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(a–h) The correlation between the scaled effective pressure PEff as empirically defined in equation (5) and the MHD-calculated loss rate for O+, O+2 , CO+2 , and total ions, respectively. In Figures 5a–5d, the black lines represent the ion loss rates integrated over a spherical surface of 6 RM, with a scale on the left axis. The red lines represent PEff, while the solid blue and green lines show its dayside and terminator components, PSD(t) and PST(t), respectively. The blue dotted lines show the time-lagged PSD(t-Δts). These scaled pressures are displayed using the right axis. In Figures 5e–5h, the correlation is examined through scatterplots. The points are sampled every 4 min. The best fit regression lines and the correlation coefficients are marked.
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We present results from a global Mars time-dependent MHD simulation under constant solar wind and solar radiation impact considering inherent magnetic field variations due to continuous planetary rotation. We calculate the 3-D shapes and locations of the bow shock (BS) and the induced magnetospheric boundary (IMB) and then examine their dynamic cha...
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This work studies the dynamic response of solar wind charge exchange (SWCX) soft X-ray emission in the Earth’s magnetosphere to the solar wind proton flux. Unlike previous studies that attempted to use complex magnetohydrodynamic models to match the details of observed SWCX of a necessarily limited number of cases, this work focuses on determining...
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... A 3D spherical MHD model with multiple species (H + , O + , + O 2 , and + CO 2 ) based on the block adaptive-tree solar wind Roetype upwind scheme (BATS-R-US) is used to discuss the energy transfer of the MPB; it was originally developed by Ma et al. (2004). This model has been used in many previous studies (Fang et al. 2010(Fang et al. , 2015(Fang et al. , 2017Ma et al. 2014) on the interaction between the solar wind and Mars. ...
Using a global magnetohydrodynamics numerical simulation, this work compares the interaction of the solar wind with Mars and Earth from the perspective of energy transfer under north–south interplanetary magnetic fields (IMFs). Mars lacks a global dipole magnetic field like Earth’s and instead has a small-scale crustal magnetic field near highlands in the southern hemisphere. Unlike Earth’s magnetopause reconnection (at the subsolar point or tail under a southward IMF, or behind the cusp under a northward IMF), the reconnection of the Martian magnetic pileup boundary (MPB) occurs near solar zenith angle (SZA) ≈ 45° (SZA ≈ 30° and 60°) for a southward (northward) IMF, resulting in asymmetric energy transfer between the northern and southern hemispheres. The Martian outflow of mechanical energy appears near SZA ≈ 45° (SZA ≈ 30° and 60°) under a southward (northward) IMF, accompanied by an inflow due to the process of “solar wind pickup.” For energy transfer across the MPB, whether the IMF is northward or southward, the input of electromagnetic energy is twice as large as the input of mechanical energy, which is similar to Earth’s magnetopause for a southward IMF, but opposite to it for a northward IMF. The energy transfer rate of the MPB is slightly higher in a northward IMF than in a southward one, whereas the energy transfer rate of Earth’s magnetopause is far higher in a southward IMF than in a northward one.
... Although Mars has no global magnetic field, areas of the crust have rocks holding onto remanent magnetization from four billion years ago, when it is believed that a global dynamo was present (Acuna et al. 1998;Connerney et al. 2001). These crustal magnetic fields form "mini-magnetospheres" and can increase the altitudes of boundaries over these areas (Mitchell et al. 2001;Fang et al. 2017;Garnier et al. 2022b). ...
... Crustal magnetic fields are known to trap the planetary plasma, and Fang et al. (2017) found a shielding effect for atmosphere loss occurring over crustal fields. We suggest that, over crustal fields, the confinement of charged particles here leads to lower rates of ionization compared to elsewhere on the planet. ...
... We acknowledge that solar EUV may also be influencing the data, but we have looked at the F10.7 flux and found that they do not indicate an influence on our results. Previous work (Edberg et al. 2008;Fang et al. 2017;Gruesbeck et al. 2018;Garnier et al. 2022aGarnier et al. , 2022b observed that the bow shock bulges over the southern hemisphere due to the crustal fields, but did not consider only times of dust events on Mars. ...
