Week 8

Question 1

Thunderstorms

Answer 1

• Smallest cyclonic storm
• Form when there is moisture and instability in the atmosphere, driven by some lifting mechanism
• In Ontario, most of the atmospheric moisture comes from the Great Lakes
• Most atmospheric instability occurs at or near the boundaries of warm and cold air masses

Question 2

Lifecycle of a Thunderstorm

Answer 2

Towering Cumulus Stage
Mature Stage
Dissipating Stage

Question 3

Towering Cumulus Stage

Answer 3

A lifting mechanism forces warm air up to produce a ~6km-high cumulus cloud

Question 4

Mature Stage

Answer 4

The produced cloud can suddenly grow in size, up to 18km-high; air movement is tumultuous, with strong updrafts holding back large amounts of rain and hail

Question 5

Dissipating Stage

Answer 5

As the moisture in the cloud is dropped, the storm enters the Dissipating Stage, where upward moisture supply has been removed and the storm will weaken

Question 6

Three main types of thunderstorms

Answer 6

Multi Cell Storms
Squall Line Storms
Supercell Storms

Question 7

Multi Cell Storms

Answer 7

The combination of many smaller thunderstorm cells to produce a larger, violent storm that can last for hours

Question 8

Squall Line Storms

Answer 8

As a weather front moves forward, it can produce a line of storms 100+ km long; sudden rain produces a ‘gust front’, lifting more moisture to feed the storm

Question 9

Supercell Storms

Answer 9

Gigantic, long-lasting single cells responsible for most of the tornadoes and most damaging weather in North America each year

Question 10

Hurricanes

Answer 10

• A hurricane is a type of Tropical Cyclone
• A severe cyclonic tropical storm in the North Atlantic Basin
• Originates from the tropical trade winds, between 5°N - 20°N
• Rotates counterclockwise, with a central ‘eye’ attaining minimum wind speeds of 119km/h
• In the Central Pacific, tropical cyclones are called ‘typhoon’
• In the South Indian Ocean, tropical cyclones are called ‘cyclone’

Question 11

Hurricane Hazards

Answer 11

• Heavy rain, damaging winds, and strong waves
• Storm Surge is the result of strong waves moving in-land, damaging cars, trees, and infrastructure

Question 12

Hurricane Formation

Answer 12

• These storms begin with a disturbance in westward winds over the warm ocean 26°C
• As the water vapour rises, it condenses in the troposphere releasing a large amount of latent heat energy
• With strength, the storm is given the names, ‘tropical wave’ or ‘tropical storm’, with ‘hurricane’ being the strongest

Question 13

Production of Cyclones

Answer 13

• A mature hurricane has spiraling bands of high wind and torrential rain surrounding the eye
• These bands of rain are known as Rainbands and rotate counterclockwise, while the overlying Cirrus Overcast rotates clockwise

Question 14

Two velocities of a hurricane

Answer 14

• Hurricane-Wind Velocity
• Storm-Centre Velocity

Question 15

Hurricane-Wind Velocity

Answer 15

The speed of the wind inside the storm, travelling counterclockwise around the eye; Range: 119 – 252+ km/h

Question 16

Storm Center Velocity

Answer 16

The travel speed of the entire storm across the Earth, being pushed by outside regional winds; Range: 8 – 100 km/h

Question 17

Hurricane Andrew (1992)

Answer 17

• Hurricane Andrew made landfall south of Miami, producing destructive storm surge and sustained winds
• 4/5 on Scale
• 50 deaths, US$25 billion Damages

Question 18

Hurricane Andrew Importance

Answer 18

• Forced scientists to rethink how Cyclonic storms worked
• Andrew did not produce the strongest winds around the eye like other hurricanes, leading to the postulation of Spin-Up Vortices
• These are small, intense vortices of wind developed within the winds of a storm, and produce the highest wind speeds of a hurricane
• The presence of vortices would explain the seemingly selective damage noticed in Homestead following the disaster

Question 19

Hurricane Katrina (2005)

Answer 19

• The 6th strongest hurricane ever recorded
• 1,604 people, the storm caused the greatest damage ever, estimated at ~US$75 billion
  -Picked up immense strength in the warm Gulf of Mexico, intensifying from a Category 3 to Category 5 (max of scale!) overnight
• Huge storm surges were resultant along the Mississippi-Louisiana coast, with measured winds reaching 280km/h
• Upon making landfall in Louisiana, the storm was measured as 190km wide, with 120-205km/h winds

Question 20

Predicting Storms

Answer 20

• There are no easily-measurable metrics to determine whether a storm will develop or not – there is usually great uncertainty over the potential of a cyclone to develop into a cyclonic storm
• The National Hurricane Center tracks tropical storms forming and/or occurring near the US coast

Question 21

Project Stormfury

Answer 21

• An ambitious US endeavor, Project Stormfury aimed to weaken storms before they make landfall to mitigate the damage incurred
• The idea was that if a airplane flew over a hurricane, it would be able to “seed” the storm with either silver iodide or dry ice
• The goal of adding these seeds was to both increase the freezing temperature of water and to produce ice crystals within the storm
• The idea of growing ice crystals was leaning on the hope that this change in state would release some of the stored latent heat energy driving the storm
• Even a reduction of ~10% the storm’s intensity would be a huge achievement
• After trying to seed 4 hurricanes, the project was abandoned due to lack of perceivable evidence