Variability of neutral temperature in the high-latitude upper atmosphere

高纬度高层大气中性温度的变化

• 批准号: NE/N004051/1
• 负责人: Daniel Whiter
• 金额: $ 48.16万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FN004051%2F1
• 关键词: Variability; neutral; temperature; latitude; upper; Variability; neutral; temperature; latitude; upper

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.

高纬度地区的高层大气是一个被电子和质子轰炸的区域，这些区域是极光的来源，在黑暗的天空中通常被视为壮观的颜色和动态的灯光。我们仪器所在的Svalbard上的Aurora（LAT 78.2 N，LON 16.0 E）具有特殊的特性，使其成为研究上层气氛的理想场所。该位置尤其重要，因为它在冬季的白天是黑暗的，这是这个北端最北端的特殊属性。发出的光的颜色或发光的波长取决于传入颗粒的能量，以及在颗粒通过期间如何损失的能量，以及颗粒穿过的大气的组成。结果，特定波长的光学测量可以提供有关大气以及关于沉淀种群的能量的详细信息。此项目将使用高级设计光谱仪，可同时对不同的波长进行测量。一种发射来自激发的氧离子O+，它是低能电子沉淀的标志（通常是能量约为100 eV的电子），并且高度约为300 km。我们最近发现（Whiter等人AP.J 2014），在Aurora中产生O+离子的过程具有一些特殊的特性，因此，发射可用于获得其发射的区域中O原子的温度。该温度称为中性温度，到目前为止，在极光区域并不容易测量。该项目提供了一种令人兴奋的新方法，以量化极光能量输入过程中发生的变化，并将这些变化与建模研究以及现有经验模型进行比较，而现有经验模型已知具有较大的不确定性。中性温度是研究更多全球尺度变化的重要参数，尽管我们的研究来自一个特定位置，但我们使用的数据在2003年以来在黑暗的时间内一直是连续的。我们测量的另一个发射来自羟基分子，这些发射受超紫罗兰辐射激发的羟基分子。该发射被称为气流，来自高度85-90公里的地区，被称为中间。这些排放的精确测量可用于在这些高度处获得大气温度。因此，我们可以将这些观察值添加到上述（从约300公里）中所描述的观察结果，以确定是否存在任何相关性，然后尝试了解该机制可能是什么。在大气中移动稍高的位置，最强的排放之一是分子氮的峰值发射高度在100-150 km之间。我们已经开发了发射的“合成光谱”，这是发射光谱形状的理论解。这种形状取决于分子的温度，因此我们可以使测量光谱与理论上的最佳拟合，以估计发射高度处的中性温度。因此，我们可以根据极光条件来测量三个不同高度的中性温度。从本文中，我们将利用非常高的分辨率极光摄像机，我们在北极在靠近光谱仪的北极进行操作。 AUS（极光结构和动力学）摄像机在约5x5 km（高度100 km）的框架中提供了极高的时间和空间分辨率（1/32 s和10 m）图像。问答由三个相机组成，它们在不同的波长下提供相同的图像，这些摄像机与建模相结合，用于在极光结构中找到能量输入。沉淀带电颗粒的空间和时间变化是极性上层大气行为的物理学的核心。