Mars's magnetosphere is a sensitive system, varying due to external and internal factors, such as solar wind conditions and crustal magnetic fields. A signature of this influence can be seen in the position of two boundaries; the bow shock and the induced magnetospheric boundary (IMB). The bow shock moves closer to Mars during times of high solar activity, and both the bow shock and IMB bulge away from Mars over crustal magnetic fields in the southern hemisphere. This study investigates whether large-scale atmospheric events at Mars have any signature in these two magnetic boundaries, by investigating the 2007 storm. The 2007 global storm lasted for several months and increased atmospheric temperatures and densities of both water vapor and carbon dioxide in the atmosphere, leading to an increase in atmospheric escape. Using Mars Express, we identified boundary locations before, during, and after the event, and compared these to modeled boundary locations and areographical locations on Mars. We find that, while it is unclear whether the bow shock position is impacted by the storm, the IMB location does change significantly, despite the orbital bias introduced by Mars Express. The terminator distance for the IMB peaks at longitudes 0°–40° and 310°–360°, leaving a depression around 180° longitude, where the boundary usually extends to higher altitudes due to the crustal magnetic fields. We suggest this may be due to the confinement of ionospheric plasma over crustal fields preventing mixing with the dust, creating a dip in ionospheric pressure here.
... The first global map of the crustal fields of Mars was established based on Mars Global Surveyor (MGS) data (Acuña et al., 1998(Acuña et al., , 1999, which showed highly variable spatial distributions near the surface with the field strength up to ∼1,500 nT. These crustal fields play an important role regarding solar wind-ionosphere interactions resulting in both local and global effects on the plasma environment of Mars, such as modifying draped interplanetary magnetic field (IMF) around the planet (e.g., Brain et al., 2003;Dong et al., 2019;Harada et al., 2018;Kallio et al., 2008), shaping the ionosphere (e.g., Andrews et al., 2015;Dubinin et al., 2016;Mitchell et al., 2001), diverting ion flows (e.g., Fan et al., 2020;Li et al., 2022), influencing plasma boundaries (e.g., Brain et al., 2005;Edberg et al., 2008;Fang et al., 2017), and affecting ion escape (e.g., Brain et al., 2010;Brecht & Ledvina, 2014;Fang et al., 2015;Nilsson et al., 2011;Ramstad et al., 2016;Weber et al., 2021). It is well known that the polar cusps of the Earth's magnetosphere, where shocked solar wind in the magnetosheath can access ionosphere directly usually thought to be through magnetic reconnections, play an important role in the ionosphere-magnetosphere coupling (Smith & Lockwood, 1996 and references therein). ...
... There have been some simulation works regarding the role of crustal fields in the plasma environment of Mars. The global effects of crustal fields on the Martian induced magnetosphere and ion escape have been discussed based on magnetohydrodynamic (MHD) and hybrid models (e.g., Brecht & Ledvina, 2014;Fang et al., 2015Fang et al., , 2017Kallio et al., 2008;Ma et al., 2002;Ma et al., 2014). Furthermore, Ma et al. (2018) applied Hall-MHD embedded with particle-in-cell (PIC) simulations to study the reconnection between crustal field and nightside draped field and the effects on magnetotail dynamics. ...
