ascension Rate Meters / Second 999.0 11 8 F8.3 Longitude Degrees 9999.0 12 7 F7.3 Latitude Degrees 999.0 13 5 F5.1 Range Kilometers 999.0 14 5 F5.1 Azimuth Degrees 999.0 15 7 F7.1 Altitude Meters 99999.0 16 4 F4.1 QC for Pressure Code (see below) 99.0 17 4 F4.1 QC for Temperature Code (see below) 99.0 18 4 F4.1 QC for Humidity Code (see below) 99.0 19 4 F4.1 QC for U Component Code (see below) 99.0 20 4 F4.1 QC for V Component Code (see below) 99.0 21 4 F4.1 QC for Ascension Rate Code (see below) 99.0 Fields 16 through 21 contain the Quality Control information derived at the UCAR Joint Office for Science Support (UCAR/JOSS). Any QC information from the original sounding is replaced by the following JOSS codes: Code Description 99.0 Unchecked (QC information is "missing.") ("UNCHECKED") 1.0 Checked, datum seems physically reasonable. ("GOOD") 2.0 Checked, datum seems questionable on physical basis.("MAYBE") 3.0 Checked, datum seems to be in error. ("BAD") 4.0 Checked, datum is interpolated. ("ESTIMATED") 9.0 Checked, datum was missing in original file. ("MISSING") Sample Data The following is a sample record of ESOP 1996 ARM-CART High-Resolution Upper-Air data in JOSS CLASS format. The data portion is much longer than 80 characters and, therefore, wraps around to a second line. See section 2.1 for an exact format specification Data Type: Sounding Project ID: ARM-CART 2 sec class format sounding Launch Site Type/Site ID: C1 : Central_Facility Launch Location (lon,lat,alt): 097 30.00'W, 36 36.00'N, -97.50, 36.60, 315.0 GMT Launch Time (y,m,d,h,m,s): 1997, 04, 02, 05:24:00 / / / / / / Nominal Launch Time (y,m,d,h,m,s): 1997, 04, 02, 06:00:00 Time Press Temp Dewpt RH Uwind Vwind Wspd Dir dZ Lon Lat Rng Ang Alt Qp Qt Qh Qu Qv Qdz sec mb C C % m/s m/s m/s deg m/s deg deg km deg m code code code code code code ------ ------ ----- ----- ----- ------ ------ ----- ----- ----- -------- ------- ----- ----- ------- ---- ---- ---- ---- ---- ---- 0.0 979.2 14.9 7.2 60.0 -1.8 2.0 2.7 138.0 999.0 -97.490 36.610 999.0 999.0 315.0 2.0 2.0 2.0 99.0 99.0 9.0 2.0 977.5 15.1 6.9 58.0 9999.0 9999.0 999.0 999.0 7.0 -97.490 36.610 999.0 999.0 329.0 2.0 2.0 2.0 9.0 9.0 99.0 4.0 975.8 15.4 6.7 56.0 9999.0 9999.0 999.0 999.0 7.5 -97.490 36.610 999.0 999.0 344.0 2.0 2.0 2.0 9.0 9.0 99.0 2.2 Data Remarks The ARM-CART files were delivered as netcdf files which JOSS converted to JCF. These files have two-second vertical resolution thermodynamic data and 10-sec vertical resolution wind data. At each of the boundary facilities (B1, B4, B5, and B6) soundings were typically released once per weekday at 1800 UTC and at the central facility five times per weekday at 06, 12, 15, 18, and 21 UTC. However, during Intensive Observing Periods (IOPs) the sounding frequency increased to up to 8 per day (3-hourly; including weekends) at each of the sites. 2.3 Information from ARM 2.3.1 List of Components The BBSSs consist of disposable radiosondes and fixed ground stations. All facilities use the same radiosondes, but the Central Facility ground station is different from the boundary facility ground stations. Radiosondes: Manufacturer: Vaisala, Inc. Type: RS80-15LH (Loran-C windfinding, H-Humicap, 403 MHz) Ground Stations: Central Facility: Manufacturer: Vaisala, Inc. Station Type: PC-CORA Components: UR-15 UHF Receiver SPL-11 Loran-C Receiver CG-21 Antenna Set including CAS-21 VLF Antenna UHF Omnidirectional Antenna RAA-20M Antenna Amplifier SPT-11 Paper Tape Reader SPU-11 Sounding Processor GC-22 Ground Check Set PC 486 MS-DOS Boundary Facilities (All) Manufacturer: Vaisala, Inc. Station Type: MW-11 Digi-CORA Components: MF-12 Floppy Disk Drive B5 (Morris) CG-21 Antenna Set including CAS-21 VLF Antenna UHF Omnidirectional Antenna RAA-20M Antenna Amplifier UPP-15 Receiver Processor UIF-15A IF Unit URO-15 Oscillator URR-15 RF Unit B1 (Hillsboro), B4 (Vici), and B6 (Purcell) RB-21 Directional UHF Antenna UPP-15A Receiver Processor (B1) in place of UPP-15 UPP-20 Receiver Processor (B6) in place of UPP-15 Note that at B6 (Purcell) the UIF-15A, URO-15, and URR-15 are all replaced by a URR-20 Combined IF/RF/Oscillator Unit. 2.3.2 Description of System Configuration and Measurement Methods Current sampling rate: Thermodynamic variables (PTU) output every 2 seconds throughout the flight. Wind variables (speed, direction) output every 10 seconds throughout the flight. Balloons and rate of ascent: ARM uses 350 g balloons at the SGP/CART. The nominal ascent rate is approximately 5 m/s, although this is variable during the flight. The data file includes a variable 'asc' which, for each sample, estimates the current rate of ascent. This rate is actually a 30-second average rise rate based on the calculated sonde altitudes. 