Aerosols in London Experiment on Radiative Transfer (ALERT)

据报道，由于城市气溶胶的存在，全球各地到达地球表面的太阳辐射量大幅减少。在长波中，气溶胶的影响是不确定的，然而，一些模拟和测量研究表明，城市气溶胶的存在可以显著地增强向地面的下流通量。更耐人寻味的是，最近的工作表明，地表下行长波辐射频谱中包含的信息可以用来诊断气溶胶对云微物理的影响：这是一种间接影响，预计将极大地改变短波和长波的云天表面通量。在这里，我们建议通过ALERT，首次同时测量城市环境中的短波和长波城市气溶胶辐射效应。通过以伦敦市中心为重点的独特的观测和模拟工具的组合，我们将检验两个主要假设：假设1：由于气溶胶，在地表存在可测量的城市晴空长波和短波直接辐射效应。假设2：由于云有效半径的可测量变化，对城市短波和长波地面通量有间接的气溶胶辐射效应。

A substantial reduction in the amount of solar radiation reaching the Earth's surface, due to the presence of urban aerosol, has been reported for a variety of global locations. In the long-wave, the aerosol impact is more uncertain, however, a number of modeling and measurement studies suggest that the presence of urban aerosol can act to enhance downwelling fluxes to the surface significantly. Even more intriguingly, recent work has indicated that information contained in the spectrum of downwelling long-wave radiation at the surface can be employed to diagnose an aerosol effect on cloud microphysics: an indirect impact which would be expected to substantially modify both short-wave and long-wave cloudy-sky surface fluxes. Here, through ALERT, we propose to simultaneously measure, for the first time, the short-wave and long-wave urban aerosol radiative effect on the urban environment. Through a unique combination of observational and modeling tools, focused on central London, we will examine two principal hypotheses: Hypothesis 1: There is a measurable urban clear-sky long-wave and short-wave direct radiative effect at the surface due to aerosols. Hypothesis 2: There is an indirect aerosol radiative effect on urban short-wave and long-wave surface fluxes due to measurable shifts in cloud effective radius