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59 Cards in this Set
- Front
- Back
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the force exerted by the weight of a column of air above a particular location.
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Air pressure
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What are two ways in which air pressure can be increased?
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1. increase in density
2. increase in temperature |
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Mechanical changes in pressure occur when...
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air flow is impeded causing a mass of air to build up over a particular location thus increasing air pressure.
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Thermal changes in air temperature occur when...
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air is heated or cooled... When air is heated it rises, and if pushed away aloft, surface air pressure decreases. Conversely if air is cooled, it subsides toward the surface causing air pressure to increase
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Under average sea level conditions the atmospheric pressure is...
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1013.2 millibars
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Serves as the division between what we call "high pressure" and "low pressure" at the surface.
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Average sea level pressure
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A map showing the distribution of pressure at sea level.
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Constant height map
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lines connecting points of equal air pressure are used to show pressure patterns on constant height maps.
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Isobars
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A map that shows the change in elevation of an isobaric surface
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Constant pressure map
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a surface upon which the pressure is the same at all locations.
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Isobaric surface
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the movement of air molecules from one place to the next.
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Wind
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The direction and speed of the wind represents the balance between three basic forces acting on it:
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the pressure gradient, the Coriolis force, and surface friction.
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the change in pressure over distance
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Pressure gradient
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We can induce a change in pressure over distance by...
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the unequal heating of earth's surface
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The creation of a pressure gradient initially causes the air to flow from higher toward lower pressure creating a wind. So in terms of a cause-and-effect relationship:
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Energy gradient > temperature gradient > pressure gradient > wind
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The orientation or direction of a pressure gradient is always described as being from...
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higher to lower pressure
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The speed of the wind is controlled by...
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the strength of the pressure gradient
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On a weather map, the strength of the pressure gradient can be discerned by...
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the distance between isobars
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Though the air is deflected to the right of its path in the Northern hemisphere, in the Southern Hemisphere wind is deflected to the left of its path. Why the difference?
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It is due to the difference in perspective... looking down upon the north pole, the earth appears to be spinning in a counter-clockwise direction while from the opposite perspective in the southern hemisphere it rotates in a clockwise direction.
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Generally speaking wind speed ________ with height above the surface as the frictional force of surface diminishes with height.
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Increases
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the layer of air that is influenced by friction caused by the surface.
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friction layer
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Around high pressure systems (H), air is directed...
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outward from the center
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Around low pressure systems (L) air is directed...
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inward toward the center
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in the Northern hemisphere, air takes on a _______ flow around highs and _______ around lows.
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clockwise, counterclockwise
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in the Southern hemisphere, air takes on a _______ flow around highs and _______ around lows.
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counterclockwise, clockwise
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Cyclones are areas of ____ pressure
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low
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Anticyclones are areas of ____ pressure
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high
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Explain how cyclones work in the northern hemisphere...
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The coriolis effect causes winds to deflect to the right of its path. This creates a counterclockwise rotation around a low and a convergence towards the center. As the air collides near the center it is forced upwards where it diverges away from the center. This divergence is what maintains the low pressure system.
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Explain how anticyclones work in the nothern hemisphere.
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For high pressure areas, air descends toward the surface due to convergence aloft. As the air nears the surface it is forced outward (divergence) from the center. The Coriolis effect bends the air to the right of its path creating a clockwise rotation around the high.
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created along coasts where land and water create variations in pressure due to differences in the way these two bodies heat and cool.
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land-sea breeze
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During the day, land heats more rapidly than water resulting in ____ pressure forming over land and _____ pressure over water.
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low, high
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During the daytime, air moves from over the water toward land in response to the pressure gradient creating a...
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sea breeze
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During the evening, the land cools more rapidly than water promoting _____ pressure over the land and _____ pressure over water.
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high, low
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The pressure gradient in the evening induces the air to flow from the land toward the water as a...
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land breeze
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Local scale circulation generally operates over a distance of...
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10 to 100 kilometers
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During the daytime, mountain slopes warm causing the air over the slope to be warmer than the air over the valley at the same elevation. Warming the air causes it to rise upwards creating a...
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Valley wind
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During the evening, the air chills due to a loss of surface energy to space. The cool dense air moves down slope as a...
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mountain wind
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As air descends the leeward side of a mountain it is compressed and adiabatically heated. Warming the air causes the saturation point to increase resulting in a decrease in its relative humidity (assuming the water vapor content remains the same). The newly created warm and dry wind moves down slope quite rapidly, and during the Spring causes substantial melting of mountain snow packs.
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Chinook
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Over plateau regions in the desert region of the United States, high pressure pushes air off the plateaus forcing the air into narrow mountain valleys. As the air is forced through the valley it is compressed and warms. As the air warms the saturation point rises and its relative humidity drops.
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Santa Ana winds
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What is the connection between wildfires in Southern California and the Santa Ana winds?
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the warm and dry winds fuel wild fires by dessicating the surface and whipping the wildfires into raging firestorms.
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wind that changes direction with season.
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Monsoon
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What is the cause of the summer monsoon?
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During the summer, the continent of Asia heats up more than the surrounding ocean due to the differences in the way land and water heat. The warm surface creates a large area of low pressure over north-central Asia and a smaller one over India. This creates an onshore wind bringing the moisture laden maritime air from the Pacific and Indian oceans onto land.
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what causes the rainfall during the wet monsoon season...
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As the air streams across the land during the wet monsoon season...
1. convection from the warm surface, 2. convergence onto areas of low pressure, 3. and uplift along major mountain systems like the himalayas cause the air to rise and creating abundant rainfall. |
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During the winter the asian continent cools rapidly creating an area of high pressure known as the...
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Siberian High
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The convective rise of air promotes a broad area of low pressure that straddles the equator called the...
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Intertropical Convergence Zone
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The location of majors deserts like the Sahara Desert, coincides with the presence of the Subtropical Highs, why?
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Subsidence towards the surface prevents the uplift of air needed to produce large scale condensation, cloud formation and precipitation. In addition, compressional heating of the air as it descends causes a drop in the relative humidity of the air.
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Why was the region equatorward of the subtropical highs between 30 and 35 degrees both north and south reffered to as the "horse latitudes" by spanish sailors?
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Because the winds here are realtively light and variable. The conditions could remain calm for days on end. To conserve water, sailors would throw horses overboard.
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Equatorward of the subtropical high, the pressure gradient between the high at 30o N and the low over the equator creates the...
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Northeast Trade winds
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The convergence of the northeast and southeast trades create the...
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ITCZ
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The converging tradewinds form a zone of calms and weak winds with no prevailing wind direction between about 5o north and south latitude called the...
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Doldrums
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On the poleward side of the subtropical highs the air heads poleward but is turned to create a westerly wind pattern between 30o N and 60o N in the Northern hemisphere known as the...
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Westerlies
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The loss of energy at the poles creates very cold air that subsides towards the surface. This creates a dome of high pressure called the...
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Polar high
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Air moving equatorward from the poles in the nothern hemisphere is turned in an easterly direction creating the...
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Polar easterlies
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The polar easterlies collide with the westerly wind belt at about 60 N and S creating a broad belt of low pressure called the...
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Subpolar lows
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Global pressure systems play a direct role in the geographic distribution of...
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precipitation
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Adiabatic warming of subsiding air creates a _______ ______ which acts as a cap to upwardly moving air.
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subsidence inversion
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corridors of warm water moving from the tropics poleward where they release energy to the air
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warm ocean currents
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corridors of cold water moving from higher latitudes toward the equator. They absorb energy received in the tropics thus cooling the air above.
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cold ocean currents
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The major ocean currents are driven by...
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wind
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