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, 29-31 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 coneFlux 90o 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