Traveling convection vortices at cusp latitudes observed by the magnetometer array for cusp and cleft studies.

摘要

Traveling Convection Vortices (TCVs) are a dayside, transient type of event observed at high latitudes in ground magnetometer records and are thought to be the result of pressure pulses in the solar wind hitting the magnetopause, the earth's magnetospheric boundary. They consist of a series of vortical ionospheric currents traveling away from local noon. Field-aligned currents at the center of each vortex couple perturbations from the magnetopause to the ionosphere. We used data from the Magnetometer Array for Cusp and Cleft Studies (MACCS), a two-dimensional chain of magnetometers located in the Canadian Arctic at cusp latitudes. Building the systems for MACCS was the starting point of this Ph.D. work. The stations were installed during the summers of 1992 and 1993.; We studied the morphology of TCV events by combining a one-year statistical study and mapping of two-dimensional TCV currents in time. By investigating possible source mechanisms, we found that TCV signatures actually represent more than one mode of interaction between the magnetosphere and the solar wind. We identified two possible source mechanisms. First, pressure pulses in the solar wind do cause TCV signatures in the ionosphere. This mode of interaction seems to favor the weak, radial interplanetary magnetic field (IMF). To create a localized perturbation at the magnetopause, the disturbance must have a 100% change of pressure occurring within minutes. We found that existing models for this mode of coupling between the solar wind and the magnetosphere are incomplete. Observed signatures indicate more complicated current structures. Another class of TCVs are caused by changes in the direction of the IMF east-west component, which in turn cause changes in the large-scale convection pattern of the high-latitude ionosphere. The readjustment of the large-scale convection is associated with sets of vortical currents propagating away from magnetic local noon. All types of TCVs favor geomagnetically quiet times.; We found that TCVs occur more frequently than once per day, the majority being localized events. The currents associated with them propagate away from magnetic local noon but not in a uniform fashion. Individual vortices tend to accelerate as they strengthen and decelerate as they disappear.