There's No Wind Chill On Mars

sciencehabit writes: Even though daytime temperatures in the tropics of Mars can be about –20C, a summer afternoon there might feel about the same as an average winter day in southern England or Minneapolis. That's because there's virtually no wind chill on the Red Planet, according to a new study — the first to give an accurate sense of what it might feel like to spend a day walking about on our celestial neighbor. "I hadn't really thought about this before, but I'm not surprised," says Maurice Bluestein, a biomedical engineer and wind chill expert recently retired from Indiana University–Purdue University Indianapolis. The new findings, he says, "will be useful, as people planning to colonize Mars need to know what they're getting themselves into."

Comments

that settles it

[Anonymous Coward]

Meteorologists will lobby against colonization. The weather reports on Mars simply wouldn't be exciting enough without wind chill.

Wind chill on a space suit?

[michelcolman]

Wind chill works because of evaporation on the skin, right? I don't think anyone is going to be walking around on Mars outside a biosphere, in a T-shirt. If you're wearing a space suit, wind chill is totally irrelevant or am I missing something?

Re:Wind chill on a space suit?

[Chrisq]

Wind chill works because of evaporation on the skin, right? I don't think anyone is going to be walking around on Mars outside a biosphere, in a T-shirt. If you're wearing a space suit, wind chill is totally irrelevant or am I missing something?

Only partially - its also the continual replenishment of cold air against the skin. You don't sweat when you'r really cold.

Re:Wind chill on a space suit?

[mysidia]

Wind chill works because of evaporation on the skin, right?

Aside from the affects of evaporative cooling: wind chill also works due to air movement.

Moving air dissipates heat more quickly than stagnant air.

By the way.... since there is essentially little or no air on mars... there is essentially no wind, so it follows and is quite expected that there would be no wind chill; however, this is not very interesting, because: humans cannot survive in this environment.

It is necessary to have an artificial environment that includes air.

The environment that includes air.... if it is large enough: will be subject to wind chill, whenever a sufficient difference in pressure or temperature from one area another is large enough to cause quick air movement.

Re:Wind chill on a space suit?

[Anonymous Coward]

By the way.... since there is essentially little or no air on mars... there is essentially no wind,
so it follows and is quite expected that there would be no wind chill; however, this is not very interesting,
because: humans cannot survive in this environment.

Without assistance.
It is highly interesting for a manned Mars mission. If temperature doesn't cause an issue you can make the protective-suit a lot more flexible.
Just because the air on Mars is too thin to be breathable (And lacking oxygen.) doesn't mean that it will be directly harmful to your skin.
If gloves are optional or could be made very thin then a lot of things will be easier.
Walking around in scuba gear is preferable compared to walking around in a full pressure suit.

Re:Wind chill on a space suit?

[Anonymous Coward]

Mars is known for kicking up some pretty severe dust storms and dust devils have been recorded. None of which would be possible if there was no wind.

Re:Wind chill on a space suit?

[xororand]

Unfortunately the atmospheric pressure on Mars (0.6 kPa) is far below the Armstrong Limit (6.3 kPa) at which your blood boils at body temperature.
https://en.wikipedia.org/wiki/...

Re:Wind chill on a space suit?

[Thanshin]

Yes. It's unfortunate. It takes away the once in a lifetime opportunity of breathing 96% CO2.

Re:Wind chill on a space suit?

[Anonymous Coward]

Wind chills main effect lies in conduction. The rate of heat transfer from one medium to another is based on the temperature difference. The greater the difference the higher heat transfer. If you have stale air around you a temperature gradient will form and the transfer of heat from you to the air will decrease. If the air moves, the stale warm air will be replaced with cold air keeping the heat loss constant and higher than in the case of no wind flow.

Re:Wind chill on a space suit?

[Anonymous Coward]

Unfortunately the atmospheric pressure on Mars (0.6 kPa) is far below the Armstrong Limit (6.3 kPa) at which your blood boils at body temperature.
https://en.wikipedia.org/wiki/...

I thought the Armstrong limit had to do with how many times you can win a Tour de France without getting busted for doping?

Re:Wind chill on a space suit?

[queazocotal]

And if you continue reading past the first paragraph - you find that that is only true if the blood is no longer in your body.
The blood pressure of a live person means the blood does not boil at any pressure, as the pressure inside the blood exceeds the boiling point - even if the skin is under vacuum.

Re:Wind chill on a space suit?

