Space Physics Seminar fall-2018

Extremely Low (ELF) and Very Low Frequency (VLF) emissions are naturally occurring magnetospheric plasma waves in the frequencies of 3 Hz to 30 kHz. Through wave-particle interactions they can accelerate electrons to higher energies or scatter them into the atmosphere by changing their pitch angle. Thus, they play a fundamental role in radiation belt dynamics. We use simultaneous and conjugated observations in ground and space to report propagation characteristics of mainly chorus and quasi-periodical (QP) emissions. Waves were observed on the ground at Kannuslehto (MLAT=64.4N, L=5.46, KAN), Finland and by the Japanese Arase (ERG) satellite in the inner magnetosphere. During the 2017-2018 campaign we studied 84 days of possible conjugated observations. We used magnetic field and electric field measurements on board ERG to calculate the observational electric to magnetic field ratio (E/B_obs). Using measured plasma parameters and the cold plasma dispersion relation, we theoretically estimate the E/B ratio (E/B_th) for a range of wave normal angles. Comparing both ratios, we discuss the direction and manner of wave propagation. We compare these results with those obtained separately by the Single Value Decomposition method. We use the lack or presence of waves at KAN, as well as actual one-to-one correspondence between KAN and ERG to further discuss wave propagation properties. For selected cases, showing one-to-one correspondence, we calculate the ray path that the waves follow from their detection in space until they reach the ionosphere above KAN. Using these ray tracing calculations based on observational facts we further discuss wave propagation and quantify the proportion of unducted and ducted propagation.