An Etymological Dictionary of Astronomy and Astrophysics

A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → Lorentz forces to
→ Coriolis forces. It is given by: Λ = σB²/(ρΩ), where σ s the → electrical conductivity of the fluid, B is the typical → magnetic field strength within the fluid, ρ is the fluid → density, and Ω is the → angular velocity. A typical value for the Earth is Λ ~ 1.

See also: Named after Walter Maurice Elsasser (1904-1991), American theoretical physicist of German origin; → number.