Capitola today

well, I know the answer to the riddle of small amplitude and long period.

the south swell waves start out 20 to 80 feet high, with long period, but 10,000 miles away in the southern hemi.

the amplitude decays as they travel and the wave front spreads out, but the speed and the period do not.

why? I don't know, ask professor Bascom, the author of that famous book on waves. physics at work!

So you have a big fetch (area where wind blows) generating big waves of all periods.  the longer the fetch the longer
the maximum period of the waves because they are accelerated by the wind over a longer area.
but you still have some waves with shorter period too.

The long period ones go faster so for southern hemi swells that means they get here first.  the short period stragglers
show up last. 

80 foot high waves with 20 second period get here as 4 foot 20 second period waves and we can all go get tubed at
low tide in front of jacks house (not sure of those numbers, but you get the idea)

In the winter, the swells don't have to travel as far (coming from storms in the north pacific), so the waves of different
periods get here closer together.

A south swell event can be spread over 5 days or even more cause it comes from farther away.

A north swell event is usually 3 days or less cause it comes from closer.

There are a lot of other facts like how long period waves feel the bottom more than short period waves. long period
waves refract around headlands etc much better too.

my theory is that the long period south swells make the halibut go surfing. 



J

That Swell Breakdown makes me hungry for S.Hemi-Surf-Hunt!I haven't been out since I bought one of these Fishin-Yaks!

I think the reason the period doesn't change could be explained by relating it to sound waves. As you get farther from the origin the sound becames less loud (amplitude) but the frequency, which relates to wave period, does not change since the sound will still be the same pitch. Just finished up a semester of wave physics...

sounds like you passed,