Chapter 7

- Trade Winds are steady winds that occupy most of the tropics (20° North or South) and blow northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.

- Around 30° North and South, also known as the Horse Latitudes, winds are usually light or calm.

- In looking at global climatology, a band of thunderstorms extends around the world near the Equator, while around 30° North and South, a lack of clouds exist.

- The cloud band around the Equator produces upward vertical motions in this region, which causes the cloud and precipitation patterns of the tropics.

- This northward air is deflected to the right by the Coriolis Force, resulting in Westerly Winds north of the Equator (around 30° North).

- Jet Streams are narrow regions of relatively strong winds (speeds greater than 70 knots) usually located in the upper troposphere.

- Angular Momentum is the product of mass, rotation velocity, and perpendicular distance from the axis of rotation.

- Conservation of Angular Momentum is the principle that the angular momentum of a spinning body must remain constant. It is usually conserved by increasing the spin when the distance from the axis of rotation is decreased, or by decreasing the spin when the distance from the axis of rotation is increased.

- The Subtropical Jet Stream is a region of strong winds in the upper troposphere between 20°- 40° latitude. It is caused by the need to conserve angular momentum.

- The Intertropical Convergence Zone (ITCZ) is a convective region of thunderstorms separating the northeast and southeast trade winds. Upward vertical motions near the Equator explain this zone.

- The Hadley Cell is a thermally driven circulation pattern comprised of arising air near the Equator, poleward flow in the upper troposphere, sinking air over the deserts, and the trade winds.

- Around 30° N and 30° S latitudes, high pressure is typically observed. These semi-permanent high pressure systems are referred to as Subtropical Highs.

- These Subtropical Highs greatly impact the weather and climate of the Subtropics and Middle latitudes, causing pressure gradients to be weak and surface winds to be light.

- Equatorward of these highs, winds are known as Trade Winds , and converge into the ITCZ.

- Doldrums are located near the Equator where trade winds do not dominate and are regions of light winds and high temperatures.

- Near the Poles, air is cold and sinks which warms adiabatically causing an inversion with the cold surface and inhibiting precipitation.

- Polar Easterlies (around 60° N and 60° S) are low level air flowing towards the Equator that, due to the Coriolis force, have a strong east-to-west track.

- Mid-Latitude Westerlies are regions of strong west-to-east winds around 40-50° N and S.

- The Polar Front is the region where Polar Easterlies meet Mid-Latitude Westerlies separating warm tropical air from cold polar air.

- This clash of winds in the Polar Front results in the Polar Front Jet, which is another westerly jet stream caused by strong temperature gradients.

- Rossby Waves are atmospheric waves that are located in the midlatitude westerly winds with very long wavelengths that typically drift slowly eastward.

- A Zonal Flow Pattern occurs when a small-amplitude pattern results in mostly west-to-east winds, which are closely parallel to lines of constant latitude. Cold air tends to stay toward polar regions and warm air remains equatorward.

- A Meridional Flow Pattern occurs when the wave have large amplitude with deep troughs and peaked ridges. Cold air flows equatorward and warm air flows poleward.

- The Zonal Index determines the type of flow pattern, with high zonal index situation indicating zonal flow and low values indicating meridional flow.

- Split Flow and Blocking Patterns also exist.

- Circulations in the atmosphere help to transfer heat poleward, where energy losses exceed gains, while in the tropical regions energy gains exceed losses.

- This is done by transferring heat poleward and cold polar air equatorward.

- The region of maximum energy transport by the atmosphere occurs between 30° and 60° latitude in both hemispheres.

- The global circulation pattern made up of the ITCZ, the polar front, the subtropical highs, and the jet streams, shifts with the Sun seasonally, moving poleward in Spring, and equatorward in Autumn.

- The ITCZ, subtropical highs, and polar jet streams also vary seasonally in their positions, generally all shifting poleward during the hemisphere’s summer season.

- Monsoons are a weather feature driven by seasonal differences in the heating of land and ocean along with seasonal shifts in global scale circulations. Summer Monsoon is generally the wet season and the Winter Monsoon is typically the dry season.