Wind Chill

[Neofolis]

I was wondering, since most weather sites include information about actual temperature and wind chill/real feel, whatever they like to call it, what effect does this have on palms.

Obviously wind can have a detrimental effect, but, in terms of cold hardiness, how would a calm night of -6°C/21°F with no added wind chill compare with a night of -4°C/25°F with a slight breeze and a wind chill factor of -8°/18°F.  Is it possible that the surface temperature of the foliage could be lower on the warmer breezier night and thus more prone to cellular damage?  This is not really an issue for me, because the coldest nights here are always calm nights with radiational freezes and the windier nights don't even compare temperature wise, but I am interested to know what other people think or have observed.

[Rusty on Pine Is.]

Hmmm, interesting question....

IMO, although it may be pure semantics, there isn't a wind chill on anything other than humans, since it is a "feels like" measurement.

....but the wind certainly does have an effect on foliage with dessication. all of my Veitchia winins (in pots) got hammered during a 32.5 event with 30+ mph winds, while many less hardy plants that were below the fence and out of the wind were OK.

This is just the drying effects of wind and temp, and not a "chilling" effect due to wind......i don't think the wind can lower surface temps past the actual air temp to cause cell rupturing.  in this case  5 degree warmer night probably would not have seen any damage at all, windy or not.

[Palm Guy]

Corey,

Palms are not affected by windchill. I remember searching an article to the same effect that Rusty was talking about. Plants do not feel perceived temperature. They are unfortunately affected by the physical battering of wind though!

Cheers,

Mike F

[tjwalters]

I believe the wind has an even greater effect if the root zone is frozen, since the plant can't replace any of the water being lost through dessication.  Of course, not often applicable to palms - perhaps Rhapidophyllum hystrix, Sabal minor and a handful of others.

[Neofolis]

Thank you all for your thoughts.  The thing that made me wonder about foliar surface temperature was the fact that surfaces of various kinds often fall below air temperatures, hence the formation of frost with air temperatures above freezing.  Generally, I would expect air movement to reduce this effect, but I wasn't sure given the concept of wind chill.

I'm still not convinced that plants have no feeling, although, if they do, it is unlikely to equate to feeling in human terms.  If you think about how some carnivorous plants respond to touch with movement, there is obviously the capacity to sense touch, surface pressure, tension or whatever.  Whether or not that corresponds to anything akin to feeling or not would be difficult to determine 100%.

[sonoranfans]

Wind chill basically describes the loss of heat that increases with wind velocity due to convective heat transfer.  So yes, the wind velocity and duration of the cold both matter.  If the duration of the cold is very long(days), the plant will stabilize in a steady state temperature equivalent to the ambient regardless of wind.  However, if the temp drops overnight, a wind can take extra heat away from the palm faster because it maximizes the thermal gradient at the plant cell/air interface.  Thus with and without wind at the same ambient temp, the palm can drop to a lower temperature, or stay cold for longer overnight with wind.

To paraphrase, wind causes the palm temp to drop faster towards the ambient temp.  In the case of overhead canopy, the wind can carry away trapped heat by blowing it from under the tree canopy(convection).  This could cause the temps under the canopy to drop off quite a bit.  This is why I plan mid height windblock(10-15') as well as overhead canopy to protect my more cold sensitive palms.

Another effect of a dry wind is to accelerate transpiration(water loss through leaves) from the plant by increasing the moisture gradient at the plant/air interface.  In high humidity this is not a problem, but in low humidity it can be dramatic, the "drying wind" effects.

[JimR]

In my own palms and particularly in an episode last March, I have seen much greater damage done by 35F with a strong North wind than by 28F with little wind to speak of.

[rsproule]

Agree with that wind chill will effect plants and is not limited to humans. Air flow carries away surface heat which in turn reduces internal heat.  It's a concept relied upon be engineers of motorcycle, car and airplane engines. We reley on the cooling effects of wind chill when we blow on the hot soup in our spoon.  However, the wind temp does need to be cooler than the surface it's blowing on.

[Neofolis]

Your blowing of soup is a good analogy, but using a similar analogy.  If I breathe on my hands I can warm them up, but if I blow on them, I can cool them down.  Surely the temperature each time is the same, because the "air" that I am breathing out is coming from the same place, just at different speeds.  That would suggest that the relationship between air temperature and surface temperature is not as you describe and that warm air can further reduce a lower surface temperature, if it is moving fast enough.  If a surface can cool to below air temperature through radiaitional energy loss, such as a frosty car windscreen in temperatures of 2°C/36°F, surely air movement will also increase that rate of energy loss, as it will move the heat being lost from the surface away from the surface more rapidly, maintaining a greater margin of temperature difference between the surface and the air.  Whilst I appreciate that the surface temperature will cool to below the air temperature due to it's faster rate of cooling, if wind causes that rate of cooling to further increase, surely it will allow the surface to cool further as well.  That would suggest that it is only the initial surface temperature that needs to be higher than the air temperature.