[fnj]

The other problem is the entire wind chill factor is still being disputed about, here on earth. I could be -20F outside with no wind and the dry air alone would suck the moisture from your body.

[raises hand] Nobody, but nobody, who has experienced a cold climate in both still air and high winds disputes the wind chill factor.

Re:Wind chill on a space suit?

[michelcolman]

Maybe the blood doesn't actually boil, but you may get the bends (vapour bubbles forming in your blood) which will probably be lethal.

Re:Wind chill on a space suit?

[fnj]

Actually the Armstrong limit describes the PRESSURE at which water and similar fluids boil at body temperature. Yeah, if you withdrew some of your blood and put it in an open container, it would boil. But the blood in your blood vessels is not at outside pressure. Arthur C. Clarke had it right in 2001. You can experience a vacuum briefly without the blood in your blood vessels boiling. You do need to mind your eyeballs, mouth, trachea and alveoli though.

You probably know this already, but the truth of the matter of exposure of the human body to a vacuum is a bit less horrific than uninformed lurid speculation has it. You're not going to last long, but your body does not quickly blow up like a balloon from the blood boiling. There is actual experience of 10+ second exposure.

Re:Wind chill on a space suit?

[tomhath]

Even without wind the air is moving. Convection of the air from your body heat will cool you, and at -20F it will cool you a lot..

Re:Wind chill on a space suit?

[invid]

So I'm not going to be able to walk around in shirt sleeves after taking an oxygen pill? Bummer.

Re:Wind chill on a space suit?

[stenvar]

Such suits, in fact, exist and have been tested:

http://en.wikipedia.org/wiki/S...

They do allow gas exchange between your body and the space outside (vacuum, Martian atmosphere).

Re:Wind chill on a space suit?

[rossdee]

"in the truly -20ÃC temperatures it feels closer to an average winter's day in the UK."

Except theres no snow, sleet, or rain, so its not really like a UK winters day.

Re:Wind chill on a space suit?

[dreamchaser]

The pressure is too low. If you pour a cup of water on the Martian surface it will immediately start to boil due to the low pressure. You really don't want your bare skin exposed at all.

Re:Wind chill on a space suit?

[Impy the Impiuos Imp]

Not true. They've known for decades you only need an oxygen mask and a good winter coat -- no space suit required.

Re:Wind chill on a space suit?

[Charliemopps]

Wind chill works because of evaporation on the skin, right? I don't think anyone is going to be walking around on Mars outside a biosphere, in a T-shirt. If you're wearing a space suit, wind chill is totally irrelevant or am I missing something?

Windchill has nothing to do with sweat. It's more like stirring a pot of spaghetti sauce to make it heat up faster. You're helping the heat diffuse faster. Your body sweating is designed to take advantage of the process, but it would still happen with our without the sweat.

Re:Wind chill on a space suit?

[TheCarp]

While that might happen, it would also be the least of your worries, from the same article:
"no amount of breathable oxygen delivered by any means will sustain life for more than a few minutes"

and by the least of your worries, I mean....in the short period before you lose consciousnous.

Re:Wind chill on a space suit?

[Jason Levine]

I think the original comment posited that you might be able to have some kind of modified SCUBA suit instead of a full space suit. Perhaps a face mask with a hose leading to an oxygen tank but keeping your skin either exposed or covered with minimal material. Of course, the atmospheric pressure might be so low that this would be uncomfortable or could even result in injury. As a comparison, I looked up the pressure on the top of Mount Everest and got 58 kPa which is far above Mars' 0.6 kPa. It's quite possible that skin exposure to Mars' lack of pressure would result in serious injury and that a pressurized suit would still be needed.

Re:Wind chill on a space suit?

[gstoddart]

Only partially - its also the continual replenishment of cold air against the skin. You don't sweat when you'r really cold.

LOL ... depends on the humidity.

I was in a coastal area in late summer once ... the air temperature was enough to be chilly, but the soupy humidity meant I was sweating.

I didn't think that it was actually possible to be cold and sweating at the same time, but 90+% humidity and a temperature just below comfortable room temp showed me otherwise.

Now, I wasn't 'really' cold as you say ... but, nonetheless, it sucked.

Re:Wind chill on a space suit?

[mlyle]

For one, the pressures still need to work out that you can move your chest to breathe, if you're just going to wear a mask/helmet.

Re:Wind chill on a space suit?

