蘭嶼大氣輻射場觀測與分析

Measurement and Analysis of the Atmospheric Radiation Field at Lanyu

柳中明(Chung-Ming Liu)

《大氣科學》 22卷2期 (1994/06) Pp. 219-245

摘要

本研究運用一套完整的大氣輻射場觀測設備，在蘭嶼中央氣象局測站進行觀測。主要測量太陽向下短波輻射通量（S ↓），地表向上反射短波輻射（S ↑）。大氣向下波長輻射通量（IR ↓），淨輻射通量（net），與紫外射線向下輻射通量（UV ↓）。並據以估算地表向上長波輻射通量（IR ↑）。此測量系統，曾在台北與中央氣象局的全天空太陽輻射通量數據相比較，誤差尚屬合理。另外也與國外觀測相比較，其日變化特性與數據大小，大略上與國外資料相吻合。在蘭嶼觀測期間，由於許多人為誤失，目前僅存有1992年5月、6月、9月下半月與10月上半月的資料。經分析後，認為S ↑、IR ↑、net與UV ↓的變化相關，也即S ↓強時，地表反射能量S ↑增加，同時氣溫日變化增大，因此地表向上長波IR ↑也增加。但此時大氣向下長波IR ↓，則多因晴朗無雲與水汽含量少，而致波長輻射來自高層，所以輻射量減少，因此IRnet = IR ↓ - IR ↑的絕對值會增大。不過IR的絕對值至少小於S ↓2倍，所以淨輻射量，仍因S ↓增加而增加。反之，陰雨日S ↓減少，地表反射能量S ↑減少，IR ↑因地表溫度變化少而減少。同時IR ↓因輻射來自雲底而上升，因此IR絕對值會減少。淨輻射量net亦會同步減少。以上結果可以參數方程式來表達日累積能量的變化，至於小時變化則可以正常化函數來統一表示，或以柳等（1990）的複雜函數來估算逐時的S ↓變化，再據以估算其他輻射通量的逐時變化。

關鍵字

大氣輻射場 ； 觀測 ； 參數方程式

並列摘要

In this research, we have used a complete set of instruments to measure the atmospheric radiation field at the Lanyu meteorlogical station. The measured components are the solar downward flux (S↓), solar upward flux (S↑), IR downward flux (IR↓), net flux (net) and UV flux (UV↓). Further, the IR upward flux (IR↑) is estimated based on the above-measured data. The S↓ data and has been compared with the measurement by the Central Weather Bureau at Taipei. The difference can be reasonably explained. Also, the measured data has been compared with data obtained abroad. The diurnal variation pattern and the data scale are close to those data. During the Labyu observation period, due to unexpected ignorance, part of the data have lost. Only those collected during May, June, Mid-September to Mid-October, 1992, have remained. After thorough analysis, it is concluded that the variation of S↑, IR↑, net and UV↓ has a positive correlation with that of S↓. When S↓ is strong, the surface-reflected S↑ with be increased and the diurnal temperature change with be enhanced. Therefore, the IR↑ will be enhanced. As to IR↓, since strong S↓ is usually associated with clear sky, low cloud amount and water vapor, the long-wave radiation will be from higher altitude with low air temperature. Hence, the intensity of IR↓ will be decreased. By estimating IRnet =IR↓ - IR↑, it is noted that the absolute value of IRnet will be enhanced. However, the absolute value of IRnet is usually much smaller than that of S↓. Hence, the net flux will still be enhanced when the S↓ is enhanced. On the contrary, on cloudy or even rainy days, the intensity of S↓ will be decreased, so as the surface-reflected S↑. The surface emitted IR↑ will also be decreased due to minor temperature variation. However, the IR↓ will be enhanced as the long-wave radiation is now mainly from the bottom of cloud. Hence, the absolute value of IRnet will be deceased, same as the net flux. The above-stated findings can be expressed by a few empirical formula to estimate daily-sum radiative flux. As to the hourly variation pattern, it can be either unified by the normalized functions or estimated by using the complicate formula developed by Liu et al. (1990).

並列關鍵字

Atmospheric Radiation ； Measurement ； Empirical Formula