[tjwalters]

(Neofolis @ Mar. 12 2008,04:22)

QUOTE

If I breathe on my hands I can warm them up, but if I blow on them, I can cool them down.  Surely the temperature each time is the same, because the "air" that I am breathing out is coming from the same place, just at different speeds.

Actually, I believe the temperature is different.  Don't quote me on this - and there must be someone here more knowledgeable on this subject than I - but when one blows, the air being released was under pressure, and the rapid expansion causes cooling (some property/law of physics). When just breathing, OTOH, one's breath remains close to its original temperature.

[Turtile]

The wind does cool plants.  Plants must transpire in order to survive.  Water evaporates from the leaves which lowers the temperature (the reason why we sweat).

[buffy]

(Neofolis @ Mar. 12 2008,04:22)

QUOTE

Your blowing of soup is a good analogy, but using a similar analogy.  If I breathe on my hands I can warm them up, but if I blow on them, I can cool them down.  Surely the temperature each time is the same, because the "air" that I am breathing out is coming from the same place, just at different speeds.  That would suggest that the relationship between air temperature and surface temperature is not as you describe and that warm air can further reduce a lower surface temperature, if it is moving fast enough.  If a surface can cool to below air temperature through radiaitional energy loss, such as a frosty car windscreen in temperatures of 2°C/36°F, surely air movement will also increase that rate of energy loss, as it will move the heat being lost from the surface away from the surface more rapidly, maintaining a greater margin of temperature difference between the surface and the air.  Whilst I appreciate that the surface temperature will cool to below the air temperature due to it's faster rate of cooling, if wind causes that rate of cooling to further increase, surely it will allow the surface to cool further as well.  That would suggest that it is only the initial surface temperature that needs to be higher than the air temperature.

You're violating the laws of thermodynamics. Your blowing air analogy is not accurate. Blowing and breathing out create two different air profiles with different temperature and humidity values. You cannot use warmer air to cool another body. There's the concept of evaporational cooling, but that's not what we're talking about. You are making a lot of incorrect assumptions. Sonarafan has the concept down pat. I humbly note that I have, and it sounds like he/she has, taken plenty of thermo and heat transfer classes to lean on.

Keep it simple:

1. Warm wind warms faster than just warm air.

2. Cool wind cools faster than just cool air.

There are exceptions related to changes in pressure, volume and water content of the air, but again, keep it simple. Also, air is a fluid, you can have localized changes in values due to flow. That's why they don't measure air temperature at ground level.

[Tyrone]

OK. I would say this in relation to the real world of growing palms. Let's say it has just rained all over your garden, saturated it. Now a 90kph ie 55mph wind picks up and the ambient air temp is 14C. The wind chill will bring the plants down to near zero Celcius or 32F. This will undoubtedly be evaporating the rain that just fell, but the plant will feel that as a zero celcius figure, and freeze. I remember a particular website that had a windchill calculator and I remember those data points well. I will try and find it again.

True, moving air will not drop anything below it's temperature, but we're talking about the atmosphere which has moisture in it, and plants which have moisture in them, and these plants are generally accepting and releasing moisture through the cell walls all the time, so wind will have some cooling effect on them almost always.

regards

Tyrone

[Tyrone]

(Turtile @ Mar. 12 2008,17:09)

QUOTE

The wind does cool plants.  Plants must transpire in order to survive.  Water evaporates from the leaves which lowers the temperature (the reason why we sweat).

Agree. Transpiring without wind, will not lower the temp of the plant.

regards

Tyrone

[sonoranfans]

(Tyrone @ Mar. 12 2008,22:24)

QUOTE

OK. I would say this in relation to the real world of growing palms. Let's say it has just rained all over your garden, saturated it. Now a 90kph ie 55mph wind picks up and the ambient air temp is 14C. The wind chill will bring the plants down to near zero Celcius or 32F. This will undoubtedly be evaporating the rain that just fell, but the plant will feel that as a zero celcius figure, and freeze. I remember a particular website that had a windchill calculator and I remember those data points well. I will try and find it again.

