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Berg wind (from Afrikaans ''berg'' "mountain" + ''wind'' "wind", i.e. a mountain wind) is the South African name for a katabatic wind: a hot dry wind blowing down the Great Escarpment from the high central plateau to the coast. When the air that has been heated on the extensive central plateau flows down the escarpment to the coast it undergoes further warming by adiabatic processes. This accounts for the hot and dry properties of these off-shore winds, wherever they occur along South Africa's coastline.〔Danielson, Levin, and Abrams (2003). ''Meteorology'', McGraw Hill〕 Although berg winds are often called a Föhn winds, this is probably a misnomer, as Föhn winds are rain shadow winds that result from air moving over a mountain range, resulting in precipitation on the windward side. This releases latent heat into the atmosphere which is then warmed still further as the air descends on the leeward side (e.g., the Chinook or the original Föhn).〔 Berg winds do not originate in precipitation, but in the mostly dry, often arid central plateau of Southern Africa. On the other hand, katabatic winds are technically drainage winds, that carry high density, usually cold air from a high elevation down a slope under the force of gravity.〔 These are thus "fall winds", which occur most typically down the coastal ice slopes of Antarctica and Greenland. Berg winds blow off the African escarpment in response to large scale weather systems in the South Atlantic Ocean, the African interior, and the Southern Indian Ocean. ==Coastal lows and berg winds== Berg winds are usually accompanied by coastal lows.〔 These coastal lows owe their existence to the configuration of the plateau, escarpment and coastal plain (see diagram on the right, above), in that they are confined to the coastal areas, always below the escarpment. Though they can arise almost anywhere along the coast, they often first appear on the west coast, or even on the Namibian coast. They are then always propagated counter-clockwise along South Africa's coastline at between 30-60 km/h, from the west coast southwards to the Cape Peninsula and then eastward along the south coast, and finally north-eastward along the KwaZuluNatal coastline, to finally dissipate north of Durban, due to the divergence of the coastline from the plateau which disappears altogether in the vicinity of the Limpopo valley.〔Carter, T.J. (2005). The evolution of coastal lows along the coast of South Africa. ( Masters Thesis, University of Zululand. ) retrieved 3 June 2015.〕 There is always a hot off-shore berg wind ahead of a coastal low, which can blow for several days or for only for a few hours. This is then followed by cool onshore winds which bring low cloud, fog or drizzle to the region, but may, on occasions, produce substantial precipitation when coupled to an approaching cold front.〔 Coastal lows are a common feature of the coastal weather in South Africa with an average of about 5 lows of varying intensities passing through Port Elizabeth per month.〔 They are shallow (not more than 1000-1500 m deep), mesoscale (medium sized) systems that that are generally not more than 100-200 km across, trapped on the coastal plain by the escarpment on the inland side, Coriolis effects on the oceanic side, and an inversion layer above. The pressure minima of these systems lie just off-shore. In the south-west corner of the country the coastal lows are bounded on the inland side by the Cape Fold Mountains,〔 which tend to have a higher elevation than the escarpment, and form an almost continuous 1000 km mountain barrier running parallel to the coast from the Cederberg, 300 km to the north of Cape Town, to Cape Hangklip on the east side of False Bay and then eastwards for 700 km to Port Elizabeth, where they eventually peter out (see the map above). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Berg wind」の詳細全文を読む スポンサード リンク
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