DIAGNOSIS OF NWP SYSTEMATIC FORECAST ERRORS IN ZONAL MEAN CIRCULATION

It is proved in this paper that NWP systematic forecast errors in the zonal mean circulation are due to the difference in westerly acceleration process during the forecasting period between model and real atmospheres.Those forcing factors which evoke the zonal mean wind variation can be split into various linear terms according to the non-acceleration theorem in a primitive equation system,By applying this technique to the diagnosis of the forecast produets of the T42L9 model in January 1992 and in July 1992,it is indicated that the model has the ability to forecast the zonal mean wind to a reasonable extent,but there are still some errors in several places,especially in the upper troposphere and lower stratosphere in the mid-latitude region as well as near the surface.The results of analysis by employing this scheme reveal the reason responsible for the systematic forecast errors of the zonal mean wind in the model and the possible way of improving it.It is also shown that non-acceleration theorem can be used as an efficient tool to diagnose the physical processes of NWP models.