Global Environment Chapter 5
How is air pressure measured?
A barometer can measure changes in air pressure. The two types of barometers are the mercurial barometer, which is more accurate but less easily transportable, and the aneroid barometer, which is less accurate but more portable.
Explain air pressure tendency.
Air pressure tendency is important, along with the air pressure reading on a barometer. Falling air pressure, which corresponds to a decrease in the length of mercury in the column on a mercurial barometer, generally indicates stormy weather.
Thermal equator?
An isoline connecting all points of highest mean temperature.
What is an isopleth?
An isopleth is a line on a weather chart that represents an equal value of some quantity.
What are doldrums?
Doldrums refers to a broad east-west belt of light winds that occur along the equator where the Trade Winds from the northern and southern hemispheres converge.
Isoheight or contour line is what?
Equal elevation.
Isobar?
Equal pressure.
Isohyet?
Equal rainfall.
Isotherms are equal to what?
Equal temperature.
Isotach?
Equal wind speed.
Describe friction forces.
Friction forces drag winds as they move across various surfaces. This effect decreases with height above a surface, and causes air spiraling out of a high pressure cell to turn clockwise (anticyclone). Air spiraling out of a low pressure cell turns counter-clockwise (cyclone). NOTE that in the Southern Hemisphere, this effect is in reverse: high pressures produce cyclones, and low pressures produce anticyclones.
What is the ITCZ?
The ITCZ stands for the Intertropical Convergence Zone, which is the area along the equator where a discontinuous series of thunderstorms occurs, due to the uplift caused by the convergence of winds and solar heating of the ground along the equator.
What is the Jet Stream?
The Jet Stream is a relatively narrow corridor of very strong winds near the tropopause.
Describe the Polar High Pressure area.
The Polar High Pressure consists of polar easterlies and the Antarctic High pressure area.
Describe the Subpolar Low Pressure area.
The Subpolar Low Pressure area consists of the Aleutian Low, the Icelandic Low, and the Polar Front.
Describe the Subtropical High Pressure area.
The Subtropical High Pressure area consists of Westerlies, the Bermuda High, the Azores High, and the Pacific High.
What four factors affect atmospheric circulation?
The four factors that affect atmospheric circulation are as follows: the Coriolis Effect, gravity, friction forces, and changes in air pressure.
What are the four major pressure areas on Earth?
The four major pressure areas on Earth are the Equatorial Low (warm, wet 10 degrees N/S), Polar High (cold, dry 90 N/S), Subtropical High (hot, dry 20-35 N/S), and the Subpolar Low (cool, wet 60 N/S).
Equatorial low-pressure trough
a thermally caused low-pressure area that almost girdles Earth, with air converging and ascending all along its extent; also called the intertropical convergence zone (ITCZ)
Geostrophic winds
a wind moving between areas of different pressure along a path that is parallel to the isobars. It is a product of the pressure gradient force and the Coriolis force
Monsoon
an annual cycle of dryness and wetness, with seasonally shifting winds produced by changing atmospheric pressure systems; affects India, Southeast Asia, Indonesia, northern Australia, and portions of Africa. From the Arabic word mausim, meaning "season."
Downwelling current
an area of the sea where a convergence or accumulation of water thrusts excess water downward; occurs, for example, at the western end of the equatorial current or along the margins of Antarctica
Constant isobaric surface
an elevated surface in the atmosphere on which all points have the same pressure, usually 500 mb. Along this constant-pressure surface, isobars mark the paths of upper-air winds
Jet streams
an irregular, concentrated band of wind occurring at several different locations that influences surface weather systems
Isobar
an isoline plotted on a weather map to connect points of equal pressure
Rossby waves
an undulating horizontal motion in the upper-air westerly circulation at middle and high latitudes
Pressure gradient force (PGF)
causes air to move from an area of higher barometric pressure to an area of lower barometric pressure due to the pressure difference
Thermohaline circulation
deep-ocean currents produced by differences in temperature and salinity with depth; Earth's deep currents
Wind vane
determines wind direction; standard measurement is taken 10 m (33 ft) above the ground to reduce the effects of local topography on wind direction
Anemometer
measures wind speed in kilometers per hour (kmph), miles per hour (mph), meters per second (mps), or knots (a nautical mile per hour, covering 1 minute of Earth's arc in an hour, equivalent to 1.85 kmph, or 1.15 mph)
Upwelling current
occurs where surface water is swept away from a coast, either by surface divergence I (induced by the Coriolis force) or by offshore winds
Subtropical high-pressure cells
one of several dynamic high-pressure areas covering roughly the region from 20° to 35° N and S latitudes; responsible for the hot, dry areas of Earth's arid and semiarid deserts
Air pressure
pressure produced by the motion, size, and number of gas molecules in the air and exerted on surfaces in contact with the air; an average force at sea level of 1 kg/cm (14.7 lb/in). Normal sea-level pressure, as measured by the height of a column of mercury (Hg), is expressed as 1013.2 millibars, 760 mm of Hg, or 29.92 inches of Hg. Air pressure can be measured with mercury or aneroid barometers
Mountain and valley breezes
result when mountain air cools rapidly at night, and valley air gains heat energy rapidly during the day
Westerlies
the dominant surface winds from the subtropics to high latitudes
Friction force
the effect of drag by the wind as it moves across a surface; may be operative through 500 m (1600 ft) of altitude. Surface friction slows the wind and therefore reduces the effectiveness of the Coriolis force
Western intensification
the piling up of ocean water along the western margin of each ocean basin, to a height of about 15 cm (6 in.); produced by the trade winds that drive the oceans westward in a concentrated channel
Trade winds
the winds converging on the equatorial low-pressure trough
Polar easterlies
variable, weak, cold, and dry winds moving away from the polar region; an anticyclonic circulation
Polar high-pressure cells
weak, anticyclonic, thermally produced pressure systems positioned roughly over each pole; that over the South Pole is the region of the lowest temperatures on Earth
Land and sea breezes
wind along coastlines and adjoining interior areas created by different heating characteristics of land and water surfaces—onshore (landward) breeze in the afternoon and offshore (seaward) breeze at night
What do high pressure cells tend to do?
