Abstract
During May and June (the Meiyu season) of 2017, Taiwan was affected by three heavy frontal rainfall events, which led to large economic losses. Using satellite observations and reanalysis data, this study investigates the impact of boreal summer intra-seasonal oscillations (BSISOs, including a 30–60 day ISO mode named BSISO1 and a 10–30 day ISO mode named BSISO2) on the heavy rainfall events in Taiwan during the 2017 Meiyu season. Our examinations show that BSISO2 is more important than BSISO1 in determining the formation of heavy rainfall events in Taiwan during the 2017 Meiyu season. The heavy rainfall events generally formed in Taiwan at phases 4–6 of BSISO2, when the enhanced southwesterly wind and moisture flux convergence center propagate northward into the Taiwan area. In addition, we examined the forecast rainfall data (at lead times of one day to 16 days) obtained from the National Centers for Environmental Prediction Global Forecast System (NCEPgfs) and the Taiwan Central Weather Bureau Global Forecast System (CWBgfs). Our results show that the better the model’s capability in forecasting the BSISO2 index is, the better the model’s capability in forecasting the timing of rainfall formation in Taiwan during the 2017 Meiyu season is. These findings highlight the importance of BSISO2 in affecting the rainfall characteristics in East Asia during the Meiyu season.
Highlights
During May and June (i.e., MJ, the so-called Meiyu season in Taiwan), one of the most frequently observed weather systems affecting rainfall formation in Taiwan is the frontal event [1,2]
Longwave Radiation (OLR) data provided by the National Oceanic and Atmospheric Administration, and the daily precipitation estimation data provided by the Global Precipitation Measurement (GPM) Integrated Multi-satellitE Retrievals for GPM (IMERG)
Various distinct features revealed from the observational data regarding the potential impact of BSISOs in modulating the rainfall formation over Taiwan are documented and discussed as follows
Summary
During May and June (i.e., MJ, the so-called Meiyu season in Taiwan), one of the most frequently observed weather systems affecting rainfall formation in Taiwan is the frontal event [1,2]. Compared to issues related to other types of rainfall, the issue of how the circulation changes associated with BSISOs can modulate the formation of frontal rainfall (or the heavy rainfall) in Taiwan during the Meiyu season has been rarely discussed This will be examined in detail . The impact of BSISOs on various research subjects have been documented in many journal articles [13,15,16,17,18,23,24,25], but not in only the technical reports The importance of this kind of study [13,15,16,17,18,23,24,25] is that they can provide useful information for understanding how the local weather can be affected by the intra-seasonal variability of large-scale atmospheric circulations.
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