A population dominated by people who are no longer economically active (65+). Caused by a falling birth rate and an increased life expectancy. See Ageing Population: Causes & Impacts
Pressure Gradient,Coriolis force and Geostrophic winds
Wind is the horizontal movement of air resulting in pressure differences on the earth's surface.Winds move from high to low pressure areas.Factors affecting winds are:
Pressure gradient force
PGF is the initial driving force of wind.Closely spaced isobars results in a steep(high) PGF thus high wind speeds while a weak PGF is caused by widely spaced isobars.(Isobars are lines connecting areas of equal pressure.)
Insted of wind moving in a straight path,it is deflected in its direction of flow by the Coriolis Force.The Coriolis Force is a result of earth's rotation and redirects wind to the left in the Southern Hemisphere and to the right in the Northern Hemisphere.The Coriolis force is affected by high wind speeds,the higher the wind speed the more air will be deflected in its line of path. The Coriolis force act at right angles to thr direction of air flow.
This is when wind flows parallel to the isobars caused by a balance between the Coriolis force and the PGF.A geostrophic wind occurs at higher elevations where friction is less.Friction at lower layers(surface) affects wind speeds thus the Coriolis Force.