meteorology chapter 4

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horizontal and vertical movements
meteorologist find it helpful to separate of _____ and _____ air motions
horizontal motions are much stronger than vertical motions with the exceptions of a few turbulent phenomena
what is the reason to seperate vertical and horizontal movements
wind
horizontal air motions
wind velocity
a vector quantity
vector quantity
has a magnitude and a direction
scalar quantities
temperture and pressure, which only have magnitude
wind speed
the magnitude of the wind velocity
wind direction
direction from which the wind is blowing, measured in degrees, or to eight or sixteen points of a compass, clockwise from true north
360 degrees
what is true north
true north
meteorologist always state their wind direction relative to what?
magnetic north
ATC always state wind direction in terms of what?
at the surface
where is wind velocity measured
anemometers and wind vanes
what are used to measure wind velocity at the ground
tracking of free balance balloons, doppler radar, aircraft navigation system, and satellite
how is the wind velocity measured for winds aloft?
> or = 15 Knots
when the windsock becomes fully inflated
sustained speed
the average wind speed is aka
gust
reported when there is at least a ten-knot variation between instantaneous peaks and lulls during the last ten minutes
squall
reported when there is a sudden increase of wind speed by atleast 16 knots to a sustained speed of 22 knots or more for a one- minute period
peak wind speed
is the maximum instantaneous wind speed greater than 25 knots since the last hourly observation
variable
if the metar shows VRB. what does it stand for
if direction varies 60 degrees or more and the speed is above 6 knots
when will you see VRB on metar
G
how are gusty winds reported
F(total)=MA
in an object of mass,M, is isubjected to an unbalanced force, F(total), it will undergo an acceleration, A,: what is the formula
acceleration
is the change of the speed and/or direction of a mass of air as it moves along its path
pressure gradient force, coriolis force, and frictional force
the most important forces that affect air motions are:
pressure gradient
the difference in pressure between two points divided by the distance between the points
deal with gases under pressure
pressure gradient has an influence on air movement is obvious when you deal with what?
pressure gradient force
The larger the pressure difference, the greater the acceleration through the opening describes what force
horizontal pressure gradient force
the atmosphere causes air parcels to be accelerated across the surface of the earth toward low pressure
horizontal pressure gradient force
the root cause of wind
differential heating by horizontal temp gradient
the example of the sun heating the land faster than the water, this causes the pressure to move from high to low
pressure gradient
simply the difference in pressure between two points divided by the distance between the points
thermal circulation
the movement of air which results from differential heating
upper and lower branch
thermal circulations have two horizontal branches:
return flow
another name for upper branch
pressure gradient
the ___ ____ force is always directed perpendicular to the isobars toward lower pressure
thermal circulations
the stronger the temperature gradient, the stronger the pressure gradient, and the stronger the winds
Coriolis force
as soon as fir begins to move , what is it affected by
Coriolis force
when we attempt to describe the motion of the atmosphere relative to the rotating earth, we must also consider what?
different latitudes
the coriolis force is different at different wat
counterclockwise
what way does the toliet flush in the northern hemisphere
wind direction
coriolis force acts 90 degrees to the right of the wind in the N.H., therefore the force only affects what?
wind speed
coriolis force depends on what to make it stronger or weaker?
latitude
coriolis force depends on what? it varies from zero at the equator to a maximum at the poles
left
naviation across large distances requires corrections for the influence of coriolis force, aircrafts tracks must be corrected to the ____ in the northern hemisphere
tend to equal in magnitude, but opposite in direction causing them to equal each other out
when air travels over distances of hundreds of miles or more, Coriolis and pressure gradient forces tend to do what?
geostrophic balance
when the Coriolis and pressure gradient equal each other out
geostrophic wind
the related wind is called what
90 degrees to the left
what was does pressure gradient force have to be traveling if the corolis force is 90 degrees to the right in the N.H. to create a geotrophic balance
with the lowest pressure on the left
in the N.H. the geostrophic wind is parallel to the isobars with the what?
with your back to the wind, the low pressure is on your left
the Buys-Ballot laws
the stronger the pressure gradient and the stronger the geostrophic windspeed
the closer together the isobars
counterclockwise
the N.H. winds tend to blow ____ around low pressure centers (cyclones)- cyclonic flow
pressure gradient force > than coriolis force
geostrophic balance doesnt occur in small scale circulations such as sea breezes, thunderstorms, tornadoes, and dust devils
because why?
isobars on the surface analysis are close together
the pressure gradient force is large and windspeeds are strong when?
wind direction
what can be inferred from isobaric patterns
coriolis force
why dont winds blow directly from large scale high pressure areaas to low-pressure areas?
Geostrophic wind
practical tool for the interpretation of large scale weather charts
estimate the winds from the pressure field
why is the geostrophic wind heloful
characteristics of geostrophic winds
weak winds in areas with weak pressure gradient, strong winds in regions with strong pressure gradients, counterclockwise circulations of air around lows, and clockwise circulations around high (in N.H.)
500 mb constant pressure chart
is suitable for flight planning at FL 180.
conditons along the proposed route
the 500 mb constant pressure chart gives observes temps and wind info for ?
friction
force that resists the relative motion of two bodies in contact
friction
also occurs within fluids, such as the atmosphere, and at the interface between fluids and solids (skin friction)
drag
the resistance of the atmosphere to the relative motion of the aircraft
drag
includes skin friction as well as form drag, which is caused by turbulence induced by the shape of the aircraft
surface friction (2000ft)
describes the resistive force that arises from a combination of skin friction and turbulence near the earth surface
boundary layer
the transition zone between large surface frictional effects near the ground and negligible effect above the boundary layer
...
effects of friction in the boundary layer
above the surface
winds increase with altitude in the atmospheric boundary layer, with the greatest increase where?
clockwise
the wind changes direction _____ with increase altitude
near the surface
winds near _____ are stronger, the boundary layer is turbulent and winds are gusty
boundary layer
is deeper during the day, and in the warmer months. shallower at night and during colder months
rough terrains
when winds are strong, te boundary layer is deeper over what?
counterclockwise
clockwise
winds near the ground tend to spiral __________ in to cyclones and spiral ____ out of anticyclones
stormy conditions
some of the affects listed here may be masked when?
wind
___ is caused by pressure differences and modified by the earth's rotation and surface friction
when an air parel moves vertically for any reason, it carried its horizontal winds (actually horizontal momentum
one way to cause the pressure gradient to change
stronger winds are brought from the top of the boundary layer to the ground, producing gustiness
when the pressure gradient change occurs, what happens to the wind
centripetal acceleration (centrifugal force)
when air moves along a curved path, even if it is traveling at constant speed, it is subject to an acceleration; that is, the direction of motion is constantly changing along the path
imbalance forces
what is centripetal acceleration due to
cyclostrophic balance
where the scale is so small that the pressure gradient is larger than the Coriolis force, the pressure gradient and centrifugal forces may be in what?
cyclostrophic winds- dust devils and tornadoes
cyclostrophic balance produces what?