Properties of strong off-shore Borneo vortices: A composite analysis of flow pattern and composition as captured by ERA-Interim

Abstract

The Borneo vortex (BV) is an important source of extreme weather for Malaysia. We describe climatological properties of strong off-shore BVs using a potential vorticity (PV) threshold analysis of ERA-Interim data. The composite BV at the location of most likely high PV occurrence has a warm core with enhanced specific humidity between 800 and 200 hPa, and a dry layer above. Two effects contribute to this structure: Air is vertically transported upwards in the BV whilst precipitating and the large scale flow in which the BV is embedded advect dry, ozone-rich air from the equatorial tropical tropopause layer towards higher latitudes. © 2012 Royal Meteorological Society.