The Role of Scale Interactions in the Interannual Variability of Typhoon in Autumn
碩士 === 國立臺灣師範大學 === 地球科學系 === 99 === Many previous studies have shown that tropical storms (TSs) in summer are influenced by different large-scale phenomena such as El Niño–Southern Oscillation (ENSO) and intraseasonal oscillation (ISO). However, the interannual variability of the typhoon activity i...
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| Format: | Others |
| Language: | zh-TW |
| Published: |
2011
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| Online Access: | http://ndltd.ncl.edu.tw/handle/00700100243626222193 |
| Summary: | 碩士 === 國立臺灣師範大學 === 地球科學系 === 99 === Many previous studies have shown that tropical storms (TSs) in summer are influenced by different large-scale phenomena such as El Niño–Southern Oscillation (ENSO) and intraseasonal oscillation (ISO). However, the interannual variability of the typhoon activity in autumn has received less attention. This study investigates the energy budget of the interannual variability of synoptic disturbances over western North Pacific (WNP) in autumn by using a new eddy kinetic energy equation that separates the effects of mean-synoptic eddies interaction and ISO-synoptic eddies interaction.
The interannual variation of the TSs is classified into active and inactive years based on accumulated cyclone energy (ACE). Composites of the energy results indicate that the positive eddy barotropic energy conversion (CK) and eddy baroclinic energy conversion (CE) are enhanced and extended eastward to the dateline during active years. The enhancement of CK is contributed by both the mean–synoptic eddies interaction and ISO-synoptic eddies interaction. The southwest-northeast tilted synoptic eddies extract more eddy kinetic energy from the low-level anomalous seasonal mean and ISO cyclonic circulation and anomalous westerly jet during active years. Vigorous air-sea interaction in lower troposphere and latent heat release in middle to upper troposphere may be account for the enhancement of CE during active years.
It is suggested that the enhancement and eastward extension of positive CK and CE to the vicinity of dateline might be favorable for the eastward displacement of formation and development of typhoon over the east side of WNP. Hence, typhoon can last longer and have greater intensity over the ocean. In consequence, ACE which represents the combined effect of the number, life span and the strength of TSs are significantly greater during active years.
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