Cyclones Lecture Notes

Overview

• Cyclones: Atmospheric phenomena driven by atmospheric dynamics.
• Two main types: Tropical Cyclones and Extratropical Cyclones.
• Named differently based on regions: Hurricanes, Typhoons, Cyclones.

Cyclone Characteristics

• Low-pressure systems: Form when warm, moist air rises, creating low pressure.
• Coriolis Effect: Causes systems to spin, creating the signature swirling motion.

Types of Cyclones

• Extratropical Cyclones (Mid-Latitude Cyclones):

  • Occur outside tropics, driven by interactions between different air masses.
  • Develop along fronts where cold and warm air masses meet.
  • Driven by horizontal temperature contrasts.
  • Occur year-round, impacting mid-latitude weather.
  • Can cause weather disruptions, travel delays, and intense storms.

• Tropical Cyclones:

  • Fueled by warm ocean water.
  • Transform into hurricanes or typhoons depending on region.
  • Driven by latent heat and ocean heat.

Extratropical Cyclone Formation

• Driven by interaction of cold and warm air masses along a frontal boundary.
• Creates instability, leading to low-pressure system development.
• Involve lifting of warm air, condensation, releasing latent heat, and creating stormy weather conditions.

Famous Extratropical Cyclones

• Halloween Nor'Easter (The Perfect Storm) of 1991:
  • Resulted from interaction of various meteorological conditions.
  • Caused severe coastal damage, high winds, and unprecedented wave heights.

Tropical Cyclone Formation

• Stages of development: Tropical Wave, Tropical Depression, Tropical Storm, and Hurricane.
• Requires warm ocean waters (≥26.5 °C), a Coriolis effect, surface disturbances, and low vertical wind shear.
• Positive feedback loop: Warm water evaporation fuels storm intensification.
• Dissipation when moving over cooler waters or land.

Anatomy of Hurricanes

• Eye: Calm, low-pressure center.
• Eyewall: Surrounds the eye, contains the strongest winds and rain.
• Rain Bands: Spiral outward from the center, causing heavy rains and sometimes tornadoes.

Hurricane Tracks and Influences

• Influenced by large-scale wind and pressure systems, such as trade winds and jet streams.
• Sea surface temperatures and El Niño/La Niña can affect hurricane intensity and frequency.

Example Hurricanes

• Hurricane Harvey (2017):
  • Category 4 at landfall, caused catastrophic flooding in Houston.
  • Highlighted the impact of stalling storms and heavy rainfall.

Hurricane Impacts

• Storm Surge: Abnormal rise in seawater during a storm.
  • Influenced by pressure, wind direction, storm speed, and tidal levels.
• Coastal flooding and heavy rainfall can extend impacts inland.
• Overwash can reshape barrier islands, impacting ecosystems.

Predicting Hurricanes

• Utilizes computer models, real-time data (satellites, buoys), and historical patterns.
• Includes numerical dynamic models and statistical models based on past storms.

Recent and Historical Context

• Global warming and Saharan dust influence hurricane intensity and frequency.
• Dendrochronology assists in studying past climate conditions and hurricane history through tree rings.