av weather exam 2

no

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

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