Thunderstorms obscured by massive cloud layers that cant be seen.
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Convergence:
Net horizontal inflow of air into an area
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When does convergence happen?
Wind speeds slow down in direction of flow or when opposing airstreams meet.
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Divergence
Net horizontal outflow of air in an area.
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When does Divergence happen?
Wind speeds increase in direction of flow or when airstreams spread out.
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What happens when surface winds converge?
Flowing in air is removed due to rising upward
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What happens when surface winds diverge?
Air sinks from aloft to replace air being removed at lower levels
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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
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Where does air tend to rise and sink?
rise in low pressure, sink in high pressure.
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Convergent winds tend to flow
into low pressure areas
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divergent winds tend to flow
out of high pressure areas
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Which ways do low and high pressure winds spiral?
low pressure are counter-clockwise, high pressure clockwise
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When does friction cause surface winds to blow across isobars at a slight angle toward lower pressure?
in large scale flow (nearly geostrophic balance)
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Orographic lifting:
The lifting of an airmass when it encouters a hill or mountain
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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.
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What does strength of vertical velocities depend on?
The speed of the wind blowing perpendicular to the mountain and the steepness of the terrain
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can orographic lifting cause storm activity?
yes but not usually. causes turbulence such as mountain lee waves
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front:
transition zone between two air masses of different densities
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airmass
an extensive body of air where the conditions of temperature and moisture are essentially uniform
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frontal lifting:
when a warm airmass lifts over a relative cold airmass, note that air can also descend over fronts
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convective lifting
occurs in unstable atmospheric conditions when a rising parcel of air is warmer than its surroundings
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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
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what vertical motion is cloud and storm formation associated with
convection/convective lifting
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mechanical turbulence
the turbulence produced when airflow is hindered by surface friction and/or obstruction
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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
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gravity waves
vertical oscillations of air parcels in a stable atmosphere
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how does gravity support equilibrium?
gravity plays are major role in return of displaced particles to their equilibrium level
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what doe speed, length, and direction of propagation depend on?
magnitude of initial displacement, atmospheric stability, wind
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what occurs under unstable atmospheric conditions and what occurs under stable atmospheric conditions
unstable: convection stable: gravity wave
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stable
when the airmass returns to its initial position after displacement
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unstable
airmass continues moving away after displacement
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neutral
airmass remains in new place after displacement
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atmospheric stability
a condition that makes it difficult for air parcels to move vertically
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atmospheric instability
a condition that promotes vertical motion of air parcels
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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
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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.
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dry adiabatic process
cooling of an unsaturated parcel of air by expansion and the warming of a parcel of air by compression
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dry adiabatic process temp change:
3 degrees C (5.4 farenheit) per 1000 feet
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adiabatic cooling:
cooling of gas by expansion, it is always associated with upward motion
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adiabatic heating
warming of gas by compression, always associated with downward motion
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why do air parcels cool when increasing in altitude?
because they expend energy while expanding to match the pressure of surrounding air
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unsaturated air flowing upslope cools at:
3 degrees C per 1000 feet
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why is ISA 2 degrees per 1000 feet?
isa doesnt account for vertical movement and air cooling by expansion
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sounding
measurement of meteorlogical conditions between the surface and some altitude
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lapse rate
decreased of temp rate with height
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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
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surface based inversion
an inversion with its base at ground level, often the result of surface cooling
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when the observed lapse rate is steep,
it approaches or exceeds the dry adiabatic lapse rate
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stable air is ________ than unstable air
smoother
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formation of stratiform or cumuliform clouds depends on
stability of air
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stable environment means vertical movements are
small and smooth
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unstable environments mean that vertical movements are
large and turbulent
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visibility in unstable condition is usually:
good
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surface based temp inversions occur on
clear cool nights with light or calm winds
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stability of airmasses are decreased by
heating from below
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unstable air is associated with
good visibility and rough low level flying especially in the afternoon and summer
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high pressure areas where the air is generally descending, atmosphere is most likely
stable
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low pressure areas where air is generally rising, atmosphere is most likely
unstable
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presence of fog, smoke, or haze indicates atmosphere is
stable
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what is an area of definite turbulence and wind shear?
elevated stable layer capping off an unstable area
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Which trace gas is the most important in weather formation?
water vapor
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water vapor:
colorless ordorless tasteless gas in which molecules are free to move about
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how is water vapor unique?
it can exist in 3 states in the atmosphere
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h2o transfering to higher energy states
melting (ice to water), evaporation (water to water vapor), sublimation (ice to water vapor)
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h2o transfering to lower energy states
condensation (water vapor to water). freezing (water to ice), and deposition (water vapor to ice)
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Change in molecular motion always is due to
temperature change
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latent heat
amount of heat absorbed or released during a change of state
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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
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vapor pressure
partial pressure exerted by water vapor
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saturation
when the same amount of h2o is leave a water surface as returning
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saturation vapor pressure
partial pressure of water pressure at equilibirum
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what is saturation vapor pressure dependent on
temperature
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Relative humidity is relative to
saturation vapor pressure
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dew point:
temperature which air must be cooled to to become saturated
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what does dew point help anticipate?
precipitation, thunderstorms, icing
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dew
condensation that forms on an object when it loses heat energy through nocturnal radiation
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white dew
dew that has frozen
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frost
ice crystal deposition
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frostpoint
critical temp of frost
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cloud
a suspension of water droplet or ice crystals in the atmosphere
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3 requirements for a cloud
water vapor, condensation nuclei, cooling
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condensation nuclei
microscopic particles that serve as surfaces for water vapor to condense or depose on, examples are dust, salt, fog
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hygroscopic
having tendency to draw water from atmosphere
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cooling is usually the result of
contact of air with cold surface and adiabatic expansion
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contact cooling
process by which heat is conducted away from warmer air to colder surface, one way clouds are formed
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Contact cooling causes air stability to
increase
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advection fog
results from the transport of warm humid air over a cold surface
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radiation fog
occurs when radiation cooling of earth surface lowers air temp near ground to or below its initial dewpoint on calm clear nights.
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