Datta-Barua Seebany, Pedatella Nicholas, Greer Katelynn, Wang Ningchao, Nutter Leanne, Harvey V Lynn
Department of Mechanical, Materials, and Aerospace Engineering Illinois Institute of Technology Chicago IL USA.
High Altitude Observatory National Center for Atmospheric Research Boulder CO USA.
J Geophys Res Space Phys. 2021 Sep;126(9):e2020JA028834. doi: 10.1029/2020JA028834. Epub 2021 Sep 9.
We show that inter-model variation due to under-constraint by observations impacts the ability to predict material transport in the lower thermosphere. Lagrangian coherent structures (LCSs), indicating regions of maximal separation (or convergence) in a time-varying flow, are derived in the lower thermosphere from models for several space shuttle water vapor plume events. We find that inter-model differences in thermospheric transport manifest in LCSs in a way that is more stringent than mean wind analyses. LCSs defined using horizontal flow fields from the Specified Dynamics version of the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCMX) at 109 km altitude are compared to Global Ultraviolet Imager (GUVI) observations of the space shuttle main engine plume. In one case, SD-WACCMX predicts an LCS ridge to produce spreading not found in the observations. LCSs and tracer transport from SD-WACCMX and from data assimilative WACCMX (WACCMX + DART) are compared to each other and to GUVI observations. Differences in the modeled LCSs and tracer positions appear between SD-WACCMX and WACCMX + DART despite the similarity of mean winds. WACCMX + DART produces better tracer transport results for a July 2006 event, but it is unclear which model performs better in terms of LCS ridges. For a February 2010 event, when mean winds differ by up to 50 m/s between the models, differences in LCSs and tracer trajectories are even more severe. Low-pass filtering the winds up to zonal wavenumber 6 reduces but does not eliminate inter-model LCS differences. Inter-model alignment of LCSs improves at a lower 60 km altitude.
我们表明，由于观测约束不足导致的模型间差异会影响预测低热层中物质传输的能力。拉格朗日相干结构（LCS）表明了时变流中最大分离（或汇聚）区域，它是从几个航天飞机水汽羽流事件的模型中在低热层推导出来的。我们发现，热层传输的模型间差异在LCS中表现出来的方式比平均风分析更为严格。将在109千米高度使用全大气社区气候模型的指定动力学版本（SD-WACCMX）并带有热层-电离层扩展（SD-WACCMX）的水平流场定义的LCS与航天飞机主发动机羽流的全球紫外成像仪（GUVI）观测结果进行比较。在一个案例中，SD-WACCMX预测一个LCS脊会产生观测中未发现的扩散。将SD-WACCMX和数据同化的WACCMX（WACCMX + DART）的LCS和示踪剂传输相互比较，并与GUVI观测结果进行比较。尽管平均风相似，但SD-WACCMX和WACCMX + DART之间在模拟的LCS和示踪剂位置上仍存在差异。对于2006年7月的一个事件，WACCMX + DART产生了更好的示踪剂传输结果，但不清楚哪个模型在LCS脊方面表现更好。对于2010年2月的一个事件，当模型之间的平均风相差高达50米/秒时，LCS和示踪剂轨迹的差异甚至更加严重。对纬向波数6以下的风进行低通滤波可减少但不能消除模型间的LCS差异。在较低的60千米高度，LCS的模型间对齐有所改善。
