|
|
 |
|
|
|
Radiosondes were launched at synoptic times and the data were forwarded to the US Weather service, so that the data were incorporated in the operational forecasts as well as the gridded data archives.
Radiosonde Wind Vectors: In all plots winds speeds are in m/s. The horizontal wind vectors are plotted with arrows the whose length is proportional to the wind speed. The length of a standard wind vector of 20 m/s is shown at the bottom of each plot. Arrows pointing down indicate wind from the north, Arrows pointing right indicate wind from the west.
The following text is from the UCAR/JOSS CD-data archive
Title: Discoverer ISS High Vertical Res. Balloon Data
Contact:
Bob Rilling
NCAR RDP
PO Box 3000
Boulder, CO 80307-3000
USA
E-Mail Address: rilling@ucar.edu
Or
E. R. Miller
NCAR RDP
PO Box 3000
Boulder, CO 80307-3000
USA
E-Mail Address: millere@ucar.edu
Data Set Description:
During ACE-1 soundings were taken from the NCAR/ATD/SSSF
ISS site on the R/V Discoverer during ACE-1.
For each original sounding taken there were three files created,
the "m" file, the "x" file, and the "i" file.
The "m" file is the raw thermodynamic data file containing
radiosonde thermodynamic data obtained approximately
every 1.5 seconds.
The "x" file is the ten second data file containing thermodynamic,
wind, and position data. NOTE: With the new reprocessing scheme
we have recently implemented, the "x" file pressure, temperature,
and relative humidity (PTU) data are currently nearly as
good as the heretofore final product, the "i" file, PTU data.
However, the wind data in this product are NOT finalized.
All calculated wind data are included accompanied by a quality
flag.
The "i" file, the 5mb interpolated data file, is the final
processed data file generated from the ten second data file.
Quality control constraints are applied in the creation of
this file and it is considered the final product.
These original files were named "m", "x", or "i" followed by:
"mddhhmm.sit"
where: m = month (1-9,a,b,c for Jan -> Dec),
dd = day of month,
hh = hour of day GMT,
mm = minute of hour,
and ".sit" refers to the site.
The ACE-1 CD-ROM contains only "x" files that were processed
by the UCAR/Joint Office for Science Support (UCAR/JOSS).
JOSS processed the original "x" files into the JOSS CLASS format and then
quality controlled the JOSS CLASS formatted data. The JOSS CLASS form of the
data is available on JOSS' web based data delivery system named CODIAC
and on this ACE-1 CD-ROM. The "m", "i", and the original "x" files
are available only upon request from Bob Rilling.
For detailed information on the general sounding processing performed
by Bob Rilling and NCAR/RDP, refer to the information on the "Web" site
given below. At that web site, there is a document online with a chapter
on sounding data processing:
"SSSF Observing Facilities: Description and Specification Version 1"
The URL is:
http://www.atd.ucar.edu/sssf/facilities/sssf_facility_descrip/sssf.html
Chapter 6.0 on that web site deals with sounding data processing. This will
give you an idea of what is done in Bob Rilling's processing and details of
the different files produced. However, please note that a new automated
PTU data outlier removal scheme has been implemented in reprocessing but that
scheme may not be discussed in the documentation online. That will be updated
in the near future.
For now, some brief IMPORTANT information regarding the processing
done by Bob Rilling NCAR/RDP:
Ten-second data file ("x" file):
- A newly implemented PTU data outlier removal scheme has greatly
improved the ten-second data file PTU data quality.
- The first point is surface data point (independent of sonde data,
it does not affect or influence sonde data in normal processing).
- Each ten-second PTU point is obtained from smoothing the raw
sonde thermodynamic data over a ten-second interval centered on that
ten-second point. (e.g. the point at 10 seconds is obtained from
data obtained between 5 and 15 seconds). THE SURFACE POINT DOES
NOT influence the first ten-second data point (PTU) in normal data
processing.
The surface thermodynamic data and sonde thermodynamic data are
completely independent, neither is influenced or altered by the other
in normal processing.
(NOTE: The surface point DOES influence the subsequent 10 second
PTU data when the low-level humidity correction is applied. That
surface value is required for the correction. Also note that when the
correction is applied, the corrected values converge to the old
uncorrected values within the first minute of the sounding.)
