Understanding energetic particle effects on atmospheric processes

点击翻译按钮获取中文摘要

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.