SGP97 National Weather Service High-Resolution Upper-Air Dataset 1.0 General Description This is one of the upper air sounding datasets developed for the Southern Great Plains - 1997 (SGP97). This data set includes high resolution sounding data from 12 NWS sites over the SGP97 region. See Section 4.0 for a list of sites. These soundings were typically released at 00 12 UTC, however, several stations had additional releases on an as requested basis. The final dataset consists of 6-sec vertical resolution files. 2.0 Detailed Data Description 2.0.1 National Weather Service High-Resolution Sounding Algorithms The detailed description of NWS sounding collection and instrumentation is located in NWS (1991). 2.1 Detailed Format Description All upper air soundings were converted to University Corporation for Atmospheric Research/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 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 dataset 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 6 Ascension No: Ascension number of the site for the year . 7 Radiosonde Serial Number: Serial number of this radiosonde. 8 Radiosonde Manufacturer: Manufacturer of this radiosonde. 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 SGP97 NWS 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: NWS Project ID: SGP'97 class format six second resolution sounding Launch Site Type/Site ID: EPZ Santa Teresa, NM Launch Location (lon,lat,alt): 106 42.00'W, 31 54.00'N, -106.70, 31.90, 1257.0 GMT Launch Time (y,m,d,h,m,s): 1997, 06, 15, 23:01:00 Ascension No: 1312 Radiosonde Serial Number: 649250809 Radiosonde Manufacturer: Vaisala / / / Nominal Launch Time (y,m,d,h,m,s): 1997, 06, 16, 00:00:00 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 ------ ------ ----- ----- ----- ------ ------ ----- ----- ----- -------- ------- ----- ----- ------- ---- ---- ---- ---- ---- ---- 0.0 870.6 21.9 15.5 67.0 -3.6 2.0 4.1 120.0 999.0 -106.700 31.900 999.0 999.0 1257.0 2.0 2.0 2.0 1.0 1.0 9.0 6.0 865.1 20.9 12.9 60.0 6.3 14.8 16.1 203.0 9.5 -106.700 31.901 999.0 999.0 1314.0 3.0 2.0 2.0 1.0 1.0 99.0 12.0 863.7 20.7 13.4 63.0 8.0 14.4 16.5 209.0 2.3 -106.699 31.902 999.0 999.0 1328.0 3.0 1.0 1.0 1.0 1.0 99.0 2.2 Data Remarks The NWS soundings during SGP97 utilized either the VIZ Inc. 2B or the Vaisala RS-80 radiosonde. See section 4.0 for the list of sites and the radiosondes they used. The use of the raw 6-sec resolution elevation and azimuth angle data to derive the winds sometimes led to large oscillations in wind speed, due to the presence of oscillations in the elevation angle data, particularly at low elevation angles. The general approach to correct this problem was to remove the outlier radiosonde position data before computing the wind components (Williams et al. 1993). For both the azimuth and elevation angles from 360 sec to the end of the sounding, a ninth order polynomial was fit to the curve. The residuals were calculated and compared to the observed values. The outliers of the residuals were then removed. Then to help correct the more extensive problems at low elevation angles within 10 degrees of the limiting angles (LA) some additional smoothing was applied. If the elevation angle was between (LA + 7.5) and (LA + 10), the new elevation angle was computed with a 2 min linear fit. If the elevation angle was between (LA + 5) and (LA + 7.5), the new elevation angle was computed with a 3 min linear fit. If the elevation angle was less than (LA + 5), the new elevation angle was computed with a 4 min linear fit. If the number of observations with low elevation angles was greater than 20% of the total number of observations for the sounding no frequency smoothing occurred. Then, for the elevation angle only, a finite Fourier analysis was performed on the residuals. Periods from 90-190 sec were removed and those below 30 sec were flattened. Finally, a 2 min second order polynomial was then fit to the position to derive the u and v wind components, except for the beginning and end minute (or 1.5 minutes if over 50 mb) which used a 3 min fit. If there were less than 15% of the total number of points, not counting the beginning or end of the flight, on one side of the point for which the wind value was being computed, a linear fit was used. For further information on this methodology and its changes since Williams et al. (1993) please see Williams, et al. (1998). 3.0 Quality Control Processing This dataset underwent a two-stage QC process. First, the dataset underwent internal consistency checks. This included two types of checks, gross limit checks on all parameters and rate-of-change checks on temperature, pressure and ascension rate. Second, each sounding was visually examined to verify those parameters that are too variable for automatic checks (wind speed, wind direction and moisture). This stage of the QC process also allows for a verification of the QC flags generated by the automatic checks. 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 the 1996 sounding dataset. 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 neighboring 6-sec data points (except at pressures less than 100 mb where 30-sec average values were used. 