氣膠總體參數法之研發與應用

Abstract

本研究主要著重發展適用於區域及全球尺度的氣膠總體參數法，此參數法不僅能準確且快速的計算氣膠的各種過程，同時能搭配雲參數法，應用於討論雲與氣膠交互作用。為瞭解氣膠與雲的交互作用，本研究第一部份改進全球耦合氣候-化學模式，討論硫酸對輻射及氣候上的影響；第二部份則包括Interactive Cloud and Aerosol Parameterization scheme (ICAPs)的方法介紹及目前ICAPs在箱型模式、三維區域沙塵以及空氣品質模式的應用。 氣膠與雲之間的交互作用相當複雜，在此採用全球耦合氣候─化學模式，每個時步計算硫酸的化學反應及其對輻射與雲滴數量的影響（第一間接效應），模擬達平衡後氣象場與化學場的變化。模擬結果估計硫酸的直接效應約為-0.32 W m-2，第一間接效應為-1.69 W m-2。與模式內部變化相比，直接效應的訊號不明顯，容易與模式內部變化混淆，第一間接效應則明顯的多，尤其在溫度與短波輻射的影響更是遠大於模式內部變化。使用不同的硫酸─雲滴數量濃度關係式估計出的第一間接效應甚至可達-6 W m-2，顯示模式中氣膠對雲滴數量濃度的影響，必須使用更精準的方式計算，不能只用簡單的經驗關係式。 第二部份首先介紹ICAPs的概念，ICAPs 採用矩量法(moment method)，使用3個矩量描述完整的氣膠粒徑分佈。發展參數式時，先將氣膠依粒徑分成許多細節(bin)，用原始的成長方程式計算每個細節裡的粒子變化情況，再對整個粒徑譜積分得到矩量的變化，再使用軟體將矩量的變化參數化成簡單關係式。ICAPs的優點包括: 容易使用、將環境參數分離以得到更準確的結果、當解析解不存在時仍然可以得到準確的結果以及計算快速。ICAPs除了提供氣膠在各種過程包括核化、凝結/蒸發、碰撞、乾濕沈降等產生的變化之外，還提供了診斷方程包括有效粒徑、曲率效應等等，更方便使用者應用。 與解析解及細節模式結果相比，ICAPs的結果不論是簡單的乾沈降速度或非常複雜的碰撞過程，與解析解和細節模式結果都很接近，顯示ICAPs能準確的描述氣膠因各種過程造成的變化。ICAPs應用於箱型模式並與傳統氣膠參數法相比，結果顯示ICAPs比傳統氣膠模式更接近細節模式的結果；而應用於區域沙塵模式TAQM/kosa，與原先TAQM/kosa中的細節模式相比，ICAPs不僅能模擬出3天後沙塵的空間分佈，也能反演出沙塵粒徑分佈，而且因為減少變數，電腦計算時間僅有原來TAQM/kosa 的67%。應用於區域空氣品質模式CMAQ，與CMAQ中傳統氣膠參數法結果類似，由於變數數目不變，電腦計算時間減少18％。

This thesis seeks to develop a new aerosol parameterization scheme which not only can describe the chemical and physical processes of aerosols in detail but also enable the study of aerosol-cloud interactions and their impact on climate. The first effort is to incorporate a sulfur cycle into a coupled global climate-chemistry model and use it to estimate the direct and indirect radiative effects due to anthropogenic sulfate. Climate forcing from sulfate aerosols is analyzed by a set of simulations that turns of an off anthropogenic emissions, and turn on and off the direct effect and the first indirect effect. The results show that anthropogenic sulfate aerosols may produce a global direct forcing of about -0.32 W m-2, and indirect forcing of about -1.69 W m-2. The signals from the first indirect effect are larger than the internal climate variability of the model, but those from the direct effect are not. The first indirect effect not only influence surface temperature but also other climate parameters, such as cloud cover, precipitation and circulation pattern, on the global and regional scales. Concentrations of chemical species, including sulfate itself, also change somewhat due to the sulfate 1st indirect effect. This implies the aerosol-cloud interaction is important to climate and chemistry in both regional and global scales. The second part of this study is to develop an “Interactive Cloud-Aerosol Parameterization scheme” (ICAPs) that is suitable for application in regional and global models. This scheme applies the modal approach by describing the size distribution of each aerosol mode with three moments. Fundamental growth equations for the whole group of aerosols are integrated numerically for a wide range of conditions, and the results are analyzed and fitted into simple parameterization formulas that are functions of the three moments. The advantages of this scheme are (i) easy to use, (ii) separate out environment properties for better accuracy, (iii) provide solution when analytical solution is not available, and (iv) computational efficient. Besides the dynamic processes of aerosol evolution, diagnostic properties such as effective radius can be are also provide. This ICAPs is shown to perform well by comparing with analytical solutions and detailed bin models for either simple or complicated aerosol processes such as the Brownian coagulation. The ICAPs was applied into a box model and a regional air quality CMAQ, and showed good performance in aerosol processes against a traditional aerosol parameterization scheme. It is also applied into a regional mineral dust model (TAQM/kosa) and showed very good agreement with that calculated with a binned approach.. The CPU time saved for running TAQM/kosa with ICAPs instead of the binned approach is about 33%, while that saved for running CMAQ is about 18%.