Three‐dimensional, multifluid, high spatial resolution MHD model studies of the solar wind interaction with Mars

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95318/1/jgra21138.pd

Formation and Evolution of the Large‐Scale Magnetic Fields in Venus’ Ionosphere: Results From a Three Dimensional Global Multispecies MHD Model

Large‐scale magnetic fields have been observed in Venus’ ionosphere by both the Pioneer Venus Orbiter (PVO) and Venus Express spacecraft. In this study, we examine the formation and evolution of the large‐scale magnetic field in the Venus ionosphere using a sophisticated global multispecies Magnetohydrodynamics (MHD) model that has been developed for Venus (Ma et al., 2013, https://doi.org/10.1029/2012JA018265). A time‐dependent model run is performed under varying solar wind dynamic pressure. Based on model results, we find that (1) the initial response of the induced magnetosphere is fast (~min), (2) a large‐scale magnetic field gradually forms in the ionosphere when the solar wind dynamic pressure suddenly exceeds the ionospheric thermal pressure, (3) both the penetration and decay of the large‐scale magnetic field in the ionosphere are slow (~hr), and (4) the ion escape rate has a nonlinear response to the change of solar wind dynamic pressure.Plain language SummaryLarge‐scale magnetic fields have been observed at Venus’ ionosphere by previous Venus missions. In this study, we examine the formation and evolution of the large‐scale magnetic field in the Venus ionosphere using a sophisticated global model. A time‐dependent model run is performed under varying solar wind dynamic pressure (density). Model results show that the outside interaction region responds quickly (~min) to the solar wind variation, while the response time of the ionosphere is long (~hr). We also found that the ion escape rate has a nonlinear response to the change of solar wind dynamic pressure.Key PointsThe global MHD model self‐consistently reproduces the formation and evolution of the large‐scale magnetic fields in the Venus ionosphereModel results show that it takes quite long time (~hr) for the magnetic field to penetrate into and decay in the ionosphereThe large‐scale magnetic fields in the ionosphere act as an additional obstacle to the solar windPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155482/1/grl60596.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155482/2/grl60596_am.pd

Solar wind interaction with Mars upper atmosphere: Results from the one‐way coupling between the multifluid MHD model and the MTGCM model

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106987/1/grl51608.pd

A Target Sequential Effect on the Forced-Choice Prime Visibility Test in Unconscious Priming Studies: A Caveat for Researchers

In unconscious priming studies, most researchers adopt a combination of subjective and objective measures to assess the visibility of the prime. Although some carry out the visibility test at the end of the experiment separately from the unconscious priming task, others suggest that the forced-choice visibility test should be conducted immediately after the response to the target within each trial. In the present study, the influence of prime and target on the forced-choice prime discrimination was assessed within each trial. The results showed that the target affected the response in the forced-choice prime visibility test. Participants tended to make the same response or avoid repeating the same response they made to the target as in Experiments 1 and 3 rather than randomly guessing. However, even when the forcedchoice visibility test was conducted separately from the priming experiment, the problem was not completely solved, because some participants tended to make one same response in the forced-choice visibility test as in Experiments 2. From another point of view, using these strategies in the forced-choice task can be seen as a helpless move by the participants when they are unaware of the stimuli. Furthermore, the results revealed that the forced-choice test performed immediately after the response to the target within each trial could possibly impair the unconscious priming as well as produce misleading visibility test results. Therefore, it is suggested that the forced-choice prime visibility test and the unconscious priming task may better be conducted separately

The importance of pickup oxygen ion precipitation to the Mars upper atmosphere under extreme solar wind conditions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98793/1/grl50415.pd

Pickup oxygen ion velocity space and spatial distribution around Mars

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94939/1/jgra19106.pd

Effects of Global and Regional Dust Storms on the Martian Hot O Corona and Photochemical Loss

