Cyclones and Hurricane Formation

Cyclones

• Cyclones are low-pressure systems where air rises in the center and spirals inward in a counterclockwise direction in the Northern Hemisphere (clockwise in the Southern Hemisphere).
• Cyclones are associated with stormy weather because the rising air cools, leading to condensation and precipitation.
• They are also called hurricanes, cyclones, or typhoons depending on location.

Hurricane Formation

• Tropical cyclones, also called hurricanes, cyclones, or typhoons depending on location, are low-pressure circular storms that form over warm ocean water with temperatures above 26.5 °C.
• Hurricanes get their energy from the ocean's heat and convert this heat energy into the storm's mechanical spinning motion.
• Easterly waves are one trigger that can lead to hurricane formation. They are waves in the jet stream that flows from east to west in the Sahara desert.
• Small disturbances, such as dust devils, can grow into large eddies, which then form clusters of thunderstorms that move west across Africa and into the warm Atlantic Ocean.
• These thunderstorms can become organized and rotate around each other, ultimately developing into a hurricane.

Hurricane Impacts

• A tropical cyclone track is the path a tropical cyclone follows.
• Storm surge occurs when a hurricane makes landfall. Strong winds push water toward the shore, causing coastal flooding.
• Cyclone families are groups of cyclones that form and move together.

Vorticity

• Vorticity refers to how fast a cyclone or anticyclone spins.

Traveling Cyclones

• Three types of traveling cyclones include:

  Mid-latitude Cyclones

  • These storms form along the polar front, where cold polar air meets warmer air from lower latitudes.

  Tropical Cyclones

  • Tropical cyclones are low-pressure circular storms that form over warm ocean water with temperatures above 26.5 °C.

  Tornadoes

  • Rapidly rotating columns of air that extend from the base of a thunderstorm to the ground.

Mid-Latitude Cyclones

• Mid-latitude cyclones are the dominant weather systems in mid and high latitudes, forming along the polar front and moving from west to east.
• They are associated with fronts (boundaries between air masses).

Anticyclones

• Anticyclones are high-pressure systems where air sinks in the center and spirals outward in a clockwise direction in the Northern Hemisphere (counterclockwise in the Southern Hemisphere).
• Anticyclones are associated with fair weather because the sinking air warms and inhibits cloud formation.

Weather Systems/Air Masses

• A weather system is a specific set of meteorological conditions occurring over a particular area at a given time.
• An air mass is a large volume of air with relatively uniform temperature and humidity.
• Air masses are named based on their source region, which determines their characteristics.
  • For example, a tropical continental air mass originates over the Sahara Desert and is hot and dry.
  • A polar continental air mass comes from the North Pole and travels over land, bringing cold temperatures and potentially snowstorms.
  • A maritime air mass that travels across the Atlantic Ocean to Britain will bring a mix of sunshine, hail, sleet, rain, and snow.

Fronts

• Fronts are boundaries between air masses of different temperatures.
• They influence cyclone formation because the convergence of air along a front can create circulation.
• The interaction of cold and warm fronts can lead to the development of mid-latitude cyclones.

Thunderstorms

• Thunderstorms are convective storms with vertical motion that produces lightning and thunder.
• Convection refers to the process of warm air rising and cooler air sinking.
• Cumulonimbus clouds are associated with thunderstorms.
• Thunderstorms form when warm, moist air rises, cools, and condenses, forming cumulonimbus clouds.
• The updrafts within these clouds can become strong enough to create lightning.

Air-Mass Thunderstorms

• Air-mass thunderstorms are isolated storms that develop from daytime heating of the land surface
• They typically occur in the spring and summer afternoons when the environmental lapse rate increases due to heating, leading to unstable air and the formation of cumulus clouds.
• These storms are usually short-lived.

Severe Thunderstorms

• Severe thunderstorms are characterized by high winds, large hail, or the presence of tornadoes.
• They have organized convection cells and strong wind shear, which contributes to their longer lifespan.

