HR: 1340h
AN: SM13A-0319 [Abstracts]
TI: Estimation Techniques of Dispersion Curves of
Lightning Whistlers Propagating in the Geospace
AU: * Kasahara, Y
EM: kasahara@is.t.kanazawa-u.ac.jp
AF: Kanazawa Univ., Kakuma, Kanazawa, 920-1192
Japan
AU: Oka, K
EM: oka@cie.is.t.kanazawa-u.ac.jp
AF: Kanazawa Univ., Kakuma, Kanazawa, 920-1192
Japan
AU: Goto, Y
EM: ygotou@is.t.kanazawa-u.ac.jp
AF: Kanazawa Univ., Kakuma, Kanazawa, 920-1192
Japan
AB:
It is well known that electron density profile in the geospace
changes day by day and thus remote sensing techniques
using electromagnetic waves are useful for obtaining
the global electron density profile in the earth's plasmasphere
with high time resolution.
As whistler mode wave originated from lightning discharge
has a unique spectrum characterized by so-called "dispersion curve",
an electron density profile in the plasmasphere can be estimated
by solving the inverse problem
from the trend of dispersion curve obtained along an trajectory of
a satellite.
In the present paper, we introduce estimation techniques of
dispersion curves of lightning whistlers propagating
in the plasmasphere and present some features of dispersions
of lightning whistlers observed by the Akebono satellite.
We developed an automatic detection method of lightning whistlers
from the wide-band spectrum data obtained by the VLF instrument
onboard Akebono.
First, a smoothing in the frequency space and a simple noise
filtering are carried out.
Secondly, a template matching method is adopted in order
to achieve a rapid and simple detection of lightning whistler.
We also propose an additional method in order
to quantify the dispersion curves for non-ducted whistlers,
because the non-ducted whistlers are, in general, not characterized
by a simple dispersion parameter.
The developed method was applied to
the VLF wide-band spectrum, whose maximum frequency is 20 kHz and the time
and frequency resolution are 20msec and 50Hz, respectively.
The results are satisfactory enough to analyze the trend
of dispersion curve along the trajectory of the satellite.
For example, lightning whistlers originated from northern
hemisphere were continuously
observed and the estimated dispersion of the whistlers became
larger as the satellite
moved from northern to southern hemisphere.
Computation time for the analysis was
practical enough for the real-time application.
In other words, our proposed method can be applied
to a onboard software for VLF wave receiver
so as to detect and estimate important properties
of lightning whistlers automatically.
DE: 2768 Plasmasphere
DE: 6939 Magnetospheric physics (2700)
DE: 6974 Signal processing (0674)
DE: 6982 Tomography and imaging (7270, 8180)
DE: 6984 Waves in plasma (7867)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005