Nightside ionosphere of Mars: Modeling the effects of crustal magnetic fields and electron pitch angle distributions on electron impact ionization

Lillis, Robert J.; Fillingim, M. O.; Peticolas, L. M.; Brain, David; Lin, R. P.; Bougher, S. W.

doi:10.1029/2009je003379

Cited by 96 publications

(149 citation statements)

References 69 publications

Supporting

Mentioning

140

Contrasting

Order By: Relevance

“…We try to minimize the impact of this assumption by choosing a dip angle of the magnetic field that matches the dip angle given by the crustal magnetic field model of Cain et al (2003) near 150 km, the altitude of greatest ionization. As recently shown by Lillis et al (2009), strong magnetic gradients can reflect a significant portion of the downward-travelling electrons and can greatly affect the ionization profile. However, if the down-going spectrum is isotropic, the electron flux remains approximately constant with altitude because loss of electrons by magnetic reflection is balanced by the decrease in area of the flux tube through which the electrons travel; only the area upon which the electrons precipitate will decrease.…”

Section: Discussionmentioning

confidence: 99%

“…However, if the down-going spectrum is isotropic, the electron flux remains approximately constant with altitude because loss of electrons by magnetic reflection is balanced by the decrease in area of the flux tube through which the electrons travel; only the area upon which the electrons precipitate will decrease. (However, Lillis et al (2009) showed that, by including altitude dependent scattering effect of the atmosphere, magnetic gradients can also impact the ionization profile due to isotropic distrubutions changing the peak ionization rate by ∼20% between the zero crustal field case and the strongest crustal field gradient they considered.) Brain et al (2006) showed that throughout most of the interval shown in the top panel of Fig.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

On wind-driven electrojets at magnetic cusps in the nightside ionosphere of Mars

Fillingim¹,

Lillis²,

England³

et al. 2012

Earth Planet Sp

View full text Add to dashboard Cite

Mars has a complex magnetic topology where crustal magnetic fields can interact with the solar wind magnetic field to form magnetic cusps. On the nightside, solar wind electron precipitation can produce enhanced ionization at cusps while closed field regions adjacent to cusps can be devoid of significant ionization. Using an electron transport model, we calculate the spatial structure of the nightside ionosphere of Mars using Mars Global Surveyor electron measurements as input. We find that localized regions of enhanced ionospheric density can occur at magnetic cusps adjacent to low density regions. Under this configuration, thermospheric winds can drive ionospheric electrojets. Collisional ions move in the direction of the neutral winds while magnetized electrons move perpendicular to the wind direction. This difference in motion drives currents and can lead to charge accumulation at the edges of regions of enhanced ionization. Polarization fields drive secondary currents which can reinforce the primary currents leading to electrojet formation. We estimate the magnitude of these electrojets and show that their magnetic perturbations can be detectable from both orbiting spacecraft and the surface. The magnitude of the electrojets can vary on diurnal and annual time scales as the strength and direction of the winds vary. These electrojets may lead to localized Joule heating, and closure of these currents may require field-aligned currents which may play a role in high altitude acceleration processes.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

On wind-driven electrojets at magnetic cusps in the nightside ionosphere of Mars

Fillingim¹,

Lillis²,

England³

et al. 2012

Earth Planet Sp

View full text Add to dashboard Cite

show abstract

“…Further investigation (the bottom panel of Figure 7) shows this feature occurs at about the same SZA, local time (LT) and latitude for all three cases. The examination of the plots of echo intensity as a function of time and universal time at fixed frequency shows that the altitude of the peak electron density of the ionosphere is at about 160 km, which is the expected height of the ionosphere based on a Monte Carlo Model [Lillis et al, 2009]. At the other times the height of the ionosphere is at about 140 km, which is about 20 km lower than usual, suggesting compression due to solar activity.…”

Section: Datamentioning

confidence: 99%

Response of the Martian ionosphere to solar activity including SEPs and ICMEs in a two-week period starting on 25 February 2015

Duru

Gurnett

Morgan

et al. 2017

Planetary and Space Science

View full text Add to dashboard Cite

Key points:Solar activity in a two week period starting from 25 February 2015 altered the conditions in the Martian ionosphere.The solar wind conditions and nightside ionosphere of Mars are studied simultaneously, with MAVEN, MEX and Mars Odyssey.High ion escape rates and enhanced densities are observed during SEP enhancements and ICME. Atmosphere and Volatile Evolution Mission (MAVEN), and Mars Odyssey (MO). The ICME disturbances were characterized by an increase in ion speed, plasma temperature, magnetic field magnitude, and energetic electron flux. Furthermore, increased solar wind density and speeds, unusually high local electron densities and high flow velocities were detected on the nightside at high altitudes during the March 8 th event. These effects are thought to be due to the transport of ionospheric plasma away from Mars. The peak electron density at periapsis shows a substantial increase, reaching number densities about 2.7 x 10 4 cm -3 during the second ICME in the deep nightside, which corresponds to an increase in the MOHigh-Energy Neutron Detector flux, suggesting an increase in the ionization of the neutral atmosphere due to the high intensity of charged particles. SEPs show a substantial enhancement before the shock of fourth ICME causing impact ionization and absorption of the surface echo intensity which drops to the noise levels. Moreover, the peak ionospheric density exhibits a discrete enhancement over a period of about 30 hrs around the same location, which maybe due to impact ionization. Ion escape rates at this time are calculated to be in the order of 10 25 -10 26 s -1 , consistent with MAVEN results, but somewhat higher.

show abstract

“…A Monte Carlo transport code was used by Lillis et al [2009], who concluded that the coupled effects of the crustal magnetic field gradients and electron pitch angle distributions on electron impact ionization rates are high enough that they should be included in the modeling of the nightside ionosphere.…”

Section: Introductionmentioning

confidence: 99%

Nightside ionosphere of Mars studied with local electron densities: A general overview and electron density depressions

et al. 2011

View full text Add to dashboard Cite

The radar sounder Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on the Mars Express spacecraft provides local electron densities from electron plasma oscillations. Here, we use the local electron densities to study the nightside ionosphere of Mars. In this study, in which local densities were sampled to a minimum altitude of about 275 km, we measured the maximum average densities as 1000 cm−3 on the nightside. The electron density profiles on the nightside are highly variable. An inverse exponential relationship is observed between the electron density and the altitude. At low altitudes, the median electron density decreases with increasing solar zenith angle (SZA). However, at high altitudes no dependence on SZA is observed. Steep electron density gradients, similar to the ionopause at Venus, are also observed in 15% of the passes in the nightside ionosphere. A commonly encountered structure on the nightside is an ionospheric density depression, which is a deep trough in the electron density. Nightside density depressions are large features, with an average width of 950 km. In some cases, the depressions in MARSIS data are associated with ion flow features in the Analyzer of Space Plasma and Energetic Atoms (ASPERA‐3) data. In other cases, the depressions correspond to density depletion regions. Half of the depressions are aligned with the edge of the dayside‐generated photoelectrons. It is concluded that several different conditions can cause the electron density depressions.

show abstract

Nightside ionosphere of Mars: Modeling the effects of crustal magnetic fields and electron pitch angle distributions on electron impact ionization

Cited by 96 publications

References 69 publications

On wind-driven electrojets at magnetic cusps in the nightside ionosphere of Mars

On wind-driven electrojets at magnetic cusps in the nightside ionosphere of Mars

Response of the Martian ionosphere to solar activity including SEPs and ICMEs in a two-week period starting on 25 February 2015

Nightside ionosphere of Mars studied with local electron densities: A general overview and electron density depressions

Contact Info

Product

Resources

About