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題 名 | 雲輻射效應及其不確定性問題之探討=A Study on Cloud Radiative Effects and Associated Uncertainties |
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作 者 | 馮欽賜; 劉其聖; 鄭明典; | 書刊名 | 大氣科學 |
卷 期 | 24:1/2 民85.03-06 |
頁 次 | 頁25-52 |
分類號 | 328.48 |
關鍵詞 | 雲輻射效應; 雲輻射驅動量; Cloud radiative effect; Cloud radiative forcing; |
語 文 | 中文(Chinese) |
中文摘要 | 本文的主旨是奠基在一維架構之下,針對雲輻射效應的基本性質與輻射模式中關於雲因子所衍生的不確定性問題,作廣泛且清楚地探討。文中採用典型的寬帶輻射參數化模式,貫穿所有雲個案的輻射傳遞計算。定量分析上,則特別著重以雲輻射驅動量的觀念來量化和解釋雲對大氣地表輻射能量收支的影響,彌補以往類似分析僅注意雲對大氣輻射加熱/冷卻作用的不足。 研究的主要內容劃分為三個部份。首先在第一部份,藉由包括十二個雲個案的實驗組合,分析比較雲輻射效應在不同條件、狀態下所呈現的共同特徵和差異性。這些雲個案不僅包含不同雲類(高)和雲層厚度,並且涵蓋三種從暖濕到乾冷的背景大氣。第二部份則以雲個案為例,進行一系列的敏感性測試,探索輻射傳遞模式處理雲輻射效應過程中,所蘊含的一些不確定因子如何影響輻射收支的估算。子題有三,分別是(1)雲量垂直疊合之假設,(2)雲光學參數之變動,(3)雲層垂直解析度之限制。研究發現,對於雲輻射模式中採用不同的假設或參數化方法,所引起輻射收支的影響,值得注意的是,它不僅使大氣加熱/冷卻率剖面呈現明顯的差異,其中更蘊含地表大氣能量重新分配的藕合作用;其次,亦發現雲輻射問題在不確定因子相互交織作用下,顯現的收支現象更具複雜性。 最後第三部份,我們針對雲因子的不確定性問題,進一步以一維輻射對流模式,舉證說明雲因子衍生的不確定性如何對氣候系統的大氣地表輻射能量分布和地表平衡溫度,產生的影響和擾動。根據四個實驗模擬的結果顯示,氣候輻射能量分布和地表平衡溫度對模式中雲量因子參數化方式的變動,相當敏感。無論是在實驗-改變長波模式的雲量疊合假設或實驗四改變短波雲光程正比於雲量的權重函數,所引起的地表平衡溫度擾動都有十幾度之多,其中驅使地表平衡溫度的暖化/冷卻趨勢,大氣地表之間熱量傳輸的作用扮演重要的角色。此外,另兩個實驗我們探討採用不同雲光學特徵的影響,發現其對地表平衡溫度的擾動較為緩和,約2-3度左右。整體而言,相對二氧化碳倍增所引起一維氣候模式的暖化趨勢(約1.9度),這些實驗指出因雲不確定因子導致的擾動驅力似乎遠甚於二氧化碳倍增的作用。 |
英文摘要 | In this paper, cloud radiative effects and associated uncertainties are explored extensively in a one-dimensional setup. A typical broadband radiation model has been employed to calculate radiative fluxes for all cloud cases. To quantify the cloud radiative effects, the impacts on heating/cooling atmosphere profiles as well as the concept of cloud radiative forcing (CRF) was applied to explain the modulation of the Earth radiation budget between atmosphere and surface by clouds. The whole study involves three parts. In the first part, the basic characteristics of the cloud radiative effects are analysed and compared for 12 cases, which include different cloud height, cloud thickness and three from warm-wet to cold-dry different background atmospheres. In the second part, we perform sensitivity studies to access the response of the radiative fluxes and heating/cooling rates to the uncertainty in modelling clouds that is associated with a radiation scheme. Three issues are addressed in this respect: (1) the assumption of the vertical cloud overlapping, (2) the variation of the cloud optical properties and (3) the limitation of the vertical resolution. Results reveal the uncertainty in modelling cloud radiative effects causes significant differences on atmospheric heating/cooling. Notably, it also affects the earth atmosphere energy redistribution. Furthermore, these results seem more complex under the interaction between uncertainties of different kinds. In the third part, a radiative convective model is constructed to demonstrate the singnificant influences on distributing radiative energy between atmosphere and surface and changing the equilibrium ground temperature by these cloud uncertaint factors. Four experiments were done and indicate a significant sensitivity to the variation of cloud uncertainty factors. Compared to the control run, the equilibrium gound temperature perturbs up to more 10K both in experiment 1, where the assumption of the cloud overlap in longwave radiation is different, and in experiment 4, where the weighting function of the shortwave cloud optical depth based on cloud fraction is modified. The energy exchange between surface and atmosphere plays an important role in adjusting the equilibrium gound temperature. The other two experiments, where explore the impact of the cloud optical property, show the perturbation appears smaller and the change of the ground temperature is about 2-3K. However, according to the ID climate model, the forcings induced by cloud uncertainty factors shown in these above experiments show much larger than those caused by CO₂ doubling. |
本系統中英文摘要資訊取自各篇刊載內容。