Timescales Of The Influence Of IMF Clock Angle In Controlling The Characteristics Of Magnetospheric Dynamics

We exploit a database of high-latitude ionospheric electric potential patterns, derived from radar observations of plasma convection in the northern hemisphere from the years 2000 - 2006, to investigate the timescales of interplanetary magnetic field (IMF) penetration into the magnetosphere. We parameterise the convection observations by IMF clock angle, θ (the angle between geocentric solar magnetic (GSM) north and the projection of the IMF vector onto the GSM Y-Z plane), and by an IMF timescale, τ_B (the length of time that a similar clock angle has been maintained prior to the convection observations being made). We find that the nature of the ionospheric convection changes with IMF clock angle, as expected from previous time-averaged studies, and that for τ_B ~ 30 mins the convection patterns closely resemble their time-averaged counterparts. However, we also find that for certain IMF clock angles, in particular those with a northward B_Z component and significant B_Y (dusk-dawn) component, the patterns evolve with increasing τ_B to less resemble their time-averaged counterparts, showing a marked enhancement in dusk-dawn asymmetry as τ_B approaches 10 hours. We discuss these findings in terms of the effects of the persistent penetration of a quasi-steady IMF into the magnetosphere, and its implications for understanding different modes of magnetospheric dynamics.