We examine here for the first time the effects of both global and regional dust storms on the formation of the Martian hot O corona and associated photochemical loss of O. Our study is conducted by utilizing our integrated model framework, which couples our Martian hot O corona model with a multifluid magnetohydrodynamic model for Mars for the dusty and clear atmospheric condition cases. We present our results with the most up‐to‐date cross sections for the O(3P)‐CO2 collisions. The main effect of dust storms on the ionosphere is the upward shift of the ionosphere on the dayside, which results in an increase in production of hot O at all altitudes above the ionospheric peak. However, the dust‐induced inflation of the neutral upper atmosphere results in an enhancement in collisional loss of hot O and thus effectively suppresses the hot O density, reducing the global photochemical loss rate by ~28% for the global dust storm scenario. The relative density structure of the hot O corona does not show any significant changes, while its magnitude decreases at all altitudes.Key PointsWe investigated the effect of dust storms on photochemical escape from Mars using up‐to‐date cross sections for O‐CO2 collisionsThe storm‐induced upward shift of the ionosphere causes increased production of hot O and efficient thermalization occurs by the inflated thermosphereThe net result is a global photochemical escape rate that is suppressed by ~28% during the global dust storm scenarioPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154658/1/jgra55566_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154658/2/jgra55566.pd

Martian low‐altitude magnetic topology deduced from MAVEN/SWEA observations

The Mars Atmosphere and Volatile Evolution mission has obtained comprehensive particle and magnetic field measurements. The Solar Wind Electron Analyzer provides electron energy‐pitch angle distributions along the spacecraft trajectory that can be used to infer magnetic topology. This study presents pitch angle‐resolved electron energy shape parameters that can distinguish photoelectrons from solar wind electrons, which we use to deduce the Martian magnetic topology and connectivity to the dayside ionosphere. Magnetic topology in the Mars environment is mapped in three dimensions for the first time. At low altitudes (<400 km) in sunlight, the northern hemisphere is found to be dominated by closed field lines (both ends intersecting the collisional atmosphere), with more day‐night connections through cross‐terminator closed field lines than in the south. Although draped field lines with ~100 km amplitude vertical fluctuations that intersect the electron exobase (~160–220 km) in two locations could appear to be closed at the spacecraft, a more likely explanation is provided by crustal magnetic fields, which naturally have the required geometry. Around 30% of the time, we observe open field lines from 200 to 400 km, which implies three distinct topological layers over the northern hemisphere: closed field lines below 200 km, open field lines with foot points at lower latitudes that pass over the northern hemisphere from 200 to 400 km, and draped interplanetary magnetic field above 400 km. This study also identifies open field lines with one end attached to the dayside ionosphere and the other end connected with the solar wind, providing a path for ion outflow.Key PointsPitch angle‐resolved electron energy shape parameters are used to deduce magnetic topologyClosed magnetic field lines dominate low altitudes (<400 km) of the northern hemisphere on the daysideThe 3‐D view of the Martian magnetic topology is presented for the first timePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136484/1/jgra53291.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136484/2/jgra53291_am.pd

Mars Dust Storm Effects in the Ionosphere and Magnetosphere and Implications for Atmospheric Carbon Loss

Mars regional and global dust storms are able to impact the lower/upper atmospheres through dust aerosol radiative heating and cooling and atmospheric circulation. Here we present the first attempt to globally investigate how the dust impact transfers from the neutral upper atmosphere to the ionosphere and the induced magnetosphere above 100‐km altitude. This is achieved by running a multifluid magnetohydrodynamic model under nondusty and dusty atmospheric conditions for the 2017 late‐winter regional storm and the 1971–1972 global storm. Our results show that the dayside main ionospheric layer (below ∼250‐km altitude) undergoes an overall upwelling, where photochemical reactions dominate. The peak electron density remains unchanged, and the peak altitude shift is in accordance with the upper atmospheric expansion (∼5 and ∼15 km for the regional and global storms, respectively). Controlled by the day‐to‐night transport, the nightside ionosphere responds to the dust storms in a close connection with what happens on the dayside but not apparently with the ambient atmospheric change. At higher altitudes, dust‐induced perturbations propagate upward from the ionosphere to the magnetosphere and extend from the dayside to the nightside, within a broad region bounded by the induced magnetospheric boundary. It is found that the global dust storm is able to dramatically enhance the CO2+ loss by a factor of ∼3, which amounts to an increase of ∼20% or more for total carbon loss (in the forms of neutrals and ions). Strong dust storms are a potentially important factor in atmospheric evolution at Mars.Key PointsThe dayside main ionosphere is lifted in accordance with dust‐induced atmospheric expansion, with peak electron densities unchangedDust‐induced perturbations propagate upward from the ionosphere to the magnetosphere and extend from the dayside to the nightsideStrong dust storms may enhance CO2+ loss by a factor of ∼3 and increase total carbon loss (neutrals and ions) by ∼20% or morePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154511/1/jgra55184_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154511/2/jgra-sup-0001-2019JA026838-Text_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154511/3/jgra55184.pd