A statistical study of the Field-Aligned Electron Events

(status report)

Solène Lejosne, Forrest Mozer and Oleksiy Agapitov SSL, University of California, Berkeley

solene@ssl.berkeley.edu

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