GG101 Lecture 7: geo lesson 7
geo lesson 7
Tornadoes
• Result of large differences in atmospheric pressure over short distances that typically
occur during the thunderstorm event
• 4 stages
o Organization
o Mature o Shrinking o Rope
• Predictive conditions
o Northerly flow of marine tropical air from Gulf of Mexico >25 degrees o Cold dry air
from Canada
o Jet winds >240 km/h
• Locations
o More in US than in CAN
o Tornado Alley= south-central US
o CAN: central Sask and Alberta (Prairies), most common in June
Where they occur
• Hurricanes: Atlantic and Pacific strong tropical storms – after native Caribbean word for
an evil god of winds and destruction. Suatined winds of at least
• Typhoons: Pacific Oceans and north of the equator- Chinese word meaning scary wind
or wind from four direction
• Cyclones: South Pacific Ocean and Indian Ocean based on greek “coil of a snake” Process
Tropical Cyclones
• Large thunderstorm complexes rotating around an area of low pressure that has
formed over warm tropical or subtropical ocean water
• Low-intensity are called tropical depression and tropical storms
• High intensity are tropical cyclones and hurricanes
• Oceans warmer than 26 degree Celsius
• Most hurricanes start out as tropical disturbances = low pressure called a trough
• Tropical disturbances develop into a tropical depression – if winds increase and
rotate around the area of disturbed weather