[gstoddart]

Aside from the affects of evaporative cooling: wind chill also works due to air movement.

I don't know about you, but where I live, by the time they're discussing the wind-chill, there's no 'evaporative cooling'. There's a biting wind which travels through your clothes, pulls the heat from you, and tries to kill you. It also leads to things like frostbite happening faster.

You're describing the cooling effects of a breeze on a hot day ... you want windchill? Think downtown Chicago in the dead of winter while the wind rips along at a zillion miles per hour.

I've never heard anybody describe wind-chill for anything less than well below freezing, so there isn't a whole lot of sweat to be subject to evaporative cooling, just having your body heat sucked out of you.

Re:Wind chill on a space suit?

[Sentrion]

From your Wikipedia link: "The human body can briefly survive exposure to the hard vacuum of space unprotected,[2] despite contrary depictions in some popular science fiction. Human skin does not need to be protected from vacuum and is gas-tight by itself. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon."

Next thing you know the FDA is going to be pulling vacuum chambers after fattys have used them to take selfie's to "prove" they are or used to be body builders.

Re:Wind chill on a space suit?

[gstoddart]

The other problem is the entire wind chill factor is still being disputed about, here on earth.

That sounds like bullshit.

I've experienced -40C, which oddly enough, is also -40F.

The difference between wind and no wind at those temperatures is enormous, and can be the difference between your skin freezing in minutes or seconds.

Wind-chill is only experienced by things which generate their own heat (so it doesn't affect bridges), but if you don't think it affects animals ... well, you've never really seen winter then.

As far as I know, the only dispute about wind-chill is how, exactly, you calculate it. That it exists and is real isn't really ever disputed.

Re:Wind chill on a space suit?

[crunchygranola]

Wind chill works because of evaporation on the skin, right?

Wrong. The phenomenon know as "windchill", and is represented by "windchill factors" and such, has nothing to do with evaporation. It is the effect of forced convection on heat removal, the windchill tables were generated by examining the removal of heat from a dry cylinder. Evaporative cooling is an entirely separate phenomenon.

I don't think anyone is going to be walking around on Mars outside a biosphere, in a T-shirt. If you're wearing a space suit, wind chill is totally irrelevant or am I missing something?

Does your space suit need to only provide pressurized air, or must it be a parka too? This is an important question for designing and wearing the darned things.

According to the actual paper (TFP) on Mars (at -60 C) the subjective temperature in still air is equivalent to only -8 C on Earth. This is because the air is too thin to remove much heat, wind or no. BTW -- "still air" is actually only an ideal limiting case of windchill, when air speed is zero and you are yourself are not moving. Genuine still air is a very rare in the open in nature.

It looks like Mars is something like a happy medium in terms of air pressure for a really, really cold place. In a hard vacuum the loss of heat from your body through radiation alone is a problem, getting rid of the heat your body and equipment produce is a problem in orbit. On Mars the air is thin enough that it has limited ability to remove heat, enough to prevent over-heating, but not too much. Space suits use evaporating water to dump heat form the suit.

Re:Wind chill on a space suit?

[TheCarp]

> Also, don't confuse this kind of "boiling" with high temperature - it is more like a very rapid evaporation that cools
> the remaining liquid

Nope its actual boiling. Need to remember what the definition of the boiling point is. A liquid can evaporate at any temperature it is a liquid, but the boiling point is the highest temperature it can maintain (lets ignore superheating) without transitioning into gas.

This is the same principle upon which pressure cookers work.... raise the pressure and you raise the maximum temperature of the fluid before gas transition, any more energy you put into it gets converted into phase transition rather than heat....at least until enough water boils off that the concentrating impurities start to raise the BP but I think we can mostly ignore that if we are already calling saliva "water"

Boiling does not "lower the temperature" below its own boiling point. However, if there was no more energy input at this point (ie it wasn't say, in contact with your warm skin) it would begin to cool via evaporation at that point, but that seems unlikely while you are still.....alive....at least in these scenarios.

Re:Wind chill on a space suit?

[mysidia]

so there isn't a whole lot of sweat to be subject to evaporative cooling

Your skin is made of mostly water and always contains exposed moisture... unless it's frozen, cold air is very dry, and being bundled up with warm clothing can even increase the amount of moisture, so there will always be evaporation removing heat and moisture being replaced with cold air as air pressure fluctuates due to the wind.

