• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
REFRACTIVITY FORECASTS USING ATMOSPHERIC REFRACTIVITY PROFILE GENERATOR (ARPGEN)
Altimeter  Errors  (Temperature)

Aerographers Mate 1 & C
Page Navigation
  182    183    184    185    186  187  188    189    190    191    192  
evaporation duct is zero. When the N-unit gradient is zero or negative and the atmosphere is stable (positive bulk-Richardson number), the evaporation duct height is  a  linear  function  of  the  N-unit  gradient  and  the atmospheric stability; when the atmosphere is unstable, the evaporation duct height is a power function of the N-unit gradient and the atmospheric stability. When the computed value of the evaporation duct height is  AO m, it is set to 40 m. 2.  Radiosonde  Data  Set  Selection  -  Using  this option, an M-unit profile is entered by operator selection of  a  radiosonde  data  set  from  the  atmosphere environmental  file  (AEF).  M-unit  versus  height  pairs are extracted for the first 30 levels of the sounding or for levels  between  0  and  10,000  m  heights.  When  the lowest  sounding  level  is  not  at  the  0  m  height,  a sea-surface  M-unit  value  is  extrapolated  using  the lowest M-unit value/height pair in the profile, assuming a standard atmospheric gradient. The surface wind speed and evaporation height complete  the  information  required  to  generate  an  RDS. The  evaporation  duct  height  is  computed  in  the  same manner  as  when  an  M-unit  profile  is  entered.  The location and the date and time of the RDS are specified by  the  operator  on  the  Evaporation  Duct-Height Parameters Input form. 3. Historical Refractivity Data Set - Using this option,  a  historical  RDS  is  generated  for  an operator-specified location, month, and profile type (standard atmosphere, surfiace-hosed duct, elevated duct, or combined surface-based and elevated duct). The  upper  air  data  used  to  specify  the  M-unit  profile with respect to height are retrieved from the Radiosonde Data file. The mean surface wind speed and evaporation duct  height  are  retrieved  from  the  Surface  Observation Data  tile.  Note  that  the  closest  long-term  mean radiosonde  observation  location  and  Marsden  square containing  the  information  desired  are  retrieved  from the PDB. In some data-void regions, this may result in an   inappropriate   RDS   being   created.   Use   the climatological  electromagnetic  propagation  conditions summary function to evaluate the general climatologic electromagnetic propagation conditions before using this  option.  The  use  of  climatological  refractivity  data sets  should  be  limited  to  planning  functions. 4. Analysis of an AMR tape - This option allows the operator to create an RDS by analyzing a tape generated  by  the  AN/AMH-3  electronic  refractometer set. These devices are routinely flown on E-2C aircraft. Refer  to  the  functional  description  for  additional information. FORECASTING  ALTIMETER SETTINGS LEARNING  OBJECTIVES:  Discuss the basic considerations  in  forecasting  altimeter  settings. Determine  altimeter  setting  errors  due  to surface pressure variation and nonstandard temperatures.   Describe   the   forecasting   of altimeter  settings. Under certain conditions it may be necessary to forecast or develop an altimeter setting for a station or a location for which an altimeter setting is not received. There is also a possibility that an altimeter setting may be required for an area not having a weather station. A forecast  of  the  lowest  altimeter  setting  (QNH)  for  the forecast  period  is  required.  For  these  reasons  it  is import  ant  that  forecasters  have  a  basic  understanding  as to the importance of correct altimeter settings and a knowledge  of  procedures  for  forecasting  altimeter settings. The altimeter is generally corrected to read zero at sea level. A procedure used in aircraft on the ground is to set the altimeter setting to the elevation of the airfield. BASIC CONSIDERATIONS An altimeter is primarily an aneroid barometer calibrated to indicate altitude in feet instead of units of pressure.  An  altimeter  reads  accurately  only  in  a standard  atmosphere  and  when  the  correct  altimeter setting is used. Since standard atmospheric conditions seldom  exist,  The  altimeter  reading  usually  requires corrections. It  will  indicate  10,000  feet  when  the atmospheric  pressure  is  697  hectopascals,  whether  or not the altitude is actually 10,000 feet. Altimeter Errors (Pressure) The atmospheric pressure frequently differs at the point of landing from that of takeoff; therefore, an altimeter correctly set at takeoff maybe considerable y in error at the time of landing. Altimeter settings are obtained in flight by radio from navigational aids with voice  facilities. Otherwise, the expected altimeter setting for landing should be obtained by the pilot before takeoff. To  illustrate  this  point,  figure  10-1  shows  an example of altimeter errors due to change in surface pressure. The figure shows the pattern of isobars in a cross  section  of  the  atmosphere  from  New  Orleans  to Miami. The atmospheric pressure at Miami is 1019 10-4





Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.