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Notes and Problems


Since each original database was in a different format, some adjustments and changes were required to make all soundings consistent. A number of problems were also noted during processing and as a result of manual spot checks. These are summarized below. Users encountering additional problems are urged to contact the authors of this document. All soundings subsequent to 1987 were obtained from NCAR tapes, which are in the ID=1 format.

Through a processing oversight on the part of M. Serreze, the pressure quality codes (QP) are missing in Volumes 1 through 4 and set to '9'. This problem has been corrected in Volume 5. Soundings in earlier volumes also appear to have some remaining problems related to the sort/merge routines. Again, these have been corrected in Volume 5.

ID=1: (Asian Arctic for 1976-1987; All stations for 1988, Onward)

  1. Winds were originally in knots and were changed to meters per second.
  2. Longitudes were originally reported 0 to 360 degrees clockwise from the Greenwich Meridian. They were converted to 0 to 360 degrees counterclockwise as viewed from the North Pole.
  3. If categories 2, 3, and 4 were missing (the data categories for soundings of type ID=1 were discussed in Section 3a above), the surface report was padded with missing values.
  4. The geopotential height of the surface level is not given in categories 2 to 4. The value has been set equal to the station elevation. However, reported station elevations do not always match those listed by WMO.
  5. Geopotential heights are usually available only for mandatory levels.
  6. If the indicated surface pressure is < 930 mb, the surface report is assumed to be missing.
  7. As noted previously, the requirement to merge duplicate levels means that any quality codes referring to agreement/disagreement between duplicate levels reported in different categories should be ignored.

ID=2: (Victor Starr, 1958-63)

Of all the original data, the Victor Starr soundings contained the most frequent errors. As such, we tried to use soundings from other sources whenever possible (i.e., during periods of overlap).

  1. Occasional surface reports with a value of 1000 mb should be present in any large sounding archive. Very few are noted in the original data, however. It is suspected that, at some point in time, 1000 mb surface reports were lost due to a processing error.
  2. Numerous reported surface pressures from 950 to 960 mb were encountered. In most cases, these must be errors. While such levels will often be flagged as errors on the basis of the geopotential height limits check, many were observed to pass this check.
  3. Temperature values were frequently flagged by the limits check algorithm. Surface temperature values in these situations were sometimes above 20 degrees C, with suspiciously high values throughout the profiles.
  4. Winds were originally reported in U and V components. They were converted to speed (meters per second) and direction (0-360 degrees).
  5. At times, the highest reported level had a geopotential height of 0 m. Temperatures also appear bogus in these cases. These are flagged as errors. The problem seems to only occur when 27 levels (the maximum possible) are reported. This appears to be a problem with the original data, and may have resulted from a bad array size.
  6. Errors are particularly common at 1200 GMT. The presence of a systematic error in the original processing is suspected. These soundings should be viewed with caution.

ID=3: (Canadian)

  1. The geopotential height of the surface report and the station elevation were supplied in the original sounding. Situations were frequently encountered in which the geopotential height at the surface was lower than the station elevation. Also observed were cases in which the surface geopotential height was greater than the station elevation.
  2. Surface pressure reports are sometimes shown as higher than the adjacent level by approximately 0.1 mb. (Only with ID=3 data are surface pressures commonly given to nearest 0.1 mb.) However, the adjacent level shows geopotential height lower by 1 to 2 m.
  3. In the original tapes, the five-digit code for the Canadian stations had a '2' or '4' as the second byte (variable STATION in the header record). The second byte was changed to '1' to match WMO codes.
  4. Wind speed was originally in knots, and was converted to meters per second.

ID=4: (Alaska and Thule, Greenland)

  1. As discussed earlier, these soundings have two additional quality codes LTYPE (type of level, e.g., significant, mandatory, surface, etc.) and LQUAL (overall quality code for each level). LQUAL should not be confused with LEVCK, which is the overall quality code for the level based on our limits check used through 1987.
  2. Wind speed was originally in knots, and was converted to meters per second.
  3. Original moisture data were reported as relative humidity, and were converted to dewpoint depression.
  4. In some early soundings, a 1000-mb level is reported as a mandatory level even when the surface pressure is < 1000 mb.

ID=5: (Soviet, 1962-75)

  1. If categories 2, 3, or 4 were missing (the data categories for soundings of type ID=5 are discussed in Section 3a above), the surface report was padded with missing values.
  2. If categories 2, 3, or 4 were available, but indicated surface pressure was < 930 mb, the surface report was assumed to be missing, and was padded with missing values.
  3. As for ID=4, longitude values were converted to 0 to 360 degrees counterclockwise as viewed from the pole.
  4. Wind speed was originally in knots, and was converted to meters per second.
  5. Station elevation was not included in the sounding reports until 12/16/63. All station elevations were set to missing for years before 1964.