However.. wind definitely does improve thermal conductivity, by increasing your contact with air particles, even beneath warm clothing, and by quickly blowing away and replacing cold gas particles that were recently heated when they came in contact with your skin.

Re:Wind chill on a space suit?

[RockDoctor]

You'll probably die of suffocation from the (multiple, at least one per lung) air embolisms before you get around to noticing the bends.

Re:Wind chill on a space suit?

[JabberWokky]

It is likely that Arthur C. Clarke, the co-author of Space Odyssey, was the one who was right on the science for that bit of plot. Since he also did things like invent the idea for communication satellites and was a member of the British Interplanetary Society, it was likely on his capable shoulders that making the scene realistic fell. It would have been interesting to be a fly on the wall as that scene came together, with a great cinematic genius working with somebody explaining the harsh realities of microgravity, explosive decompression (and the velocity that causes Bowman to bounce around), and the very limited window of time in which the human body could get back into the airlock and survive. Then scripting, filming, and editing it together to convey that committed step leading to frantic, chaotic urgency.

The whole movie is a great example of collaboration. It sure wound up as one of the more memorable scenes in a movie packed with memorable scenes.

Re:Wind chill on a space suit?

[someoneOtherThanMe]

Yes, he should have stopped at 6.3 wins!

Wind chill on a solar collector

[Anonymous Coward]

Not too relevant for people, but if you're designing a solar collector to warm an underground settlement this is pretty important. You would still need some large mirrors to get enough energy to be useful. But the low atmospheric pressure would dramatically reduce the insulation requirements. Maybe just a couple of layers of reflective foil around the pipework and behind the collector to reduce radiation losses.

Similarly, if you're planning a high pressure (from a mars perspective) greenhouse this has a real bearing on heat losses.

Re:Wind chill on a solar collector

[fnj]

Mod parent up. Good points.

Re:Wind chill on a solar collector

[stenvar]

I assume they'd be dependent on electrical solar panels, and those work less efficiently the warmer it gets.

Re:Wind chill on a solar collector

[DigitalReverend]

Wind chill does not affect inanimate objects. Yes they might cool down to the ambient temperature faster but they will never go lower than the ambient temperature regardless of the wind speed. Wind chill is what it "feels" like and last I check solar collectors don't feel.

http://www.nws.noaa.gov/om/win...

Re:Wind chill on a solar collector

[EvanED]

Wind chill does not affect inanimate objects. Yes they might cool down to the ambient temperature faster but they will never go lower than the ambient temperature regardless of the wind speed.

The second half of the second sentence doesn't imply the first sentence. If you have something heated to above ambient (e.g. a structure meant for living), a wind chill absolutely will cause you to spend more heating it.

"Wind chill won't cool thing below the actual temperature" is (almost) a solid statement. "Wind chill does not affect inanimate objects" is a BS way of overgeneralizing that into falsehood.

Re:Wind chill on a solar collector

[EvanED]

Incidentally, I should point out that wind chill, as it's measured in the US, tries to incorporate effects other than just an increase in the rate at which the warmed air is swept away from something warm by the wind. Those effects, e.g. facts dealing with the fact that your skin is wet and the air is dry, will not apply to solar panels.

Re:Wind chill on a solar collector

[nedlohs]

Wind chill doesn't care if something is animate or not.

A hot inanimate rock will cool faster in the presence of a wind chill than without (holding the actual temperature constant).

4 year old children have worked this out, as evidenced by them blowing on their hot food in order to cool it faster so they can eat it faster and get back to doing far more important things.

How do you think the fan in a computer manages to keep the inanimate cpu from overheating?

Global Warming may be the solution

[Roxoff]

We could get a shitload of fossil fuels and take it there (perhaps with a really -long- petrol pump pipe) and burn it off in the atmosphere, perhaps by driving lots of 4x4 SUV's. That should help ensure that Martian average temperatures rise nicely by 1 or maybe even 2 degrees Celsius in only a century.

Re:Global Warming may be the solution

[Irate Engineer]

Ummm...you need oxygen to burn stuff.

Re:Global Warming may be the solution

[fnj]

Problem with that is that the atmosphere of Mars is already 96% CO2, buddy. The only reason it's not a furnace is because it's so goddam thin.

Re:Global Warming may be the solution

[Roxoff]

Ummm...you need oxygen to burn stuff.

But apart from that you think the extra long petrol pump is do-able?

Re:Global Warming may be the solution

[RockDoctor]

There's oxygen in carbon dioxide. Use that!

