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 downdrafts 2)Eye wall – strongest winds, updrafts and downdrafts 3)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 Arthur Bertha Cristobal Dolly Edouard Fay Gustav Hanna Isidore Josephine Kyle Lili Marco Nana Omar Paloma Rene Sally Teddy Vicky Wilfred Ana Bill Claudette Danny Erika Fabian Grace Henri Isabel Juan Kate Larry Mindy Nicholas Odette Peter Rose Sam Teresa Victor Wanda Alex Bonnie Charley Danielle Earl Frances Gaston Hermine Ivan Jeanne Karl Lisa Matthew Nicole Otto Paula Richard Shary Tomas Virginie Walter Arlene Bret Cindy Dennis Emily Franklin Gert Harvey Irene Jose Katrina Lee Maria Nate Ophelia Philippe Rita Stan Tammy Vince Wilma Alberto Beryl Chris Debby Ernesto Florence Gordon Helene Isaac Joyce Kirk Leslie Michael Nadine Oscar Patty Rafael Sandy Tony Valerie William Andrea Barry Chantal Dean Erin Felix Gabrielle Humberto Ingrid Jerry Karen Lorenzo Melissa Noel Olga Pablo Rebekah Sebastien Tanya Van Wendy Hurricane Names – from World Meteorological Organization

NameYearNameYear Agnes1972Eloise1975 Alicia1983Fifi1974 Floyd1999 Allen1980Flora1963 Andrew1992Fran1996 Anita1977Frederic1979 Audrey1957Georges1998 Betsy1965Gilbert1988 Beulah1967Gloria1985 Bob1991Gracie1959 Camille1969Hattie1961 Carla1961Hazel1954 Carmen1974Hilda1964 Carol1965Hortense1996 Celia1970Hugo1989 Cesar1996Inez1966 Cleo1964Ione1955 Connie1955Janet1955 David1979Joan1988 Keith2000 Diana1990Klaus1990 Lenny1999 Diane1955Luis1995 Donna1960Marilyn1995 Dora1964Mitch1998 Edna1968Opal1995 Elena1985Roxanne1995 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

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