Cyclones are huge revolving storms caused by winds

Cyclones are huge revolving storms caused by winds blowing around a central area of low atmospheric pressure. Wind blows anti-clockwise in the NH and clockwise in the SH Typhoon- termed used when it formed in the Pacific ocean Hurricane- termed used when it formed in the Atlantic ocean Cyclone- termed used when it formed in the southern ocean and Indian ocean Willy-willy- termed used in Australia

� Classification of cyclone according to synoptic scale � 1. Polar cyclone (polar regions, vast) � 2. Polar lows (polar regions, short) � 3. Extratropical cyclone (mid-latitude cyclone) � 4. Subtropical cyclone (between the equator and 50 o N and S) � 5. Mesocyclone (associated with tornado formation) � 6. Tropical cyclone (tropics)

Tropical cyclone is non-frontal synoptic scale lowpressure system over tropical waters with organized convection (i. e. Thunderstorm activity) and cyclonic surface circulation. This low pressure creates violent storms that are characterised by winds over 100 km/h and heavy rainfall. They have caused the loss of life on a number of occasions due to there intensity.

TC has synoptic scales of 100’s km

Average number of typhoons in the different areas of the world

� 1. Warm ocean waters at least (26. 5°C) to provide the heat. � 2. Availability of moisture. Moisture is necessary for providing latent heat of condensation. � 3. Coriolis force to provide the rotation. (they do not form within 5 o of the equator due to the negligible CF there). � 4. A seedling or cyclonic weather disturbance with extra cloud cover. � 5. Almost uniform large scale wind with little vertical shear to allow heat to accumulate (less than 10 m/s). � 6. An exhaust system consisting of a divergent upper level disturbance.

� Peak intensity of a typhoon is the maximum intensity the storm reaches during its entire lifetime. � It results from an accumulation of intensification, which is equivalent to speed being an accumulation of acceleration. � Cyclone can grow depends on two oceanic factors: � pre-storm sea surface temperature � difference in temperature between the surface and subsurface. �A warmer sea surface generally provides more energy for storm development and thus favors higher intensification rates.

� Evaporation increases rapidly as temperature increases. � Evaporation= energy in the form of latent heat that fuels the cyclone.

Orange/yellow regions- tropics between June and December

� Cold currents � Without the Coriolis force, surface winds cannot gain sufficient rotation to converge and the low pressure of the disturbance cannot be maintained. � Large values of vertical wind shear disrupt the formation of a tropical cyclone by interfering with the organization of deep convection around the cyclone center. ◦ Wind shear- refers to a change in wind speed or direction with height in the atmosphere.

Dry air from Sahara can weaken storms Dust blocks the sun and cools the ocean

� � � Eye: A region 30 -65 km in diameter found at the center where skies are often clear, winds are light, and the storm's lowest pressure readings are obtained. Eye Wall: A ring of cumulonimbus clouds that swirl around the eye. The heaviest precipitation and strongest winds are found here. Spiral Rainbands: Bands of heavy convective showers that spiral inward toward the storm's center. Thunderstorms are observed here.

� � In the “eye”, air is slowly sinking (causes compressional warming) and “warm core” The eyewall has a net upward airflow as a result of numerous updrafts and downdrafts Near the top of the eye-wall clouds relatively dry air flows outwards from the center. This diverging air aloft extending outwards for 100 s km. As the outflow reaches the cyclones edges it sinks. In the spiral rain bands, air converges at the surface, ascends through these bands, diverges aloft, and descends on both sides of the bands.

� Strong pressure gradient within eyewall � Responsible for strong typhoon winds. Speed is fastest on “right” side of the typhoon: sum of rotational and forward velocity. � Rain occurs in eyewall (heaviest) and spiral rainbands. � Temperature increases in the eye because of descending air.

� � � Tropical Disturbance: The birth of a hurricane, having only a slight circulation with no closed isobars around an area of low pressure. Tropical disturbances commonly exist in the tropical trade winds at any one time and are often accompanied by clouds and precipitation. Tropical Depression A tropical cyclone in which the maximum sustained wind speed less than 64 KPH. Depressions have a closed circulation

Tropical Storm A tropical storm has a maximum sustained surface wind speed between 64 KPH and 117 KPH. The convection in tropical storms is usually more concentrated near the center with outer rainfall organizing into distinct bands. � Typhoon or Hurricane Typhoon has a maximum winds exceed 117 KPH. �

There a variety of metrics commonly used to measure storm size. The most common metrics include the radius of maximum wind, the radius of 34 -knot wind , the radius of outermost closed isobar (ROCI), and the radius of vanishing wind Size descriptions of tropical cyclones ROCI Type Less than 2 degrees latitude Very small/midget 2 to 3 degrees of latitude Small 3 to 6 degrees of latitude Medium/Average 6 to 8 degrees of latitude Large Over 8 degrees of latitude Very large 1 o lat= 60 nm

� Weather stations � Buoys � Ships � Radar � Aircraft Reconnaissance � Visible/Infrared Satellites � Microwave satellites � Satellite record estimates account for vast majority of the

Tropical cyclones out at sea cause large waves, heavy rain, and high winds, disrupting international shipping and, at times, causing shipwrecks. 2. Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favourable for subsequent tropical cyclones. 3. On land, strong winds can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. 4. The storm surge, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths. 5. The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes. 6. Tropical cyclones have been responsible for the deaths of about 1. 9 million people worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. 7. Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and the hampering of reconstruction efforts. 1.