Open‐closed field line boundary position: A parametric study using an MHD model

Кабин, К.; Rankin, R.; Rostoker, G.; Marchand, R.; Rae, I. J.; Ridley, A. J.; Gombosi, T. I.; Clauer, C. R.; Zeeuw, Darren L. De

doi:10.1029/2003ja010168

Cited by 48 publications

(54 citation statements)

References 27 publications

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“…However, their studies have not considered events under the northward IMF condition. When the clock angle >65 • , the midnight polar caps are at the same latitudes in the Northern as in the Southern Hemisphere, which deviates from previous studies stating that the summer polar cap in the midnight is located at higher latitude than the winter (Kabin et al, 2004). The summer polar cap around noon is in general located at lower latitude than the winter polar cap, which is consistent with previous results showing that the winter open/closed polar cap boundary is located at higher latitudes than in the summer on the dayside (Kabin et al, 2004).…”

Section: Polar Cap Boundary and Plasma Sheetcontrasting

confidence: 99%

“…This is quite comparable to previous observation results that for the development of the FACs from the magnetopause to the ionosphere an average delay of 15-22 min has been considered (Clauer and Friis-Christensen, 1988;Vennerstrom et al, 2002;Kabin et al, 2003). The model results also indicate that it takes a little longer for the south (i.e.…”

Section: Time Delaysupporting

confidence: 90%

“…The hemispheric difference of the open/closed polar cap boundary on the nightside can reach 12 • , while previous studies reported that changing the dipole tilt angle by 35 • results only in 1-2 • latitude change in the open/closed boundary (Kabin et al, 2004). However, their studies have not considered events under the northward IMF condition.…”

Section: Polar Cap Boundary and Plasma Sheetmentioning

confidence: 90%

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SWMF simulation of field-aligned currents for a varying northward and duskward IMF with nonzero dipole tilt

2008

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Abstract. This study concentrates on the FACs distribution for the varying northward and duskward interplanetary magnetic field (IMF) conditions when the dipole tilt is nonzero. A global MHD simulation (the Space Weather Modeling Framework, SWMF) has been used to perform this study. Hemispheric asymmetry of the time evolution of northward IMF B z (NBZ) FACs is found. As the IMF changes from strictly northward to duskward, NBZ FACs shift counterclockwise in both summer and winter hemispheres. However, in the winter hemisphere, the counterclockwise rotation prohibits the duskward NBZ FACs from evolving into the midday R1 FACs. The midday R1 FACs seem to be an intrusion of dawnside R1 FACs. In the summer hemisphere, the NBZ FACs can evolve into the DPY FACs, consisting of the midday R0 and R1 FACs, after the counterclockwise rotation. The hemispheric asymmetry is due to the fact that the dipole tilt favors more reconnection between the IMF and the summer magnetosphere. When mapping the NBZ and DPY FACs into the magnetosphere it is found that the NBZ currents are located on both open and closed field lines, irrespective of the IMF direction. For the DPY FACs the hemispheric asymmetry emerges: the midday R1 FACs and a small part of R0 FACs are on closed field lines in the winter hemisphere, while a small part of the midday R1 FACs and all the R0 FACs are on open field lines in the summer hemisphere. Both IMF B y and dipole tilt cause the polar cap hemispheric and local time asymmetric. When the IMF is northward, the summer polar cap is closed on the nightside while the winter polar cap is open. The polar cap boundary tends to move equatorward as the IMF rotates from northward to duskward, except in the summer hemisphere, the polar cap on the dawnside shifts poleward when the clock angle is less than 10 • . The further poleward displacement of the polar cap boundary on one oval side is caused by the Correspondence to: H. Wang (whui@umich.edu) twist of the tail plasma sheet, which is in accordance with the changing open field lines topology in the magnetotail.

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Section: Polar Cap Boundary and Plasma Sheetcontrasting

confidence: 99%

Section: Time Delaysupporting

confidence: 90%

Section: Polar Cap Boundary and Plasma Sheetmentioning

confidence: 90%

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SWMF simulation of field-aligned currents for a varying northward and duskward IMF with nonzero dipole tilt

2008

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“…The University of Michigan's MHD code is the Block Adaptive Tree Solar-wind Roe-type Upwind Scheme (BAT-SRUS) (Powell et al, 1999b;Ridley et al, 2002; that can model the Earth's global magnetosphere (Kabin et al, 2003Vogt et al, 2004;Ridley et al, 2006;Watanabe et al, 2005;Ridley, 2007;, as well as the solar corona (Manchester et al, 2004b), the inner and outer heliosphere (Opher et al, 2003;Manchester et al, 2004c,a), Mercury (Kabin et al, 2000), Venus, Mars (Ma et al, 2004), Jupiter (Kabin et al, 2001), Saturn (Hansen et al, 2000(Hansen et al, , 2005, Uranus , Titan (Ma et al, 2009), andcomets (Gombosi et al, 1999). Because BATSRUS is a general MHD solver, and is not explicitly designed for solving a specific problem, it has many more options than typical magnetospheric MHD codes.…”

