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- Title
Enhanced Densities in the Martian Thermosphere Associated With the 2018 Planet‐Encircling Dust Event: Results From MENCA/MOM and NGIMS/MAVEN.
- Authors
Venkateswara Rao, N.; Gupta, Neha; Kadhane, Umesh R.
- Abstract
Response of the Martian upper thermosphere to the lower atmospheric dust activity is studied using unique observations made together by the Mars Orbiter Mission (MOM) and the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. The Mars Exospheric Neutral Composition Analyzer (MENCA)/MOM and the Neutral Gas and Ion Mass Spectrometer (NGIMS)/MAVEN have simultaneously (on the same day) measured the neutral densities in the Martian thermosphere on 5, 8, 10, 13, 16, and 29 June 2018. The measurement period falls in the onset and progression time of the planet‐encircling dust event (PEDE) in the Mars lower atmosphere. During this time, the inbound trajectories of MAVEN and MOM spacecraft occurred on the dawnside and duskside, respectively. Using these observations, we found that thermospheric densities both on the dawnside and duskside are enhanced associated with the onset and growth of PEDE‐2018. The enhancement, however, is more on the duskside than on the dawn, showing the dawn‐dusk asymmetry. The densities on the duskside reach their maximum on 29 June 2018, close to the time of peak dust activity. These results are explained by considering the local time asymmetries in radiative heating of the lower atmosphere and subsequent expansion of the thermosphere due to PEDE‐2018. Furthermore, O/CO2 ratios below 220‐km altitude become one on the dawnside, whereas they are always <0.2 at the dusk. This indicates that radiative cooling is more effective on the dawnside than the duskside. Plain Language Summary: Characterizing the Martian upper atmosphere is extremely important as it acts as a buffer zone for escape of its gases to outer space. Toward achieving this goal, NASA's Mars Atmosphere and Volatile Evolution (MAVEN) and ISRO's Mars Orbiter Mission (MOM) spacecraft have been providing valuable information of the Martian upper atmosphere. During 5–29 June 2018, these spacecraft have made simultaneous observations of the Martian upper atmosphere such that MAVEN was on the morningside while MOM was on the eveningside. Both the spacecraft have observed a significant increase in neutral densities in the Martian upper thermosphere (150–220 km) associated with the development of a global dust storm in the lower atmosphere. The increase, however, is larger in the evening time than in the morning. The largest changes are observed when the lower atmospheric dust activity is at its peak. These upper atmospheric changes are interpreted as due to warming and expansion of the Martian thermosphere due to radiative heating of the dust aerosols in the lower atmosphere. Furthermore, the observations suggest that radiative cooling of the Martian thermosphere, due to collisions between O and CO2, is more effective in the morning hours than in the evening. Key Points: The upper thermosphere of Mars is investigated using simultaneous observations by NGIMS/MAVEN on the dawnside and MENCA/MOM on dusksideThermospheric densities on both the terminator sides show enhancement during the onset and growth of the 2018 planet‐encircling dust eventThe enhancement is larger on the duskside than on the dawnside, particularly during the mature phase of the dust event
- Subjects
THERMOSPHERE; EARTH sciences; WIND pressure; THERMOPHYSICAL properties; TOPOGRAPHY
- Publication
Journal of Geophysical Research. Planets, 2020, Vol 125, Issue 10, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2020JE006430