Temperature, Pressure and Potential Vorticity Fields at Theta Surfaces from the European Centre for Medium-Range Weather Forecasting

The PV and temperature on the different isentropic levels are calculated from the ECMWF T213 initialized analysis extracted as a 1.25 degree lat-lon grid. PV is calculated using a centered difference scheme except between the two upper levels (10 and 30hPa) of the ECMWF model. There are substantial errors on PV.

This is primarily due to the coarse vertical interpolations and unreal small-scale structures in The only difference is that the trajectory calculation is done in a 1.5 degree distance grid, so the difference between them is small. The data are, however, only available in a 2.5 degree distance grid at NILU, but PV is calculated for every station using the finer grid and are available in the directory: /nadir/data/ecmwf/pvatstat/YYYY/MM The isentropic data are organised into year(YYYY) and month(MM) in the subdirectories: /nadir/data/ecmwf/isentrop/YYYY/MM The data are stored in files with names: atYYMMDD.HHH where YYMMDD gives the date of the analyses and HHH is the forecast hour.

HHH equals 000 for the 12 UT analysis. HHH equals 12, 36 and 60 hoursfor the forecast based on on the 0UT analyses, while HHH equals 24, 48, 72, 96, 120 and 192 for the forecast based on the 12 UT analyses. Thus, at951128.012 is the 12 hour forecast from 0 UT analysis on November 28, 1995, which is valid at 12 UT on November 28, 1995.

The forecast in at951127.24 is also valid at this time, but since it is a longer forecast, it should not be used. However, the forecasts based on the 0 UT analyses, will arrive later at NILU (at about 6 UT). Note, that on the first day of a month you have to go to the directory of the previous month, to get the forecast based on the 12 UT analysis.