Diurnal Variation of Clouds over the Maritime Continent

本研究利用日本氣象衛星（GMS-5）所提供之高解析度的亮度溫度(Tbb)資料來探討1997-2003年冬季在海洋大陸地區雲的日夜變化。利用25小時滑動平均的方法，將原始資料分成兩種時間尺度：一天內時間尺度（日夜變化）、大於一天以上時間尺度。結果顯示，在大的島嶼地區，雲的擾動主要是由於日夜變化的影響，而受到一天以上時間尺度的影響較小；在海洋地區，情況相反，日夜變化對於雲振盪的影響較小，一天以上時間尺度的振盪對於雲振盪的貢獻較大。區域性的熱力影響是造成島嶼上方雲振盪的主因，大尺度的大氣擾動則是對海洋上方的雲變化有較大的影響。 結果也顯示，雲日夜變化的振幅在對流活躍時期會增強；但是，日夜變化的相位則與島嶼或海洋上的大尺度對流的強度無關，而只和區域性的熱力過程有關。在對流活躍時期，海洋上雲日夜變化振幅的增強效果比島嶼的來的明顯。 陸地上的雲的日夜變化主要和太陽加熱低層熱力直接作用有關；在海洋上則可約略分離出三種型態：在對流海域區域，太陽直接熱力過程造成午後雲的生成；在非對流海域，輻射冷卻的效應使得最高/最多的雲發生在晚上；在鄰近島域的海面地區，雲的日夜變化主要受到鄰近大島嶼的影響，從陸地發展的雲系有向外傳播的現象，在海洋大陸相位傳播的速度約5-10m/s，此現象可傳播到距島嶼幾百公里遠的海面上。The high resolution (hourly, resampled to 0.50×0.50) window (11.5μm~12.5μm ) brightness temperature (Tbb) data from Japan’s Geostationary Meteorological Satellite-5 (GMS-5) during 1997－2003 were used to investigate the diurnal variation of clouds in the Maritime Continent during boreal winter. The results showed that a low value of the mean Tbb accompanied a high value of the Tbb standard deviation in the Maritime Con-tinent during boreal winter. Over large islands, the total variance of cloud fluctuation was primarily contributed from the diurnal variation with only a minor contribution from the variations with a time scale longer than one day. Over the oceans, on the other hand, the diurnal variation had an insignificant contribution to the total variance of cloud fluctuations. We can conclude that the local thermodynamic effect is the domi-nating factor causing cloud variations over island. The large scale atmospheric distur-bances have a large impact on cloud variations over oceans but not over islands. The results also showed that the diurnal variation of clouds is enhanced during the active phase periods, and the diurnal phase is only related to the local dynamic process but not related to the intensity of large-scale convection over both islands and oceans. During the active phase, the diurnal amplitude is much amplified over oceans than that over lands. The diurnal variation of clouds over the land region is mainly due to local thermo-dynamic response to the solar heating cycle. Over the oceans, three types of mecha-nisms could be separated. Over the convective ocean, it could be suggested that ther-modynamic response contributes to the maximum cloudiness in the afternoon. Over non-convective oceans, the radiation cooling could be the reason for the maximum cloudiness during night time. Over the oceans adjacent to lands, the diurnal variation of clouds is highly influenced by land effect resulting in a phase propagating to several hundred kilometers oceans from lands.List of Figures V List of Tables X Chapter 1. Introduction 1 Chapter 2. Data and Methods 5 Chapter 3. Results 8 3.1 General features 8 3.2 Cloud variations during boreal winter 9 3.3 Diurnal variations 10 3.3.1 Borneo and New Guinea 10 3.3.2 Oceanic regions 11 3.4 Tbb with wind field pattern 12 3.5 Active and inactive phases 13 3.5.1 Borneo and New Guinea 13 3.5.2 Oceanic regions 14 Chapter 4. Discussion 16 4.1 Over lands 16 4.2 Over oceans 17 4.2.1 Non-convective oceanic regions 17 4.2.2 Convective oceanic regions 17 4.2.3 Oceanic regions adjacent to island 18 4.3 Active phase and inactive phase 19 Chapter 5. Summary 21 Appendix- 1998-2002 JJA 23 References 2