AMSU分析颱風參數的方法及個案分析之測試

A Case Study on the Analysis of Typhoon Parameters Using AMSU Data

周鑑本(Chien-Ben Chou) ； 黃清勇(Ching-Yuang Huang) ； 王光華(Peter Wang) ； 葉天降(Tien-Chiang Yeh) ； 胥立南(Lee-Nan Shee)

《大氣科學》 33卷4期 (2005/12) Pp. 341-355

摘要

自1998年5月13日發射升空的NOAA-15號繞極軌道衛星，其上所載的The Advanced Microwave Sounding Unit(AMSU)是新一代的微波探空儀器，由於AMSU較原先的Microwave Sounding Unit(MSU)於水平及垂直解析度，都有長足的改進，而且微波比較不受雲雨的阻擋，因此可以用於反演颱風的氣象參數。由以往的研究結果顯示，颱風中心的增溫與最大風速及颱風中心氣壓存在著線性關性。並且由衛星資料反演得到的氣溫垂直分布，經由梯度風平衡公式可推導出颱風的梯度風場。輻散輻合風場可利用Omega方程式與連續方程，和大氣垂直速度場一併求得，在Omega方程中的非絕熱加熱項可用AMSU的頻道估算降雨率而求得，邊界層的磨擦項，可使用適當的參數化加以描述。本文建立一個分析溫度場及颱風風場結構的計算程式，利用中央氣象衛星中心所接收的AMSU資料對海燕及納莉兩個颱風進行個案分析。就海燕颱風而言，最大風半徑隨著高度向颱風中心外側傾斜，符合成熟颱風的典型特徵，此外由於海燕颱風處於緯度較高的地方，受到高層西風帶的影響，颱風中心呈現高層向東北傾斜現象。相較於海燕颱風，納莉颱風的環流水平尺度較小，颱風中心並無傾斜的情形，反演得到的風場，與測站觀測比對，也有良好的契合，基本上而言，AMSU資料確可提供颱風三維溫度及風場之結構分析。

關鍵字

微波 ； 颱風 ； 溫度剖面反演 ； 亮度溫度

並列摘要

The Advanced Microwave Sounding Unit (AMSU) aboard the NOAA-15 platform launched in May 1998. The microwave can be used to retrieve the parameters of typhoon, because the obstructed effect of the cloud to the microwave is minor than to the infrared. And, the resolution of AMSU is better than the Microwave Sounding Unit (MSU) on aboard the earlier NOAA satellites. Previous studies showed that there are relationships between the temperature anomalies in the core of typhoon and other typhoon parameters such as the maximum wind speed, and the center surface pressure. The rotational winds component can be obtained by solving the nonlinear balance equations using the retrieval temperature from AMSU. The divergent wind component can be evaluated from the vertical velocity field that can be diagnosed by using the omega equation. The diabatic term in the omega equation was estimated from the rainfall rate that obtained from AMSU observations. The frictionally-induced convergence in the boundary layer was represented by a relevant parameterization. In this article we formulate a procedure to analyze the structure of temperature and winds in typhoon through AMSU observation. Two cases (typhoon Haiyan and Nari) have been presented. In the case of Haiya the radius of maximum wind slopes outward with height, which is typical of intense tropical cyclones. Because typhoon Haiyan move into midlatitudes, the center core of typhoon becomes tilted away from the vertical by the advection of upper level westerlies. In the case of typhoon Nari, the result showed that typhoon Nan is smaller horizontal scale compared with that of typhoon Hayai and the downshear tilt has not been found. Comparing the retrieved wind fields with the traditional observation showed that the retrieved wind fields are good match with the sounding profiles. Basically, the AMSU data can provide the temperature and wind structure of typhoon.

並列關鍵字

Microware ； Typhoon ； Temperature profiles retrieval ； Brightness temperature