If a small-scale ionospheric current vortex [smallj.wpd] passes overhead of a ground magnetometer [
magdesc.wpd] then a bipolar signature is likely to be seen in one of the horizontal magnetic field
components and a monopolar variation in the other two field components. Such signatures are seen
on the dayside propagating anti-sunward and are known as Travelling Convection Vortices (TCVs; Friis-
Christensen et al., 1988). They may appear singly or as a chain with alternating polarity.
Similar signatures are also seen on the nightside propagating sunwards, associated with the substorm DP1 [dp1.wpd] electrojet. They are the Westward Travelling Surge (WTS) at the western edge of the electrojet and the omega band propagating eastwards from the eastern edge of the electrojet. They will normally be associated with small scale auroral forms [all-sky camera] in which the conductivity may be greatly enhanced. The strong conductivity gradients complicate the current structure and ground magnetic signature somewhat. However, in both the WTS [wts.wpd] and omega [omega.wpd] band there is a strong vortical nature to the current flow and some sort of transient pulse remains evident in the typical magnetogram signatures.
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