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Explain: Cyclone Testing Station

## So what did we just observe?

Why is the force experienced by each house in the direction observed?

As the wind travels over the roof of a building, a pressure is induced to the components. The pressure “felt” by the roof is due to the velocity of the air above (wind). Bernoulli’s Principle states that the pressure exerted by a fluid decreases as its velocity increases. As the velocity of a fluid (or air in our case) increases, the pressure decreases so the static air inside the house has a higher pressure than the fast moving air outside, creating a pressure difference. As the wind speed increases, the pressure difference between the inside and outside of the house (area above the roof) gets larger until it reaches a point where the pressure difference is sufficiently large enough to “pop” the roof off the top of the house. This is due to for things to move from high to low pressure areas. This phenomenon is exploited when designing aeroplane wings in order to maximise lift and help keep it in the air.

If you would like a more detailed explanation of the physics behind this using Bernoulli’s Equation, please watch the video below:

## Cyclones, Hurricanes and Typhoons

Hurricanes, cyclones, and typhoons all refer to the same type of weather phenomenon. Different names are given to these storms depending on where they occur:

• Cyclone: Southeast Indian Ocean and Southwest Pacific
• Hurricane: Atlantic and Northern Pacific
• Typhoon: Northwest Pacific

## What Drives Cyclones?

The formation of a tropical cyclone is called “Tropical Cyclogenesis”, from the word “genesis” which means “the origin or mode of formation”. Tropical cyclones begin as low pressure systems over the ocean, and can grow into sustained cyclones if a number of environmental conditions are present. In particular, cyclone formation requires at a minimum:

Cross-section through a tropical cyclone (click to enlarge).
• Warm ocean waters of at least 26.5°C: the warm water, via evaporation, heats the inflowing air.
• An atmosphere which cools fast enough with height: this drives the thunderstorm activity (see the image on the right) which transports the warm air near the ocean surface higher into the atmosphere.
• Enough Coriolis force: this force (which is caused by Earth’s rotation) sustains the low-pressure system by forcing the cooler air approaching the low-pressure system to circle around it, instead of rushing straight in and cancelling it out.
• A small vertical wind shear: “vertical wind shear” means the rate at which the wind speed changes with increasing height. Large vertical wind shears can interfere with the deep convection around the cyclone center.