2:45 PM - 3:00 PM
[MIS12-05] Influence of marginal seas' hotspot on extratropical cyclones: Rossby number dependence
Keywords:Marginal seas' hotspot, Extratropical cyclone, Rossby number
Strong surface heat flux area over North Pacific marginal seas is called a "hotspot" in the climate system (e.g., Nakamura et al. 2015), to which the atmospheric response has been studied in idealized atmospheric general circulation models from the viewpoint of geophysical fluid dynamics, to discuss the temperature decrease around the east coast of the continent and cyclonic activity over the North Pacific Basin (Kaspi & Schneider 2011) and the formation of binary lows and explosive cyclones near the hotspot (Yamamoto 2021). Yamamoto (2021) applied the setup of Held & Suarez (1994) to the global WRF (Weather Research and Forecasting model), and assumed that the North Pacific marginal seas' hotspot heats the lower atmosphere. In this model, the steady and localized heating was given by the triangular region and several sensitivity experiments were conducted by varying the location and thickness of this heating region. The previous study showed that the hotspot increases the frequencies of explosive pressure drop and binary-low appearance
The purpose of the present study is to elucidate the optimal condition of forming binary lows and explosive cyclones near Japan, based on the Rossby number dependence of the atmospheric response to localized heating over marginal seas of the western North Pacific. By altering the planetary radius, I change the Rossby number and also change the location and intensity of the westerly jet. This study introduces the two Rossby numbers: RoNJ (for the jet in the northern hemisphere) and RoHS (for the lower atmosphere over the hotspot). Associated with the relative position between the hot spot and westerly jet core, the frequencies of explosive pressure drop and south-to-north trough reach their maxima at RoNJ ~ 0.04. In the lower-level atmosphere over the hotspot of RoHS ~ 0.03, different cyclone activities were seen in relation to the upper-level jet configuration for the same RoHS. This suggests that the coupling process with the upper-level atmosphere is important, along with atmospheric forcing over the hotspot. In my presentation, I would like to discuss the optimal conditions for the emergence of binary lows and explosive cyclones.
The purpose of the present study is to elucidate the optimal condition of forming binary lows and explosive cyclones near Japan, based on the Rossby number dependence of the atmospheric response to localized heating over marginal seas of the western North Pacific. By altering the planetary radius, I change the Rossby number and also change the location and intensity of the westerly jet. This study introduces the two Rossby numbers: RoNJ (for the jet in the northern hemisphere) and RoHS (for the lower atmosphere over the hotspot). Associated with the relative position between the hot spot and westerly jet core, the frequencies of explosive pressure drop and south-to-north trough reach their maxima at RoNJ ~ 0.04. In the lower-level atmosphere over the hotspot of RoHS ~ 0.03, different cyclone activities were seen in relation to the upper-level jet configuration for the same RoHS. This suggests that the coupling process with the upper-level atmosphere is important, along with atmospheric forcing over the hotspot. In my presentation, I would like to discuss the optimal conditions for the emergence of binary lows and explosive cyclones.