Factors affecting atmospheric vertical motions as analyzed with a generalized omega equation and the OpenIFS model

Abstract

A statistical analysis of the physical causes of atmospheric vertical motions is conducted using a generalized omega equation and a one-year simulation with the OpenIFS atmospheric model. Using hourly output from the model, the vertical motions associated with vorticity advection, thermal advection, friction, diabatic heating, and an imbalance term are diagnosed. The results show the general dominance of vorticity advection and thermal advection in extratropical latitudes in winter, the increasing importance of diabatic heating towards the tropics, and the significant role of friction in the lowest troposphere. As this study uses notably higher temporal resolution data than previous studies which applied the generalized omega equation, our results reveal that the imbalance term is larger than the earlier results suggested. Moreover, for the first time, we also explicitly demonstrate the seasonal and geographical contrasts in the statistics of vertical motions as calculated with the generalized omega equation. Furthermore, as our analysis covers a full year, significantly longer than any other previous studies, statistically reliable quantitative estimates of the relative importance of the different forcing terms in different locations and seasons can be made. One such important finding is a clear increase in the relative importance of diabatic heating for midtropospheric vertical motions in the Northern Hemisphere midlatitudes from the winter to the summer, particularly over the continents. We also find that, in general, the same processes are important in areas of both rising and sinking motion, although there are some quantitative differences.Peer reviewe