Upper Air Winds and the Jet Streams Winds at the top of the troposphere are generally poleward and westerly in direction. Figure 7q-1 describes these upper air westerlies along with some other associated weather features.
What type of winds are most common at lower elevation?
If the foehn flow is weak and remains aloft, only the higher elevations in the mountains are affected by the strong, dry winds. Local circulations, such as the sea breeze and slope winds, are predominant at lower elevations, particularly to areas away from the major passes.
What is an upper air chart?
A sample 500 millibar level upper air chart. This depicts the wind speed and direction at an altitude around 18,000 feet (5,700 meters). The term "upper air" refers to the earth's atmosphere above about 5,000 feet (1,500 meters). It is from the upper air where we get our rain and drought, wind and calm, heat and cold at the earth's surface.
What is the wind called when it flows down the mountains?
If the down flowing wind is warm and dry, it is called a foehn wind. The wind is called a bora or fall wind if the air is originally so cold that even after it is warmed adiabatically in flowing down the mountain slopes it is still colder than the air it is replacing on the leeward side.
What are the characteristics of upper level wind?
Upper-level wind speeds generally occur on the order of tens of metres per second and vary with height. The characteristics of upper-level wind systems vary according to season and latitude and to some extent hemisphere and year. Wind speeds are strongest in the midlatitudes near the tropopause and in the mesosphere.
What are the 4 types of wind?
Types of Wind - Planetary, Trade, Westerlies, Periodic & Local Winds.
What winds are found in the upper troposphere?
Upper Air Winds and the Jet Streams. Winds at the top of the troposphere are generally poleward and westerly in direction. Figure 7q-1 describes these upper air westerlies along with some other associated weather features.
What are upper winds called?
Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. The winds blow from west to east in jet streams but the flow often shifts to the north and south. Jet streams follow the boundaries between hot and cold air.
What are upper air winds?
This depicts the wind speed and direction at an altitude around 18,000 feet (5,700 meters). The term "upper air" refers to the earth's atmosphere above about 5,000 feet (1,500 meters). It is from the upper air where we get our rain and drought, wind and calm, heat and cold at the earth's surface.
What are the upper layers of the atmosphere?
Exosphere. This is the outermost layer of the atmosphere. ... Thermosphere. Between about 53 miles (85 km) and 375 miles (600 km) lies the thermosphere. ... Mesosphere. This layer extends from around 31 miles (50 km) above the Earth's surface to 53 miles (85 km). ... Stratosphere. ... Troposphere.
How are upper level winds measured?
Upper-level winds are primarily measured by tracking the position of radiosonde balloons as they rise through the atmosphere. Radiosondes are released from a global network at 0000 utc and 1200 utc each day, and data are quickly available to the world's weather services, as well as to the public.
Why are upper winds called FD?
Winds aloft, officially known as the winds and temperatures aloft forecast, (known as "FD" in the US and Canada, but becoming known as "FB", following the World Meteorological Organization [WMO] nomenclature), is a forecast of specific atmospheric conditions in terms of wind and temperature at certain altitudes, ...
How often are upper winds issued?
Issue and Valid Times. Graphic area forecast charts are issued four times daily, approximately ½ hour before the beginning of the forecast period. The GFA is issued at approximately 2330, 0530, 1130 and 1730 UTC and is valid at 0000, 0600, 1200 and 1800 UTC respectively.
What is Anabatic and katabatic winds?
Anabatic Winds are upslope winds driven by warmer surface temperatures on a mountain slope than the surrounding air column. Katabatic winds are downslope winds created when the mountain surface is colder than the surrounding air and creates a down slope wind.
What does upper air mean?
upper air in American English noun. Meteorology. the atmosphere above the lower portion of the troposphere.
How fast are winds in upper atmosphere?
The highest zonal winds are around 60–70 metres per second (135–155 miles per hour) at 65–70 km (40–43 miles) above Earth's surface.
What do upper air maps show?
1. Upper-air weather maps differ from surface weather maps. Whereas surface weather conditions are plotted on a map of constant altitude (normally sea- level), upper-air weather conditions are plotted on maps of constant air pressure. The altitude at which the particular pressure is located is reported on these maps.
What are two characteristics of the upper troposphere?
Of all five layers, the troposphere has the highest density, greatest air pressure, 75% of the atmospheric mass, nearly all water vapor, and a temperature range from 62 to -60 degrees F. The temperature in the troposphere decreases steadily with altitude.
What can you find in the troposphere?
In fact, the troposphere contains three-quarters of the mass of the entire atmosphere. The air here is 78% nitrogen and 21% oxygen. The last 1% is made of argon, water vapor, and carbon dioxide.
Where are the trade winds?
The trade winds can be found about 30 degrees north and south of the equator. Right at the equator there is almost no wind at all—an area sometimes called the doldrums.
What is Anabatic and katabatic winds?
