The effect of transient eddy on interannual meridional displacement of summer East Asian subtropical jet

Using ERA-40 reanalysis daily data for the period 1958--2002, this study investigatedthe effect of transient eddy (TE) on the interannual meridional displacement of summerEast Asian subtropical jet (EASJ) by conducting a detailed dynamical diagnosis.The summer EASJ axis features a significant interannual coherent meridional displacement.Associated with such a meridional displacement, the TE vorticity forcing anomalies arecharacterized by a meridional dipole pattern asymmetric about the climatological EASJ axis.The TE vorticity forcing anomalies yield barotropic zonal wind tendencies with a phase meridionallyleading the zonal wind anomalies, suggesting that they act to reinforce further meridionaldisplacement of the EASJ and favor a positive feedback in the TE and time-mean flow interaction.However, The TE thermal forcing anomalies induce baroclinic zonal wind tendencies thatreduce the vertical shear of zonal wind and atmospheric baroclinicity and eventually suppress the TE activity,favoring a negative feedback in the TE and time-mean flow interaction. Although the two types of TEforcing tend to have opposite feedback roles, the TE vorticity forcing appears to be dominant in theTE effect on the time-mean flow.