[A-AS03] Extreme Events and Mesoscale Weather: Observations and Modeling

[AAS03-01] Cold surge vortex dynamics and their impact on tropical heavy rainfall during MJO

*Cathrene Lagare¹, Junshi Ito¹, Giuseppe Torri², Takeshi Yamazaki¹ (1.Graduate School of Science, Tohoku University, Japan, 2.School of Ocean and Earth Science and Technology, University of Hawai'i at Mānoa, USA)

Keywords:cold surges, vortices, mesoscale convective systems, numerical simulations

During the boreal winter, the intensification of the Asian winter monsoon can often lead to cold air outbreaks or cold surges that propagate to the Maritime Continent. These surges can facilitate the formation of mesoscale cyclonic circulations known as cold surge vortices. The development of heavy precipitating mesoscale convective systems (MCSs) in the presence of cold surge vortices is often observed, which can cause torrential rainfall, flooding, and significant crop and infrastructural damage. Two types of cold surge vortices have been previously classified in the Maritime Continent, the Borneo and the Philippine vortices (Chen et al., 2015). While the former has been numerically well studied, the development of Philippine vortices in relation to the organization of MCSs has yet to be fully explored. In this study, semi-idealized simulations were performed to investigate the environmental characteristics and dynamics of the cold surge vortices in relation to the MCS organization during the active phases of the Madden-Julian Oscillation (MJO). Results show that the numerical simulations reproduce the vortices and their intense rainfall concentration. For the Philippine vortex, a combination of northerly cold surges and moist easterly trade winds were found important in both the formation and intensification of the vortices, with some indication that the westerly bursts further reinforce vortex rotation. Trajectory analysis of the moisture sources revealed contributions from moist easterlies and dry MJO westerlies, with additional moisture from cold surges. Meanwhile, forward trajectories demonstrated moisture pickup from the South China Sea and its interactions with the convections, indicating complex dynamics of moisture transportation that contribute to the formation and intensification of these vortices. Sensitivity experiments are also performed by modifying the terrains to see their influence on the vortex formations. Further results on the structure and dynamics of the cold surge vortices, as well as a comparison between Borneo and Philippine vortices, will be presented.


References:

Chen, T. C., Tsay, J. D., Matsumoto, J., & Alpert, J. (2015). Development and formation mechanism of the Southeast Asian winter heavy rainfall events around the South China Sea. Part I: Formation and propagation of cold surge vortex. Journal of Climate, 28(4), 1417-1443.