Winds

Winds Winds are defined as the horizontal movement of air. Winds are named by where they blow from.

Local Winds Different materials heat at different rates. (specific heat) Along the shore the land surfaces will heat faster during the day. The water surfaces will be cooler due to the slower heating.

Local Winds This results in the air over land being warmed. As it warms it expands and floats up creating an area of low pressure.

Local Winds The area over water cools causing the air to contract. This creates an area of high pressure.

Local Winds The high pressure forces the air from the ocean to the low pressure on the land.

Local Winds This is called an on shore or Sea Breeze

Winds You will see that winds always blow from an area of High pressure to an area of Low pressure. WINDS BLOW FROM HIGH TO LOW

Local Winds At night the process is reversed. The land cools quickly creating a high pressure over land. The water retains its heat creating a low pressure over land.

Local Winds This results in the high pressure over land pushing the air to the low pressure over the ocean. This is called a land or off shore breeze.

Global Winds Heating of the planet is not uniform because of Earth’s shape. The Earth receives more heat at the equator and less heat at the poles (angle of insolation) This results in low pressure at the equator and high pressure at the poles

Global Winds If winds blow from high pressure to low pressure you would expect the winds to blow in a straight line from the poles to the equator.

The winds do not blow in a straight line. This is because of the rotation of the Earth. Also called the Coriolis Effect. The rotation causes the winds to shift and the convection cells to break up into 3 cells in each hemisphere.

Winds shift to the right in northern hemisphere.

Winds shift to the left in the southern hemisphere.

Global Winds All of these factors combine to form our Global wind patterns.

Jet Streams During WWII we discovered another set of wind belts found near the top of the troposphere. These are located at the sub polar low and sub tropical high regions. The winds blow from west to east at between 200 to 400 km/h.

Prevailing Westerlies A majority of the United States lies within a wind belt called the prevailing westerlies. This wind belt is responsible for moving “weather systems” from Southwest to Northeast across the United States.

Measuring Wind To measure wind speed scientists use an anemometer. To measure wind direction scientists use a wind vane.

Reading Isobars… On a weather map you can determine the wind speed by looking at the isobars. If the bars are close, the wind is fast (large gradient). If the bars are spaced apart, the wind is slow (small gradient).

Calculating Gradient Finding the gradient (how fast the wind is moving) is the same as finding the gradient of a mountain side (how steep the mountain is). The formula is in the front page of the ESRT. Change in Field Value/Distance