The difference between warm and cold wind and sea

[mike_bryon]

I’ve sailed in both and get the impression that warm waves are move tippy and break more often while cold wind seems stronger than warm air of the same wind speed. Is this my imagination or are there real and noticeable differences?

 

[sarabande]

here's air temp against density.

Temp in degrees C, and density in kg/m3

35 1.146
30 1.164
25 1.184
20 1.204
15 1.225
10 1.247
5 1.269
0 1.292
-5 1.316
-10 1.341
-15 1.367
-20 1.394

So you are right, the warmer it is the less dry air weighs, and the less impact it has on you (momentum is a function of speed and mass).

There's a problem with humidity though, as water vapour at a molecular level weighs less than air molecules. So if you have damp air, the water vapour 'displaces' air molecules in any given volume, otherwise the pressure or temp would rise. Air of high humidity has a lower mass than air of low humidity.


I haven't come across anything related to the 'shape' of waves in relation the temp of water. Perhaps something to do with viscosity. VicS would know.

 

[sarabande]

Oooh, look !

All about water, temperature and viscosity. And the Jones-Ray effect

http://www.btinternet.com/~martin.chaplin/explan5.html#Pvisc

I've been sailing with my eyes shut for decades and decades, not looking at wave shape and correlating a particular profile with the ambient water temp. I must do some serious observation next weekend.

Thank you MB, that has opened a nice little door of enquiry.

 

[mike_bryon]

Hi Sara

Interesting link. So the large viscosity increase as temp is lowered means different shaped and less breaking waves. Especially noticeable in the med where the waves are steep and tippy but also the Caribbean sea. I think these waters have relatively high salt concentrations.

Thanks for confirming it.

Mike

 

[sarabande]

I reckon there is empirical truth in your comment and the OP's. It's just that I have never, to my shame, considered wind density and water temp / salinity as having an effect on wave shape.

Sounds like a candidate for a research grant

 

[KellysEye]

>that warm waves are move tippy and break more often while cold wind seems stronger than warm air of the same wind speed.

As has been said cold air is heavier, a force 8 in the UK is worse than Force 8 in the Caribbbean. I don't think waves are materially affected by anything other than wind strength, fetch, wave period and underlying swell. For example strong wings in deep water with a long fetch have long wave periods so big waves are not a problem, in cold or warm water. Just as strong winds (at any temperature) in shallow water creates short period steep seas which are a problem.

 

[sarabande]

I'd like to think that such variables as depth of water were taken out of the equations. Also perception due to pain of cold wind in the UK and warmth further south.

Given a good, common, depth of water, does the 'shape' of waves change with air and water temp for the same wind force ?

 

[mike_bryon]

“does the 'shape' of waves change with air and water temp for the same wind force ?”

Put time into the equation. A wind arrives and the waves develop in warm water in my experience faster than in cold and they start out steeper and much more tippy. The Med is deep and there is plenty of scope. Take the North Sea, it is shallow and the waves do break but for example in a snow storm in mid November in 50 kns around the top of Denmark I experienced hell but was expecting worse in terms of breaking waves. Equally I found an Atlantic gale in August more like a washing machine than a winter gale in Biscay.

I think it is more complicated than the view that waves are materially affected by anything other than wind strength.