Weather & Climate Exam #2 Review

Dr. O UWF

stable equilibrium

• condition of the atmosphere in which a parcel of air resists vertical motion and naturally returns to its original position

• cooler, denser

• ELR < DAR

• calm breeze, clear skies or stratus clouds, light drizzle, trapped fog/smoke/pollution stays near ground

unstable equilibrium

• condition of the atmosphere in which a parcel of air accepts vertical motion and rapidly moves away from its original position

• warmer, less dense

• ELR > DAR

• gusty winds, cumulus clouds, severe storms, turbulence

rising parcel =

expands + cools

sinking parcel =

shrinks + warms

adiabatic processes

• thermodynamic processes in which no heat is gained OR lost by a system between its surroundings

• temperature changes due to pressure changes, not heat mixing with surroundings

• ex. expanding cooling parcel, shrinking warming parcel

unsaturated parcel

• RH < 100%

• contains invisible water vapor

• constant cooling and warming rate

• cools by expansion

• DAR = 10 C / 1000 m

saturated parcel

• RH = 100%

• contains water vapor and liquid droplets

• warming rate > cooling rate

• cools by releasing latent heat through condensation

• DAR > MAR

• MAR = 6 C / 1000 m

latent heat

• energy absorbed or released by a substance during a phase change without changing its temperature

• “hidden” heat

dry adiabatic rate (DAR)

• rate of temperature change in a rising or sinking unsaturated parcel

• applies to BOTH rising and sinking air

• RH < 100%

DAR =

10 C / 1000 m

moist adiabatic rate (MAR)

• rate of temperature change in a rising saturated parcel

• applies ONLY to rising parcel; sinking parcel dries instantly

• RH = 100%

• latent heat of condensation

MAR =

6 C / 1000 m

local convective uplift

• atmospheric process in which unequal surface heating causes a localized patch of air to become warmer and less dense than surroundings

• air patch RISES

regional convergence

• atmospheric process in which opposing air masses flow into the same area, forcing the air upwards (uplifting)

• spans over a large region

• air masses RISE

frontal wedging

• atmospheric process in which cooler, denser air physically wedges warmer, less dense air above it

• warmer air mass RISES

orographic uplift

• atmospheric process in which air is physically forced upwards over a topographic barrier

• ex. mountain, plateau

• air mass RISES

atmospheric stability

• measure of the atmosphere’s tendency to resist or accept vertical motion

• density and temperature comparisons between air parcels and surroundings

↑ temp =

↓ density

warm air will

↑ over cold air

parcel temp > surrounding temp =

• parcel rises

• parcel is unstable

environmental lapse rate (ELR)

• real time rate at which air temperature DECREASES as altitude INCREASES

• helps determine atmospheric stability

average ELR =

6.5 C / 1000 m

↑ aloft air temp =

↓ ELR

↓ surface air temp =

↓ ELR

surface air cooling processes:

• radiative cooling

• cold-air advection

• air moving over cold surface

radiative cooling

• process in which the surface or atmosphere lose heat by emitting longwave infrared radiation into space

• surface air cooling process

cold-air advection

• horizontal transport of a cold air mass into a warm region via wind

• surface air cooling process

advection

• horizontal transport of temperature or moisture by wind movement

• cold → warm or warm → cold

surface air warming processes:

• insolation

• warm-air advection

• air moving over a warm surface

warm-air advection

• horizontal transport of a warm air mass into a cold region by wind

• surface air warming process

insolation

• process of shortwave solar radiation being absorbed by the surface, heating the air directly above it through conduction, and radiating longwave radiation to the surface air

• surface air warming process

stable ELR =

4 C / 1000 m

stable DAR =

10 C / 1000 m

stable MAR =

6 C / 1000 m

absolute stability =

ELR < MAR

↓ ELR =

↑ stability

subsidence inversion

• temperature inversion occurring when a large air mass slow sinks over a wide area, compressing and warming adiabatically

• associated with HIGH PRESSURE systems

• any inversion is ABSOLUTELY STABLE

unsaturated air:

ELR = DAR

saturated air:

ELR = MAR

unstable ELR =

11 C / 1000 m

unstable DAR =

10 C / 1000 m

unstable MAR =

6 C / 1000 m

absolute instability =

ELR > DAR

conditional instability =

MAR < ELR < DAR

absolute stability

• BOTH dry and wet air parcels are colder and denser than enviro, both sink

• ELR < MAR

• clear skies, calm winds, flat stratus clouds, trapped fog/smoke

• resistence

absolute instability

• BOTH dry and wet air parcels are warmer and less dense than enviro, both rise

• ELR > DAR

• rising thermals, severe storms, gusty winds, tornadoes

• acceleration

conditional instability

• unsaturated air = stable

• saturated air = unstable

• MAR < ELR < DAR

• “average” conditions, fair weather

vertical mixing

• upward and downward movement and exchange of air parcels driven by temperature gradients and wind turbulence

• leads to destabilization

• can steepen the ELR

cloud development

• process of invisible water vapor transforming into water droplets or ice crystals through:

  1. lifting

  2. cooling

  3. condensation (RH = 100%)

uplift mechanisms

• convective lifting (hot air balloon)

• orographic lifting (mountains)

• front lifting (warm over cold)

