Violent Weather Tornadoes (diameter 0.25 km/0.16 miles) Thunderstorms: (diameter up to tens of km) Tropical Cyclones (600 km/375miles in diameter) 

Thunderstorm Definition: A storm that produces lightning and thunder. It frequently produces gusty winds, heavy rain and hail, may be tornadoes. Frequency: About 2000 thunderstorms are in progress at any given time, 45,000/day, 16,000,000/yr globally. ~100,000 T-storms/yr in the US. Types: Air-mass thunderstorms: Occur in mT air mass unequal heating of Earth surface causing the warm/moist air to rise. They are often short-lived with a preference in midafternoon. Sever Thunderstorms: criteria: wind speed reach >58mph or produce hail > 0.75in in diameter or generate a tornado. Formation: (i) unequal heating; (ii) other mechanisms upper lifting warm air Supercell Thunderstorm: A very powerful storm cell with clouds reaching 20 km in height, and diameter 20-50 km. Less than half of supercell T-storms produce tornados, but virtually all the strongest and most violent tornados are spowned by supercells. 2000~3000 in the US Cause most of the damage from T-storms. 2

Thunderstorms Figure 8.19

Thunderstorms Mapped in Space Figure 8.20

Hailstones Figure 8.21

Tornado Damage Storm track and damage left behind on May 3, 1999 45 miles southwest of Oklahoma City, killing 49 people! A violent wind storm that takes the form of a rotating column of air that extends down from a cumulonimbus cloud. It does not occur alone, but associated with sever T-storms (< 1%) or supercell T-storms (<50%). 6

Mesocyclone and Tornado Figure 8.22 7

Tornado Figure 8.22 8

Tornado Figure 8.22 9

Super Cell Tornado and Eye Wall Figure 8.23 10

Tornadoes Figure 8.24 11

Hurricanes Hurricane Isabel A whirling tropical cyclones with sustained wind speed 74 mph (119 kph). Size: 600 km (375 miles) in diameter Similar storms are known as Typhoon in western Pacific (China, Japan, Philippines etc), and as Cyclones in the Bay of Bengal and Arabian Sean. Figure 8.28

Hurricane Formation Figure 8.25 Tropical disturbance caused by the Easterly wave of air movement, the undulation of trade wind from east to west. Warm and moist air, thus sea surface temp (SST) > 27oC or 80oF. Rising of warm and moist air release tremendous latent heat, causing the air to rise more. Stronger Coriolis force, thus no hurricane below 5o latitudes. No hurricane above 15o latitude due to low SST. Figure 8.25

Profile of a Hurricane Figure 8.27

Hurricanes Gilbert and Catarina Figure 8.26

Tropical Cyclones Figure 8.26