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Flux Footprint
Flux footprint (also known as atmospheric flux footprint or footprint) is an upwind area where the atmospheric flux measured by an instrument is generated. Specifically, the term flux footprint describes an upwind area "seen" by the instruments measuring vertical turbulent fluxes, such that heat, water, gas and momentum transport generated in this area is registered by the instruments. Another frequently used term, fetch, usually refers to the distance from the tower when describing the footprint. Visualization of the concept Consider an instrument measuring a flux of water (evapotranspiration) a few meters above the surface in a situation with no wind. In such a case, the instrument would measure evapotranspiration generated just underneath the instrument location and brought upwards by mostly non-turbulent exchange. In a situation with a strong wind, the wind would blow air located under the instrument away. The wind would bring in air generated somewhere upwind and brought upwa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Upwind
Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference, i.e. along the direction towards which the wind is going. The side of a ship that is towards the leeward is its "lee side". If the vessel is heeling under the pressure of crosswind, the lee side will be the "lower side". During the Age of Sail, the term ''weather'' was used as a synonym for ''windward'' in some contexts, as in the ''weather gage''. Because it captures rain, the windward side of a mountain tends to be wet compared to the leeward it blocks. Origin The term "lee" comes from the middle-low German word // meaning "where the sea is not exposed to the wind" or "mild". The terms Luv and Lee (engl. Windward and Leeward) have been in use since the 17th century. Usage Windward and leeward directions (and the points of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |