From the Suggestions page, contributor J. Martin writes:
I wonder if other people have any views on the idea that the Mpemba effect might also come into play in Arctic Antarctic behaviour ? I would welcome a discussion on this subject.
Mpemba effect ?
The increased ice melt which is largely driven by warmer Arctic currents, then re-freezes at a faster rate. Are we seeing the Mpemba effect in action here ?
Whilst we have figures for Arctic air temperature and graphs for sea ice extent and area, we seem to lack data for Arctic water temperatures to allow a fuller discussion of future Arctic behaviour.
With warmer Arctic currents set against a background of solar cooling we may see wider oscillation between record low ice extent in summer and increasing (perhaps record) ice extent in winter.
The Mpemba effect is where warmer water will freeze before the same amount of cooler water. An experiment easily carried out at home, and one for which it is claimed that no scientist has yet satisfactorily explained.
The effect is named after Tanzanian Erasto Mpemba. He first encountered the phenomenon in 1963 in Form 3 of Magamba Secondary School, Tanganyika when freezing ice cream mix that was hot in cookery classes and noticing that they froze before cold mixes. After passing his O-level examinations, he became a student at Mkwawa Secondary (formerly High) School, Iringa, Tanzania. The headmaster invited Dr. Denis G. Osborne from the University College in Dar Es Salaam to give a lecture on physics. After the lecture, Erasto Mpemba asked him the question “If you take two similar containers with equal volumes of water, one at 35 °C (95 °F) and the other at 100 °C (212 °F), and put them into a freezer, the one that started at 100 °C (212 °F) freezes first. Why?” only to be ridiculed by his classmates and teacher. After initial consternation, Dr. Osborne experimented on the issue back at his workplace and confirmed Mpemba’s finding. They published the results together in 1969.[4]
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I’m running a test now, and will update the thread in an hour.
Tallbloke's Talkshop 
TB,
I find momentum has interesting effects.
The momentum of hot to cold is the speed with which it is freezing compared to a volume that has to “catch up” with the speed of the other.
This is very likely the effect.
Our sun has not had much activity and our atmosphere is very weak at the moment.
The distance difference from the sun is why the antarctic is colder and it would be the first to show signs of much colder IF an Ice Age were to occur.
But that would be just cold and not precipitation’s differences which would be snow to evaporation which would be a wet Ice Age compared to a dry one which is strictly cold air.
OK, I ran a simple test by putting near boiling water in one compartment of a plastic ice cube tray and 14C water in the other end of the tray. After 20 minutes in the freezer the cooler water has started to skin over with ice first.
Anyone else game to try it?
There’s a neat short video here that found the same as you Tallbloke but the glass with the hot water was completely frozen before the glass with the cold water. Could be that the film of ice on your cold water is now starting to act as an insulator.
Good find Caz. I got back to my cubes a bit late and they have both frozen. The ‘hot’ cube has a large air bubble moving around in it though so I guess it’s not frozen right through yet though, whereas the ‘cold’ cube has a smaller bubble not moving as far inside.
I wonder if the conductivity and/or heat capacities of the containers or water volume to container surface area ratio has anything to do with the opposite results.
I’ve got them both out of the freezer now to see which melts first.
Have a gin and tonic!
I heard on the radio the other day but I can’t recall which programme, That Hydro electric schemes are destroying winter ice cover, the theory being that they are used mainly to generate at peak demand in the winter and the relatively warm water stored in them is melting the ice. Now that didn’t seem quite correct to me at the time and the Mpembo effect would certainly disprove that theory. Yes the warm water would initially melt some ice but it would quickly refreeze again. I learnt this at a young age when I thought I was doing my mum a favour by throwing the hot washing up water over the snow on the garden path, it cleared the snow all right but the resultant sheet of ice nearly broke her neck.
Sorry I don’t want to hog the thread but another experience of hot water quickly freezing comes to mind. Try washing your car with hot water on a very cold day especially just before the sun goes down. In your hand you have a chammy holding very hot water but as soon as it is applied to the car, the bodywork is covered in a rime of ice, apply even more hot water and the rime is eaily melted but almost instantly the bodywork now has a film of ice.
Caz: no worries, it’s a fine thread for brainstorming. I’ve noticed the car thing too. It’s a good puzzle.
Here’s a pretty comprehensive page discussing the Mpemba effect.
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/General/hot_water.html
I have no idea what is going on, but let’s have a go.
Let’s assume there is a hysteresis loop governing freezing and melting (or the energy transfer):
compare rise time between solid red curve, large energy differential (loss ?) and dotted red with less energy differential ?.
Wrong?
Very crude, but did this comparing hot water from the tap at c.50C, with boiling water from the kettle at c.100C..
The boiling water is freezing first…..
OK! We have a majority with the empirical tests. Excellent!
Something we have to consider here is that a fridge has a thermostat which will allow the hotter liquid to cool faster but the arctic has no thermostat so the arctic air temperature must become less cold if heat from the water is transferred to air which will slow down freezing.
How about the hot water freezes from the bottom up and the cooler water freezes from the top down? And as Caz says the film of ice at the top acts as an insulator.
How does it work with sealed (or covered) containers, preventing evaporation?
Re above: hard sealing won’t work because of ice expansion, so say just a loose plastic film laid on the surface?
Apparently it makes no difference, or at least not enough difference:
http://www.phys.ncku.edu.tw/mirrors/physicsfaq/General/hot_water.html#Experiments
Water is immensely complex. I have no reason to suppose there is anything going on but oddities to do with the liquid, no law breaking.
You can for example have liquid water at -30C, so far as I know all liquids which can freeze have a supercooled state.
One possibility. Heating water is likely to help clear it of nucleating particles.