True, moving air will not drop anything below it's temperature, but we're talking about the atmosphere which has moisture in it, and plants which have moisture in them, and these plants are generally accepting and releasing moisture through the cell walls all the time, so wind will have some cooling effect on them almost always.

regards

Tyrone

As buffy says, we must separate evaporation from heat loss due to convection(wind).  Wind can cause more rapid evaporation(and transpiration), especially if it is dry wind(larger moisture gradient).  The rate of evaporation will determine the degree of cooling and the rate of evaporation slows alot near freezing temps and at high relative humidity for any temp.  Evaporation can cause a 14c cooling at 80-90F(27-30C) degrees and dry, but the cooling effect will be lower at an ambient of 14 degrees C, and a dry wind(low humidity) will evaporate water faster(cool more) at any ambient temp.  The problem is that the rain leads to high humidity, and low evaporation(low cooling rates), unless its in the desert and humidity plummets right after the rain(or is low when it is raining).

Having lived in the desert for almost 10 years, I have seen some very unusual temp effects, especially with rain.  But I have never seen a sensor drop from 14C to freezing after a rain.  After a rain AND the sun goes down, thats another matter.  My sensors have dropped 15C in 15 minutes when it rained at 104 F ambient temp with humidity plummeting after the rain(massive evaporative cooling).

[gsn]

Okay  I can't deal with this scientific disscussion any more!

I beleive the question was, does WIND CHILL affect (impact) palm/plants.

The very simple answer is no it does not! Wind chill is a perceived sensation affecting humans,not plants.The actual air around the skin is not any colder or warmer because of the wind( with the caveate of mixing air). We as humans don't actually feel the temp of the wind,or the  actual temp of the air surrounding us. Your SKIN is what feels/ senses the temperature.

Only in extremely cold enviroments does the wind chill actually pose a serious threat to humans.

The formula for wind chill was basically created by METEROLOGISTS to HYPE the weather. Well it's only going to get down 35F degrees but the wind chill is going to make it feel like 20F, and colder that witches ... because of the wind.

Directly from Wikipedia

"  A wind-chill factor of 25° F (- 4° C) will not freeze water if the air temperature is 35° F (2° C). Water changes state according to the temperature of the body of the water. In this case, the water and air temperature are about the same — too high to freeze water." This is the same with a  palm/plant, 35 F is to high to freeze the plant cells. That is somewhat of an over simplification,as other factors do play a part,but in general this a factual statement.

Having said all that the wind in some circumstances near freezing actually helps keep plants/palms from freezzing. As it mixes the air so that the actual temp around the plant stays,warmer. Happens all the time here in Florida: no wind high  humidity temp between 33 and 39 frost can form. Add some wind ,with the same conditions and frost usually doesn't form.

Wind dissecation and transporation are  ENTIRELY different animals than WIND CHILL!

Yes high winds can cause dissecation,and evaporation from plant/palm leaves,but it is NOT because of WIND CHILL that the plant is damaged!

rant over!

[Neofolis]

I was thinking of the rate of cooling effect.  I know that warm water freezes faster than cooler water due to the rate of cooling, which means it overtakes the water that started at the lower temperature.  Does this mean that with the plants being cooled faster with wind, their temperature could drop lower than the air temperature once the cooling effect has started and thus fall to a lower temperature than the plant cooling slowly in a cooler, but wind free atmosphere?  I realize that water and solids probably react differently in terms of accelerated rates of cooling, but if the water within the cells is cooling faster, surely that would cause the surrounding tissue to cool faster as well.

[sonoranfans]

(gsn @ Mar. 13 2008,14:05)

QUOTE

Okay  I can't deal with this scientific disscussion any more!

I beleive the question was, does WIND CHILL affect (impact) palm/plants.

The very simple answer is no it does not! Wind chill is a perceived sensation affecting humans,not plants.The actual air around the skin is not any colder or warmer because of the wind( with the caveate of mixing air). We as humans don't actually feel the temp of the wind,or the  actual temp of the air surrounding us. Your SKIN is what feels/ senses the temperature.

Only in extremely cold enviroments does the wind chill actually pose a serious threat to humans.

The formula for wind chill was basically created by METEROLOGISTS to HYPE the weather. Well it's only going to get down 35F degrees but the wind chill is going to make it feel like 20F, and colder that witches ... because of the wind.

Directly from Wikipedia

"  A wind-chill factor of 25° F (- 4° C) will not freeze water if the air temperature is 35° F (2° C). Water changes state according to the temperature of the body of the water. In this case, the water and air temperature are about the same — too high to freeze water." This is the same with a  palm/plant to high to freeze the plant cells.

