st599
Well-Known Member
Re: Currents and tidal streams - what\'s the difference?
Have used the Straits Sailing handbook in that area. It was very good.
Have used the Straits Sailing handbook in that area. It was very good.
Currents and tidal streams - what's the difference?
- Thread starter BlueSkyNick
- Start date
Jobs_a_ good_ un
Well-Known Member
Re: Currents and tidal streams - what\'s the difference?
Hi
I was told that the main reason is because the eastern end of the med is lower than the western end hence the height difference in the land causes the constant current
That may be wrong but it would explain it
But then in my 1st job i was sent down to the local DIY store to collect some *skyhooks* and was asked what type of sky do you intend to hang them from!!!!!!!!!!!!!!!!
Hi
I was told that the main reason is because the eastern end of the med is lower than the western end hence the height difference in the land causes the constant current
That may be wrong but it would explain it
But then in my 1st job i was sent down to the local DIY store to collect some *skyhooks* and was asked what type of sky do you intend to hang them from!!!!!!!!!!!!!!!!
pgod
Member
Re: Currents and tidal streams - what\'s the difference?
The difference between the two is fundamental though. Tides are created from the gravitational forces exerted on the oceans by the moon and sun. Currents are caused by earth forces such as water being heated by the sun, rotation of the earth, barometric pressure, rainfall, landmass etc.
Tides are also affected by such things but the reason we can predict tides with confidence but not currents is that the astronomical forces are overwhelming in comparison to the forces that establish currents. So the rotation of the earth produces the choreolus effect that makes object free of the earth such as water, turn towards the equator, causing higher and therefore stronger tides on the french side of the channel. The funnelling of the land either side of the Bristol channel or constriction of the English at the Cherbourg peninsular cause the wter flow to increase, but it isi the gravitational pull that is driving it.
As far as currents are concered this variation is why the Gulf Stream is variable off Florida and Why El Nino happens for example - the forces are not constant.
So in the English Channel its really all tide, both along and up and down. In the middle of the Atlantic its all current, along only, and in the Straits its a fantastic combination of flows which are mainly currents. There's hardly any tide in the Med mainly because the straits of Gib are too narrow to allow much water through in the limited time the tide flows in a particular direction, although of course the further east you go in the Med the more there is a tidal effect, because the gravitational pulll has the 'fetch' to pull water with it.
What I can't get my head round is why some parts of the world have two tides a day and others only one? Where does it change over?
The difference between the two is fundamental though. Tides are created from the gravitational forces exerted on the oceans by the moon and sun. Currents are caused by earth forces such as water being heated by the sun, rotation of the earth, barometric pressure, rainfall, landmass etc.
Tides are also affected by such things but the reason we can predict tides with confidence but not currents is that the astronomical forces are overwhelming in comparison to the forces that establish currents. So the rotation of the earth produces the choreolus effect that makes object free of the earth such as water, turn towards the equator, causing higher and therefore stronger tides on the french side of the channel. The funnelling of the land either side of the Bristol channel or constriction of the English at the Cherbourg peninsular cause the wter flow to increase, but it isi the gravitational pull that is driving it.
As far as currents are concered this variation is why the Gulf Stream is variable off Florida and Why El Nino happens for example - the forces are not constant.
So in the English Channel its really all tide, both along and up and down. In the middle of the Atlantic its all current, along only, and in the Straits its a fantastic combination of flows which are mainly currents. There's hardly any tide in the Med mainly because the straits of Gib are too narrow to allow much water through in the limited time the tide flows in a particular direction, although of course the further east you go in the Med the more there is a tidal effect, because the gravitational pulll has the 'fetch' to pull water with it.
What I can't get my head round is why some parts of the world have two tides a day and others only one? Where does it change over?
sarabande
Well-Known Member
Re: Currents and tidal streams - what\'s the difference?
[ QUOTE ]
There's hardly any tide in the Med mainly because the straits of Gib are too narrow to allow much water through in the limited time the tide flows in a particular direction
[/ QUOTE ]
err, No.
There are two streams of water well below the surface where the Atlantic Ocean comes in constantly, and the Med flushes out constantly. The surface layer is the tidal current layer, which is affected by wind, baro pressure.
There are number of proposals in your other comments which also go contrary to established scientific knowledge. /forums/images/graemlins/grin.gif
[ QUOTE ]
There's hardly any tide in the Med mainly because the straits of Gib are too narrow to allow much water through in the limited time the tide flows in a particular direction
[/ QUOTE ]
err, No.
There are two streams of water well below the surface where the Atlantic Ocean comes in constantly, and the Med flushes out constantly. The surface layer is the tidal current layer, which is affected by wind, baro pressure.
There are number of proposals in your other comments which also go contrary to established scientific knowledge. /forums/images/graemlins/grin.gif
Cruiser2B
Well-Known Member
Re: Currents and tidal streams - what\'s the difference?
[ QUOTE ]
I wonder how much silt has to be in fresh water before it becomes heavier than sea water ?
[/ QUOTE ]
That's an interesting query. I would think since the silt is only in suspension, the fresh water carrier would still be less dense than the saltwater (where the salt is in solution), but I could be completely wrong. On the Canadian West coast there are hazardous freshets, which are large-volume freshwater outflows that create strong surface currents. The reduced density is also a hazard as more than a few heavily-laden fishboats have suddenly found themselves with negative freeboard.
[ QUOTE ]
I wonder how much silt has to be in fresh water before it becomes heavier than sea water ?
[/ QUOTE ]
That's an interesting query. I would think since the silt is only in suspension, the fresh water carrier would still be less dense than the saltwater (where the salt is in solution), but I could be completely wrong. On the Canadian West coast there are hazardous freshets, which are large-volume freshwater outflows that create strong surface currents. The reduced density is also a hazard as more than a few heavily-laden fishboats have suddenly found themselves with negative freeboard.