The localized crustal magnetic fields of Mars play an important role in the planet’s ionosphere‐solar wind interaction. Various physical processes in the induced magnetosphere, such as particle precipitation, field‐aligned currents, and ion outflow, are usually associated with the crustal magnetic cusp regions, where field lines are mostly vertical and open to space. Due to the small spatial scale (a few hundred km) of the Martian crustal magnetic cusps, localized models with high spatial resolutions and ion kinetics are needed to understand the physical processes. We adapt the simulation platform HYB developed at the Finnish Meteorological Institute to a moderately strong magnetic cusp above the Martian exobase with a 2‐D simulation domain assuming periodic boundary conditions on the third dimension. Two plasma sources are included in the simulation: hot protons from the induced magnetosphere and cold heavy ions (O⁺) from the ionosphere. Our model results can qualitatively reproduce the vertical electric potential drop, particle transport, and field aligned current in the cusp region. The vertical electric potential is built up mostly by the Hall electric field as a result of the separation between ion and electron fluxes of the downward plasma flow. By varying the model inputs, we found that the vertical potential drop depends on ionospheric ion density and magnetic field strength. These results tell us that energy is transferred from magnetospheric plasma to ionospheric plasma through the vertical electric potential buildup in magnetic cusps and how this process may affect electron precipitation, ion escape, and ionosphere conditions at Mars.
... Evidence from Mars missions have shown variations in magnetic field topology presumed to be a result of reconnection with crustal fields (Xu et al., 2020). Similarly, ionospheric composition and ion loss have been shown to vary depending on crustal field strength and location (Dubinin et al., 2020;Fang et al., 2017;Flynn et al., 2017;Fränz et al., 2006;Weber et al., 2021;Withers et al., 2019;Zhang et al., 2021). Crustal fields are thought to lead to departures from the nominal magnetic field draping that would occur for an un-magnetized planet. ...
The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been orbiting Mars since 2014 and now has over 10,000 orbits which we use to characterize Mars' dynamic space environment. Through global field line tracing with MAVEN magnetic field data we find an altitude dependent draping morphology that differs from expectations of induced magnetospheres in the vertical (Z^ $\hat{Z}$ Mars Sun‐state, MSO) direction. We quantify this difference from the classical picture of induced magnetospheres with a Bayesian multiple linear regression model to predict the draped field as a function of the upstream interplanetary magnetic field (IMF), remanent crustal fields, and a previously underestimated induced effect. From our model we conclude that unexpected twists in high altitude dayside draping (>800 km) are a result of the IMF component in the ±X^ $\pm \hat{X}$ MSO direction. We propose that this is a natural outcome of current theories of induced magnetospheres but has been underestimated due to approximations of the IMF as solely ±Y^ $\pm \hat{Y}$ directed. We additionally estimate that distortions in low altitude (<800 km) dayside draping along Z^ $\hat{Z}$ are directly related to remanent crustal fields. We show dayside draping traces down tail and previously reported inner magnetotail twists are likely caused by the crustal field of Mars, while the outer tail morphology is governed by an induced response to the IMF direction. We conclude with an updated understanding of induced magnetospheres which details dayside draping for multiple directions of the incoming IMF and discuss the repercussions of this draping for magnetotail morphology.
... This distinctive crustal anomaly exerts noticeable influences on near-Mars space phenomena, such as aurora (e.g., Brain & Halekas, 2011;Lundin et al., 2006), magnetic reconnection (e.g., Eastwood et al., 2008), and bulges in plasma density distributions above the regions of the strong crustal field (e.g., Duru et al., 2006). Magneto-hydrodynamics (MHD) simulations (e.g., Fang et al., 2017;Ma et al., 2014) as well as observations from missions such as Mars Express (e.g., Nilsson et al., 2011;Ramstad et al., 2016) and MAVEN (e.g., Dubinin et al., 2020) have explored the effects of a rotating crustal magnetic field on the interaction between the solar wind and atmospheric escaping ions under varying solar activity conditions. The presence of strong crustal magnetic fields also raises the location of the dayside magnetic field pile-up boundary (e.g., Brain et al., 2005;Crider et al., 2004) and the bow shock (e.g., Edberg et al., 2008). ...
... The absence of trapped thermal crustal magnetospheric plasma in the induced magnetosphere can explain this difference. The intrusions of solar wind in Figures 4e and 4l indicate that thermal ions from an induced magnetosphere are more easily lost along open magnetic field lines, which is consistent with simulations by Fang et al. (2017) and Ma et al. (2014). The observed pressures during the crossing of the magnetopause in Figure 4d fulfills the following equation: ...
