 |
| Titel |
A determination of the hydromagnetic waves polarization from their perturbations on the terminator |
| VerfasserIn |
L. Alperovich, B. Fidel, O. Saka |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 14, no. 6 ; Nr. 14, no. 6, S.647-658 |
| Datensatznummer |
250012324
|
| Publikation (Nr.) |
 copernicus.org/angeo-14-647-1996.pdf |
|
|
|
|
|
| Zusammenfassung |
| The influence of the homogeneous and
inhomogeneous ionosphere on the orientation angle of the horizontal magnetic
vectors of the long-time geomagnetic pulsations is under consideration in this
study. It was realized that this angle is small in the case of the homogeneous
ionosphere for both the Alfvén and magnetosonic types of oscillations. An
increase in the ionospheric electric field was discovered as the ionospheric
conductivity changes during the switch from day to night conditions. It is valid
only for the initial Alfvén wave. The ionospheric equivalent current systems
excited by the initial magnetospheric waves of Alfvén
and magnetosonic types as well as their behavior near the terminator were
studied for different seasons. For the Alfvén source,
seasonal variations of the orientation angle close to sunrise at the equator
depend on the type of source: odd or even modes of Alfvén
oscillations excite observable pulsations. It was found that the ionospheric
two-vortex equivalent current system of the long-period pulsations arising in
high-latitudes in the equatorial region alters not only its direction, but its
intensity too. The largest anomaly (~25% of the source value) would be expected
near the terminator. A new experimental method was suggested to recognize the
type of incident magnetospheric waves by implementing observations either at a
single observatory or at a couple of observatories. In the case of a single
observatory it is proposed to study the frequency dependence of the orientation
angle of their magnetic components close to sunrise. If the initial wave is
magnetosonic, this angle must not be changed as a function of the local time
within the wide frequency range of pulsations. When pulsations have an
orientation angle sensitive to the presence of the terminator, they may be
classified as both Alfvén and magnetosonic. For the Alfvén
waves no frequency dependence of the orientational angle is peculiar. On the
contrary, magnetosonic waves should be determined as oscillations with an
orientational angle proportional to the frequency. These oscillations may be
revealed at observatories located on the high-resistance cross sections. The
example of the spectral-temporal analysis of pulsation at the equatorial
observatory in Huancayo was demonstrated to confirm the proposed experimental
technique. A weak dependence of the orientation angle anomaly on the frequency
near the terminator was found. The latter is evidence for the dominant
contribution of the Alfvén waves to low-latitude and
equatorial oscillations. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|