GRBSANL FILES ------- ----- Revision: After requests from NCAR, the GRBSANL files now use the 192x94 Gaussian grid. All non-Gaussian grbsanl files have been regenerated and sent NCAR. -------------------------- old documentation --------------------- The NCEP/NCAR Reanalysis GRBSANL files are on an unusual grid. The dimensions of the grid are the same as the appropriate Gaussian grid but the data are on a lat-lon grid (i.e., evenly spaced latitudes and longitudes). Consequently this grid is unique to the GRBSANL files. The advantages of this grid is that there are pole points and it easier to do averaging. The disadvantages are the potential for mistakes. The Mistakes --- -------- The GRBSANL data are on a 192x94 equally spaced lat-long grid. The pre-Y2K system labelled the grids as a 192x94 Gaussian grid. The error was not found because data on the Gaussian grid are very similar to data on the lat-lon grid and people naturally assumed the data was on the familiar Gaussian grid as suggested by the GRIB header. Apparently the grib libraries changed and by the time of the Y2K system, the GRIB header described the grid as a 192x94 Gaussian grid with the northern-most point at 90N. This mistake was finally discovered 3/28/2001 and fixed the next day. Some documentation many have labelled the GRBSANL fields to be on a Gaussian grid. Fix-up: There will be no fix-up to the archived files as the data was unaffected by the problem. Only the old grid description are misleading. The consequences of the mistake are be relatively minor. If you are working near the equator, the differences between the Gaussian latitudes and equally spaced latitudes are much smaller than the resolution of the Reanalysis model. (See following table.) Even for the worst case, near the poles, the error is less than 1 1/2 degree which smaller than the nominal resolution of the model. Gaussian Lat Equal spaced Lat 88.542 90.000 86.653 88.065 84.753 86.129 82.851 84.194 80.947 82.258 79.043 80.323 77.139 78.387 75.235 76.452 73.331 74.516 71.426 72.581 69.522 70.645 67.617 68.710 65.713 66.774 63.808 64.839 61.903 62.903 59.999 60.968 58.094 59.032 56.189 57.097 54.285 55.161 52.380 53.226 50.475 51.290 48.571 49.355 46.666 47.419 44.761 45.484 42.856 43.548 40.952 41.613 39.047 39.677 37.142 37.742 35.238 35.806 33.333 33.871 31.428 31.935 29.523 30.000 27.619 28.065 25.714 26.129 23.809 24.194 21.904 22.258 20.000 20.323 18.095 18.387 16.190 16.452 14.286 14.516 12.381 12.581 10.476 10.645 8.571 8.710 6.667 6.774 4.762 4.839 2.857 2.903 0.952 0.968 -0.952 -0.968 -2.857 -2.903 -4.762 -4.839 -6.667 -6.774 -8.571 -8.710 -10.476 -10.645 -12.381 -12.581 -14.286 -14.516 -16.190 -16.452 -18.095 -18.387 -20.000 -20.323 -21.904 -22.258 -23.809 -24.194 -25.714 -26.129 -27.619 -28.065 -29.523 -30.000 -31.428 -31.935 -33.333 -33.871 -35.238 -35.806 -37.142 -37.742 -39.047 -39.677 -40.952 -41.613 -42.856 -43.548 -44.761 -45.484 -46.666 -47.419 -48.571 -49.355 -50.475 -51.290 -52.380 -53.226 -54.285 -55.161 -56.189 -57.097 -58.094 -59.032 -59.999 -60.968 -61.903 -62.903 -63.808 -64.839 -65.713 -66.774 -67.617 -68.710 -69.522 -70.645 -71.426 -72.581 -73.331 -74.516 -75.235 -76.452 -77.139 -78.387 -79.043 -80.323 -80.947 -82.258 -82.851 -84.194 -84.753 -86.129 -86.653 -88.065 -88.542 -90.000