Early September is peak hurricane season (as you may have gathered with what’s going on in the news!). A hurricane is one of mother nature’s most powerful weapons – a swirling power-house of roof-lifting winds and sideways rain. You may have wondered what it would be like to be in one, but have you also ever wondered how they are formed, and why they spin the way they do? Well put up your wind-breaker and close your shutters, as we explore the science behind hurricanes!
Hurricanes rely on four key ingredients: warm tropical oceans, moisture, moderately light winds, and a weather disturbance. If these factors are around for a long enough period, then they can combine to create the intense, wave moving winds and flood shaping rains that hurricanes are known for. Consider this: in one day, an average hurricane releases as much energy as half a million atomic bombs! That’s one mighty wind!
Did you know that the direction of a hurricane’s spin is different depending on the hemisphere is brewing in? Let us explain! This is in part due to the centre of the hurricane, known as ‘the eye’. The other part is to do with physics. Each spin differently due to Earth’s rotation!
If the Earth didn’t rotate, winds of up to 300 mph would howl from the poles to the Equator and back. Since the Earth is a sphere (well, almost…) that is continuously spinning on its axis, not all parts of the planet are moving at the same speed (bear with us, this will make sense!) regions closer to the equator are moving faster than those towards the poles over a set period of time, as they don’t have to travel so far. Standing on the equator, you would rotate much further, in terms of distance, than standing on the north pole for the same time period.
This is where the Coriolis effect comes in! It is named after the French engineer and mathematician Gaspard-Gustave de Coriolis, in the 19th century. This mind-numbingly complex physical phenomenon explains why hurricanes spin in different directions. Here is how it works:
1) As Earth spins, cold dense air at the north and south poles is very heavy so it tumbles to the ground and is pushed down toward the equator. Warmer, lighter air near the equator is less dense and tends to rise and move towards the poles. These movements generate natural circular currents due to the air flowing up and down from the poles to the equator.
2) When these winds collide, it pushes the air to the right as it travels northward and hurricanes to spin in the counter-clockwise direction. And when travelling from the equator to the south, the air curves to the left they spin in the clockwise direction.
This also explains why hurricanes do not cross the equator! Simply, the Coriolis effect there is too weak to get the air spinning fast enough. So one of the safest places from hurricanes is right on the equator because hurricanes have never formed there!
So, if you have two friends from different hemispheres arguing over the direction of hurricanes, show them this little piece of information and ask them to be a bit more accepting in their opinions!