Date:  Wednesday, February 22, 1995
Time:  4:15 PM   Refreshments at 4:00
Location:  ERL 126



 Schumann-resonances in the Magnetic Field Components

Dr. Martin Fullekrug
STARLAB / Stanford University

Abstract

The transition zone of the ULF/ELF-range is characterized by the
eigenmodes of the earth-ionosphere cavity, denoted
Schumann-resonances. Local observations in this frequency range are
mainly disturbed by antrhopogenic noise and lightning flashes of nearby
thunderstorms. During quiet intervals, transient signals with amplitudes
of about 1O pT are superimposed on a continuous noise level of about 1
pT, both exhibit the Schumann-resonance periodicities.  The signals show
a tendency to repeat after about 2 seconds which suggest an excitation
by Whistler-trains.

The Schumann-resonances are interpreted as a pure resonance phenomenon
by approaching the describing linear dynamic system with its finite
difference representation. The associated equations are solved via the
Prony algorithm where the autoregressive filter is derived by an
analysis of a shifted autocovariance matrix. This modified technique
results in a robust estimation of the amplitude, damping and frequency
of the Schumann-resonances.

All these parameters show a characteristic directional dependence and
variability during the day. The amplitude summarizes the excitation by
different source locations of lightning activity, mainly located in the
tropical belt around the world. The damping and frequency are related to
the solar activity coupling into the lower ionosphere. Different
observations of the considered parameters near Gottingen/Germany and
Table Mountain/California are displayed and disussed in detail.