A. W. Degeling

The Role of Localized Compressional Ultra‐low Frequency Waves in Energetic Electron Precipitation

Typically, Ultra-Low Frequency (ULF) waves have historically been invoked for radial diffusive transport leading to acceleration and loss of outer radiation belt electrons. At higher frequencies, Very-Low Frequency (VLF) waves are generally thought to provide a mechanism for localized acceleration and loss through precipitation into the ionosphere of radiation belt electrons. In this study we present a new mechanism for electron loss through precipitation into the ionosphere due to a direct modulation of the loss cone via localized compressional ULF waves. We present a case study of compressional wave activity in tandem with riometer and balloon-borne electron precipitation across keV-MeV energies to demonstrate that the experimental measurements can be explained by our new enhanced loss cone mechanism. Observational evidence is presented demonstrating that modulation of the equatorial loss cone can occur via localized compressional wave activity, which greatly exceeds the change in pitch angle through conservation of the first and second adiabatic invariants. The precipitation response can be a complex interplay between electron energy, the localisation of the waves, the shape of the phase space density profile at low pitch angles, ionospheric decay timescales, and the time-dependence of the electron source; we show that two pivotal components not usually considered are localized ULF wave fields and ionospheric decay timescales. We conclude that enhanced precipitation driven by compressional ULF wave modulation of the loss cone is a viable candidate for direct precipitation of radiation belt electrons without any additional requirement for gyroresonant wave-particle interaction. Additional mechanisms would be complementary and additive in providing means to precipitate electrons from the radiation belts during storm-times.

Control of ULF Wave Accessibility to the Inner Magnetosphere by the Convection of Plasma Density

During periods of storm activity and enhanced convection, the plasma density in the nafternoon sector of the magnetosphere is highly dynamic due to the development of plasmaspheric ndrainage plume (PDP) structure. This significantly affects the local Alfven speed and alters the propagation nof ULF waves launched from the magnetopause. Therefore, it can be expected that the accessibility of ULF nwave power for radiation belt energization is sensitively dependent on the recent history of magnetospheric nconvection and the stage of development of the PDP. This is investigated using a 3-D model for ULF waves nwithin the magnetosphere in which the plasma density distribution is evolved using an advection model for ncold plasma, driven by a (VollandStern) convection electrostatic field (resulting in PDP structure). The wave nmodel includes magnetic field day/night asymmetry and extends to a paraboloid dayside magnetopause, nfrom which ULF waves are launched at various stages during the PDP development. We find that the plume nstructure significantly alters the field line resonance location, and the turning point for MHD fast waves, nintroducing strong asymmetry in the ULF wave distribution across the noon meridian. Moreover, the ndensity enhancement within the PDP creates a waveguide or local cavity for MHD fast waves, such that neigenmodes formed allow the penetration of ULF wave power to much lower L within the plume than noutside, providing an avenue for electron energization.

Spatial Distribution and Semiannual Variation of Cold‐Dense Plasma Sheet

The cold‐dense plasma sheet (CDPS) plays an important role in the entry process of the solar wind plasma into the magnetosphere. Investigating the seasonal variation of CDPS occurrences will help us better understand the long‐term variation of plasma exchange between the solar wind and magnetosphere, but any seasonal variation of CDPS occurrences has not yet been reported in the literature. In this paper, we investigate the seasonal variation of the occurrence rate of CDPS using Geotail data from 1996 to 2015 and find a semiannual variation of the CDPS occurrences. Given the higher probability of solar wind entry under stronger northward interplanetary magnetic field (IMF) conditions, 20 years of IMF data (1996–2015) are used to investigate the seasonal variation of IMF Bz under northward IMF conditions. We find a semiannual variation of IMF Bz, which is consistent with the Russell‐McPherron (R‐M) effect. We therefore suggest that the semiannual variation of CDPS may be related to the R‐M effect.

Dayside Magnetospheric and Ionospheric Responses to a Foreshock Transient on 25 June 2008: 1. FLR Observed by Satellite and Ground‐Based Magnetometers

NASA [NAS5-02099]; NSF [AGS-1004814, PLR-1341359]; National Natural Science Foundation of China [41574157, 41322031, 41628402]; STFC [ST/N000722/1]; NERC [NE/L007495/1, NE/P017150/1, NE/P017185/1]; [NSFAGS-1352669]; [NASANNX17AD35G]

Observations of Kelvin‐Helmholtz Waves in the Earth's Magnetotail Near the Lunar Orbit

Kelvin‐Helmholtz waves (KHWs), which have been widely observed at the magnetopause in the region near the Earth, play an essential role in the transport of solar wind plasma and energy into the mag ...