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.