Erika Megan Harnett

Three‐dimensional multifluid simulations of ionospheric loss at Mars from nominal solar wind conditions to magnetic cloud events

conditions. Ionospheric losses on the order of 10 25 O2 ions per second are found for quiet solar wind conditions. This is of the same order as that estimated from Phobos 2 measurements. Varying the orientation of Mars’ magnetic anomalies relative to the incident solar wind direction leads to only minor variation in the ionospheric loss rates of O2 for each set of solar wind conditions studied. Solar wind parameters were varied from nominal solar wind conditions to conditions with high-speed flows, high densities, and large IMF magnitudes. Outflow rates on the order of 10 26 O2 ions per second were seen for storm-like conditions. The simulations indicate that ionospheric outflow rates increase by a larger percentage for high solar wind number density when compared to high solar wind speed or strong IMF conditions alone. This is due to the higher solar wind density and temperature of the precipitating ions. The results also indicate a significant influence of pickup on ionospheric loss.

Two-dimensional MHD simulation of the solar wind interaction with magnetic field anomalies on the surface of the Moon

Two-dimensional magnetohydrodynamic simulations of the solar wind interaction with the magnetized regions on the surface of the Moon suggest “mini-magnetospheres” can form around the regions on the Moon when the magnetic anomaly field strength is above 10 nT at 100 km above the surface (for a surface field strength of 290 nT) and when the solar wind ion density is below 40 cm−3, with typical observations placing anomalous magnetic field strengths around 2 nT at 100 km above the surface. The results suggest that not only can a bow shock and magnetopause form around the small anomalies, but their position and shape can change dramatically with changes in the solar wind conditions. A switch from southward to northward interplanetary magnetic field (IMF) causes the size of the mini-magnetosphere to increase by 90% and the magnetic field at various positions inside the bow shock to increase by a factor of 10. In addition to affecting the stand-off distance, changes in the IMF can also cause the mini-magnetosphere to go from very round to flat and elongated. The scale size of the mini-magnetospheres is 100 km for the range of typical solar wind conditions and the surface magnetic field strengths measured by Lunar Prospector. A stagnation point inside the shock region also exists for several solar wind conditions.

The influence of a mini-magnetopause on the magnetic pileup boundary at Mars

[1] 3D single fluid non-ideal MHD simulations are used to predict positions for the bow shock and magnetic pileup boundary (MPB). The positions are in agreement with those calculated from Mars Global Surveyor data. The simulations were run with the strong southern magnetic anomalies facing into the solar wind, and the IMF in either the northward or southward direction. The simulations show that the strong southern magnetic anomalies create a magnetopause-like structure (i.e., a mini-magnetopause) in place of an MPB but plasma signatures for both types of boundaries are similar. Distinguishing characteristics include the magnetic field orientation, pressure, and the current. The current regions associated with a mini-magnetopause are larger in scale and greater in magnitude than those at the MPB. The simulations also show that including non-ideal MHD physics is important in resolving both the magnetic pileup boundary and the mini-magnetopause.

Erosion of the dayside magnetosphere at Mercury in association with ion outflows and flux rope generation

[1] In preparation for the arrival of the MESSENGER spacecraft at Mercury, and to further understanding of the Mariner 10 and ground-based observations, 3-D multifluid simulations are used to predict Mercury’s magnetospheric response to forcing from the solar wind. The model, which includes both heavy (Na + ) and light (He + ) ionospheric ion populations, predicts that solar wind access to Mercury’s surface is highly asymmetric and dependent on the strength and direction of the interplanetary magnetic field (IMF). In particular, during southward IMF much of the dayside magnetic field can be eroded, and enhanced plumes of sodium ions (with geometry similar to ground-based emission observations) outflow at high latitudes into the solar wind. Development of reconnection in association with flux ropes similar to those at Earth are seen but with a shorter time scale of development and a closer radial distance (3–5 RM).

Multiscale/multifluid simulations of flux ropes at the magnetopause within a global magnetospheric model

[1] The magnetopause current sheet is known to have a thickness comparable to an ion gyroradius/skin depth where the magnetic and electric field can differ markedly from that assumed in MHD treatments. Multifluid/multiscale simulations are used to provide the first investigation of these processes in a global simulation that includes high-resolution (200 km) gridding around the magnetopause. It is shown that the model is able to capture the quadrupole core magnetic field and the fast (tens of ion cyclotron periods) reconnection seen in idealized studies reconnection for a Harris current sheet. Within a global magnetosphere, multiple X-line reconnection occurs for southward IMF due to localized pinching of the magnetopause current sheet via the convection of the magnetosheath plasma against a three-dimensional magnetopause. Localized flux ropes with a thickness of a few hundred to a few thousand kilometers develop and can expand laterally due to current sheet acceleration of ions that have a gyroradius comparable to the current sheet thickness. These flux ropes are shown to have essentially the same properties as flux transfer events (FTEs), including being quasi-periodic with a curvature greater on the magnetosheath side than on the magnetospheric side, a strong core magnetic field, and a mixture of magnetospheric and magnetosheath plasma. The speeds of the plasma flows associated with flux ropes are also similar to those observed with FTEs. The presence of multiple X-line reconnection is shown to produce the rippling of the magnetopause and gives a nature explanation to the multiple magnetopause encounters that typically occur for slow moving spacecraft. These small-scale processes are shown to have global effects with a reduction of the cross-polar cap by as much as 20% seen between simulations with and without high resolution about the magnetopause.

EXTRASOLAR GIANT MAGNETOSPHERIC RESPONSE TO STEADY-STATE STELLAR WIND PRESSURE AT 10, 5, 1, AND 0.2 au

A three-dimensional, multifluid simulation of a giant planets magnetospheric interaction with steady-state stellar wind from a Sun-like star was performed for four different orbital semi-major axes - 10, 5, 1 and 0.2 AU. We simulate the effect of the increasing, steady-state stellar wind pressure related to the planetary orbital semi-major axis on the global magnetospheric dynamics for a Saturn-like planet, including an Enceladus-like plasma torus. Mass loss processes are shown to vary with orbital distance, with the centrifugal interchange instability displayed only in the 10 AU and 5 AU cases which reach a state of mass loss equilibrium more slowly than the 1 AU or 0.2 AU cases. The compression of the magnetosphere in the 1 AU and 0.2 AU cases contributes to the quenching of the interchange process by increasing the ratio of total plasma thermal energy to corotational energy. The strength of field-aligned currents (FAC), associated with auroral radio emissions, are shown to increase in magnitude and latitudinal coverage with a corresponding shift equatorward from increased dynamic ram pressure experienced in the hotter orbits. Similar to observed hot Jovian planets, the warm exo-Saturn simulated in the current work shows enhanced ion density in the magnetosheath and magnetopause regions, as well as the plasma torus which could contribute to altered transit signals, suggesting that for planets in warmer (

A comparison of global models for the solar wind interaction with Mars

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2.5‐D fluid simulations of the solar wind interacting with multiple dipoles on the surface of the Moon

0.1 AU) orbits, planetary magnetic field strengths and possibly exomoons - via the plasma torus - could be observable with future missions.