Cyclone

Cyclone
Name	Cyclone
Caption	A tropical cyclone as seen from NASA's Aqua satellite.
Formation	Over warm ocean waters or along weather fronts.
Season	Varies by basin; commonly summer and autumn.
Effect	Storm surge, flooding, high winds, tornadoes.

Cyclone. In meteorology, a cyclone is a large-scale air mass that rotates around a strong center of low atmospheric pressure. These systems are characterized by inward-spiraling winds that rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, a pattern governed by the Coriolis effect. Cyclones are the engine for most significant weather phenomena, ranging from localized thunderstorm complexes to planet-spanning extratropical cyclones, and are primarily classified by their thermal characteristics and geographic location.

Etymology and terminology

The term originates from the Greek word *kyklōn*, meaning "moving in a circle, whirling around." It was first used in a modern meteorological context by Henry Piddington in the mid-19th century. Terminology varies globally; such systems in the Atlantic Ocean and northeastern Pacific Ocean are called hurricanes, while in the northwestern Pacific, they are known as typhoons. In the Indian Ocean and South Pacific, the generic term tropical cyclone is commonly used. The World Meteorological Organization maintains standardized lists of names for these storms through regional bodies like the Regional Specialized Meteorological Centre.

Formation and development

Cyclogenesis, the development of a cyclone, requires specific conditions. For tropical cyclones, these include warm ocean waters (typically above 26.5°C), atmospheric instability, high humidity in the mid-troposphere, and pre-existing low-level disturbance, often from waves like the African easterly wave. A key driver is the release of latent heat from condensing water vapor, which fuels the storm's updrafts. For extratropical cyclones, formation typically occurs along the polar front due to temperature contrasts, a process described by the Norwegian cyclone model. The intensification of these systems is often analyzed using parameters like potential vorticity.

Types and classification

Cyclones are broadly categorized by their core structure and energy source. The primary types are tropical cyclones, extratropical cyclones, and subtropical cyclones. Tropical cyclones are warm-core systems with symmetric wind fields and are further classified by wind speed: systems below 39 mph are tropical depressions, those between 39-73 mph are tropical storms, and those exceeding 74 mph attain hurricane, typhoon, or cyclone status. The Saffir–Simpson scale categorizes Atlantic hurricanes from Category 1 to Category 5. Extratropical cyclones are cold-core, frontal systems common in the mid-latitudes, while mesocyclones are smaller-scale rotations within supercell thunderstorms that can spawn tornadoes.

Impacts and effects

The primary hazards include destructive high winds, torrential rainfall leading to inland flooding, and a storm surge that can inundate coastal regions, as catastrophically demonstrated during Hurricane Katrina in New Orleans. Secondary effects include landslides, widespread power outages, and the outbreak of waterborne diseases. Economically, cyclones can cause billions in damage, severely impacting infrastructure, agriculture, and insurance markets, as seen after events like Typhoon Haiyan in the Philippines and Cyclone Idai in Mozambique. The National Hurricane Center and similar agencies issue watches and warnings to facilitate public preparedness and evacuation.

Notable cyclones

Historically significant cyclones have shaped disaster preparedness policies. The 1970 Bhola cyclone, which struck East Pakistan (now Bangladesh), is among the deadliest on record. In the Atlantic basin, Hurricane Mitch devastated Central America in 1998, while Hurricane Andrew ravaged Florida in 1992. The Pacific Ocean has experienced immense storms such as Typhoon Tip, the largest recorded, and Super Typhoon Yolanda. In the Southern Hemisphere, Cyclone Tracy destroyed much of Darwin in 1974, and more recently, Cyclone Gabrielle caused significant damage in New Zealand.

Observation and forecasting

Modern observation relies on a network of geostationary satellites like GOES and Himawari, reconnaissance aircraft such as the WC-130J, Doppler radar networks, and oceanic data buoys. Forecasting is conducted by centers including the National Hurricane Center, the Japan Meteorological Agency, and the India Meteorological Department. Numerical weather prediction models, including the Global Forecast System and the European Centre for Medium-Range Weather Forecasts model, simulate storm track and intensity. Despite advances, forecasting rapid intensification, as occurred with Hurricane Patricia, remains a significant challenge for meteorologists.

Category:Tropical cyclone Category:Meteorology Category:Natural hazards