Above is a depiction of the ARM SGP CART site, located in northern Oklahoma and southern Kansas. The CAGEX 3x3 .3 degree spatial grid is centered over the ARM Central Facility. The figure below shows an enlargement of the CAGEX grid showing latitudes, longitudes, and average elevation in meters above mean sea level (at the top of each square). The center of the CAGEX grid, as well as the ARM Central Facility, is at 36.61 N latitude, and 97.49 W longitude. The elevation at the Central Facility is approximately 314 meters above mean sea level. Available at the central facility are validation measurements of several types (see the data description pages for a list of the datasets we use in the various CAGEX versions).
One should note that the radiometry sites depicted on the above image were available during April 1994 (V1). It is now safe to say that almost all of the green squares above now have radiometry associated with them, although CAGEX will not make use of these.
Version 1 of CAGEX is based upon the April 1994 ARM Intensive Observation Period (IOP). There are 26 days of CAGEX data, beginning on April 5th and continuing through April 30th. The dataset is in half-hour timesteps, daytime only, beginning at 1409 UTC and continuing through 2239 UTC. These times correspond to 8:09 A.M. to 4:39 P.M. Central Standard Time.
Version 2 corresponds with the October 1995 ARESE IOP, September 25 through November 1. This version is also in half-hour timesteps, but it covers the entire 24 hour day, at 19 at 49 minutes after the hour, again, corresponding with GOES snapshots. Each day begins at 0619 UTC, or 0019 CST.
Version 3 will cover the August 1998 IOP, again with 24 hour coverage and times corresponding to GOES snapshots. As of this writing, we're not sure if we will use UTC or CST as a starting point for our days.
The vertical resolution of CAGEX is variable, although it will always have somewhere in the neighborhood of 45 - 50 levels. The number of levels is dependent upon the surface pressure. Beginning at the top-of-atmosphere, the levels are as follows: .4, 1, 2, 5, 10, 20, 30, 50, and 100 mb. From 100 to 700 mb, levels are in 25 mb increments. Now, moving upward from the surface pressure, the levels are in 10 mb increments up to (surface - 40 mb). From (surface-40) to (surface - 100 mb) the levels are spaced 20 mb apart. Above this level, increments are 25 mb up until near 700 mb. If this level configuration produces a pressure which is less than 10 mb away from the 700 mb level, the 700 mb level is discarded. The figure below shows the vertical configuration in graphical form, using three examples. In the first example, the surface pressure is 1013, resulting in a 50 level profile. In the second example (red) the surface pressure is 1003. Note that the 700 mb level is gone. In the third (blue) example, the surface pressure is 900 mb, resulting in only 45 levels.
This vertical configuration will require a further interpolation should the user desire to maintain constant pressure surfaces below 675 mb. However, CAGEX is more concerned with the tight vertical resolution near the surface, hence this configuration.