How surprising... not

[Jesrad]

Mars' atmosphere is about 1.5 % of Earth's atmospheric density. It's around 20 mBar, or eight times too thin for sustaining life even if it was pure dioxygen. For all practical purposes it's near-vacuum. And vacuum makes for a very good thermal insulator.

Re:How surprising... not

[OolimPhon]

Mars' atmosphere is about 1.5 % of Earth's atmospheric density. It's around 20 mBar, or eight times too thin for sustaining life even if it was pure dioxygen. For all practical purposes it's near-vacuum. And vacuum makes for a very good thermal insulator.

Well, yes, but then the thin atmosphere doesn't interfere as much with radiative effects. If this were not so, Mars would be hot because of the continuous radiation input from the Sun, retained by the rock.

Re:How surprising... not

[MancunianMaskMan]

Mars' atmosphere is .. around 20 mBar ..it's near-vacuum. And vacuum makes for a very good thermal insulator.

"For all practical purposes" is not correct. The thermal conductivity of a gas is near-independent of pressure down to very low pressures, until the mean free path of particles becomes large compared to the distance to the solid where the heat gets dumped. 20mBar and the MFP is still tiny.
You need a pretty good vacuum (10^-4mbar or so) in a coffee flask otherwise it doesn't change a thing.

Re:How surprising... not

[Jason Levine]

Except that Mars is much further away from the Sun than we are (1.5 times as far) and so gets much less radiation from it.

Re:How surprising... not

[arth1]

It's also much smaller than Earth and Venus, so the area exposed to the sun (from the sun's point of view) is around 12% of Earth's. So it gets much less heat.
And light. The images we see from Mars are not what we would see if we were there - the cameras are adjusted for less light, and exposure pushed up so we can see things clearly.

I wish we would ditch the Mars efforts, and instead look at more interesting destinations like Venus (floating platform habitats) and Titan. If it's just rocks we want to visit, the moon is a better place than Mars.

Re:How surprising... not

[mlyle]

> It's also much smaller than Earth and Venus, so the area exposed to the sun (from the sun's point of view) is around 12% of Earth's. So it gets much less heat.
And light.

It's dimmer on Mars because of the inverse square law, not because of Mars being smaller. Mars being smaller doesn't have much of a direct effect on temperature, either.

> The images we see from Mars are not what we would see if we were there - the cameras are adjusted for less light, and exposure pushed up so we can see things clearly.

I think you -severely- underestimate the dynamic range of the eye compared to practical cameras.

Re:How surprising... not

[Jesrad]

I seem to remember the thermal conductivity of an ideal gas is directly proportional to the molar density times molar heat capacity, so this sounds very counter-intuitive...

"an average winter day in southern England"

[ironduke-particle]

Mmmm no. Southern England may be at the same latitude as Minneapolis, but because of the North Atlantic Drift (branch of the Gulf Stream) the climate is very different. -20C is generally not encountered in Southern England even on a very cold night in a very harsh winter.

Re:"an average winter day in southern England"

[ironduke-particle]

Dear Lord... so I followed the link. It even says "Summer afternoons in the tropics of Mars might even feel as comfortable as an average winter day in the south of England" in the paper's abstract. Tsk.

Re:"an average winter day in southern England"

[ironduke-particle]

I did misread the post, but not the day/night thing ... the clue was in the article's title, "Martian Windchill in Terrestrial Terms" ... in the absence of windchill, subjectively it should feel far warmer because of reduced heat losses.

Not an entirely useless observation

[JonathanHart]

The real use for this info is understanding and designing for thermodynamic exchanges with the Martian atmosphere. The useful takeaway from this article is that heat dissipation from a source will be dominated by infrared emission rather than contact exchange with the atmosphere. Useful knowledge for the design of electronics, pressure suits, and habitats.

Re:"People planning on colonizing Mars ..."

[burisch_research]

No joke. Elon's planning to make this happen really quite soon, and I'm inclined to believe him.

http://en.wikipedia.org/wiki/M...

Still not at all cozy

[fnj]

Somebody already beat me with the post about the surface of Mars being beyond the Armstrong limit.

