A statistical study of the Field-Aligned Electron Events (status report) Solène Lejosne, Forrest Mozer and Oleksiy Agapitov SSL, University of California, Berkeley Special thanks to the HOPE team SWG Meeting, July 2015, APL

Field-Aligned Electron Events? 5 panels of electron pitch angle distributions measured by HOPE (<50 keV) -Bursts of usually <10min duration of field-aligned electrons (mostly in both directions) -Indications of possible precipitation Motivation (1/2) Energy (eV)

-[Mozer et al., 2015] + [Lejosne et al., … under review, JGR]: relation between TDS, field-aligned electrons, and auroras -“field-aligned electron distributions are indeed quite interesting, and determining when they occur would be important” -[Abel et al., 2002a, 2002b]: statistical study of field-aligned events using CRRES data (15 months) no statistical link between the observed events and the wave power of the whistler mode and ECH waves Motivation (2/2)

Approach (1/3) (Pitch Angle) Ratio = Flux near loss cone Flux 90 o particles Energy (eV) Playing with HOPE data (Pitch Angle) Ratio > 1 => precipitation?

Approach (2/3) An example of chorus waves in the presence of field aligned electrons An example of broadband noise (TDS) in the presence of field aligned electrons

Approach (3/3) -Designed an algorithm to detect Field-aligned Electron Events from daily pitch angle ratio matrixes -For each event: time_start duration average ratio by energy ch“max” EFW (BFW) by freq ch - Statistical analysis from November 2012 to June 2015

First results: where can I see field-aligned electron events? (1/3) Probability to see field-aligned electrons as a function of the radial distance

First results: where can I see field-aligned electron events? (2/3) Max(EFW) >0.5mV/m Probability to see active field-aligned electron events as a function of MLT

First results: where can I see field-aligned electron events? (3/3) Probability to see active field-aligned electron events as a function of energy and MLT Max(EFW) >0.5mV/m

First results: what about the wave content? (1/2) Max(EFW) >0.5mV/m

First results: what about the wave content? (2/2) Max(EFW) >0.5mV/m

Conclusion The occurrence frequency of the field aligned electron events increases with the radial distance. There are more ~300eV field aligned electron events than ~10keV field-aligned electron events 300 eV field-aligned electron events are : -Observed predominantly on the premidnight sector (~22MLT) -Associated with broadband electrostatic noise in the filterbank => TDS cause field-alignment of electrons of ~300 eV in the premidnight sector ~10 keV field-aligned electron events are: -Observed predominantly on the morning side (~6MLT) -Associated with a signal of high frequency in the filterbank => Chorus cause field-alignment of electrons of ~10 keV in the morning sector