Swenson G R, Vargas F, Jones M, Zhu Y, Kaufmann M, Yee J H, Mlynczak M
Department of Electrical and Computer Engineering University of Illinois Urbana IL USA.
Space Science Division U.S. Naval Research Laboratory Washington DC USA.
J Geophys Res Atmos. 2021 Dec 16;126(23):e2021JD035343. doi: 10.1029/2021JD035343. Epub 2021 Dec 6.
Atomic oxygen (O) in the mesosphere and lower thermosphere (MLT) results from a balance between production via photo-dissociation in the lower thermosphere and chemical loss by recombination in the upper mesosphere. The transport of O downward from the lower thermosphere into the mesosphere is preferentially driven by the eddy diffusion process that results from dissipating gravity waves and instabilities. The motivation here is to probe the intra-annual variability of the eddy diffusion coefficient (k ) and eddy velocity in the MLT based on the climatology of the region, initially accomplished by Garcia and Solomon (1985, https://doi.org/10.1029/JD090iD02p03850). In the current study, the intra-annual cycle was divided into 26 two-week periods for each of three zones: the northern hemisphere (NH), southern hemisphere (SH), and equatorial (EQ). Both 16 years of SABER (2002-2018) and 10 years of SCIAMACHY (2002-2012) O density measurements, along with NRLMSIS 2.0 were used for calculation of atomic oxygen eddy diffusion velocities and fluxes. Our prominent findings include a dominant annual oscillation below 87 km in the NH and SH zones, with a factor of 3-4 variation between winter and summer at 83 km, and a dominant semiannual oscillation at all altitudes in the EQ zone. The measured global average k at 96 km lacks the intra-annual variability of upper atmosphere density data deduced by Qian et al. (2009, https://doi.org/10.1029/2008JA013643). The very large seasonal (and hemispherical) variations in k and O densities are important to separate and isolate in satellite analysis and to incorporate in MLT models.
中层大气和低热层（MLT）中的原子氧（O）是由低热层光解离产生与中层上部复合化学损失之间的平衡形成的。O从低热层向下传输到中层主要由重力波耗散和不稳定性导致的涡动扩散过程驱动。本文的目的是基于该区域的气候学研究结果，探究MLT中涡动扩散系数（k ）和涡动速度的年内变化，该研究最初由加西亚和所罗门（1985年，https://doi.org/10.1029/JD090iD02p03850）完成。在当前研究中，将北半球（NH）、南半球（SH）和赤道（EQ）三个区域的年内周期划分为26个两周时段。利用16年的SABER（2002 - 2018年）和10年的SCIAMACHY（2002 - 2012年）O密度测量数据，以及NRLMSIS 2.0来计算原子氧涡动扩散速度和通量。我们的主要发现包括：在NH和SH区域87公里以下存在显著的年振荡，在83公里处冬季和夏季之间变化幅度为3 - 4倍；在EQ区域所有高度存在显著的半年振荡。在96公里处测量的全球平均k 缺乏钱等人（2009年，https://doi.org/10.1029/2008JA013643）推导的高层大气密度数据的年内变化。k 和O密度非常大的季节（和半球）变化对于卫星分析中的分离和隔离以及纳入MLT模型很重要。
