Lecture 4 Flashcards
What causes horizontal pressure variations?
Changes in temperature and air density
What do isobars (lines of equal pressure) describe?
Pressure distribution at the surface
When representing pressure in e.g. Isobar charts, regions with high pressure will present themselves as?
Ridges.
Low pressures = troughs
What is the pressure gradient force?
The force that drives the air from high pressure areas to low pressure areas.
E.g. a warm location, like the equator, and a cold region, like the North Pole. Air at the equator is warmed with more solar energy than the air at the North Pole, so it rises and then moves horizontally toward the North Pole. As it cools, it sinks back down toward the warmer equatorial region. The air pressure difference between the two locations is called the pressure gradient and the force that moves the air = PGF
Horizontal transport of air or wind consists of a balance of…
Friction, pressure gradient force, coriolis, centripetal
The coriolis effect
Causes wind to deflect due to the earths rotation. (Effects direction not speed)
Northern hemisphere - deflects right
Southern Hemisphere- deflects left
Stronger the wind, greater the deflection
The coriolis force increases with latitude, being 0 at the equator. The amount of deflection depends on:
Rotation of the earth
Latitude
Moving objects speed
Circumference of lower latitudes are _______ than at higher latitudes
Larger
E.g. The city of Quito ‘travels’ a greater distance within 24hrs compared to Buffalo (located at a higher altitude)
Geostrophic wind balance
High altitude (no ground friction influence) Pressure gradient force will result in wind motion until a speed is reached where PGF and Coriolis balance each other out.
Consequently, wind will flow parallel to isobars and won’t accelerate further.
Centripetal force (circular motion)
Combination of PGF + coriolis = centripetal force (circular motion)
What does the centripetal force cause?
Northern hemisphere=
Wind motion travels anti clockwise around a low pressure system
Clockwise around a high pressure system (anticyclone)
Opposite in Southern H =
Low pressure system flows clockwise
Friction influences the atmospheric flow between the surface and 1000m altitude, this lower part of the atmosphere is called…
Planetary boundary layer
Friction reduces wind speed and in turn the coriolis force. What does this cause?
An imbalance between coriolis force and pressure gradient force, wind blows across isobars
At stable stratification and smooth terrain, how far does the effect of the surface friction extend?
Only a relatively short distance upwards above the ground.
Unstable and terrain is rough =surface friction extends further upwards
Explain how trade winds are formed?
Intense heating at equator warms air near the surface causing it to rise high into the atmosphere.
Rising air creates space + the equatorial low pressure zone (which sucks air in from higher latitudes) forms trade winds
This produces trade winds which meet at the inter tropical convergence zone (ITCZ)
What is the atmopheric vs ocean heat transport?
Trade winds blowing into ITCZ + climate system = trying to export heat away from equator.
In blowing winds do nothing to help this.
Describe the Hadley cell
Adiabatic cooling and advective cooling takes place At about 30 degrees N+S it sinks = sub-tropical high pressure zone Air sinks (lost most of its moisture, so dries area it sinks onto) Some sinking air pulled back towards equator = Hadley cell
Some of the air at 30 degrees N flows towards the poles, what is this called?
Westerlies
Atmosphere takes over as main poleward of heat
When does the poleward movement of warm sub-tropical air cease?
When it meets the air mass at the polar front
Why are there high pressures over the poles?
Intense cold at poles causes air to become super chilled and sink
(The polar high + ‘blow out winds’)
What occurs when cold air mass meets warmer westerlies at the polar front? And what are the other 2 cells called?
Condensation and precipitation
Forces warm sub-tropical air to rise, as cold polar air = more dense
Rising air completes 2 other cells = Ferrell cell and Polar cell
What are the important components of the 3 cells?
High altitude
Fast flowing
Narrow air currents called ‘jet streams’
Where do jet streams occur?
Tropopause, driven by spin at the earth and strong differences in temperature
What’s the strongest jet stream?
Polar jet
What way to jet streams typically flow?
West to east
What can happen if a jet stream meanders?
Forms a rossby wave (large kinks in westerly flows)
What is an air mass?
Large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any given altitude
Arctic, polar, tropical, equatorial, maritime and continental are classifications of…
Air masses
What controls the flow of air (winds) on earth?
Latitude variation in solar irradiance
Earths tilt and seasons
Mean sea level pressure (MSL)
