Re: WIND_TALK digest 63

From: Jim Paugh (James.Paugh@Eng.Sun.COM-DeleteThis)
Date: Fri Aug 25 1995 - 11:09:50 PDT

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Date: Fri, 25 Aug 1995 11:09:50 -0700
From: James.Paugh@Eng.Sun.COM-DeleteThis (Jim Paugh)
Message-Id: <199508251809.LAA08807@jalama.Eng.Sun.COM-DeleteThis>
To: wind_talk@opus.hpl.hp.com-DeleteThis
Subject: Re: WIND_TALK digest 63

Jim Paugh asks:

> "What I would like to hear is an explanation of why slack current occurs
> after say, a low tide. For instance, today, low tide at Crissy is at
> 5:03pm, but low slack is at 7:29pm! How is it that slack current occurs
> 2.5 hours after low tide? "

Will Estes writes:

> The best explanation I have heard on this was Ken Poulton's a few
> months ago on the wind_talk list. He compared tidal dynamics to
> electron flow within a wire. At the outside, resistance to the flow
> is greater than in the middle. So at the point where the flow stops
> on the outside, the flow is still moving at the center.
>
> Consider the analogy to the Bay: at the edges we have relatively
> shallow mud flats that offer a lot of resistance to the current. In
> the center you have a deep shipping channel where the water flows more
> freely. So at the low tide, the resistance of the mud flats on the
> edges just matches the current flow, and you have a zero current at the
> edge. But in the middle of the channel the ebb is still continuing,
> and it doesn't stop until a later time, because there is less
> resistance to stop the outward flow.

Kirk Lindstrum writes:

> It has to do with the shape of the bay. If you are an EE, then you can
> model the bay as a bunch of capacitors in each big, deep section and
> each "straight" as an inductor with the largest inductor at the Golden
> Gate. The "system" is driven by tide height (Voltage input) at the
> Golden Gate. Voltage is the same as tide height and current is the same for
> both with one being water and the other electrons.

Oh, NO! The dreaded EE analogy! Picture a blank stare on my face, eyes
glazed over, mouth agape :^o

Thanks guys, for trying, but I think I'll stick to the tidal wave rolling
through the Golden Gate analogy!

~Jim

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