I'll just reinforce that by pointing out that the atmosphere at the surface of Mars is the same density as Earth's atmosphere at 34,600 m of altitude. Feeling a bit chilly is about the LAST thing you would have to worry about on Mars. Saliva vaporizing from the surface of your tongue, tears vaporizing in your eyes, and fluids evaporating from the alveoli in your lungs will be a bit bothersome if you open your mouth and eyes before you pass out from anoxia. Ever see the space-suit-looking contraption with full helmet that you have to wear in an SR-71? Well, the ceiling of the SR-71 is a good 8700 m below 34,600. Then there's the itsy bitsy detail that Mars' atmosphere is 96% CO2.

An oxygen mask alone just won't do any good.

Minneapolis or Southern England?

[Anonymous Coward]

These places aren't comparable.

Average January temperature in Minneapolis: -9C
Average January temperature in London: 4C

Re:Minneapolis or Southern England?

[Nethemas the Great]

As a Minnesota resident I also don't find their statements particularly comforting. An average Minnesotan winter day is still pretty F'ing cold, especially if they are allowing for the wind chill.

Nice to know while your blood boils away

[Squidlips]

There is almost no air pressure on Mars. You might enjoy the temperature for the minute or so until you body fluids start to boil. Then the experience would change.

Re:Nice to know while your blood boils away

[tibit]

I didn't know the body fluids had a timer and had to wait until it expires. Surface moisture on all of our body's surfaces exposed to the atmosphere evaporates plenty even in standard conditions. At pressures below the Armstrong limit , there'll be boiling of water at the surface, but that's not the end of the world. Some of the critical fluids inside of your body most definitely are not at ambient pressure. Hypotension let loose will kill you :)

Your lungs certainly don't take lightly to the surface boiling "treatment", but that's a reversible effect. When exposed to vacuum, it's really anoxia that kills you. The oxygen in your blood, circulating through the lungs, will off-gas into the vacuum in the airway. That's the primary mechanism of oxygen loss when exposed to vacuum. That's why you can hold your breath for minutes at atmospheric pressure - nothing is removing the dissolved oxygen from your blood. Yet, in vacuum, you'll pass out from hypoxia in ~10 seconds.

If you were, prior to being exposed to vacuum, to evacuate your lungs and then fill them with an oxygenated buffer liquid like perflubron, you'd probably stay conscious for much longer than the ballpark 10 seconds. Yeah, your skin would be swelling like crazy, and you'd be frothing from the nose, but so what - it's reversible. My rear-end-sourced estimate is that you'd have 20 seconds of ambulation for airlock-to-airlock stroll on Mars with such pre-treatment, assuming you'd be trained not to get too excited about it.

Even without wind chill

[Anonymous Coward]

Mars ain't the kind of place to raise your kids. In fact it's cold as hell.

Re:Even without wind chill

[wanted]

Space is one cold motherfucker.
https://www.youtube.com/watch?...

Wind chill on Venus?

[jfdavis668]

So, what is the wind chill on Venus? Would a very dense, hot atmosphere have a wind chill?

Why do you need wind for wind chill?

[viperidaenz]

Isn't wind chill a lower apparent temperature due to increased evaporative cooling caused by moving air?
When the atmosphere is of such low pressure than water can't maintain a liquid state, as soon as any skin is exposed, all surface water will evaporate and suck the heat away with it.

Assuming your head is still sealed so you've got air to breathe, it also wouldn't be nice having 1 bar of pressure trying to suck your blood through your skin.

Re:no sweat

[PopeRatzo]

It has more to do than "little".

According to the explanation of wind chill, it is one of the three methods of transference of heat that causes the phenomenon:

A solid surface loses heat through evaporation, conduction, and radiation.[1] The rate of conduction depends on the difference in temperature between the surface and its surroundings. As conduction from a warm surface heats the air around it, an insulating boundary layer of warm air forms against the surface. Moving air disrupts this boundary layer, or epiclimate, allowing for cooler air to replace the warm air against the surface. The faster the wind speed, the more readily the surface cools.

The effect of wind chill is to increase the rate of heat loss and reduce any warmer objects to the ambient temperature more quickly. It cannot, however, reduce the temperature of these objects below the ambient temperature, no matter how great the wind velocity. For most biological organisms, the physiological response is to generate more heat in order to maintain a surface temperature in an acceptable range. The attempt to maintain a given surface temperature in an environment of faster heat loss results in both the perception of lower temperatures and an actual greater heat loss. In other words, the air 'feels' colder than it is because of the chilling effect of the wind on the skin. In extreme conditions this will increase the risk of adverse effects such as frostbite.

h/t Wikipedia