利用衛星紅外線資料分析颱風中對流之特性

The Analysis of Convective Characteristics Associated with Typhoon Using Satellite Infrared Data

李清勝(Cheng-Shang Lee) ； 吳鳳娥(Feng-Er Wu)

《大氣科學》 17卷4期 (1989/12) Pp. 331-354

摘要

本文之目的在利用日本地球同步氣象衛星（GMS）每3小時的紅外線數據資料，分析颱風之強度與其所伴隨之對流強度（以雲頂相當黑體溫度代表）或對流分佈的關係，紅外線數據資料乃由高解像類比（影像）資料轉換而來。本文分析了1985和1986年中位於西北太平洋海域之21個颱風，總共有593張影像資料；分析時，颱風中心位置採用衛星資料所決定之颱風中心位置而非最佳路徑。分析結果顯示，約有百分之八十的颱風，其衛星定位中心和最佳路徑中心的差距在1度緯度（約111公里）範圍内。不同半徑環狀區之平均對流強度或強對流所佔面積和颱風強度的相關不高，但個別颱風之相關性則有很大變化。颱風強度、強度變化、所在緯度以及發生季節之不同，都可能影響相關性。此外，強對流所占面積亦有明顯的日夜變化，最大值出現於05地區時（LT）：最小值於17LT。平均灰度值則受補償下沈無雲區之影響，其日夜變化呈相反之情情，且較不明顯。合成結果顯示颱風南半部之對流較北半部強，此特徵不因颱風之強度或強度變化而改變；但是移動速度大於等於20 kts的颱風，其特徵改變為東半部的對流強渡較西半部為強。在颱風發展初期，東半部對流增強較顯著，而西北象限對流並無明顯增強。到達中度颱風強度後，若強度增加，則西北方的對流顯著增強；而東半部兩度外對流並無明顯增強。若於分析時，採颱風移動方向為參考方位，則上述之對流特徵常變得較不明顯；此結果顯示導致颱風強度改變之物理過程似乎具有地理方位性，而與颱風之移動方向無密切關聯。

關鍵字

颱風 ； 颱風強度 ； 衛星資料

並列摘要

This paper analyzes the correlation between the intensity and distribution of convection associated with typhoons using three-hourly digitized Japanese GMS infrared data. The digitized data were converted from the high resolution analog data and can represent the cloud top black body temperature (or equivalently the intensity of convection). Totally, we analyzed twenty one typhoons (593 imageries) which occurred in the western North Pacific during 1985 and 1986. In the analysis, the typhoon centers were determined according to the satellite imageries instead of the best track.Results show that the distance between the best track typhoon center and the satellite-determined center is within one degree latitude (111 Km) for about 80% of all typhoon cases. The correlations between typhoon intensity and average intensity of convection (or percentage of area occupied by deep convection) at various radial domains are generally not high. However, the case variations are large. The correlation coefficients also vary among different categories off typhoon with different intensities, intensity changes, occurring latitudes or seasons. The results also indicate a strong diurnal variation in the area occupied by the deep convection. The maximum area occurs at 05LT (Local Time) and the minimum at 17LT. The average gray scale values, however, show a weaker but opposite diurnal variation. This is likely due to the influence of the compensating subsidence.The composite results show that the convection associated with typhoons is stronger in the southern half than that in the northern half. These characteristics do not change for typhoons with different intensities or intensity changes. However, for those typhoons with movement speed of 20 knots or greater, the convection is stronger in the eastern half than that in the western half. During the early developing stage of a typhoon, the convection strengthens in the eastern half but shows no change in the northwestern quadrant. At later stages, the convection strengthens in northwestern quadrant but shows almost no change beyond 2° latitude radius in the eastern half. The above characteristics appear less apparent if the composite was done using the typhoon movement direction as reference. These results suggest that those physical processes influencing typhoon intensity change are more geographically oriented than associated with movement direction.

並列關鍵字

Typhoon ； Typhoon intensity ； Satellite data