Week 11, Extreme Weather and Hurricanes Flashcards
Lightning
- Intrinsically linked to thunderstorms
- Exchange of charges between clouds/ground, heats atmosphere
- Electrical charge separation in thunderclouds due to updraft/downdraft collisions between super cooled water droplets and ice crystals
- Lightning strike is electrical discharge between opposite charge accumulations: cloud to cloud, within a cloud, cloud to ground.
What cause thunder
Lightning is fast and hot, expansion of atmosphere produces thunder
Stepped Leader
- Negative part of cloud wants to connect with positive charge in the ground. But it’s very high up.
- 50m jumps are used to make it to the ground.
- Lightning just needs to get within 50m of the ground for us to see the return stroke.
Hail
- Layered ice ball formed in thunderstorms with large vertical temperature contrasts and strong updrafts which cycle hailstones up and down through cloud until the weight of the stones overcomes the updraft and it falls to the ground.
- As the hail goes higher it gains additional ice layers.
Tornadoes
- We need an air mass that can spin. This is generated in North America by a jet stream moving West/East, the warm/humid air we get from the gulf of Mexico, and mid altitude cold winds moving to the SouthWest.
- These triple winds spin the air mass, prolonged and stable spinning forms a tornado.
- Also need a SUPERCELL THUNDERSTORM.
Supercell Thunderstorm
Wind shear tilts thundercloud into anvil shape, the separating of the warm updraft and cold downdraft allow for a more intense storm and a higher chance of tornadoes.
True or false, single cell storms will help themselves to dissipate and turn into a rain storm because the particles moving downward are making the storm weaker.
True.
What kind of structure is the most vulnerable to a tornado?
Mobile homes.
Hurricanes
- A form of cyclone
- Most deadly and destructive weather hazard
- Rotating low pressure systems with a warm core, the warm core provides the energy
- No Hurricanes at the equator
- Hurricanes form over warm water
What direction is the wind at the centre of a hurricane moving?
The wind is moving upward.
Hurricane Formation
- Driven by summer heating of tropical oceans
- Need water surface temperature of at least 27 degrees Celsius in the upper 60m of the ocean
- Nee warm, humid, unstable air (the source of energy)
- Need weak upper level winds so the air does not get dissipated, the build up without strong winds increase the humidity in the air
- Coriolis force from Earth’s rotation is crucial to the hurricane spin
4 forces balanced to produce cyclone flow
- Pressure gradient: force toward low pressure at the eye, constant pressure
- Coriolis effect: perpendicular to motion
- Centrifugal force: radially outward
- Friction: opposes motion
4 stages of hurricane formation
- Tropic disturbance: low pressure zone draws in surrounding thunderstorms, weak winds
- Tropical depression: strengthening winds, moisture condensing and sucking in more air and energy coming from vaporization
- Tropical storm
- Hurricane: forms the eye.
Hurricane Eye
- Generally circular region, 30-65km diameter, usually calm, clear weather at the low-pressure centre of the hurricane
- Surrounded by the EYE WALL
Eye Wall
Cylindrical area of upward spiralling winds, in opposite directions. Do not leave shelter during eye passages.
The main source of energy that fuels a hurricane is derived from ___ ___ from condensation. The ____ ____ just makes the hurricane spin. We need ___ _____ first to form the hurricane.
The main source of energy that fuels a hurricane is derived from latent heat from condensation. The coriolis force just makes the hurricane spin. We need warm water first to form the hurricane.
Where is the magnitude of the coriolis force at a maximum?
Near the poles.
Hurricane Decline
- Hurricanes decline when they reach landfalls or cold water because they are then cut off from their source of energy.
- Hurricanes can gain strength from weather systems at mid-altitudes.
Storm surges
Rise in sea level due strong onshore winds pushing on ocean surface causing water to pile up higher than ordinary sea level.
Hurricane Scale
Simpson Hurricane Scale
Category 1: minimal
Category 2: Extensive
Category 3: Catastrophic: Katrina
Floods
- An overflow or accumulation of an expanse of water that submerges land
- Affects more people worldwide than any other disaster
- Occur every month in every province/territory in Canada
- Spring is the most common time of year for flooding in Canada
Flood types: hydrometeorological floods
Cause by specific weather events:
- rainfall
- snowmelt
- rain on snow
- ice jam
