RE: Time and Tide waits for Gnomon

[Roger Bailey]

Hi Chuck and all,

 

Thanks for the visual solution. You clearly demonstrate what I had suspected, a combination of latitude and declination  affect the time of low low tides. I had originally expected the tides to behave as outlined by Richard Hollands, with peaks shifting with the moon by about 55 minutes a day. Local observations proved otherwise. The time shift is apparent but there is a change through the month on which bulge creates the lowest tides. This is clearly shown in the harmonic analysis predictions. It is great to have these available on line so we can change time, date and locations and see the effects.

 

Seasons Greetings,

 

Roger Bailey

.

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]On Behalf Of Chuck Nafziger
Sent: December 24, 2003 2:44 PM
To: sundial@rrz.uni-koeln.de
Subject: Re: Time and Tide waits for Gnomon

I, like Roger, live in the Pacific Northwest and have always wondered about the extreme tides only during the daylight in the summer and the extreme tides only at night during the winter.  Roger’s thoughts about the tides as a time and season clock coaxed me to look at my globe for a visual solution to this quandary.

 

While looking at the globe and picturing a 23.5 degree cone projecting below the equator (over the tropic of Capricorn: the path of the sun during the winter solstice), I spun the globe and visualized the places on the globe where the ocean bulges would be.  The bulges from the solar component of the tides occur on the points directly under the sun and directly on the other side of the globe from the sun (along the tropic of Cancer).  Due to the distance factor associated with gravity, the sun’s pull is greater than Earth average under the sun, and less directly opposite so at the solstices, there are two solar caused bulges, one on each tropic under which the Earth rotates.

 

By spinning the globe and visualizing the bulges, it was obvious that the Pacific Northwest was near the bulge only at night during the winter and off to the side during the day.  Then using the same mental gymnastics visualizing a 23.5 degree cone above the equator (the path of the sun during the summer equinox) it could be seen that we are near the bulge only when the sun is nearly over head during the summer and off to the side during the night.

 

The lunar component is not seasonally oriented but the total tide cannot find a maximum that is not associated with day/summer, night/winter solar maximums.

 

Thank you Roger for the impetus to look at these clearly seen, but perplexing phenomena in a new, more visual way.

 

Happy Solstice all,

 

Chuck Nafziger

46.7 N

122.4 W

----Original Message Follows----
From: "Edley McKnight" <[EMAIL PROTECTED]>
Reply-To: sundial@rrz.uni-koeln.de
To: sundial@rrz.uni-koeln.de
Subject: Re: Time and Tide waits for Gnomon
Date: Wed, 24 Dec 2003 10:19:36 -0800

Hi Roger,

Even though the apparent tides are the resultant of quite a few
influences there are places where they seem quite regular. Wind
driven surges, movements of the earth, interfering reflected waves
from other coastal features, all seem to make an effect. If the basic
sun/moon tidal effects are put in as the inputs to a time series filter
which has been derived by difference equations for the effect of the
other influences, I'm told predictions can be quite close, even in
difficult areas. I've seen a few papers on this, but long ago. I'm not
sure what the current best mathematical approach is. After all, the
tides are basically waves that circle the earth. As! such they are not
a fully driven phenomena, but include multiple time delayed
elements.

Hope this helps!

Happy Christmas Eve!

Edley.

From: "Roger Bailey" <[EMAIL PROTECTED]>
To: "Sundial Mail List"
Subject: Time and Tide waits for Gnomon
Date sent: Tue, 23 Dec 2003 18:02:16 -0800
Send reply to: sundial@rrz.uni-koeln.de

> Hello Sundials Friends,
>
> Three things came together yesterday:
> Winter Solstice: Maximum negative solar declination,
> Moon at Perigee: At 358338 km, the moons closest to earth in its orbit,
> New Moon: Earth, moon and sun aligned.
>
> The results, as warned in my RASC "Observers Guide", are "High Tides". Some
> time ago I proposed a tidal correction device for moon dials. Most of you
> recognized this modest proposal as a bit of lunacy and not to be taken
> seriously. But the concept has cau! sed me to observe tides and solar lunar
> dynamics more! closely . The tidal range today was higher than I have seen
> before. Logs normally high on the beach have floated away today. The low
> tide last night exposed more shore than I have seen.
>
> You are familiar with the effect of solar declination on shadow lengths
> particularly at this time of year. I am now learning about the effect of
> lunar declination on tides through observations over the last three months.
> One frustration that I have had with tides is that the low tides occur in
> the middle of the night. This makes it very difficult to enjoy long
> beach/nature walks. At my location, there are no low low tides during
> daylight hours all winter. The phenomenon is reversed with the low low tides
> occurring during the day all summer.
>
> I believe that this is due to the lunar declination and invite you comments
> on this theory. The declination of the moon is equal and oppos! ite to solar
> declination when the moon is full and equal when the moon is new. Since the
> moon has a greater effect on tides than the sun, the timing of tides follows
> the lunar cycle being high during the day when the sun's altitude is low and
> conversely low at night during the winter.
>
> Click on the site that I use to for tide prediction tables and charts is:
> http://www.lau.chs-shc.dfo-mpo.gc.ca/cgi-bin/tide-shc.cgi?queryType=showFram
> eset&zone=9&language=english®ion=1&stnnum=7260 Change the presentation
> from table to Graphic to see the charts. You can change the date and the
> location from my location, Sidney BC. This is a Canadian site. There are
> many other good tide predictors on the web. The are good tidal prediction
> sites as well as freeware like WXTide32 by Mike Hooper
> http://www.wxtide32.com/
>
> Enjoy the Solstice and the return! of the sun, the high/low tides of the
> perigee and th! e dark s kies of the new moon. Cheers,
>
> Roger Bailey
> N 48.6 W 123.4
>
> -


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