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Your article refers to the Earth’s magnetic field only at very long wavelengths. In over 70 years’ exposure to science, I have never heard of our magnetic field having wavelengths. Please elaborate.

Kenneth E. Stone
Cherryvale, Kan.

Looking at Earth’s magnetic field at long wavelengths is analogous to looking at a picture in low resolution, says Cathrine Fox Maule of the Center for Planetary Science in Copenhagen. Small variations in the field due to local anomalies in the crust disappear, leaving only regional variations, which scientists can interpret as differences in heat flow through the crust .—S. Perkins