What aspect of the solar wind is often the most crucial factor in determining a severe geomagnetic storm?

Answer

The direction of the interplanetary magnetic field embedded within the wind

While average speed is known, the direction of the interplanetary magnetic field carried in the solar wind is often the most critical factor determining whether a solar event will deflect against or severely impact Earth’s magnetic field.

What aspect of the solar wind is often the most crucial factor in determining a severe geomagnetic storm?
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