2.3.3 Assessment of System Uncertainties for Primary Quantities Measured Standard BBSS data are subject to several levels of quality control and quality assurance. The process of converting the raw 1.5-second PTU samples to values output every 2 seconds involves filtering, editing, and interpolation intended to provide the best estimate of the atmospheric state at every level. The details of the processing are not well documented, however, and are being analyzed by the instrument mentor and more information will be provided when it is available. Upon ingest, each sounding is checked for violations of simple physical limits on each data field (maximum, minimum, maximum change). Samples that exceed these criteria are flagged and these flags are included in the netCDF files. Several situations may arise during a sounding that may affect the quality of the data but which may not be flagged or otherwise corrected and the user should be aware of these. Among these are incorrect surface conditions, humidity sensor saturation or icing, interference and signal confusion from other radiosondes. General data quality reports (DQRs) have been issued describing these conditions and the user is urged to read and understand these. Specific DQRs are issued for those cases when incorrect surface conditions are included in the soundings. Cases of sensor saturation (which may lead to unrealistic lapse rates or humidity values aloft, and of sonde-to-sonde interference which may result in incorrect data values are not generally called out in individual DQRs Soundings done at the boundary facilities include a STATUS message in the netCDF metadata. This STATUS message contains information about the overall quality of the sounding. Among the information included in the status message is the percent of good telemetry, and the percent of samples that did not pass the internal quality checks. The format of the STATUS message is explained below in the FAQ section. 2.3.4 Description of Observational Specifications The manufacturer's specifications for the thermodynamic sensors are as follows: PRESSURE Type: Capacitive aneroid Range: 1060 hPa to 3 hPa Resolution: 0.1 hPa Accuracy: 0.5 hPa TEMPERATURE Type: Capacitive bead Range: +60 degC to -90 degC Resolution: 0.1 degC Accuracy: 0.2 degC Lag: <2.5 s (6 m/s flow at 1000 hPa) HUMIDITY Type: H-HUMICAP thin film capacitor Range: 0 to 100 %RH Resolution: 1 %RH Accuracy: 2 %RH (0 to 80 %RH) 3 %RH (80 to 100 %RH) Lag: 1 s (6 m/s flow at 1000 hPa, +20 degC) Note that the "accuracy" figures given by the manufacturer represent the standard deviation of the differences obtained from repeated calibrations. As such, these values are more properly termed "precision." Operational experience at the SGP/CART site (Lesht, 1995) showed that the RMS error in RH was approximately 1% RH at low humidity and surface temperature and that the RMS error in temperature was approximately 0.3 deg C. WINDS Wind information is obtained by tracking the radiosonde's position using the Loran-C navigation system. The accuracy of the wind information depends on the configuration of the Loran-C stations that are used to locate the sonde. Loran-C coverage in the SGP/CART area is fairly good, and we estimate the accuracy of the wind speed to be approximately 0.5 m/s. 3.0 Quality Control Processing The ARM soundings were Quality Controlled (Lesht 1995) and provided to UCAR/JOSS by the ARM Project. This data set underwent a JOSS QC process which consisted of internal consistency checks. This included gross limit checks on all parameters and rate-of-change checks on temperature, pressure and ascension rate. JOSS did not perform visual quality control procedures on this data. Some further information on the QC processing conducted by JOSS can be found in Loehrer et al. (1996) and Loehrer et al. (1998). 3.1 Gross Limit Checks These checks were conducted on each sounding and data were automatically flagged as appropriate. Only the data point under examination was flagged. JOSS conducted the following gross limit checks on this sounding data set. In the table P = pressure, T = temperature, RH = relative humidity, U = U wind component, V = V wind component, B = bad, and Q = questionable. ________________________________________________________________ Parameter(s) Flag Parameter Gross Limit Check Flagged Applied ________________________________________________________________ Pressure < 0 mb or > 1030 mb P B Altitude < 0 m or > 35000 m P, T, RH Q Temperature < -80C or > 45C T Q Dew Point < -99.9C or > 30C RH Q > Temperature T, RH Q Relative Humidity < 0% or > 100% RH B Wind Speed < 0 m/s or > 100 m/s U, V Q > 150 m/s U, V B U Wind Component < 0 m/s or > 100 m/s U Q > 150 m/s U B V Wind Component < 0 m/s or > 100 m/s V Q > 150 m/s V B Wind Direction < 0 deg or > 360 deg U, V