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Long‐term variations in the intensity of polar cap plasma flows inferred from SuperDARN
Author(s) -
Koustov A. V.,
Fiori R. A. D.,
Abooali zadeh Z.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021625
Subject(s) - noon , ionosphere , interplanetary magnetic field , polar , physics , atmospheric sciences , intensity (physics) , solar cycle , diurnal temperature variation , diurnal cycle , environmental science , plasma , solar wind , geophysics , astronomy , quantum mechanics
Multiyear (1995–2013) velocity data collected by the Super Dual Auroral Network (SuperDARN) HF radars are considered to investigate the diurnal, seasonal, and solar cycle variation of the polar cap plasma flow speed. By considering monthly data sets, we show that the flows are systematically faster in the dawn/prenoon sector. The effect is particularly strong for interplanetary magnetic field (IMF) B z < 0, B y > 0 and in summer months. For B z < 0, the flow speed increases with intensification of the IMF transverse component B t at a rate of 20–30 m/s/nT during near noon summer hours. The dependence is weaker for other seasons and away from noon. For IMF B z > 0, the flow speed response to the increase in B t is weak. Despite the general sensitivity of the flow speed to B t intensity and season, the speed for specific IMF bins and seasons or the speed averaged over a year does not change much over the solar cycle. Overall, the velocity is reduced during years of lowest solar activity, but a progression of the effect throughout the solar cycle was not observed. Inferred diurnal and seasonal trends of the polar cap flow speed are generally consistent with variations in the occurrence of VHF echoes whose onset depends on the strength of the ionospheric electric field or equivalently the magnitude of the plasma flow speed.