Solar wind creates a surprising imbalance in Earth’s magnetic shield

New simulations reveal why solar wind waves favor one side of Earth's magnetic shield and how the sun's magnetic field influences their location.

Wind blowing across a lake raises waves. The same thing happens where the gas streaming off the sun slides past the outer edge of Earth’s magnetic field.

Those waves are known to form on the flanks of that boundary, and the usual mental picture puts them on both sides at once.

A new simulation suggests these waves favor one side.

In a model of Earth’s magnetosphere run with the sun’s magnetic field pointing one way, the waves grew along the dawn flank and barely formed at dusk.

When the field direction was reversed, the waves switched sides.

In both simulations, they formed only in the northern hemisphere, which was tilted away from the sun.