Abstract/Summary

Using the objective feature tracking algorithm and hourly reanalysis data, seasonal behaviors of the cyclonic transient eddies (cyclones) at different levels around the Tibetan Plateau (TP) have been examined to reveal the effects of the TP on cyclones. Results show that TP tend to change moving directions of the remote cyclones when they are close to the TP, only some 250-hPa cyclones can directly pass the TP from west to east. Their moving speeds and relative vorticities suddenly weaken around the TP, suggesting the suppression effect of the TP. Over 70% of these cyclones die out over the TP regardless of the altitude, which slightly decreases to around 65% during summer, exhibiting a weak summertime suppression effect. On the other hand, TP has a strong excitation effect on local cyclones through dynamic forcing in winter, thermodynamic forcing in summer, and both in transitional seasons. Numbers of these local cyclones, especially at 500hPa that is almost the surface height of the TP, are greatly larger than that of the remote cyclones during all seasons. About half of these local cyclones dissipate over the TP. Nonetheless, cyclones moving off the TP are more than the cyclones entering the TP, with the differences ranging from 0 to 6 cyclones per month. Only the 250-hPa wintertime moving-off cyclones are less than the cyclones entering the TP, which may be caused by the relatively weak excitation and strong suppression effects of the TP on the wintertime upper-level cyclones.