TELEX 2004 Quality Controlled MCASS Data Set Contents: I. Contacts II. System/Data Set Overview III. File Naming Conventions IV. Data Records V. Data File Specifics VI. Tail Information VII. Data Quality Control I. Contacts: Dean Lauritsen lauritsn@ucar.edu Junhong Wang junhong@ucar.edu Kate Young kbeierle@ucar.edu Mailing Address: NCAR/Atmospheric Technology Division P.O. Box 3000 1850 Table Mesa Drive Boulder, CO 80307; USA **Additional summary and processing notes have been provided to users in the TELEX 2004 (MCASS) Reprocessing Notes.txt and TELEX_2004_Sonde_Tracking.xls documents provided with the data set. II. System/Data Set Overview The Mulit-Channel Atmospheric Sounding System (MCASS) is an AVAPS dropsonde system adapted for balloon launches. The AVAPS system, and thus MCASS, are unique in that they have the capability to fly up to four sondes simultaneously. MCASS is a mobile system that uses NCAR GPS dropsondes to collect dual atmospheric profiles, both ascending and descending. The sondes are launched from the ground attached to a balloon. After the balloon bursts a parachute is deployed helping to ensure a slow decent. During TELEX 2004, 37 dropsondes were launched from various locations around Oklahoma between May 13 and June 29, 2004. III. File Naming Conventions The data files are one-half-second files with appropriate corrections and and quality control measures applied. The naming convention for these files is the same - "D", followed by "yyyymmdd_hhmmss_Rzp.#.QC" where yyyy = year, mm = month, hh = hour of the day GMT, mm = minute of the hour, ss = seconds, # is the channel number, between one and four , and ".'QC" refers to it being quality controlled. IV. Data Records The data records each contain sonde ID, GMT date and time, pressure, temperature, relative humidity, wind speed and direction, vertical velocity, balloon position, and both geopotential and GPS altitude. Field Parameter Units Missing Value No. ------------------------------------------------------------------------------------------ 1 System Type ------ ------ 2 Data flags* ------ ------ 3 Sonde ID ------ ------ 3 GMT Date yymmdd ------ 4 GMT Time hhmmss.ss ------ 5 Pressure Millibars 99999.00 6 Dry-bulb Temp Degrees C 999.00 7 Relative Humidity Percent 999.00 8 Wind Direction Degrees 999.00 9 Wind Speed Meters/Second 999.00 10 Vertical Velocity Meters/Second 999.0 11 Longitude Degrees 999.000000 12 Latitude Degrees 99.000000 13 Geopoten Alt Meters 99999.00 14 GPS Wnd Sat ------ ------ 15 Sonde RH1 Percent 999.00 16 Sonde RH2 Percent 999.00 17 GPS Snd Sat ------ ------ 18 Wind Error Meter/Second 99.00 15 GPS Altitude Meters 99999.00 The MCASS data flags indicate the integrity of the recieved telemetry signal from the sonde but say nothing about the accuracy or quality of any sensor measurement. The data flags only tell us whetehr the measuremetns made by the sonde were corrupted during the data trasmission to the recieving station. *Data is flagged as follows: S00 - neither PTU nor Wind data have telemetry bit errors. S10 - one or more PTU bit errors; no Wind data bit errors. S01 - no PTU data bit errors; one or more Wind data bit errors. S11 - Both PTU and Wind data have telemetry bit errors. IV. Data File Specifics The files contain data calculated at half-second intervals . The variables pressure, temperature, and relative humidity are calibrated values from measurements made by the sonde. The vertical velocity is a direct GPS measurement. The position (lat, lon) also come directly from the GPS. All wind data are computed from GPS navigation signals received from the sonde. The raw wind values are calculatd at a one second data rate by a commercial processing card. II. Tail Information The tail records contain a variety of information which may include such things as data type, project name, launch time, launch observations, operator comments and other specialized information. The launch location is given as : lon (dec. deg), lat (dec deg), alt (m), (lon (deg min), lat (deg min)) 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 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. V. Data Quality Control Typical QC of radiosonde data begins with running the soundings through ATD's Atmospheric Sounding Profiling ENvironment (ASPEN) which analyzes the data, performs smoothing, and removes suspect data points. This was not the case with the soundings launched during TELEX 2004 for two reasons. ASPEN is unable to process soundings that have both ascending and descending data. This obstacle could have been easily overcome by separating each flight in two separate files, however the higher precision (six decimal places) GPS latitude and longitude found in the raw soundings was favorable to that which is output by ASPEN (two decimal places). It was also believed that the quality of the raw PTU and wind data was high enough that the soundings could be released with minimal QC. The quality control flags mentioned in section IV indicate whether PTU and/or wind data are reasonable. In the data files, the flagged wind data were previously set to missing values, but this was not the case for the flagged PTU data. The first step in the QC process was to change the flagged (both S10 and S11) PTU data to missing values. The remaining data were used to create profiles of both temperature and relative humidity versus pressure, and wind speed versus pressure which were visually evaluated for outliers and any other problems. Each profile contained both the ascending and descending data from each flight. Obvious outliers were changed to missing values, and data collected while the sondes sat on the ground, prior to launch, were removed because while the pressure remained constant the temperature and wind measurements did not. Users may notice low frequency oscillations in the ascending data for both the wind speed and wind direction measurements which are a result of the fact that no corrections were applied to account for sonde pendulum motion beneath the balloon. The corrections that were applied were documented in the telex04.errorlog file provided with the data set.