Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm54b..05l&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM54B-05
Physics
[2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions, [2744] Magnetospheric Physics / Magnetotail, [2764] Magnetospheric Physics / Plasma Sheet
Scientific paper
The interaction between the magnetotail and ionosphere in a region of reconnection flow braking is analyzed in a global (LFM) MHD simulation. The simulation includes electrostatic coupling at the low-altitude simulation boundary using the ionospheric Ohm’s law, current continuity, mapping of field-aligned current through the MI gap region with allowance for a field-aligned potential drop, and the effects of electron precipitation using the Knight-Fridman-Lemaire formulation for the number and energy fluxes of precipitating electrons in the Robinson et al (1987) empirical relations for dependence of Pedersen and Hall conductances on auroral precipitation. The simulation is driven by constant SW/IMF conditions with Vsw = 400 km/s, Nsw = 5/cc, and Bz = - 10 nT. It settles into a quasi-stationary, steady magnetospheric convection (SMC) state after an initiating substorm. The magnetotail and braking of the reconnection flow in the SMC state exhibit significant dawn-dusk asymmetry due to the interaction with the ionosphere, which also exhibits dawn-dusk asymmetry due to the effects of intense electron precipitation in the pre-midnight region of upward field-aligned current. These strong asymmetries in the magnetosphere and ionosphere disappear when the ionospheric Hall conductance is treated as constant. The electromagnetic dynamo (local magnetotail Jy < 0) produced by braking of the more intense, duskside reconnection flow powers ionospheric Joule dissipation in a pre-midnight (Bostrom) Type 1 auroral current circuit, which develops at the poleward edge of the conductance gradient in the nightside convection throat. Hall currents are diverted into field-aligned currents in this region as the convection streamlines begin to turn sunward (see figure). Hall currents also connect these field-aligned currents to the R2 current dynamo that projects from the inner magnetosphere to lower latitudes. Large Alfvénic Poynting fluxes flow into the premidnight auroral zone from the simulated SMC flow brake, with a time-average pattern resembling statistical patterns from Polar satellite data (Keiling et al, 2003) and FAST satellite data (Chaston et al, 2003). Intense Alfvénic aurora is expected in these regions. Synthetic satellite data in and around the time-variable flow brake resemble observed bursty bulk flows (BBFs) in some regions, but the intense SMC flow is more regular and persistent than is typical of BBFs. Nightside equatorial plasmasheet with flow vectors, plasma pressure contours (yellow) and Bz = 0 contour (white) overlaid on j.E in color. (Right) Ionosphere with potential contours overlaid on field-aligned current in color. Braking of duskside BBF near (x,y) = (-13, 3) RE is evident.
Brambles O. J.
Lotko William
Zhang Baigang
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