IHOP_2002 Soundings Rawinsonde NWS(6-sec vertical levels) JOSS 1.0 General Description This is one of the upper air data sets developed for the International H2O Project 2002 (IHOP 2002). Included in this data set are 14 National Weather Service (NWS) rawinsonde stations in the IHOP 2002 domain. The soundings were typically released at 00 and 12 UTC, however, stations released additional sondes during IHOP 2002 intensive observing periods (IOPs). Extra rawinsondes were released at 03,06,and 09 or 15,18, and 21, UTC. The data set contains rawinsonde profiles released from 12 May 2002 thru 26 June 2002. The final data set 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 Release Site Type/Site ID: Description of release site. 4 Release Location (lon,lat,alt): Position of release 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 labels are padded to 35 characters to match the standard header lines. Records for this dataset include the following three non-standard header lines. Line Label (padded to 35 char) Contents 6 Ascension No: 1299 7 Radiosonde Serial Number: 152551614 8 Radiosonde Manufacturer: Vaisala Data Records The data records each contain time from release, pressure, temperature, dew point, 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 Elevation Angle Degrees 999.0 14 5 F5.1 Azimuth Angle 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 IHOP 2002 Sounding Rawinsonde NWS 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: IHOP 2002 NWS 6-sec resolution class format sounding Release Site Type/Site ID: MAF Midland, TX Release Location (lon,lat,alt): 102 12.00'W, 32 0.00'N, -102.20, 32.00, 873.0 UTC Release Time (y,m,d,h,m,s): 2002, 05, 27, 23:05:00 Ascension No: 1299 Radiosonde Serial Number: 152551614 Radiosonde Manufacturer: Vaisala / / / Nominal Release Time (y,m,d,h,m,s):2002, 05, 28, 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 ------ ------ ----- ----- ----- ------ ------ ----- ----- ----- -------- ------- ----- ----- ------- ---- ---- ---- ---- ---- ---- 0.0 909.6 22.4 18.0 76.0 -0.5 3.0 3.0 171.0 999.0 -102.200 32.000 999.0 999.0 873.0 2.0 2.0 2.0 99.0 99.0 9.0 6.0 900.5 25.2 14.1 50.0 -0.3 2.9 2.9 174.0 14.7 9999.000 999.000 999.0 999.0 961.0 3.0 2.0 2.0 4.0 4.0 99.0 12.0 898.3 25.3 13.2 47.0 -0.1 2.7 2.7 178.0 3.7 9999.000 999.000 999.0 999.0 983.0 3.0 99.0 99.0 4.0 4.0 99.0 18.0 895.9 25.4 11.9 43.0 0.1 2.6 2.6 182.0 3.8 -102.201 32.006 39.5 191.8 1006.0 2.0 2.0 2.0 4.0 4.0 99.0 24.0 893.3 24.9 11.1 42.0 0.3 2.4 2.4 187.0 4.3 -102.201 32.007 35.2 183.3 1032.0 2.0 2.0 2.0 4.0 4.0 99.0 2.2 Data Remarks NWS soundings during IHOP 2002 utilized either the VIZ type radiosonde produced by Sippican Inc. (http://www.sippican.com/meteorological.html) or the Vaisala RS-80 radiosonde (http://www.vaisala.com, under "Product and Systems/Radiosonde,dropsondes,rockectsondes"). Only Amarillo and Dodge City used VIZ rawinsondes. The remaining sites utilized Vaisala radiosondes. 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 out-lier 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). 2.3 Station List ID SITE STATE LONG LAT ELEV (m) SONDE TYPE ------------------------------------------------------------------ ABQ Albuquerque NM -106.6 35.0 1615.0 VIZ B2 AMA Amarillo TX -101.7 35.2 1094.0 Vaisala DVN Davenport IA -90.6 41.6 229.0 Vaisala DNR Denver INT APT CO -104.9 39.8 1611.0 Vaisala DDC Dodge City KS -100.0 37.8 788.0 VIZ B2 FWD Fort Worth TX -97.3 32.8 198.0 Vaisala LIT Little Rock AR -92.3 34.8 172.0 Vaisala MAF Midland TX -102.2 32.0 873.0 Vaisala OUN Norman OK -97.4 35.2 357.0 Vaisala LBF North Platte NE -100.7 41.1 849.0 Vaisala OAX Valley NE -96.4 41.3 350.0 Vaisala SHV Shreveport LA -93.8 32.5 83.0 Vaisala SGF Springfield MO -93.4 37.2 390.0 Vaisala TOP Topeka KS -95.6 39.1 270.0 Vaisala 3.0 Quality Control Processing This dataset underwent an automated QC process. The dataset underwent internal consistency checks which included two types of checks, gross limit checks on all parameters and rate-of-change checks on temperature, pressure and ascension rate. 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 IHOP 2002 NWS 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 > 1050 mb P B Altitude < 0 m or > 40000 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 > 50 C/km (not applied at p < 250mb) P, T, RH Q < 100 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 Quality Control Methodology An algorithm removing unusually high low level winds speeds was developed and applied to all IHOP 2002 NWS soundings. The algorithm utilized a four step quality control procedure. The best one minute wind data was retained and along with the surface wind values used to interpolate the first three minutes of the wind profile. This procedure effectively removed most anomalously high low level wind speeds or at least reduced their magnitude. Due to the problem described in section 3.3.1, many NWS radiosonde derived profiles contain missing low level winds and the interpolation routine using the surface wind values replaced the missing data with reasonable. values. The wind processing algorithm described in section 2.0, generally only smoothes wind data after the first 360 seconds. This time interval increases when missing wind data is present in the first three minutes of the sounding. The wind quality control (wind qc) procedure provides some quality control on the winds during the first 360 