Wind patterns in FNL and MM5 simulations during the EPIC2001 project

A comparison was made between the FNL data and measurements from the field project of the East Pacific Investigation of Climate (EPIC2001), for the period 1 September - 15 October 2001. The results suggest that the zonal wind component at 850 hPa and the surface meridional wind from FNL compares fairly well with the observations made within the box of 4 lat by 4 long, centered at 95W and 10N. The EPIC2001 observations indicated 4 periods of westerly zonal winds that corresponded to the passage of tropical storm precursors, which are apparent also in the FNL data. The surface wind speed, zonal and meridional wind and the surface pressure averaged over 93W - 97W and over the period of EPIC2001 also showed a good agreement with measurements.

A simulation with the mesoscale meteorological model MM5 for the whole EPIC2001 was made to analyze to what extent the model was able to correctly reproduce the physical processes in that region. Initial and boundary conditions for MM5 were supplied by the FNL data. The preliminary comparison suggests that the MM5 model could not reproduce the observed wind patterns at 850 hPa. The results from the simulations clearly indicated a bias in the MM5 model towards the generation of tropical storms in the East Pacific region that were not observed.

More comparisons between the FNL data and observations from EPIC as well as changes in the parameterization used will be carried out in order to determine the validity of the FNL data and to better assess the performance of MM5 in the region.