Boreal Summer Intraseasonal Oscillation Impact on Western North Pacific Typhoons and Rainfall in Taiwan

Abstract

This study discusses the boreal summer intraseasonal oscillation (BSISO) impact on the western North Pacific (WNP) typhoons and the summer rainfall in Taiwan. The real time BSISO1 and BISISO2 indices are created using the first two and the third and fourth principal components of the multivariate empirical orthogonal function analysis, based on outgoing long-wave radiation and zonal wind at 850 hPa from Lee et al. (2013). The results show that heavy rainfall in Taiwan and the associated WNP typhoon frequency patterns are closely related to the 10 -30 days BSISO2 phases during the typhoon season (July -October). Taiwan has larger rainfall during BSISO2 phases 3, 4, and 5 when the major BSISO2 convection moves northwestward from the Philippine Sea to the Taiwan area. During phases 3 and 4 the anomalous low-level cyclonic flow and the increased typhoon frequency directly result in larger rainfall in Taiwan. Phase 5 exhibits enhanced low-level southwesterly flow which transports the moisture to Taiwan responsible for more summer rainfall on the island.

Impact of boreal summer intra‐seasonal oscillations on warm season diurnal convection activity in Taiwan

“…The main difference between Figure and Figure S6 is the magnitude of the moisture supply and the rainfall intensity, which implies the potential influence of BSISOs on other types of rainfall events (e.g. Hung et al ., ).…”

“…Thus, more recent studies have adopted the two BSISO indices instead of the MJO index to examine the intra‐seasonal modulations of local weather/climate changes over the East Asian summer monsoon regions (e.g. Li et al ., ; Hsu et al ., ; Hung et al ., ; Chen and Zhai, ).…”

“…E-mail: wrhuang@ntnu.edu.tw;mjudyisu@gmail.com instead of the MJO index to examine the intra-seasonal modulations of local weather/climate changes over the East Asian summer monsoon regions (e.g. Li et al, 2015;Hsu et al, 2016;Hung et al, 2016;Chen and Zhai, 2017).…”

Impact of Boreal Summer Intra-Seasonal Oscillations on the Heavy Rainfall Events in Taiwan during the 2017 Meiyu Season

“…Lee et al [10] have proposed a specific metric for better characterizing the intra-seasonal variability of Asian summer monsoon circulation related to the 30-60 day ISO (named BSISO1) and 10-30 day ISO (named BSISO2) from observations. Using the index of BSISOs proposed by Lee et al [10], more recent observational studies have examined the impact of changes in atmospheric circulations related to BSISOs (hereafter refers to the impact of BSISOs) in affecting rainfall characteristics over various areas of the East Asian summer monsoon region [13][14][15][16][17][18][19]. Among these studies, the impact of BSISOs in affecting the typhoon type of rainfall [17] and the diurnal type of rainfall [13] in Taiwan have been examined in detail.…”

“…Using the index of BSISOs proposed by Lee et al [10], more recent observational studies have examined the impact of changes in atmospheric circulations related to BSISOs (hereafter refers to the impact of BSISOs) in affecting rainfall characteristics over various areas of the East Asian summer monsoon region [13][14][15][16][17][18][19]. Among these studies, the impact of BSISOs in affecting the typhoon type of rainfall [17] and the diurnal type of rainfall [13] in Taiwan have been examined in detail. Chen et al [20] pointed out that the MJJASO rainfall in Taiwan is mainly modulated by different types of weather systems in different months.…”