CHAPTER 4 Focus Points

• Cause of the wind: Wind is caused by unequal heating of Earth’s surface and the release of latent heat within clouds.

• Wind names: Most winds are named for the direction from which they blow.

• Causes of pressure: Warm air is associated with low pressure, and cold air is associated with high pressure, but dynamic pressure can override thermal pressure.

• Wind controls: Pressure-gradient force, Coriolis force, and friction force control wind speed and direction near Earth’s surface. Air always flows from areas of high pressure to areas of low pressure.

• Cyclones and anticyclones: Cyclones and anticyclones are important meteorological systems created by deflected flowing wind.

• Pressure systems: The four global pressure systems are the ITCZ, the subtropical high, the subpolar low, and the polar high.

• Surface winds: The trade winds, the westerlies, and the polar easterlies are the major global surface winds.

• Effect of seasons: The strength and latitude of the global pressure systems are strongly affected by the seasonal shift of the subsolar point and by landmasses. In the Northern Hemisphere, all the systems move north in June and south in December.

• Semipermanent pressure: The Bermuda high is a semipermanent pressure system that brings summer precipitation to the East Coast of the United States. The Pacific high brings aridity to the West Coast.

• Wind systems: Earth’s local and regional wind systems are set in motion by energy from the Sun. These wind systems range from microscale valley breezes to the synoptic-scale Asian monsoon system.

• Land and sea winds: Sea and land breezes and the Asian monsoon result mainly from heating differences between the ocean and the land. The ITCZ, orographic uplift by the Himalayas, and heating of the Indian landmass generate the Asian monsoon.

• Winds in sloped terrain: Valley and mountain breezes, chinook and foehn winds, Santa Ana winds, and katabatic winds form in sloped terrain and experience adiabatic temperature changes.

• Wind energy: Wind is a clean and renewable energy source that is being rapidly developed.

• Wind energy hurdles: There are many hurdles to wind energy development, including storage and transport of the generated energy, bird and bat kills, and the “wumps” and NIMBY problems.