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