Nightside Ionospheric Convection Asymmetries During the Early Substorm Expansion Phase: Relationship to Onset Local Time

• Published in: Geophysical research letters 2017-12, Vol.44 (23), p.11,696-11,705
• Main Authors: Grocott, A., Laurens, H. J., Wild, J. A.
• Format: Article
• Language: English
• Subjects: Asymmetry; Atmosphere; Atmospheric models; Charging; Communication satellites; Convection; Convection modes; Convection patterns; Empirical models; Geophysics; Global positioning systems; GPS; Interplanetary magnetic field; Ionosphere; Ionospheric convection; Latitude; Magnetic field; Magnetic fields; magnetosphere; Magnetospheres; Magnetospheric substorms; Morphology; Radar; Radar networks; Radio communications; Satellite navigation systems; Satellite orbits; Satellites; Space weather; substorm; superdarn; Weather effects
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL075763

We present Super Dual Auroral Radar Network observations of ionospheric convection during substorms. Substorms were grouped according to their onset latitude, onset magnetic local time, and the prevailing sense of interplanetary magnetic field (IMF) BY. The radar observations were then sorted according to substorm group and average convection patterns produced. Here we discuss the patterns corresponding to substorms with onsets occurring in the 65∘–67∘ onset latitude range, at either early (20–22 h) or late (01–03 h) magnetic local times, during intervals of either dominant positive or negative IMF BY. We show that the morphology of the convection patterns differs from that predicted by existing empirical models, with the location of the nightside convection throat being largely consistent with the location of substorm onset. The expected IMF BY‐induced dawn‐dusk convection asymmetry can be enhanced on the nightside when the substorm onset occurs at a fortuitous location but can equally be removed or even reversed from this expected state. Thus, the nightside convection asymmetries are seemingly unrelated to the instantaneous sense of IMF BY. Plain Language Summary One of the main drivers of the aurora, or northern lights, is a phenomenon called the “magnetospheric substorm.” Substorms deposit large amounts of energy into the atmosphere, affecting the flow of plasma—an electrically charged gas—high up in the atmosphere, and producing various “space weather” effects that can disrupt radio communications, satellite orbits, and GPS transmissions. Substorms occur on the nightside of the planet, at a variety of local times from 2100 to 0300 h and their effect on the plasma flow is correspondingly variable. In this paper, we show what form the atmospheric plasma flows take during substorms occurring at different local times. We conclude that clear differences in the flows associated with substorms at different local times are apparent. These effects are distinct from those currently included in geophysics models. Key Points Substorm onset location is related to the morphology of the nightside ionospheric convection pattern Substorm local time‐related asymmetries override those associated with IMF By Substorm onset local time is associated with an enhancement, reduction or mirroring of the expected By asymmetry