Understanding a Regime Shift of Pure Tropical Night Occurrence during Boreal Summer and a Role of Pacific Decadal Oscillation

Understanding a regime shift of pure tropical night occurrence during boreal summer and a role of Pacific Decadal Oscillation

Eun-Hye Lee and Sang-Wook Yeh

Hanyang University, Korea

It is known that the occurrence of extreme weather events is increasing as global mean surface temperature gradually increases. In this study, we analyzed the statistics of heat wave and tropical night occurrence in boreal summer by analyzing CPC Global Daily maximum temperature (Tmax) and minimum temperature (Tmin) data for 1980 to 2018. Heat wave is defined as the day when Tmax distribution exceeds 90^th percentile threshold on each grid, on the other hand, tropical night is defined as the day when Tmin distribution exceeds 90th percentile threshold on each grid. In particular, we mainly focused on the occurrence of pure heat waves without tropical night occurrence and a pure tropical night without heat wave occurrence. We found that there is a distinct regime shift in the occurrence of pure tropical night before and after the late 1990s, which is closely associated with a phase shift of Pacific Decadal Oscillation (PDO). We analyzed the physical processes associated with the role of PDO leading to a regime shift of pure tropical night occurrence.