The daytime cycle in dust aerosol direct radiative effects observed in the central Sahara during the Fennec campaign in June 2011
The daytime cycle in dust aerosol direct radiative effects observed in the central Sahara during the Fennec campaign in June 2011
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DOI：
10.1002/2014jd022077
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发表时间：
2014-12
期刊：
影响因子：
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通讯作者：
J. Banks;H. Brindley;M. Hobby;J. Marsham
中科院分区：
文献类型：
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作者：
J. Banks;H. Brindley;M. Hobby;J. Marsham
在2011年6月的Fennec活动期间，在撒哈拉中部的Bordj Badji Mokhtar（BBM）超级站点上诊断了大气矿物尘的直接晴空辐射效应（DRE）。在此期间，观测到厚尘事件，气溶胶光学厚度值峰值为3.5。Meteosat-9的卫星观测与地面辐射通量测量相结合，以获得地表、大气层顶（TOA）和大气层内的DRE估计值。在TOA，净DRE存在明显的日间周期。短波（SW）和长波（LW）DRE在中午左右达到峰值，并导致地球-大气系统变暖。黄昏和黎明时，LW DRE减小，而SW效应可以转换信号触发净辐射冷却。净TOA DRE平均值从上午的-9 Wm−2到中午附近的+59 Wm−2。在表面，SW尘埃的影响大于TOA：SW散射和尘埃吸收导致平均表面辐射冷却为145 Wm −2。相应的平均表面加热所造成的增加向下LW排放的尘埃层是一个小的因素6。沙尘天气对大气辐射辐散的影响主要是由地表的西南冷却作用引起的，在到达时间点，沙尘天气对地表的西南和长波影响较小。因此，沙尘对大气的平均日间净辐射变暖效应为153 Wm −2。
The direct clear‐sky radiative effect (DRE) of atmospheric mineral dust is diagnosed over the Bordj Badji Mokhtar (BBM) supersite in the central Sahara during the Fennec campaign in June 2011. During this period, thick dust events were observed, with aerosol optical depth values peaking at 3.5. Satellite observations from Meteosat‐9 are combined with ground‐based radiative flux measurements to obtain estimates of DRE at the surface, top‐of‐atmosphere (TOA), and within the atmosphere. At TOA, there is a distinct daytime cycle in net DRE. Both shortwave (SW) and longwave (LW) DRE peak around noon and induce a warming of the Earth‐atmosphere system. Toward dusk and dawn, the LW DRE reduces while the SW effect can switch sign triggering net radiative cooling. The net TOA DRE mean values range from −9 Wm−2 in the morning to heating of +59 Wm−2 near midday. At the surface, the SW dust impact is larger than at TOA: SW scattering and absorption by dust results in a mean surface radiative cooling of 145Wm−2. The corresponding mean surface heating caused by increased downward LW emission from the dust layer is a factor of 6 smaller. The dust impact on the magnitude and variability of the atmospheric radiative divergence is dominated by the SW cooling of the surface, modified by the smaller SW and LW effects at TOA. Consequently, dust has a mean daytime net radiative warming effect on the atmosphere of 153Wm−2.