Time‐history influence of global dust storms on the upper atmosphere at Mars

Liemohn, Michael W.; Ava, Dupre,; Bougher, S. W.; Trantham, Matthew; Mitchell, David; Smith, M. D.

doi:10.1029/2012gl051994

Cited by 19 publications

(34 citation statements)

References 27 publications

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“…For the running average case, the time length is around 210 Earth days (approximately 110° Ls at Mars) for most bins. Notice that the time‐history length of the maximum value case is different from Liemohn et al [] (which said 210 Earth days for both cases). It is because the method of determining this window length is different between the two studies.…”

Section: Resultscontrasting

confidence: 63%

“…Figure e is the local EUV proxy, i.e., F 10.7 cm solar flux at Mars multiplying a solar zenith angle‐dependent Chapman function [ Trantham et al , ], against time. The very low values during southern summer [ Liemohn et al , , Figure 1c], when the crustal fields were at LT 2 A.M. but partially illuminated due to the tilt of the planet, are also excluded as the partially illuminated magnetic loops very likely straddle the terminator, and therefore, these fluxes may behave differently. Figures b–d are time‐history dust opacity values against time.…”

Section: Methodsmentioning

confidence: 99%

“…Figures b–d are time‐history dust opacity values against time. Liemohn et al [] came up with two different methods to determine dust storms' long‐term effects, time‐history averages, and maximums of dust opacities within a certain time window. In other words, for a data point, tracing back across a specified time length, either the averaged dust opacity or maximum within this window will be the new value.…”

Section: Methodsmentioning

confidence: 99%

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Mars photoelectron energy and pitch angle dependence on intense lower atmospheric dust storms

Liemohn

Mitchell

et al. 2014

J. Geophys. Res. Planets

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We have conducted a survey of the Mars Global Surveyor (MGS) electron data across all the pitch angles of 12 usable energy bins (11-746 eV) for dayside photoelectron observations over regions of strong crustal fields. Studies have shown that solar EUV flux is the main controlling factor, but dust storms play an important role as well. Our study of different energies and pitch angles has shown that the unusual bimodal solar flux dependence is not a common feature but mainly found in low energies and a few bins of higher-energy channels. By multiplying time-history dust opacity with a solar EUV proxy as a new controlling function, the statistically significant increase of the correlation of photoelectron flux against this function indicates that dust storms have a long-lasting influence on high-altitude photoelectron fluxes, especially at low energies and the pitch angle source regions of high-energy channels. The correlation increases experienced by the pitch angle source regions of all examined energy channels suggest that dust storms' influence most likely happens in the thermosphere-ionosphere source region of the photoelectrons, rather than at exospheric altitudes at or above MGS. Furthermore, by isolating the global-scale dust storm in Mars year 25 (2001) from the rest, the results suggest that this storm is entirely responsible for the second solar flux-dependent trend. While not excluding the possibility of this phenomenon being a one-time event, we hypothesize that there is a threshold of dust opacity at which the low-altitude dust's influence on high-altitude photoelectron fluxes begins to be significant.

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Section: Resultscontrasting

confidence: 63%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Mars photoelectron energy and pitch angle dependence on intense lower atmospheric dust storms

Liemohn

Mitchell

et al. 2014

J. Geophys. Res. Planets

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“…Mars Global Surveyor (MGS) observations of the dayside photoelectrons revealed that dust storms can alter the atmosphere even up to the thermosphere for several months, thereby effecting the production, loss rates, and the flux of the photoelectrons in the upper ionosphere [cf. Liemohn et al ., ]. Large dust storms on Mars grow in the extratropics of southern hemisphere during spring/summer seasons [ Smith et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Long‐term variability of dust optical depths on Mars during MY24–MY32 and their impact on subtropical lower ionosphere: Climatology, modeling, and observations

