懸浮微粒衰減直達太陽輻射研究：1995年2～3月台南永康監測分析

Attenuation of Direct Solar Flux by Aerosols: Monitoring Study at Yukang, Tainan, Taiwan, during February-March 1995

柳中明(C. M. Liu) ； 沈金清(K. S. Shen) ； 李崇德(C. D. Lee) ； 張修武(H. W. Chang)

《大氣科學》 25卷2期 (1997/06) Pp. 235-266

摘要

本研究在中央氣象局台南永康測站進行密集太陽輻射、懸浮微粒與雲相觀測，以探討晴日時，大氣中懸浮微粒對直達太陽輻射之衰減；並建立利用太陽輻射觀測資料，反演垂直上空懸浮微粒之大氣混濁度的方法。同時探究近地面懸浮微粒對衰減直達太陽輻射之重要性。結果發現：在只選取晴空無雲的條件下，懸浮微粒約造成直達太陽輻射衰減-78~20%，大致與天頂角呈正相關，即天頂角愈大輻射衰減愈多。所反演得之寬頻（0.3~4μm）大氣混濁度（turbidity:τ），在1995年2月份為約0.34±0.25，3月份為0.43±0.15。此外，分析大氣混濁度與實測之（散射／直射）輻射通量密度比之相關，發現相關係數非常高，如2月份為0.97，3月份為0.98，大致顯示僅利用直射輻射通量密度資料所反演得之寬頻大氣混濁度，與實測之散射輻射量之變動呈正相關。同時分析在台南永康測站所測之懸浮微粒散射係數（藍、綠與紅光），以及懸浮微粒粒徑數譜，大致除單一個案外，均與τ變化呈現正相關，相關係數可達0.9左右。同時分析窄頻區間的類似現象。大致上，懸浮微粒造成直達輻射量的衰減率，415nm為-80~-66 %，500nm為-74~-55 %，610nm為-60~-20 %，862nm為-50~-5 %。2月內窄頻415nm平均τ值為0.93±0.29，500nm為0.7±0.21，610nm為0.31±0.14，862nm為0.16±0.12。3月內窄頻415nm平均τ值為0.94±0.32，500nm為0.78±0.21，610nm為0.38±0.10，862nm為0.20±0.06。2~3月間τ值變動不大。本文同時探討寬頻、窄頻與後甲PM10間之相關，發現在相關性高的日子裏，如2月7日、2月12日、3月8日等，垂直空氣柱中懸浮微粒對太陽輻射的衰減，主要受近地面微粒的影響。但在彼此相關性不高的日子裏，如3月4日，近地面懸浮微粒的影響在整個垂直空氣柱中較不重要，因此可能與當時之綜觀大氣環境與長程物質的傳送等因素有關聯。由於大氣混濁度之反演主要在尋找垂直方向上懸浮微粒特性之改變，雖然大多數的狀況下，τ的數值與近地面懸浮微粒的變化相關極高，但是仍有少數情形例外。因此，未來如何進行垂直方向上懸浮微粒特性的監測，當為進一步推動相關工作的重點。

關鍵字

懸浮微粒 ； 太陽輻射 ； 大氣混濁度

並列摘要

An intensive field operation to measure the surface solar radiative flux, the aerosol size spectrum and backscattering coeffcient, etc., was done during February - March, 1995 at Yukang meteorological site. The main purpose was to study the effect of aerosols on attenuating the solar flux and to retrieve the atmospheric turbidity based on the surface solar flux dataset.In all, we note that under clear conditions, aerosols tend to attenuate the direct solar flux by -78 ~ -20%, which has a positive correlation with the change of the solar zenith angle. As to the retrieved mean turbidity for broadband (0.3 ~ 4 um) flux, it is 0.34 ± 0.25 in February and 0.43 ± 0.15 in March. Meanwhile, we have calculated the correlation coefficient between the retrieved turbidity and the observed diffuse/direct flux ratio, which is 0.97 in February and 0.98 in March. The analyses do show that the retrieved turbidity reflects very well the variation of the observed diffuse flux. Meanwhile, we have analyzed the correlation between the retrieved turbidity and the scattering coefficient or the aerosols number spectrum measured at surface, except for one case, good correlation are obtained and the correlation coefficients can be up to 0.9.The study in the narrow band region shows that aerosols tend to attenuate the direct solar flux by -80 ~ -66% at 415nm, -74 ~ -55% at 500nm, -60 ~ -20% at 610nm and -50 ~ -5% at 862nm. In February, the mean turbidy τ is 0.93±0.29 at 415nm, 0.7±0.21 at 500nm, 0.31±0.14 at 610nm and 0.16±0.12 at 862nm. In March, the mean turbidy τ is 0.94±0.32 at 415nm, 0.78±0.21 at 500nm, 0.38±0.10 at 610nm and 0.20±0.06 at 862nm.In the future, we shall pursue to do measurements of the aerosol profile, in order to clarify the relationship between the retrieved turbidity and aerosols along the vertical direction.

並列關鍵字

Aerosols ； Solar flux ； Atmospheric turbidity