Microburst

• A microburst is a strong downdraft from a severe thunderstorm that produces a sudden, localized burst of high winds at the surface.
• Microbursts form when rain evaporates below a thunderstorm, cooling the air and causing it to descend rapidly.

Mesoscale Convective Systems and Complexes

• Mesoscale convective systems (MCSs) are collections of thunderstorms that act as a single weather system.
• They are larger and longer-lasting than air-mass thunderstorms.
• Mesoscale convective complexes (MCCs) are a type of MCS that is round or oval-shaped.
• MCCs are common in the Plains and Midwest and are known for heavy rainfall.

Squall Line

• A squall line is a line of thunderstorms that can form along a cold front.
• They are associated with strong winds and heavy precipitation.

Thunder and Lightning

• Thunder is the sound produced by the rapid heating and expansion of air surrounding a lightning bolt.
• Lightning is an electrical discharge that occurs within a cloud, between clouds, or between a cloud and the ground.
• Lightning forms when ice particles within a cumulonimbus cloud collide, creating static electrical charges.
• The separation of charges creates an electric field, and when the electrical potential difference becomes large enough, lightning occurs.
• Cloud-to-ground lightning is a type of lightning that strikes the Earth's surface

Tornado

• A tornado is a violently rotating column of air that extends from the base of a thunderstorm to the ground.
• Tornadoes are characterized by extremely low pressure and high wind speeds.
• A mesocyclone is a rotating updraft within a thunderstorm that can lead to tornado formation.
• The "Perfect Storm" of 1991 was an unnamed hurricane that merged with a storm from inland Canada, creating a powerful and destructive extratropical cyclone.
• The Texas Freeze of 2021 was caused by an unusually large expansion of the polar vortex, a low-pressure system of cold air normally located over the Arctic.
• This expansion allowed the vortex to dip much farther south than usual, bringing frigid temperatures and winter storms to Texas.
• The extreme cold overwhelmed Texas's power grid, which was not designed to handle such low temperatures, leading to widespread blackouts and significant disruptions.

The Polar Vortex

• The polar vortex is a low-pressure system of cold air normally located over the Arctic.
• It can expand and dip farther south, bringing frigid temperatures and winter storms to lower latitudes.
• During winter, the vortex can expand and be pulled down in latitude because the sun is sitting over 23.5 degrees south of the equator, usually bringing it down to Canada.

Climate Change and Hurricanes

• The warmth of the ocean increases hurricane intensity.
• The frequency of extreme hurricanes increasing with climate change.
• Climate modeling shows changes in the amount of Category 4-5 hurricanes.
• The amount of rain during hurricanes is increasing.

Atmospheric Rivers

• Atmospheric rivers are long, narrow bands of concentrated water vapor that produce major amounts of rainfall.
• They are responsible for over half of California's yearly precipitation.
• They usually cause rainfall along the California coastline.
• Atmospheric rivers create even more additional rain and snow as they travel inland towards the Sierra.
• Climate change is intensifying atmospheric rivers.

Why are we seeing more polar vortexes even with climate change?

• The poles are warming faster than the mid-latitudes, creating an extreme temperature difference between the two.
• This makes our jetstream weaker and wavier, allowing the polar vortex to dip farther south.

The Texas Freeze

• The Texas Freeze of 2021 was caused by an unusually large expansion of the polar vortex, a low-pressure system of cold air normally located over the Arctic.
• This expansion allowed the vortex to dip much farther south than usual, bringing frigid temperatures and winter storms to Texas.
• The extreme cold overwhelmed Texas's power grid, which was not designed to handle such low temperatures, leading to widespread blackouts and significant disruptions.

Texas Freeze 2021 Takeaways

• Aging infrastructure
• Rethinking energy infrastructure
• Building in grid resilience to combat changing climate conditions
• Better outage management

The Troposphere

• The troposphere is the lowest layer of the Earth's atmosphere.
• As an object rises in the troposphere, it cools.

