+ Scales of Atmospheric Motion Small- and large-scale circulation: Microscale Mesoscale Macroscale
+ Scales of Atmospheric Motion Microscale winds: The circulation is small and chaotic. They can last from seconds to minutes. They can be simple gusts, downdrafts, and small vortices, such as dust devils.
+ Scales of Atmospheric Motion Mesoscale winds: They can last from minutes to hours. They are usually less than 100 km across. Some mesoscale winds (thunderstorms and tornadoes) also have a strong vertical component.
+ Scales of Atmospheric Motion Macroscale winds: These winds are the largest wind patterns. These planetary-scale patterns can remain unchanged for weeks at a time. Smaller macroscale circulation is called synoptic scale. These wind systems are about 1000 km in diameter. Smaller macroscale systems are tropical storms and hurricanes.
+ Scales of Atmospheric Motion Structure of wind patterns: Global winds are a composite of motion on all scales. Hurricanes appear as a large cloud moving slowly across the ocean. The large cloud contains many mesoscale thunderstorms. The thunderstorms consist of numerous microscale bursts.
+ Global Circulation Single-cell circulation model Hadley model Hadley proposed that the contrast in temperatures between the poles and the equator creates a large convection cell in both the Northern and Southern hemispheres.
+ Global Circulation A three-cell circulation model was proposed in the 1920s. Warm air rises at the equator (Hadley cell). As the flow moves poleward, it begins to cool and sinks at 20°–35° latitude. Trade winds meet at the equator, in a region with a weak pressure gradient, called the doldrums.
+ Pressure Zones Drive Winds Idealized zonal pressure belts: 1. The equatorial low is an intertropical convergence zone (ITCZ). Low pressure and trade winds converge 1. Subtropical highs (STH) are high-pressure zones in the belts about 20°–35° latitude on either side of the equator. Where westerlies and trade winds originate.
+ Monsoons Monsoon refers to a seasonal reversal of winds. The Asian monsoon, which affects India and its surrounding areas, China, Korea, and Japan. The monsoon is driven by pressure differences. The North American monsoon occurs in the southwestern U.S. and northwestern Mexico. This monsoon is driven by the extreme temperatures, which generate a low-pressure center over Arizona and results in a circulation pattern that brings moist air from the Gulf of California and from the Gulf of Mexico, to a lesser degree.
+ The WesterliesWhy Westerlies? Difference between pole and equator drive these winds Pressure gradient from equator to pole and Coriolis force deflects winds and a balance is reached.
+ The Westerlies Waves in the westerlies: Westerliesflow in wavy paths that have long wavelengths. The longest wave patterns are known as Rossby waves, which usually consist of 4–6 waves that encircle the globe. Rossby waves can have a large impact on weather.
+ Jet Streams Jet streams: Embedded in westerlies Widths vary from less than 100 km to more than 500 km. Speeds can attain 100–400 kph. (60-240 mph) Polar and subtropical
+ Jet Streams The polar jet stream is the most prevalent. It occurs along a major frontal zone, the polar front. The jet stream moves faster in winter. During the winter, occasionally it moves north– south. If the jet stream is more equatorward weather will be colder and drier than normal. More poleward, weather will be warmer and more humid.
+ Jet Streams The subtropical jet stream is a semipermanent jet stream over the subtropics. It is a west-to-east current, centered at 25° N and S. It is mainly a winter phenomenon. The subtropical jet stream is slower than the polar.
+ Jet Streams Jetstreams and Earth’s heat budget Relatively mild temperature occur south of jet stream and cold temperature north of jet stream the waves begin to meander.
+ Global Winds and Ocean Currents Gyres are found in each major ocean basin centered around subtropical high-pressure systems The Gulf stream is strengthened by westerly winds and continues northeastward.
+ Global Winds and Ocean Currents Importance of ocean currents: Ocean currents have an important on climate, which helps maintain the Earth’s heat balance. Cold currents offshore result in a dry climate. Warm offshore current produce a warm moist climate. Ocean currents account for ¼ of total heat transport. Wind accounts for the other ¾.
+ Global Winds and Ocean Currents Ocean currents and upwelling: Upwelling is the rising of cold water from deeper layers to replace warmer surface water. A wind-induced vertical movement It occurs where winds blow parallel to the coast toward the equator.
+ El Niño and La Niña and the Southern Ocean ElNiño is a gradual warming of eastern Pacific waters in December or January. Periodof abnormal warming happen at irregular intervals of 2-7 years and persist for spans of 9 months to 2 years. La Niña is the opposite of El Niño and refers to colder-than-normal ocean temperatures along the coast of Ecuador and Peru
+ El Niño and La Niña and the Southern Ocean Impact of El Niño: It is noted for its potentially catastrophic impact on weather and economies of Chile, Peru, Australia, and other countries. Arid areas can receive a lot of precipitation. A change in surface water temperature can kill fish. El Niño has been recognized as part of the global atmospheric circulation pattern.
+ El Niño and La Niña and the Southern Ocean Impact of La Niña: La Niña is also an important atmospheric phenomenon. In the western Pacific, wetter than normal conditions occur. There are also more frequent hurricanes in Atlantic.