Atmospheric Circulation Flashcards
Barometer
Is used to measure air pressure
Wind
Is the horizontal motion across the Earths surface
- It is created by gradients in air pressure/density
- The greater the pressure gradient/difference the stronger the wind is
Forces that determine winds:
- Pressure gradient force
- Coriolis Effect
- Frictional Force
Pressure Gradient Force
- Is responsible for generating wind to blow from high pressure to low pressure perpendicular to the isobars
- Fluids like air/water move from areas of high pressure to low pressure
Wind blows which was to the isobars?
They blow perpendicular to the isobars from a high pressure zone to low pressure zone
When considering PGF on its own, the angle is…
Perpendicular
How are convection loops created?
They are created by unequal heating a cooling of the surface
Pressure gradient controls…
Horizontal air movement
Air temperature controls…
Vertical air movement
Coriolis Effect
Is an apparent force caused by the Earth’s rotation
Coriolis force is always ____ to the wind
Perpendicular
Coriolis Force =
PGF, then the wind blows parallel to the isobars with low pressure to the left if you’re in the Northern Hemisphere
Geostrophic Winds
Are upper atmospheric winds with no friction
- Upper level winds run parallel to the isobars, with low pressure to the left when you’re unfacing the wind in the northern hemisphere
Friction Force
- Friction from the surface slows wind speed and combines with other forces to influence wind direction, basically friction slows down wind
The effect of friction extends to about…
500m above the surface
The winds from a northern hemisphere cyclone rotate
counter-clockwise
The winds from a low pressure system in the Southern Hemisphere rotate:
clockwise
Why do cyclones in the northern and southern hemisphere spine in opposite directions?
Because of the Coriolis effect
Will land or land near the water be cooler? Why?
Land near the water will be cooler as land warms up quickly during the day and cools down quickly at night
Why will the water stay warm at night?
Because water has the capacity to store heat for a longer period of time
It is always low pressure…
Along the surface of the equator as it is near the tropics (its always warm near the equator)
What kind of cells does the subtropics have?
High pressure cells
Why do the poles have high pressure?
Cause it is so cold at the poles, the air falls
Atmospheric circulation between the equator and the sub tropics is called:
Hadley cells
Winds coming from the north east are called:
Northeast trade winds
Winds coming from the south east are called:
South east trade winds
Where does the low pressure belt exist?
The ITCZ
The subtropics has what type of pressure?
High pressure
Winds blow from…
High pressure to low pressure
What is a front?
Two air masses with contrasting temperatures
- At mid latitude we receive air from the poles (cold) and air coming from the subtropics (warm) this causes cold air to meet with the warm air and is called a front
What do high poles generate?
Easterlies
Hadley cells generate…
Northeast and Southeast trades
Westerlies
Are the dominant surface winds from the subtropics to high latitudes
What is associated with the equator?
The intertropical convergence zone
Equatorial Low Pressure Trough
- High insolation warms equatorial air, the air rises and produces a zone of low pressure
- Air from both hemisphere flow toward the surface low and moves aloft as part of the Hadley cell
- This area of convergence is known as the ITCZ
Subtropical High Pressure Belts
- Air descending part of Hadley cell is heated by compression and becomes drier
- The surface air diverging form the subtropical highs generate earth’s principle surface (mid latitude westerlies, tropical trade winds)
- Like the ITCZ, the high pressure cells “follow” the sun migrating 5-10 degrees in latitude
Polar High Pressure Cells
- Weak high pressure cells with little energy
- Winds move away from the polar region in an anti-cyclonic direction producing the polar easterlies
The ITCZ changes…
Above or below the equator depending on the time of year
Upper Atmospheric Circulation:
- Pressure decreases less rapidly with height in warmer air
- Differential heated causes air to flow poleward, therefore the pressure gradient is greater at altitude and winds tend to be stronger
Jet streams
Are narrow high speed upper level air flows
- It is a river of fast moving air in the upper atmosphere
- It steers storms and moves weather patterns across the globe
Jet streams are driven by…
- The temperature differential between the Arctic and mid latitudes.
- If the temperature differential is large, then the jet stream speeds up
- If the temperature differential reduces cause of a warming Arctic, then the jet stream weakens
When the jet stream goes up (ridge) we see…
Warm and dry weather
When the jet stream goes down (trough) we see…
Cooler and wetter weather
Rossby Waves
Are the undulations of the upper level westerly winds
- As viewed from space, they have half the rotational speed of Earth