High pressure cells tend to descend and diverge.
What are the rules for isopleths?
Isopleths must be continuous and cannot intersect other isopleths. All values above the isopleth should be on one side of the line and all values below an isopleth should be on the other side of the isopleth. The position of the isopleth should be interpolated in between points of known data. They should choose a contour interval and start at an area of high or low values.
Describe land-sea breezes.
Land-sea breezes are driven by the thermal inertia of water. When land and sea receive the same amount of insolation, the land heats up faster than the water. This temperature gradient causes winds to blow. At night, radiational cooling cools the land faster than the water so that the temperature gradient makes a wind blow from land to sea. These breezes also occur for large bodies of water, such as the Great Lakes.
What do low pressure cells tend to do?
Low pressure cells tend to ascend and converge.
Explain pressure gradients.
Pressure gradients drive air from an area of high pressure to an area of low pressure, creating winds.
What does primary circulation in the atmosphere entail?
Primary circulation entails global circulation - the mass movement of air all over the globe.
What does secondary circulation in the atmosphere entail?
Secondary circulation consists of the migration of high and low pressure cells. Major pressure cells move from high pressures to lower pressures, bringing with them fluctuations of temperature and moisture, causing climate.
What does tertiary circulation in the atmosphere entail?
Tertiary circulation is the movement of local high and low pressure cells, and parcels of air will cause local weather patterns, such as the weather patterns of a coastal city that is influenced by the body of water nearby.
Describe the Coriolis Effect.
The Coriolis Effect deflects winds fro ma straight line in relation to the Earth's rotating surface. Earth's rotation adds the Coriolis Effects and a "twist" to air movements. In the Northern Hemisphere, winds are deflected to the right, or the east. In the Southern Hemisphere, winds are deflected to the left, or the west.
Describe the Equatorial Low Pressure.
The Equatorial Low Pressure area occurs along the Intertropical Convergence Zone (ITCZ) and is the area where the Trade Winds and doldrums occur.
What is the rule for naming winds?
The wind direction is always reported as the direction from which the wind is blowing. Winds which blow from the west, for example, are westerlies. They blow towards the east. Winds which blow from the south are called southerlies. They blow towards the north.
What are Trade Winds?
Trade Winds blow out of the equator side of the anticyclones. In the Northern Hemisphere, they are the Northeasterly Trade Winds. They are the most persistent winds in the world, blowing in the same direction about 80% of the time.
Antarctic high
a consistent high-pressure region centered over Antarctica; source region for an intense polar air mass that is dry and associated with the lowest temperatures on Earth
Mercury barometer
a device that measures air pressure using a column of mercury in a tube; one end of the tube is sealed, and the other end is inserted in an open vessel of mercury
Aneroid barometer
a device that measures air pressure using a partially evacuated, sealed cell
Anticyclone
a dynamically or thermally caused area of high atmospheric pressure with descending and diverging airflows that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere
Cyclone
a dynamically or thermally caused area of low atmospheric pressure with ascending and converging airflows that rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere
Pacific high
a high-pressure cell that dominates the Pacific in July, retreating southward in the Northern Hemisphere in January; also known as the Hawaiian high
Subpolar low-pressure cells or Aleutian low or Icelandic low
a region of low pressure centered approximately at 60° latitude in the North Atlantic near Iceland and in the North Pacific near the Aleutians as well as in the Southern Hemisphere. Airflow is cyclonic; it weakens in summer and strengthens in winter
Polar front
a significant zone of contrast between cold and warm air masses; roughly situated between 50° and 60° N and S latitude
Azores high
a subtropical high-pressure cell that forms in the Northern Hemisphere in the eastern Atlantic (see Bermuda high); associated with warm, clear water and large quantities of sargassum, or gulf weed, characteristic of the Sargasso Sea
Bermuda high
a subtropical high-pressure cell that forms in the western North Atlantic.
Wind
generally the horizontal motion of air across Earth's surface
Katabatic winds
gravity drainage winds
Coriolis force
the apparent deflection of moving objects (wind, ocean currents, missiles) from travelling in a straight path, in proportion to the speed of Earth's rotation at different latitudes. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere; maximum at the poles and zero along the equator
Intertropical convergence zone (ITCZ)
the combination of heating and convergence forces air aloft
