Neep tides

[Jo Zebedee]

Hi I'm in the middle of a short story where a spring tide/ neep tide exposes a hidden grotto.

Firstly, does anyone know if its the spring or autumn tide which pulls the sea out, or is it both? For the purposes of the story autumn would be better as the sea's warmer, but I had a notion it might be a spring one? Also, is the Neep tide which does this? Tried to look it up on line, but I started to get really confused, which also made me wonder, is it the same globally?

 

[The Judge]

er... spring tides have nothing to do with spring...

Spring tides happen twice a month at full and new moon; neap tides (neeps = turnips or swedes in Scotland) happen in between. It's the springs which give the greatest tidal range.

I try and picture it as the sun and moon both pulling the water. When the moon is full or new the sun and moon and earth are all in line, and so the double effect pulls more greatly. When it's a half moon, it's because the sun is at right angles to the moon, and the gravitational effects cancel each other out more.

Because the moon's orbit isn't perfectly circular, sometimes it's nearer to Earth, at which time the pull is greater and the tidal range is therefore more extreme. I've just checked on wikipedia, and apparently that happens about every 7.5 lunar months. So you can have it in spring or autumn whichever you want.

That help?

 

[Ursa major]

There is a special sort of spring tide, the perigean spring tide, when the effect is greater than normal.

See http://en.wikipedia.org/wiki/Perigean_spring_tide.

 

[Jo Zebedee]

Yes, that helps a lot; I've seen it happening here a couple of times a year, so I assume it's the Perigean effect. TY both