Sailing the Magnetic Seas in Calm Winds

Our magnetic tour will now look at those natural magnetic fields that are expected to occur everywhere about the Earth, every day of the year, in some regular and predictable fashion when the stormy winds of activity are absent. The principal field contributor arises deep in the Earth's interior. Generated by dynamic processes, this main field extends out into surrounding space and has the shape of a distorted dipole field, the magnetosphere. The word "dynamic" is used because we have evidence that the source of the Earth's main field is slowly changing, so that the pole locations gradually move westward over the years. We will sail into this part of our tour with an examination of the cause of the Earth's main field. We will look at the magnetic pole locations marked on global maps and learn why there are so many different reported positions.

Our visit to the regularly appearing fields includes an examination of the second most important undisturbed field, a variation called Sq for the solar quiet conditions during which this field is most prominent. Sq arises from a daily variation of current systems driven by winds and tides in the sunward side of the upper atmosphere. This chapter ends with a description of special polar-region fields. Our Earth's quiet field seems to be almost alive, changing in differing ways at the many special regions about the Earth.

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