On the relationship between auroral absorption, electrojet currents and plasma convection

• Main Authors: Hansen, Truls Lynne, Kellerman, A. C., Makarevich, R. A., Honary, F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications on behalf of the European Geosciences Union 2009
• Subjects: VDP::Mathematics and natural science: 400::Physics: 430::Space and plasma physics: 437; Ionosphere; Auroral ionosphere; Electric fields and currents; Particle precipitation; VDP::Mathematics and natural science: 400::Physics: 430::Electromagnetism; acoustics; optics: 434; Tromsø; EISCAT
• Online Access: https://hdl.handle.net/10037/2386

This is the publisher’s version/PDF (Published in Annales Geophysicae, an open access journal of the European Geosciences Union) In this study, the relationship between auroral absorption, electrojet currents, and ionospheric plasma convection velocity is investigated using a series of new methods where temporal correlations are calculated and analysed for different events and MLT sectors. We employ cosmic noise absorption (CNA) observations obtained by the Imaging Riometer for Ionospheric Studies (IRIS) system in Kilpisj¨arvi, Finland, plasma convection measurements by the European Incoherent Scatter (EISCAT) radar, and estimates of the electrojet currents derived from the Tromsø magnetometer data. The IRIS absorption and EISCAT plasma convection measurements are used as a proxy for the particle precipitation component of the Hall conductance and ionospheric electric field, respectively. It is shown that the electrojet currents are affected by both enhanced conductance and electric field but with the relative importance of these two factors varying with magnetic local time (MLT). The correlation between the current and electric field (absorption) is the highest at 12:00– 15:00MLT (00:00–03:00MLT). It is demonstrated that the electric-field-dominant region is asymmetric with respect to magnetic-noon-midnight meridian extending from 09:00 to 21:00MLT. This may be related to the recently reported absence of mirror-symmetry between the effects of positive and negative IMF By on the high-latitude plasma convection pattern. The conductivity-dominant region is somewhat wider than previously thought extending from 21:00 to 09:00MLT with correlation slowly declining from midnight towards the morning, which is interpreted as being in part due to highenergy electron clouds gradually depleting and drifting from midnight towards the morning sector. The conductivitydominant region is further investigated using the extensiveIRIS riometer and Tromsø magnetometer datasets with results showing a distinct seasonal dependence. ...