Propagation of low-level circulation features in the vicinity of mountain ranges.

Abstract

Investigates the local effect of mountains on large and synoptic scale low level atmospheric circulations. The data set consists of twice daily winter sea level pressure and 850,700 and 500mb height fields on the NMC octagonal grid. Examines the topographically trapped features (after removal of the climatological mean annual and seasonal cycles). Presents correlation maps and discusses also the behaviour of baroclinic waves in the vicinity of mountains, based on high pass filtered data. Compares the correlation maps with positive and negative anomaly composite maps. Notes the phase propagation of lower tropospheric circulation and relates this to conservation of potential vorticity over variable terrain. Most observations can be interpreted in terms of topographic Rossby waves, but some cases (Tibetan plateau) indicate Kelvin.