Bergwind

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.

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.

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. 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.

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