What is katabatic wind, how and where does it form?
A katabatic wind is a dense and cold air stream downward from mountain peaks, as well as downdrafts of cold air in cumulonimbus clouds. Although not all downslope winds are katabatic.
The katabatic wind brings cold and dry air to the foothills of the mountains, which can reach hurricane speeds. The most common types of katabatic winds are bora, glacial wind, stock wind, and mistral.
Katabatic incident winds are formed on the tops of glaciers and mountain plateaus. At night, the plateau radiates heat, cools the air, increases the cold, dry air mass and makes it denser until it breaks through any natural barriers such as mountain ranges, and gravity pulls cold, dense dry air down the slopes. If there is also a valley below in such a terrain, the wind usually reaches a speed of over 100 knots.
For example, katabatic south california wind, which carries cool, dry, dense air from inland, creates high pressure along the western side of the Great Basin Desert until it reaches the gorges in the Sierra Nevada mountain range and becomes hot by the time it reaches the Pacific coast. Accordingly, in Antarctica stock wind always very cold.
Most often, katabatic winds blow from ice-covered highlands Antarctica and Greenland. In Greenland, winds are especially strong when a low pressure area forms near the coast. A very cold layer of air is formed over the central surface of the Antarctic ice sheet, which diverges in all directions along the slopes of the ice sheet, forming katabatic winds moving towards the ocean.
In addition to the pressure gradient, the air movement is influenced by the force of gravity. As the air approaches the coastline, a very high wind speed can develop, up to more than 20 m / s, with very strong gusts. Together with the strong winds caused by the constant passage of deep cyclones around the Antarctic continent, katabatic winds make many areas of the Antarctic coastline the most windy and dangerous places on the planet.
Glacial wind blowing downstream of the glacier. It does not have a daily periodicity, since the temperature of the glacier's surface around the clock produces a cooling effect on the air. Temperature inversion prevails over the ice, and cold air flows down. The vertical power of the glacial wind flow is several tens of meters, rarely rises to hundreds of meters. Glacial winds, at their brightest, form over the ice plateaus of Antarctica.
On the archipelago Tierra del Fuego in South America and Alaska, squall winds are especially dangerous. They appear on the snow and ice fields of the coastal mountains and hit the coast at a speed of 200 - 300 km / h.
Katabatic winds are also common in Norway, Brazil and Japan, and are even found in less obvious places such as France and Croatiabecause in these places there are conditions suitable for their occurrence.
In France, cold air accumulates over a plateau-like ridge in the Massif Central, and then descends into the Rhône Valley at Golfe-le-Lyons. The wind is known as mistraland it is often associated with high pressure over the Bay of Biscay and low pressure over the Ligurian Sea, as the opposite rotation of the air drives the wind from the plain to the valley.
Mistral - a cold northwest wind blowing on the Mediterranean coast of France in the spring months and is formed when the Atlantic anticyclone and the North Sea cyclone meet. The wind is often so strong that it uproots trees, and its constant influence on the coast is especially noticeable on lonely growing trees, which are often strongly inclined to the south. In the eastern part of the Côte d'Azur, the effect of the mistral is much weaker.
Katabatic wind in Croatia known as Bora, or Bura. The cold, dense air mass creates high pressure in the high Hungarian Plains until the air mass passes through the gorges in the Dinaric Alps and falls to the lower, warmer coastal slopes, at a lower atmospheric pressure.
Bora - a very strong, cold and gusty wind, which occurs when the flow of cold air meets a hill on its way, and overcoming the obstacle, the bora falls with great force on the coast. And the vertical dimensions of the bora reach several hundred meters.
Boron is also classified as black and white. Black pine forest occurs on the coast, when a cyclone passes through the sea. In the rear of the cyclonic vortex, northeastern winds arise, which intensify when the flow collapses from the leeward slopes of the mountains on the seashore. The wind is accompanied by precipitation and powerful low clouds.
This wind manifests itself exclusively in winter as a result of the passage of a very deep Genoese cyclone over the southern part of the Adriatic Sea. At this time, it rains over the southern Adriatic and the south wind blows, and the low pressure of the center of the cyclone sucks in air masses from the north.
White bora occurs during an anticyclone, with a strong northeast wind. With a white pine forest there is no precipitation, usually a clear sky, but with a white pine forest, the wind strength is usually greater than with a black pine forest.
Katabatic airflow also often occurs when there is no wind, because any headwind can prevent air from descending from the mountain, and also because the wind tends to mix air masses, increasing the average air temperature.
How to determine if the wind is katabatic or not
Katabatic winds are associated with strong sudden gusts, but can be confused with other phenomena. Technically, katabatic winds are found in many other places. This happens at night when the air on the mountain slopes cools and slides down. However, to call them full-blown katabatic winds, they usually lack cold, high plains. However, there are many reports around the world of similar sudden, high winds, often at night and near rocks. In this case, there are two possible explanations: turbulence or downdrafts.
If you are on the leeward side of a cliff or hill during a sea breeze and when the wind hits the top of the hill, this mixture of conditions will create chaotic, turbulent winds that seem to blow from all directions at once.
For example, the downdrafts formed during a thunderstorm, in the process of how lightning is formed and the ensuing colossal flow of air that can sweep a boat in a second and spin it.
Anabatic winds are in many ways the opposite of katabatic winds. They form in calm weather and during the day, mainly where the sun shines on one side of the valley. This heats up the air on the slope, which then rises, often forming cumulus clouds over the top of the ridge as the warm, humid air cools. A well-defined haze forms at the top of the anabatic stream, often at the same height as nearby peaks.
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