The Internal Surge in Loch Ness

Abstract

THE large temperature changes which occur at depth in Loch Ness are caused by an internal seiche or standing wave^1,2, which develops a pronounced front or surge like a tidal bore and is sometimes followed by a periodic oscillation of the isotherms. The surge is produced by the stress of the wind on the water surface^2,3, which causes a flow of near-surface water to one end of the Loch and a depression of the thermocline at that end. When the wind falls, the tendency of the thermocline to recover a level position initiates the surge, which is often over 10 m in height. The following wave train, when it occurs, is of comparable height and contains waves about 1 km long. No effects are seen, or are expected to be seen, at the surface. In calm weather the surge progresses up and down the Loch for more than a week, during which time it travels more than 200 km (refs. 2 and 4).