Annual and Seasonal Occurrence Pattern of Auroral Kilometric Radiation Associated with the Interplanetary Magnetic Field*

Abstract

Abstract Auroral kilometric radiation (AKR) is a widely existing strong radio emission from the Earth’s magnetosphere and is generated by suprathermal (1–10 keV) electrons in the polar cavity. Previous works have demonstrated that AKR can contribute to the coupling of the magnetosphere–ionosphere–atmosphere, but its relation to the interplanetary magnetic field (IMF) has not been studied so far. Here, we examine the data of Van Allen Probes and identify a total of 5000 AKR events from 2012 October to 2019 July. Most AKR events (4282) correspond to the dominant parallel component B ∥ ( = ( B x ) 2 + ( B y ) 2 ) of IMF. There are the most (1391) events in 2018 (the solar minimum year) and the least (258) events in 2014 (the solar maximum year), corresponding to more (less) occurrences for the longer duration (> 30 minutes) of southward IMF (B z < 0) in 2018 (2014). In the Earth’s Northern Hemisphere, there are the most (865) events in the autumn (August–October), corresponding to dominant B x < 0. In the Earth’s Southern Hemisphere, there are the most (830) events in the autumn (February–April), corresponding to dominant B x > 0. The probable reason for the above results is that the longer duration of B z < 0 can yield the longer magnetic reconnection, and the dominant B x < 0 (B x > 0) is favorable for the single-lobe magnetic reconnection in the northern (southern) hemisphere, allowing more suprathermal electrons into the polar source cavity and generating more AKRs. These current results suggest that IMF is very important for the occurrence of AKR and can be widely applied to similar auroral radio emissions in other magnetized planets of the solar system.