High latitude dayside aurora (HiLDA) ionospheric electrodynamics using data assimilation

Under favorable conditions, the interaction between the interplanetary magnetic field (IMF) and Earth’s magnetic field can produce a dayside aurora at magnetic latitudes above approximately 80 degrees, commonly referred to as the High Latitude Dayside Aurora (HiLDA). This term encompasses various recently identified dayside auroras, including phenomena like space hurricanes and 15 MLT polar cap auroras (15MLT-PCA). These auroras are most frequently observed during the northern hemisphere's summer, particularly when the solar wind exhibits a northward IMF and a positive By component.

This study investigates HiLDA events occurring during northern hemisphere summers, with a specific focus on their ionospheric electrodynamics under two distinct IMF conditions: (1) a dominant positive By IMF combined with a northward Bz component, and (2) a dominant northward Bz IMF with a near-zero By component. Utilizing the Local Mapping of Polar Ionospheric Electrodynamics (Lompe) data assimilation method, the following key insights were identified:

• Under both IMF configurations, the HiLDA spot is positioned at the center of a clockwise lobe convection cell or within the clockwise convection region of the NBZ current system.
• The location of the HiLDA spot is not at the peak but rather at the edge of an intensified upward field-aligned current (FAC) associated with the convection vortex.
• Significant Joule heating occurs in both IMF scenarios, with more pronounced heating observed under the By-dominated condition compared to the Bz-dominated condition.