2.5D MPD Multiple Dipole simulations
Initial 2D MHD simulations indicated that mini-magnetospheres
can form around magnetic anomalies on the
surface of the Moon, but required magnetic field
strengths at 100 km above the surface an order of magnitude larger
than in situ measurements.
Modeling the lunar magnetic anomalies with multiple dipoles in 2.5D
MHD simulations inflates the size of the mini-magnetospheres
for only small increases in the magnitude of the
total magnetic field. Multiple dipoles increase the lateral distance over
which solar wind plasma is held off the surface.
This extended magnetic field geometry inflates the mini-magnetosphere
by inhibiting fluid flow within the shock region. With multiple dipoles, a
mini-magnetosphere will form with magnetic field magnitudes
smaller than the lower limit for a single dipole.
These results indicate that the higher order moments of the anomalous
magnetic fields play a significant role in deflecting the solar wind
and determining the size and shape of the mini-magnetosphere.
Density plots and magnetic
field lines for four different cases with two dipoles.
The dipole moments are in the +z direction producing a large magnetic
field at 100 km in (a) then both dipoles are flipped to the -z
direction with the same magnitude in (b). In (c) the dipole moments
are opposing directions, and then each dipole moment is flipped
180 degrees in (d). The moon has a
constant density of 4.0 \(\rm{cm}^{-3}\) and the solar wind a density of
10.0 cm^-3. The boxes contain an area 870 km by 1218 km,
with each tick mark equal to 5 grid points or 43.5 km. The density
contours were smoothed slightly to reduce minor pixilation. The maximum
value in the density corresponds to white on the color bar.
(From Harnett and Winglee, JGR, vol. 108, 2003).
The inner
dipole moments in (a) are in the +z direction while the outer dipoles
in the -z direction. Each dipole in (b) is180 degrees rotated from
its neighboring dipoles. The middle dipoles in (c) are in the +x
direction while the outer dipole moments are in the -x direction.
The dipoles in (d) are radial, alternating between +r and -r. The sharp
kinks in the magnetic field lines in (d) are due to numerical
uncertainties in calculating the magnetic field lines for dipoles not
aligned with one of the axes.
(From Harnett and Winglee, JGR, vol. 108, 2003).
eharnett at ess.washington.edu
Last modified: Tue Jun 22 14:28:07 PDT 2004
