Responses of the subseasonal to seasonal atmospheric variability to the recent Pacific SST anomaly
Abstract
The sea surface temperature anomalies (SSTA) is a key factor controlling the tropical cyclone (TC) activity over the western North Pacific (WNP). Recently, primary impacts of the warm SSTA over the Pacific subtropical SSTA on the WNP TC activity was highlighted (Qian et al. 2019, GRL). It is also well known that the WNP TC activity is significantly modulated by the boreal summer Intraseasonal Oscillation (ISO). We investigate how the SSTA affect the WNP TC (and the precursor) activity through (1) large-scale mean fields and (2) the ISO activity by a case study of 2018 boreal summer season, using a suite of sensitivity simulation dataset with a global cloud-system resolving model (NICAM). In 2018, Asian summer monsoon was active with enhanced lower tropospheric westerlies, and clear ISO episodes repeatedly took place. These provided favorable condition for the WNP TC activity. The impacts of regional SSTA (e.g., subtropical/tropical Pacific) are examined by comparisons between the simulations forced by all SSTA (climatological SST) and those by removing the reginal SSTA (adding only the regional SSTA). It was found that (1) the warm SSTA in the subtropical Pacific in 2018 was responsible for the enhanced TC precursor activity over the central Pacific with the anomalous upward motion of Walker circulation and zonal convergence in the lower troposphere, and (2) the strong monsoon westerlies in 2018 were critical to the enhanced TC precursor activity in the western Pacific (<150E), which was maintained by warm SSTA in the tropical Pacific. The removal of the SSTA in the topics and subtropics disrupted the continuous northward migration of ISO signals and their relationship with TC precursor activity.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA062.0022N
- Keywords:
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- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 4504 Air/sea interactions;
- OCEANOGRAPHY: PHYSICAL;
- 4572 Upper ocean and mixed layer processes;
- OCEANOGRAPHY: PHYSICAL