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 3.3.1 Near Surface Winds A common problem in near surface wind speed values calculated from the 6-second position data is that the first radiosonde wind speed is much higher than the independently measured surface value. The calculated radiosonde winds then decrease rapidly so that within about 60 s (20-30 mb) after release the wind speeds are more realistic. The cause of this appears to be the acceptance of radiosonde position data prior to a "good lock" being achieved on the radiosonde by the tracking system. Thus there appear to be rapid positional shifts of the radiosonde while the tracking system "searches" for the radiosonde. 3.3.2 Wind Oscillations Despite the extensive efforts to remove oscillations in wind speeds caused by oscillations in elevation angles (see Section 2.2) there are occasional cases with remaining oscillations. Most of the remaining oscillations have periods just slightly longer than the 190 s maximum point of our notch filter. 3.3.3 Low Level Humidity Problems Santa Teresa Low Level Humidity Problem A new variety of low level humidity problem has appeared at Santa Teresa, NM (formerly El Paso, TX) since its conversion over to the Vaisala radiosonde. This type of problem did not appear in previous years when the site used VIZ soundings. This problem appears as an anomalous moist layer near the surface. An example is shown below for the sounding taken at 00 UTC 22 June 1996 at EPZ. Time Press Temperature Dew Relative Point Humidity -------------------------------------------------------- 0.0 868.8 40.0 4.0 11.0 6.0 865.4 39.4 2.2 10.0 12.0 862.1 38.8 0.3 9.0 18.0 858.5 38.2 2.6 11.0 24.0 854.9 37.6 4.5 13.0 30.0 851.3 36.9 7.0 16.0 36.0 847.7 36.3 8.2 18.0 42.0 844.0 35.7 10.0 21.0 48.0 840.5 35.1 10.9 23.0 54.0 837.7 34.6 7.6 19.0 60.0 835.0 34.1 2.9 14.0 66.0 832.2 33.6 -2.2 10.0 72.0 828.8 33.3 -2.4 10.0 78.0 825.8 33.0 -2.6 10.0 84.0 823.7 32.7 -1.6 11.0 90.0 821.5 32.4 -1.8 11.0 In this example the RH starts at about 11% then increases to over 20% then returns back to about 11%. But the temperature lapse rate is nearly dry adiabatic and indicative of a well mixed atmosphere which should not show such dramatic humidity contrasts. This problem appeared almost exclusively at EPZ (it did rarely appear at other sites, and always under the same atmospheric conditions as when it occurred at EPZ) and it appeared almost exclusively at 00 UTC under dry adiabatic conditions. There are often many missing (and hence interpolated by the Vaisala system) data points surrounding these anomalous moist layers and such missing data points do not appear nearly as often in soundings without this moist layer. The exact cause is not yet known, but given the prevalent occurrence of missing data surrounding these anomalous moist layers, there are significant instrumentation problems occurring. It may be due to some atmospheric effects that occur in such hot and dry conditions, possibly dust is having some effect. But it is not yet clear. General Low Level Humidity Problem Another frequent occurrence in NWS soundings is what appears to be a very dry surface relative to the radiosonde values. An example is shown below from Albuquerque, NM at 00 UTC 25 April 1996. Time Press Temperature Dew Relative Point Humidity ------ ------ --------------- ----- ----------- 0.0 834.4 28.9 -14.5 5.0 6.0 830.9 28.1 -8.7 8.4 12.0 827.4 27.7 -9.7 7.9 18.0 823.9 27.3 -10.0 7.9 24.0 820.5 26.8 -10.4 7.9 The independently measured surface RH is about 4% less than the first radiosonde value. Then the remainder of the radiosonde values appear to be consistent with the first radiosonde value and not the surface value. It has been suggested (Wade 1995) that when this problem occurs, the entire sounding RH may be to moist. 4.0 Radiosonde Stations Included within Data Set ABQ Albuquerque NM VIZ B2 AMA Amarillo TX Vaisala RS-80 EPZ Santa Teresa NM Vaisala RS-80 MAF Midland TX Vaisala RS-80 SHV Shreveport LA VIZ B2 FWD Fort Worth TX VIZ B2 LIT Little Rock AR VIZ B2 OUN Norman OK VIZ B2 SGF Springfield MO VIZ B2 DDC Dodge City KS VIZ B2 TOP Topeka KS VIZ B2 DNR Denver INT APT CO Vaisala RS-80 5.0 References 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. NWS, 1991: Micro-ART Observation and Rework Programs Technical Document, National Weather Service, National Oceanic and Atmospheric Administration, Washington, D.C., March 1991. Wade, C. G., 1995: Calibration and data reduction problems affecting National Weather Service radiosonde humidity measurements. Preprints, Ninth Symposium on Meteorological Observations and Instrumentation, Charlotte, NC, Amer. Meteor. Soc., 37-42. Williams, S. F., C. G. Wade, and C. Morel, 1993: A comparison of high resolution radiosonde winds: 6-second Micro-ART winds versus 10-second CLASS LORAN winds. Preprints, Eighth Symposium on Meteorological Observations and Instrumentation, Anaheim, California, Amer. Meteor. Soc., 60-65. Williams, S. F., S. M. Loehrer, and D. R. Gallant, 1998: Computation of high-resolution National Weather Service rawinsonde winds. Preprints, Tenth Symposium on Meteorological Observations and Instrumentation, Phoenix, AZ, Amer. Meteor. Soc., 387-391.