尺度交互作用於秋季熱帶氣旋年際變化之影響

The Role of Scale Interactions in the Interannual Variability of Typhoon in Autumn

李庭慧(Ting-Hui Lee)

指導教授 ： 鄒治華

國立臺灣師範大學/理學院/地球科學系/碩士(2011年)

摘要

過去有許多研究顯示，夏季的熱帶氣旋會受到不同尺度的系統所影響而有明顯的年際變化，如聖嬰現象、季內振盪等。然而較少研究針對秋季熱帶氣旋進行討論。本研究將使用三維綜觀尺度擾動動能方程，來探討西北太平洋地區，秋季綜觀尺度擾動的能量收支，在年際變化上的差異。本研究將此方程的擾動部分分為綜觀尺度擾動(10天以下)以及季內振盪(10-90天)兩部分，因此可以進一步探討平均流及季內振盪與綜觀尺度擾動之交互作用。
利用累積氣旋能量，定義出年際變化的活躍期與非活躍期，並做能量的合成分析，探討兩時期能量轉換之差異。研究結果發現在活躍期時，正壓能量轉換與斜壓能量轉換皆有向東、南延伸的情形。正壓能量轉換項包含平均流與綜觀尺度擾動之交互作用，以及季內振盪與綜觀尺度擾動之交互作用。由於在西北太平洋地區有東北-西南走向之綜觀尺度擾動，且該波列呈西北-東南走向，故有利於綜觀尺度擾動從大尺度環境場擷取能量。另外，該區也存在一異常氣旋式風切距平、異常季內振盪的氣旋事風切距平以及異常西風噴流距平，故有利於平均流場與季內振盪將能量轉換給綜關尺度擾動。而對斜壓能量轉換項而言，由於在低層有明顯的海氣交互作用、中高層有較大的潛熱釋放，因此造成活躍期時斜壓能量轉換也增強。
因此可知在活躍期時，正壓與斜壓能量轉換皆增強且向東、南延伸，會有利於颱風在西北太平洋東南側之生成與發展，生成後颱風在海上停留的時間亦較久，故較有機會發展成為較強烈的颱風。

關鍵字

年際變化 ； 熱帶氣旋 ； 能量

並列摘要

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.

並列關鍵字

interannual variability ； tropical cyclone ； energetic

參考文獻

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