Oceanic and land relay effects linking spring tropical Indian Ocean sea surface temperature and summer Tibetan Plateau precipitation

The present study investigates the characteristics and factors of the variability of summer precipitation over the Tibetan Plateau (TP). It is found that interannual variations of summer precipitation tend to be opposite over the eastern and western TP, manifesting an east-west TP precipitation dipole pattern (TPPD). The summer TPPD is significantly correlated with the spring sea surface temperature (SST) in the tropical Indian Ocean, and the latter can be considered an important precursor for the former. The impacts of spring SST in the tropical Indian Ocean on summer TPPD are through oceanic and land relay effects. For the oceanic relay effect, the positive SST anomaly (SSTA) in the tropical Indian Ocean persists from spring to summer and induces the upper-tropospheric positive geopotential height anomaly and anomalous anticyclone to the south of the TP by stimulating a Rossby wave response. Winter El Nin similar to o and Indian Ocean Dipole (IOD) contribute to the persistence of the SSTA in the Indian Ocean from spring to summer through modulating a spring asymmetric mode in the Indian Ocean. The SSTAs in the Indian Ocean affect the western North Pacific anticyclone at lower troposphere through modulating the Indo-Western Pacific Ocean capacitor (IPOC) mode. These circulation anomalies adjust the variability of the summer TPPD. For the land relay effect, the SSTA in the tropical Indian Ocean induces the soil moisture (SM) anomaly in the Turan Plain through modulating atmospheric circulation around the Arabian Peninsula and the Mediterranean Sea during spring. The SM anomaly in the Turan Plain is maintained from spring to summer and induces the upper-tropospheric negative geopotential height anomaly and anomalous cyclone north of the TP during summer by stimulating an anomalous vertical motion. Through the above oceanic and land processes, a north-south opposite pattern of geopotential height anomalies around the TP appears and eventually modulates water vapor transport into the TP and hence the formation of the TPPD during summer. Further analyses reveal that the impact of the winter El Nin similar to o and IOD and spring tropical Indian Ocean SST on the summer TPPD becomes weaker when one of the abovementioned relay effects is absent.