Effects Of East Asian Summer Monsoon On Precipitation Intensity And Distribution For Landfall Typhoons Over China

In this paper,59 typhoons making landfall over China from 2006 to 2016 are taken as research objects.They are classified into three clusters:western cluster,northwestern cluster and northern cluster based on landfall location and post-landfall track.Each cluster is then divided into strong monsoon influenced category and weak monsoon influenced category according to the East-Asian summer monsoon index.Using CMORPH-AWS merged precipitation product,JRA 55 reanalysis data and TBB data from FY-2E satellite,precipitation intensity and distribution characteristics of strong monsoon influenced typhoons and weak monsoon influenced typhoons were compared through composite analysis and comparative analysis between western cases "Bilis" and "Sepat",and further to explore the possible influence mechanisms of summer monsoon on typhoon precipitation.Results show that the stronger(weaker)the monsoon flow is,the stronger(weaker)the precipitation intensity of post-landfall western typhoons.Monsoon flow provides a sufficient amount of water vapor through direct moisture channel.The stronger the monsoon flow is,the more obvious the coupling of low-level convergence and upper-level divergence,and thus provides a stronger lifting for typhoon precipitation.A strong monsoon condition is more conducive to the genesis and development of mesoscale convection system.A strong monsoon condition is also favorable for the maintenance of post-landfall typhoons' warm core structure,thereby prolonging the precipitation through delaying the decay of typhoons.The comparative analysis between western cases "Bilis" and "Sepat" shows that the strong convergent updraft and convective instability under the strong monsoon background are the main factor causing the heavy rain of "Bilis",while the heavy rain of "Sepat" was mainly caused by local orographic lift and baroclinic instability under the weak monsoon background.Moreover,monsoon flow could lead to obviously asymmetric precipitation by changing vertical shear of environmental winds indirectly.