Description:
This file contains the long-term annual means (23 years from 1979-2001) of the variables on the 500 hPa constant pressure level, the first free atmospheric constant pressure level above the surface of the entire continent.  Note that the U and V components of the wind are oriented with respect to GRID (not true) north.  This makes it easier to plot using software, but for comparison with annual/seasonal mean U and V observations at various stations, the direction must be rotated by adding or subtracting the longitude of the gridpoint from 0 degrees (the central meridian of the Polar MM5 grid).  The latitudes and longitudes of the respective gridpoints can be found in the constants file provided with separately under the "CONSTANTS" heading.

Format:
This file is ASCII text, with 1 each 121 x 121 grids

Column Designations:
1. I - I value on MM5 grid 
2. J - J value on MM5 grid
3. YEAR - this variable doesn't matter in this case, since the data is a 23-year mean from 1979-2001.
4. DUMMY1 - Not used in this case
5. DUMMY2 - Not used in this case
6. DUMMY3 - Not used in this case
7. 500-hPa geopotential height (m)
8. 500-hPa temperature (K)
9. 500-hPa specific humidity (g/kg)
10. 500-hPa U-component of the wind speed (m/s)
11. 500-hPa V-component of the wind speed (m/s)
12. 500-hPa scalar wind speed (m/s)
13. 500-hPa vertical velocity (m/s)