Understanding energetic particle effects on atmospheric processes

我们温和的气候使地球上的生命成为可能。为了预测未来我们的气候将如何变化，有必要了解所有可能导致气候变化的过程，包括自然和人为的。气候科学家对人为因素有相当好的把握，但我们对自然变异性对气候变化的贡献的认识存在差距。不确定性的主要来源之一是太阳引起的变化性。太阳的亮度通过加热直接影响地球的气候，并且主要在11年的时间尺度上变化。这一直接影响是相对较好的理解，然而，还有其他间接影响(与太阳输出有关，但在两者之间需要另一个物理过程)被认为影响了地球的气候，但完全没有被很好地理解。如果我们要在预测未来气候变化时准确地考虑太阳影响，那么更好地理解这些间接影响是至关重要的。我的研究将调查太阳变化对大气过程的潜在间接影响之一，即电荷对云的影响。电荷是由银河宇宙射线(GCR)(来自太阳系外的高能粒子)的电离在大气中产生的。当GCR接近地球时，它们会受到太阳和地球磁场的偏转，这对GCR来说是一个选择性的能量屏障。太阳的磁场主要在11年的时间尺度上变化，因此GCR通量，因此大气中的电荷受太阳活动的控制。由于大气中持续不断的电荷垂直流动，电荷在层云的上下边界积累(阴天你会看到非常常见的一种云)。电荷附着在云滴上，这被认为会影响液滴的行为，比如它们如何生长和粘在一起，这可以在云高度等大规模云特性中看到。由于这种云控制着大气中的加热和冷却，并且一次覆盖了大约40%的地球表面，因此云上的电荷效应可能会对气候产生影响。我的研究将调查大气中控制电荷的因素，确定电荷是否在云过程中发挥作用，并最终确定这是否对气候重要。为了表征大气中控制电荷的因素以及层云中存在的典型电荷，将使用一套新开发的传感器进行测量，这些传感器被设计为与传统天气气球一起飞行。这些重量轻、一次性的传感器提供了一种经济高效的方法，可以从全球气象服务机构已经在世界各地发射的气象气球上获取地表以上的额外科学数据。这些空中测量将与世界各地不同地点的电荷和大气电量的地面测量相结合，以了解全球电荷对太阳变率变化的反应。这样的测量很少见，对于理解调节垂直电荷流动的物理机制以及空间天气和低层大气之间的耦合至关重要。这个主题位于物理学和气象学的交叉点上，为我们提供了一个调查过程的机会，我们仍然处于理解的初级阶段。在这一领域有大量令人兴奋的、可能非常重要的基础研究要做，这些研究最终将帮助我们了解这些新的过程是否与气候有关。

Our moderate climate makes life on Earth possible. In order to predict how our climate will change in future, it is necessary to understand all of the processes, both natural and man made, which can contribute to climate change. Climate scientists have a fairly good grasp of the anthropogenic factors, but there are gaps in our knowledge about the contribution to climate change from natural variability. One of the major sources of uncertainty is the variability caused by our sun. The brightness of the sun influences Earth's climate directly by heating, and varies mainly on an 11 year timescale. This direct effect is relatively well understood, however there are other indirect effects (which are linked to solar output, but require another physical process in between) which are thought to influence Earth's climate, and are not at all well understood. It is essential that these indirect effects are better understood if we are to accurately account for solar effects in predicting future climate change. My research will investigate one of the potential indirect effects of solar variability on atmospheric processes, which is the effect of electrical charge on clouds. Charge is created in the atmosphere by ionisation from Galactic Cosmic Rays (GCRs) (highly energetic particles from outside our solar system). When GCRs approach Earth, they are deflected by both the Solar and Earth's magnetic field, which act as a selective energy barrier to GCRs. The sun's magnetic field varies mainly on an 11 year timescale, therefore GCR fluxes, and thus charge in the atmosphere is controlled by solar activity. Due to constant vertical flow of charge in the atmosphere, charge accumulates at the upper and lower boundaries of layer clouds (the very common sort of clouds that you see on an overcast day). The charge sticks to the cloud droplets, which is thought to influence the behaviour of the droplets, such as how they grow and stick together, which can be seen in large scale cloud properties like cloud height. Since such clouds control heating and cooling in the atmosphere, and cover around 40% of the Earth's surface at one time, charge effects on clouds may have implications for climate. My research will investigate the factors that control charge in the atmosphere, determine whether charge plays a role in cloud processes, and ultimately determine whether this is important for climate.In order to characterise the factors controlling charge in the atmosphere, and the typical charge present inside layer clouds, measurements will be made using a suite of newly developed sensors which have been designed to fly alongside conventional weather balloons. These lightweight, disposable sensors provide a cost effective method of obtaining extra science data above the surface, from weather balloons which are already being launched around the world by global meteorological services. These airborne measurements will be combined with surface measurements of charge and atmospheric electricity at various sites around the world to understand the global response of charge to changes in solar variability. Such measurements are rare and are vital to understand the physical mechanisms responsible for modulating vertical charge flow and therefore coupling between Space Weather and the lower atmosphere. This topic sits at the intersection of physics and meteorology and presents an opportunity to investigate processes that we are still very much in our infancy of understanding. There is a great deal of exciting and potentially very important fundamental research to be done in this field, which will ultimately help us to understand whether these new processes are relevant to climate.