- The wind data in the ten-second data file are NOT considered the final
wind data. All wind data appear in this file as does a wind data
quality flag (see online documentation for details). Note that wind
data through the first 120 seconds are obtained by interpolation between
the surface wind and the first OMEGA wind (obtained from a 240 second
smoothing interval).
SPECIFICS WITH REGARD TO ACE-1
------------------------------
1) Reprocessing and Low Level Temperature and RH Correction:
Briefly:
Many of the soundings have been corrected for low-level humidity
sensor errors. These errors were due to sonde sensor arm heating
that was a result of the pre-launch environment. This occurred in
both the Cape Grim and NOAA Discoverer soundings.
The first line of the header in all re-processed files indicates
if that sounding had this low-level humidity correction applied or
not.
Sonde Sensor Arm Heating:
In sonde sensor arm heating, the sensor arm itself heats up
resulting in too high a temperature reading and too low a rela-
tive humidity reading.
The humidity reading is low due to the way in which the sensor
works. The humicap sensor gives a reading of humidity relative
to the temperature of the sensor arm itself. If the sensor arm
is warmer than the environment, that humidity reading will be
lower than ambient as the ambient vapor pressure remains unchanged,
but the saturation vapor pressure (based on the temperature of
the sensor arm) is higher than ambient.
At launch, the sonde is ventilated by the rising balloon. The
temperature sensor is mounted in a very thin cylinder at the
end of the radiosonde sensor arm. The thermal time constant of
this cylinder is such that the temperature data recovers completely
within the first ten seconds of ascent. The humidity sensor is
mounted on a flat plate which has a slower thermal time constant.
(The thermal time constant of the flat plate was determined to be
nearly 14 seconds at 3.0 m/s ventilation in wind tunnel tests.
NOTE: this is NOT the relative humidity sensor time constant.)
Thus, it takes from up to 60 seconds for the humidity sensor to
come to equilibrium with the environment.
A correction has been developed for the sensor arm heating.
That correction uses the SURFACE DATA and determined thermal
characteristics of the sensor arm to correct the data over
the first portion of the sounding.
The details of the correction can be obtained in Cole and Miller, 1995.
2) NOTE: There was no reliable surface humidity data available for the
soundings taken on the "Southern Surveyor". The processed
soundings from the "Southern Surveyor" used sonde RH data prior to
launch as the surface relative humidity data point for the sounding.
3) OMEGA WINDS: There is one major inherent problem with OMEGA winds
that is clearly present in the ACE soundings. That problem is one of
"modular" interference (beyond the scope of this presentation). The
result of this is an oscillation in the wind data with height. This
oscillation in apparent in several, but not all soundings and is
purportedly dependent on station geometry.
Steps WERE taken to reduce this effect - 1) an elevated signal to noise
cut off threshold and 2) elimination of a station from the solution
if it is too close to the sounding site.
These steps obviously did not completely mitigate the situation and
the investigator should be aware of this when dealing with the data.
Format: JOSS CLASS
All upper air soundings ("x" files) were originally converted to University
Corporation for Atmospheric Research/Joint Office for Science Support
(UCAR/JOSS) Cross Chain LORAN Atmospheric Sounding System (CLASS)
Format (JCF). JCF 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:
Line Label (padded to 35 char) 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 site,
in format described below.
5 GMT Launch Time (y,m,d,h,m,s): 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
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 non-standard header lines may contain any label and
contents. The label is padded to 35 characters to match the standard
header lines.
Data Records
The data records each contain 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 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:
Field Format
No. Width Parameter Units Missing Value
--- ----- --------- ----- -------------
1 6 F6.1 Time Seconds 9999.0
2 6 F6.1 Pressure Millibars 9999.0
3 5 F5.1 Dry-bulb Temperature Degrees C 999.0
4 5 F5.1 Dew Point Temperature Degrees C 999.0
5 5 F5.1 Relative Humidity Percent 999.0
6 6 F6.1 U Wind Component Meters / Second 9999.0
7 6 F6.1 V Wind Component Meters / Second 9999.0
8 5 F5.1 Wind Speed Meters / Second 999.0
9 5 F5.1 Wind Direction Degrees 999.0
10 5 F5.1 Ascension Rate Meters / Second 999.0
11 8 F8.3 Longitude Degrees 999.0
12 7 F7.3 Latitude Degrees 999.0
13 5 F5.1 Range Kilometers 999.0
14 5 F5.1 Azimuth Degrees 999.0
15 7 F7.1 Altitude Meters 99999.0
16 4 F4.1 QC for Pressure Code (see below) 99.0
17 4 F4.1 QC for Temperature Code (see below) 99.0
18 4 F4.1 QC for Humidity Code (see below) 99.0
19 4 F4.1 QC for U Component Code (see below) 99.0
20 4 F4.1 QC for V Component Code (see below) 99.0
21 4 F4.1 QC for Ascension Rate Code (see below) 99.0
Fields 16 through 21 contain the Quality Control information
derived at the UCAR Joint Office for Science Support (UCAR/JOSS).
