A2 GEOGRAPHY REVISIONHAZARDOUS ENVIRONMENTS

9.3 HAZARDOUS ENVIRONMENTSRESULTING FROM ATMOSPHERING

DISTURBANCES

KEYTERMSANDDEFINITIONSFujita Scale is a scale devised by Dr Theodore Fujita to measure damage done by tornadoes. It varies from T0 (winds less than 73 mph) with little damage, to F5 (winds greater than 261 mph) with ‘incredible damage’. Mesocyclone is a large-scale region of rotation, typically around 3–8 km in diameter and often found in the rear flank of a supercell. The circulation of a mesocyclone covers an area much larger than the tornado that may develop within it.Supercell tornado is a tornado associated with large, long-lived thunderstorms, possessing strong mid-level rotation. (Nonsupercell tornadoes are smaller but may still contain damaging winds in excess of 120 knots.)

KEYTERMSANDDEFINITIONSTornado is a violent, destructive weather system, with powerful rotating winds (up to 300 km/h). Tornadoes are intense low pressure systems, and their development depends on instability in the atmosphere, convergence and strong updrafts in the air. Vortex is a whirling and rising mass of air and cloud in a tornado. Hurricane is a tropical storm that forms over the North Atlantic, with winds over 74 mph (120 km/h). Tropical cyclone is the generic name to include hurricanes (North Atlantic), cyclones (Indian Ocean and the Bay of Bengal) and typhoons (Japan). A tropical cyclone is a low-pressure system commonly up to 600 km in diameter with wind speeds of up to 300 km/h (typically 160 km/h) and bringing up to 30–50 cm of rainfall.

TOPICSUMMARYHurricanes are intense hazards that bring heavy rainfall, strong winds and high waves, and cause other hazards such as flooding and mudslides. ● Hurricanes are the most violent and frequent hazard to affect many tropical regions. ● Damage is caused by high winds, floods and storm surges. ● The Saffir-Simpson Scale measures a hurricane’s intensity. ● The unpredictability of hurricane paths makes the effective management of hurricanes difficult. ● National governments can help prepare for a hurricane through risk assessment, land-use control, floodplain management and reducing the vulnerability of structures.

TOPICSUMMARYTornadoes are small and short-lived but highly destructive storms. ● Tornadoes consist of elongated funnels of cloud that descend from the base of a well-developed cumulonimbus cloud, eventually making contact with the ground beneath. ● Moisture, instability, lift and wind shear are the four key ingredients in tornado formation. ● The most destructive and deadly tornadoes occur from supercells; rotating thunderstorms with a well-defined low pressure system called a mesocyclone.

TOPICSUMMARYA tornado’s impact is threefold: first, the winds are often so strong that objects in the tornado’s path are severely damaged; second, strong rotational movement tends to twist objects from their fixing, and strong uplift can carry some debris upwards into the cloud; and third, the very low atmospheric pressure is a major source of damage. ● Although winds from the strongest tornadoes far exceed those from the strongest hurricanes, hurricanes typically cause much more damage individually and over a season, and over far bigger areas. ● The Fujita Scale relates tornado damage to the intensity of the wind. ● There are limited ways of dealing with a tornado other than staying indoors and staying under cover.

ADDITIONALWORK1. Outline the conditions necessary for the formation of hurricanes. 2. Outline the main hazards associated with hurricanes. 3. How does the impact of hurricanes vary with levels of economic

development? 4. To what extent is it possible to manage the impacts of hurricanes? 5. Explain the main hazards associated with tornadoes. 6. Describe, and suggest reasons for, the distribution of tropical storms

(hurricanes). 7. To what extent is it possible to manage the impacts of hurricanes and

tornadoes

SUGGESTEDWEBSITEShttp://coastal.er.usgs.gov/hurricanes/ivan/ for Hurricane Ivan impact studies. http://coastal.er.usgs.gov/hurricanes/jeanne/ for Hurricane Jeanne impact studies. http://coastal.er.usgs.gov/hurricanes/charley/ for Hurricane Charley impact studies. http://coastal.er.usgs.gov/hurricanes/charley/lidar.html shows the breach in the barrier islands caused by Hurricane Charley. http://coastal.er.usgs.gov/hurricanes/isabel/ for the effects of Hurricane Isabel