| 摘要: | 溫室氣體會吸收地表以及大氣放射出的長波輻射，減少離開地球大氣系統的長波輻射通量，並對地球大氣系統造成溫室效應。自1750年工業革命至今，〖CO〗_2、〖CH〗_4以及N_2 O為影響氣候變化最顯著的溫室氣體，而這三種溫室氣體的濃度增加會影響地球大氣系統的輻射收支平衡，並影響氣候變化。
本研究選擇常用的輻射傳遞模式LBL與CLIRAD作為研究工具，並使用三個大氣剖面資料（熱帶、中緯度夏季與副極地冬季），瞭解輻射強迫作用在不同溫室氣體濃度，以及不同大氣條件下的結果，並討論兩模式計算結果差異的原因。同時為瞭解從1750年至2012年三種溫室氣體所造成的輻射強迫作用，因此使用輻射傳遞模式計算此兩年溫室氣體的輻射通量與冷卻率，並討論輻射通量以及冷卻率差異的原因。
從2012年溫室氣體濃度倍增的模擬結果，發現〖CO〗_2會減少最多長波輻射通量離開地球大氣系統，即〖CO〗_2所造成的輻射強迫作用最強，以及對地球大氣系統暖化最明顯，其次為N_2 O，最弱的為〖CH〗_4。從對流層頂向上淨輻射通量，發現三種溫室氣體在濃度倍增後，離開對流層的長波輻射通量明顯的減少，表示溫室氣體濃度倍增後有許多長波輻射能量被留在對流層與海洋，使得對流層與海洋的溫度上升。
將2012年的溫室氣體輻射通量與1750年相比，發現溫室氣體在三種大氣剖面所造成的輻射強迫作用，熱帶、中緯度夏季與副極地冬季分別為2.89W m^(-2)、2.53 W m^(-2)以及1.33 W m^(-2)。比較兩年的冷卻率結果，發現在高層大氣有明顯的差異，原因為〖CO〗_2濃度改變所致。
比較兩輻射傳遞模式LBL與CLIRAD發現，兩模式所計算的輻射通量在每一個頻段有些許的差異，這是因為CLIRAD限制了溫室氣體計算輻射通量的頻段，若非該溫室氣體的主要吸收頻段則不納入該頻段計算輻射通量。從冷卻率結果發現，兩模式在〖CO〗_2的結果差異不大，但〖CH〗_4與N_2 O在高層大氣有明顯的差異，原因為在CLIRAD內三種溫室氣體對透射率參數化的方法不同，〖CO〗_2使用查表法，〖CH〗_4與N_2 O使用K分布法。
;Greenhouse gases (GHGs) absorb the longwave radiation which is emitted by the earth’s surface and atmosphere, reduce the outgoing longwave radiation, and cause the greenhouse effect. Increasing the concentrations of GHGs 〖CO〗_2, 〖CH〗_4 and N_2 O has an impact on the Earth’s climate since 1750. Because these gas concentrations increase in the atmosphere and it makes the radiation unbalance at the top of atmosphere.
Two radiative transfer models, LBL and CLIRAD, are used in the study to calculate the radiation fluxes and cooling rate. Radiative forcing due to a doubling of the GHG concentrations in three atmospheric profiles (tropical, mid-latitude summer and sub-arctic winter) are investigated. In this study, we also have discussions on the difference in fluxes and cooling rate between 1750 and 2012.
Doubling the concentration of 2012 GHG, 〖CO〗_2 would decrease much longwave radiation more than the other two GHGs to leave the Earth, which means that 〖CO〗_2 has the strongest radiative forcing among the three GHGs. The weakest radiative forcing is 〖CH〗_4. Increases of these GHGs concentration increasing have positive radiative forcing at the tropopause. This means that increasing the concentration of GHGs will warm the troposphere and the surface.
Comparing fluxes between 1750 and 2012, the radiative forcing at the top of the atmosphere of the tropical, mid-latitude summer and sub-arctic winter is 2.89W m^(-2), 2.53W m^(-2) and 1.33W m^(-2), respectively. For the cooling rate, there is a little difference in the stratosphere, which is primarily by the 〖CO〗_2 concentration change.
Comparing the radiative transfer models LBL and CLIRAD, it is found that there are some difference in radiation fluxes at each spectral band. Because the GHGs are not considered at each band to calculate the fluxes. Only at the GHGs major and minor absorption band will consider the GHGs and calculate the fluxes. In cooling rate, two model doesn’t have obviously different on 〖CO〗_2, but 〖CH〗_4 and N_2 O has. The cause of this result is the use of different transmittance parameterizations; 〖CO〗_2 uses table lookup, 〖CH〗_4 and N_2 O use K-distribution method. |
