SALLJEX: Upper Air Santa Cruz Sounding Data (NCAR/ATD)
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 data 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 "yyyymmddhhmm.cls" where yyyy = year, mm = month,
hh = hour of the day GMT, mm = minute of the hour, and ".cls" refers to the 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. Release Site Type/Site ID: Description of launch site.
4. Release Location (lon,lat,alt): Position of launch
5. UTC Release Time: 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 9999.0
7 V Wind Component Meters/Second 9999.0
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. Histograms of the data are created
to check the range, and number of occurances, in values of pressure, temp, RH,
wind speed and direction, and are derived from data at all levels for all soundings.
Lastly, we created profiles and scatter plots of temperature and RH,
in order to check for any major inconsistencies.
VI. Important Note to Users.
While visually analyzing the skew-t diagrams it became apparent that there were problems
near the surface. It seems that the surface met relative humidity sensor
recorded measurements more moist than those recorded from the radiosonde. The mean
RH(sonde-sfc) was -5.35%, with differences as great as -35%. From talking with
one of the operators who was at the project, we learned that rather than transporting
surface sensors from NCAR to the site, the investigators chose to use sensors
already located at the site. It is our belief that this sensors
accuracy is questionable, and therefore neither the humidity (RH or dewpoint) nor the
temperature data at the surface collected by the surface sensors (first line in the data
at -1 second) should be used. We suggest the user use the prelaunch data collected by the
radiosonde sensor (second line in the data at 0 second) as the surface value.
VII. Contacts:
Kate Beierle
kbeierle@ucar.edu
Tim Lim
tdlim@ucar.edu
Junhong Wang
junhong@ucar.edu
Mailing Address: NCAR/Atmospheric Technology Division
P.O Box 3000
1850 Table Mesa Drive
Boulder, CO 80307; USA
Phone: (303)-497-8743
Fax: (303)-497-8770