Loss Processes

D. Sibeck, R. Millan, H. Spence

Outline

• 1. Quantify magnetopause losses– Magnetopause motion and shell splitting– ULF waves– Orbit bifurcation– Ring current inflation

• 2. Quantify precipitation mechanisms• 3. Quantify relative importance over solar

cycle

Losses and Magnetopause Motion• Compression

• Rapid (1-2 min) increase in dayside field strengths (betatron acceleration and flux increase),• Gradual decrease in nightside equatorial field strengths • Enhanced drift shell splitting• 90° pitch angle particles on closed paths gain access to

magnetopause and are lost from outer magnetosphere.

Losses and Magnetopause Motion• Causes of Magnetopause Motion– Erosion (requires 30-60 minutes)• No change in subsolar magnetic field strength

therefore no opening of drift paths.• R1 currents gradually diminish dayside field strengths

while cross-tail currents gradually reduce nightside equatorial magnetic field strengths • High energy 90° pitch angle particles conserve 1st ad.

inv. and move inward, low energy particles also conserve 3rd ad. inv. and move outward, lose energy but may not be lost to the magnetosphere.

Diffusion Driven By ULF Waves

• Diffusion resulting from ULF (and other) waves requires– ~1 hr [Shprits et al., 2006]– days [Morley et al., 2010] to

remove electrons

from locations deep in the magnetosphere. Mayneed some other process tohelp [Ukhorskiy et al., 2009]

Bifurcation Enhanced Diffusion

• 1 MeV electrons at 4 times. Bifurcation moves electrons both outwards to MP and inwards

Ring Current InflationRemoves Electrons

Ukhorskiy et al. [2015]

With ring currentWithout ring current

1.25-1.5 MeV e 90° P. A.

P.A.

# ParticlesDrift echoes

Adiabatic CoolingCompressionalEnergization

Tasks

• 1. Survey radiation belt responses to abrupt solar wind pressure and IMF Bz variations.

• 2. Survey ULF wave activity and cf. radiation belt behavior.• 3. Look for enhanced losses on field lines subject to

bifurcation.• 4. Look for ring current effects on loss from inner

magnetosphere.• 5. Use MMS/THEMIS to survey losses at the

magnetopause, cf. with particle loss deeper in the magnetosphere.

Quantify Precipitation Mechanisms

• 1. Quantify extent, significance of– EMIC waves [Halford et al., 2010; Usanova et al.,

2014; Kersten et al., 2014].– Chorus [Thorne et al., 2010]

not only as function of geomagnetic indices or solar wind

conditions, but of storm phase.• 2. Compare with precipitation patterns

(cubesats, BARREL).

Solar Cycle Variations

• More substorms and particle injections during declining phase of solar cycle

• More chorus waves • More particle loss?• Work with MMS/ERG/THEMIS to determine

extent of wave fields, rate of loss, cf. observations, compare at different stages of solar cycle.