Section: Modeling the Magnetospherementioning

confidence: 99%

Numerical considerations in simulating the global magnetosphere

et al. 2010

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Abstract. Magnetohydrodynamic (MHD) models of the global magnetosphere are very good research tools for investigating the topology and dynamics of the near-Earth space environment. While these models have obvious limitations in regions that are not well described by the MHD equations, they can typically be used (or are used) to investigate the majority of magnetosphere. Often, a secondary consideration is overlooked by researchers when utilizing global models -the effects of solving the MHD equations on a grid, instead of analytically. Any discretization unavoidably introduces numerical artifacts that affect the solution to various degrees. This paper investigates some of the consequences of the numerical schemes and grids that are used to solve the MHD equations in the global magnetosphere. Specifically, the University of Michigan's MHD code is used to investigate the role of grid resolution, numerical schemes, limiters, inner magnetospheric density boundary conditions, and the artificial lowering of the speed of light on the strength of the ionospheric cross polar cap potential and the build up of the ring current in the inner magnetosphere. It is concluded that even with a very good solver and the highest affordable grid resolution, the inner magnetosphere is not grid converged. Artificially reducing the speed of light reduces the numerical diffusion that helps to achieve better agreement with data. It is further concluded that many numerical effects work nonlinearly to complicate the interpretation of the physics within the magnetosphere, and so simulation results should be scrutinized very carefully before a physical interpretation of the results is made. Our conclusions are not limited to the Michigan MHD code, but apply to all MHD models due to the limitations of computational resources.

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“…The SWMF consists of several numerical modules, such as the ideal MHD solver (BATS-R-US) [13,14], Ionospheric Electrodynamics (IE) model [15], and Rice Convection Model (RCM) [16]. The SWMF family of models has been used extensively to study various solar wind influences on the magnetosphere; for example, convection under the northward IMF [17], IMF B Y [18], and Parker spiral [19] conditions and storm dynamics [20,21]. Welling and Ridley [22] discussed validation of the SWMF magnetic field and plasma using satellite measurements.…”

Section: Global Mhd Model Of Space Weather Modeling Framework (Swmf)mentioning

confidence: 99%

Dependence of magnetic field just inside the magnetopause on subsolar standoff distance: Global MHD results

Wang

Liu

et al. 2012

Chin. Sci. Bull.

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The subsolar magnetopause is the boundary between the solar wind and the Earth's magnetosphere, where reduced solar wind dynamic pressure is equal to the magnetic pressure of the Earth's outer magnetosphere. We use a global magnetohydrodynamic (MHD) model to estimate the ratio f of the compressed magnetic field just inside the subsolar magnetopause to the purely dipolar magnetic field. We also compare our numerical results to a similar work by Shue, which used Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. Our results show that the ratio f is linearly proportional to the subsolar magnetopause standoff distance (r 0 ) for both the northward and southward interplanetary magnetic field, properties consistent with Shue but with a smaller proportionality constant. However, previous theoretical studies show that f is nearly independent of the subsolar standoff distance. The global model results also show that f is smaller for the southward Interplanetary Magnetic Field (IMF) under the same r 0 , and that the proportionality constant for the southward IMF is larger than that for the northward IMF. Both conclusions agree with statistical results from observations by Shue. Previous theoretical studies without consideration of the impact of the solar wind take the internal magnetic field of the earth as a purely dipolar field. In the sun-earth line, knowing the distance from the earth, we can calculate the magnetic field at this position, as follows [1]:where B d0 is the magnetic field for a purely dipolar field, M=8.1×1025 Gs cm 3 is a constant, and r is the distance from the earth.When the solar wind flows toward the earth around the magnetosphere, the solar wind dynamic pressure D p is reduced. The reduced dynamic pressure is equal to the magnetic pressure of the earth's magnetosphere at the subsolar magnetopause [2]:where k is the reduction factor of the solar wind dynamic pressure, B g0 is the compressed magnetic field just inside the subsolar magnetopause, and μ 0 is the permeability in free space.Typically one can assume that k is a constant (k=0.881); then, B g0 becomes a variable about solar wind dynamic pressure D p . B d0 is a variable about the distance from the earth on the sun-earth line for a purely dipolar field, so we take a ratio f of the magnetic field just inside the subsolar magnetopause (B g0 ) to the purely dipolar magnetic field (B d0 ), for quantifying the compression level of the magnetic field. That is [2], f = B g0 /B d0 . (3) Previous theoretical studies with simplified magnetosphere models assumed that f was nearly independent of r 0

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Open‐closed field line boundary position: A parametric study using an MHD model

Cited by 48 publications

References 27 publications

SWMF simulation of field-aligned currents for a varying northward and duskward IMF with nonzero dipole tilt

SWMF simulation of field-aligned currents for a varying northward and duskward IMF with nonzero dipole tilt

Numerical considerations in simulating the global magnetosphere

Dependence of magnetic field just inside the magnetopause on subsolar standoff distance: Global MHD results

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