Radiative perturbations due to dust-atmosphere interactions over north Africa and the Atlantic and their implications for global climate

太阳是推动天气和气候的基本能源。在全球平均水平上，地球系统吸收的短波太阳辐射能和地球向太空发射的长波热辐射能之间存在平衡。任何改变这种平衡的过程都有可能改变我们的天气和气候。一类过程涉及大气气溶胶，即自然存在于大气中的微小液体或固体颗粒(例如，风吹起的粉尘)，也是由各种人类活动(例如，汽车尾气)产生的。气溶胶很重要，因为它们可以改变地球的反射率，改变气候系统可用的短波能量，还可以吸收短波和长波辐射。近年来的研究表明，大气中的粉尘对大气顶部和地表的能量平衡有很大的影响。研究还表明，沙尘可能通过加热沙尘层来改变大气的温度结构。沙尘负荷的变化，例如由沙漠沙尘暴引起的变化，可能会影响区域环流模式，并对飓风等重要天气现象的发展产生影响。在更长的时间尺度上，在气候变化(例如荒漠化)下发生的土地利用变化可能会增加粉尘产生，并进一步扰乱我们的气候。粉尘的数量和颗粒大小在空间和时间上差异很大，因此很难量化其对能量平衡的总体影响。该项目的目的是汇集各种来源的新观测资料，研究尘埃气溶胶在真实大气中的辐射效应。这项研究发生在撒哈拉沙漠，这是世界上最重要的尘埃源。新的观测来源之一是位于赤道上方地球静止轨道上的气象卫星8号卫星和格林威治子午线。机上搭载了两台新仪器：地球同步辐射预算实验(GERB)和旋转增强型可见光和红外成像仪(SEVIRI)，前者旨在测量地球的能量平衡，后者可以提供有关尘埃气溶胶的信息。由于这颗卫星是对地静止的，GERB和SEVIRI不断地观察非洲，可以非常详细地监测尘埃爆发。其他卫星观测增加了不同的信息，如气溶胶的垂直分布，这对我们理解辐射效应很重要。通过合并来自所有这些传感器的信息，将获得非洲和大西洋上空尘埃-大气相互作用的全面图景。2006年期间，将在西北部非洲和大西洋开展一些特别运动，目的是利用地面和飞机测量来确定大气状况。这些观测都将被用来确定尘埃的数量、范围和可变性、相关的大气条件以及对区域辐射平衡的总体影响。最后，为了帮助解释观测结果，英国气象局的同事将提供沙尘事件、气象条件和辐射场的模拟。最后，我们希望对这些令人着迷的沙尘暴可能如何影响我们的气候，以及这种影响可能如何随着时间的推移而变化有一个更全面的了解。

The Sun is the fundamental energy source driving weather and climate. In the global mean, there is a balance between the shortwave solar radiative energy absorbed by the Earth system, and the longwave thermal radiative energy emitted by the Earth to space. Any process that changes this equilibrium has the potential to alter our weather and climate. One class of processes involve atmospheric aerosols, small liquid or solid particles, found in the atmosphere naturally (e.g. as wind blown dust), and also generated by a variety of human activities (e.g. from car exhausts). Aerosols are important because they can change the reflectivity of the Earth, altering the amount of shortwave energy available to the climate system, and can also absorb both shortwave and longwave radiation. Recently it has been shown that airborne dust can exert a large effect on the energy balance at the top of the atmosphere and the surface. Studies also suggest that the dust may alter the temperature structure of the atmosphere through heating of the dust layer. A change in dust loading, for example caused by a desert dust storm, can affect regional circulation patterns, with implications for the development of important weather phenomena such as hurricanes. On longer timescales, changes in land use occurring under climate change (e.g. desertification) could increase dust production and further perturb our climate. Dust amount and particle size vary greatly in space and time, making it difficult to quantify its overall effect on the energy balance. The aim of this project is to bring together new observations from a variety of sources to study just what the radiative effect of dust aerosol is in the real atmosphere. This study takes place in the Sahara, the most important dust source in the world. One of the new sources of observations is the Meteosat-8 satellite, located in geostationary orbit at a point over the equator, and the Greenwich meridian. On board are two novel instruments: Geostationary Earth Radiation Budget experiment (GERB), designed to measure the Earth's energy balance, and the Spinning Enhanced Visible and Infrared Imager (SEVIRI), which can provide information about dust aerosols. Because the satellite is geostationary GERB and SEVIRI see Africa continuously and can monitor dust outbreaks in great detail. Other satellite observations add different information, such as the vertical distribution of aerosol, which is important for our understanding of the radiative effects. By merging information from all of these sensors a comprehensive picture of dust-atmosphere interactions over Africa and the Atlantic will be obtained. During 2006 a number of special campaigns will take place over north-west Africa and the Atlantic, aimed at characterizing the atmospheric state using ground-based and aircraft measurements. These observations will all be used to determine the amount, extent and variability of the dust, the associated atmospheric conditions and the total effect on the regional radiative balance. Finally, to help with the interpretation of the observations, colleagues at the UK Meteorological Office will provide simulations of the dust events, meteorological conditions and radiative fields. In the end, we hope to have developed a much more complete understanding of how these fascinating dust storms might be influencing our climate, and how this might be changing with time.