Lesson 16 How do Tropical Revolving Storms Form?

We need to understand how tropical revolving storms are created, their impacts and know how people respond to them. We should also take into account the effects of global warming on such events.

What drives a Tropical Storm? Cold polar air moves towards the warm equator. Hot tropical air moves towards the cold poles. The planet is not evenly heated. At A the heating is more direct = intense. Whereas at B it is spread over a larger surface area = less intense.

What causes wind? This uneven heating causes air to move around the planet, trying to even out the temperature. This uneven heating causes air to move around the planet, trying to even out the temperature. Air moving around the planet causes our wind, which generally follows a known pattern. Air moving around the planet causes our wind, which generally follows a known pattern.

Tropical storms form between 5ºand 20º North & South of the equator. They need warm water ~ above 27ºc – hence their location. As the Earth rotates, this provides the ‘spin’ needed to start the tropical storm on its journey across the Atlantic towards America.

Tropical revolving storms occur all around the world, but are called different names. 11% 17% 8% 11% 20% 33%

Warm Oceans The ‘food’ of a tropical storm is the warm moist water found near the equator. The air here is under LOW pressure, which means it can lift easily. This lifting encourages the air to cool and condense, as it does latent heat is released. This is the name given to energy produced when a substance changes state ie vapour to a liquid.

Here is a check list of what is needed for a tropical revolving storm to grow. A storm can travel anywhere from 15 to 40mph Once the storm has developed it can grow 400 miles wide.

Here is a 3D image of a Tropical revolving storm. Notice the lower level winds being drawn in and spiralling counter clockwise. The lines ‘isobars’ get closer together, indicating faster flowing air.

Launch the hyper link How Hurricanes form How Hurricanes form

Tropical Storm / Hurricane Key Facts Hurricanes are located in the low-pressure belt near the equator as the sun heats the oceans to a critical temperature of 27  C. The oceans heat up all through the summer making their warmest temperatures in the Autumn (specific heat capacity); this is Hurricane season in the Atlantic. The hurricane starts as a tropical depression, gaining more and more energy from the warm ocean as it crosses the Atlantic. The circulation of the depression gets tighter (isobars are closer together) and the wind speed increases into a tropical storm. The wind speeds continue to increase, becoming a category 1 up to category 5 for the most violent storm. As the hurricane makes landfall damage is done by the winds and rain and an advancing storm surge, which raise sea level by 5m+ in some cases. The hurricane quickly looses its energy as it crosses the cooler land, as the energy supply has been cut off. The hurricane dies. Sometimes remnants of hurricanes are brought across back across the Atlantic at the mid latitudes giving us very strong depressions in the UK.

How are they measured? Although developed in the USA, the Saffir-Simpson scale is used to grade tropical storm wind strength in many parts of the world. Category Wind Speed km/hr Wind Speed Mph Storm Surge m Tropical storm Tropical depression >250>155<5.5

Problems with the Saffri Simpson? Q… Using wind speed and storm surge levels – what problems could you encounter?

A tropical storm has many friends! Other phenomena which can be just as damaging than the wind frequently accompany tropical storms: high seas - large waves of up to 15 metres high are caused by the strong winds and are hazardous to shipping; storm surge - a surge of water of up to several metres can cause extensive flooding and damage in coastal regions; heavy rain - the tropical cyclone can pick up two billion tons of moisture per day and release it as rain. This also leads to extensive flooding - often well inland from where the tropical revolving storm hit the coast; tornadoes - tropical cyclones sometimes spawn many tornadoes as they hit land which can cause small areas of extreme wind damage. These phenomena can cause major destruction, especially when the tropical cyclone's path takes it over land. However, a path over land also causes the destruction of the tropical cyclone itself. As it moves over land, its energy source is depleted and friction across the land surface distorts the air flow. This leads to the eye filling with cloud and the tropical cyclone dies.

3D model of a Tropical Storm Create your own 3D model – remember to add a key!

Homework AQA A2 book Pg Read and make notes Visit these web sites and read around the topic – what else can you add to your notes about tropical revolving storm formation? Waugh Pg 235 & Nagle Pg 421+ has extra reading, (pay particular attention to Places 30 for Stretch & Challenge!) ing/hurricane_cycle.shtml ing/hurricane_cycle.shtml ne/facts.html ne/facts.html