Global and Local Winds

• Wind is the movement of air caused by differences in air pressure.
• Differences in air pressure are caused by the uneven heating of Earth.
• Uneven heating produces pressure belts which occur every 30° latitude.
• The Coriolis effect causes winds to move from high-pressure areas towards low-pressure areas, but also deflect them to the right (in the Northern Hemisphere) or left (in the Southern Hemisphere).
• Doldrums is located along the equator where no winds blow because the warm rising air created.
• Horse Latitudes is located at 25°N and S where there is little wind due to sinking cooler air.
• The jet streams are narrow belts of high-speed winds that blow in the upper troposphere and lower stratosphere
• The Intertropical Convergence Zone (ITCZ) is the low-pressure area near the equator in the boundary between the two Hadley Cells.
• Early mariners called the ITCZ the doldrums because their ships were often unable to sail due to the lack of steady winds.
• The ITCZ migrates slightly with the season. Land areas heat more quickly than the oceans. Because there are more land areas in the Northern Hemisphere, the ITCZ is influenced by the heating effect of the land.
• In the Northern Hemisphere summer, it is approximately 5 degrees north of the equator, while in the winter it shifts back and is approximately at the equator.
• Local winds generally move short distances and can blow in any direction.
• Land breeze occurs overnight as cooler air sinks downward over the land, replacing the rising warm air. This creates an area of higher pressure onshore, which causes cooler air to flow outward from the coast towards the ocean or lake.
• Sea breeze occurs during daytime hours as warmer air rises over land, creating an area of low pressure. Cooler air moves into this region from the ocean or lake, resulting in a wind blowing toward the shoreline.
• Monsoon winds are larger-scale versions of land and sea breezes; they blow from the sea onto the land in summer and from the land onto the sea in winter.
• Monsoon winds occur when very hot summer lands are next to the sea. Thunderstorms are common during monsoons.
• Northeast Monsoon: Brings chilly mornings from early December to about the middle of February.
• Southwest Monsoon: The rainy season in the Philippines, which brings heavy rainfall from March to about November resulting in hot rising air over the country.