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What does vertical motion contribute to?
Atmospheric Stability (or instability) and can be the start of severe weather
Since pressure always decreases with height, adiabatic cooling and heating will:
cooling will always accompany upward motion, heating will accompany downward motion
What causes vertical motions to typically be much smaller than horizontal motions?
Hydrostatic Balance
What weather radar should not be relied on?
Aircraft Radar
What can cause small imbalances between the gravitational force and the Vertical Pressure Gradient?
Thunderstorms that cause large vertical accelerations and vertical motions
what is it called when vertical motions are strong enough to affect aircraft motion?
VErtical gusts
What are the most significant causes of vertical motion?
convergence/divergence, orography, fronts, convection
What are embedded thunderstorms?
Thunderstorms obscured by massive cloud layers that cant be seen.
Convergence:
Net horizontal inflow of air into an area
When does convergence happen?
Wind speeds slow down in direction of flow or when opposing airstreams meet.
Divergence
Net horizontal outflow of air in an area.
When does Divergence happen?
Wind speeds increase in direction of flow or when airstreams spread out.
What happens when surface winds converge?
Flowing in air is removed due to rising upward
What happens when surface winds diverge?
Air sinks from aloft to replace air being removed at lower levels
What happens aloft when surface winds diverge/converge?
You have both upwards and downwards motions, converging winds push out the air and diverging winds suck in the air
Where does air tend to rise and sink?
rise in low pressure, sink in high pressure.
Convergent winds tend to flow
into low pressure areas
divergent winds tend to flow
out of high pressure areas
Which ways do low and high pressure winds spiral?
low pressure are counter-clockwise, high pressure clockwise
When does friction cause surface winds to blow across isobars at a slight angle toward lower pressure?
in large scale flow (nearly geostrophic balance)
Orographic lifting:
The lifting of an airmass when it encouters a hill or mountain
What happens when wind hits mountains and peaks?
If the wind hits a mountain it goes up, when it crosses a peak it goes down.
What does strength of vertical velocities depend on?
The speed of the wind blowing perpendicular to the mountain and the steepness of the terrain
can orographic lifting cause storm activity?
yes but not usually. causes turbulence such as mountain lee waves
front:
transition zone between two air masses of different densities
airmass
an extensive body of air where the conditions of temperature and moisture are essentially uniform
frontal lifting:
when a warm airmass lifts over a relative cold airmass, note that air can also descend over fronts
convective lifting
occurs in unstable atmospheric conditions when a rising parcel of air is warmer than its surroundings
what happens as warmer air wants to rise to become cooler?
the bubbles of warm air rise and the cooler air around the bubble sinks
what vertical motion is cloud and storm formation associated with
convection/convective lifting
mechanical turbulence
the turbulence produced when airflow is hindered by surface friction and/or obstruction
what is the result of mechanical turbulence?
eddies: the surface friction slows the air in the lowest atmospheric layers, the air above still moves faster, this causes the air to roll up and cuases turbulence
gravity waves
vertical oscillations of air parcels in a stable atmosphere
how does gravity support equilibrium?
gravity plays are major role in return of displaced particles to their equilibrium level
what doe speed, length, and direction of propagation depend on?
magnitude of initial displacement, atmospheric stability, wind
what occurs under unstable atmospheric conditions and what occurs under stable atmospheric conditions
unstable: convection stable: gravity wave
stable
when the airmass returns to its initial position after displacement
unstable
airmass continues moving away after displacement
neutral
airmass remains in new place after displacement
atmospheric stability
a condition that makes it difficult for air parcels to move vertically
atmospheric instability
a condition that promotes vertical motion of air parcels
buoyancy
the property of an object that allows it to float on the surface of a liquid, or ascend through and remain freely suspended in a compressible fluid such as the atmosphere
archimedes principle
when an object is placed in a fluid, it will be subjected to an upward or downward force depending on the weight of the the object and displaced fluid.
