Oral

IAMAS

JPM04 - Indian Ocean Sciences

Tropical Indian Ocean tripole mode and its global effects

Differing from the Indian Ocean dipole (IOD) that has sea surface temperature (SST) anomalies of opposing signs over the tropical southeastern and western Indian Ocean, a tripole pattern, characterized by positive (negative) SST anomalies over the tropical central (southeastern and western) Indian Ocean, is observed and named the Indian Ocean tripole (IOT). The IOT can be identified by the third leading mode in the tropical Indian Ocean SST anomalies using empirical orthogonal function (EOF) analysis, explaining about 8.2% of the total variance. The IOT general peaks in boreal summer, significantly affecting the precipitation and temperature anomalies in globe, i.e., Indochina Peninsula, western Tibetan Plateau, Central Siberia, and western United States. During positive IOT phases, two cross-equatorial airflows are induced over the tropical eastern and western Indian Ocean. These strengthen ascending motion over the southern tropical Asia (80��?125��E, 15��?25��N), increasing precipitation in situ, as evidenced in observations and simulations by using Community Atmosphere Model. Serving as a heat source, the high-level Asian Continental Meridional Teleconnection (ACMT) pattern and the middle-level circum-global teleconnection-like (CGT?like) pattern are excited. The ACMT includes the southern tropical Asia, western Tibet Plateau, western Russian, and Central Siberia active centers, transmitting the signals from southern tropical Asia into Central Siberia. Whereas, the CGT?like pattern can propagate eastward from southern tropical Asia towards North America along the Asia subtropical westerly jet. These two teleconnections induced by the IOT lead to the positive geopotential height anomalies and anomalous anticyclones over the western Tibet Plateau, Central Siberia, and western United States. Upper-level circulation anomalies over there enhance atmospheric thickness through adiabatic processes and allow more solar radiation to reach the ground surface, consequently elevating local surface air temperature anomalies. Ultimately, the IOT is the independent mode in the tropical Indian Ocean, impacting the global climate, and the ACMT and CGT-like patterns serve as the atmospheric bridge connecting the IOT and the climate variations over the western Tibet Plateau, Central Siberia, and western United States.