D. A. Brain

Effects of crustal field rotation on the solar wind plasma interaction with Mars

The crustal remnant field on Mars rotates with the planet at a period of 24 h 37 min, constantly varying the magnetic field configuration interacting with the solar wind. Until now, there has been no self-consistent modeling investigation on how this varying magnetic field affects the solar wind plasma interaction. Here we include the rotation of this localized crustal field in a multispecies single-fluid MHD model of Mars and simulate an entire day of solar wind interaction under normal solar wind conditions. The MHD model results are compared with Mars Global Surveyor (MGS) magnetic field observations and show very close agreement, especially for the field strength along almost all of the 12 orbits on the day simulated. Model results also show that the ion escape rates slowly vary with rotation, generally anticorrelating with the strength of subsolar magnetic crustal sources, with some time delay. In addition, it is found that in the intense crustal field regions, the densities of heavy ion components enhance significantly along the MGS orbit, implying strong influence of the crustal field on the ionospheric structures.

MARSIS Observations of the Martian Nightside Ionosphere During the September 2017 Solar Event

We present topside ionospheric sounding on the nightside of Mars during the September 2017 solar event by Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board Mars Express along with complementary dayside observations from Mars Atmosphere and Volatile EvolutioN (MAVEN). The MARSIS and MAVEN observations during the event suggest that (i) the nightside bottomside ionosphere was significantly enhanced by solar energetic particles, (ii) the nightside peak electron density was increased to unusually high values of ∼1–2 ×104 cm−3 around 120 km altitudes owing to enhanced electron impact ionization, and (iii) the ionospheric magnetic field was globally amplified by the high dynamic pressure during the interplanetary coronal mass ejection passage. These multipoint measurements help elucidate the global response of the Martian upper ionosphere to the solar event. Plain Language Summary The solar flare that occurred on 10 September 2017, and the subsequent coronal mass ejection had major impacts on the upper atmosphere of Mars. In this work, we study how the Martian ionosphere, which is the ionized part of the upper atmosphere, changed in response to this prominent solar event. Analysis of data from two spacecraft, Mars Express and MAVEN, reveals unusually strong magnetic fields everywhere in the ionosphere and an exceptionally high level of ionization during the night time. These results can be compared and combined with other observations and models and help the ongoing community wide effort to understand the effects of the solar event on planetary environments.

Global Aurora on Mars During the September 2017 Space Weather Event

We report the detection of bright aurora spanning Mars’ nightside during the space weather event occurring in September 2017. The phenomenon was similar to diffuse aurora detected previously at Mars, but 25 times brighter and detectable over the entire visible nightside. The observations were made with the Imaging UltraViolet Spectrograph (IUVS), a remote sensing instrument on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft orbiting Mars. Images show that the emission was brightest around the limb of the planet, with a fairly uniform faint glow against the disk itself. Spectra identified four molecular emissions associated with aurora, and limb scans show the emission originated from an altitude of ~60 km in the atmosphere. Both are consistent with very high energy particle precipitation. The auroral brightening peaked around 13 September, when the flux of solar energetic electrons and protons both peaked. During the declining phase of the event, faint but statistically significant auroral emissions briefly appeared against the disk of the planet in the form of narrow wisps and small patches. These features are approximately aligned with predicted open field lines in the region of strong crustal magnetic fields in Mars’ southern hemisphere.

Flows, Fields, and Forces in the Mars‐Solar Wind Interaction

We utilize suprathermal ion and magnetic field measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, organized by the upstream magnetic field, to investigate the morphology and variability of flows, fields, and forces in the Mars-solar wind interaction. We employ a combination of case studies and statistical investigations to characterize the interaction in both quasi-parallel and quasi-perpendicular regions and under high and low solar wind Mach number conditions. For the first time, we include a detailed investigation of suprathermal ion temperature and anisotropy. We find that the observed magnetic fields and suprathermal ion moments in the magnetosheath, bow shock, and upstream regions have observable asymmetries controlled by the interplanetary magnetic field, with particularly large asymmetries found in the ion parallel temperature and anisotropy. The greatest temperature anisotropies occur in quasi-perpendicular regions of the magnetosheath and under low Mach number conditions. These results have implications for the growth and evolution of wave-particle instabilities and their role in energy transport and dissipation. We utilize the measured parameters to estimate the average ion pressure gradient, J × B, and v × B macroscopic force terms. The pressure gradient force maintains nearly cylindrical symmetry, while the J × B force has larger asymmetries and varies in magnitude in comparison to the pressure gradient force. The v × B force felt by newly produced planetary ions exceeds the other forces in magnitude in the magnetosheath and upstream regions for all solar wind conditions.

