W&C Chapter 8

Katabatic wind

- originate when cold, dense air situated over a highelevation plateau descends downslope like a waterfall Warmed by compression, but starts so cold that when it arrives in the lowlands, it is still colder than the air it is replacing Two best locations for such winds are along the margins of the Antarctic and Greenland ice sheets

Subpolar low

A belt of low pressure in the three-cell model between the polar easterlies and midlatitude westerlies.

Sea Breeze

A flow of air from the water toward land along a coastal region

Three-Cell Model

A generalized description of global-scale circulation that calls for three large cells in each hemisphere. The cells rotate on a vertical plane with axes parallel to latitude lines, thereby moving heat and moisture in a north-south direction the circulation of each hemisphere is composed of three distinct cells: the heat Hadley Cell Ferrel cell Polar cell. Though more realistic than the single cell model, the three-cell model is so general that only fragments of it actually appear in the real world

Subtropical jet stream

A jet stream common in the upper troposphere on the poleward side of the Hadley cells, produced by the conservation of angular momentum.

Santa Ana

A local name for a foehn wind in california

El nino

A recurrent event in the tropical eastern pacific in which sea surface temperatures are significantly above normal. The inverse event (cold sea surface temperatures) is called La Nina

Subtropical high

A semipermanent cell that occupies large areas of the midlatitude oceans especially in the warm season Because descending air warms adiabatically, cloud formation is greatly suppressed and desert conditions are common in the subtropics. The subtropical highs generally have weak pressure gradients and light winds.

Single-cell Model

A simple conception of global atmospheric circulation calling for one circulation cell in each hemisphere described the general movement of the atmosphere. Assumed a planet covered by a single ocean and warmed by a fixed Sun that remained overhead at the equator. Suggested that the strong heating at the equator caused a circulation pattern in which air expanded vertically into the upper atmosphere, diverged toward both poles, sank back to the surface, and returned to the equator Winds would not simply move north and south. the rotation of Earth would deflect air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, leading to the east- west surface winds

Hadley Cell

A somewhat idealized, large-scale wind and pressure pattern found in tropical latitudes of both hemispheres. Air rises above the equator, flows poleward to about 25 degrees latitude, subsides, and flows back to the equator at low levels. Together the equatorial low, subtropical highs, the trade winds, and the upper-level westerly motions make up the Hadley cells

ITCZ/Equatorial low

Intertropical Convergence zone. Belt of low pressure around the equator. formed by the vertical ascent of warm, moist air from the latitudes north and south of the equator. Lots of precipitation. Zone of low pressure at the equator caused by strong solar heating which causes air to expand upward and diverge toward the poles. The upwards motions motions that dominate the region favor the formation of heavy rain showers, particularly in the afternoon. exists not as a band of uniform cloud cover but rather as a zone containing many clusters of convectional storms. The ITCZ is the rainiest latitude zone in the entire world doldrums - old nautical term for the area in which winds can become light or nonexistent for extended time periods.

Polar highs

Low-level anticyclones of the Arctic and Antarctic. A feature of the general circulation of the atmosphere, often absent or weakly developed.

Why does the ITCZ migrate and how does that influence climate?

Part of these effects are due to the seasonal shift in the distribution of semipermanent cells Solar declination changes seasonally, and so does the zone of most intense heating - this will result in associated pressure and windbelts to move with the season The changes in season greatly influence the climate

Trade winds

Prevailing lower troposphere winds of the tropics, associaed with Hadley circulation. Strongest in the respective winter season, the trades blow from the northeast in the Northern hemisphere and from the southeast in the Southern hemisphere.

Ferrell Cell

The mid latitude circulation cell of the three-cell model Immediately follows the Hadley cell in each hemisphere Circulates air between the subtropical highs and the subpolar lows or areas of low pressure On the equatorial side of the cell, air flowing polward away from the Northern Hemisphere subtropical high undergoes a substantial deflection to the right, creating a wind belt called the westerlies. envisioned as an indirect cell, meaning that it does not arise from differences in heating, but is instead caused by turning of the two adjacent cells.

Describe the seasonal changes in circulation that produce the monsoon (Asia).

The monsoon of Asia results from a reversal of the winds between the winter and summer. During winter, dry air flows southward from the Himalayas. The North Equatorial Current is strong (inset) as would be expected with strong trade winds. When summer arrives, moist air is drawn northward from the equatorial oceans. Surface heating, convergence, and a strong orographic effect cause heavy rains over the southern part of the continent. In the ocean clockwise circulation forms a gyre not present in the winter months.

La Nina

The opposite pattern to an el nino, in which below normal sea surface temperatures exist in the tropical eastern pacific

Which model (single cell or three cell) matches actual observations best and why?

The three cell model. The three-cell model provides a good beginning for describing the general distribution of wind and pressure, but the real world is not covered by a series of belts that completely encircle the globe. Instead, we find a number of alternating semipermanent cells of high and low pressure

Mountain breeze

a breeze that flows down a hill at night

Monsoon

a regional circulation pattern in which there is a seasonal reversal of wind and pressure, generally characterized by onshore flow during the summer and offshore flow during the winter

Foehn wind

a synoptic scale wind that flows downslope and warms by compression In Europe - foehns develop when midlatitude cyclones approach the Alps from the southwest. The air rotates counterclockwise toward the center of low pressure and descends the northern slopes. These winds bring unseasonably warm conditions to much of northern Europe during the winter, when they are most prevalent. the term foehn strictly applies to winds coming from the Alps of Europe, we generally use it to describe this type of wind anywhere in the world.

Trade winds in the northern hemisphere

as the pressure gradient force directs surface air from the subtropical highs to the ITCZ, the weak Coriolis force deflects the air slightly to the right to form the northeast trade winds (or simply the northeast trades).

Chinook

downslope winds that arm because of adiabatic compression foehn wind that descends the eastern slopes of the Rocky Mountains in North America Low-pressure systems east of the mountains cause these strong winds to descend the eastern slopes at speeds that can exceed 150 km/hr (90 mph) when funneled through steep canyons. most common during the winter when midlatitude cyclones routinely pass over the region.

Polar cell

high-latitude circulation cell in the three-cell model having high pressure at the surface and low-level winds flowing equatorward Surface air moves from the polar highs to the subpolar lows. - Considered thermally direct circulations Air at the subpolar locations is slightly warmer than the poles, resulting in low surface pressure an rising aire Very cold conditions at the poles create high surface pressure and low-level motion toward the equator In both hemispheres, the coriolis force turns the air to from a zone of polar easterlies in the lower atmosphere Each cell consists of -one belt of rising air with low surface air pressure -a zone of sinking air with surface high pressure -a surface wind zone with air flowing generally from the high-pressure belt to the low-pressure belt -An airflow in the upper atmosphere from the belt of rising air to the belt of sinking air.

Trade winds in the southern hemisphere

the northward-moving air from the subtropical high is deflected to the left to create the southeast trade winds

Westerlies

wind belts found in the middle latitudes of both hemispheres that have a strong west to east component