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.