PowerPoint Presentation

The zebra stripes: an imprint of ionospheric winds on radiation beltsSolne Lejosne (1) and Juan G. Roederer (2)SSL, University of California, Berkeley Geophysical Institute, University of Alaska, Fairbanks, Alaskasolene@ssl.berkeley.edu

Get into the subject Within 2 min: tell why this presentation is important to the audience

We propose a new theory to explaina feature of the Earths Van Allen radiation belt particles that has defied satisfactory explanation for almost 50 yearsWe evidence for the 1st time that ionospheric winds have an effect on radiation belt intensity

1

2Outline Brief review of earlier and recent works

Developing a new explanation

Results

Conclusions and future work

2

3

3

4

The L-parameter

L

4

Zebra stripe patterns observed in electron fluxes during quiet times

The zebra stripes: a term coined by Ukhorskiy et al. [2014]

[Ukhorskiy et al., Nature, 2014]

5

5

The zebra stripes: 1st reported by Imhof et al. [1965]

Adapt. from [Ukhorskiy et al., 2014]

[Datlowe et al., 1985]Measurements of e- fluxes vs time close to Earth:6

6

from [Datlowe et al., 1985]

7

7

The zebra stripes: also in protons [Williams and Frank, 1984]

adapt. from [Sauvaud et al., 2013]8Measurements by DEMETER of proton fluxes (p+/cm2.s.sr.keV) vs time:

8

9

In short: the zebra stripes aresome structured peaks and valleys that appear in the spectrograms of energetic e- and ions in the inner belt.

ubiquitous features for L< ~ 3 and T< ~1 MeV (~80% of the time according to Datlowe et al. [1985])

Interpretation?

9

Dynamics of magnetically trapped particles

Measurements(cyclotron + bounce averaged)Cyclotron averagedExact Path

electronsprotons10

10

The usual suspect: energization by radial transport

Proposed explanation:

drift-resonance with Ew accelerate (decelerate) particles in some specific energy intervals

Origin of Ew?

[Cladis, 1966]: Equatorial electrojets[Sauvaud et al., 2013]: ULF geomag storms[Ukhorskiy et al., 2014]: rocking outer magneto

EwEwxB/B2

11

e-

11

Energization by radial transport: a suspicious suspect 12

Appearance of the zebra stripes, as observed (in blue), and as predicted (in orange)

12

MLT dependence of the stripesPeak-to-valley inversion when comparing e- fluxes at opposite MLTs.

RBSPBRBSPAL=1.913

13

Coexistence of proton and electron stripes

RBSPAL=2

INOUT

Coexistent peak-to-valley inversions in electron and ion fluxes 14

14

15

15

Magnetic and electric drifts

[Mozer, 1973]

16

16

E field associated with the motion of the ionospheric plasmaOrigin of the corotational electric field17

17

BUT: ionospheric plasma DO NOT corotate with the Earth[Fejer et al., 1985]

L=4L=2.5L=1.7L=1.1[Richmond et al., 1980]18

18

Consequence: modulation of the distribution function f(MLT)

Term responsible for the creation of zebra stripes19

19

Upper atmosphere: a traffic regulator (1/2)

Sign of div(VD)EffectLocation with perturb~cos()div(VD)