Dominant modes of interannual variability in precipitation over the Hengduan Mountains during rainy seasons

摘要

Present study investigates the dominant modes of interannual variability in precipitation over the Hengduan Mountains (HM) during rainy seasons. The leading two empirical orthogonal function (EOF) modes of HM precipitation explain 28.4 and 13.9% of the total variance, respectively. Positive EOF1 phase features enhanced precipitation anomalies over the southern HM, and a dipole structure with wet anomalies occupying large areas from the YunGui plateau to Tibetan Plateau is observed in positive EOF2 phase. Analysis of moisture budget and omega equation indicate the importance of leading EOF modes related circulation anomalies, which bring the horizontal warm advection to the HM, favouring the anomalous upward motions and precipitation increase there. For EOF1, the HM is controlled by an anomalous quasi-barotropic cyclone. This cyclone is one part of a zonally oriented barotropic wave-like pattern highly resembling the Silk Road pattern. Besides, the SST anomalies over the Indo-Pacific sector are similar to the decaying phase of La Nina, which induces the wet anomalies and further triggers the anomalous lower-level cyclone as a Rossby wave response. For EOF2, an anomalous cyclone appears over the Northeast Asia from lower to upper levels, and southerly wind anomalies prevail over the HM. The North Atlantic Oscillation and its coupled tripole SST pattern trigger a zonal wave-like pattern at middle and high latitudes emanating from the Central Europe, across Mongolia to Northeast Asia. Moreover, the SST anomalies over the Indo-Pacific sector resemble the developing phase of El Nino, which induces the meridional Pacific-Japan/East Asia-Pacific teleconnection from tropical NWP to Northeast Asia.