A factor controlling surface wind asymmetries in typhoons revealed by QuikSCAT wind data

Recent observational and modeling studies strongly suggest that environmental vertical wind shear (EVWS) plays a dominant role in the azimuthal wavenumber-one rainfall asymmetry in the eyewall region not only over open oceans but also over lands. Considering that boundary layer convergence is the main source of vertical mass flow into the eyewall cloud, the close connection between EVWS and rainfall asymmetry leads to the speculation that low-level wind distributions in the typhoon inner-core region may be strongly modulated by EVWS. To confirm the speculation, Ueno and Kunii (2009, hereafter UK09) investigated asymmetric features of near-surface wind fields in typhoons attempting both theoretical and statistical approaches. The present study is an extension of UK09. In the statistical component of UK09, the mesoscale analysis data, which have been produced operationally at Japan Meteorological Agency, were used to reveal the relationship between EVWS and near-surface wind asymmetries in typhoons. In the present study, QuikSCAT wind data obtained from the Remote Sensing Systems website are used in place of the mesoscale analysis data. One advantage of QuikSCAT wind data over mesoscale analysis data is that the former is free of any deficiencies included in the data assimilation system used (e.g., incomplete boundary layer parameterization). The results of the present study are quite consistent with those of UK09, confirming large control of near-surface wind distributions in typhoons by EVWS.