Plain Language Summary
Mars lacks a global intrinsic magnetic field. Currents in the Martian ionosphere generate a Venus‐like induced magnetosphere which deflects the solar wind flow and piles up the interplanetary magnetic field. However, local crustal magnetic fields in Mars' southern hemisphere significantly influence the nearby plasma. With the support of the MAVEN mission, this work analyses observations from passes of the spacecraft through the mini‐magnetosphere during suitable orbits and investigates plasma pressures in both single orbit data and by a 4‐year statistical analysis. We present an observation of a mini‐magnetosphere filled by trapped heavy ions above the crustal magnetic fields on the Martian dayside. Furthermore, we establish three criteria to distinguish this mini‐magnetosphere from the induced magnetosphere. Observations show that the mini‐magnetosphere reaches an altitude of 1,300 km, larger than one‐third of the Martian radius. The observed mini‐magnetosphere and the dichotomy between the crustal southern and induced northern Martian magnetosphere forms a distinct environment that may help us to test the interactions between stellar winds and magnetic or nonmagnetic bodies.
... Without a global intrinsic magnetic field, the solar wind directly interacts with the ionosphere and upper atmosphere, promoting plasma loss from the dayside and magnetotail ). However, local crustal magnetic fields, primarily distributed in the southern hemisphere, exert complex influence on the Marssolar wind interaction (Acuña et al. 1998;Connerney et al. 2005;Liemohn et al. 2006;Brain et al. 2007;Ma et al. 2014;Xu et al. 2014;Dong et al. 2015), altering plasma boundary locations (Brain et al. 2005;Edberg et al. 2008;Xu et al. 2016;Fang et al. 2017). Additionally, the local crustal magnetic fields inhibit or promote the process of plasma transport (Brain et al. 2006;Cao et al. 2019;Li et al. 2022aLi et al. , 2022b. ...
... In different seasons, the relative locations between the strongest crustal source and solar wind inflow will change. Therefore, the shielding effect will be weaker or stronger, and the tailward plasma escape will be enhanced or inhibited (Ma et al. 2014;Fang et al. 2017). Additionally, the solar radiation received by the geographical southern and northern hemispheres will be different. ...
... The rotation of Mars is also ignored in this study. In Fang et al. (2015Fang et al. ( , 2017, the static model case may underestimate the ion loss, and the crustal field near the terminator may provide an escape-fostering effect in the plasma escape process. Figure 1 shows the logarithmic magnetic field lg(|B|) and velocity of solar wind ions |V| in the X-Y and X-Z planes, where the magnetic field B is the vector sum of the induced and crustal magnetic fields. ...
Owing to its unevenly distributed crustal fields, Mars acts as a unique obstacle to the solar wind. In the presence of the crustal fields, the transport of the planetary ions on the dayside ionosphere exhibits north–south asymmetry. Additionally, the heavy-ion loss in the magnetotail is affected by the crustal fields. In this paper, a three-dimensional multispecies magnetohydrodynamic model is employed to simulate Mars–solar wind interactions. Numerical results indicate that the meridional transport is dominant in most areas on the dayside ionosphere. In the presence of the crustal fields, the meridional transport on the southern hemisphere (southward transport) is reduced by more than 70% above the strong crustal sources, and the zonal velocity shows local changes inside strong and weak crustal field regions. These effects result in an increase or decrease in the number density of the heavy ions reaching the terminator, thereby influencing the thickness of the ionosphere. Decreased southward velocity leads to a reduction in the heavy-ion loss on the southern magnetotail. The radial outward flux is reduced by more than 30% for O 2 ⁺ and CO 2 ⁺ and by 10% for O ⁺ . This study shows that in addition to the zonal transport, the meridional transport is important for the day-to-night transport on the dayside of Mars. Collectively, the horizontal plasma transport, controlled by crustal fields, is associated with the altered ionosphere structure and reduced heavy-ion loss in the magnetotail.
