 |
| Titel |
Ionospheric cusp flows pulsed by solar wind Alfvén waves |
| VerfasserIn |
P. Prikryl, G. Provan, K. A. McWilliams, T. K. Yeoman |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 20, no. 2 ; Nr. 20, no. 2, S.161-174 |
| Datensatznummer |
250014352
|
| Publikation (Nr.) |
 copernicus.org/angeo-20-161-2002.pdf |
|
|
|
|
|
| Zusammenfassung |
Pulsed ionospheric flows
(PIFs) in the cusp foot-print have been observed by the SuperDARN radars with
periods between a few minutes and several tens of minutes. PIFs are believed to
be a consequence of the interplanetary magnetic field (IMF) reconnection with
the magnetospheric magnetic field on the dayside magnetopause, ionospheric
signatures of flux transfer events (FTEs). The quasiperiodic PIFs are
correlated with Alfvénic fluctuations observed in the upstream solar wind. It
is concluded that on these occasions, the FTEs were driven by Alfvén waves
coupling to the day-side magnetosphere. Case studies are presented in which the
dawn-dusk component of the Alfvén wave electric field modulates the
reconnection rate as evidenced by the radar observations of the ionospheric
cusp flows. The arrival of the IMF southward turning at the magnetopause is
determined from multipoint solar wind magnetic field and/or plasma
measurements, assuming plane phase fronts in solar wind. The cross-correlation
lag between the solar wind data and ground magnetograms that were obtained near
the cusp footprint exceeded the estimated spacecraft-to-magnetopause
propagation time by up to several minutes. The difference can account for
and/or exceeds the Alfvén propagation time between the magnetopause and
ionosphere. For the case of short period ( < 13 min) PIFs, the onset times
of the flow transients appear to be further delayed by at most a few more
minutes after the IMF southward turning arrived at the magnetopause. For the
case of long period (30 – 40 min) PIFs, the observed additional delays were
10–20 min. We interpret the excess delay in terms of an intrinsic time scale
for reconnection (Russell et al., 1997) which can be explained by the
surface-wave induced magnetic reconnection mechanism (Uberoi et al., 1999).
Here, surface waves with wavelengths larger than the thickness of the neutral
layer induce a tearing-mode instability whose rise time explains the observed
delay of the reconnection onset. The compressional fluctuations in solar wind
and those generated in the magnetosheath through the interaction between the
solar wind Alfvén waves and the
bow shock were the source of magnetopause surface waves inducing reconnection.
Key words. Interplanetary physics (MHD
waves and turbulence) – Magnetospheric physics (magnetosphere-ionosphere
interactions; solar wind-magnetosphere interactions) |
| |
|
| Teil von |
|
|
|
|
|
|
|
|