weather fronts and cyclones. weather systems recurring atmospheric circulation patterns movement of...

Weather Fronts and Cyclones

Weather Systems

• Recurring atmospheric circulation patterns

• Movement of cyclones and anti-cyclones

• Range in size from km to 1000s of km

Air Masses

• North America gets 5 types of air masses

• Defined by areas of origination

• Highly variable in terms of temperature and moisture

Weather Fronts

Cold Fronts• Cold Front- cold air mass

advances on a warmer air mass

- Difference in density causes warm air to rise

- Blue line with triangles in direction of motion

Cold Front Weather• Steep vertical face• Result: Heavy rain or

snow • Long line of

thunderstorms• Atm pressure tends to

increase

Warm Fronts

• Warm air advances on cooler air

• Warm air rises on a “ramp” over the cool air

• Red line with half-circles in direction of motion

Warm Front Weather

• Slower and less steep than cold front

• Rising air forms stratus clouds and results in ppt

• Atm pressure tends to decrease

Stationary Front• A non-moving division

between air masses

• Shown as combination of warm and cold fronts

Occluded Front• One front overtakes

another

• Cold front typically faster moving

• Can have warm and cold occluded fronts

Occluded Front Weather

• Lifting of warm air by fast moving cold air mass creates precipitation

Traveling Cyclones

• Wave (Extratropical) Cyclones

• Tropical Cyclones

• Tornados

Wave Cyclone

• Wave cyclone over the midwest US

• Warm winds out of the SW, cold winds out of the NW

• Notice the difference in precipitation with the warm and cold fronts

Wave Cyclone

• Air moves counter-clockwise around low pressure

• System moves from west to east

Wave Cyclone• Wave cyclones often

originate in the NW and move east

• Storm evolves as it travels East

Wave Cyclones

• Wave cyclone over the great lakes

• Typical “comma” shape

Wave Cyclone

• Need divergence aloft to draw air up from the earth’s surface and keep the cyclone alive

• Convergence above the trailing anti-cyclone

Mid-latitude cyclones over North America

Tropical Cyclones

• What are the conditions necessary to form a tropical storm or hurricane?

Unstable Atmosphere

Warm Ocean

Consistent Winds

Coriolis Force (>500 km from equator)

Tropical Cyclones

• 3 parts:1) Eye – fundamental property of rotating fluids,

strong downdrafts2) Eye wall – strongest winds, updrafts and downdrafts3) Rain bands – intense areas of convective ppt

Hurricane Formation

Hurricane Structure

Studying Hurricanes

• How do forecasters make predictions about the hurricane’s path and intensity?

Air force reserve base in Biloxi, Miss houses WC-130 aircraft that fly into the center of hurricanes

stadium-effect inside the eye of Hurricane Katrina

Dropsonde to measure pressure in the eye – what does this tell you?

Pressure in the eye = 902 millibars (Katrina)4th lowest pressure ever measured in the Atlantic basin

Intense Convection

Organized system of cloud and thunderstorms with well-defined circulation; wind to 62 km/hr

More well-defined circulation; wind to 117 km/hr; storm is named

Intense system with “eye” feature wind sustained at > 118 km/hr (75 mph)

Atlantic Names

2002 2003 2004 2005 2006 2007ArthurBerthaCristobalDollyEdouardFayGustavHannaIsidoreJosephineKyleLiliMarcoNanaOmarPalomaReneSallyTeddyVickyWilfred

AnaBillClaudetteDannyErikaFabianGraceHenriIsabelJuanKateLarryMindyNicholasOdettePeterRoseSamTeresaVictorWanda

AlexBonnieCharleyDanielleEarlFrancesGastonHermineIvanJeanneKarlLisaMatthewNicoleOttoPaulaRichardSharyTomasVirginieWalter

ArleneBretCindyDennisEmilyFranklinGertHarveyIreneJoseKatrinaLeeMariaNateOpheliaPhilippeRitaStanTammyVinceWilma

AlbertoBerylChrisDebbyErnestoFlorenceGordonHeleneIsaacJoyceKirkLeslieMichaelNadineOscarPattyRafaelSandyTonyValerieWilliam

AndreaBarryChantalDeanErinFelixGabrielleHumbertoIngridJerryKarenLorenzoMelissaNoelOlgaPabloRebekahSebastienTanyaVanWendy

Hurricane Names – from World Meteorological Organization

Name Year Name Year

Agnes 1972 Eloise 1975

Alicia 1983 Fifi 1974

Floyd 1999

Allen 1980 Flora 1963

Andrew 1992 Fran 1996

Anita 1977 Frederic 1979

Audrey 1957 Georges 1998

Betsy 1965 Gilbert 1988

Beulah 1967 Gloria 1985

Bob 1991 Gracie 1959

Camille 1969 Hattie 1961

Carla 1961 Hazel 1954

Carmen 1974 Hilda 1964

Carol 1965 Hortense 1996

Celia 1970 Hugo 1989

Cesar 1996 Inez 1966

Cleo 1964 Ione 1955

Connie 1955 Janet 1955

David 1979 Joan 1988

Keith 2000

Diana 1990 Klaus 1990

Lenny 1999

Diane 1955 Luis 1995

Donna 1960 Marilyn 1995

Dora 1964 Mitch 1998

Edna 1968 Opal 1995

Elena 1985 Roxanne 1995

Retired Hurricane Names

Tropical Storms

• Given what we know about the formation of tropical storms:

Where would they originate?

When would they occur?

Tropical Storm Life Span

Tropical Storm Life Span

Tropical Storm Life Span

• How do tropical storms and hurricanes dissipate?

1) Cooler ocean waters

2) Landfall (no warm water source)

3) Land is rough surface, drag weakens convection

Hurricanes and Climate Change

• How can we expect the number and intensity of hurricanes to change if climate is warming?

Sea Surface Temperatures

Webster et al, 2005

Number of Hurricanes and Tropical Storms

Hurricanes in Different Regions of the World

Hurricane Intensity

Hurricane Power

Power Dissipation Index (PDI):

maximum wind x life span = energy expended

Hurricane Damage

• Why is hurricane damage increasing with time?

• Hurricane Andrew (1992) was most expensive natural disaster in history - $25 million

Effects of Katrina

Flooding and Oil Spills

Tornados

Tornado Formation

1) Form in severe thunderstorms called supercells

2) Boundary of cold, polar air and warm moist tropical air

3) Need highly unstable atmosphere which causes rapid uplift

Tornado Formation

Supercell Formation – Twisting Thunderstorm

Which way do tornados rotate?

Large Hail Formation

Tornado Facts

1) Short lived (similar to thunderstorms)

2) 75% occur in United States

3) 1000 per year on earth

Tornado Occurrence