Variability of neutral temperature in the high-latitude upper atmosphere

高纬度的高层大气受到电子和质子的轰击，这是极光的来源，通常被视为黑暗天空中壮观的彩色和动态灯光。我们的仪器所在的斯瓦尔巴群岛(北纬78.2度，东经16.0度)上空的极光具有特殊的性质，使其成为研究高层大气的理想地点。这个位置特别重要，因为在冬季的几个月里，白天是黑暗的，这是这个最北端的地方的一个特殊性质。极光的颜色，或发出的光的波长，既取决于进入的粒子的能量，也取决于粒子通过过程中能量损失的方式，以及粒子通过的大气组成。因此，对特定波长的光学测量可以提供关于大气和降水种群能量的详细信息。这个项目将使用一种先进设计的光谱仪，同时对一系列不同波长进行测量。一种发射来自激发氧离子O+，这是低能电子沉淀(通常能量约为100 eV的电子)的特征，其峰值亮度约为300公里高。我们最近发现(Whiter等人，2014年4月)，在极光中产生O+离子的过程具有一些特殊的性质，因此可以利用发射来获得O原子在发射区域的温度。这一温度被称为中性温度，在极光区域迄今并不容易测量；该项目提供了一种令人振奋的新方法来量化极光能量输入期间发生的变化，并将这些变化与模型研究以及已知具有很大不确定性的现有经验模型进行比较。中性温度是研究更多全球尺度变化的一个重要参数，虽然我们的研究是从一个特定的位置进行的，但我们使用的数据自2003年以来一直在黑暗时间内连续进行。我们测量的另一种发射来自于紫外线辐射激发的羟基分子。这种辐射被称为气辉，来自大约85-90公里高的区域，也就是所谓的中层顶。对这些排放物的精确测量可以用来获得这些高度的大气温度。因此，我们可以将这些观测结果添加到上面描述的(从大约300公里处)，以确定是否存在任何关联，然后尝试了解可能的机制。在大气层中移动到稍微高一点的地方，最强的排放之一是来自分子氮的排放，它的峰值排放高度在100-150公里之间。我们开发了发射的“合成光谱”，这是发射光谱形状的理论解。这种形状依赖于分子的温度，所以我们可以将测量的光谱与理论进行最好的拟合，以便估计发射高峰期的中性温度。因此，根据极光条件，我们有可能在三个不同的高度测量中性温度。最后，我们将利用我们在北极靠近光谱仪的地方操作的非常高分辨率的极光相机。ASK(极光结构和动力学)相机提供了高时间和空间分辨率(1/32 S和10米)的极光图像，帧长约5x5千米(在100千米高度)。ASK由三个相机组成，它们在不同的波长下提供相同的图像，与建模相结合，用于寻找极光结构内的能量输入。沉淀带电粒子的空间和时间变异性是极地高层大气行为物理的核心。

The upper atmosphere at high latitudes is a region which is bombarded by electrons and protons, which are the source of the aurora, often seen as spectacular coloured and dynamic lights in the dark sky. The aurora over Svalbard (lat 78.2 N, lon 16.0 E) where our instruments are located, has special properties which make this an ideal place to study the upper atmosphere. The location is particularly important because it is dark during the daytime in the winter months, a special property of this most northerly site. The colour of the aurora, or wavelength of the light emitted, depends on both the energy of the incoming particles and how that energy is lost during the passage of the particles, and on the composition of the atmosphere that the particles travel through. As a result, optical measurements of specific wavelengths can provide detailed information about the atmosphere, and about the energy of the precipitating populations.This project will use an advanced design spectrograph which makes measurements over a range of different wavelengths simultaneously. One emission is from excited oxygen ions O+, which is a signature of low energy electron precipitation (typically electrons with energies of about 100 eV) and has a peak brightness at around 300 km in height. We have discovered recently (Whiter et al Ap.J 2014) that the processes that produce the O+ ion in aurora have some special properties, and as a result the emission can be used to obtain the temperature of the O atoms in the region where they emit. This temperature is known as the neutral temperature, which in the auroral region has not been easy to measure so far; this project provides an exciting new method to quantify the changes that occur during auroral energy input, and to compare these changes to modelling studies and also to existing empirical models, which are known to have large uncertainties. The neutral temperature is an important parameter for studying changes on more global scales, and although our studies are from one specific location, the data we are using has been continuous during the dark hours since 2003.Another emission that we measure is from hydroxyl molecules which are excited by ultra violet radiation. The emission is known as airglow, and is from a region around 85-90 km in height, known as the mesopause. Precise measurements of these emissions can be used to obtain the temperature of the atmosphere at these heights. Consequently, we can add these observations to those described above (from around 300 km) to determine if there are any correlations, and then try to understand what the mechanisms may be. Moving a little higher up in the atmosphere, one of the strongest emissions is from molecular nitrogen, which has a peak emission height of between 100-150 km. We have developed a "synthetic spectrum" of the emission, which is a theoretical solution of the shape of the emission spectrum. This shape is dependent on the temperature of the molecules, and so we can make a best fit of the measured spectrum to the theoretical, in order to estimate the neutral temperature at the height of the emission. In combination we therefore have the possibility of measuring the neutral temperature at three distinct heights, depending on the auroral conditions.Finally we will make use of very high resolution auroral cameras which we operate in the arctic close to the spectrograph. The ASK (Auroral Structure and Kinetics) cameras provide high time and spatial resolution (1/32 s and 10 m) images of the aurora in a frame approximately 5x5 km (at 100 km altitude). ASK consists of three cameras which provide the same image at different wavelengths which, in combination with modelling, are used to find the energy input within the auroral structure. The spatial and temporal variability of precipitating charged particles is at the heart of the physics of the behaviour of the polar upper atmosphere.