Abstract
Recent years have seen debate regarding the ability of electromagnetic ion cyclotron (EMIC) waves to drive EEP (energetic electron precipitation) into the Earth's atmosphere. Questions still remain regarding the energies and rates at which these waves are able to interact with electrons. Many studies have attempted to characterize these interactions using simulations; however, these are limited by a lack of precise information regarding the spatial scale size of EMIC activity regions. In this study we examine a fortuitous simultaneous observation of EMIC wave activity by the RBSP-B and Arase satellites in conjunction with ground-based observations of EEP by a subionospheric VLF network. We describe a simple method for determining the longitudinal extent of the EMIC source region based on these observations, calculating a width of 0.75 hr MLT and a drift rate of 0.67 MLT/hr. We describe how this may be applied to other similar EMIC wave events.
Plain Language Summary The Earth is surrounded by the Van Allen radiation belts, rings of high-energy charged particles trapped by the Earth's magnetic field. These particle populations are constantly changing, driven by forces from the Sun, Earth, and from the belts themselves. One of the most important drivers of this dynamism is the interaction between particles and electromagnetic waves. One such wave species, known as Electromagnetic Ion Cyclotron (EMIC) waves, has come under scrutiny recently due to experimental results calling into question the theoretical energy limits of their interactions with radiation belt electrons. Studying these waves and their interactions is hampered by our inability to accurately determine the size of the source region of these waves. In this study, we investigate a single EMIC wave event observed simultaneously by two separate satellites and use a network of ground-based radio wave receivers to estimate the size of the EMIC region. We also explain how the method used in this study may be generalized to other EMIC wave events. This method will allow us to carry out statistical analysis of the size of EMIC wave regions in general, aiding future research into the impacts of these waves on the radiation belts.