First study of the global Nickel and Aluminium Layers in the upper atmosphere (NIALL)

地球大气层的边缘大约在地表以上100公里处，位于一个被称为中间层/低层热层（MLT）的区域。这部分大气受到来自上方以极端紫外线辐射和高能粒子降水形式输入的高能量的影响，以及来自低层大气向上传播的大气重力波的破碎所产生的大致等量的能量。MLT还充当从对流层传播到电离层的波的过滤器，这对空间天气具有重要意义。此外，来自辐射带的高能太阳质子和电子在MLT中产生高活性物质，这些物质随后可被输送到平流层，影响臭氧层并影响对流层气候。由于二氧化碳等温室气体的增加、平流层臭氧的耗损以及大尺度大气环流的变化，MLT对气候变化也极为敏感。然而，这是一个很难进行直接测量的区域，因为它比研究气球或飞机到达的高度高出40多公里，比短寿命卫星轨道至少低100公里。火箭运载的测量确实提供了直接访问，但不适合持续的全球测量。幸运的是，从太空进入大气层的宇宙尘埃粒子的烧蚀使金属原子（如Na和Fe）沉积在海拔90公里左右的层中。这些层可以用地面的激光（激光雷达）和卫星上的光谱仪进行观测，提供有关该地区化学和物理（风、温度、重力波）的详细信息。越来越多的证据表明，对地球气候变化的精确模拟需要具有分辨率高且精确的平流层和中间层的模型，因此高层大气中的金属物种提供了一种观察该地区和测试气候模型准确性的独特方法。这一提议的目的是在MLT中首次研究Ni和Al的化学性质。Ni层最近首次被观察到：它比Na和Fe等被充分研究的层要宽得多，并且Ni原子的浓度比基于其宇宙丰度的预期高10倍以上。这些非常意想不到的特征需要被理解，因为有很明显的潜力来发展镍层的激光雷达观测，作为整个MLT从70到115公里的探针。铝和镍形成了非常有趣的对比。Al-O键非常强，很可能在MLT中存在一层大量的AlO自由基。这个物种在可见光谱的绿色部分有很强的光吸收，因此有一个令人兴奋的前景，使激光雷达观测到AlO和开发一个精确的温度探测器在整个中间层温度范围内。该项目将首先对气相中关键的中性和离子分子反应速率进行一系列实验研究，以了解Ni层的独特特性和AlO层的可能浓度。同时，我们将使用一种新型仪器来模拟从阿连德和默奇森等微米级陨石碎片中烧蚀Ni和Al的过程。由此将建立一个模型，预测这些元素作为位置和季节的函数注入MLT的速率。Ni和Al的化学性质，连同它们的大气消融率，将被放入一个全球化学-气候模型中。人们特别感兴趣的是如何预测Ni层和AlO层对主要太阳风暴、11年太阳周期和过去70年MLT气候变化造成的扰动的反应，并预测到2100年。

The edge of the Earth's atmosphere is approximately 100 km above the surface, in a region known as the mesosphere/lower thermosphere (MLT). This part of the atmosphere is subject to high energy inputs from above in the form of extreme UV radiation and energetic particle precipitation, and a roughly equal amount of energy from breaking atmospheric gravity waves which propagate up from the lower atmosphere. The MLT also acts as a filter of waves that propagate from the troposphere into the ionosphere, which has important implications for space weather. Furthermore, energetic solar protons and electrons from the radiation belts produce highly reactive species in the MLT, which can then be transported down into the stratosphere, affecting the ozone layer and impacting on tropospheric climate. The MLT is also extremely sensitive to climate change, due to the cooling effect of increasing greenhouse gases such as CO2, ozone depletion in the stratosphere, and changes to the large-scale atmospheric circulation. However, it is a difficult region in which to make direct measurements, because it is more than 40 km higher than altitudes reached by research balloons or aircraft, and is at least 100 km lower than short-lived satellite orbits. Rocket-borne measurements do provide direct access, but are unsuitable for sustained global measurements. Fortunately, the ablation of cosmic dust particles entering the atmosphere from space deposits metal atoms such as Na and Fe in layers around 90 km altitude. These layers can be observed with lasers from the ground (lidar) and by satellite-borne spectrometers, providing detailed information about the chemistry and physics (wind, temperature, gravity waves) of the region. There is increasing evidence that accurate simulations of changes to the Earth's climate require models with a well resolved and accurate stratosphere and mesosphere, and so metal species in the upper atmosphere offer a unique way of observing this region and of testing the accuracy of climate models.The purpose of this proposal is to make the first ever study of Ni and Al chemistry in the MLT. The Ni layer has recently been observed for the first time: it is much broader than the well-studied layers such as Na and Fe, and the concentration of Ni atoms is more than 10 times higher than expected based on its cosmic abundance. These very unexpected features need to be understood, since there is the clear potential to develop lidar observations of the Ni layer as a probe of the entire MLT from 70 to 115 km. Aluminium makes a very interesting contrast with Ni. The Al-O bond is so strong that it is very likely there is a substantial layer of the AlO radical in the MLT. This species has a strong optical absorption in the green part of the visible spectrum, and so there is the exciting prospect of making lidar observations of AlO and developing an accurate temperature probe over the full range of mesospheric temperatures.The project will involve first making a series of experimental studies of key neutral and ion-molecule reaction rates in the gas phase, in order to understand the unique characteristics of the Ni layer and the likely concentration of the AlO layer. At the same time, we will use a novel instrument to simulate the ablation of Ni and Al from micron-sized fragments of meteorites such as Allende and Murchison. From this a model will be developed which predicts the injection rates of these elements into the MLT as a function of location and season. The chemistry of Ni and Al, together with their meteoric ablation rates, will then be placed into a global chemistry-climate model. Of particular interest will be to see how the Ni and AlO layers are predicted to respond to perturbations caused by major solar storms, the 11-year solar cycle, and climate change in the MLT over the past 70 years and projected forward to 2100.