Atmospheric and Oceanic Circulation

Comprehensive vocabulary flashcards covering atmospheric pressure, governing forces, global and upper-air circulations, local breezes, and monsoons from Parts A and B.

Air Pressure

The weight of an atmospheric column of air at a specific location, which decreases with increasing altitude due to diminishing mass above.

Normal Sea-Level Pressure

Standard barometric pressure measured at sea level, equivalent to $760\,\text{mm of Hg}$, $29.92\,\text{in.}$, $1013.2\,\text{mb}$, or $101.325\,\text{kPa}$.

Pressure Gradient Force

The primary force that drives air movement and creates wind, directed from areas of higher barometric pressure toward areas of lower barometric pressure.

Isobar Spacing and Wind Speed

Close spacing of isobars denotes a steep pressure gradient associated with strong winds, whereas wider spacing represents a gradual pressure gradient producing light winds.

Coriolis Force

An apparent deflective force caused by Earth's rotation that turns moving air toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere, reaching maximum deflection at the poles and zero deflection at the equator.

Geostrophic Wind

Upper-tropospheric wind flowing nearly parallel to isobars under conditions of negligible friction, resulting from a direct balance between the pressure gradient force and the Coriolis force.

Earth Rotational Velocity by Latitude

The speed of Earth's eastward rotation that influences Coriolis deflection, decreasing poleward from $1675\,\text{kmph}$ ($1041\,\text{mph}$) at the equator, to $1450\,\text{kmph}$ ($900\,\text{mph}$) at $40^\circ\,\text{N}$, and to $838\,\text{kmph}$ ($521\,\text{mph}$) at $60^\circ\,\text{N}$.

Equatorial Low-Pressure Zone (ITCZ)

A thermally induced, circum-equatorial convergence belt driven by intense solar radiation that features rising air, heavy cloudiness, and abundant precipitation.

Polar High-Pressure Cells

Thermally induced pressure systems caused by minimal solar radiation and strong surface cooling, producing subsiding air and divergence that intensify in winter and yield minimal precipitation.

Subtropical High-Pressure Cells

Dynamically induced high-pressure belts centered near $30^\circ$ latitude caused by mechanical forcing and subsiding air, creating persistent dry climates especially along the western margins of continents.

Subpolar Low-Pressure Cells

Dynamically induced low-pressure centers located prominently over Iceland and the Aleutian Islands that generate winter precipitation via mid-latitude cyclones.

Trade Winds

The most constant global surface wind systems, which blow from the subtropical highs toward the equatorial trough and serve as source regions for tropical storms and hurricanes.

Westerlies

Mid-latitude global winds whose velocity and intensity correlate positively with the temperature gradient between the equator and the poles.

Polar Easterlies

Cold, dry surface wind systems that blow outward from polar high-pressure cells toward subpolar regions, increasing in strength during winter.

Polar Front

A discontinuous, storm-prone boundary zone of convergence where cold polar easterlies collide with warmer mid-latitude westerlies.

Jet Stream

A high-velocity ribbon of westerly geostrophic winds concentrated within the upper levels of the troposphere along steep temperature boundaries.

Jet Stream Dimensions

An idealized upper-air stream with an altitude of $7600\text{--}10{,}700\,\text{m}$ ($24{,}900\text{--}35{,}100\,\text{ft}$), a width of $160\text{--}480\,\text{km}$ ($100\text{--}300\,\text{mi}$), a vertical depth of $900\text{--}2150\,\text{m}$ ($3000\text{--}7000\,\text{ft}$), and core velocities up to $300\,\text{kmph}$ ($190\,\text{mph}$).

Rossby Waves

High-amplitude undulating waves in the upper-air polar jet stream whose troughs generate cold, persistently wet conditions and whose ridges create warm, dry weather southward.

Local Winds

Mesoscale wind circulations generated by local differential heating and cooling of surfaces, forming most clearly under calm, cloudless conditions.

Sea Breeze

A daytime local circulation where solar heating of land relative to adjacent water lowers inland pressure, driving cool air onshore from late morning through early evening.

Land Breeze

A nighttime local circulation that develops when nocturnal terrestrial radiation cools the land faster than adjacent open water, driving an offshore flow of denser air.

Valley Breeze

A daytime thermal upslope wind occurring when sunlit mountain slopes heat rapidly relative to surrounding free air at identical elevations, causing warmer air to ascend and often yield cumulus clouds.

Mountain Breeze

A nocturnal gravity-driven katabatic or drainage wind that occurs when air along high slopes cools rapidly, increases in density, and slides downslope into valley floors.

Monsoonal Wind Systems

Continental-scale seasonal wind reversals driven by shifting land-ocean thermal contrasts, generating humid onshore winds and heavy rainfall during summer and dry offshore flows in winter.