1. Global air circulation Mr Askew

2. Pressure gradient, Coriolis force and Geostrophic flow  Wind is produced by different air pressure between places.  Isobars indicated air pressure on a map, in some areas the isobars are close together and in others wide apart.  The rate at which air pressure changes over horizontal distance as measured in direction from HP -> LP is called the pressure gradient.  At any point the pressure gradient is at right angles to the isobars.

3. How the pressure gradient force works:  Pressure gradient is described as gentle (if isobars are widely spread) or steep (close together).  The pressure gradient is a force acting on the atmosphere as a result of the pressure gradient.  It moves air from a HP -> LP and determines the speed of the wind.  (isobars wide apart = gentle wind/ close together = strong wind.  Figure 61 pg 62

5. The impact of Coriolis force on wind  When air flows it is affected by the Coriolis force, it deflects winds and ocean currents from their initial direction.  The deflections to the right in the northern hemisphere, and to the left in the southern hemisphere.  Characteristics of the Coriolis force: 1. Causes a change in wind direction for all winds on the earths surface. 2. Is stronger in proportion to any increase in speed. 3. Weaker near the equator. http://education.nationalgeographic.com/education/encyclopedia/coriolis- effect/?ar_a=1

6. How the Coriolis force and pressure gradient affect wind  Combined effects produce a geostrophic wind. (figure 63)  Ferrell's law: if you stand with your back to the wind, any horizontal movement in the northern hemisphere will show a deflection to the right and in the southern hemisphere to the left.  The pressure gradient remains equal throughout.  The stronger the wind the stronger the Coriolis force is acting on it.  The pressure gradient is always perpendicular to the isobars.  When the wind reaches equilibrium, it is blowing parallel to the isobars and called geostrophic wind.

7. Geostrophic winds  Found in the upper atmosphere.  Example is the Jet stream.  Nearer the earths surface friction causes the winds to blow more diagonally across the isobars.  https://www.youtube.com/watch?v=RVjwH4Pyz0s https://www.youtube.com/watch?v=RVjwH4Pyz0s  Activity 7 pg 63

8. Winds related to global air circulation  1. Tropical Easterlies:  Blow from sub tropical high pressure areas to the equatorial low pressures.  Found between 5 – 35 ⁰ latitudes.  Where the winds originate: the air is usually dry and warm because of the strong descent of air. This produces fine weather sunshine.  As these winds travel towards the equator they change.  Absorb moisture over the oceans, warmed and become unstable = clouds form = rainfall along the equator.  Disturbances in the tropical easterlies (trade winds) give rise to tropical cyclones.

9. Westerlies  Blow from sub tropical high pressure zones to low pressure areas of the sub polar regions (60 ⁰ latitude)  Initially North westerleis in the southern hemisphere and south westerly's in the northern hemisphere.  The further from the equator they move, the more the direction changes because they experience a greater Coriolis force.  As westerlies blow from cold to warm regions, they carry warm air to the colder regions causing the temperatures to rise  The colder regions will cause the temperature of the air to drop, which may lead to condensation and precipitation.

10. Polar Winds  Originate in HP areas near the north and south poles.  Blow towards sub polar low pressure areas.  Very fierce, esp within polar circles, where they develop into howling snow storms.

12. Air mass Characteristics  Air mass: Large body of air with uniform temperature and humidity characteristics picked up from the region where it develops.  Main source regions for air masses are:  1. Where the surface is geographically uniform: oceans, ice fields, deserts  2. Areas of relatively stable atmospheric conditions.

13. How air masses classified:  The latitude where they originate.  The surface which they develop affects their humidity and precipitation, for example over the sea producing wet maritime air (m) or over the land producing dry continental air (c)  Table 9 pg 65  Activity 8 pg 65