The impact of the Indian Ocean sea surface temperature (SST) on stratosphere has received extensive attention, yet mainly focused on the impact of Indian Ocean warming. The warming is contributed by the increasing trend of positive phase of Indian Ocean basin mode (IOBM) and Indian Ocean dipole mode (IOD), respectively characterized by greater SST magnitude and gradient. IOD can significantly affect tropospheric climates while its impact on stratosphere needs more investigation. This study investigates the impact of incensement of IOD positive events on stratosphere and compared with that of IOBM, using Whole Atmosphere Community Climate Model version 4 (WACCM4). Results show the IOD (IOBM) moistens (dries) tropical lower stratosphere as they cause different cold-point tropopause temperature (CPTT) responses. Specifically, IOD (IOBM) induces a local anomalous Walker (Hadley) circulation, thus positive (negative) CPTT appears over eastern (entire) Indian Ocean and causes water vapor (drier air) entering stratosphere. Both modes enhance the northern stratospheric polar vortex, which can be attributed to weakened wave1 activity. The impact of IOD equals to that of IOBM although SST anomalies of IOD are much smaller. Our results imply that, for the impact of the Indian Ocean warming on the Northern Hemisphere stratosphere, the Indian Ocean SST gradient is more important than the Indian Ocean SST magnitude. Both modes weaken the southern stratospheric polar vortex, but IOD’s effect is insignificant since its wave activities responses are excessively weaker. Contrary to the northern stratosphere, the impact of the Indian Ocean SST magnitude on southern stratosphere is more important.
 

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