GCIP/EAOP-99 National Weather Service High-Resolution Upper-Air Dataset 1.0 General Description This is one of the upper air sounding datasets developed for the GEWEX Continental-scale International Project (GCIP) 1999 Enhanced Annual Observation Period (EAOP-99). This data set includes high resolution sounding data from 14 NWS sites over the GCIP LSA-E region which is 33-43 N latitude and 76-90 W longitude. These soundings were typically released at 00 12 UTC, however, several stations had additional launches 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 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 EAOP 1998 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: GCIP/EAOP-99 6-second class format sounding. Release Site Type/Site ID: JAN Jackson, MS Release Location (lon,lat,alt): 090 6.00'W, 32 18.00'N, -90.10, 32.30, 91.0 UTC Release Time (y,m,d,h,m,s): 1998, 12, 30, 23:02:00 Ascension No: 1734 Radiosonde Serial Number: 84750738.CSN Radiosonde Manufacturer: VIZ B2 / / / Nominal Release Time (y,m,d,h,m,s):1998, 12, 31, 00:00:00 Time Press Temp Dewpt RH Uwind Vwind Wspd Dir dZ Lon Lat Elev Azim Alt Qp Qt Qh Qu Qv Qdz sec mb C C % m/s m/s m/s deg m/s deg deg deg deg m code code code code code code ------ ------ ----- ----- ----- ------ ------ ----- ----- ----- -------- ------ - ----- ----- ------- ---- ---- ---- ---- ---- ---- 0.0 1007.8 8.3 -4.8 39.0 -0.5 1.4 1.5 160.0 999.0 -90.100 32.30 0 999.0 999.0 91.0 99.0 99.0 99.0 99.0 99.0 9.0 6.0 1003.9 8.4 -5.8 36.1 9999.0 9999.0 999.0 999.0 5.3 9999.000 999.00 0 999.0 999.0 123.0 99.0 99.0 99.0 9.0 9.0 99.0 12.0 1000.0 8.5 -6.7 33.3 9999.0 9999.0 999.0 999.0 5.3 9999.000 999.00 0 999.0 999.0 155.0 99.0 99.0 99.0 9.0 9.0 99.0 2.2 Data Remarks The NWS soundings during EAOP-1999 utilized either the VIZ Inc. VIZ B2 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 one-stage QC process. 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. 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 1998 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 < 250mb) P, T, RH Q > 30 C/km (not applied at p < 250mb) P, T, RH B > 100 C/km (not apllied at p > 250mb) P, T, RH Q > 200 C/km (not applied at p > 250mb) 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 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 FFC Atlanta GA Vaisala RS-80 BMX Birmingham AL Vaisala RS-80 RNK Roanoke VA Vaisala RS-80 BUF Buffalo NY VIZ B2 DTX Detroit MI Vaisala RS-80 GSO Greensboro NC Vaisala RS-80 JAN Jackson MS VIZ B2 ILX Lincoln IL Vaisala RS-80 BNA Nashville TN VIZ B2 MHX Newport NC Vaisala RS-80 PIT Pittsburgh PA VIZ B2 IAD Sterling VA Vaisala RS-80 ILN Wilmington OH 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.