The Earth is a dipole magnet?

[SRH]

It is commonly said that the Earth is a dipole magnet.

My question is...
Why isn't the Earth described as a Helmholtz coil?
A Helmholtz coil has effectively the same magnetic field as a dipole, but seems like a more elegant description given the oblateness of the Earth caused by the Earth's rotation.

Any thoughts?

[antoniseb]

Are you sure there is some coil with wire-density and current density that you want to describe? The Earth has a superposition of many magnetic fields and the general result is overall a dipole. If you want to model it like an HC, go ahead. If it works for your calculations, that's fine with anyone you explain it to.

[SRH]

Is the field that a HC makes an electrical field or a magnetic field?

[antoniseb]

Is the field that a HC makes an electrical field or a magnetic field?

Magnetic. The coil is not retaining charge.

[Swift]

There have been times in Earth's history, such as during magnetic field reversals, when the Earth's field was not a dipole.

NASA article about it, with a graphic showing the complex field during a reversal