A statistical analysis of near-core surface wind asymmetries in typhoons obtained from QuikSCAT data

The relationships between near-core surface wind asymmetries in typhoons and both the environmental vertical wind shear and typhoon movement are examined using the historical quikscat (nasa quick scatterometer) wind data,putting stress on the azimuthal location of the tangential wind maximum. the results clearly show that the highest winds occur preferentially to the left of shear as well as to the right of storm motion when their effects on the wind fields are separately evaluated using a composite approach.a further composite analysisrevealsthatthe magnitude of left to right asymmetry with respect to storm motion or shear depends largely on the directional difference between shear and storm motion with the largest asymmetry being generated when their directions are opposite to each other. in cases where shear and storm motion vectors point toward a similar direction under relatively strong shear conditions,the left to right asymmetry is very small and a significant percentage of the cases exhibit a left-of-motion maximum. these results are highly consistent with previous ones which were obtained from the jma (japan meteorological agency) operational mesoscale analysis wind data. in the present study,the effect of inner-core rainfall asymmetry on the azimuthal location of the tangential wind maximum is also examined. the results show that the relation between shear and surface wind asymmetry can be described in terms of rainfall asymmetry in place of shear,as expected from the increasingly well-documented strong connection between shear and rainfall asymmetry,suggesting that the asymmetric features of over-ocean wind fields in typhoons could be estimated to some degree using information on typhoon motion and rainfall asymmetry. © 2011,meteorological society of japan.