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Lower Thermospheric Material Transport via Lagrangian Coherent Structures.
Seebany Datta-Barua1, Nicholas Pedatella2, Katelynn Greer3
1Department of Mechanical, Materials, and Aerospace Engineering Illinois Institute of Technology Chicago IL USA.
Journal of Geophysical Research. Space Physics
|July 22, 2022
Summary
Model differences in lower thermosphere transport, revealed by Lagrangian Coherent Structures (LCSs), challenge accurate prediction. These LCSs highlight how model variations impact material transport, even when mean winds appear similar.
Area of Science:
- Atmospheric Science
- Space Physics
- Computational Fluid Dynamics
Background:
- Accurate prediction of material transport in the lower thermosphere is crucial for understanding atmospheric dynamics.
- Inter-model variations in atmospheric models can lead to uncertainties in transport predictions.
- Lagrangian Coherent Structures (LCSs) offer a robust method for analyzing transport in time-varying flows.
Purpose of the Study:
- To investigate the impact of inter-model variations on predicting material transport in the lower thermosphere.
- To utilize LCSs to identify and quantify differences in transport predictions between atmospheric models.
- To compare model-derived LCSs and tracer transport with observational data.
Main Methods:
- Derived LCSs in the lower thermosphere using model outputs for space shuttle water vapor plume events.
- Compared LCSs derived from Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCMX) against Global Ultraviolet Imager (GUVI) observations.
- Contrasted LCSs and tracer transport between SD-WACCMX and data assimilative WACCMX (WACCMX + DART).
Main Results:
- Inter-model differences in thermospheric transport are more pronounced in LCSs than in mean wind analyses.
- SD-WACCMX predicted LCS spreading not observed in one space shuttle plume event.
- WACCMX + DART showed improved tracer transport for a July 2006 event, but LCS performance comparison was inconclusive.
- Significant LCS and tracer trajectory differences were observed between models for a February 2010 event with large mean wind discrepancies.
- Low-pass filtering winds reduced but did not eliminate inter-model LCS differences; alignment improved at lower altitudes (60 km).
Conclusions:
- Inter-model variations, stemming from observational under-constraint, significantly impact lower thermosphere material transport predictions.
- LCS analysis provides a more sensitive method than mean winds for detecting model transport differences.
- Data assimilation (WACCMX + DART) can improve tracer transport accuracy, but LCS behavior requires further investigation.
- Model resolution and data assimilation strategies are critical for accurate thermospheric transport modeling.
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