Atmospheric Pressure and Wind

Define the following terms: barometer , millibar , isobar .

A barometer measures atmospheric pressure, a millibar is the expression of force per the surface area, and an isobar are isolines of equal pressure.

What causes a dynamic high near the surface? A dynamic low

A dynamic high happens when there is strongly descending air. A dynamic low is the opposite, caused by strongly rising air.

foehn winds

A föhn or foehn is a type of dry, warm, down-slope wind that occurs in the lee (downwind side) of a mountain range. Föhn can be initiated when deep low pressures move into Europe drawing moist Mediterranean air over the Alps

When referring to air pressure, what is a high, a low, a ridge, and a trough?

A high is pressure that is higher than surrounding areas, a low is pressure lower than surrounding areas, a ridge is a stretched area of high pressure, and a trough is stretched area of low pressure

Seasonal shifts:

All of the belts move north during the northern summer and south during the northern winter. Because global heating and cooling lags behind the position of the sun, they reach their northernmost latitude at or after the end of the northern summer. This brought the trade winds within reach of the Spain and Portugal and determined the sailing time of the Spanish treasure fleet. The northernmost position of the wind belts corresponds to the Atlantic hurricane season.

Doldrums:

At about the equator is Intertropical Convergence Zone or doldrums, a region of light and irregular wind broken by occasional thunderstorms and squalls. The width and exact location of the doldrums is hard to predict. Sailing ships are sometimes becalmed here for many days waiting for a proper wind.

Polar Easterlies:

At about the latitude of Norway and northward (60-90 degrees), the Polar easterlies blow irregularly from the east and north. Polar Front: Between the polar easterlies and the westerlies is the polar front.

Prevailing Westerlies:

At about the latitude of Western Europe and the U.S. (30-60 degrees), the Westerlies blow from the west, tending somewhat toward the north. This causes most weather in the United States to move from west to east.

How and why are friction layer (surface) winds different from upper-atmosphere geostrophic winds?

Friction layer winds are disrupted by the earth's surface, in contrast the geostrophic winds do not have the disruption and flow parallel to the isobars

Southern hemisphere

In the southern hemisphere the belts are reversed. The southeast trade winds blow from the southeast toward the equator. The southern equivalent of the horse latitudes (or Variables of Cancer) is called the Variables of Capricorn. The southern westerlies start somewhat south of South Africa. They tend to be stronger than the northern westerlies because they are mostly over water (roaring forties). The southern polar easterlies are mostly over Antarctica.

katabatic winds

Katabatic wind (from the Greek: katabaino - to go down) is the generic term for downslope winds flowing from high elevations of mountains, plateaus, and hills down their slopes to the valleys or planes below.

Land and sea breezes:

Land gains and loses heat more rapidly than water. During the day, the land warms more rapidly than the water. The air above land warms, becomes thinner, and rises, drawing cooler air landward from the sea. At night, the process reverses, and cool heavy air from the land flows out to sea. These land and sea breezes are important along the coast.

rossby waves

Rossby waves, also known as planetary waves, are a natural phenomenon in the atmosphere and oceans of planets that largely owe their properties to rotation of the planet. Rossby waves are a subset of inertial waves.

Trade Winds:

South of about 30 degrees the northern or northeast trade winds blow mostly from the northeast toward the equator. These were the sailor's favorite winds, since the weather was warm, and the winds usually blew steadily in an advantageous direction. Columbus used these to sail to the Caribbean.

santa ana winds

The Santa Ana winds are strong, extremely dry down-slope winds that originate inland and affect coastal Southern California and northern Baja California. ... The winds are known especially for the hot dry weather (often the hottest of the year) that they bring in the fall, and are infamous for fanning regional wildfires.

walker circulation

The Walker circulation, also known as the Walker cell, is a conceptual model of the air flow in the tropics in the lower atmosphere (troposphere). According to this model, parcels of air follow a closed circulation in the zonal and vertical directions.

Monsoon:

The annual equivalent of the daily land and sea breezes is the yearly monsoon. During summer, the continents heat more rapidly than the oceans. Air over the continents warms, thins and rises drawing cooler moist ocean air landward, producing a wet season. During winter, the process reverses and cold, dry heavy air flows outward from the continents, producing a dry season. The monsoon is most striking in south Asia because of the size of the Eurasian landmass and because the Himalayas tend to bottle up the air above the continent. Approximations of the Indian monsoon exist in other places, but they are poorly developed.

Ocean Gyre:

The fact that the westerlies and trade winds blow in opposite directions and that the continents prevent water from circling the globe contributes to the formation of circular ocean currents, clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. The Coriolis force also plays a part. The trade winds push water west. At the doldrums it flows back east producing the equatorial countercurrent. See Ocean gyre.

What is meant by a pressure gradient ?

The pressure gradient is the horizontal rate of pressure change.

What three factors influence the direction of wind?

The three factors of wind flow are the Coriolis effect, the pressure gradient, and surface friction

Explain how atmospheric pressure is related to air density and air temperature.

There is more pressure when gas is denser. And when the density is higher, the molecules move around more, thus crea±ng heat, or higher temperatures

What causes a thermal high near the surface? A thermal low?

Thermal highs come from cold surface temperatures and thermal lows caused by warm surface temperatures.

Horse Latitudes:

Where the Westerlies meet the trade winds at about 30 degrees (Jacksonville, Florida) is the Horse latitudes, also Variables of Cancer, Subtropical High, or Subtropical ridge. This is a region of high pressure, dry air, and variable winds, and is associated with deserts over land.

Global wind patterns

Winds are named by the direction from which they blow. The globe is encircled by six major wind belts, three in each hemisphere. From pole to equator, they are the polar easterlies, the westerlies, and the trade winds. All six belts move north in the northern summer and south in the northern winter. Each belt occupies about 30 degrees of latitude, that is, one third of the way from the pole to the equator.

Hadley Cells

a large-scale atmospheric convection cell in which air rises at the equator and sinks at medium latitudes, typically about 30° north or south.

Cyclone

a system of winds rotating inward to an area of low atmospheric pressure, with a counterclockwise (northern hemisphere) or clockwise (southern hemisphere) circulation; a depression.

chinook winds

a warm dry wind that blows down the east side of the Rocky Mountains at the end of winter.

Anticyclone

a weather system with high atmospheric pressure at its center, around which air slowly circulates in a clockwise (northern hemisphere) or counterclockwise (southern hemisphere) direction. Anticyclones are associated with calm, fine weather.

what happens to atmospheric pressure as altitude increases

pressure decreases with increasing altitude. The pressure at any level in the atmosphere may be interpreted as the total weight of the air above a unit area at any elevation. At higher elevations, there are fewer air molecules above a given surface than a similar surface at lower levels.

Describe the relationship between the "steepness" of a pressure gradient and the speed of the wind along that pressure gradient. Describe the general wind speed associated with a gentle (gradual) pressure gradient and a steep (abrupt) pressure gradient.

the steeper the pressure gradient, the more rapidly the air is accelerated between pressures differences, thus the wind speed is greater. It is the opposite with a gentle pressure gradient