Lecture 4: Global atmospheric circulation Flashcards
Flow of air- my notes
- must involve circulation
- -intense solar heating over the equator- air- hot – expands- rises- goes towards the poles- doing so – it cools- as it cools becomes dense- more dense than surroundings- therefore will sink- and air gets sucked back to the tropics
- however, earth rotates- so sun is not always over the equator- only on equinox- 12 hour day and 12 nigh time, wherever you are In the earth
- summer solstice and winter solstice- those dictates the longest or shortest night/days
Pressure gradient force
- my notes
- driving force of the winds motion of the earth
- look at calculation
The Coriolis force - my notes
- the rotation of the earth is constant
- proportional to wind speed
- variables make an impact on this force
- closer to the equator the more faster you are moving- difference in distance travel at different latitudes – i.e Singapore much quicker than us or north pole
Geostrophic wind balance
- my notes
- high pressure to low pressure- shifted towards the right- as the wind speeds up the coriolis force will pull it to the right
- anti clockwise motion- low pressure system- hurricane- cyclone
- northern hemisphere and southern- different directions
pressure- my notes
Pressure doesn’t change affect the pressure gradient force- but it will affect the Coriolis force
Tropics and poles- my notes
Tropics – east to west- the wind direction- and the opposite in higher latitudes
Trade winds meet at the intertropical convergence zone
Over the poles- air is do dense – high pressure- therefore sinks- going to the left- lot of condensation- rainfall- polar cell
Jet stream - my notes
- high up in the atmosphere
- extreme differences in temperature- extreme air – not much in this module
west- east
GLOBAL CIRCULATION… WITHOUT A SPINNING EARTH
- George Hadley (1735) developed theory of one single cell
- Energy transfer from hot tropical regions to cold polar regions
- This might be the case if Earth would not rotate and had a uniform surface
- Not realistic!
MEAN SEA LEVEL (MSL) PRESSURE
Horizontal pressure variations are caused by changes in temperature and air density.
• As pressure varies with altitude, pressure values in synoptic surface charts need to be converted to their equivalent values at mean sea level (MSL).
• In order to perform this calculation accurately it is necessary to know the vertical temperature profile at the location of the pressure reading.
• Further corrections need to be applied for variation of gravity with latitude.
PRESSURE REPRESENTATION IN CHARTS
- Isobars (Lines of equal pressure) describe the pressure distribution at the surface.
- In order to obtain a 3-dimensional picture of the atmospheric pressure distribution it is common to plot the altitude of an isobaric surface (surface of constant pressure)
- In such a representation regions with high pressure manifest themselves as ridges, whereas low pressure regions are troughs.
PRESSURE GRADIENT FORCE
- The Pressure Gradient Force is directed from higher toward lower pressure at right angles to the isobars.
- Magnitude of the force is directly related to the pressure gradient.
- Closely spaced isobars on a surface map indicate steep pressure gradients and a large PGF.
More on pressure gradient force
- In order for air to move a force has to act ( compare with Newton’s Laws of Motion)
- The net force acting on a mass of air, which results in horizontal transport of air or wind, usually consists of a balance between the following forces:
- Pressure gradient force
- Coriolis force
- Centripetal force
- Friction
THE CORIOLIS FORCE
• The Coriolis force describes an apparent force that is due to the rotation of the earth.
• It causes the wind to deflect to the right of its intended path in the Northern Hemisphere and to the left of its intended path in the Southern Hemisphere.
• The force acts at right angles to the wind, thus only influencing wind direction and never wind speed.
• The stronger the wind speed, the greater the deflection.
• The force increases with latitude while being zero at the equator.
• The amount of deflection depends on:
1. the rotation of the earth (constant) 2.the latitude
3.the moving object’s speed
CORIOLIS FORCE (CONT.)
- At lower latitudes the circumference of the latitude circle is larger than at higher latitudes.
- Consequently the city of Quito “travels” a greater distance within 24 hours (1 revolution) compared with the city of Buffalo which is located at a higher latitude.
CORIOLIS FORCE (CONT.) 2
- If a cannon ball were shot from Buffalo to Quito, travelling at a straight line, it will appear to be deflected to the right when seen from an observer located on Earth.
- An observer in Earth’s orbit (outside the rotating frame of reference) will see the cannonball travelling a straight line but will also notice the Earth rotating underneath the flight path of the ball.
