Observational relationship of climatologic beta drift with large‐scale environmental flows

Abstract

While many numerical studies suggested that large‐scale environmental flows significantly affect beta drift, this influence was not verified observationally and included in assessing changes of tropical cyclone (TC) tracks under the background of global warming. This study investigates the influence of large‐scale environmental flow on climatologic beta drift in the northern West Pacific using the best track dataset from Joint Typhoon Warming Center (JTWC) and the NCEP monthly reanalysis over the period from 1965 to 2007. Consistent with most previous numerical studies, the meridional shear of zonal wind, vertical shear of zonal wind and meridional gradient of relative vorticity, which are mainly associated with the zonal environmental wind, play an important role in affecting beta drift. For the meridional shear of zonal flows, the northward beta drift in an anticyclonic shear is faster than that in a cyclonic shear. A poleward (equatorward) gradient of relative vorticity leads to faster (slower) westward beta drift than in a resting environment. TCs tend to move to the left of the vector of vertical wind shear.