Elsasser number

Summary

The Elsasser number is a dimensionless number that compares the Lorentz force with the Coriolis force in a rotating, electrically conducting fluid. It is one of the dimensionless numbers of fluid mechanics used in magnetohydrodynamics. In the Earth's outer core it is of order one, which means that magnetic and rotational forces are comparable there. This balance is called the magnetostrophic regime and is central to theories of the geodynamo.