GIST ETA Model Analysis Imagery
     
     
     1.0  General Description
     
          The Eta Model Analysis map imagery is one of several image
     datasets provided in the GEWEX Continental-scale International Project
     (GCIP) Integrated Systems Test (GIST). The Eta model analysis cover
     basically North America at 1000, 850, and 500 mb pressure levels. The
     imagery contain daily maps (valid 1200 UTC) for the GIST time period
     (01 April through 31 August 1994). The purpose of these maps are to
     summarize surface and upper air meteorological conditions during GIST.
     
     2.0  Detailed Data Description
     
          The National Meteorological Center (NMC) began operations for
     the Eta model in June 1993 with a resolution of 80 km and  38 levels. 
     The top level was 50 mb.  In late 1994, the domain of the Eta model was
     increased and the resolution became 48 km with 38 levels.  The Eta
     analysis and forecast fields are generated every 12 hours at 0000 and 1200
     UTC daily.  The Eta model analyses for 1000, 850, and 500 mb were
     routinely ingested and plotted at 1200 UTC daily by the National Severe
     Storms Laboratory (NSSL).  OFPS received these analyses plots and
     produced GIF imagery. These GIF images can be viewed using any
     standard GIF display software package. 
     
          The 1000 mb Eta model analysis (essentially surface) covers
     basically North America and denotes mean sea level pressure (mb) and
     1000 to 500 mb thickness contours (hundreds of meters).  Low and high
     pressure centers are shown with corresponding pressure values (mb). 
     Isobars are solid lines and thickness contours are dashed lines.
     
          The 850 mb Eta model analysis covers basically North America and
     these maps denote heights, temperatures, and winds at the 850 mb pressure
     surface.  Height contours are solid lines and labeled in units of hundreds
     of meters.  Wind barbs are plotted on a grid basis showing the direction
     and speed (knots). Temperatures are color coded in degrees Celsius with
     a "color scale" included on each image.
     
          The 500 mb Eta model analysis covers basically North America and
     these maps denote heights and vorticity at the 500 mb pressure surface. 
     Height  contours are solid lines and labeled in units of hundreds of meters. 
     Vorticity contours are dashed lines and color contoured for easier
     identification of centers.  A "color scale" has been included on each image. 
     
     2.1  Detailed Format Description
     
          General information on GIF files, structure and format are provided
     in the References.
     
     2.2  Data Remarks
     
          Eta Model Analysis map imagery was not available for the
     following dates:
          
          940401 through 940405, 940417, 940508, 940521, 940527, 940610
          through 940612, 940614, 940615, 940625, 940626, 940709,
          940710, 940717, 940718, 940807, 940824 through 940828,
          940830.
     
          In addition to the above list, Eta 500 imagery was also not
     available for 940409, Eta 1000 imagery was not available for 940721.
     
     3.0  Quality Control Processing
     
          No additional quality control was performed on the imagery by the
     UCAR/Office of Field Project Support. 
     
     4.0  References
     
     Kay: Graphics File Formats, 2/E.  ISBN: 0-07-034025-0, McGraw Hill.
     
     Luse, M: Bitmapped Graphics Programming in C++. ISBN: 0-201-
          63209-8, Addison-Wesley.