1. Where Do the Hurricanes Come From?

2. Radiation Vapor/Cloud/precipitation Shallow convection Boundary layer turbulence Mesoscale convective system Thunderstorm Tornado Heat wave Midlatitude cyclone Tropical cyclone Diurnal variation Madden-Julian Oscillation Tropical waves Annular modes 100,000yr100yr10yr1yr1mon1day1min1sec10 -15 sec Global Climate System Globe Continent State City Football field 1 mm 1  m Spatial Scale Time Scale 10 -4  m Composition Monsoon El Nino Biennial Oscillation Global warming Multi-decadal Oscillation Ice age Glacial cycle

3. The most common atmospheric circulation structure L H H L Heating Cooling or No Heating Imbalance of heating  Imbalance of temperature  Imbalance of pressure  Wind Radiation Convection Latent/Sensible Conduction Land/Ocean/Ice Feedback

4. Video: Hurricane Katrina The Storm that Drowned a City https://www.youtube.com/watch?v=974O47UmrII https://www.youtube.com/watch?v=974O47UmrII

5. Observation of tropical cyclones: Aircrafts (The hurricane hunters)

6. Observation of tropical cyclones: Satellite (1960s-Now)

7. Genesis and tracks of tropical cyclones –Different names: hurricanes, typhoons, cyclones –Genesis region generally in the tropics, especially between 5N-15N and 5S- 15S. –Western Pacific has the highest average number of tropical cyclones per year 16 4.4 8.9 5.4 2.5 3.4 4.3

8. 1.SST > 27 o C (Poleward of about 20 o 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 (do not form between 5N-5S where Coriolis force is too weak) 6.Pre-existing low-level rotating circulations (tropical waves and other disturbances) Necessary environmental conditions for tropical cyclone formation

9. Four stages of tropical cyclone formation Organized convection >200 km, >24 hours Vortex w/ max wind <38 mph Vortex w/ max wind 39-73 mph Vortex w/ max wind >74 mph

10. 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

11. Vertical Structure: Wind flow L H

12. Vertical Structure: Heating, temperature, pressure and wind Warm core - fueled by thermal energy - core warmer than outside at upper levels Maximum rainfall occur in the region of eye wall Minimum surface pressure occurs in the region of central eye Maximum winds occur in the region of eye wall L H

13. Vertical Structure: Feedbacks 1.Convergence-Convection (CISK): positive 2.Surface flux-Convection (WISHE): positive 3.Air-sea interaction: negative Sea surface temperature

14. The most common atmospheric circulation structure L H H L Heating Cooling or No Heating Imbalance of heating  Imbalance of temperature  Imbalance of pressure  Wind Radiation Convection Latent/Sensible Conduction Land/Ocean/Ice Feedback

15. Saffir-Simpson scale classifies hurricanes into five categories based on: - central pressures (ended in 1990s) - maximum sustained wind speeds (used now) Hurricane Intensity Scale Categories 3, 4, 5 are collectively called major hurricanes. They account for 21% of hurricane landfall in U.S., but cause 83% of the damage.

16. Hurricane Landfall

17. Destruction caused by: Hurricane-scale winds (>74 mph) Rainfall (10 in/day) 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

18. Trends and variability in Hurricane Activity Destructive hurricane seasons result in public awareness and general concern that hurricane activity is related to global warming. There is evidence for an increase trend in major Atlantic hurricanes. The Atlantic Multidecadal Oscillation (AMO) is a 60yr oscillation in water temperatures and is a major factor in the increase in Atlantic hurricane activity.

19. Summary Tropical cyclone genesis: Western Pacific has the highest averaged number per year. 6 necessary conditions. 4 stages. Tropical cyclone structure: 3 major components, rotation direction of inflow and outflow, location of maximum wind and rainfall, 3 feedbacks Tropical cyclone intensity scale. Category 1: 74mph, category 5: 155mph Tropical cyclone destruction: 4 reasons? Which side has the most intense destruction? Trends and variability in tropical cyclone activity