# Presentation: 460657

## What role do energetic particles present in the dayside cusp play in magnetospheric processes?

**THEODORE A. FRITZ**
**Center for Space Physics at Boston University**

-  **Polar PI Telecon**
***March 7, 2008***** **

- Thanks to Jiasheng Chen, Jon Niehof, Mike Klida, Kate Whitaker, Brian Walsh, Charlotte Wong, Zhang Hui,
- the Polar CAMMICE team and the Cluster RAPID team

## The McIlwain E3 model does not look anything like the classical ideas of the origin of the cross-tail electric field 

**The McIlwain E3 model does not look anything like the classical ideas of the origin of the cross-tail electric field **

- Lyons and Williams, 1984

- What does this have to do with the cusp?

## Slide 3

## Slide 4

## Slide 5

## Slide 6

## Slide 7

## Slide 8

## The conclusion to draw from this:

- Within the cusp there appear to be embedded regions containing diamagnetic cavities (CDC).
- Within the CDCs the field and particle pressures are strongly anti-correlated whereas within the cusp outside the CDCs the anti-correlation no longer holds.
- Within the cusp, ions with energies >20 keV up to many 100s of keV (CEP) are present only in those portions of the cusp associated with diamagnetic cavities (CDC).
- Polar sees CDC that are very large (>6 RE and lasting for hours)
- At the Polar team meeting in October I presented strong evidence from a combination of Polar, Cluster, and ISEE that the CEPs are energized locally in the cusp from a source population of shocked solar wind ions and up-flowing ionospheric ions.

## Slide 10

## These CEP/CDC regions are present all of the time independent of solar wind and IMF conditions—the only criteria from the perspective of the Polar satellite being that a satellite must be in the right position to observe them.

- These CEP particles have pitch angle distributions in which the anti-field aligned direction  (=1800) is full with the opposite direction basically empty.  These particles will paint the magnetopause with a layer of energetic particles.
**The questions that now remain are what effects, if any, these particles have on magnetospheric processes?**
**Are they the source of the ring current via gradient and curvature drifts to the nightside inner magnetosphere?**
**Do these particles create, via charge separation, the cross polar-cap potential?**

## Conclusions

- Since these particles are mostly on “open” field lines they will paint the magnetopause with a layer of energetic particles and will populate the upstream medium when an appropriate IMF orientation is present.

- In addition many of these energetic ions in the cusp will gradient and curvature drift, --ions to the west and electrons to the east, --separating and drifting along what we have described as a Shabansky orbit that will carry the particles to the equatorial plane around dusk and dawn.

- These energetic particles on the magnetopause will reenter the magnetosphere -- ions along the dawn flank and electrons along the dusk flank.

## Only slight imbalances of these charges is sufficient to establish large charge-separation electric fields.

- Such charge-separation electric fields can explain most of the features of the McIlwain E3 model.

## The E3 model of Carl E. McIlwain was based on plasma measurements at 6.6 RE

**The E3 model of Carl E. McIlwain was based on plasma measurements at 6.6 R****E**

- Note the strong radial field in the post-midnight/pre-dawn sector and a dawn to dusk field only near the midnight sector.

- McIlwain, 1976