VORTEX National Weather Service High-Resolution Upper-Air Dataset 1.0 General Description This is one of the upper air sounding datasets developed for the Verification of the Origins of Rotation in Tornadoes EXperiment (VORTEX) conducted from 01 April to 15 June 1994. The VORTEX domain extends from approximately 91W to 107W longitude and 31N to 40N latitude. Included in this dataset are 12 NWS sounding stations in the VORTEX domain. The soundings were typically released at 00 and 12 UTC, however, several stations had additional launches on an as requested basis, particularily Norman OK (OUN). The final dataset consists of 6-sec vertical resolution files. 2.0 Detailed Data Description For each sounding, this dataset contains the data type, project ID, site ID, site location, release time and ascension number. Additionally, for each sounding level, the dataset contains 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 QC code description). QC Code Description 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") 2.1 Data Remarks The NWS soundings during VORTEX were comprised of two types: Space Data radiosondes (Amarillo, El Paso, Midland, and Stephenville TX and Albuquerque NM) and VIZ radiosondes (Denver CO, Dodge City KS, Little Rock AR, Longview TX, Monett MO, Norman OK, Topeka KS, Albuquerque NM, and Stephenville TX). Albuquerque NM and Stephenville TX both used Space Data radiosondes from 01 April to 31 May 1994. From 01 June to 15 June 1994 they used the VIZ radiosondes. OFPS applied a correction to the Space Data radiosonde relative humidity calculations. The NWS Micro-ART sounding system, in the resistance ratio and RH calculations, used, instead of the observed temperature, the observed temperature divided by 100. The OFPS applied correction was to rederive the resistance ratio, using the observed temperature divided by 100 and the observed RH, by iteration using the so termed "1A" and "1B" coefficients. Now with the new calculated resistance ratio, the observed temperature and using the "1A" coefficients only, the new RH was calculated. OFPS also applied a correction to the VIZ radiosonde RH calculations. Using the observed temperature and RH, the resistance ratio was rederived by iteration using both the "1A" and "1B" coefficients. With the calculated resistance ratio, the observed temperature and using the "1A" coefficients only, the new RH was calculated. In both of the radiosonde types, 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, particularily at low elevation angles. The general approach to correct this problem was to remove the outlier radiosonde position data before computing the wind components. 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. 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, "reasonable" 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 paramters 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. 4.0 Reference Micro-ART Observation and Rework Programs Technical Document, National Weather Service, National Oceanic and Atmospheric Administration, Washington, D.C., March 1991. 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.