Anabatic Winds are upslope winds driven by warmer surface temperatures on a mountain slope than the surrounding air column. Katabatic winds are downslope winds created when the mountain surface is colder than the surrounding air and creates a down slope wind.
Which direction are the winds in the troposphere?
Winds at the top of the troposphere are generally poleward and westerly in direction. Figure 7q-1 describes these upper air westerlies along with some other associated weather features. Three zones of westerlies can be seen in each hemisphere on this illustration . Each zone is associated with either the Hadley, Ferrel , ...
What is the wind speed of the jet stream?
Wind velocity is highest in the core of the polar jet stream where speeds can be as high as 300 kilometers per hour. The jet stream core is surrounded by slower moving air that has an average velocity of 130 kilometers per hour in winter and 65 kilometers per hour in summer. Associated with the polar jet stream is the polar front.
Why is the subtropical jet stream slower than the polar jet stream?
The reason for its formation is similar to the polar jet stream. However, the subtropical jet stream is weaker. Its slower wind speeds are the result of a weaker latitudinal temperature and pressure gradient.
What determines the intensity of a mid-latitude cyclone?
The shape and position of waves in the polar jet stream determine the location and the intensity of the mid-latitude cyclones. In general, mid-latitude cyclones form beneath polar jet stream troughs .
How is the jet stream formed?
The polar jet stream is formed by the deflection of upper air winds by coriolis acceleration (see Figure 7q-3 below). It resembles a stream of water moving west to east and has an altitude of about 10 kilometers. Its air flow is intensified by the strong temperature and pressure gradient that develops when cold air from the poles meets warm air from the tropics. Wind velocity is highest in the core of the polar jet stream where speeds can be as high as 300 kilometers per hour. The jet stream core is surrounded by slower moving air that has an average velocity of 130 kilometers per hour in winter and 65 kilometers per hour in summer.
What is the jet stream associated with?
Associated with the polar jet stream is the polar front. The polar front represents the zone where warm air from the subtropics ( pink ) and cold air ( blue ) from the poles meet (see Figure 7q-3 below). At this zone, massive exchanges of energy occur in the form of storms known as the mid-latitude cyclones.
What are upper level wind systems?
Upper-level wind systems, like all wind systems, may be thought of as having parts consisting of uniform flow, rotational flow (with cyclonic or anticyclonic curvature), convergent or divergent flow (in which the horizontal area of masses of air shrinks or expands), and deformation (by which the horizontal area of air masses remains constant while experiencing a change in shape). Upper-level wind systems in the midlatitudes tend to have a strong component of uniform flow from west to east (“ westerly ” flow), though this flow may change during the summer. A series of cyclonic and anticyclonic vortices superimposed on the uniform west-to-east flow make up a wave train (a succession of waves occurring at periodic intervals). The waves are called Rossby waves after Swedish American meteorologist C.G. Rossby, who first explained fundamental aspects of their behaviour in the 1930s. Waves whose wavelengths are about 6,000 km (3,700 miles) or less are called short waves, while those with longer wavelengths are called long waves. In addition, short waves progress in the same direction as the mean airflow, which is from west to east in the midlatitudes; long waves retrogress (that is, move in the opposite direction of the mean flow). Although the undulating current of air is composed of a number of waves of varying wavelength, the dominant wavelength is usually around several thousand kilometres. Near and underneath the tropopause, regions of divergence are found over regions of gently rising air at the surface, while regions of convergence aloft are found over regions of sinking air below. These regions are usually much more difficult to detect than the regions of rotational and uniform flow. While the horizontal wind speed is typically in the range of 10–50 metres per second (about 20–110 miles per hour), the vertical wind speed associated with the waves is only on the order of centimetres per second.
Where are wind speeds strongest?
Wind speeds are strongest in the midlatitudes near the tropopause and in the mesosphere. Rossby wave patterns over the North Pole depicting the formation of an outbreak of cold air over Asia. Encyclopædia Britannica, Inc.
What are the characteristics of air flow?
Characteristics. The flow of air around the globe is greatest in the higher altitudes, or upper levels. Upper-level airflow occurs in wavelike currents that may exist for several days before dissipating. Upper-level wind speeds generally occur on the order of tens of metres per second and vary with height.
What is a weather balloon called?
Balloon-borne instrument packages designed to track upper-level winds and capable of being tracked by radar are called rawinsondes.
What is the dominant wavelength of air?
Although the undulating current of air is composed of a number of waves of varying wavelength, the dominant wavelength is usually around several thousand kilometres. Near and underneath the tropopause, regions of divergence are found over regions of gently rising air at the surface, while regions of convergence aloft are found over regions ...
How fast is the horizontal wind?
While the horizontal wind speed is typically in the range of 10–50 metres per second (about 20–110 miles per hour), the vertical wind speed associated with the waves is only on the order of centimetres per second.
Which direction do short waves progress?
In addition, short waves progress in the same direction as the mean airflow, which is from west to east in the midlatitudes; long waves retrogress (that is, move in the opposite direction of the mean flow). Although the undulating current of air is composed of a number of waves of varying wavelength, the dominant wavelength is usually ...
