PLOWS 5-mb Resolution Upper-Air Sounding Composite Data Set

1.0 General Description

This dataset contains upper-air sounding data interpolated to a constant vertical resolution of 5 hPa in the National Center for Atmospheric Research (NCAR) Earth Observing Laboratory (EOL) Sounding Composite Format from stations stations in the following networks in the Profiling of Winter Storms (PLOWS) domain:

• National Center for Atmospheric Research (NCAR) Earth Observing Laboratory (EOL) Mobile Integrated Sounding System (MISS) GPS Advanced Upper-Air Sounding System (GAUS) Rawinsonde Data (2008-2009 field season),
• NCAR/EOL MISS GAUS Rawinsonde Data (2009-2010 field season),
• National Weather Service (NWS) Rawinsonde Data (2008-2009 and 2009-2010 field seasons),
• University of Missouri Rawinsonde Data (2008-2009 and 2009-2010 field seasons)
• NCAR/EOL C-130 Dropsonde Data (2009-2010 field season)

Data for the PLOWS domain (37°N to 46°N latitude and 88°W to 99°W are contained within this dataset and during the 2009-2010 field season soundings from additional NWS stations outside of this region are included during specific PLOWS IOPs. The dataset covers the time period 1 February 2009 through 31 March 2009 and 1 November 2009 through 11 March 2010. This PLOWS 5-mb Resolution Upper-Air Sounding Composite Dataset contains 979 soundings from 3 platforms and 2432 soundings from 4 platforms during 1 November 2009 through 11 March 2010. Version 2 of this data set was released in February 2017. See Section 3.3 for details on the changes.

Complete information on the PLOWS IOPs are available from the PLOWS field catalog: http://catalog.eol.ucar.edu/plows_09-10/missions/missions.html

Section 2.1 contains a detailed description of the format of the composite dataset. See Section 3.0 below for the quality control processing performed by NCAR/EOL on this dataset. Section 4.0 contains references.

2.0 Detailed Data Description

The `native' resolution data for every sounding were interpolated to 5 hPa vertical resolution files. The surface data point was kept as the initial level in each sounding. The first interpolated data point was at the next lowest pressure evenly divisible by 5 and then every 5 hPa pressure level beyond that point to either 50 hPa or the lowest pressure level reached by the radiosonde, whichever came first. The first 15 lines of each file (the header information) were kept without change.

For the interpolation, the software searched for two data points around the desired pressure level. The search was conducted by looking for two valid (i.e. non-missing) data points around the desired pressure level, while also paying attention to the time difference between the two data points as well as their quality control flags. There was a search for the two best possible data points to use in the interpolation. If the desired pressure level was within the original dataset, that data point was used without interpolation.

There was first a search for values flagged as good within some time range (50 sec for temperature, humidity, and wind and 100 sec for pressure; hereafter termed the ARANGE) and the interpolated data point was flagged as good. Failing that, it searched for values flagged as estimated within the same time range and the interpolated data point was flagged as estimated. Then the search went for good values within a wider time range (100 sec for temperature, humidity, and wind and 200 sec for pressure; hereafter termed the BRANGE) the flag for the interpolated data point here was then degraded (even though two `good' data points were used there was a significant time difference between them) to questionable. Then, in turn, estimated values within the BRANGE were used (flag set to questionable), questionable values within the BRANGE (flag set to bad), good values greater than the BRANGE apart (flag set to bad), estimated values greater than BRANGE apart (flag set to bad), questionable values greater than BRANGE apart (flag set to bad), finally any bad values (flag set to bad). This search was conducted separately for each interpolated variable (pressure, temperature, relative humidity, and the u and v wind components.

Thus for each interpolated data point, the quality control flag was set to the worst case among the data points used in the interpolation, except, for each time range apart, the quality control flag was degraded one level (i.e. good to questionable, etc).

The quality control flags should be carefully heeded in these files. While some of the data may look good, it may have been interpolated over large pressure intervals, and thus be suspect.

For each interpolated data point the dew point was calculated from the temperature and relative humidity (Bolton 1980) and the total wind speed and direction were calculated from the interpolated u and v component values. Also, the altitude and time were interpolated using the same data points used for the pressure interpolation. The ascension rate was recalculated based on the time and altitude values from the two data points used to interpolate the 5 hPa data point. Thus the ascension rate values do not reflect the values based on the interpolated data. The latitude and longitude values were interpolated using the same data points used in the wind component interpolation.

2.1 Detailed Format Description

All upper air soundings were converted to National Center for Atmospheric Research/Earth Observing Laboratory (NCAR/EOL) Sounding Composite Format (ESCF). ESCF 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:

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 nonstandard 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 nonstandard header lines.

