Geography: Year 9 Term 2: Tropical Storms and GAC


Pressure & the Coriolis Effect

Solar energy creates air movement. Warm air rising = low pressure. Cool air sinking = high pressure.

Low pressure causes cyclones. High pressure causes anticyclones.

Low pressure in the centre of a storm tries to get to the higher pressure air and is deflected so spins.

High pressure air sinks and moves outwardsLow pressure air rises and ground winds move towards it.

In an attempt to  equalise pressure, wind moves from  high to low  pressure areas.

The  Coriolis Effect  is when wind  curves from its original trajectory  due to the  spin of the Earth. Points on the  equator spin faster  because the  equator has to spin faster than the poles  to get its full width round 360 in the same time as the smaller poles.

 North  = curve  right 

 South  = curve  left 



1 of 8

Global Circulation Systems

 Cold air sinking = no clouds = dry environment = low millibars.

 Warm air rising = clouds = wet environment = high millibars.

 Below the Equator  are the  Southeast trade winds, which go from  SE to NW. This is a  Hadley cell.

 Above the Equator  are the  Northeast trade winds, which go from  NE to SW. This is a  Hadley cell.

 Below the Tropic of Capricorn  are the  Westerlies, which go from  NW to SE. This is a  Ferrel cell.

 Above the Tropic of Cancer  are the  Easterlies, which go from  SE to NW. This is a  Ferrel cell.

 Below the Sub-Polar Low  are the Polar Easterlies, which go from  SE to NW.  This is a  Polar cell.

 Above the Northern Sub-Polar Low  are the  Polar Westerlies, which go from  NW to SE. This is a  Polar Cell.

2 of 8

Climate Change & Tropical Storms

Milankovich Cycles: Changes in the Earth's orbit, fluctuating over millenia and changing the heat Earth recieves from the sun depending on our distance away.

Hotspots: Hot areas on the sun's surface which, when aligned with Earth, warm the planet more than usual.

How Climate Change Affects Tropical Storms:  INTENSITYWHEN/WHEREUNCERTIANITY 

- Warmer oceans breed a larger amount of more violent storms

- Thermal expansion causes sea levels to rise, causing larger storm surges and making flooding easier

- Air holds more moisture, meaning more rainfall and flooding caused by storms or other weather systems

 Oceans will be warmer all the time and create more energetic storms 

 Hotter oceans mean storms will be less limited in range and happen more often as it will always be warm.

 Random weather patterns and constant high temperatures will make storms unpredictable 

3 of 8

Formation of Tropical Storms

I) The sun warms up the oceans.

II) Water temperatures reach 27 degrees C.

III) Moist air rises, creating a low-pressure eye.

IV) Air cools as it rises, causing condensation into rainclouds.

V) Cool air sinks to create the eyewall.

VI) As air circulates in an effort to equalise pressure, winds form.

VII) The storm moves but is made to spin due to the Coriolis Effect.

The eye, up to 50km across, has descending air + low pressure. Wind is light and it is hot; no rain/clouds.

The eyewall has spiralling, rising air + high pressure. Wind is strong and it is cold; lots of heavy rain.

Between the edges and the eyewall, pressure falls. Winds are heavy and there is lots of hevy rain still.

At the edges of the storm, there are some clouds. There's less wind, clouds & rain + higher temperatures.

4 of 8

Hurricane Severity Scale

Saffir-Simpson Scale

Category I: 74-95mph sustained winds; low level of damage

Category II: 96-110mph sustained winds; moderate level of damage

Category III: 111-130mph sustained winds; extensive level of damage

Category IV: 131-155mph sustained winds; extreme level of damage

Category V: 155+mph sustained winds; catastrophic level of damage

LDCs can be hit harder by a low-level hurricane than an MDC faced with a high-level hurricane as they have worse infrastructure; less resources; and often high disease rates and/or overpopulation.

5 of 8

UK Extreme Weather

Extreme cold weather is an extreme and/or unseasonal bout of very cold weather, often coming with snow. eg: Winds and snow in the NE, December 2010

The UK is under threat from storms, with lots of rain, high winds and large waves on the coast caused by winds over seas/oceans. eg: Storm Stella, 2017

A drought is when there is a prolonged peiod of no rain or other precipitation. This causes a shortage of water and crops, as they are unable to grow. eg: UK-wide drought, 2010-12

Flooding occurs when there is a lot of rain or other precipitaion in a short period of time, and this build upon the ground or in rivers, which then overflow. eg: Carlisle Floods, 2015

Causes of St. Jude's Day Storm, 2013

- Depression formation: a cold front of northern air undercut warm southern air, causing a pressure difference at full occlusion

- Powerful jetstream: strong winds 5-7 miles up in the atmosphere at a lower-than-usual latitude travelling from west (USA) to east (UK).

6 of 8

St Jude's Day Mini Case Study

Environmental:10 million trees destroyed; power cabes fell; large waves on coast

Economic: Building damages insurance; economy losses; disrupted travel to work

Social:4 people killed; homes had no electricity; lack of communication

Prediction: 5 days' warning; MET computer accurately predicte path; warnings issued for different areas 

Protection: Trees felled so they couldn't be blown over; isurance companies recruited extra staff for the expected amount of claims

Planning: Warnings meant people could plan their activities around the dangers and disruptions caused by the storm

Warnings: Yellow - severe weather possible/could affect you; Amber - largeish likelihood of severe weather affecting you; Red - extreme weather is expected

7 of 8

Distribution of Tropical Storms

Tropical storms form between the Tropic of Cancer (23.5° north) and the Tropic of Capricorn (23.5° south) and most are 5-30° north or south of the equator, as the sea temperatures are above 27°C, which is required for the formation of tropical storms.

Areas affected include Central America, Africa, South Asia and Indonesia, as they are in the path of this area close to the equator.

8 of 8


No comments have yet been made

Similar Geography resources:

See all Geography resources »See all Natural hazards resources »