Influence of Indian Ocean Warming on Extreme Precipitation in the Western Tianshan Mountains from Late Spring to Early Summer

The National Oceanic and Atmospheric Administration Climate Prediction Center’s daily grid precipitation data is used to analyze the spatial–temporal change of extreme precipitation in the Tianshan Mountains from late spring to early summer (May and June), as well as the mechanism of the Indian Ocean Basin Mode (IOBM) on extreme precipitation. The results show a clear spatial difference in extreme precipitation in the Tianshan Mountains from late spring to early summer. Extreme precipitation increased dramatically in the western Tianshan Mountains, whereas other regions experienced little variation. The diagnostic and numerical simulation results consistently showed that the increase in extreme precipitation in the western Tianshan Mountains was caused by a coetaneous positive anomaly of IOBM, which promoted the convergence of warm and cold airflows in the western Tianshan Mountains. On the one hand, the positive anomaly of IOBM strengthened the anticyclonic anomalies located in Eastern Europe and the northern part of Central Asia, promoting cold airflow southward transportation. On the other hand, it induced the Indian Ocean to warm unevenly, resulting in abnormal vertical circulation and subsidence, which caused the anticyclonic anomalies in the Arabian Sea and the Indian peninsula. Warm moisture from the Indian Ocean was delivered to the western Tianshan Mountains by the anomalous anticyclone and southerly airflow, which aided in the increase of extreme precipitation in the western Tianshan Mountains.