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

地球大气层的边缘距离地表约100公里，位于一个被称为中间层/低热层（MLT）的区域。这部分大气受到来自上方的高能量输入，其形式为极端紫外线辐射和高能粒子沉淀，以及来自从低层大气向上传播的破碎大气重力波的大致等量的能量。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中产生高度反应性的物质，然后这些物质可以向下输送到平流层，影响臭氧层并影响对流层气候。MLT对气候变化也非常敏感，这是由于二氧化碳等温室气体增加的冷却效应，平流层臭氧消耗以及大规模大气环流的变化。然而，这是一个难以进行直接测量的区域，因为它比研究气球或飞机所达到的高度高出40多公里，比短寿命卫星轨道至少低100公里。火箭载测量确实提供了直接的获取，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消融将Na和Fe等金属原子沉积在大约90公里高度的层中。这些层可以用地面激光（激光雷达）和星载光谱仪观察，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，精确模拟地球气候变化需要具有良好分辨率和精确的平流层和中间层模型，因此高层大气中的金属物种提供了一种独特的方法来观察这一区域并测试气候模型的准确性。该提案的目的是在MLT中首次研究Ni和Al化学。Ni层最近首次被观测到：它比Na和Fe等已被充分研究的层宽得多，Ni原子的浓度比基于其宇宙丰度的预期高出10倍以上。这些非常意想不到的功能需要理解，因为有明确的潜力，开发激光雷达观测镍层作为整个MLT从70到115公里的探测。铝与镍形成了非常有趣的对比。Al-O键是如此的强，以至于在MLT中很可能存在大量的AlO自由基层。该物种在可见光谱的绿色部分具有很强的光吸收，因此，对AlO进行激光雷达观测和开发在整个中间层温度范围内的精确温度探测器具有令人兴奋的前景。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，以便理解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镍和铝从阿连德和默奇森等陨石的微米级碎片中的烧蚀。由此将开发一个模型，该模型预测这些元素作为位置和季节的函数注入MLT的速率。镍和铝的化学性质，以及它们的流星消融率，将被放入一个全球化学-气候模型。特别令人感兴趣的是，将看到镍和铝层预测如何响应大太阳风暴，11年太阳周期，以及在过去70年的MLT气候变化所造成的扰动，并预计到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.