Received: from hplms26.hpl.hp.com by opus.hpl.hp.com with SMTP (1.37.109.8/15.5+ECS 3.3+HPL1.1) id AA15702; Fri, 25 Aug 1995 00:05:19 -0700 Return-Path: <westes@usc.com-DeleteThis> Received: from netcomsv.netcom.com (uucp6.netcom.com) by hplms26.hpl.hp.com with ESMTP ($Revision: 1.36.108.11 $/15.5+ECS 3.3+HPL1.1S) id AA215624384; Fri, 25 Aug 1995 00:06:24 -0700 Received: by netcomsv.netcom.com with UUCP (8.6.12/SMI-4.1) id XAA05409; Thu, 24 Aug 1995 23:55:24 -0700 Received: by usc.com (NX5.67d/NX3.0M) id AA16218; Thu, 24 Aug 95 23:11:08 -0700 From: Will Estes <westes@usc.com-DeleteThis> Message-Id: <9508250611.AA16218@usc.com-DeleteThis> Subject: Re: WIND_TALK digest 63 To: wind_talk@opus.hpl.hp.com-DeleteThis Date: Thu, 24 Aug 1995 23:11:06 -0700 (PDT) In-Reply-To: <Pine.SUN.3.91.950824222534.14227A-100000@crl10.crl.com-DeleteThis> from "Bob Galvan" at Aug 24, 95 10:56:55 pm X-Mailer: ELM [version 2.4 PL23] Content-Type: text Content-Length: 1325
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? "
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.
--
Will Estes U.S. Computer
Internet: westes@usc.com-DeleteThis POB 3150
Saratoga, CA 95070
FAX: 408-446-1013
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