Studying Ice and Mixed Phase clouds using Laboratory EXperiments - SIMPLEX

在任何时候，地球上的云层覆盖率平均在70%左右，在某种程度上，它们可能会使地球变暖或变冷。我想英国的每个人都熟悉云层阻挡太阳光线并使其变冷，厚厚的液体云通常通过将太阳辐射反射回太空来做到这一点。然而，大气中的高空冰云实际上可能通过捕获和释放热辐射而在地表造成变暖效应。冷却冰和加热冰的相对数量取决于高云中冰粒子的数量和大小。我们目前对真实大气的测量无法量化这些云的辐射特性，因为目前从飞机上测量小冰粒的仪器存在困难。降水也是气候变化的一个重要因素，其中冰粒发挥了巨大作用。早在1789年，本杰明·富兰克林（Benjamin Franklin）就提出：“当雨水到达地球表面时，大部分雨水在开始下降时可能是雪……”这是千真万确的，目前的估计表明，热带地区的大部分降水是由冰期造成的（60%）。在我们生活的地球大气层中，温度随着高度的升高而显著降低。此外，人们还必须考虑冰雹风暴每年对农作物造成的损害。认为冰粒是在温度低于0摄氏度时形成的，这是一个普遍的误解。目前的理论表明，只有当液态水含有足够的杂质时，这种现象才会发生。例如，当水接触到肮脏的表面，比如地面，甚至车窗——即使你的车窗是干净的，它们仍然含有足够的杂质来形成冰晶——水就会结冰。然而，在大气中，水滴处于非常纯净的状态，直到温度低至-35℃时，它们中的大多数才会冻结。但是大气中有一些杂质，尽管很少，如果这些颗粒包含在云中，那么冰粒将在零下5摄氏度的温度下形成。问题是，单凭这些杂质的数量并不能解释在云中观测到的冰粒子的数量。人们提出了几种理论来解释这一点，其中一些理论有很好的实验证据。然而，为了准确地评估气候变化，我们需要定量地确定它们的重要性。这项工作将通过在模拟实验室条件下了解雪的形成效率，并进行冰粒子形成的物理实验，寻求解决上述三个问题。曼彻斯特大学地球、大气与环境科学学院的科学家们将在一个所谓的冰落室中制造出真实的云。他们将模拟自然云形成本身的物理过程，并使用最先进的仪器探测云中的粒子。通过了解基础物理学，他们将能够与英国气象局和其他大学合作，更好地了解气候变化问题。曼彻斯特大学的科学家们还寻求与赫特福德大学、德国和美国的顶尖科学家合作，以便在这一领域取得进展。

At any one time cloud coverage over the earth is around 70% on average and to some extent they may warm or cool the planet. I think everybody in the UK is familiar with clouds blocking the suns light and making it cooler, thick liquid clouds generally do this by reflecting the suns radiation back to space. However, ice clouds that are high up within the atmosphere may actually cause a warming effect at the surface by trapping and emitting thermal radiation. The relative amount of cooling vs heating ice dependent on the number and size of ice particles within high clouds. Our current measurements in the true atmosphere have failed to quantify the radiative properties of these clouds due to current instrumental difficulties in measuring small ice particles from aircraft. Precipitation is also an important factor in climate change and one that ice particles play a huge role in. As early as 1789 Benjamin Franklin suggested that `much of what is rain, when it arrives at the surface of the earth might have been snow when it began its descent...'. And this is very true, current estimates place the ice phase responsible for the majority of precipitation in the tropics (60%). In the part of the earths atmosphere in which we live, temperature decreases significantly with height. Furthermore, one must also consider the annual damage to crop caused by hail storms. It is a wide misconception that ice particles form when the temperature is colder than 0C. The current theories show that this only happens when liquid water has enough impurities. So for example when the water touches a dirty surface like the ground or even a car window - even if your windows are clean they still contain enough impurities to form ice crystals - the water can freeze. However, in the atmosphere water droplets are in a very pure state, and most of them do not freeze until the temperature is as cold as -35C. But there are some impurities albeit few in the atmosphere, and if these particles are contained within the cloud, then ice particles will form at temperatures perhaps as warm as -5C. The problem is that the number of these impurities alone can not explain the number of ice particles that are observed within the cloud. There are several theories that have been put forward to explain this and some have good experimental evidence for them. However, in order to accurately assess climate change we need to quantitatively determine their importance. This work will seek to resolve the three aforementioned problems by gaining an understanding of effiency of snow formation under simulated laboratory conditions and perform experiments looking at the physics of ice particle formation. Scientists at the University of Manchester, School of Earth, Atmospheric and Environmental Sciences will produce realistic clouds in a so called ice-fall chamber. They will simulate the physics of natural cloud formation itself and use state-of-the-science instrumentation to probe the particles within the cloud. By understanding the fundamental physics, they will be able to work with the met office and other universities to better understand the problem of climate change. The Manchester scientists also seek to collaborate with leading scientists from Hertfordshire university, Germany and the US in order to make progress in this area.