Weather Systems I: Tropical Cyclones - shorstmeyer.com · tropical cyclone formation. Tropical...
Transcript of Weather Systems I: Tropical Cyclones - shorstmeyer.com · tropical cyclone formation. Tropical...
• Forces acting on a cloud/rain droplet. Terminal velocity. How does it change with cloud drop radius?
• Growth mechanisms for rain and snow
Review of last lecture
Summary of Precipitation processes:Condensation
Collision-coalescence
Bergeron Process
Rain Snow(can change to rain, sleet, or any other type of precipitation depending on underlying atmosphere
Riming/Aggregation
Genesis and tracks of tropical cyclones
– Different names: hurricanes, typhoons, cyclones– Genesis region generally in the tropics, especially between 5N-15N and
5S-15S.
164.4
8.95.4
2.5
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1. SST > 27 oC (Poleward of about 20o SST too cold for formation. Highest frequency in late summer to early autumn when water is warmest.)
2. Warm ocean mixed layer is thick enough to supply energy (this is why they weaken quickly upon landfall)
3. Unstable atmosphere with a moist lower/middle troposphere (central and western ocean basins)
4. Low vertical windshear (Otherwise upward transfer of latent heat disrupted)5. Coriolis force (hurricanes do not form between 5N-5S)6. Pre-existing low-level rotating circulations (tropical waves and other
disturbances)
Necessary environmental conditions for tropical cyclone formation
Tropical waves often cause tropical cyclone formation (e.g. African easterly waves,
Madden-Julian Oscillation)
Hurricane names2007 2008 2009 2010 2011 2012Andrea Arthur Ana Alex Arlene AlbertoBarry Bertha Bill Bonnie Bret BerylChantal Cristobal Claudette Colin Cindy ChrisDean Dolly Danny Danielle Don DebbyErin Edouard Erika Earl Emily ErnestoFelix Fay Fred Fiona Franklin FlorenceGabrielle Gustav Grace Gaston Gert GordonHumberto Hanna Henri Hermine Harvey HeleneIngrid Ike Ida Igor Irene IsaacJerry Josephine Joaquin Julia Jose JoyceKaren Kyle Kate Karl Katia KirkLorenzo Laura Larry Lisa Lee LeslieMelissa Marco Mindy Matthew Maria MichaelNoel Nana Nicholas Nicole Nate NadineOlga Omar Odette Otto Ophelia OscarPablo Paloma Peter Paula Philippe PattyRebekah Rene Rose Richard Rina RafaelSebastien Sally Sam Shary Sean SandyTanya Teddy Teresa Tomas Tammy TonyVan Vicky Victor Virginie Vince ValerieWendy Wilfred Wanda Walter Whitney William
• Total diameter: about 600km• Lifetime: up to a week or more• Make up: many thunderstorms arranged in pinwheel formation• Three components: 1. Central eye - clear skies, light
winds (25 km diameter)2. Eye wall - strongest winds (can be
200 mph), max precip. (up to 2500 mm/day)3. Spiral rainbands
• Cylonic inflow, anticyclonic outflow. Outflow creates cirrus shield that often obscures pinwheel structure
Horizontal Structure of tropical cyclones
Vertical cross-section: Structure
• Warm core - fueled by thermal energy - core warmer than outside at upper levels
Vertical cross-section: Feedbacks
1. Convergence-Convection (CISK): positive
2. Surface flux-Convection (WISHE): positive
3. Air-sea interaction: negative
Destruction caused by:• Hurricane-scale winds• Rainfall • Storm surge (winds blowing coast-ward + lower atmosphere pressure)• Fine-scale Tornadoes
Destruction most intense on right side of cyclone (wind + storm speed)
Tropical cyclone Destruction and Fatalities
Saffir-Simpson scale classifies hurricanes into five categories based on:
- central pressures- maximum sustained wind speeds- storm surge
Hurricane Intensity Scale
Summary
• Tropical cyclone genesis: 6 necessary conditions, 4 stages
• Tropical cyclone tracks• Tropical cyclone structure: 3 major
components, rotation direction of inflow and outflow, 3 feedbacks
• Tropical cyclone destruction: 4 reasons? Which side has the most intense destruction?
• Tropical cyclone forecast: track and intensity Currently which skill is better?