The Impact of Cold Oceanic Eddies on Typhoon Intensity Evolution in the Western North Pacific Ocean

• Main Authors: Tze-Chieh Hsia, 夏子傑
• Other Authors: 林依依
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/67583357540173518642

碩士 === 國立臺灣大學 === 大氣科學研究所 === 99 === For improving the typhoon warning system, we should improve the track and intensity forecasting. In the recent three decades, it had been well studied in track forecasting related to intensity forecasting. There are three important factors in tropical cyclone intensity evolution, including atmospheric synoptic condition, cyclone''s own structure and oceanic condition. Especially, the role of oceanic condition in typhoon intensity evolution is not well understood. There is a complicated oceanic subsurface in the western North Pacific ocean, because of the eddy rich zone. The oceanic eddy could let the upper ocean heat content have 100% anomaly. It deeply influences the intensity of typhoon. There were a lot of researches about the impacts of WOEs (warm oceanic eddy) on typhoon intensity evolution. In the eddy rich zone, there also exists SSHA (sea surface height anomaly) negative feature of COEs (cold oceanic eddy). This study focused on the interaction of COEs on typhoon intensity evolution. For example, 2007 category 5 typhoon Sepat dropped 35 knots in one day after encountered a COE. This study included the cases of 2007-2009 typhoon encountered COEs. It is found that there is an average of 25 knot intensity decay in one day when Category 4-5 typhoons encountering COEs. By the multiple altimetry satellite and oceanic float, we had good observations on COEs. One dimensional oceanic mixed layer model is used for simulating typhoon-induced SST cooling. This study examined the synoptic atmospheric condition and calculated enthalpy flux between the typhoons and COEs, then trying to understand the role of COEs in different intense typhoon and the impacts of COEs on typhoon intensity evolution. It is found that the impacts of typhoon encountered COEs depends on the encountered typhoon intensity, because the more intense typhoon has the bigger wind speed on inducing SST more cooling. The more intense typhoon needs more enthalpy flux for intensity maintenance. So that COEs make the more intense typhoon’s intensity decay.