Testing the theory behind ULF pulsation-related precipitation
Thursday, 8 March 2018
Lakehouse (Hotel Quinta da Marinha)
Jonathan Rae1, Kyle R Murphy2, Clare Watt3, Alexa Jean Halford4, Andrew R Inglis5, Ian Robert Mann6, Louis Ozeke7, Mark A. Clilverd8, Craig J Rodger9, David G Sibeck2, Alexander W Degeling10 and Howard J Singer11, (1)University College London, Mullard Space Science Laboratory, London, United Kingdom, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)University of Reading, Reading, United Kingdom, (4)Dartmouth College, Hanover, NH, United States, (5)Catholic University of America, Washington, DC, United States, (6)Univ Alberta, Edmonton, AB, Canada, (7)University of Alberta, Edmonton, AB, Canada, (8)British Antarctic Survey, Cambridge, United Kingdom, (9)University of Otago, Department of Physics, Dunedin, New Zealand, (10)Shandong University at Weihai, Institute of Space Science, Weihai, China, (11)NOAA Boulder, Boulder, CO, United States
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Abstract:
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 to demonstrate that experimental measurements can be explained by our new enhanced loss cone mechanism. These observations demonstrate that modulation of the equatorial loss cone via localized compressional wave activity greatly exceeds the change in pitch angle through adiabatic motions leading to enhanced precipitation. 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.
We further investigate this mechanism using a novel analysis to statistically investigate the relationship between compressional, poloidal and toroidal mode ULF waves and ULF-modulated ionospheric precipitation. We find no relationship between the amplitude of toroidal-mode ULF waves and ULF-modulated precipitation. However, we find a significant relationship between ULF wave modes that have a compressional component and ULF-modulated precipitation. This is true for compressional waves at any MLT. A similar relation is found for day-side poloidal mode ULF waves.
These results are strong evidence that ULF waves can provide a direct effect in encouraging electrons close to the nominal loss cone to precipitate without any additional requirement for gyroresonant wave-particle interactions. Additional mechanisms would naturally be complementary and additive in providing means to precipitate electrons from the radiation belts during storm-times.
