Weather Watch

How nature mimics the shell sound

I took my 6-year-old son to the beach at Montaña de Oro State Park. He picked up an empty shell from a Lewis’ moon snail, held it to his ear and said he could hear the ocean.

The seashell captures the ambient noise from the environment. The sound resonates inside the shell and produces a wavelike noise, no matter how far away one is from the ocean.

The walls of the seashell capture and direct sound to our ears; the atmosphere can do the same.

Those of us living in the coastal communities often hear the waves breaking along our coastline. There are times when the waves are fairly high but the sound is barely noticeable; and other times when the swell is low, but the sound along our coastline is quite loud.

On many a morning while walking from my house in Los Osos, I have heard the sound of individual waves crashing on the sand spit and thought by mistake that the wave was much higher than I had imagined.

When the sound is loud enough, I have actually checked the Diablo Canyon waverider buoy on the Internet and found that the wave height was as predicted.

When the atmospheric conditions are right, the sound from the crashing waves is captured much like the seashell.

This occurs when the air is calm and still, most likely during the early morning before the afternoon northwesterly (onshore) winds build.

The cool and dense air sinks towards the Earth's surface and produces a temperature inversion layer. This layer of cool and dense air produces a sound channel, which can range from a few feet above the ocean surface to hundreds of feet high.

Some of the sound from the waves reflects or skips off the inversion layer towards the ground.

In other words, the sound of the crashing waves is captured in the ­surface channel and propagates toward our coastal communities with little loss in intensity.

At other times, the winds blow fast enough to mix out the temperature inversion layer, allowing the sound to spread out in all directions, with a much greater loss in sound intensity, making it seem much quieter regardless of the swell conditions. I guess you could say that the sound of the waves was lost on the wind.

As any submariner will tell you, sound channels also exist in the ocean. In 1991 a research ship with the U.S. Navy in the Indian Ocean lowered transducers into the deep sound channel and transmitted low frequency sound.

About 31⁄2 hours later, the sound was picked up by another research ship off the Central Coast of California — 11,000 miles away! The sound traveled in the water at more than 3,140 mph. Sound travels much faster in water than air due to water having a greater density.

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

Experiments utilizing Navy underwater sound surveillance systems, stationed throughout the Pacific, have shown that travel times for sound can be measured down to a few milliseconds over thousands of miles.

As seawater warms, the speed of sound increases due to water molecules’ increased elasticity.

This week’s forecast

The weather system that crossed our area from Friday evening into Saturday produced gusty southerly winds and periods of heavy rain.

Except for dense ground fog in the North County this morning, clearing skies are forecast today.

Temperatures will be mild, with highs mostly in the high 50s to low 60s.

Another cold front will cross our area from northwest to southeast on Tuesday with light rain showers and gentle to moderate (8-18 mph) southerly winds.

Dry weather is expected for Wednesday into Thursday, then more wet and windy weather will return Friday into next weekend with potentially much lower snow levels.

Surf and sea report

This morning’s 14- to 16-foot westerly (270-degree deep-water) swell (with a 14- to 16-second period) will decrease to 9 to 11 feet (with an 11- to 14-second period by tonight.

An intense 950-millibar storm with hurricane force winds developed near the International Date Line late Friday. This powerful storm will move into the Gulf of Alaska.

A very long-period northwesterly (290-degree deep-water) swell from this storm is expected to arrive along our coastline late Monday at 5 to 7 feet (with a 20- to 22-second period), increasing to 13 to 15 feet (with a 17- to 19-second period) along the coastline Tuesday.

This swell should peak on Wednesday at 14 to 16 feet (with a 15- to 17-second period), decreasing to 12 to 14 feet Thursday.

Another very long-period west-northwesterly (285-degree deep-water) swell will arrive along our coastline on Friday at 5 to 7 feet (with a 20- to 22-second period), increasing to 10 to 12 feet by Saturday.

Preliminary Analysis:

A long-period northwesterly swell will arrive along the coastline on March 8.

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John Lindsey is a media relations representative for Pacific Gas and Electric Co. He is also a local weather expert and has lived along the Central Coast for more than 23 years.