P. Schmoldt, PhD - MTNet - DIAS

Tab. 2.1 – Continued
2.2. Electric currents in the magnetosphere
Type Symbol τ A (nT) Source
Polar magnetic storms and short-lived substorms Polar (or auroral)
centre of disturbance in
the night-time auroral
zone
with correlated irregular
variations in low latitudes
DP1 10 m - 2 h
DP2 10 m - 2 h
Special effects in connection to polar magnetic storms
bays (substorms as
observed in mid latitudes)
b 30 m -2 h
Sudden storm commencement
1000 (a)
100 (m,l)
100 (a)
10 (m,l)
100 (d,d)
20 - 100 (a,m)
5 - 25 (l)
electrojet PEJ in the
ionosphere with
connecting field-aligned
currents to plasma regions
of the magnetosphere
see DP1
ssc 2 - 5 m 10 - 100 m Impact of intense solar
particle stream on magnetopause
Solar flare effect sfe 10 - 20 m 10 Short-lived enhancement
of Sq currents in the
ionosphere
Ultralow frequency waves
(Pulsations)
regular continuous
pulsations
irregular transient
pulsations
Very low frequency emissions,
including whistlers
ULF (P) 0.2 - 600 s
Pc5 150 - 600 s
100 (a)
10 (m)
Pc4 45 - 150 s 2
Pc3 10 - 45 s 0.5
Pc3 5 - 10 s 0.5
Pc1 0.2 - 5 s 1
Pi2 45 - 150 s 1
Pi1 1 - 45 s 1
VLF 10 −5 − 10 −3 s
2.2.1. Ultralong periodic variation
Standing and propagating
hydromagnetic waves in
the magnetosphere
In this Section geomagnetic variations with extremely long periods are examined that are
not directly related to conventional MT measurements, which are, for logistic reason, usually
limited to a duration of a few months or less. Signals of such ultralong variations are
more suitable for studies using magnetovariational (MV) datasets, recorded at stationary
observatories that provide time series of sufficient length. However, the results of those
MV studies can be used to compare findings of MT methods and help to predict structures
at greater depth, which in turn can aid interpretation of MT studies.
a Schmucker [1985] assigns the Lunar daily variations to have a fundamental period of 1 d but as the
determining value is the time that it takes the Moon to orbit the Earth this variation has a period of
around 24 h 50 m (1 lunar day) instead, e.g. Merrill and McElhinny [1983], p.53; National Oceanic and
Atmospheric Administration (NOAA) [2010].
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