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Photochemical escape on Mars during the global dust storm and the solar flare

Presentation #318.08 in the session Mars’s Story as Told and Influenced by Dust and Water (Oral Presentation)

Published onOct 23, 2023
Photochemical escape on Mars during the global dust storm and the solar flare

Atmospheric escape is crucial for driving the long-term climate evolution and habitability on Mars. Traditional studies usually focused on the long-term variations of atmospheric escape on Mars with solar radiation or Martian seasons. However, the variability of atmospheric escape with short-term drivers, such as the dust storm and solar flare, have not been thoroughly investigated. With the aid of multi-instrument measurements made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft as well as a one-dimensional Monte Carlo model, we have evaluted the effects of the 2018 global dust storm (GDS) and the 2017 X8.2 solar flare on the photochemical escape of hot atomic C, N, and O on Mars.

During the GDS, our calculations suggest that the C, N, and O escape rates are generally reduced by ~30-40% relative to the quiet, pre-GDS state, in direct contrast to the well-known result of GDS-induced strong enhancement of atomic H escape. During the solar flare, we find a modest decrease in the C escape rate of 8% about 1 h after the flare peak, followed by a recovery to the pre-flare level several hours later. However, an opposite trend is found for the N escape rate during the same period, which shows an increase of 20% followed by a recovery to the pre-flare level.

We further propose that the above variations of photochemical escape essentially reflects the competition between two effects: the modification of hot atom production (enhancement for photodissociation or reduction for dissociative recombination) driven by the variation of the background atmosphere and the reduction of escape probability due to atmospheric expansion. During the GDS, the latter is usually more effective and responsible for the overall reduction of photochemical escape on Mars. During the solar flare, the former dominates the atomic N and O escape, while the latter dominates the atomic C escape.

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