What happens to the air in a polar cell?
Polar cell- Air rises, diverges, and travels toward the poles. Once over the poles, the air sinks, forming the polar highs. At the surface air diverges outward from the polar highs. Surface winds in the polar cell are easterly (polar easterlies).
Which cell dominates tropical and subtropical climates?
Hadley cell- Low latitude air movement toward the equator that with heating, rises vertically, with poleward movement in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates.
Do land breezes affect the coast?
Land and sea breezes are very local and affect only a narrow area along the coast.
Global winds
Global winds are winds that blow across the globe. They are also known under the term "global wind patterns". The two main types of global winds are trade winds and monsoons.
Local winds
Local winds are winds that occur and are regularly observed in a certain place due to certain local characteristics (usually the terrain). So the main features of a local wind are its regularity and the limited area where it is observed. The most common example of a local wind are breezes and mistral.
Other types of winds based on various characteristics
At the border of air masses — especially large homogeneous volumes of air with a strong temperature difference — veery strong winds occur, capable of reaching hundreds of kilometers per hour. Such winds were called jet streams.
What direction does a north wind blow?
Thus, a north wind blows from the north toward the south, a northeast wind from the northeast, and so on around the points of the compass. Direction is also described in degrees of azimuth from north-a northeast wind is 45°, a south wind 180°, and a northwest wind 315°.
Which direction does the wind move in a trough?
This means that as a trough, with its front, passes a particular location the wind direction shifts clockwise. The wind behavior during the frontal passage depends upon the type of front, its speed, the contrast in temperature of the air masses involved, and upon local conditions of surface heating and topography.
What is surface wind?
Surface winds often vary considerably in both speed and direction over short intervals of time. They tend to blow in a series of gusts and lulls with the direction fluctuating rapidly. This irregular air motion is known as turbulence, which may be either mechanical or thermal in nature. At the surface, turbulence is commonly identified in terms of eddies, whirls, and gusts; aloft it is associated with "bumpy" flying.
What causes mechanical turbulence?
Mechanical turbulence increases with both wind speed and the roughness of the surface. Roughness creates mechanical turbulence, while surface heating causes thermal turbulence in the airflow. Thermal turbulence is associated with instability and convective activity.
How to tell wind direction on a weather map?
Surface wind direction is indicated on weather maps by a wind arrow flying with the wind. The number of barbs on the tail represent the wind speed. At the top of the friction layer the wind blows parallel to the isobars, as shown by the large arrow.
How does friction affect the wind?
We learned in the previous chapter that friction with the earth's surface slows down the wind and results in changes of direction so that the surface wind blows at an angle across the isobars from high to low pressure. The amount of reduction in speed and change of direction depends upon the roughness of the earth's surface. It follows then that the effect of friction is least over smooth water and greatest over mountainous topography.
How does a wind vane work?
A wind vane indicates wind direction by pointing into the wind-the direction from which the wind blows. The method of describing the direction of both surface winds and winds aloft, by the direction from which the wind blows, is ordinarily very practical.
How does the equator affect the atmosphere?
The air at the equator receives more solar energy than the air at the poles. This creates winds that move heat as well as water vapor around the globe. Air rises at the equator and sinks at the poles. Due to the rotation of Earth, air is deflected on its path creating surface winds. These move from east to west (easterlies) in the tropics and polar areas. Winds in the middle latitudes moves from west to east and are called westerlies. One type of wind called trade winds from the southern and northern latitudes converge on latitudes of 10 degrees north and south which causes the ITCZ or Intertropical Convergence Zone. This area is characterized by low pressure and calm winds. In the upper troposphere, due to the convergence of wind, a descending motion in the air column leads to an increase in surface pressure and a clear sky. Likewise, divergence can cause ascending motion in the air column which leads to a decrease in surface pressure and cloudy weather. In an upper air chart, contour lines can be viewed with a trough and ridges. Winds blow faster in the ridge ( high pressure) than the trough (low pressure) and as it approaches the slower moving air in the trough, the air piles up producing convergence. The slower moving air, when it approaches the ridge, spreads out or diverges. The strongest divergence occurs on the northeast side of the trough, where a surface low develops and the strongest convergence occurs on the northwest of the trough where a surface high develops. Therefore, in the upper troposphere, the wind can converge as well as diverge.
How many layers are there in the atmosphere?
The atmosphere is divided into four layers--troposphere, stratosphere, mesosphere and thermosphere. These vary in altitude as well as temperature. The troposphere is the layer closest to Earth's surface and extends to 12 km (7.5miles) above Earth. As one travels up through this layer, the temperature decreases by -6 degrees Celsius (-11 degrees Fahrenheit) for every kilometer. Turbulent wind occurs in the troposphere along with clouds and storms. The uneven heating of the parts of the troposphere by solar radiation causes convection currents.