Why does the ocean seem noisier during certain seasons? | John Lindsey | Local News


Mary Power-Hall from Los Osos asked this question:

“There was a discussion among many of Nextdoor’s neighbors in the Morro Bay / Los Osos area today about the fickle sound of waves on the shore and how the sound of the sea spreads inside. from land to the neighborhoods of Los Osos and Morro Bay. You “I would be amazed at how many people are wondering about this! Sometimes we can hear the waves as if they are just through our windows, and other times the sea is silent for months. Can you tell us? say why that would be the case? is it a seasonal wind direction (the ocean always seems noisier in winter)? is air clarity a factor? wave size? other factors? “

Ted from Vandenberg Space Force Base recently asked the same question, which is often asked in the fall and here’s why:

Those of us who live in coastal communities often hear the waves crashing along our coastline. There are times when the waves are high, but the sound is barely noticeable; other times the swell is weak, but the sound along our coast is quite loud. Obviously, last week the same weather conditions occurred along the entire central coast from Big Sur to Point Conception to produce these temporary atmospheric sound channels.

Let me explain.

Many years ago I took my son to the beach, and he picked up an empty shell of a Lewis moon snail, brought it to his ear and said he could hear the ocean. The shell captures the ambient noise of the environment. The sound resonates inside the shell and produces a wave-like sound no matter how far away from the ocean.

Just as the shell walls pick up and direct sound to our ears, so can the atmosphere.

In the fall, atmospheric temperature inversion layers come and go at a faster rate as the Santa Lucia winds (northeast / offshore) and northwest winds (onshore) fight for the supremacy. You can see it by the ebb and flow of low coastal clouds along the beaches. Combined with this condition, high energy waves from Gulf of Alaska storms are starting to arrive along our coastline.

Several fall mornings as I walked near the coast I heard individual waves breaking and mistakenly thought the swell was much higher than I expected.

When the sound was loud enough I was forced to check the Diablo Canyon Power Plant Waverider Buoy on the CDIP website at www.cdip.edu and found the wave heights to be that planned.

When the weather conditions are good, the sound of crashing waves is captured much like the ambient sounds of the seashell.

This occurs when the air is calm and still, most likely during the early hours of the morning before afternoon northwest winds form.

Cool, dense air moves down to the Earth’s surface and produces a temperature inversion layer. This layer of cool, dense air creates a sound channel, ranging from a few feet above the ocean’s surface to hundreds of feet high.

Some of the sounds of the waves reflect or jump from the inversion layer to the ground. In other words, the sound of crashing waves is picked up in the surface channel and propagates to our coastal communities with minor loss of intensity.

At other times, the winds blow fast enough to mix up the temperature inversion layer, allowing sound to travel in all directions, with a much greater loss of intensity, making it sound much quieter no matter what. be the swell conditions. I guess you could say the sound of the waves got lost in the wind.

As any submariner will tell you, sound channels also exist in the ocean.

In 1991l, a US Navy research vessel in the Indian Ocean lowered transducers in the deep sound channel and transmitted low frequency sound. About 3.5 hours later, the sound was picked up by another research vessel off the central coast of California, 11,000 miles away. The sound traveled through the water at over 3,140 mph. The speed of sound in air is approximately 760 mph, depending on atmospheric pressure and temperature. Sound travels much faster in water than in air due to the greater density of water.

It is believed that marine mammals such as whales use the deep sound channel to communicate thousands of miles across the oceans.

Experiments using Navy underwater sound monitoring systems stationed across the Pacific have shown that sound travel times can be measured in milliseconds over thousands of kilometers. As seawater warms, the speed of sound increases due to the increased elasticity of water molecules.

John Lindsey is the marine meteorologist for Pacific Gas and Electric Co.’s Diablo Canyon Power Plant and a media relations representative. Email him at [email protected] or follow him on Twitter @PGE_John.


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