MAVEN/NGIMS Thermospheric Neutral Wind Observations: Interpretation Using the Mâ GITM General Circulation Model
Roeten, Kali J.; Bougher, Stephen W.; Benna, Mehdi; Mahaffy, Paul R.; Lee, Yuni; Pawlowski, Dave; González‐galindo, Francisco; López‐valverde, Miguel Ángel
2019-12
Citation
Roeten, Kali J.; Bougher, Stephen W.; Benna, Mehdi; Mahaffy, Paul R.; Lee, Yuni; Pawlowski, Dave; González‐galindo, Francisco ; López‐valverde, Miguel Ángel (2019). "MAVEN/NGIMS Thermospheric Neutral Wind Observations: Interpretation Using the Mâ GITM General Circulation Model." Journal of Geophysical Research: Planets 124(12): 3283-3303.
Abstract
Using a new observational technique, the NGIMS (Neutral Gas and Ion Mass Spectrometer) instrument on the MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft has the unique capability to measure horizontal thermospheric winds. Measured along the orbit track from periapsis (â ¼150Â km) to â ¼200Â km, these are the first in situ observations of thermospheric winds at Mars. Significantly, this also means that simulated winds from a global circulation model can be compared to in situ observations from this part of the Martian atmosphere for the first time. In this study, observations from five NGIMS neutral wind campaigns have been compared to simulations from the Mars Global Ionosphereâ Thermosphere Model (Mâ GITM), a ground to exosphere 3â D general circulation model. By comparing NGIMS neutral wind observations to model simulations, the processes driving the winds and their variations in the upper atmosphere are examined. These comparisons show that for certain observational periods, the Mâ GITM simulated winds can generally replicate the magnitude and/or direction of the NGIMS wind observations, while in others, significant differences occur. In general, wind observations from NGIMS campaigns with large orbitâ toâ orbit variability are not well replicated by Mâ GITM, while campaigns with higher observed wind speeds are better captured by the model. Additionally, using these dataâ model comparisons, the relative role of normal solar forcing and corresponding differential heating in driving thermospheric winds at Mars is found to be variable, likely acting as the primary driver under some conditions and secondary to other physical processes under others.Plain Language SummaryThe MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft, which is currently in orbit around Mars, has been taking monthly measurements of the speed and direction of the winds in the upper atmosphere of Mars between about 150 and 200 km above the surface. The observed wind speeds and directions change with time and location, and sometimes fluctuate quickly. These measurements are compared to simulations from a computer model of the Mars atmosphere called Mâ GITM (Mars Global Ionosphereâ Thermosphere Model). This is the first comparison between direct measurements of winds in the upper atmosphere of Mars and simulated winds and is important because it can help to inform us what physical processes are acting on the observed winds. Some wind measurements have similar wind speeds or directions to those predicted by the Mâ GITM model, but sometimes, there are large differences between the simulated and measured winds. The disagreements between wind observations and model simulations suggest that processes other than normal solar forcing may become relatively more important during these observations and alter the expected circulation pattern. Understanding the processes that drive the winds in the upper atmosphere of Mars provides key context for understanding how the atmosphere behaves as a whole system.Key PointsNew thermospheric wind observations at Mars are compared to a global circulation model for the first timeWinds during observational campaigns with high average wind speeds and little variability were best replicated in model simulationsDataâ model disagreements suggest processes other than normal solar forcing may become important and alter the expected circulation patternPublisher
International Workshop Wiley Periodicals, Inc.
ISSN
2169-9097 2169-9100
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