... As a comparison, although the model supports the decrease of the altitude with increasing SZA near the subsolar regime, only a moderate change (up to 70 km near SZA = 35°) is found in the median IMB location (see Figure S4 in Supporting Information S1). Second, as discussed by Fang et al. (2015Fang et al. ( , 2017 and also seen in Figure S4 in Supporting Information S1, there is a pronounced spatial asymmetry in the shapes and locations of the IMB and BS. Furthermore, the boundary locations are not static but dynamically vary in response to external and internal driving (Garnier et al., 2022a(Garnier et al., , 2022b, and references therein). ...
... To facilitate an understanding of the scale, a 2° longitude by 2° latitude mesh at the equator occupies about 0.01% of the spherical surface. Note that the influence of the crustal field is not locally confined, but extends to a much broader area (e.g., Fang et al., 2015Fang et al., , 2017Garnier et al., 2022b). Therefore, the irregular distribution of the crustal field contributes to the cylindrical asymmetry, which fortunately is weakened by its non-local influence. ...
We study the average global distribution of the external magnetic field at Mars, and its variability with the upstream solar wind dynamic pressure and interplanetary magnetic field as well as with the ambient crustal magnetic field strength. Our approach involves excluding the intrinsic planetary field from the total magnetic field by applying a crustal field model previously derived using low altitude measurements. The distribution of the average external field that remains is statistically analyzed using nearly 8 years of Mars Atmosphere and Volatile EvolutioN (MAVEN) observations and several global, time‐dependent magnetohydrodynamic simulations. Overall consistent results have been obtained from the data and model, which are complementary to each other and cross validate the findings. It is found that the external field is significantly enhanced from the upstream across the bow shock (BS) and further intensifies closer to the planet in the topside ionosphere. It peaks at ∼170 km altitude near the subsolar point, significantly decreasing with increasing solar zenith angle. There is a strong day‐night asymmetry in the external field, with a typical dayside intensity of ∼15–50 nT and a nightside intensity of ∼5–15 nT. Under high solar wind dynamic pressures and IMFs, the external field may be enhanced by a factor of ∼2 everywhere below the BS, on both the dayside and nightside. In addition, our model results suggest that strong crustal fields, which effectively withstand the penetration of the solar wind, reduce the external field at low altitudes.
... From Figure 6, we can see that r 0 and k are nearly independent of the subsolar longitude, and r 0 and k are slightly greater than others when the subsolar longitude equals 180°( −180°). The difference of r 0 due to the subsolar longitude location (from ∼1.20 R M to ∼1.30 R M ) in this work is slightly less than that reported by Fang et al. (2017; from ∼1.20 R M to ∼1.35 R M ), which might be caused by the different determination method of r 0 . However, the magnetic compression factor changes dramatically with the subsolar longitude, and f gets the relatively larger value when the subsolar longitude is close to −100°, 0°, 100°. ...
... Moreover, the effects of the IMF clock angle on r 0 and f might also be related to the local magnetic reconnection, which needs further investigation. Along with the longitude effect, latitude information is also important, as demonstrated by Fang et al. (2017); the changes in latitude at the subsolar point will undoubtedly affect the location of the strong crustal field and the topology of the magnetic field in the north-south direction of the MSO coordinates. Moreover, the planet's rotation and the anomalous crustal magnetic field add to the complexity of the situation. ...
