AOSC200 FinalExam

Pressure Gradient Force (PGF)

Force that results from differences (i.e. gradients) in pressure across a surface

Larger gradients (tightly packed isobars) result in faster winds

Smaller gradients (spaced out isobars) result in weaker winds

In a low pressure system, PGFs will travel...

Inward (PGF)

In a high pressure system, PGFs will travel...

Outward (PGF)

Sea breeze

Air blows from sea to land, occurs during the day

Land breeze

Land loses energy faster than water, causes breeze from land to sea, occurs at night

Coriolis Force

In northern hemisphere, always deflect to the right, maximum at the poles, zero at the equator

Geostrophic balance

Balance between two forces equal magnitude and opposite in direction, such that air parcel continues to move at constant speed

geostrophic wind

Isobars are straight, PGF and CF are balanced

As isobars get closer, pressure gradient force, Coriolis force and speed all...

Increase when isobars get closer

Low pressure system (Gradient Wind)

PGF points towards low pressure (Inward), Centrifugal and Coriolis towards high pressure (Outward), PGF= Coriolis + Centrifugal

High pressure system (Gradient Wind)

Coriolis points towards high pressure (Inward), Centrifugal and PFG point towards low pressure (Outward), Coriolis= PFG+ Centrifugal

subgeostrophic

slower than geostrophic flow, low pressure system

supergeostrophic

faster than geostrophic flow, high pressure system

In the norther hemisphere, winds blow\_____ around low pressure systems and \_____ around high pressure systems

counterclockwise, clockwise

Frictional force

Will always go against wind direction

Surface winds

Account for friction, when slower, centrifugal and Coriolis forces are weaker

Wind Process

1. Most warm rotating around a low pressure system converges and rises
2. Warm air cools and diverges, creating clouds
3. Cold air sinks, converges again, moves towards high pressure system
4. High pressure system causes air to diverge, air spreads out

Valley breeze

Sun creates warm, thin air that rises quickly creating a low pressure system, air from valley rushes into low pressure system

Mountain breeze

Cold thin air becomes denser and sinks, forms local high pressure system

Katabatic winds

Air cools down at higher elevations, leads to pressure gradient, warms up as it falls causing winds to be fast

Santa Ana winds

Katabatic wind that occurs in SoCal, cold dense air from desert moves through mountains, warms as it descends creating hot dry air, causes wildfires sometimes

Hadley Cell

Explains trade winds, winds near equator blow from NE to SW

Angular Momentum and Wind

Wind speeds up as it moves farther from equator, faster wind= stronger Coriolis forces

Jet streams

Form where fronts meet, PFG will push air from south to north, Coriolis forces will move it to the right of northern hemisphere

convection

air converges at low pressure system, can get pushed up and condenses

subsidence

Air will warm as it sinks and gets drier

Deserts

Caused by subtropical highs where hot air rises, cold air sinks and heats up

ITCZ (intertropical convergence zone)

Region where trade winds meet, near equator

During the summer, sea level pressure is \_______ and thermal lows travel\_________

lower, northward

During the winter, low pressure seal level systems...

remain around the ITCZ

dry season monsoons

ITCZ is south, dry surface air flows of the Tibetan plateau

wet season monsoons

ITCZ is north, moist surface air flows off of Indian Ocean onto land

Ekman Transport

Ocean water pushed by wind, affected by Coriolis forces, causes cold water from lower ocean to rise up

El Niño

Easterly trade winds weaken, warm water transported east, shifts jetstream south, more thunderstorms

La Niña

Westerly trade winds become stronger, temperatures become dry and hot in south, shifts jet stream northward

snowmageddon

Moderate El Niño provided storm and Negative NAO provided cold air to this event

Continental air mass

Formed over land, generally dry air mass

Maritime air mass

Formed over the ocean, generally moist

Continental arctic (cA)

extremely cold and dry air mass

continental polar (cP)

cold, stable and dry air mass, comes from Canada

continental tropical (cT)

unstable, hot, dry air mass

maritime polar (mP)

cold, moist, unstable air mass

maritime tropical (mT)

warm, moist, usually unstable air mass

Siberian express

Cold air mass that moves down to Florida

Nor'easter

cyclone that moves northeast, filled with mP air

Dry line

Place where cT and mT meet, supercell storms form here, conductive to tornado development

lake effect snow

cA or cP blows over warm water, picks up moisture and drops snow on downwind side of the lake

Front

Transition between two air masses

Cold front

Indicated by blue triangles, warm air forced up, cools, latent heat released

Warm fronts

Represented by red semi circles that point towards cold air, warm air slides over cold air and slowly cools

Stationary fronts

Represented by triangles and semi circles, front doesn't move, winds blow along front but in opposite directions

Cold type occlusion

very cold cP air mass moves cool mP air up, surface is cold

Warm type occlusion

mP cool air rides up the back of the cP very cold air, clouds form ahead of surface occlusion

