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Hurricanes: The Tempestuous Atmosphere (How a Hurricane Forms (3 main…
Hurricanes: The Tempestuous Atmosphere
General Circulation of the Atmosphere
The bigger the difference in pressure, the stronger the winds
The atmosphere transports heat from low latitudes to high latitudes
Coriolis effect
Northern hemisphere: veer to the right
Southern Hemisphere: veer to the left
Null at equator
bodies which are moving to different latitudes move along curved paths
The magnitude of the Coriolis effect increases with increasing speed of the moving bodies and increasing latitude
High pressure areas are associated with cold air that sinks, leading to fair weather and stable air
Low Pressure areas are associated with warm air that rises, leading to stormy weather and unstable air
Rotating air bodies: winds tend to blow into and around low pressure areas
Northern hemisphere: rising warm air creates a low pressure area, in the counterclockwise direction (cyclone). In contrast, sinking cold air creates a high pressure area, hence air flows away from the high pressure area, in the clockwise direction (anticyclone)
General Definition of a Hurricane
Large tropical cyclones
Convert heat of tropical ocean waters into strong winds and waves (can exceed 240 km/hr)
Surges of water can be pushed onshore, 6m above sea level
Heavy rains can cause floods
In Indian Ocean, they are called cyclones, in western pacific they are called typhoons
How a Hurricane Forms
3 main requirements:
Seawaters must be at least 27 C in the upper 60m
The air must be warm, humid and unstable
Must be weak, upper level winds, preferably blowing in the same direction as the developing storm
Begins with
tropical disturbance
, which is a low pressure zone with thunderstorms and weak surface winds
Becomes a
tropical depression
when surface winds strengthen and flow into low pressure core, rotating counterclockwise
Becomes a
hurricane
when winds flow up the central core and send warm moist air upwards, release of energy in the form of latent heat, which warms the air and leads to more updrafts
When the winds exceed 63km/hr it is a
tropical storm
When the winds exceed 119km/hr it is a
hurricane
Eye: centre of storm, can be calm and clear if winds are strong enough
Eye wall: cylinder-shaped area of spiralling upwards winds around the eye, holds the strongest winds
Right side of the hurricane: wind speed + travel speed of the hurricane
Left side of the hurricane: wind speed - travel speed of the hurricane
Geographic distribution
Form on west sides of oceans, where warm water is concentrated and ocean is wide enough
Develop between 5-20 latitude before travelling to mid and high latitudes
Do not form on the equator because Coriolis effect is zero, and cannot cross equator once formed
Assessing Hurricane Strength
Using Saffir Simpson Scale
Category 1: Wind damages trees, mobile homes
Category 2: Wind blows down trees, with major damage to mobile homes and some roofs
Category 3: Winds blow down large trees, strip foliage, destroy mobile homes, damage small buildings
Category 4: All signs are blown down, heavy damage to buildings, major damage to coastal buildings, flooding
Category 5: buildings suffer severe damage, especially those located less than 5m above the sea level and within 500m of shoreline; small buildings blown away
Naming system works according to six year cycle, alternating male and female names
Hurricane Hazards
Deaths are down, damages are up
Storm Surges
in the northern hemisphere the highest storm surge occurs 15-30km to the right of the path of the eye
Low atmospheric pressure causes water to mound up under the eye of the hurricane
Heavy rains and Inland flooding
After moving on land, no more water vapour is absorbed causing it lose strength
The precipitation of the massive volume of water in the dissipating hurricane can cause massive flooding, causing the majority of deaths
Hurricane-Related Evacuation Dilemmas
Almost 50 million people live in the Atlantic Ocean/Gulf of Mexico coastline region
72 hours are needed for evacuation, but the path of a hurricane is subject to change
Steps to minimize damage
Tougher building codes
Roofs: prevent liftoff by elimination of strengthening eaves, strapping roofs to walls, banning use of stapled asphalt roofing sheets plywood
Protection from wind-borne debris: shatter proof glass, shutters/plywood, securing loose objects outside
Land-use planning and development restrictions: lowlands for parks, farms, golf courses, not urban development