B Ascent Rate < -10 m/s or > 10 m/s P, T, RH Q ________________________________________________________________ 3.2 Vertical Consistency Checks These checks were conducted on each sounding and data were automatically flagged as appropriate. These checks were started at the lowest level of the sounding and compared to neighboring 6-sec averaged values to reduce the flagging frequency of the checks. In the case of checks ensuring that the values increased/decreased as expected, only the data point under examination was flagged. However, for the other checks, all of the data points used in the examination were flagged. All items within the table are as previously defined. _________________________________________________________________ Vertical Consistency Parameter(s) Flag Parameter Check Flagged Applied _________________________________________________________________ Time decreasing/equal None None Altitude decreasing/equal P, T, RH Q Pressure increasing/equal P, T, RH Q > 1 mb/s or < -1 mb/s P, T, RH Q > 2 mb/s or < -2 mb/s P, T, RH B Temperature < -15 C/km P, T, RH Q < -30 C/km P, T, RH B > 5 C/km (not applied at p , 150mb) P, T, RH Q < 30 C/km (not applied at p , 150mb) P, T, RH B Ascent Rate change of > 3 m/s or < -3 m/s P Q change of > 5 m/s or < -5 m/s P B _________________________________________________________________ 3.3 Data Quality Issues from UCAR/JOSS In terms of items checked by the automated quality control processing, the ARM soundings performed well, with about average numbers of data points flagged. However, since these data have not undergone visual quality control processing, there are many problems that have not been flagged. This is especially true for the wind and relative humidity values. So these values should be used with some caution. As in past years, the B4 (Vici, OK) soundings had much higher occurrence rates of superadiabatic layers than the other sites. This year, however, the problem has been significantly reduced. The other sites had 0.5 - 0.7% of all data points registering as superadiabatic (< -15 C/km). These values were typical of soundings from other projects. B4, however, had 1.3% of all data points registering as superadiabatic. 3.4 Data Quality Issues from ARM 3.4.1 Jump in pressure value B4 sounding 970616:1730 Platform/Measurement: sgpsondewrpnb4/ (alt, asc, press) What level data: (raw,a0,a1,b1,c1 etc): all Period of time in question Begin Date 6/16/97 Time 17:30 (GMT) End Date Time (GMT) Data should be labeled: _X_ questionable _X_ All data fields affected Discussion of Problem: The first pressure value reported by the radiosonde (t = 2 sec) is 931.4. The surface pressure value was 936.9 hPa. This difference is slightly greater than the expected (normal) change and may mean that either the pressure sensor was jarred during launch or the system mis-identified the actual launch start time. Further clarification requires analysis of the raw data which will take some time. The altitude values for this sounding may be incorrect. The ascent rate values during the first 30 seconds also will be wrong. Because the system will reject samples with out of bound ascent rates (i.e., during the first 30 seconds), the temperature and rh values also will be incorrect (result of interpolation). Relative height values after 30 seconds should be okay. Suggested Corrections of the Problem: Flag data. 3.4.2 Jump in pressure value B6 sounding 970619:0530 Platform/Measurement: sgpsondewrpnb6/ (alt, asc, press) What level data: (raw,a0,a1,b1,c1 etc): all Period of time in question Begin Date 6/19/97 Time 05:30 (GMT) End Date Time (GMT) Data should be labeled: _X_ questionable _X_ Only some data fields affected Discussion of Problem: The first pressure value reported by the radiosonde (t = 2 sec) is 970.4. The surface pressure value was 975.1 hPa. This difference is greater than the expected (normal) change and may mean that either the pressure sensor was jarred during launch or the system mis- identified the actual launch start time. Further clarification requires analysis of the raw data which will take some time. The altitude values for this sounding may be incorrect. The ascent rate values during the first 30 seconds also will be wrong. Because the system will reject samples with out of bound ascent rates (i.e., during the first 30 seconds), the temperature and rh values also will be incorrect (result of interpolation). Relative height values after 30 seconds should be okay. Suggested Corrections of the Problem: Flag data. 3.4.3 Jump in pressure value B6 sounding 970619:1130 Platform/Measurement: sgpsondewrpnb6/ (alt, asc, press) What level data: (raw,a0,a1,b1,c1 etc): all Period of time in question Begin Date 6/19/97 Time 11:30 (GMT) End Date Time (GMT) Data should be labeled: _X_ questionable _X_ Only some data fields affected Discussion of Problem: The first pressure value reported by the radiosonde (t = 2 sec) is 968.0. The surface pressure value was 974.5 hPa. This difference is greater than the expected (normal) change and may mean that either the pressure sensor was jarred during launch or the system mis-identified the actual launch start time. Further clarification requires analysis of the raw data which will take some time. The altitude values for this sounding may be incorrect. The ascent rate values during the first 30 seconds also will be wrong. Because the system will reject samples with out of bound ascent rates (i.e., during the first 30 seconds), the temperature and rh values also will be incorrect (result of interpolation). Relative height values after 30 seconds should be okay. Suggested Corrections of the Problem: Flag data. 3.4.4 SGP/SONDE - Dry bias in sonde RH START DATE: 05/27/1992 END DATE: 12/31/1999 DATASTREAMS AFFECTED: B1, B4, B5, B6 and C1 Vaisala has confirmed ARM findings of an apparent dry bias in the relative humidity measured by RS-80H radiosondes. The cause of the dry bias is thought to be contamination of the humidity sensor by volatile organic substances originating from some plastic parts of the radiosonde. The amount of contamination is a function of the time between the date of sonde manufacture and its use. All RS-80H sondes manufactured before week 34 of 1998 will show this bias. After week 34 of 1998 Vaisala changed its packaging to reduce, but not eliminate the contamination problem. Further changes in packaging intended to eliminate the problem are expected to be put into production soon. Vaisala is in the process of developing an algorithm that can be used to estimate the correct RH from knowledge of the sonde age. All of the ARM sounding data have sufficient metadata available to apply the correction. 3.4.5 Possible telemetry interference/interpolated data START DATE: 07/15/1997 START TIME: 1836 END DATE: 07/15/1997 END TIME: 1851 DATASTREAMS AFFECTED: B5 It appears that this sonde lost signal briefly a little after an hour into the flight at 18:36:42 (altitude approx 17 km. Signal was recovered, but it is possible that the signal was from a different sonde - temp and RH data appear to be interpolated in the interval from 17 to 20 km. I would treat all data above 17 km (after 18:36:42) as questionable. 3.4.6 Pressure jump at launch START DATE: 07/15/1997 START TIME: 2030 END DATE: 07/15/1997 END TIME: 2030 DATASTREAMS AFFECTED: B5 The first pressure value returned by the radiosonde after launch (985.2) is somewhat lower than would be expected based on the entered surface pressure (990.0). It is likely that either the pressure sensor was jarred at launch or that the system mis-identified the launch time. Altitude and absolute pressure values will be affected and ascent rate values during the first 30 sec of flight will be incorrect. 3.4.7 Missing/Questionable data 970715:0530 sounding START DATE: 07/15/1997 START TIME: 604 END DATE: 07/15/1997 END TIME: 705 DATASTREAMS AFFECTED: B6 o Data should be labeled: questionable, missing This file has two problems. The first is possible interference and incorrect data from 34:32 into the flight (06:04:32 or 9673 m) to 38:48 (06:08:48 or 10718 m). I would treat these data a questionable. There is a gap in the data, possibly due to SDS communication problems from 38:48 to 95:42 (07:05:42 or 25112 m) in which all data are missing. o Suggested Corrections: Reprocess file from raw data (companion PIF will be submitted). Flag data. 3.4.8 Pressure jump after launch START DATE: 07/17/1997 START TIME: 2340 END DATE: 07/17/1997 END TIME: 2340 DATASTREAMS AFFECTED: B6 First pressure value returned by the sonde after launch was 966.8, somewhat lower than would be expected given the surface pressure reading of 971.3. This resulted in an apparent ascent rate that is greater than the QC flag trigger. Ascent rates during the first 30 s of flight are likely incorrect. Absolute altitudes also are likely incorrect. Relative pressure differences after launch should be okay. 4.0 References Lesht, B. M., 1995: An evaluation of ARM radiosonde operational performance. Preprints, Ninth Symposium on Meteorological Observations and Instrumentation, Charlotte, NC, Amer. Meteor. Soc., 6-10. Loehrer, S. M., T. A. Edmands, and J. A. Moore, 1996: TOGA COARE upper-air sounding data archive: development and quality control procedures. Bull. Amer. Meteor. Soc., 77, 2651-2671. Loehrer, S. M., S. F. Williams, and J. A. Moore, 1998: Results from UCAR/JOSS quality control of atmospheric soundings from field projects. Preprints, Tenth Symposium on Meteorological Observations and Instrumentation, Phoenix, AZ, Amer. Meteor. Soc., 1-6.