 |
| Titel |
Sounding of the Plasmasphere by McMAC Magnetometers |
| VerfasserIn |
P. J. Chi, The McMAC Team |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250070700
|
|
|
|
|
|
| Zusammenfassung |
| Properly positioned ground magnetometers can be used to detect resonance of magnetospheric
field lines as a way to make unique observations of the plasma mass density of the
magnetosphere. In this paper we describe the field line resonance (FLR) frequencies
systematically observed by the Mid-continent MAgnetoseismic Chain (McMAC), which
consists of 10 stations in the United States and Mexico along 300° magnetic longitude. With
an average separation by 272 km between adjacent stations McMAC is well suited to
remotely sensing the plasma density at L-values between 1.6 and 3.3 through the gradient
method of FLR measurements. We analyzed a full year of McMAC observations
spanning between July 2006 and June 2007, and FLR frequencies were automatically
identified in cross-phase and cross-power spectrograms by a computer routine. In all of
the FLR observations by pairs of McMAC stations, the occurrence rate of FLR
can reach as high as 55% around local noon at L = 2.7. The occurrence rate drops
at lower latitudes due to weaker FLR signals. At L = 3.3 the FLR occurrence is
clearly reduced in afternoon hours, possibly because of occasional presence of the
plasmapause that can obstruct FLR generation and/or detection. By examining
the results from all possible pairs of McMAC stations, we find that, at L -¤ 2.5,
FLR signatures can still be found even when the separation between two stations
exceeds 1000 km. The fundamental mode FLR frequencies, in addition to the inferred
equatorial plasma mass densities of the magnetosphere, are tabulated with respect
to L-value and time. The most probable fundamental mode frequency is found
to be approximately 75 mHz at L = 1.6 and decreases with increasing L-value.
The distribution of the fundamental mode frequency at L = 3.3, however, exhibits
two distinct groups: The lower frequencies centered at 10 mHz representing the
measurements inside the plasmasphere whereas the higher frequencies centered at 39
mHz indicating the faster field line oscillations in the more tenuous plasmatrough.
Through statistical analysis we also examine the effects of local time, solar flux, and
geomagnetic conditions on the fundamental mode frequency and the inferred density of the
plasmasphere. |
|
|
|
|
|
|