利用衛星資料研究低平流層的重力波時空特性

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题名:	利用衛星資料研究低平流層的重力波時空特性
作者:	鄭凌韻;Cheng,Ling-yun
贡献者:	太空科學研究所
关键词:	重力波;平流層
日期:	2014-08-20
上传时间:	2014-10-15 14:38:42 (UTC+8)
出版者:	國立中央大學
摘要:	本研究利用TIMED/SABER衛星從2002年1月至2013年12月共12年的溫度資料，探討大氣重力波在全球低平流層的時間和空間特性。將內插後的溫度資料使用高通濾波取垂直波長2到10公里的擾動，進而計算20公里到34公里低平流層處重力波位能值（Potential energy，Ep），該值通常用於表示重力波活動。透過長時間的資料研究重力波的全球活動分布狀況，在南北緯20度總是呈現較高的Ep值，且12月至2月的Ep值略比其他季節強；中高緯度則是冬季半球較夏季半球有較高的Ep值、太平洋區域長年有較陸地低的Ep值；當北半球從夏季轉秋冬季的時候，Ep低值的邊界向南移動且向東退後，南半球則呈現帶狀分佈沒有明顯的海陸差異。研究中並區分赤道區（±10°）、低緯度區（±10°~30°）、中高緯度區（±30°~60°）的不同時間和高度分別討論。在赤道區重力波呈現的準兩年振盪（Quasi-biennial oscillation，QBO）發生於緯向風場由東風轉為西風的零風場線下達到最大值，但年變化主要是受對流影響產生，當重力波垂直傳播時與風場的交替互相影響其分布狀況。低緯度重力波介於中高緯度和赤道區之間，因此在時間和高度上同時包含了赤道區和中高緯度的半年、一年、準兩年的變化。中高緯度重力波Ep值在經度分布上和地形相似、高度分布上在22到25公里有較強的Ep值、時間上在北半球的冬季和南半球的早春晚冬季節時較強，本區時空變動受到副熱帶高壓和高緯天氣系統的交替影響。以上分析可以知道重力波在不同的地區的特性和成因皆不同，有助於我們瞭解更多的氣候資訊。 ;The 12-year global temperature data from January 2002 to December 2013 retrieved from TIMED/SABER observations are employed to study the atmospheric gravity waves in the lower stratosphere. Temperature fluctuations containing vertical wavelengths between 2 and 10 km were derived from the interpolated temperature data. For each profile we can evaluate a potential energy (Ep) profile from 21 to 34 km which is assumed to be caused by atmospheric gravity waves. We obtained the global morphology using the long term database. Large Ep values have been found over tropical latitudes (±20°) and especially during December to February. Investigation of Ep over seasonal scales shows an annual variation over middle and high latitudes with maxima in the winter hemisphere. There are small Ep values over Pacific Ocean and large Ep values over continents. The small Ep region over Pacific Ocean would shift southward and eastward from summer to winter in northern hemisphere (NH). On the other hand, there is no significant topographic variation in the southern hemisphere (SH). Therefore, we separate the study region into different latitude bands to investigate gravity waves, as equatorial region (±10°), low latitudes (±10°~30°), middle and high latitudes (±30°~60°). Over equatorial region, the enhancements of Ep values are identified at a quasi-biennial period occurring below the altitude of zero zonal wind (u=0) contours that correspond to the descending eastward shear phase of the quasi-biennial oscillation (QBO). But the annual variation is mainly caused by the convections and they have wave-mean flow interaction with the mean zonal wind while propagating vertically. A transition between equator and middle/high latitude regimes occurred at low latitude where semi-annul, annual, and quasi-biennial variations are observed. At the middle and high latitudes, the annual oscillation is more prominent with a longitudinal distribution of high Ep values consistent with topography. The Ep values at middle and high latitudes maximise between 22 and 25 km altitude in winter and early spring. It has some relation with the subtropical high and synoptic systems. This analysis shows that there are a variety of reasons for the observed characteristics of the gravity wave climatology over different latitude regions and helps us better understand the global morphology of the small scale atmospheric dynamics.
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