dry adiabatic process
cooling of an unsaturated parcel of air by expansion and the warming of a parcel of air by compression
dry adiabatic process temp change:
3 degrees C (5.4 farenheit) per 1000 feet
adiabatic cooling:
cooling of gas by expansion, it is always associated with upward motion
adiabatic heating
warming of gas by compression, always associated with downward motion
why do air parcels cool when increasing in altitude?
because they expend energy while expanding to match the pressure of surrounding air
unsaturated air flowing upslope cools at:
3 degrees C per 1000 feet
why is ISA 2 degrees per 1000 feet?
isa doesnt account for vertical movement and air cooling by expansion
sounding
measurement of meteorlogical conditions between the surface and some altitude
lapse rate
decreased of temp rate with height
how to evaluate stabilitiy?
dry adiabatic lapse rate = 3 degrees per 1000 ft when the LR is greater than DALR, atmosphere is absolutely unstable, when LR = DALR atmosphere is neutral, when LR<DALR the atmosphere is stable
surface based inversion
an inversion with its base at ground level, often the result of surface cooling
when the observed lapse rate is steep,
it approaches or exceeds the dry adiabatic lapse rate
stable air is ________ than unstable air
smoother
formation of stratiform or cumuliform clouds depends on
stability of air
stable environment means vertical movements are
small and smooth
unstable environments mean that vertical movements are
large and turbulent
visibility in unstable condition is usually:
good
surface based temp inversions occur on
clear cool nights with light or calm winds
stability of airmasses are decreased by
heating from below
unstable air is associated with
good visibility and rough low level flying especially in the afternoon and summer
high pressure areas where the air is generally descending, atmosphere is most likely
stable
low pressure areas where air is generally rising, atmosphere is most likely
unstable
presence of fog, smoke, or haze indicates atmosphere is
stable
what is an area of definite turbulence and wind shear?
elevated stable layer capping off an unstable area
Which trace gas is the most important in weather formation?
water vapor
water vapor:
colorless ordorless tasteless gas in which molecules are free to move about
how is water vapor unique?
it can exist in 3 states in the atmosphere
h2o transfering to higher energy states
melting (ice to water), evaporation (water to water vapor), sublimation (ice to water vapor)
h2o transfering to lower energy states
condensation (water vapor to water). freezing (water to ice), and deposition (water vapor to ice)
Change in molecular motion always is due to
temperature change
latent heat
amount of heat absorbed or released during a change of state
partial pressure
pressure exerted by any one of the gases that make up the mixture of gases in the atmosphere: all added together make the current pressure
vapor pressure
partial pressure exerted by water vapor
saturation
when the same amount of h2o is leave a water surface as returning
saturation vapor pressure
partial pressure of water pressure at equilibirum
what is saturation vapor pressure dependent on
temperature
Relative humidity is relative to
saturation vapor pressure
dew point:
temperature which air must be cooled to to become saturated
what does dew point help anticipate?
precipitation, thunderstorms, icing
dew
condensation that forms on an object when it loses heat energy through nocturnal radiation
white dew
dew that has frozen
frost
ice crystal deposition
frostpoint
critical temp of frost
cloud
a suspension of water droplet or ice crystals in the atmosphere
3 requirements for a cloud
water vapor, condensation nuclei, cooling
condensation nuclei
microscopic particles that serve as surfaces for water vapor to condense or depose on, examples are dust, salt, fog
hygroscopic
having tendency to draw water from atmosphere
cooling is usually the result of
contact of air with cold surface and adiabatic expansion
contact cooling
process by which heat is conducted away from warmer air to colder surface, one way clouds are formed
Contact cooling causes air stability to
increase
advection fog
results from the transport of warm humid air over a cold surface
radiation fog
occurs when radiation cooling of earth surface lowers air temp near ground to or below its initial dewpoint on calm clear nights.
ground fog
radiation fog that is less than 20ft deep
adiabatic cooling
cooling of gas by expansion
if a cloud forms, the air likely was
moving upward
if a cloud dissipates, the air likely was
moving down
Note
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