Rossby waves in the atmosphere and ocean are large-scale waves whose restoring mechanism is the variation of the Coriolis parameter with latitude (the beta effect); atmospheric Rossby waves propagate much faster than oceanic Rossby waves because the atmosphere is a much less dense, more dynamically responsive fluid, so the time required for each type of wave to cross a given ocean basin width differs by roughly an order of magnitude, with atmospheric Rossby waves crossing in a matter of days to weeks and oceanic Rossby waves requiring months to cross the same distance.