Handbook Number 3. In some cases. there may be more
than one tropopause. one below the 100-hPa level and
the other above the 100-hPa level. In this case. both
Parts A and C may report tropopause data.
Following the mandatory level data. three groups,
88PPP, TTTaDD, and ddfff, contain information very
similar to the mandatory level information that pertains
to the tropopause level. If the sounding did not locate a
tropopause, the group 88999 is used in place of the data
groups.
INDICATOR AND PRESSURE LEVEL.—The
88 is the indicator that tropopause data follows. The
PPP is the pressure level. to the nearest hectopascal, at
which the tropopause is located.
T E M P E R A T U R E A N D D E W - P O I N T
DEPRESSION.—The TTTaDD is the temperature
and dew-point depression. encoded in the same manner
as the mandatory level data.
Q48.
Q49.
Q50.
Q51.
Q52.
Q53.
Q54.
Q55.
WINDS.—The wind direction and speed. ddfff,
are encoded in the same manner as the mandatory
levels.
Maximum Wind
In table 1-8. section 4 contains information on
maximum winds. Information on the highest winds
observed between the 500-hPa level and the 100-hPa
level, in excess of 60 knots. is contained in the
Maximum Wind data group. Maximum winds located
above the 100-hPa level are reported in an identical
section in message Part C. Maximum wind data is
reported in two or three groups. In the first group, 77 is
the indicator for maximum wind. followed by PPP, the
pressure level of the maximum wind to the nearest
hectopascal. The second group. ddfff, contains the
wind direction and speed. as preciously described. The
third group. 4vbvbvava, is optional. and is used to report
the absolute value of the vertical wind shear. The vbvb
reports the vertical wind shear difference between the
level of maximum wind and the winds 3.000 feet below
the level of maximum wind, while the vava reports the
vector difference between the level of maximum winds
and the winds 3.000 feet above the level of maximum
wind. The vertical wind shear values are important
indicators for clear air turbulence (CAT). The
procedure to calculate vertical wind shear is discussed
in the FMH-3.
When no winds in excess of 60 knots are observed
between the 500-hPa level and the 100-hPa level. the
group 77999 is reported. If two winds with identical
wind speeds satisfy the criteria for a maximum wind,
the levels will be encoded successively, beginning with
the lowest altitude.
REVIEW QUESTIONS
How would the position of a ship located at
27.0N 152.0W be encoded?
What information is contained in Part A of the
TEMP code?
Given the following:
"85397
02659
24035."
What is the altitude of this level?
When is 50 added to the dew-point depression?
How are mandatory pressure level winds
reported?
How should the following information "70910
09163 33514" in Part A of a TEMP message be
decoded?
What is the indicator for tropopause data in Part
A?
How should the following information "77220
07602 40508" in Part A of a TEMP message be
decoded?
PART B - LOWER SIGNIFICANT LEVELS
The second part. Part B of the TEMP coded
messages (see table 1-9), contains data on levels that are
considered significant because of changes noted in the
temperature. humidity, or wind data. Although the
significant levels are selected by, the MRS, you must
verify the selection of significant levels. When the
MRS processor selects levels, it first considers the
mandator) significant level criteria. followed by the
"supplemental" significant level criteria. Then, the
MRS automatically encodes Part B. Remember
however, some stations do not report significant wind
levels.
Selection of Significant Levels
Proper evaluation of an upper-air sounding requires
that the operator select significant levels when a
sounding is conducted using manual equipment. The
Mini Rawinsonde System automatically searches for
and encodes significant levels. MRS operators must
review and verify the computer-selected levels. In
general. significant levels are selected with respect to
temperature. humidity, and wind changes.
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