[Everyone] Space Physics Seminar, Friday May 9th: Magnetospheric Particle Injections and their Relation to Impulsive, Localized Electric Fields (C. Gabrielse, EPSS/IGPP)

[Emmanuel V. Masongsong]

SPACE PHYSICS SEMINAR 

DEPARTMENT OF EARTH, PLANETARY AND SPACE SCIENCES 

DEPARTMENT OF ATMOSPHERIC AND OCEANIC SCIENCES 

UNIVERSITY OF CALIFORNIA, LOS ANGELES 

(EPSS M288A, AOS M275A ) 










Christine Gabrielse 


UCLA EPSS & IGPP 





Magnetospheric Particle Injections and their Relation to Impulsive, Localized Electric Fields 








Abstract: 


Energetic particle injections in the near-Earth plasma sheet are critical for supplying particles and energy to the radiation belts and ring current. Their origin, however, has been elusive due to the lack of equatorial, multi-point observations. After the launch of NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission in 2007, intense electric fields and elevated energetic particle fluxes have been observed to accompany localized (1-4 RE wide) bursty bulk flows and to propagate from the mid-tail regions (at geocentric radial distances R > 25RE) towards Earth, up to and at times inside of geosynchronous orbit (GEO, R=6.6RE). Motivated by these observations, I model simultaneous multi-point observations of electron injections using guiding center approximation in prescribed but realistic electric and magnetic fields to better understand the nature of their acceleration. Additionally, I perform a statistical analysis of the electron and ion injections to better understand their properties observationally. I find a good correlation between injections and azimuthally localized fast flows, reconnection fronts and impulsive, dawn-dusk electric field increases. This 
correlation is present regardless of distance, from inside GEO out to 30 RE. The findings are inconsistent with the classical concept of injections forming from an azimuthally wide injection boundary moving earthward from ~9-12 RE to GEO under an enhanced, large-scale, duskward electric field. Modeling of electron injections assuming a localized, impulsive, potential electric field transported from mid-tail to near-Earth at bursty flow speeds of ~400 km/s successfully reproduces the observations at multiple spacecraft. Addition of a small, inductive electric field component, related to the dipolarizing magnetic field consistent with observations, further improves the agreement between modeled and observed electron spectra. The impulsive, localized, and vortical nature of the earthward-propagating electromagnetic pulse is what makes this model particularly effective 
in reproducing both the injection and the dispersed decrease in energy flux often observed simultaneously with the injection but at lower energies. The results suggest that particle acceleration and transport towards the inner magnetosphere can be thought of as a superposition of individual bursts of varying intensity and cadence depending on 
global geomagnetic activity levels. 




Friday, May 9, 2014 

Room 6704 Geology 

3:30 - 5:00 PM 



Refreshments served after the seminar in Room 6850. 



In-Charge 
V. Angelopoulos 

X.-Z. Zhou 
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