What is katabatic wind, under what conditions and in what areas of the Earth does it form? Katabatic winds are currents of cool and dense air directed from the mountains down the side slope in thunderclouds. At the same time, not all winds blowing from mountain ridges can be considered katabatic. If you are interested not only in the topic of yachting, but also yacht charter in your chosen region, we advise you to contact the specialists company 2Yachts - you will be offered only the most relevant and advantageous offers available on the yacht market.
The katabatic wind lowers cold air masses of low humidity to the foothills of the mountains, which sometimes gain hurricane speed (several hundred km / h). The most common types of particular katabatic winds are glacial wind, mistral, bora, and downdraft wind. This type of wind is formed on glacial peaks and plateaus. During the dark period of the day, the air on the hills cools down, becomes denser until it overcomes a natural obstacle (for example, a small ridge), and the force of gravity pulls dry and compacted air masses downward. If at the same time there is also a depression at the bottom, then the wind speed can reach hundreds of knots or more.
For example, Santa Ana, a katabatic wind that carries dry and dense air from the continent, builds up pressure on the western side of the Great Basin Desert (one of the largest deserts in the United States) and reaches the Sierra ranges -Nevada, where heat is gathered and becomes hot by the time it reaches the ocean.
It is clear that in Antarctica the stock wind, on the contrary, is frosty and only in the oceanic expanses its temperature gradually increases. Most often, katabatic winds blow from the elevated glacial fields of Greenland and Antarctica. From the territory of Greenland, the winds blow especially fiercely when a zone of low pressure forms below, near the coast. A layer of air with extremely low temperatures is formed over the middle territory of Antarctica, diverging in different directions along the glacial slopes and creating katabatic winds blowing from the coast to the ocean.
In addition to the pressure difference in different areas, the force of gravity affects the speed and propagation of katabatic winds. So, as you approach the coast, the wind speed can reach tens of meters per second. And combined with powerful cyclonic winds near the shores of the southernmost continent, katabatic winds make some places near the shores of Antarctica the most dangerous for navigation.
Glacial winds blow down the slope towards the coast (without a diurnal direction, because the glacier has a cooling effect on the air masses all the time of the day). The most pronounced manifestation of glacial winds is obtained over the ice fields of Antarctica, with a vertical flow thickness of several tens, and sometimes hundreds of meters.
In the Chilean archipelago of Tierra del Fuego, located at the southern tip of South America between the Atlantic and Pacific oceans, squally winds are of great danger arising in the snow-covered mountain fields adjacent to the ocean. Gusty winds are directed to the coast at a speed of up to two to three hundred km / h.
Katabatic winds have spread (more precisely, this is what nature has ordered) also in Japan, Norway and Brazil. They are also present in the coastal regions of the French Republic and Croatia.
In France, the world famous Mistral is formed when cold air accumulates over the Massif CENTRAL plateau in the center and south of the country and travels to the Rhone Valley, where it reaches its maximum speed. This wind blows not only in the near-surface layer, but also in the atmosphere - at altitudes up to 3 km. The Mistral is very strong at Mont Ventoux, 1900 m above sea level. The characteristics and causes of the mistral are very similar to those of the north wind of Tramontane, following a different corridor.
The word “mistral” is translated from French as “masterly”, and there is an explanation for that - after the arrival of the mistral, the whole south of France plunges into a rolling chime, according to local residents, the wind “beats all the bells” and does it masterfully. Dry and cold, the Mistral blows in the spring months from the northwest and owes its formation to the collision of the Atlantic anticyclone and cyclone from the North Sea regions. Often the wind reaches such a force that it is able to uproot trees (its speed can exceed 90 km / h) and destroy crops, and its constant impact on the southern coast is especially easy to notice from trees bent to the side. where the wind usually blows. However, already in the eastern part of the coast of the French Riviera, the impact of the Mistral is not so strong. Locals consider Mistral to be healthy, but in some patients it causes suffocation and heart failure.
In Croatia, the wind with a vertical component directed downward is called bora. Bora usually blows during the winter, there are also Montenegrin and Slovenian bora, blowing in gusts. This is a very strong, cold and gusty wind, formed when air currents coming from the tops of the mountains collapse on the coast after overcoming a natural relief obstacle - hills, hills, plateaus, etc.
There are black and white boron varieties. Black is formed when a cyclone moves along the sea, creating combined streams of northeastern winds with descending jets of cooled air from the mountains. Indispensable attributes of the black pine forest - heavy precipitation and increased low clouds. The emergence of the white bora is associated with the action of an anticyclone, under the influence of wind from the north-east directions. At the same time, there is no precipitation at all, however, the wind strength is higher than in the case of black pine forest.
As experienced yachtsmen say 2yachts, you can find out if it is katabatic wind or not by observing the air currents ... Purely technical, air currents going from top to bottom at night in many parts of the planet can also be called katabatic, but reports from many regions of the world about unexpected strong and squally downgrading winds (often occurring at night or near rocks) can be explained by turbulence or downdrafts.
If this is turbulence, then being on the leeward side of a cliff or hill during the refreshing sea wind and when the wind hits the top of the hill, a mixture of chaotic air currents will be created that, as it might seem, blown out from all sides.
Downdrafts can form, for example, during a thunderstorm, when during the formation of lightning powerful air currents are created that can instantly catch and spin the ship.
In contrast to katabatic winds, anabatic winds form during the day and in calm weather. They usually take place where solar heat only hits one side of the lowland. Subsequently, the air on the slope, warming up, rises, often forming rare wavy clouds over the peaks of the ridge when the air of high humidity cools. The top of the anabatic wind can be distinguished by a well-defined haze, often forming at the same height as mountain ranges.