1. n. [Geophysics]

A mode of the electromagnetic field that involves only one component of the magnetic field and the two components of the electric field perpendicular to it; e.g., the x-component of the magnetic field and y- and z-components of the electric field. The TM mode is useful in describing 2D models in which the magnetic field is perpendicular to the 2D plane of the model. For this case, Maxwell's equations can be reduced to a single scalar equation for the magnetic field component, which simplifies calculations tremendously.

Alternate Form: transverse magnetic mode