Kellerman A. C., R. A. Makarevich, F. Honary, T. L. Hansen, (2009), On the relationship between auroral absorption, electrojet currents and plasma convection, Annales Geophysicae, 27, 473–486, doi:10.5194/angeo-27-473-2009

Abstract

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 Kilpisjärvi, 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 12:00–15:00 MLT (00:00–03:00 MLT). It is demonstrated that the electric-field-dominant region is asymmetric with respect to magnetic-noon-midnight meridian extending from 09:00 to 21:00 MLT. 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 09:00 MLT with correlation slowly declining from midnight towards the morning, which is interpreted as being in part due to high-energy electron clouds gradually depleting and drifting from midnight towards the morning sector. The conductivity-dominant region is further investigated using the extensive IRIS riometer and Tromsø magnetometer datasets with results showing a distinct seasonal dependence. The region of high current-absorption correlation extends from 21:00 to 06:00 MLT near both equinoxes, however, it is narrower and rotated towards the morning (02:00–07:00 MLT) in summer, while in winter the correlation shows much greater variability with MLT. During periods of high current-electric-field correlation, the relationship between electric field and absorption can be described as an inverse proportionality, which can be explained by limitation of the electrojet current by the magnetospheric generator. Possible cases of electron heating absorption are also investigated with absorption showing no obvious dependence on the ion velocity or electron temperature.

Authors (sorted by name)

Hansen Honary Kellerman Makarevich

Journal / Conference

Annales Geophysicae

Acknowledgments

This research was supported by the Australian Research Council Discovery grant to R. A. M. (project DP0770366). The Imaging Riometer for Ionospheric Studies (IRIS) is operated by the Department of Communications Systems at Lancaster University (UK) in collaboration with the Sodankyla Geo- ¨ physical Observatory, and funded by the Science and Technology Facilities Council (STFC). The IMAGE magnetometer data are collected as a Finnish-German-Norwegian-Polish-Russian-Swedish project conducted by the Technical University of Braunschweig and Finnish Meteorological Institute. EISCAT is an International Association supported by Finland (SA), France (CNRS), Germany (MPG), Japan (NIPR), Norway (NFR), Sweden (NFR), and the UK (STFC). The authors thank H. Yamagishi, A. Grocott, and Y. Bogdanova for useful discussions and suggestions

Bibtex

@Article{angeo-27-473-2009,
AUTHOR = {Kellerman, A. C. and Makarevich, R. A. and Honary, F. and Hansen, T. L.},
TITLE = {On the relationship between auroral absorption, electrojet currents and plasma convection},
JOURNAL = {Annales Geophysicae},
VOLUME = {27},
YEAR = {2009},
NUMBER = {2},
PAGES = {473--486},
URL = {https://www.ann-geophys.net/27/473/2009/},
DOI = {10.5194/angeo-27-473-2009},
abstract = {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 Kilpisjärvi, 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 12:00–15:00 MLT (00:00–03:00 MLT). It is demonstrated that the electric-field-dominant region is asymmetric with respect to magnetic-noon-midnight meridian extending from 09:00 to 21:00 MLT. 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 09:00 MLT with correlation slowly declining from midnight towards the morning, which is interpreted as being in part due to high-energy electron clouds gradually depleting and drifting from midnight towards the morning sector. The conductivity-dominant region is further investigated using the extensive IRIS riometer and Tromsø magnetometer datasets with results showing a distinct seasonal dependence. The region of high current-absorption correlation extends from 21:00 to 06:00 MLT near both equinoxes, however, it is narrower and rotated towards the morning (02:00–07:00 MLT) in summer, while in winter the correlation shows much greater variability with MLT. During periods of high current-electric-field correlation, the relationship between electric field and absorption can be described as an inverse proportionality, which can be explained by limitation of the electrojet current by the magnetospheric generator. Possible cases of electron heating absorption are also investigated with absorption showing no obvious dependence on the ion velocity or electron temperature.}
}