Any QC information from the original sounding is replaced by the
following JOSS codes:
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")
Data Remarks:
Conversion to JOSS CLASS format (ASCII text)
The files arrived at JOSS in NCAR CLASS format and were converted into
JOSS CLASS format. There was only one primary change: in general JOSS
replaced the NCAR flags with the JOSS unchecked flag. However, in the case
of "88.0" flag (when it occurred in the U and V wind components) in the
NCAR system, JOSS replaced this with the JOSS questionable flag (2.0).
This was done because the NCAR ISS system used a 240 second interval for
its wind computation and thus the first 120 seconds of wind data did not
have a complete 240 second interval for wind computation (Miller 1993).
Quality Control Processing
The final JOSS CLASS dataset underwent a two-stage QC process. First,
the dataset underwent internal consistency checks. This included two types
of checks, gross 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 parameters 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.
Gross Limit Checks
These checks were conducted on each sounding and data were
automatically flagged as appropriate. Only the data point under
examination was flagged. JOSS conducted the following gross limit
checks on the sounding dataset. In the table P = pressure, T =
temperature, RH = relative humidity, U = U wind component, V = V wind
component, B = bad, and Q = questionable.
_______________________________________________________________
Parameter(s) Flag
Parameter Gross Limit Check Flagged Applied
_______________________________________________________________
Pressure < 0 mb or > 1030 mb P B
Altitude < 0 m or > 35000 m P, T, RH Q
Temperature < -80C or > 45C T Q
Dew Point < -99.9C or > 30C RH Q
> Temperature T, RH Q
Relative Humidity < 0% or > 100% RH B
Wind Speed < 0 m/s or > 100 m/s U, V Q
> 150 m/s U, V B
U Wind Component < 0 m/s or > 100 m/s U Q
> 150 m/s U B
V Wind Component < 0 m/s or > 100 m/s V Q
> 150 m/s V B
Wind Direction < 0 deg or > 360 deg U, V B
Ascent Rate < -10 m/s or > 10 m/s P, T, RH Q
_______________________________________________________________
Vertical Consistency Checks
These checks were conducted on each sounding and data were
automatically flagged as appropriate. These checks were started at the
lowest level of the sounding and compared neighboring 10-sec data points
(except at pressures less than 100 mb where 50-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.
____________________________________________________________________
Vertical Consistency Parameter(s) Flag
Parameter Check Flagged Applied
____________________________________________________________________
Time decreasing/equal None None
Altitude decreasing/equal P, T, RH Q
Pressure increasing/equal P, T, RH Q
> 1 mb/s or < -1 mb/s P, T, RH Q
> 2 mb/s or < -2 mb/s P, T, RH B
Temperature < -15 C/km P, T, RH Q
< -30 C/km P, T, RH B
> 5 C/km (not applied
at p , 150mb) P, T, RH Q
< 30 C/km (not applied
at p , 150mb) P, T, RH B
Ascent Rate change of > 3 m/s
or < -3 m/s P Q
change of > 5 m/s
or < -5 m/s P B
_____________________________________________________________________
File Name Conventions:
disMDDHH.dat where M is a single hex digit indicating the month
("a" for October, "b" for November, "c" for December),
and DD is the date, and HH is the hour of the nominal launch time.
An example for 15 November 1995 at 1200 hours is disb1512.dat.
References:
Cole, H. L., and E. R. Miller, 1995: A Correction for Low-Level
Radiosonde Temperature and Relative Humidity Measurements. Proc.,
Ninth Symp. on Meteorological Observations and Instrumentation,
Charlotte, Amer. Meteor. Soc., 32-36.
Miller, E., 1993: Surface and sounding data. TOGA COARE Integrated
Sounding System data report Vol 1. Surface and Sounding Systems Facility,
National Center For Atmospheric Research, 41 pp.
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry