Oscillating nocturnal slope flow in a coastal valley

Observations of slope flows in a coastal valley are analyzed. The diurnal variation of upslope and downslope flows depends on season in a systematic way which appears to be related to the high latitude of the observational site and the presence of a nearby layer of marine air. Summer nocturnal flow over the sloping valley floor was studied during a special observing campaign. A downslope gravity flow interacts with even colder surface air at the valley floor. The latter originates as cold marine air or previous drainage of cold air. Regular oscillations, which appear to be trapped, terrain-related, internal gravity waves, exert a major influence on the downslope flow and its interaction with pre-existing cold air at the floor of the valley.