Waves of Victoria

No other country in the world offers more bang for your buck than Australia when it comes to surfing. Hordes of surfers come to explore our endless coastline every year. And it’s with good reason. Most of the world’s best surf spots (think Hawaii, California, southwest Europe) only get waves during winter. On the south coast of Australia we are blessed with surf all year round. Here’s why.

The origin of waves

In a nutshell, waves are generated by winds. As the wind blows over the ocean, friction between the air and the surface of the water creates ripples. Ripples amplify the friction between the two layers, allowing the ocean to capture more of the wind’s energy. Over time these ripples grow into the waves surfers love so much.

An Australian lineup from Maxpixel.com (licensed under Creative Commons Zero).

 

The characteristics of a wave are the result of three factors:

  1. The speed of the wind
  2. The length of time for which the wind is blowing
  3. The distance over which the wind blows (the fetch).

As you might expect, strong, sustained winds with a large fetch generate the biggest waves. In a storm, where winds are intense, waves of all different sizes and frequencies are formed, producing a disorganised, stormy mess. As these waves travel away from their source, they organise themselves into groups of waves moving at similar speeds – so-called ‘wave trains’. These wave trains are what we know as swell. The further the swell is from its source, the more organised and ‘cleaner’ the waves are.

Surfers refer to two different types of swell: wind swell, the initial, stormy mess and ground swell, the organised wave trains that have traveled thousands of kilometres from their source.

It’s a seemingly endless supply of these ground swells that Victoria is so blessed with. To see why, we must look as far south as possible.

The overwhelming majority of waves hitting the south coast of Australia are born far away in the ocean’s surrounding Antarctica. Down here almost constant storm activity dominates the polar climate.

A storm is essentially an intense low pressure system, where strong gradients of air pressure generate powerful winds. If you’ve ever looked at a weather map of the Southern Ocean, you’ve probably seen the pattern of lows that perpetually encircles the continent.

But what makes the Southern Ocean so stormy?

The answer lies in the unique climate of the Southern Hemisphere.

It’s the unenviable job of the Earth’s climate system to transport heat and energy from the warm areas near the equator to the cold Polar Regions. Without this redistribution of heat, the Earth’s energy balance would fail. The tropics would get hotter and hotter and the poles colder. South of Australia, this job is primarily done by something scientists call Rossby waves (named after Swedish-born American meteorologist Carl-Gustaf Rossby).

Rossby waves around Antarctica. The five ‘bulls eyes’ close to the continent are intense low pressure systems. Image from the Bureau of Meteorology

Strong temperature contrasts between mid-latitude regions (somewhere not tropical but not quite polar, like here in Melbourne) and Antarctica lead to the development of weather systems that act to drag heat from warmer northern areas and deposit it near Antarctica. These weather systems manifest themselves as the wave-like pattern of low pressure systems surrounding Antarctica on your weather map. Put simply, these are Rossby waves.

An average low pressure system has a lifespan of roughly a week, but as soon as one dies, and the Earth’s energy balance begins to tip, a new one develops to take its place. The waves generated by the intense winds in these low pressure systems travel north to constantly batter the south coast of Australia and make Victoria such a special place for surfers.

 

 

 

 

 

 

 

 


5 Responses to “Waves of Victoria”

  1. Dominic Thorn says:

    Thanks for the link, NSW gets a lot of its waves from low pressure systems in the Tasman Sea, while as you say most of it’s big swells come from east coast lows and tropical cyclones, both of which are changing in a changing climate. Luckily for us here in Vic there’s not too much of a warming signal around Antarctica yet (apart from on the Antarctic Peninsula). The jury’s still out on how climate change will affect Victoria’s waves, but for now they’re not going anywhere.

  2. Richard Proudlove says:

    I have been surfing the coast of Victoria for over a decade, so this post was a great insight. Unfortunately climate change will mean fewer East Coast lows, which will mean fewer waves – https://theconversation.com/surfs-down-climate-change-likely-to-bring-fewer-big-waves-24126

  3. Dominic Thorn says:

    Wave theory tells us that deep water waves (like these waves formed in the Southern Ocean) are dispersive. This means that the speed of propagation of an individual wave is dependent on its wavelength. So waves of different sizes travel at different speeds, but waves of the same size move at the same speed. The turbulent nature of winds during a storm means that waves of all different sizes are being formed all the time. So waves of similar size and speed will remain together in a group, while smaller waves, for example, will form their own slower moving group and drop behind.

    Also, as a swell moves further from its source the waves attenuate. Many of the smaller waves have long decayed to nothing by the time they reach Australian shores. The swells we see here are generally made up of the largest waves generated by the storm. Larger waves reach deeper into the ocean and are hence less prone to decay.

  4. mcdonaldw says:

    It was interesting to see that waves arrange themselves by speed. Is that because waves change their speed to match those around them or waves leaving at similar times have similar velocities? Or something else?

  5. Ellen Rochelmeyer says:

    Fascinating to read about the mechanisms behind waves! I had no idea that Australia was special in that it receives waves all year round. It seems strange to think that some places only get waves at certain times of the year.