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:

Fields 16 through 21 contain the Quality Control information derived at the NCAR Earth Observing Laboratory (NCAR/EOL). Any QC information from the original sounding is replaced by the following EOL Sounding Composite Format codes:

Sample Data

The following is a sample record of a PLOWS 5-mb rawinsonde data in EOL Sounding Composite 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:                         Univ. of Missouri Soundings/IMET1 AB/Ascending
Project ID:                        PLOWS_2008-2009
Release Site Type/Site ID:         UMO
Release Location (lon,lat,alt):    088 10.00'W, 41 30.00'N, -88.167, 41.500, 179.2
UTC Release Time (y,m,d,h,m,s):    2009, 02, 11, 12:20:28
Radiosonde Serial Number:          S7074
Radiosonde Manufacturer:           IMET1 AB
Cloud Code:                        8767/
/
/
/
Nominal Release Time (y,m,d,h,m,s):2009, 02, 11, 12:20:28
 Time  Press  Temp  Dewpt  RH    Ucmp   Vcmp   spd   dir   Wcmp     Lon     Lat   Ele   Azi    Alt    Qp   Qt   Qrh  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  978.9  10.0   8.6  91.0   -0.7   -1.9   2.1  20.0 999.0  -88.167  41.500 999.0 999.0   179.2  1.0  1.0  1.0  1.0  1.0  9.0
  11.6  975.0  10.5  10.5 100.0   -6.3   -3.5   7.2  60.7   5.3 9999.000 999.000 999.0 999.0   212.5  1.0  1.0  1.0  1.0  1.0 99.0
  19.7  970.0  10.4  10.4 100.0   -8.5   -4.6   9.7  61.8   5.3 9999.000 999.000 999.0 999.0   255.4  1.0  1.0  1.0  1.0  1.0 99.0
  27.6  965.0  10.4  10.4 100.0  -10.1   -5.1  11.3  63.5   5.4 9999.000 999.000 999.0 999.0   298.5  1.0  1.0  1.0  1.0  1.0 99.0

2.2 Station List

The NSF/NCAR C-130 dropsondes were deployed only for the 2009-2010 field season and are available during IOP-6, 8, 10, 11 and 18.

The NCAR/EOL MISS radiosondes are available during IOP-3, 4, 7-10, 14-15, 17-19, 21, and 23-24.

The University of Missouri radiosondes are available during IOP-1, 2, 5, 7-10, 13-14 and 21.

The NWS stations outside of the core PLOWS domain are only included for specific IOP time periods:

13-15 December 2009 (IOP-11) - International Falls, MN (INL).

17-19 December 2009 (IOP-12) and 16 -17 January 2010 (IOP-13) - Birmingham, AL (BMX) and Nashville, TN (BNA).

28-30 January 2010 (IOP-15) - Little Rock, AR (LZK)

3-6 February 2010 (IOP-17) - Shreveport, LA (SHV), Jackson, MS (JAN) and Little Rock, AR (LZK)

26-27 February 2010 (IOP-22) - Little Rock, AR (LZK), Norman, OK (OUN), Dallas, TX (FWD) and Shreveport, LA (SHV)

1-3 March 2010 (IOP-23) - Norman, OK (OUN), Little Rock, AR (LZK), Dallas, TX (FWD), Charleston, SC (CHS), Peachtree City, AL (FFC)

8-9 March 2010 (IOP-24) - North Platte, NE (LBF), Rapid City, SD (UNR)

Complete information on the PLOWS IOPs are available from the PLOWS field catalog: http://catalog.eol.ucar.edu/plows_09-10/missions/missions.html

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 EOL can be found in Loehrer et al. (1996) and Loehrer et al. (1998).

3.1 Gross Limit Checks

These checks were conducted on each high resolution sounding and data were automatically flagged as appropriate. Only the data point under examination was flagged. EOL conducted the following gross limit checks on the PLOWS sounding datasets. In the table P = pressure, T = temperature, RH = relative humidity, U = U wind component, V = V wind component, B = bad, and Q = questionable.

3.2 Vertical Consistency Checks

These checks were conducted on each high resolution sounding and data were automatically flagged as appropriate. These checks were started at the lowest level of the sounding and compared neighboring 2-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.

3.3 Data Quality Issues

Version 2.0 of this data set was released in Febraury 2017. In this version a dry bias in the RD94 relative humidity measurements was corrected. The dry bias was strongly temperature dependent, being considered quite small at warm temperature and more substantial at cold temperatures. More complete information on the origin, magnitude, and impact of the bias is available in an NCAR Technical Note (Voemel, et al 2016):
http://dx.doi.org/10.5065/D6XS5SGX

Complete information on the processing and data quality of each network can be found in their respective documentation files:

University of Missouri (both field seasons)

NCAR/EOL MISS (2008-2009 field season)

NCAR/EOL MISS (2009-2010 field season)

National Weather Service (both field seasons)

NCAR/EOL C-130 Dropsondes (2009-2010 field season)

4.0 References

Bolton, D., 1980: The Computation of Equivalent Potential Temperature. Mon. Wea. Rev., 108, 171-180.

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.

NCAR/EOL, cited 2006: GPS Dropsonde [Available online from http://www.atd.ucar.edu/rtf/facilities/dropsonde].

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.