The Effect of Spatial Resolution on the Correlation Structure of GateⅢRainfall Fields

空間解析度對熱帶降水特性之影響

王作臺(Jough-Tai Wang) ； 中本正一郎(Shoichiro Nakamoto)

《Terrestrial, Atmospheric and Oceanic Sciences》 2卷1期 (1991/03) Pp. 51-74

摘要

本文比較（科羅拉多州）單次微爆及多次微爆暴風雨的內部動力結構，而重點放至邊界層現象，其中包括了多都普勒風場及熱動力場的討論。結果顯示，兩種狀況有相異之處也有相同之處。相同的特性包括：(1)微爆現象是包括於高回波降水區內。(2)濕的微爆伴隨弓形回波，外流之方向平行於最大回波強度梯度。(3)高壓存在於微爆之核心區，而低壓在最強外流區。(4)外流區產生垂直的渦流(rotor)，其係因外流與環境相遇而生而。(5)在微爆現象内，水平擾動動量及動能向下傳遞。(6)壓力及浮力項是在微爆層内，產生及削減水平動量與擾動動能之主要貢獻者。另一方面，不同處有：(1)兩組各有不同之環境條件，如風向，風速，垂直風切，穩定度，及濕度等。(2)環境風風向相反。(3)單次微爆之下沈氣流區有很強的下降氣流，而多次微爆者之下降氣流則較弱。(4)單次微爆之狀況中，無明顯之環流中心，而多次微爆者則有中尺度氣旋。(5)單次微爆之狀況中，微爆核心爲暖濕，而多次微爆者則為冷濕之核心。

並列摘要

The present study uses a fine scale data set from GATE phase III to investigate spatial effects on rainfall characteristics and its lagged autocorrelation. Due to the finer structure of the present data set, the physical processes invloved for a shorter distance scale can be identified, which has crucial information in the estimation for the sampling errors of a rain field.
It is found that for a rainrate less than 4 mm/hr, a 1 km by 1° and 4 km by 4° data set will not make any noticeable difference to accumulated rainfall statistics. This is directly implied by stratiform rainfall associated with the mesoscale circulation system. The rainfall within that physical region is continuous with a rainrate less than 6 mm/hr. A rainfall rate greater than 40 mm/hr contributes 20% to the total rainfall in 1 km by 10 data, in contrast to an 8% contribution from the 4 km by 4° data. The area-averaged processes suppress extreme rainfall considerably (the extreme would have come from the convective scale).
The variance and the autocorrelation calculated in this study reveal that the slope of the variance and autocorrelation for a smaller scale are different from those estimated through a larger area data. This is an indication that the convective scale rainfall field caused this change, and the existence of a horizontal integral length scale for the shorter scale end is postulated. The implications of a horizontal integral length scale and suggestions for further research are discussed.