Contents: I. File Naming Conventions II. Header Information III. Data Records IV. Data File Specifics V. Data Quality Control VI. Important Note to Users VII. Contacts I. File Naming Conventions The "QC CLASS" files are typically one-second data files with appropriate corrections and and quality control measures applied. The naming convention for most of these files is the same - "D", followed by "yyyymmddhhmmQC.cls" where yyyy = year, mm = month, hh = hour of the day GMT, mm = minute of the hour, and "QC.cls" refers to the quality controlled NCAR CLASS format. II. Header Information The header records contain data type, project ID, site ID, site location, actual release time, nominal release time, and possibly other specialized information. The first five header lines contain information identifying the sounding, and have rigidly defined form. The following 6 header lines contain auxiliary information and commments about the sounding, and they can vary from data set to data set. 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) signifying the end of the header. The six standard header lines are as follows: Line Label (fixed to 35 chars in length) Contents 1. Data Type: Description of type and resolution of data. 2. Project ID: ID of weather project. 3. Launch Site Type/Site ID: Description of launch site. 4. Launch Location (lon,lat,alt): Position of launch 5. GMT Launch: 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 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 six non-standard header lines may contain any label and contents. The label is fixed to 35 characters to match the standard header lines. III. 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. Field Parameter Units Missing Value No. ------------------------------------------------------------------------------------------ 1 Time Seconds 9999.0 2 Pressure Millibars 9999.0 3 Dry-bulb Temp Degrees C 999.0 4 Dew Point Temp Degrees C 999.0 5 Relative Humidity Percent 999.0 6 U Wind Component Meters/Second 999.0 7 V Wind Component Meters/Second 999.0 8 Wind Speed Meters/Second 999.0 9 Wind Direction Degrees 999.0 10 Ascension Rate Meters/Second 999.0 11 Longitude Degrees 999.0 12 Latitude Degrees 999.0 13 Range Kilometers 999.0 14 Angle Degrees 999.0 15 Altitude Meters 99999.0 16 QC flag for Pressure 99.0 17 QC flag for Temp 99.0 18 QC flag for Humidity 99.0 19 QC flag for U Component 99.0 20 QC flag for V Component 99.0 21 QC flag for Horizontal Wind 99.0 IV. Data File Specifics The files contain data calculated at one-second intervals . The variables pressure, temperature, and relative humidity are calibrated values from measurements made by the sonde. The dew point is calculated from the relative humidity. The altitude value is calculated from the hydostatic equation using pressure, temperature, and dew point. The rate of ascent is obtained from the altitude difference between two successive time steps. The position (lat, lon), angle and range come from the GPS and altitude data. This data is interpolated to one second in order to match the wind data. All wind data are computed from GPS navigation signals received from the sonde. The raw wind values are calculatd at a one half second data rate by a commercial processing card. These raw values are subjected to a digital filter to remove low frequency oscillations due to the sonde pendulum motion beneath the balloon. The resolution of the data is reduced to one second. This time record is used in the interpolation of the pressure, temperature, and humidity data. V. Data Quality Control The raw soundings are first run through the Atmospheric Sounding Processing ENvironment (ASPEN), which analyzes the data, performs smoothing, and removes suspect data points. The soundings are then visually evaluated for outliers, or any other obvious problems. Scatter plots of the data are then created to check for discrepencies between PTU data collected from the surface met station and data from the radiosonde. Lastly, we create profiles of temperature, RH, and dewpoint (one plot per flight) in order to check any major inconsistencies found. VI. Important Note to Users. While visually analyzing the skew-t diagrams from the CR1 (Costa Rica mobile 1) system it became apparent that there were problems near the surface. The data collected from the surface met temperature and humidity sensors are much warmer (mean diff=3.1 degC) and drier (mean RH diff = 9.19%) than the pre-launch data collected from the radiosondes. We attribute these errors to a couple of factors. First, a hand held device was bought from a local store to make surface pressure, temperature, and humidity measurements (rather than the surface met sensors typically used by ATD). Secondly, the sondes were launched by non-ATD staff. Thirdly, it is unknown how they made the surface measurements, i.e. under direct sunlight, under shaded area or right above heated surfaces. Those conditions could have affected the measurements. We believe improper handling of the surface instrument was most likely the cause because we did not see the same errors from the CR2 surface instrument that was operated by ATD staff, who did not expose the surface sensor direct heat. We recommend that the users do not use the surface met temperature, RH, and dewpoint measurements from the first line in the data file for all CR1 soundings. We suggest that users use the prelaunch data collected by the radiosonde sensor (second line in the data at 0 second) as the surface value. In addition, for 9 of the 73 radiosondes launched by the mobile 1 (CR1), we suspect that the operators failed to push the sonde launch button which prompts the system to begin recording data. This error resulted in a loss of data between the surface and approximately ~750-800 mb. The files affected are: D200303020704QC.cls D200303100918QC.cls D200303181151QC.cls D200303181752QC.cls D200303191222QC.cls D200303080913QC.cls D200303180851QC.cls D200303181451QC.cls D200303191158QC.cls VII. Contacts: Junhong Wang junhong@ucar.edu Kate Beierle kbeierle@ucar.edu Tim Lim tdlim@ucar.edu Mailing Address: NCAR/Atmospheric Technology Division P.O Box 3000 1850 Table Mesa Drive Boulder, CO 80307; USA