Sheel

Haider

2016

JGR Space Physics

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Dust optical depths (τ) for nine Martian years (MY24–MY32) in the subtropical region (25–35°S) have been used to classify distinct dust scenarios. These data are based on observations at 9.3 µm from the Mars Global Surveyor and Mars Odyssey missions and encompass the regional dust storms which occur every year around solar longitude (Ls) ~ 220° and the two major dust storms of MY25 and MY28. Constrained by these observations and the Mars Climate Sounder observations of detached dust layers, we estimate altitude profiles of dust concentrations. We discuss the characteristics of dust aerosol particles of different size between 0.2 and 3.0 µm by assuming a modified gamma distribution. We then use a comprehensive ion‐dust model to calculate ion densities and conductivities in the lower ionosphere of Mars in the absence of dust storm at τ = 0.1 and Ls = 150° and for three dust storm periods viz., (1) major dust storm at τ = 1.7 and Ls = 210°, (2) major dust storm at τ = 1.2 and Ls = 280°, and (3) regional dust storm at τ = 0.5 and Ls = 220°. The model with 12 neutral species considers galactic cosmic rays as a source of ionization. Results show that the density of the dominant hydrated cluster ions and the electrical conductivity are reduced by an order of magnitude near the surface for a few months until the dust storm settles down to its normal condition.

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“…We have no definitive answer to this puzzle and merely note two related recent observations. Liemohn et al (2012) found that periods of elevated dayside photoelectron flux at 400 km could be correlated with the average dust opacity over the preceding 7 months. Chaffin et al (2014) used MEX SPI-CAM ultraviolet observations to find that the hydrogen escape rate from Mars decreased by an order of magnitude over six months in 2007, coincident with the waning of a large dust storm in fall 2007 (Mars Year 28).…”

Section: Discussionmentioning

confidence: 92%

Recovery and validation of Mars ionospheric electron density profiles from Mariner 9

2015

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Electron density profiles from the ionosphere of Mars that were obtained by the Mariner 9 radio occultation experiment in 1971-1972 have unique scientific value because they extend to higher altitudes than comparable datasets and were acquired during a tremendous dust storm that had substantial and poorly understood effects on the ionosphere. Yet these profiles are not publicly available in an accessible format. Here, we describe the recovery of these profiles, which are made available as part of this article. The validity of the profiles was tested by using them to explore the effects of a dust storm on the topside ionosphere, the morphology of the topside ionosphere, the behavior of the M1 layer, and possible meteoric layers. The dust storm that waned over the course of the primary mission (November-December 1971) had major effects on the ionosphere of Mars. It elevated the M1 and M2 layers of the ionosphere by 20-30 km, but the separation of the two layers stayed fixed throughout the primary mission, which suggests that the neutral atmosphere at these altitudes was not heated during the dust storm. However, the altitude of the 1500 cm −3 density level, a proxy for the top of the ionosphere, decreased steadily by 74 ± 12 km over the course of the primary mission. Mariner 9 observations of the topside ionosphere differ from comparable Mars Express observations. Compared to Mars Express, the Mariner 9 data, which were acquired during a period of relatively high solar wind dynamic pressure, have lower densities at high altitudes. They are also more likely to have a "one scale height" morphology than a "two scale height" morphology. The peak density of the M1 layer depends on solar zenith angle and solar irradiance similarly to previous studies with Mars Global Surveyor observations, which indicates that dust storms do not affect the behavior of the peak density. No clear meteoric layers were identified.

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Time‐history influence of global dust storms on the upper atmosphere at Mars

Cited by 19 publications

References 27 publications

Mars photoelectron energy and pitch angle dependence on intense lower atmospheric dust storms

Mars photoelectron energy and pitch angle dependence on intense lower atmospheric dust storms

Long‐term variability of dust optical depths on Mars during MY24–MY32 and their impact on subtropical lower ionosphere: Climatology, modeling, and observations

Recovery and validation of Mars ionospheric electron density profiles from Mariner 9

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