Atomic oxygen in the mesosphere and lower thermosphere of the Earth

原子氧（O）是地球大气的重要组成部分。它从中间层延伸到低热层，即从大约80公里到500公里以上的高度。O是通过紫外线辐射光解分子氧而产生的。它是MLT中最丰富的物种，也是MLT光化学的重要组成部分。此外，O对于MLT的能量收支是重要的，因为CO2分子通过与O的碰撞而被激发，并且被激发的CO2分子在红外线中辐射并冷却MLT。这意味着全球气候变化也会影响MLT，因为MLT中CO2浓度的增加会导致更有效的冷却，从而导致MLT的收缩。O浓度受动力运动、垂直输送、潮汐和风的影响。因此，准确了解O的全球分布及其浓度廓线以及日变化和年变化对于理解MLT的光化学、能量收支和动力学是必不可少的。本建议的目标是确定柱密度和浓度分布的O在MLT使用精细结构的转变在4.74太赫兹和2.06太赫兹。这些将被分析的数据是用索菲亚平流层红外天文观测台上的GREAT/upGREAT（德国太赫兹天文接收器）外差光谱仪测量的。这是一种直接观测方法，可能会产生更准确的结果比现有的间接卫星为基础的方法，涉及光化学模型，以获得O浓度分布。该仪器从2014年5月开始提供约500，000个光谱的数据库，覆盖四个不同的地理位置，即北美、新西兰、欧洲和塔希提岛/太平洋。将研究时间变化以及太阳周期、风和重力波的影响。这些结果将与卫星数据进行比较，这些数据可用于80至100公里的高度，并与半经验模型的预测进行比较。应该指出的是，这些数据是第一次光谱解析，直接测量的O在MLT。这是一个有前途的替代方法相比，间接的卫星为基础的方法，依赖于光化学模型的O浓度的测定。

Atomic oxygen (O) is an important component of the Earth’s atmosphere. It extends from the mesosphere to the lower thermosphere (MLT), i.e. from approximately 80 km to beyond 500 km in altitude. O is generated through photolysis of molecular oxygen by UV radiation. It is the most abundant species in the MLT and an important component with respect to the photochemistry of the MLT. In addition, O is important for the energy budget of the MLT, because CO2 molecules are excited by collisions with O and the excited CO2 molecules radiate in the infrared and cool the MLT. This means that global climate change also affects the MLT, because the increase of the CO2 concentration in the MLT leads to a more efficient cooling and consequently shrinking of the MLT. The O concentration is affected by dynamical motions, vertical transport, tides, and winds Therefore, an accurate knowledge of the global distribution of O and its concentration profile as well as diurnal and annual variations are essential for understanding the photochemistry, the energy budget and the dynamics of the MLT. The goal of this proposal is to determine column densities and concentration profiles of O in the MLT using the fine structure transitions at 4.74 THz and 2.06 THz. The data, which will be analyzed, are measured with the GREAT/upGREAT (German REceiver for Astronomy at Terahertz frequencies) heterodyne spectrometer on board of SOFIA, the Stratospheric Observatory for Infrared Astronomy. This is a direct observation method which may yield more accurate results than existing indirect satellite-based methods which involve photochemical models in order to derive O concentration profiles. This instrument provides a data base with approximately 500,000 spectra starting in May 2014 and covering four different geolocations, namely North America, New Zealand, Europe and Tahiti/Pacific. Temporal variations as well as the influence of solar cycles, winds and gravity waves will be studied. The results will be compared with satellite data, which are available for altitudes from 80 to 100 km, and with predictions from a semi-empirical model. It should be noted that these data are the first spectrally resolved, direct measurement of O in the MLT. This is a promising alternative for the determination of the O concentration compared to indirect satellite-based methods, which rely on photochemical models.