meteorology exam 3

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upwelling

brings cold, nutrient rich water to the surface along the coasts of Peru and Ecuador 

El Nino events are characterized by

pooling of unusually warm water in the eastern tropical Pacific

the areas of abundant rainfall on the earth tend to be

near the equator and in midlatitudes

the major features of precipitation distribution patterns are determined by

general circulation and pressure patterns

most of the earth’s deserts are located in the 

subsidence areas of subtropical high

an air mass is a body of air

similar values of temperature and moisture at any given elevation

what is not a good region for air masses

central United States

air mass source regions are least likely to exist in

middle-latitude regions

air masses over north america

continental polar and continental arctic

cP & cA winter

• very cold & dry

• long winter night

• frozen ground

• can move into US

cP & cA summer

• no cA

• warmed from long days and higher sun

• cool & dry

maritime polar winter

• pacific mP has big effect on north america

continental tropic

• hot and dry

• only in summer in SW

cold front with warm, moist, conditional unstable air

T-storm, tornados, hail and damaging wind

cold front with warm, moist stable air

light/ no rain

• some clouds

cold front

• steeper slope

• advances fast

• harsh weather

warm front with warm, moist, unstable air

• wide spread of cloud

• T - storm

warm front with warm, moist, stable air

• layered cloud

front typically located in the southwest quadrant of cyclone

warm

front in southeast side of cyclone

cold

occluded front

cold front progress southward & eastward, warm air forced over cold masses

• small temp contrast

occluded front is most common

the eastern half of north America

cold occlusions

cold front from behind overtakes cool air in warm front

• lifts warm air — clouds and precipitation

warm occlusions

• colder air north of warm front

• less cold air behind cold front is lifted over colder air north of warm front

clouds and precipitation develop along fronts when

a significant density contrast exists

stationary front air on cold side flows

parallel to front

dryline

• boundary between moist gulf air and hot dry desert air in SW

• severe thunderstorms

identifying fronts, look for

• sharp temperature changes over a relatively short distance

• change in moisture content

• rapid shifts in wind direction

• pressure changes

• clouds and precipitation patterns

midlatitude cyclones 

low pressure, counter-clockwise, inward

midlatitude cyclones form

along jet stream between 30 - 70 latitude

cyclogenesis step 1

two air masses clash

• cold air north

• warm air south

cyclogeneses step 2

wave develops

• diverging airflow aloft 

• lifting of warm, moist air along warm front — clouds — instability

cyclogenesis step 3

cyclonic flow

• system moves east/NE

cyclogenesis step 4

mature stage

• central pressure lowest

• several isobars

• stronger cyclonic flow

• counterclockwise and inward winds

cyclogenesis step 5

occlusion

• fast moving cold front overtakes warm front 

• clouds and precipitation cover large area 

cyclogenesis step 6

storm dissipates

• cold air on both sides

• occasional new wave on westward end of trailing cold front

what produces a wave in a frontal zone

• topographic irregularities

• temperature contrast

• strong jet stream in flow aloft precedes formation of surface cyclone

wind shear in trough

cyclonic(cc)

wind shear in ridge

clockwise(ac)

middle and upper troposphere flow strongly influence

RATE at which pressure systems advance and DIRECTION they follow 

where do midlatitude cyclones form

• significant temp contracts in lower troposphere

• topographic irregularities

• middle US strip

midlatitude cyclones form 

downstream of an upper-level trough

air within a thunderstorm moves

vertically

• violent updrafts and downdrafts

4 elements of formation of thunderstorms

• warm, moist air

• unstable air

• lifting force

• vertical wind shear

where experiences thunderstorms year round

tropics

US experiences how many thunderstorms annually

100,000

air mass thunderstorms

• limited wind shear

• often form along shallow boundaries of converging surface winds

• mT in spring and summer

air mass cumulus stage

• warm, humid air rises

• cumulus cloud

• latent heat release — cloud grows

• updrafts suspend droplets

• towering cumulus 

air mass mature stage 

• droplets large enough to overcome resistance of updrafts — rain

• entrainment - dry air drawn in

• air descends in downdraft

• anvil head 

• lightning/thunder

ordinary dissipating stage

• updrafts weaken

• downdrafts cut off storms supply

storm is severe if

• produce hail-stones larger than 1 inch

• wind stronger than 95 kmh

• generate tornado

multi-cell thunderstorm

cool downdrafts leaving a mature and dissipating storm may offer relief from summer heat, but they may also force surrounding, low-level moist air upward.

mesoscale convective complex

many thunderstorms in circular cluster, common in great plains

most tornadoes move

northeast

MCC lifecycle

• group of afternoon air-mass thunderstorms

• strong low-level flow of very warm, moist air

• 12 hours - hail, tornadoes, flash floods

squall lines

narrow band of thunderstorms

• develop in warm section sector of midlatitude cyclone ahead of cold front

• combo of warm, moist air near surface and active jet stream

• boundary of dry line

• mature phase of MCC

supercell thunderstorm

single, powerful cell

• mid level rotation — mesocyclone — rotating updraft

• highest vorticity near updraft core

• most violent

supercells form under

• high CAPE

• capping layer

• cold air aloft

• large wind shear

max tornado winds can exceed

480 km per hour

pressure changes __ in 40 secs

100 mb

tornados

rotating column of air that extends down from a cumulonimbus cloud

tornado wind speed

• max winds can exceed 480 km/h

suction vortices

small intense whirls that orbit center of larger tornado

• 10 m diameter - die out in less than minute

tornadoes can form from

cold fronts, squall lines, tropical cyclones, supercells

less than what percent of all thunderstorms produce tornadoes

1

step 1 tornado

tilting wind shear causes the storm’s updraft to rotate

step 2 tornado: precondition

formation of low-level mesocyclone

step 3 tornado

rotation extends to the ground

• slowly rotating wall cloud

• vortex from the bottom forms a funnel cloud