LONG-TERM VARIATIONS IN THE HIGH-LATITUDE PLASMA FLOWS INFERRED FROM SUPERDARN RADAR DATA

Abstract

ABSTRACT

This Thesis investigates ionospheric plasma flows (commonly referred to as “convection”) at high latitudes with the objectives to assess seasonal and solar cycle variations in the shape of the flow patterns and the flow intensity in terms of external drivers of the flow, first of all the magnitude and orientation of the interplanetary magnetic field (IMF). Multi-year (2001-1011) line-of-sight Doppler velocity data collected by the Super Dual Auroral Network (SuperDARN) HF radars are considered. Two approaches are used: 1) analysis of monthly-averaged 2-dimentional patterns inferred from data of all SuperDARN radars operated and 2) analysis of near magnetic noon data from only two SuperDARN radars, Rankin Inlet and Inuvik monitoring meridional component of the flow in the near North Pole areas (polar cap). We show and discuss seasonal and solar cycle variations of three characteristics of the flows: magnetic latitudes of the region where plasma flow direction changes from toward the noon to away from the noon (convection reversal boundary), the magnetic local time location of the near noon region with stagnated flow (throat region) and, finally, the magnitude of the flow. All three parameters show trends, although not strong and consistent all the time, which agrees with previous publications where different analysis approaches and more limited data sets were used. For two specific points, one at the magnetic latitude of 72 degrees, representing the auroral oval latitudes (region where optical arcs occur most frequently) and the other one at 82 degrees, representing the polar cap latitudes we demonstrate that the average flow magnitude increases with the IMF intensity, and the effect is much stronger for the negative vertical component of the IMF Bz. In our second approach we demonstrate that the flow velocity increases almost linearly with an increase of the reconnection electric fields characterizing processes of interaction between the solar wind/IMF and the Earth`s magnetic dipole. Saturation effect is seen for strongest electric field. More clear seasonal effects are noticeable in these data; the velocity response to the reconnection electric field enhancement is stronger summer (winter) time for positive (negative) IMF Bz. The data are consistent with previous reports, where highly smoothed velocity data were considered.