During both localized and global dust storms, water is delivered to the upper atmosphere, where it is ionized and dissociated. MAVEN NGIMS measures some of the products of these ionization and dissociation reactions. The delivery of H2O to the upper atmosphere during dust storms increases the rate of H escape to space.
Thermal Structure of the Martian Upper Atmosphere
We derive neutral temperatures from Ar, CO2, and N2 abundances measured by MAVEN NGIMS over 1.5 Martian years. The temperature profiles cover an altitude range of 150 to roughly 300 km on nominal orbits. During Deep Dips, temperature profiles extend down to about 125 km, near the mesopause. We characterize thermospheric gradients and exospheric temperatures. The thermal structure of the Martian upper atmosphere is important for quantifying loss of the atmosphere to space.
Upper Atmospheric H2O and Martian Dust Storms
Each point in the figure above represents the mean relative abundance of the H2O+ ion in the ionosphere of Mars during one MAVEN orbit. The rapid increase in the relative abundance of this ion during Martian dust storms (black boxes) is indicative of the transport of water from the lower atmosphere into the upper atmosphere, where it is ionized and dissociated, eventually producing H. This atomic hydrogen is light enough to escape to space, which means that this delivery of water into the upper atmosphere is important for understanding how Mars is losing its atmosphere over time. The color of each point is roughly representative of the time of day on Mars at which the measurements where obtained: red points correspond to dayside measurements and blue points correspond to nightside measurements.
Manuscript in preparation.
Thermal Structure of the Martian Upper Atmosphere
Figures. (left or top) The diurnal variation of the temperature in the upper atmosphere of Mars, covering an altitude range of ~150-250 km. (right or bottom) Mean temperature profiles for the first 8 Deep Dips executed by the MAVEN spacecraft.
Abstract. The Neutral Gas and Ion Mass Spectrometer (NGIMS) aboard the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measures the structure and variability of the Martian upper atmosphere. We use NGIMS density profiles to derive upper atmospheric temperature profiles and investigate the thermal structure of this region. The thermal structure of the upper atmosphere is a critical component of understanding atmospheric loss to space, the main science objective of MAVEN, and measured temperatures serve as inputs to and constraints on photochemical and global circulation models. We describe proper treatment of the NGIMS data and correct for the horizontal motion of the spacecraft. Temperature profiles from week-long, low-altitude excursions executed by MAVEN, called Deep Dips, are used to investigate the diurnal variation of the temperature and the thermospheric gradient, which varies between 1.33 ± 0.16 and 2.69 ± 0.33 K km−1 on the dayside. NGIMS measurements acquired on nominal MAVEN orbits over more than a Martian year further elucidate the diurnal and latitudinal variations of the temperature. Diurnal variations of about a factor of 2, from 127 ± 8 to 260 ± 7 K, are observed high in the exosphere, and latitudinal variations of 39 ± 17 K are observed in this region. Comparisons indicate broad agreement between temperatures derived from MAVEN NGIMS with previous in situ and remote sensing observations of upper atmospheric temperatures. NGIMS temperatures are also shown to be consistent with predictions of a 1-D model which includes solar UV and near IR heating, thermal conduction, and radiative cooling in the CO2 ν2 15-μm band.
Stone, S. W., R. V. Yelle, M. Benna, M. K. Elrod, P. R. Mahaffy. (2018). Thermal structure of the Martian upper atmosphere from MAVEN NGIMS. Journal of Geophysical Research: Planets, 123, 2842–2867. https://doi.org/10.1029/2018JE005559
At the 2018 Lunar and Planetary Laboratory Conference in Tucson, Arizona, I gave an invited talk on the Martian global dust storm of 2018 and its impact on the upper atmosphere as observed by MAVEN NGIMS.
14 May 2018
52nd ESLAB Symposium
At the 52nd ESLAB Symposium on Comparative Aeronomy and Plasma Environment of Terrestrial Planets in Noordwijk, The Netherlands, I presented on measurements of protonated ions from MAVEN NGIMS and the variation of H2 in the Martian upper atmosphere.
I presented on the thermal structure of the Martian upper atmosphere as observed by MAVEN NGIMS at the International Conference on Mars Aeronomy in Boulder, Colorado.