In this paper, using a three-dimensional multispecies MHD model, we study the effect of the interplanetary magnetic field (IMF) intensity and orientation on the subsolar standoff distance of the Martian magnetic pileup boundary ( r 0 ) and the pressure balance across it. The results show that: (1) with the increasing magnitude of the Y- or Z- component of the IMF, B Y or B Z , r 0 increases, while the radial IMF component, B X , has little effect. With the increasing magnitude of B Y or B Z , the compression degree of the magnetic field ( f ) increases, while the solar wind pressure coefficient ( k ) remains unchanged, resulting in the enhancement of r 0 . (2) Under the same IMF intensity, B t , the impact of the IMF cone angle on r 0 and f is controlled by the ratio of the IMF Y- and Z- components to B t , B Y 2 + B Z 2 / B t . When the ratio is enhanced, both r 0 and f increase, while k generally remains unchanged. Compared with the IMF cone angle, the influence of the IMF clock angle is relatively less. We suggest that the stronger magnetic pileup process controlled by the perpendicular IMFs ( B Y or B Z ) causes the larger r 0 , while the weaker magnetic pileup under the radial IMF leads to the smaller r 0 . The difference in the IMF effect on the size of the Martian magnetic pileup boundary and the terrestrial magnetopause reveals different solar wind interactions with a magnetized and unmagnetized planet. Last, the location of the intense crustal field can also affect r 0 and the pressure balance condition, and the specific impact needs to be further studied.
... There is no doubt that numerical simulation is one of effective methods to explore this subject. However, although there have been many model simulation studies of interaction between solar wind and Mars (e.g., Ma et al., 2004;Najib et al., 2011;Dong et al., 2014;Li et al., 2021) and further the impact of crustal magnetic fields on modifying global Martian ion escape rate (e.g., Fang et al., 2015Fang et al., , 2017, there has been to date no global simulation results of self-consistent Mars-solar wind interaction that devote to resolve the physical mechanism of horizontal and vertical magnetic field directions on the ion vertical transport. In this study, by comparing between cases with and without local dipole magnetic field, we investigate the mechanisms that how these two field directions affect plasma vertical transport using a three-dimensional multi-fluid Hall Magneto-hydrodynamic (MHD) model, which is helpful for understanding how the escape of Martian atmospheric ions influenced by the Martian magnetic field from both local and global perspectives. ...
... Ho we ver, o wing to the existence of une venly distributed crustal sources on the surface of Mars, especially in the Southern hemisphere, the Mars-solar wind interaction is different from that on other unmagnetized planets, such as Venus and Titan (Acu ˜ na et al. 1999 ;Connerney et al. 2005 ;Brain et al. 2007 ;Liemohn et al. 2006 ). The crustal fields change the local distribution of the magnetic pressure and influence the location of plasma boundaries (Brain et al. 2005 ;Edberg et al. 2008Edberg et al. , 2009Fang et al. 2017 ;Wang et al. 2020Wang et al. , 2022a. Furthermore, owing to the interaction between the rotating crustal fields and variable interplanetary magnetic field (IMF), open and closed magnetic topologies are periodically introduced into the Martian magnetosphere (DiBraccio et al. 2018 ;Weber et al. 2020, Zhang, et al. 2022a ). ...
The interaction between impinging magnetised solar wind and Martian crustal fields produces complexly distributed magnetic topologies in the dayside magnetosphere. This study focused on obtaining the distribution of Martian dayside magnetic topology and the structures of the cross-terminator magnetic loops. A three-dimensional multispecies magnetohydrodynamic model was employed to simulate the interactions between Mars and solar winds, and a 110° spherical harmonic model was used to calculate the crustal fields. We randomly extracted more than 1000 magnetic field lines from the near-Mars region of the model results. These results indicate the existence of large-scale closed fields and high-inclination-angle open fields in the southern hemisphere, exerting their influence even above the height of the ionopause, resulting in a complex relationship between plasma motion and magnetic topology distribution. In contrast, the plasma motion patterns in the northern hemisphere are similar to those observed in unmagnetised planets. Furthermore, the model results show two types of cross-terminator magnetic loop. Small-scale cross-terminator magnetic loops connect the local atmosphere on the dayside and nightside, while many large-scale magnetic loops cross the centre-tail region and extend more than 2 RM downstream of Mars, especially in the southern hemisphere. Finally, the clock angle distribution shows magnetic field distortion at 1000 km altitude. This study provides a clearer and more detailed description of the Martian dayside magnetic topology and the structures of the cross-terminator magnetic loops.