Responses of the Martian Magnetosphere to an Interplanetary Coronal Mass Ejection: MAVEN Observations and LatHyS Results: RESPONSE OF MARS TO A CME

The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft observed a strong interplanetary coronal mass ejection (ICME) reaching Mars on 13 September 2017. In this work we analyze the interaction between such an extreme event and the Martian induced magnetosphere by means of LATMOS Hybrid Simulation (LatHyS) stationary runs and magnetic field and plasma observations obtained by MAVEN in a time interval from ∼ 5 h before the ICME shock arrival to about 5.5 h after the impact. Detailed comparisons between simulation results and such MAVEN measurements are performed and show that several stages during this interaction can be described through a combination of steady states. LatHyS results show the simulated bow shock is closer to the planet for higher magnetosonic Mach number and solar wind dynamic pressure conditions, in agreement with previous observational studies. MAVEN observations and LatHyS results also suggest a compression on the flanks of the magnetic pile‐up boundary. Finally, simulated H+ and O+ planetary escape rates increase by a factor ∼10 and ∼2.4, respectively, due to the ICME passage through the Martian magnetosphere.

Statistical Similarities Between WSA-ENLIL+Cone Model and MAVEN in situ Observations from November 2014 to March 2016: MAVEN Observations and WEC Comparison

Normal solar wind flows and intense solar transient events interact directly with the upper Martian atmosphere due to the absence of an intrinsic planetary magnetic field. Since the launch of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, there is now a means to directly observe solar wind parameters at the planet’s orbital location for limited time spans. Due to the craft’s highly elliptical orbit, in situ measurements cannot be taken while MAVEN is inside Mars’ magnetosheath. In an attempt to model solar wind conditions during these atmospheric and magnetospheric passages, this research project utilizes the solar wind forecasting capabilities of the Wang-Sheeley-Arge-ENLIL+Cone (WEC) model. These sets of tools are maintained at the Community Coordinated Modeling Center (CCMC). In this study, the model has simulated solar wind parameters such as plasma pressure, temperature, particle density, velocity and magnetic field properties during the time period from late 2014 to March of 2016, with an additional detailed simulation during December 2015 to March 2016. The accuracy of the model was examined for intervals when MAVEN was considered to be in upstream solar wind, i.e., with no exospheric or magnetospheric phenomena altering the in situ measurements. It was determined that the WEC model has the capability to provide statistically similar baseline values for continuous solar wind knowledge. These baseline values can be further improved upon in accuracy when smaller time scales (e.g. 1-2 Carrington rotations) are analyzed. Generally, this study aims to provide a larger context of solar wind driving during gaps in the in situ measurements.

Characterization of turbulence in the Mars plasma environment with MAVEN observations: TURBULENCE AT MARS

We characterize turbulence in the Mars plasma environment in a global scale for the first time by computing spectral indices for magnetic field fluctuations (slopes in the magnetic field power spectra) and determining how they vary with frequency and in different regions. In the magnetosheath, unlike in the solar wind, we find an absence of the inertial range which has a spectral index value equal to the Kolmogorov scaling value of −5/3. Instead, as observed in the magnetosheaths of other planets, we find that the spectral indices transition from low negative values close to −0.5 at low frequencies ( proton gyrofrequency). This indicates that the pristine solar wind is modified at the Martian bow shock and that the fluctuations are dominated by locally generated fluctuations in the magnetosheath. The absence of spectral indices with the Kolmogorov scaling value indicates that the fluctuations in the magnetosheath do not have sufficient time to interact with one another leading to a fully developed energy cascade. Spectral index values near the Kolmogorov scaling value are observed for the low-frequency range near the magnetic pileup boundary, and this indicates the presence of fully developed energy cascade. In the wake, we find that the spectral indices have approximately the same values, typically near −2, for both the low- and high-frequency ranges. We observe seasonal variations of the spectral indices, mainly in the upstream region, which indicate the seasonal variations of the proton cyclotron waves.