Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet

Very rapid oscillations with frequencies between 1 and, say, 100 cps
(=Hz) are called - from the radio enginieers point of view -
"very - - low - frequency emissions: VLF. Their ampl.itudes lie well below
ly. They occur usually intermittendly in "bursts" and are controlled
.in their intensity by the general magnetic activity. In exposed
shield areas they may penetrate downward a few kilometers, but
everywhere else they w i l l be totally attenuated within the very
surface layers.
- Sudden storm -- commencements and sclar flare effects: The begin of a
magnetic storm is usually marked by strong deflections in H and Z
up to 100y within one or two minutes.. This so--called "sudden - - storm
-
commencemen-t" SSC, signals. the inward :notion of the magnetopause
(separating the magnetosphere from the interplanetary space) under
the impact of a suddenly increased solar wind intensity. SSC's
are a world wide, s imultaneous1.y occuring phenornenon. They are,
however, too rarely occuring events (1 per month) for induction
studies.
The momen-tarily increased solar wave radiation, caused by sun spot
e: eruptions, produces a shortlived (5 minutes) in'tensificatrion of the
Sq-system, its magnetic effect is called a "sol.ar flare event". It:
measures a few gammas and like the ssc is a rarely observed varia-
tion type.