I assume the container is placed on the metal evaporator which has a layer of ice on it. A warmer container will tend to melt into better thermal contact. Cooling then takes place primarily via thermal conduction through the base.
Water like all things has latent heat of phase change, always a high figure.
I suspect the water is able to go below zero, maintaining internal convection and have a well of heat absence. This leads to the possibility of greater heat transfer into the refrigerating evaporator, perhaps with sudden freezing.
I think unravelling this properly would be an interesting exercise. Would need a controlled environmental chamber, nothing fancy.
The discussions of the Mpemba effect here and elsewhere all seem to relate to convection, insulation and other heat flow effects in containers. Would the same effect be seen in an effectively unbounded environment such as an ocean?
Perhaps similar to this effect, or related, is the experiments that show water molecules have a whole suite of crystal shapes that form in different temperatures (and humidities).
“The morphology diagram tells us a great deal about what kinds of snow crystals form under what conditions. For example, we see that thin plates and stars grow around -2 C (28 F), while columns and slender needles appear near -5 C (23 F). Plates and stars again form near -15 C (5 F), and a combination of plates and columns are made around -30 C (-22 F).
Furthermore, we see from the diagram that snow crystals tend to form simpler shapes when the humidity (supersaturation) is low, while more complex shapes at higher humidities….
Why snow crystal shapes change so much with temperature remains something of a scientific mystery. The growth depends on exactly how water vapor molecules are incorporated into the growing ice crystal, and the physics behind this is complex and not well understood. It is the subject of current research in my lab and elsewhere.”
As you can see by these exquisite crystals, water molecules love to vibrate and align in mysterious ways, and perhaps your warm Impemba water molecules are freer to move. Also, water molecules are stongly dipolar, so once a few of them align they begin to exert an efield collectively and more molecules will rotate and align. That is why clouds have efields of up to a half a mile surrounding them.
ref: http://www.its.caltech.edu/~atomic/snowcrystals/
http://www.holoscience.com/wp/electric-weather/
TB,
One thing NOT taken into consideration…
The elasticity and bonding of water and the difference when it is in a frozen state.
This elasticity and bonding problem is why you cannot shove a pipe into water where there is a different pressure and expect the pipe to flow due to the different pressure.
Zeke,
Snowflakes…Are on a flat plane of rotation…just like our sun and planets.
When freezing and rotating, these grow compared with just water freezing on the ground and crystallization forms in a non free environment.
This experiment mentions the insulating layer. The two graphs show the different ‘freezing curves’.
http://www.picotech.com/experiments/mpemba_effect/results.html
Their explanation goes like this:
‘The hotter sample will behave differently. The water at the surface will cool rapidly due to evaporation, and will become denser than the hot water below. The denser surface water will then sink to the bottom of the container and push the hotter water to the surface. The process is then repeated and this circulation of water causes a rapid drop in the water temperature.’
Whether that explains what happened with the ice cream is another question.
oldbrew;
except that (fresh) water is densest at +4°C. So colder water will tend to float, not sink. 😀
Brian H
For your consideration…
Ice can hold vast amounts of air which is contrary to sinking.
The other is pressure…as soon as you go down, pressure becomes a factor exerting upwards.
Joe;
your comments are generally kinda witless. The air is not held as bubbles, and has no effect on density to speak of. And the pressure comment is risible. Why would it affect one temperature of water more than another, except as a density function? Goofy.
oldbrew;
Indeed. Ice cream is notoriously resistant to convection!! LOL
Brian H,
You give a perfect example of a person who is rock headed to any “post-normal” science.
We live on a globe that each layer is smaller in size in circumference. So the parameters MUST also change.
Averaging generates witless minds that see absolutely no error as everything now fits into a fine box…even though the uncertainty is growing daily about this path.
Brian H says ‘except that (fresh) water is densest at +4°C. So colder water will tend to float, not sink’
Yes, but see the two graphs in the link I posted. The (initially) cooler water ‘stuck’ at 4°C nearly twice as long as the (initially) warmer water if I’m reading them right.
joe;
Not a phrase or sentence of your post is relevant or coherent. Par for your course.
oldbrew;
Faskinatin’. What would cause such “stickiness”, I wonder?
It’s an old one, this.
As Tim C. suggests, I’d go for the effects of absence/presence of dissolved gases and/or nucleation centres, either suspended, or on the sides of the vessel, or even particles reaching the surface from the air above.
In previous employment, I have purified dozens to hundreds of various low-melting point organic reaction products by distillation at various pressures in various containers, to various purities.
Many of them distilled fine as a liquid, then just sat there, supercooled, for hours or even days while I was wondering, or wanting, or trying to make them to crystallise. Then they might freeze solid in seconds while my back was turned. A watched pot never boils……and water can be the strangest liquid.
[Much crystallisation can still be described as a dark-art. I’ve known of more than one Chemistry Professor who has a sealed flask on their desk or window-sill, containing a compound that may, or may not, crystallise before they retire/die. I think it allows them to claim that they are always working and have an experiment running, even when they may be in the pub.]
h2o at room temperature Is “Balanced” between freezing and boiling, solid and gas. This state of balance is as perfect as it can be so naturally it will resist change more effectively i would think. I am not educated so i cant explain exactly what is going on the realm of physics and chemistry but this is how my simple mind can be content with this Mpemba effect. The water with more balance maintains longer and is in no hurry to change. The hot water is in an unbalanced/unstable state.
“in fact MANY stupidly simple physical problems that we have yet to adequately describe.” this is me —————-> ^ Measurement of balance and stability. this can be applied in alot of aspects im pretty sure.
this is a philosophical explaination i guess
maybe my own psychological explaination