Chapter 4 - Atmospheric Pressure and Wind

Pressure gradient force; friction, Coriolis effect

3 forces that determine wind strength and direction

adjustment to standard value of 0 degrees Centigrade

A correction to barometric pressure readings before data can be added to weather map (increased temps cause expansion of mercury affecting reading)

adjust if latitude was 45 degrees north

A correction to barometric pressure readings before data can be added to weather map. There is a slightly higher acceleration due to gravity at higher latitudes.

clockwise & down

Air goes ______________________________ in the Northern Hemisphere around high pressure just like a screw.

counterclockwise & up

Air goes __________________________________ in the Northern Hemisphere around low pressure.

decreases

Air pressure always _______________ with increased altitude.

uniform

Air pressure does not decrease with height at a _________ rate.

equally

Air pressure is exerted _______________ in all directions (up, down, sideways).

right

Due to the Coriolis effect, winds & ocean currents in the Northern Hemisphere act as though they're being pushed to the ____________.

left

Due to the Coriolis effect, winds & ocean currents in the Southern Hemisphere act as though they're being pushed to the ____________.

Newton's Second law

Force = mass * acceleration

upper atmosphere

Geostrophic flow only occurs in the _______________ where friction is absent and only the Coriolis force and pressure gradients apply.

increases

If air density increases while the temperature remains constant, then the pressure will ________________.

constant

If air density remains __________, an increase in temperature leads to an increase in pressure.

clear skies

In general, high pressure zones bring _________.

clouds and precipitation

In general, low pressure zones bring _______________.

surface level readings -> sea-level readings

One correction to barometric pressure readings before data can be added to weather map

wind

Pressure gradients provide the impetus for ____________, movement of air. Horizontal pressure gradients are gradients measured at constant altitude and the resulting air movement is _________.

roaring winds

Relatively tiny air pressure differences between places at the SAME ALTITUDE can cause ____________.

pressure gradient; Coriolis forces

Since friction in the free atmosphere is unimportant, winds in the upper atmosphere depend on the interaction of ___________ and __________.

speed

The Coriolis force acting on any moving object increases with the object's __________.

direction

The Coriolis force changes only the ________ of a moving object, never its speed.

increased distance

The Coriolis force increases with ______________ from the Equator.

deflection

The Coriolis force involves the _____________ that occurs over a given increment of time.

zero; increases

The Coriolis force is ______ at the Equator and _________ with increasing distances from the Equator.

poles

The Coriolis force is the greatest at the __________.

Equator

The Coriolis force operates everywhere on Earth except the ________________.

apparent

The Coriolis force produces an __________ deflection in all moving objects, regardless of their direction of motion.

right; left

The apparent deflection in the Northern Hemisphere is to the ________. The apparent deflection in the Southern Hemisphere is to the _______.

increases; wind speed

The magnitude of the Coriolis force ___________ with increased ______________.

horizontal pressure gradients

Use this term for pressure gradients measured at a constant altitude,

vertical; horizontal

____________ pressure gradients are very much greater than _______________ gradients and str ongly affect general atmospheric motion.

Three (3)

_____________ corrections must be made to barometric pressure before can be used on a weather map

horizontal; vertical

________________ pressure differences are very small compared to ____________ pressure differences.

rising air

__________________________________ in a low pressure area is cooled & condenses water vapor into clouds and precipitation

sinking air

___________________________________ in a high pressure area is warmed by the increase in pressure. As it warms, any water in the air evaporates into water vapor.

geostrophic flow (geostrophic wind)

air flow that moves at a constant speed and direction; occurs when the pressure gradient force equals the Coriolis force.

surface pressure

air pressure as it exists at the surface

pressure

amount of force per unit of surface area exerted on all surfaces by gas molecules (= air pressure)

aneroid barometer

an air-pressure measuring instrument without liquid (mercury)

high pressure zone

an area in which the air pressure is higher than the areas that surround it

low pressure zone

an area in which the air pressure is lower than the areas that surround it

Coriolis force

an imaginary deflective force arising from Earth's rotation tat is necessary to account for motions measured relative to the surface (deflects to right in N. Hemisphere; deflects to left in S. Hemisphere)

barometer

any instrument that measures air pressure

trough

areas low pressure

ridges

areas of high pressure

pressure gradient force

areas of high pressure exert force on areas of lower pressure, resulting in wind; the PGF sets air in motion

free atmosphere

atmosphere above 1.5 km (1 mile); air here experiences minimal friction

hydrostatic equation

change in pressure/change in altitude = -(density)(gravity)

acceleration

change in velocity (not speed) with respect to time

barographs

continuous barometric pressure charts created by aneorid barometers

velocity

direction and distance traveled per unit time

speed

distance traveled per unit of time

anticyclones

enclosed areas of HIGH pressure marked by roughly circular isobars or height contours

cyclones

enclosed areas of low pressure with air spiraling counterclockwise in NH and clockwise in SH

gravity

force of attraction of objects with mass; acceleration = 9.8 m/sec/sec or 32.1 feet/sec/sec; acceleration that an object would experience if gravity was only force affecting its movement

friction

force resisting movement of a fluid or object as it passes along a surface or an adjacent gas or liquid

air parcels

imaginary small volumes of air about 1 meter in diameter or so

anemometer

instrument that measures wind speed; has rotating cups that move in proportion with wind speed

isobar

line on a pressure map that connects points of equal sea-level pressure values

planetary boundary layer (boundary layer)

lowest 1.5 k (1 mile) of the atmosphere; where friction is most important

barometric pressure

often expressed as the height of the column of mercury in a barometer

equation of state (ideal gas law)

p = density*R*T where p = pressure in pascals density is mass/volume; R = constant = 287 joules/kilogram/kelvin and T = degrees kelvin

sea-level pressure

pressure that air would exert if it was at sea-level

force

push or pull

pressure gradient

rate of change in air pressure; isobars that are close together show high/steep pressure gradients; isobars farther apart show lower/shallow pressure gradients

Dalton's Law

rule that the total pressure exerted by a mixture of gas = sum of partial pressures of each gas (specific amount of pressure exerted by each specific gas)

mercury barometer

standard instrument for measuring air pressure;

pascal (Pa)

standard unit of pressure

azimuth

the degree of angle from the due north, moving clockwise

local vertical direction

the direction that is straight up for any location; in the opposite direction from the force of gravity. Also known as the zenith direction

air pressure

the force that air exerts on everything it touches

kilopascal (kPa)

unit of pressure used by Canadian meteorologists; 1 kPa = 1000 Pa

millibar (mb)

unit of pressure used by US meteorologists; 1 mb = 100 Pa

hydrostatic equilibrium

vertical pressure gradient force and the force of gravity are normally of nearly equal value & operate in opposite directions

radiosondes

weather balloons that measure a variety of variables

rawinsondes

weather balloons that measure only wind speed

gradient flow (gradient wind)

wind flowing parallel to curved isobars. Frictional forces are negligible. With gradient flow there is constant adjustment between the pressure gradient force and the Coriolis force, causing the wind to change speed and direction as it flows along the isobars.