 |
| Titel |
Plasma flow channels at the dawn/dusk polar cap boundaries: momentum transfer on old open field lines and the roles of IMF By and conductivity gradients |
| VerfasserIn |
P. E. Sandholt, C. J. Farrugia |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 4 ; Nr. 27, no. 4 (2009-04-02), S.1527-1554 |
| Datensatznummer |
250016479
|
| Publikation (Nr.) |
 copernicus.org/angeo-27-1527-2009.pdf |
|
|
|
|
|
| Zusammenfassung |
| Using DMSP F13 data in conjunction with IMF data
we investigate the newly discovered
channels of enhanced (1.5–3 km/s) antisunward
convection occurring at the dawn (06:00–09:00 MLT) or dusk (15:00–18:00 MLT)
flanks of the polar cap for different combinations of
IMF By polarity, hemisphere (NH/SH) and the dawn/dusk MLTs.
Dawn-side cases where this flow channel appears occur for the following
combinations:
NH-dawn/By>0 and SH-dawn/By<0.
The dusk-side cases are: NH-dusk/By<0 and SH-dusk/By>0.
The flow channels are
placed in the context of particle precipitation regimes/boundaries
and ionospheric conductivity gradients.
They are found to be threaded
by "old open field lines" ("time since
reconnection" >10 min) characterized by
polar rain precipitation. In the dawn-side cases
(NH-dawn/By>0 and SH-dawn/By<0)
and in a Parker spiral field,
the polar rain contains
the "solar wind strahl" component.
The convection enhancement
is attributed to the Pedersen current closure of Birkeland current
sheets (C1 and C2) in the polar cap (C1) and at the polar cap boundary (C2).
The low ionospheric conductivity in the polar
cap, particularly in the winter hemisphere,
is compensated by an enhanced
electric field driving the flow channel there.
This is momentum transfer
from the solar wind via dynamo action taking place in the
combined current system of the high-
and low-latitude boundary layers (HBL/LLBL).
The conductivity gradient at the polar cap boundary
contributes to establishing the convection channel and the
associated enhancement of the dawn-dusk convection
asymmetry extending beyond the dawn-dusk terminator
during intervals of nonzero IMF By component.
The HBL/LLBL-ionosphere coupling via Birkeland currents
C1/C2 is a source of dawn-dusk convection asymmetry
and Svalgaard-Mansurov effect which
must be added to the effect of magnetic tension acting
on "newly open field lines". |
| |
|
| Teil von |
|
|
|
|
|
|
|
|