last 101 code group. This allows other units to enter the sounding   into   their   TESS   system   and   recreate   an accurate sounding profile. Q24. Q25. Q26. Q27. Q28. Q29. Q30. Q31. REVIEW  QUESTIONS What  causes  an  upper-air  sounding  to  be automatically terminated by the MRS system? What program in the MRS produces a printout of the significant levels? What  does  the  letter  "U"  indicate  next  to  a significant level on the printout sheet? What  is  the  purpose  of  selecting  significant levels? What  is  the  criteria  for  selecting  a  significant level wind based on direction? Which  activities  in  WMO  Region  IV  do  NOT report fixed regional level winds? What do the "RI" and "MRI" columns indicate on the significant level printout sheet? What is the purpose of the 101 indicator groups? PILOT BALLOON (PIBAL) WIND OBSERVATIONS LEARNING   OBJECTIVES:   Identify   the procedures  and  equipment  used  to  conduct PIBAL  observations. Identify  the  computer software  routinely  used  to  evaluate  PIBAL observation data. Pibal observations during the 1940’s through the 1960’s  were  the  primary  method  used  to  determine atmospheric  winds,  and  the  balloons  were  tracked  as high  as  possible.  Today,  the  primary  application  for Pibal-observed winds is low-level wind measurements for  tactical  fixed  and  rotary-wing  aircraft  operations, and  para-drop  operations.  Although  most  naval  units have  little  need  to  conduct  Pibal  observations,  U.S. Marine  Corps  observers  attached  to  Mobile  Weather Support  Teams  and  Recon  Units  routinely  conduct mobile-land  station  Pibal  observations  during  field operations and exercises. The collected information is normally  distributed  locally  in  plain  language,  and rarely encoded for electronic distribution. A PIBAL is a balloon that is inflated with helium or hydrogen  to  provide  a  fixed  free  lift,  which,  in  turn, produces  a  predictable  ascension  rate.  It  is  tracked visually with an optical theodolite (an instrument used for measuring horizontal and vertical angles), with the observed azimuth and elevation angles recorded each minute. The  height  (AGL)  of  the  balloon  at  each successive minute is based on a standard ascension rate for the size of the balloon. These ascension rates are listed in the FMH-3. When inflated properly to achieve a set free-lift weight, balloons are assumed to ascend at the standard rate, and true wind speed and direction are computed from the change in the horizontal position of the  balloon. PIBAL  OBSERVATION PROCEDURES The equipment and procedures required to conduct a  Pibal  observation  are  thoroughly  described  in  the Federal   Meteorological   Handbook   Number   3. Guidance on encoding Pibal-observed winds by land, ship, or mobile observers in International code (FM32- IX  PILOT,  FM33-IX  PILOT  SHIP,  AND  FM34-IX PILOT MOBIL codes) with the required Regional and National coding practices are contained in the FMH-3. Additionally, the basic International code is covered in WMO Publication 306, Manual on Codes, Volume 1, International Codes. PIBAL  EQUIPMENT The  equipment  used  to  conduct  a  Pibal  observation is  fairly  limited.  You  will  need  an  ML-474  shore telescopic theodolite with an ML-1309 tripod (fig. 1-7) 30-  or  100-gram  balloons,  a  Universal  Balloon  Balance (PIBAL)   weight   set   or   the   MK-216/GM   balloon inflation  nozzle  and  weight  set,  and  a  pressure-reducing helium regulator with hose. To evaluate the data, you will need either an appropriate calculator or computer and  Pibal  evaluation  program,  or  you  may  use  the manual  method.  The  manual  evaluation  method requires  the  use  of  the  MF5-20  Winds  Aloft Computation  Sheet,  a  set  of  “Balloon  Distance Projected  on  a  Curved  Earth”  scales  (Horizontal Distance Out "HDO" scales) or a Horizontal Distance Computer  (FCW-19)  or  an  18-C-58  PIBAL-RAWM calculator.  An  Aerological  Plotting  Board  or  Winds Aloft Plotting Board with the appropriate wind speed scale for the board, and a Winds Aloft Graphing Board or Wind Aloft Plotting Chart could also be used. The manual  method  is  rarely  attempted  due  to  time requirements  and  the  quantity  and  weight  of  the equipment. It has been replaced by the use of PIBAL software for hand-held programmable calculators and 1-17