Tropical cyclone

Tropical cyclone

What is a Tropical Cyclone?

A tropical cyclone is a compact area of swirling winds surrounding a central region of low atmospheric pressure. About 85 of these occur annually over the warm tropical oceans. About half develop into a hurricane in Atlantic and eastern North Pacific or a typhoon in the western South Pacific.

Energy Of Winds In Tropical cyclone

Often called hurricanes or typhoons, tropical cyclones are the most destructive of all weather phenomena. They are intense circular storms that form over warm tropical oceans and have maximum sustained wind speeds of 119 kilometers per hour or greater. They are also known for their heavy rains and the associated secondary effects such as storm surge, flooding and landslides.

The energy of a tropical cyclone comes from the heat of the surrounding sea and its evaporation. The resulting rise of surface water is accelerated by the rotating winds and can produce a destructive surf known as a storm surge.

A cyclone is maintained by the extraction of energy from this process and the conversion of this energy into kinetic energy of wind and latent heat of condensation in its clouds. Upon reaching tropical storm or hurricane strength, the system develops an eye wall of thunderstorms around a central region of low pressure. These thunderstorms provide the requisite energy for the cyclone’s development, maintenance and eventual dissipation.

Because of their devastating impacts, it is important to understand the environmental costs of tropical cyclones, including their impact on the natural environment and human societies. This briefing focuses on three of these impacts: damaging winds, storm surges and rainfall.

The ability to predict the track and intensity of tropical cyclones has increased substantially over the past few decades, thanks to the use of satellite data and the development of advanced computer models of the atmosphere. Nonetheless, errors in the forecast of the speed and direction of the movement of a cyclone are substantial, even with these advances.

The Rain associated with a tropical cyclone is both beneficial and harmful

In the tropics, water evaporated from the surface of the ocean is carried up into the atmosphere by wind and condenses to form clouds. These clouds organize into bands of thunderstorms called rainbands. The evaporation and condensation process releases energy, which causes the rapid rotation of the cloud bands. This rotation is what makes a tropical cyclone.

The rain associated with a tropical cyclone is both beneficial and harmful. In arid regions, the rainfall fills reservoirs and saves crops. However, in 1998 Hurricane Mitch caused nine thousand deaths due to flooding from the rain it brought to parts of Central America.

When the cyclone makes landfall, the rain is torrential. Several factors contribute to this intense rainfall, including the duration of the cyclone, the energy/moisture supply and topography. The wind speeds of a cyclone slow as it approaches the coast. This increases the convergence, accelerates moisture condensation and intensifies the rain rate. The cyclones topography also affects the rate and amount of precipitation, especially when the cyclone crosses mountainous areas.

The National Weather Service (NWS) issues watches, warnings and advisories as the cyclone moves through or near populated areas. Advances in forecasting over the past decade allow the NWS to issue these warnings as soon as the system reaches the stage of being a tropical depression or above. This early warning enables people to take precautions and evacuate, if necessary.

Storm Surge

About 85 tropical storms form each year over warm tropical oceans, of which around half reach hurricane or typhoon intensity. They are among the most destructive natural hazards, with their devastating rains and high winds. They also produce dangerous storm surge that can cause extensive flooding, soil erosion and destruction.

Most dissipate upon moving over a large land mass or cooler waters, which deprive the storm of its primary source of energy. However, if the environmental conditions remain suitable, they can maintain their strength as they move inland.

As a tropical cyclone approaches land, the wind slows and the air mass becomes more dense. The resulting strong convergence increases the updraft and speeds moisture condensation, which leads to heavy rainfall. The amount of rain a cyclone can deliver is typically up to 10 centimetres per day, although values five to ten times higher are not uncommon in intense events or on mountainous areas.

When a cyclone approaches land, it generates a wave front that interacts with the shallow coastal waters. This produces a sharp rise in the sea level, known as the “storm surge”, which can be up to several metres high for the most intense events.

This can lead to flooding, loss of life and damage to buildings and other structures. In addition, the continuous pounding of the ocean surface by the storm waves can reshape coastlines, wearing away rocky shorelines or moving sand from beach areas. The resulting coastal erosion can also erode or destroy piers, break jetty supports and inundate or wash out buildings or other infrastructure on the coast. These time-delayed effects are often overlooked in disaster risk assessments.

Flooding In Tropical cyclone

Tropical cyclones are massive storm systems that generate intense rain, dangerous winds and destructive waves. These storms, also called hurricanes, typhoons and severe tropical cyclones.

The force of a cyclone’s wind and other variables determine its damage potential. The wind’s primary effect is destruction of structures and other infrastructure such as roads, bridges, powerlines and buildings. Continuous wind from the eyewall and rainbands can erode material and cause foundational shifts, landslides and other structural problems.

Heavy rains from a cyclone cause flooding. The most vulnerable areas are the immediate coastal zones where storm surge can overtop protective levees, and inland zones that experience inland flooding from rainfall. The high rainfall also contributes to river flooding and mudslides.

An additional hazard is debris flying at high speeds from a cyclone’s wind and rainfall. This flying debris can damage structures and create a hazard to people and pets.

A cyclone’s churning action also lowers the sea water temperature after it has passed, squelching future storm formation. The churning is caused by the rotation of the center of the storm and its outflow of air. The resulting cooling of the ocean helps maintain currents that move warm water to the poles and cold water back to the tropics.

While older empirical studies of the effects of tropical cyclones depended on insurance data and reports, more recent work uses physical data to generate objective models of a cyclone’s damage (Hsiang 2010; Strobl 2011; Felbermayr and Groschl 2014).

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