Climatic Hazards Notes KIQ1

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Tropical storms

Compound hazards (one hazard with many resulting components), consisting of large rotating storms at a centre of very low pressure. They:

  • May be up to 800km across and 12km high.
  • Have wind speeds of around 120km/h.
  • Have high intensity, high volume rainfall (500mm in one day).
  • Create storm surges.

Pressure is a key factor of the formation of tropical storms. High pressure means sinking air, which warms and results in cloudless skies. Low pressure means rising air, which condenses and forms rainclouds. In a tropical storm, there is a drop of 25 mb/100km. 

Tropical storms form at low altitudes, between the Tropics and over oceans. Due to the Coriolis effect, the move polewards and westwards. These storms need:

  • Sea temperatures greater than 27°C for a significant period of time (hence occurring at the end of summer.) This creates evaporation, which carries latent heat energy into the atmosphere. When condensation occurs, this energy is released, helping generate strong winds as it draws up more air, reinforcing instability.
  • Water with a depth of at least 50 m in order to draw up colder water.
  • Sufficient spin from the Earth's rotation, hence occurring between the Tropics. However, if it is too close to the Equator, there is insufficient rotation.

Once the rising air becomes established (a convection cell), the system is self-perpetuating. Winds converge close to the ocean's surface and force the rising air to move faster. This instability results in thunderstorms. High pressure is created in the upper atmosphere which pulls more warm air up. Wind speeds at all altitudes must be consistent otherwise the storm will break up. At the eye, air descends from the top, and, as it does so, is warmed and therefore able to hold more moisture. Condensation is reduced and the eye remains cloudless.

Monitoring Hurricanes

  • Geostationary satellites orbit at a height of 35,780 km above the Earth, taking 24 hours to complete its orbit. This means it appears to be stationary in relation to the Earth's surface.
  • Polar-orbiting satellites pass over the Earth much lower than geostationary, and provide detailed information about weather and cloud


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