• convergence (low pressure, pushed up)

convective clouds

• clouds formed through the vertical movement of warm, buoyant air rising in an unstable atmosphere

• vertical structure

• distinct, puffy, towering shapes; flat bases; cauliflower edges

cumulus

• low altitude

• dark flat bases, bright white tops

• liquid drops, some ice crystals possible the the top

cumulonimbus

• multi level altitude, vertically development

• massive, towering, dark bases, anvil top

• lower level = liquid drops

• middle = supercooled water and ice

• top = entirely ice crystals

orographic clouds

• geographically locked to topography

• driven by wind, not solar heating

• wet windward side

• dry leeward side

rainshadow effect

• effect of an orographic cloud to have heavy precipitation on the windward slope, and dryness on the leeward slope

windward

• slope facing incoming wind

• high precipitation

leeward

• slope facing away from wind, protected by elevation

• dry air

cloud droplets

• 0.02 - 0.05 mm

• tiny, liquid spheres making the visible portions of clouds

• colloidal, not precipitation

condensation nuclei

• 0.0002 mm

• tiny airborne particles which water vapor can condense on to form cloud droplets

equilibrium vapor pressure

• pressure exerted by water vapor when in a state of dynamic equilibrium between its liquid and solid phase

• net amount of water vapor and liquid water remain constant

• temperature dependent

curvature effect

• phenomenon in which high curved surfaced require a higher RH% to prevent evaporation than a flat surface

• flat surface vs smaller, highly curved surface

↓ droplet sphere size =

↑ curvature

↑ curvature =

↑ RH%

supersaturation

• atmospheric condition in which RH > 100%

• HIGHLY unstable

• required for very small cloud droplets to grow larger

• condensation > evaporation

supersaturation =

RH > 100%

hygroscopic nuclei

• specialized condensation nuclei which highly attract water molecules

• intensify and accelerate condensation well below 100% RH

colloidal

• suspension in which microscopic droplets or ice crystals are dispersed uniformly throughout the air

• NOT precipitation yet

precipitation formation

• collision-coalescence (tropics)

• Bergeron process (mid, high lats)

collision coalescence

• precipitation formation by warm clouds in the tropics

• larger droplets fall faster through cloud

• LIQUID droplets collide and merge with another as they fall

• driving mechanism: differential fall velocities

• precipitation: rain, drizzle

supercooled

• state of liquid water remaining fluid despite being below freezing point

• occurs at sub-freezing temperatures in clouds

Bergeron process

• precipitation formation by cold clouds in the mid and high latitudes

• cloud tops well below 0, creating supercooled water

• ice crystals “steal” molecules from liquid droplets as it falls

• driving mechanism: vapor pressure gradient = ice crystal growth

• precipitation: snow, rain

↑ droplet size =

↑ fall speed

ice nuclei

• airborne particles serving as a structure for ice crystals to form against at sub-freezing temperatures

accretion

• supercooled droplets freeze on contact with ice crystals, forming graupel

graupel

• small, opaque ice particles formed from the instant freezing of supercooled water droplets (accretion)

aggregation

• ice crystals collide directly and join, forming snowflakes

snowflake

• aggregate of many ice crystals formed directly from freezing water vapor and interconnecting ice crystals (aggregation)

drizzle/rain

• liquid precipitation formed by interjoining liquid water droplets (collision coalescence), or ice crystals melting before they reach the surface (bergeron)

• 0.5 mm

wet snow

• high liquid water content

• formed right at or slightly above freezing point

• crystals form through aggregation, slightly melted

• heavy, dense, packed

dry snow

• little to no liquid water content

• formed well below freezing point

• crystals remain frozen, brittle, and separated

• light, fluffy, powdery

sleet

• precipitation which starts as ice crystals, melts through a warm air layer, and refreezes through a sub-freezing air layer before landing

• hard, solid, translucent

cyclonic circulation

• fluid rotation of air masses around a well-defined, low-pressure center

• counterclockwise in NH

• driven by PGF, coriolis, and friction

• leads to cloudy, stormy weather

freezing rain

• precipitation formed by cold, supercooled droplets falling as liquid but freezing on contact with the surface

• smooth, glassy, transparent

snow temperature profile

sleet temperature profile

freezing rain temperature profile

rain temperature profile

ideal gas law

• fundamental equation relating pressure, volume, temperature, and amount of an ideal gas

• pressure is PROPORTIONAL to density

• P = (nRT)/V

• R = 8.314 J/molK

pressure =

(temp X density X gas constant)/volume

ideal gas constant =

8.314 J/molK

atmospheric pressure

• mass of air above a certain point

• vertical and horizontal differences

same temp:

• density: high pressure air > low pressure air

wind

• horizontal movement of air across earth’s surface driven by differences in atmospheric pressure (PGF)

same pressure:

• length: cold air < warm air

• density: cold air > warm air

aloft warm air =

↑ pressure

aloft cold air =

↓ pressure

pressure gradient force (PGF)

• horizontal differences in atmospheric pressure driving air naturally from high to low pressure areas

• ONLY cause of wind

millibar

• unit used to measure air pressure

isobar map

• pressure measurement map showing lines connecting points of equal pressure

• high and low systems

tropopause

• top boundary of the troposphere before the temperature reversal

• weather stops here