IMF B_y‐dependent plasma flow and Birkeland currents in the dayside magnetosphere: 1. Dynamics Explorer observations

Abstract

Plasma, magnetic‐field and dc electric‐field observations from Dynamics Explorers 1 and 2 are used to investigate the morphology of solar‐wind ion injection, Birkeland currents, and plasma convection in the morning sector for both positive and negative interplanetary magnetic field (IMF) By components. The results of the study are used to construct a By‐dependent global convection model for southward IMF. A significant element of the model is the coexistence of three types of convection cells (“merging cells,” “viscous cells,” and “lobe cells”). This model can account for observations of a nearly stationary (in local time) convection “throat,” a sunward‐antisunward convection reversal zone at the polar‐cap boundary in both the morning and afternoon quadrants, the morphology of solar‐wind ion injection and transport in the mid‐altitude polar cusp, and the By‐dependent dawn‐dusk asymmetry of polar‐cap electron fluxes.

Measuring the dayside reconnection rate during an interval of due northward interplanetary magnetic field

“…The figures are drawn assuming that the IMF B y component is small compared to the B z component, under which conditions the convection cells are symmetric and roughly equal in size. As the magnitude of the IMF B y component increases, one of these cells will start to dominate the convection and introduce asymmetry into the convection scenario (Russell, 1972;Heelis, 1984;Burch et al, 1985;Reiff and Burch, 1985). Figure 1a illustrates the scenario which results from reconnection in one hemisphere only, when no new closed flux is created.…”

Alfvén Mach number and IMF clock angle dependencies of sunward flow channels in the magnetosphere

“…The proposed flow is azimuthally directed toward the northern dusk (dawn) for negative (positive) IMF By with opposite flow directions expected in the Southern Hemisphere (SH) for the same IMF By. This is known as the Svalgaard-Mansurov effect [Svalgaard, 1968;Mansurov, 1969] which is believed to be caused by IMF By-dependent flank magnetopause reconnection [e.g., Friis-Christensen et al, 1972;Burch et al, 1985;Eriksson et al, 2005;Li et al, 2011].…”

Magnetospheric Model Performance during Conjugate Aurora

“…However, this event occurred with a clock angle ranging from 90 to 140 degrees, an average Bx of 6 nT, and a solar wind density ranging from 12 cm -3 to 20cm -3 , indicating that something else is occurring within the dusk convection cell. Crooker and Rich, [1993] found that a convection pattern like this in the summer hemisphere during a strong +By period is best explained by a lobe cell circulating within the dusk convection cell Burch et al, 1985].…”