Cyclone
A cyclone is a large-scale atmospheric system with low central pressure, around which winds spiral inward — counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere due to the Coriolis Effect. Tropical cyclones (known as hurricanes in the Atlantic and typhoons in the Pacific) are intense, warm-core systems that derive energy from warm ocean water, while extratropical cyclones are cold-core systems associated with mid-latitude weather fronts. Cyclones bring heavy rainfall, strong winds, and storm surges, and are among the most destructive natural weather phenomena.
Key Formula
v_max = sqrt(ΔP / ρ)
LaTeX: v_{max} = \sqrt{\frac{\Delta P}{\rho}}
| Symbol | Meaning | Unit |
|---|---|---|
| v_max | Maximum wind speed (approximate) | m/s |
| ΔP | Pressure difference from periphery to centre | Pa |
| ρ | Air density | kg/m³ |
Worked Example
Problem
A tropical cyclone has a central pressure of 940 hPa and ambient pressure of 1010 hPa. Air density is 1.2 kg/m³. Estimate the maximum wind speed.
Solution
Step 1: ΔP = (1010 - 940) hPa = 70 hPa = 7000 Pa. Step 2: Apply formula: v_max = √(ΔP / ρ) = √(7000 / 1.2). Step 3: v_max = √5833 ≈ 76.4 m/s ≈ 275 km/h.
Answer
Maximum wind speed ≈ 76 m/s (275 km/h)
Tropical Cyclone Categories (Saffir-Simpson Scale)
| Category | Wind Speed (km/h) | Pressure (hPa) | Expected Damage |
|---|---|---|---|
| 1 | 119–153 | > 980 | Minimal — roof and tree damage |
| 2 | 154–177 | 965–979 | Moderate — roofs damaged |
| 3 | 178–208 | 945–964 | Extensive — structural damage |
| 4 | 209–251 | 920–944 | Extreme — most walls fail |
| 5 | > 252 | < 920 | Catastrophic — total destruction |
Interactive Tools
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Related Terms
Atmospheric Pressure
Atmospheric pressure is the force per unit area exerted by the weight of the overlying column of air in the atmosphere on any surface below it. At sea level, the standard atmospheric pressure is 101,325 Pa (or 1013.25 hPa / 1 atm), and it decreases with altitude as the mass of air above decreases. Atmospheric pressure differences drive wind and weather systems: low-pressure zones are associated with storms and clouds, while high-pressure zones bring clear, calm conditions.
Coriolis Effect
The Coriolis Effect is the apparent deflection of moving objects — including air and water — caused by Earth's rotation. In the Northern Hemisphere, objects are deflected to the right of their direction of motion; in the Southern Hemisphere, they are deflected to the left. This effect is responsible for the rotation of large-scale weather systems such as cyclones and anticyclones, as well as global wind patterns like the trade winds and westerlies.
Anticyclone
An anticyclone is a large-scale high-pressure atmospheric system in which air spirals outward from a central high-pressure zone — clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Descending air in an anticyclone suppresses cloud formation, bringing clear skies, dry conditions, and stable weather. While anticyclones are often associated with fair weather, they can also cause persistent temperature extremes — heatwaves in summer and cold spells or frost in winter — and contribute to air pollution by trapping pollutants near the surface.
From Greek "kyklos" (κύκλος) meaning "circle" or "wheel," coined by British meteorologist Henry Piddington around 1848 to describe the circular wind motion in such storms. The word was used in his book "The Sailor's Horn-Book for the Law of Storms" (1848).