On the clustering extreme precipitation events over the Indo-Pacific rim and its relationship to Rossby waves

Abstract

Clustering extreme weather events are consecutive occurrences of disastrous weather in multiple regions. As the climate continues to warm up, cluster occurrence is becoming a prevailing feature of extreme weather events and leading to cumulative impacts. Understanding the associated atmospheric teleconnection patterns and their underlying mechanisms can help quantify their risk, i.e., the probability of occurrence and severity of cluster extremes in the future. In this study, over 400 clustering extreme precipitation events over South Asia, East Asia, and North America in the past 42 years are identified, and they show a significant increasing trend. This trend can be largely attributable to the increasing frequency of the Rossby wave response, including the circum-Pacific and cross-Pacific patterns due to Rossby wave activity propagation, and the Pacific anticyclone pattern due to Rossby wave breaking. The three patterns show remarkable disparity in seasonality, persistence, and hydrological impacts. They can increase the probability of most severe precipitation by up to 5, 8, and 25 times, respectively. The key driving mechanisms behind these wave patterns are as follows: 1) tropical latent heat anomaly during the Boreal Summer Intraseasonal Oscillation (BSISO) period serves as a first-order driving mechanism for the Rossby wave propagation to higher latitudes. In particular, the "wet India-dry Philippines" dipole heating anomaly can make the Rossby wave train more northeastward compared to the simply wet India condition. 2) The sea surface temperature (SST) anomaly over the Pacific will affect the atmospheric mean state to influence the Rossby wave pattern. 3) The propagation of the Rossby wave patterns in mid-latitude is modulate by the variation of the jet streams. Our findings suggest that specific Rossby wave patterns may influence the potential evolution of future clustering extrees.

Date of Award	2023
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Mengqian LU (Supervisor)