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Lecture 2 (Wind and Atmospheric Circulation in the Tropics) Part 2 -…
Lecture 2 (Wind and Atmospheric Circulation in the Tropics) Part 2
Wind is the horizontal air motion from high pressure to low pressure with respect to the Earth's surface. Winds are named according to the direction from which they originate
Factors Influencing Wind Movement
Pressure-Gradient Force
It is the rate of change in atmospheric pressure between two areas, providing a force which moves air from high to low pressure. Wind is ultimately caused by PGF.
It determines the
Origin
, Direction and Speed of wind
PGF is always perpendicular to the isobars.
The greater the pressure difference, the greater the PGF will be, the stronger/faster the wind. Closely spaced isobars indicate a steep pressure gradient and high speed winds. Widely spaced isobars indicate a weak pressure gradient and low speed winds.
Coriolis Force
It only determines the direction of the wind
Result of Earth's rotation. Apparent deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Wind
and Ocean currents are affected by this force as they travel over long distances.
Always directed at right angles to the direction of airflow (any direction). The stronger the wind, the greater the deflecting force. Force is strongest at the poles and weakens towards the equator, becoming nonexistent at the equator
Friction
With higher friction, wind speed is reduced, which in turn reduces the deflection caused by the Coriolis force (affects direction of the wind)
This effect is greater over the land than the ocean, and becomes negligible at high altitudes
With friction in play,
winds do not just blow perpendicular to the isobars or parallel with them
, but takes an immediate course between the two and crosses the isobars at an angle between 0 and 90 degrees
Example of Factors Influencing Wind Movement: Trade Winds
Wind direction will be the result of the three forces influencing wind movement acting together
Trade Winds blow from the STH belt to the ELP/ITCZ due to the PGF
Trade Winds are deflected to the right in the NH and left in the SH, thus blow from the Northeast in the NH and Southeast in the SH
Trade Winds are more consistent over oceans where there is lesser friction as compared to land. Over land, trade winds are significantly disrupted
