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.