seconds of the sounding. The first check compares U and V wind components and total wind velocities from adjacent pressure levels. This check, called the differential shear check, flags points based on the absolute difference between the velocity for the point being checked and the previous point's value. Most differences were less than 0.1 m/s/s. If the difference was 0.25 m/s/s or more, winds for that pressure level received a questionable (2.0) Qu and Qc quality control flag. Pressure levels with differences greater than 0.5 m/s/s were given bad (3.0) Qu and Qv flags. The data points used in this check must be non-missing and unchecked (i.e Qu = Qv = 99.0, unchecked Quality control flag). Most erroneous wind values failed this check. The next check compared U and V wind components and total wind velocities to the their running one minute mean. U wind components and total wind speeds larger than 0.80 standard deviations above the running one minute mean U and total wind speed were given questionable Qu and Qv (2.0) flags. Values greater than 1.2 standard deviations above the mean were given bad (3.0) Qu and Qv flags. The procedure for the V wind component was similar except that questionable and bad values were 0.85 and 1.275 standard deviations respectively. Z scores for each parameter (U and V wind components and total wind speed) were calculated for every pressure level. A running one minute mean was derived for each parameter. If the one minute interval contained at least 50% non-missing and unchecked values, the z score check was allowed. If the z score for one parameter was flagged, then both Qu and Qv flags for the pressure level being checked received that flag. The Qu and Qv flags for the pressure level inspected received the worst flag assigned by the z-score check. For example, If the V component is bad than, Qu and Qv were both assigned a bad flag even if the U component and total wind speed z-scores were less than 0.80. The final quality control check entailed identifying points "sandwiched" by questionable or bad data values. The assumption being if wind speeds immediately preceding and following the currently inspected data value were flagged questionable or bad, then this point was also questionable or bad. The procedure for the proximity check was the following. The Qu and Qv flags for data points immediately following and preceding a non-missing value were examined. If both points have been flagged, the point being checked Qu and Qv flags were assigned the minimum value of the Qu and Qv flags from these points. The last step in the wind quality control procedure involved removing wind values for points flagged questionable or bad and selecting the best one minute resolution winds from the remaining points. A cubic spline algorithm (Numerical Recipes in C,page 97) using the surface U and V wind components and the U and V components from the one minute resolution winds (if available), interpolated U and V components for the first 360 seconds of the sounding. The total wind speed and direction were derived from the U and V wind components. Interpolated wind values received a 4.0 (Estimated Quality Control Flag) Qu and Qv flags. Interpolation was limited to gaps 120 seconds or less. Interpolated U and V wind components greater than the maximum of the points used in the interpolation were set to missing. Example of wind qc methodology on North Platte wind profile from May 15th,2002 00 UTC rawinsonde release. Original profile is below followed by wind profile after application of wind quality control procedure. Time Press Ucmp Vcmp spd dir sec mb m/s m/s m/s deg ------ ------ ------ ------ ----- ------ 0.0 909.7 -3.2 8.7 9.3 160.0 6.0 907.3 9999.0 9999.0 999.0 999.0 12.0 905.0 9999.0 9999.0 999.0 999.0 18.0 902.3 9999.0 9999.0 999.0 999.0 24.0 900.6 -16.0 75.0 76.7 167.9 30.0 897.9 -13.4 64.1 65.5 168.2 36.0 896.2 -11.2 55.3 56.4 168.5 42.0 893.8 -9.6 48.0 48.9 168.7 48.0 891.2 -8.3 42.0 42.8 168.8 54.0 888.3 -7.3 37.0 37.7 168.7 60.0 884.5 -5.4 29.3 29.8 169.5 Time Press Ucmp Vcmp spd dir sec mb m/s m/s m/s deg ------ ------ ------ ------ ----- ------ 0.0 909.7 -3.2 8.7 9.3 160.0 6.0 907.3 -3.2 9.0 9.6 160.4 12.0 905.0 -3.2 9.3 9.8 161.0 18.0 902.3 -3.3 9.6 10.2 161.0 24.0 900.6 -3.3 9.9 10.4 161.0 30.0 897.9 -3.3 10.3 10.8 161.6 36.0 896.2 -3.3 10.6 11.1 162.2 42.0 893.8 -3.3 10.9 11.4 162.7 48.0 891.2 -3.3 11.2 11.7 163.2 54.0 888.3 -3.3 11.5 12.0 163.6 60.0 884.5 -3.3 11.9 12.3 164.0 Winds at the surface and 850 mb from the GTS version of the sounding were 9.3 m/s @ 160 deg and 19.0 m/s @ 170 deg respectively. These compare favorably with the surface wind (wind @ 0.0 seconds) and the wind at 849.4 mb (15.9 m/s @ 170 deg) from the high resolution sounding for that date. The wind qc methodology effectively removed the anomalously high low level wind speeds but retained the winds from higher levels. Without independent wind measures to compare the new wind profile against, determining the validity of the new profile is difficult. However, we do know that category five hurricane winds (> 69.3 m/s) did not occur at North Platte on May 15,2002. 3.3.3 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. 4.0 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. Numerical Recipes in C, edited by Press, W. H, B. Flannery, S. A., 1988 Cambridge University Press, New York, NY 1988. 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.