Lake freeze rate

[Don Monnot]

We had an early freeze-up here, but then had too much warm weather. Most of the lakes opened up again, but have since frozen over. We now have cold weather again (zero F) and lots of wind. The ice still looks a bit sketchy (with no ice fishermen on it), but will probably be safe (enough) in a day or two. Just wondering if any of you physics geeks can tell me with certainty whether the strong winds speed up the freeze rate or not. My thought was that some wind will help dissipate the heat of fusion away from the surface of the ice, but a little wind is just as effective as a lot of wind. Am I right (or am I completely off base)?

Don

[NHKitesurfer]

Wind will slow the freeze rate to some extent but I don't know if it's significant. People often think below freezing wind chill numbers means water will freeze faster but this is not true.

[Don Monnot]

Why would wind slow the freeze rate? As long as the actual temp is below freezing, that seems odd to me. I know wind chill doesn't mean anything to freezing water once a lake is frozen over. Wind on open water would tend to increase the evaporative cooling rate, but when it's iced-over that evaporation (sublimation) isn't significant. Is it an increased friction effect that slows the continued freeze rate once the lake is iced-over?

[NHKitesurfer]

It was a guess based on the assumption that moving water freezes less quickly than standing water. Lake vs stream...

[matthepp]

I have to respectfully disagree with NHK. I think the moving water case has more to do with the movement making ice crystallization difficult.
Water freezing with cold air and no wind occurs through conduction.
Water freezing with cold air and wind occurs through conduction and convection.
In either case the goal is to remove energy (heat) including the latent energy of crystallization.
I could dust off the old thermodynamics and put together a mathematical model BUT Don I think your lake will be plenty solid before reaching an answer! My quick guess is that the wind help the freeze rate just a little bit.
Wind chill affects us people so much due to the cold air convectively pulling heat off 98.6 degrees. The temperature differential of 32 degree lake water or ice is only a fraction.
I hope you get to kite soon!

[edt]

I have read some of the scientific literature about this, I get a bit impatient waiting for the lakes to freeze and first of all there is some science about how fast lakes freeze according to the temperature of the air, temperature of the water and time it's about solving some differential equations however I have not seen any model which takes into account wind.

Nor have I seen any science which takes into account solar radiation.

I think solar radiation is pretty important, not as important as air temperature but who knows for sure. If you look at a perfectly flat lake it is very silvery because more light is getting reflected back. When there is more wind the water gets rough and becomes dark because it is now absorbing more radiation, the angles of the water means the light bounces back and forth more, giving the water more chance to suck up the solar radiation.

I think when the first skim ice forms this helps the rest of the ice form more quickly because now the top of the ice is very reflective, much more reflective than plain water.

so and this is just based on general experience, a good cold night that lets some skim ice form will mean regular ice has a better chance to form. As long as there is wind, it will mechanically break up the ice and without that skim ice the sun can heat up that top layer of water and prevent skim ice from forming at all.

These are all just some hypothesis based on watching and waiting day after day for the ice to form, not actual science so I could be wrong about it.

I do think wind makes it much much harder for good decent ice to form, maybe it's not the mechanical action of the water, maybe it's not the thermal radiation maybe it's something else but I don't think ice can form if there's a lot of wind.

Oh one more thing. If your lakes get a dusting of snow right after the skim ice forms, you'll never get good ice, the snow will allow some of the thermal solar radiation through but block all of the cold wind, it's like your lake is in a styrofoam cooler with the snow on top.

In this case a really good breeze can knock off the top layer of snow, and with the bare ice touching the cold air, that will give you some solid ice more quickly.

[Hardwater Kiter]

There are a number of factors that influence how a lake freezes after the water gets cool enough to set up. As Matt pointed out moving water is much more difficult to freeze which is why lakes take a long time to set up when it's really windy and why ice where there are currents, like in flows and out flows or springs, is so dangerous. Areas with heavy vegetation or even fish activity can affect the ice production.

The depth of the water has a dramatic effect as well. For example locally one lake we ride has an average depth of 20' and we are riding on it usually by early December. Another lake approximately the same size with an average depth of 75' doesn't usually freeze until the end of January.

After a skim ice has set in, the air temp really comes into play. If it's well into the single digits or lower and there is no wind and little current ice grows amazingly fast. However, if it gets a layer of snow on top up it, the insulating effect of that snow will stop ice production. Worse yet, as the water below the ice is above freezing, the ice will actually start to degrade from below if the insulating layer isn't removed. (see pic from one of our ice inspections) There is a common misconception that snow makes ice, in fact it does the opposite.

This is why we always hope it doesn't snow until we get a good base layer of ice. Snow kills ice if the ice isn't substantial before the snow comes.

In the later part of the season snow is a benefit as it insulates the ice from the warmer air temps and the solar gain. Once that sun comes up and gets on the ice at a high angle things change quickly. Add wind to the mix, flexing a weakened ice sheet, and the ice can blow out in a day.

We had ice here in northern New England, then got hit with too much snow which weighted the ice sheet and caused water to come up over the edges and through cracks making a crappy slush situation. Once you have that you are boned as the slush under the snow never freezes, is warmer than the ice and you effectively have the ice being melted from above and below. The only solution is a warm up which we got. And a ton of rain. Two days later we dropped into single digits and went from nearly losing rideable ice to some really pristine ice.

Bob Dill has an put together an excellent resource on ice dynamics. We recommend it to our students and anyone who rides ice on a regular basis .

http://lakeice.squarespace.com/

Ice is a surprisingly dynamic thing.

[NHKitesurfer]

And don't forget altitude!!! One of my favorite lakes here in NH freezes first and has ice out after the others. Right now it's frozen across while other lakes at a lower altitude have yet to freeze. And it's a very big lake

With no snow it's looking like a very fast surface for HWK to break some speed records...maybe next weekend

[Hardwater Kiter]

Absolutely altitude! Sunapee gets and holds it's ice much better than any other lakes that far south. Even better than a lot of the lakes near us in North Conway. Seems to operate on a similar schedule as lakes up north like Umbagog. Umby sets up earlier but Sunapee seems to stay in play just as long which is really remarkable being so far south. (relatively)

I love this video. It really illustrates how the ice seems almost alive.

https://www.youtube.com/watch?v=aBhI7cNzT_E

We have really good surface for speed. Takes nothing to get moving which is good because our winds have been pretty lame lately. Today is looking pretty sweet. Getting ready to ride as I type.

No record breaks today without more wind. But it will still be a great day out there!

[Don Monnot]

Thanks for the info. We've had a couple of days with lows near zero, and high temps in the low teens. No snow at all. I'm pretty sure the ice on my local lake is rideable. No current or springs to speak of. The only springs are along the shoreline, and easy to spot and avoid. I'm going to take the whole arsenal with me: drill, skis, hockey skates, snowboard with switchblade, throw line, life jacket and ice claws. I'll hopefully see lots of ice fishermen out there (nice sunny day with temps in the low 20s), and may be able to talk some of my wimpy friends into kiting with me.

Don