1. The periodic rising and falling of the earth's oceans and atmosphere. It results from the tide-producing forces of the moon and sun acting upon the rotating earth. This disturbance actually propagates as a wave through the atmosphere and along the surface of the waters of the earth. Atmospheric tides are always so designated, whereas the term “tide“ alone commonly implies the oceanic variety. Sometimes, the consequent horizontal movement of water along the coastlines is also called “tide,” but it is preferable to designate the latter as tidal current, reserving the name tide for the vertical wavelike movement. See equatorial tide, neap tide, spring tide, tropic tide. 2. See rip current, red tide, storm tide.