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Understanding Cyclones and Their Impact

Apr 8, 2025

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.