Midlatitude cyclone

Boundary for cP and mT, low pressure system, contains cold, warm and occluded front

Birth stage

Frontal wave along stationary front separating cP and mT

Young adult stage

Open wave develops strong cold and warm fronts, precipitations falls along broad area

Mature stage

Occluded front develops, pressure reaches minimum, winds reach maximum,

Death stage

Cut-off cyclone develops, pressure rises, clouds and precipitation dissipates

Alberta clippers

Form on lee side of Canadian Rockies. Fast moving and somewhat dry

Colorado low

Form on lee side of U.S. Rockies, right spot for cold polar air to interact with warm moist air

Gulf low

Form along southern coast. Cold land and warm ocean means good probability of precipitation

Hatteras Low (Nor'easter)

Form along eastern coast (Carolinas). Warm gulf stream water provides warm air and moisture that interacts with cold air on land.

Surface high pressures are directed\_______ by jet streams

Southeast

Surface low pressures are directed\______ by jet streams

Northeast

Thunderstorms

single cloud or cluster of clouds that produce, lighting, rain, need moist and hot air mT, occur around ITCZ

Florida

Location where thunderstorms are most likely to occur due to strong sea breeze with moist air, increases convection

4 things that affect thunderstorm growth

Lifting mechanism, environment temperatures, moisture, wind speed and direction

Single Cell thunderstorm

1. Warm, moist air rises and causes water to condense and cloud to spread in all directions
2. Updraft increases causing droplets to grow more
3. Energy and moisture weaken, downdraft overtakes updraft

Gust Front

Cold air (downdraft) acts as a cold front, forces warm air up and can lead to formation of a shelf cloud

squall line thunderstorms

Lines of intense, individual storms, strong downdraft of winds will push up warm air

Mesoscale Convective Complex thunderstorms

composed of several single cell thunderstorms that are in different stages, need moist air to last long

Overshooting top

Represents a very strong updraft and warning for a more severe storm

lightining

1. Charge separation occurs due to collision of ice crystals
2. Updrafts carry positive charges up, negatively charged move towards bottom of the cloud
3. Negative charges move towards ground, positive charges move towards cloud
4. One the charges come together, lighting shoots into the cloud

supercell thunderstorm

mT air combines with cT air, unstable atmosphere with lots of wind sheer causes horizontal spinning of wind, can become vertical with the presence of convection

Tornado life cycle

1. Rising warm air meets cold down draft, air condenses and cools creating a cloud
2. Funnel cloud forms and starts to pick up debris
3. Maturity when at peak width and intensity
4. Downdraft wraps around and cuts off downdraft, funnel begins to shrink

rear flank downdraft

Downdraft that is free of rain, back of the super cell

forward flank downdraft

Downdraft that contains precipitation, behind the gust front

Upper level divergence means that...

Lower level convergence is occurring at the surface

Upper level convergence means that...

Lower level divergence is occurring at the surface

Tropical cyclone

Must have minimum 74mph wind with rotation, low pressure center

Formation of a Tropical Cyclone

1. Easterly winds blow from hot Sahara
2. Clouds/Thunderstorms form
3. Tropical depression occurs at Subtropical ridge
4. Wind speed builds, pressure decreases
5. Follows reoccurring path
6. Tropical cyclone disbands

Saffir-Simpson Scale

Measures intensity of hurricanes

Hurricanes do not occur near the equator because...

Coriolis forces aren't present, winds flow straight from high to low pressure with no rotation

3 things that cause tropical cyclones to diminish

Moving over cold ocean water, moving over land, interaction with aloft winds or system pressures

Wind shear in a tropical cyclone can...

Rip apart a storm before it has formed

Two speeds associated with tornadoes and hurricanes

Surface speed and rotation speed

Storm surge

a rising of the sea as a result of atmospheric pressure changes and wind associated with a storm.

Step 1 of numerical weather predictions

Collect obersevations

Step 2 of numerical weather predictions

Data assimilation

Step 3 of numerical weather predictions

Model integration

Step 4 of numerical weather predictions

Tweaking and Broadcasting

Ensemble forecasts

Run model numerous times for slightly different initial conditions, Perform statistical analysis of all the model runs

Milankovitch Cycle

Earths orbit changes ever 100K years, earths tilt changes every 41K years and the wobble of earths axis changes every 27K years

Volcanoes can cool earths climate by...

Particles from the volcano shade incoming solar radiation from the sun

Aerosols direct climate effect

Dark aerosols on snow will decrease albedo and lead to increased absorption of solar energy and snow melt.

Aerosolos indirect climate effect

Make up cloud condensation nuclei, causing clouds to reflect sunlight

Positive feedback loop examples

Ice-Albedo, Water Vapor, High clouds

Negative feedback loop examples

CO2 and Plants, Low clouds

what lifting mechanism is associated with an unstable atmosphere

convection

what time of day is the atmosphere most unstable

afternoon because it has the highest temps and moist air has had time to rise and form clouds