Air-Mass Thunderstorms

• Warm, moist air masses result from daytime heating of the land surface.
• The environmental lapse rate rises due to heating.
• These storms are usually short-lived as the air cools and mixes.

Severe Thunderstorms

• They have organized convection cells and strong wind shear, which contributes to their longer lifespan.

Thunder

• Thunder is from the rapid expansion of air surrounding a lightening bolt.
• The heat from the electricity of the return stroke raises the temperature of the surrounding air to around 27,000C.
• The rapid rise in temperature creates a rapid increase in the air pressure as well, rising to 10 to 100 times the normal atmospheric pressure.
• As the heated air expends, the pressure drops, the air cools, and it contracts.

Thunderstorms

• Thunderstorms are rain showers with lightning and thunder.
• There are four types: single-cell, multi-cell, squall line, and supercell.
• They are important for regulating the electrical balance of the planet.
• They are a hazard to humans.
• Lightning is a giant spark occurring between a cloud and the ground, or within a cloud itself.
• It is caused by a buildup of electrical charge within clouds, associated with how moisture/ice is moving within the cloud.
• It is still not fully understood.
• Lightning generates a huge amount of energy/heat.
• Temperatures reach up to 30,000°C.
• The greatest concentrations of lightning strikes are in Central Africa, the Himalayas, and South America.
• It occurs within the downdrafts of thunderstorms.
• The flash after a lightning strike is actually composed of thousands of tiny return strikes, back upwards into the cloud.
• Thunderclap sound is due to excessive pressure expansion during return strikes, at supersonic rates.
• In the US, lightning occurs most often in Florida due to its hot, moist climate.

Tornadoes

• Tornadoes are rapidly rotating columns of air from the base of a thunderstorm touching the ground.
• They can also occur in tropical cyclones (can be a water spout).
• The base of the funnel is 100-450 meters across.
• The funnel is dark because of water droplets, dust, and debris.
• Wind speed can be greater than 100 m/s.
• The average wind speed is ~50 m/s.
• There is extreme low pressure in the center of the circulation.
• Most, but not all, rotate counterclockwise (CCW).
• Tornadoes tend to happen in the spring and summer due to heating and rising air.
• They form most frequently over the Midwest in Tornado Alley because the formation conditions are ideal there.
• Tornadoes are a huge threat to life and property.

How Tornadoes Form:

• They begin with a thunderstorm, specifically supercells with high-force winds.
• They also need rising air (warm with condensation) and a lot of moisture at the cloud base to feed off of, which causes a vortex ("mesocyclone") to start forming.
• When the vortex touches the ground, it becomes a tornado.

Tornado Types:

• Supercell Tornadoes: Form within supercell thunderstorms. Formation is different, and they roll along the ground.
• Non-Supercell Tornadoes: Smaller and weaker, form within smaller non-supercell storms. They roll perpendicular to super-cell tornadoes.

Waterspouts and Landspouts:

• They begin with cool high-pressure air and warm, low-pressure air.
• Wind picks up and travels cyclically, causing a vortex to form.

Tornado Rating:

• All tornadoes are rated on a system known as the "Enhanced Fujita" scale (EF scale).
• The scale ranges from EF0 to EF5.
• An EF5 tornado in Oklahoma was particularly devastating.

Desert Locusts:

• They are found in North Africa and South Asia.
• They lay eggs underground.
• During dry weather they act normally.
• During the stormy season, when there is abundant vegetation available to eat, their behavior changes dramatically.
• They release a hormone from their leg hair that causes them to swarm together.
• They also release more pheromones from their poop.
• This swarming behaviour can result in a plague upon crops.
• The swarms create a "living tornado" that can destroy crops and travel easily. They can even form rafts to travel across the Atlantic Ocean.
• A plague can last up to a decade.
• Their habitat is in some of the poorest countries in the world, where people rely largely on their own food production.
• Desert locust plagues threaten 10% of humanity.
• Humans can use pesticides, a fungus that is toxic only to insects, satellite imaging, etc. to fight them.
• Climate change is making locust storms even harder to predict.