P. Schmoldt, PhD - MTNet - DIAS

2. Sources for magnetotelluric recording
Wave type
Location of generation
external (e) or internal (i)
Process of generation
Continuous pulsations
Pc5 i Drift resonance
Pc4 i Bounce resonance
Pc3 e During times when the solar wind velocity is high
and the solar wind magnetic field is radial
Pc2 i Generated by electromagnetic ion O(+) cyclotron
effects
Pc1 i Gyro resonance or cyclotron instability
Irregular pulsations
Pi2 i Bursty Earthward flows during geomagnetic activity
in the plasma sheet on the night-side of the Earth, radiating
Alfvén waves that travel to the auroral ionosphere
where they are reflected and forced to travel
back and interact with the initial flow
Pi1 i Cavity resonance between the topside of the ionosphere
and the auroral acceleration region at ∼1 Re
altitude that is excited by fluctuating field aligned
currents
Tab. 2.3.: Description of the location and process of generation for the different types of ultra low frequency (ULF) waves (also
referred to as pulsation) as they are understood by today; after McPherron [2005], extended by the information regarding Pc2 using
results presented by Inhester et al. [1985]; Sarma et al. [1974]
horizontal wave number k (i.e. the inverse of the wavelength: k = λ −1 ) with the value
1/2
of ω + k · vσµ0 . Thus, influences of the wave frequency ω, velocity of the source
v (usually assumed to be zero), and the conductivity of the subsurface σ are taken into
account. The approach by Mareschal [1986] is based on the solution of the wave equation
for electromagnetic fields (cf. Sec. 3.2), i.e.
where F is either the electric or magnetic field and
∇ 2 F = γ 2 F (2.1)
γ 2 = k 2 + ıωµσ + µεω 2
(2.2)
(for a non-moving source) with µ: magnetic permeability, ε: permittivity. Assuming that
the effect of permittivity is negligible (cf. Sec. 3.5), that µ = µ0 (cf. Sec. 3.6), and
including the contribution of the moving source yields
22
ˆγ 2 = k 2 + ı(ω + kv)µσ. (2.3)