第九届青年地学论坛

The close relationship between the Indian Ocean Basin mode (IOBM) and summer precipitation in Central Asia (CA) has been documented in several studies. Nonetheless, this relationship has weakened since the 1990s and varies with the Atlantic Multi-decadal Oscillation (AMO) phase transition. During the P1 period (1970-1998), when the AMO was in negative phase, positive IOBM events were associated with an overall warm SST anomaly in the Indian Ocean. At this time, the weakened thermal difference between the tropical Indian Ocean and the Indian continent, due to the warmer Indian Ocean, weakened the South Asian Summer Monsoon. This resulted in less water vapor being transported to northern India, leading to reduced precipitation and diminished release of latent heat of condensation, ultimately weakening the atmospheric heat source in the region. According to the thermodynamic adaptation equilibrium theory, cyclonic anomalies emerged over CA as a whole, the north-south position of the SWJ exhibited significant interannual variability, and the SWJ moves northward when AMO was in negative phase in an interdecadal context. This ultimately led to increased precipitation across the entire CA. While in P2 period (1999-2019), when AMO was in a positive phase, positive IOBM events were associated only with warm SST anomalies in the northern Indian Ocean, resulting in that the weakened thermal difference between the tropical Indian Ocean and the northern Indian continent was smaller than that in P1. This decrease led to reduced precipitation and latent heat of condensation release in the eastern part of the North Indian continent. According to the thermal adaptation equilibrium theory, there was a weaker cyclone anomaly over southern CA, and the SWJ exhibited weaker north-south movement on an interannual timescale. Along with the southward SWJ corresponding to the positive phase of the AMO during P2, it eventually led to increased but weaker precipitation in southern CA. This remarkable contrast in the impact of IOBM during different phases of the AMO offers intriguing possibilities for improving climate prediction in CA.