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, TTT_aDD, 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   TTT_aDD   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. 4v_bv_bv_av_a, is optional. and is used to report the absolute value of the vertical wind shear. The v_bv_b 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 v_av_a 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. 1-26