The Elsasser number, Λ, is a dimensionless number in magnetohydrodynamics that represents the ratio of magnetic forces to the Coriolis force.
Λ = σ B 2 ρ Ω {\displaystyle \Lambda ={\frac {\sigma B^{2}}{\rho \Omega }}}
where σ is the conductivity of the fluid, B is the magnetic field, ρ is the density of the fluid, and Ω is the rate of rotation of the body.
Applications This number is useful when studying the linear stability of an accretion disc to the magnetorotational instability.
Notes
References Gubbins, David; Herrero-Bervera, Emilio (2007), Gubbins, David; Herrero-Bervera, Emilio (eds.), Encyclopedia of geomagnetism and paleomagnetism, Springer, doi:10.1007/978-1-4020-4423-6, ISBN 978-1-4020-3992-8