Comments on 'Choice of South Asian Summer Monsoon Indices'

The choice of an appropriate index for the south Asian summer monsoon has been a subject of some controversy and received considerable attention in recent years (Webster and Yang; Goswami et al. 1999). Two major indices are the zonal wind shear index proposed by Webster and Yang (1992, hereafter referred to WYI) and the meridional shear index defined by Goswami et al. (1999, hereafter referred to as GKA; the index is hereafter referred to as MHI). In their recent article in the Bulletin, Wang and Fan (1999, hereafter referred to as WF) attempt to provide a dynamical basis for the discrepancies between different indices.