The spatial distributions, wave properties, and generation mechanisms of inner magnetosphere EMIC waves
Date of Award
Program or Major
Doctor of Philosophy
Charles W Smith
Lynn M Kistler
Marc R Lessard
Electromagnetic Ion Cyclotron (EMIC) waves play an integral role in the dynamics of the Earth’s magnetosphere. Through wave-particle interactions, EMIC waves inﬂuence the particle populations present in the magnetosphere by causing heavy ion heating (up to 1 keV), relativistic electron pitch angle scattering within the radiation belts, energetic proton scattering loss in the ring current. They are also associated with traveling convection vortices inside the magnetosphere and inﬂuence the appearance of isolated auroral arc events. Over the years, numerous case and statistical studies have been performed over diﬀering regions in the Earth’s magnetopshere pertaining to the location, wave properties, and excitation of EMIC waves. However, lack of data coverage of the inner magnetosphere has produced an incomplete understanding in where EMIC waves are observed, their associated wave properties, and the mechanisms that lead to their generation in those regions. In this dissertation, we seek to rectify this data deﬁciency by exploring inner magnetosphere EMIC waves, to understand their occurrence and generation mechanisms as they pertain to this L ≤ 7 magnetospheric region. To perform this analysis, we will use the Van Allen Probes. Launched in August 2012, the Van Allen Probes allow us to explore the inner magnetosphere (1.1 to 5.8 RE). Observations provided by the Van Allen Probes’ EMFISIS instrument allows us to observed EMIC waves in all three wave-bands (H+-, He+-, and O+-band EMIC waves). To achieve this project, we perform a statistical study of EMIC waves, investigating the spatial distribution of their occurrence, wave power, ellipticity, and normal angle. Each wave-band possesses their own unique spatial distributions within the inner magnetosphere with H+-band waves being preferably observed in the pre-noon and afternoon sectors, He+ band waves are observed throughout the dayside magnetosphere, and O+-band waves are observed in the pre-noon sector at L ≤ 4. Statistical analysis exploring how the spatial distributions of EMIC waves vary with respect to varying levels of geomagnetic activity (i.e., AE and SYM-H) and solar wind dynamic pressure are also performed. EMIC wave spatial distributions are inﬂuenced by the level of geomagnetic activity, with peak occurrence rates appearing in the prenoon sector during periods of quiet activity while the afternoon sector occurrence rates peak under more active conditions. To understand the necessary plasma conditions associated with their excitation and possible source regions, we test EMIC waves with the Linear Theory proxy and calculate their Poynting ﬂux to determine if the EMIC waves possess bi-directional propagation (a characteristic associated with newly generated EMIC waves). The observations suggest that the in situ plasma measurements most preferential for EMIC wave excitation do not consistently coincide with bi-directional propagation. Furthermore, bi-directionally propagating EMIC waves are observed beyond the MLAT = 11◦ Loto’aniu et al.  boundary. In the latter parts of this dissertation, we model EMIC wave growth and wave amplitude via in situ plasma and magnetic ﬁeld measurements. While the empirical model can replicate observed EMIC wave amplitudes, using the in situ plasma measurements to calculate EMIC wave growth rates does not accurately recreate the observed wave activity.
Saikin, Anthony Aaron, "The spatial distributions, wave properties, and generation mechanisms of inner magnetosphere EMIC waves" (2018). Doctoral Dissertations. 2428.