Land-sea wind system
Land-sea wind system is a meteorological term.
It describes both a coupled climate system made up of land and water surfaces , over which sea and land winds develop , as well as the circulation system itself generated by these winds .
The cause of the development of the respective wind is of a thermal nature and is based on the two to three times faster warming or cooling of the air over a land surface compared to a water surface. The first theoretical explanation of the phenomenon comes from James Pollard Espy (1785–1860).
Onshore wind (sea wind)
A land surface heats up much faster than a water surface, since water has a larger specific heat capacity c . In the event of strong solar radiation , convection phenomena occur on land and the associated convergence on the ground. This is a balancing flow of air masses , caused by the resulting air pressure difference in the order of magnitude of 2 hPa between the thermal soil low above the land surface and the soil high above the water surface.
- Sea wind: Air masses flow from the water onto the land, as this heats up faster during the day due to the relatively low c-value of, for example, soil, concrete, houses (roof tiles c = 0.73 kJ / (kg · K)) and asphalt. Water, on the other hand, heats up / cools down much more slowly due to the higher c value of 4.18 kJ / (kg · K). Therefore, during the day the air masses rise over land and there is a compensatory movement due to air masses advancing from the water (= sea breezes).
Offshore wind (land wind)
The water keeps the daytime warmth longer than the land surface, above which the soil and air temperature usually drops significantly in the afternoon.
- Land wind: Air masses flow from land to or to the lake. Reason: in the evening, even more so at night, this circulation turns around; Land cools down much faster than the sea, because of the much lower c-values of the substances mentioned (roof tiles, c = approx. 0.73 kJ / (kg · K)). I.e. significantly lower specific heat capacity than water (4.18 kJ / (kg · K)). Now the water is relatively warmer; now the air rises above the lake and relatively colder air masses flow away from the land to the lake.
Aspects of water sports
The various wind directions , some of which change over time, are very attractive for several forms of water sports , but they can also be dangerous if it is difficult to return to land.
For sailing , a constant wind strength and direction is usually more popular than a frequent change. The geographic location of some sections of the coast makes them ideal for this. Constant winds - which can not only occur in " good weather " - make planning a trip and cruising against the wind easier . The local, temporally changing wind systems (see above) add an additional stimulus, but can often make it much more difficult to return in the afternoons with offshore wind. Some sailing enthusiasts therefore like to spend the night on offshore islands and do not start their return journey until the next morning - mostly under easier circumstances.
For windsurfers and especially surfers , but also for kite surfers , the characteristics of a stretch of coast ( surf spot ) are particularly important and interesting. For the direction of the wind relative to the beach line , they differentiate between onshore (onshore), offshore (offshore) and sideshore ( sideways wind). Many windsurfing areas are particularly popular because of stable wind conditions of one type or another, for example parts of Scandinavia or the west bank of the Neusiedler and the north bank of Lake Garda for offshore winds (with south wind more sideshore ), or the Camargue and large parts of the Baltic Sea for onshore conditions. Not least because of this, Kiel became the "capital" of windsurfing.
Web links
Individual evidence
- ^ Napier Shaw: Manual of meteorology . Vol. II. Cambridge University Press, 2nd Edition, 1936, p. 283 . OCLC 1048803706 .