Having said all that the wind in some circumstances near freezing actually helps keep plants/palms from freezzing. As it mixes the air so that the actual temp around the plant stays,warmer. Happens all the time here in Florida: no wind high  humidity temp between 33 and 39 frost can form. Add some wind ,with the same conditions and frost usually doesn't form.

Wind dissecation and transporation are  ENTIRELY different animals than WIND CHILL!

Yes high winds can cause dissecation,and evaporation from plant/palm leaves,but it is NOT because of WIND CHILL that the plant is damaged!

rant over!

The simple answer to this complex subject is incorrect.  Wind chill can effect even a rock when ambient temps are dropping, they drop faster.  Yes wind chill DOES effect palms(outside dessication) in the case where the temps drop overnight and rise again the next day.  When temps are constant and cold, wind chill will not be a factor.  Sorry about the discussion, but wind chill is about RATES of temperature drop(heat transfer), and those will happen faster with the wind blowing.  When the temp of a plant drops faster, it will be cold longer.

Heat transfer is not limited to temperature differentials, heat exchanged is the key to the rates of temp drop.

For example, a sauna at 190 degrees F transfers much less heat to your arm than water at 190 degrees F,  Even though they are the same temp, the water will heat you up much faster than dry air.  People take saunas at 190 degrees all the time, try that with a bath and you will be burned.

[gsn]

It is REALLY  is not complex!

If you want to talk about all the complexities about whatever subjects you are disscussing that is fine.

But what you are talking about (disscussing) is NOT WIND CHILL!!!  ::

I thought Corey asked whether WIND CHILL affected palms/plants?

[gsn]

(sonoranfans @ Mar. 13 2008,14:17)

QUOTE

The simple answer to this complex subject is incorrect.  Wind chill can effect even a rock when ambient temps are dropping, they drop faster.  Yes wind chill DOES effect palms(outside dessication) in the case where the temps drop overnight and rise again the next day.Yes wind chill DOES effect palms(outside dessication) in the case where the temps drop overnight and rise again the next day.  When temps are constant and cold, wind chill will not be a factor.  Sorry about the discussion, but wind chill is about RATES of temperature drop(heat transfer), and those will happen faster with the wind blowing.  When the temp of a plant drops faster, it will be cold longer.

 

I think you need to look up the definition of wind chill? It is not about wind  affecting temps of inanimate objects. Yes I am sure there are many variable factors involved in an object/plant, and how cold it gets because of these variables.

What you are disscussing is again,and I repeat NOT WINDCHILL!

Definition of wind chill:

"Wind chill is the apparent temperature felt on exposed skin, which is a function of the air temperature and wind speed. The wind chill temperature (often popularly called the wind chill factor) is always lower than the air temperature, except at higher temperatures where wind chill is considered less important. In cases where the apparent temperature is higher than the air temperature, the heat index is used instead."

Does a rock have exposed skin to feel the perceived temperature drop, becuase of the wind?

[sonoranfans]

(gsn @ Mar. 13 2008,14:41)

QUOTE

(sonoranfans @ Mar. 13 2008,14:17)

QUOTE

The simple answer to this complex subject is incorrect.  Wind chill can effect even a rock when ambient temps are dropping, they drop faster.  Yes wind chill DOES effect palms(outside dessication) in the case where the temps drop overnight and rise again the next day.Yes wind chill DOES effect palms(outside dessication) in the case where the temps drop overnight and rise again the next day.  When temps are constant and cold, wind chill will not be a factor.  Sorry about the discussion, but wind chill is about RATES of temperature drop(heat transfer), and those will happen faster with the wind blowing.  When the temp of a plant drops faster, it will be cold longer.

 

I think you need to look up the definition of wind chill? It is not about wind  affecting temps of inanimate objects. Yes I am sure there are many variable factors involved in an object/plant, and how cold it gets because of these variables.

What you are disscussing is again,and I repeat NOT WINDCHILL!

Definition of wind chill:

"Wind chill is the apparent temperature felt on exposed skin, which is a function of the air temperature and wind speed. The wind chill temperature (often popularly called the wind chill factor) is always lower than the air temperature, except at higher temperatures where wind chill is considered less important. In cases where the apparent temperature is higher than the air temperature, the heat index is used instead."

Does a rock have exposed skin to feel the perceived temperature drop, becuase of the wind?

wind chill is a laymans term trying to simplify avery complex subject, and its apparently not very successful doing so.  Wind velocity takes heat away faster from a warmer object than the still air.  Try actually measuring the skin temperature, its not "apparent" its real.  I have done over 10,000 skin temperature measurements under various conditions.  Pediatric thermistor probes(low time constants), infrared temperature guns, and even IR cameras that render thermal images.  Skin temperaure in healthy individuals varies from 78-96F degrees.  Things that effect skin temperature are:

1) wind velocity

2) humidity

3) solar heating

4) exercise

5) skin barrier function

6) sweating

When I hear the definition of "wind chill", it just reminds me that the public needs "placebo definitions" for the understanding of higher science and engineering.  Sorry but wind can cool palms, and rocks faster than "no wind" conditions of the same temperature differential.  In the case of humans who generate heat, wind will actually cool the skin to lower temperatures.

Oh and that booger called the "heat index" is also related to the bodys ability to keep the blood cool by cooling at the skin surface(real skin temperatures and heat transfer there as well).  Its just an unscientific fudge factor like wind chill.  This is why your skin temp will be higher with a higher heat index, all else equal.

[happ]

Wind chill is almost unheard of in California except in the high mountains since the wind is either descending [“santa ana”] & heating up [frictional] or onshore over the Pacific Ocean and moderated.  Cold nights occur when it is calm.  Not to say that cold/windy weather conditions don’t exist because they do & the proof is clearly illustrated on palms!  Drying/desiccating winds & cold calm nights are winter’s aftermath in Cali.

[gsn]

(Neofolis @ Mar. 11 2008,03:05)

QUOTE

I was wondering, since most weather sites include information about actual temperature and wind chill/real feel, whatever they like to call it, what effect does this have on palms.

This was the original question,correct?

I think even though we as non sceintist maybe STOOPID , the common definition ,or vernacular  context for wind chill,is the defintion I gave. Therefore the original question Corey was asking, the answer would be NO!

The other things you are disscussing ,heat tranfer, heat radiating  to and from one object to another, the wind blowing on an object cooling it, or warming it, humdity, barometric pressure,ect. All these enviromental factors,combining to affect the physical properties of certain objects, with many variables is an  interesting, and great disscussion.  

However it is not a disscussion about WIND CHILL! At least as it is commonly known, to us intelectually challedged individuals!! ::  

In my first post response I said it was a MADE UP word/formula for weathermen to hype the weather,not science! :laugh:

[sonoranfans]

(gsn @ Mar. 13 2008,16:50)

QUOTE

(Neofolis @ Mar. 11 2008,03:05)

QUOTE

I was wondering, since most weather sites include information about actual temperature and wind chill/real feel, whatever they like to call it, what effect does this have on palms.

This was the original question,correct?

I think even though we as non sceintist maybe STOOPID , the common definition ,or vernacular  context for wind chill,is the defintion I gave. Therefore the original question Corey was asking, the answer would be NO!

The other things you are disscussing ,heat tranfer, heat radiating  to and from one object to another, the wind blowing on an object cooling it, or warming it, humdity, barometric pressure,ect. All these enviromental factors,combining to affect the physical properties of certain objects, with many variables is an  interesting, and great disscussion.  

However it is not a disscussion about WIND CHILL! At least as it is commonly known, to us intelectually challedged individuals!! ::  

In my first post response I said it was a MADE UP word/formula for weathermen to hype the weather,not science! :laugh:

what you missed is that wind blowing on an object is the biggest part of "wind chill", and yes palms will feel it and not just due to transpiration but real heat transfer where the temp of the palm actually drops faster in wind.

What your weathermen are not telling you is that wind chill and heat index ARE responsible for extra drops and increases in the temperature of skin(or palm fronds, buds).  That is the most important factor as palms are effected by THEIR temperature, not the temperature of the air specifically.  In so much as the air temperature lowers the palm temperature, they are effected and this is increased in wind, hence "wind chill".

So the correct qualified answer to the question is: yes, palms are effected by wind chill when the air is colder than the palm.  If the cold equilibrates(palm and air the same temp), then no wind chill will not effect the palm.

Humans experience wind chill even in prolonged cold, as the body never cools to the temperature of the air(you would be dead).

Yes we are not all scientists, but we can discuss these things as adults and not get our egos bruised when we are ignorant.  Overcoming ignorance is a part of every day life for everyone.  Those who persevere will overcome, those who dont ...  will remain as they are.

[sonoranfans]

[elHoagie]

At night, wind will make the temperature of a palm leaf warmer. If it's calm, the typical temperature of a leaf is 1-2C below the temperature of the ambient air. This is mainly because leaves are much more efficient at radiating energy than the atmosphere is. But, if it's windy the temperature of the leaf will be almost the same as the ambient air temperature...

The only reason wind chill applies to humans is because our body temperature is typically warmer than the surrounding air. If it's calm, then there's a thin layer of warmer air around us, and we don't have to work as hard to maintain our body temperature. But, if it's windy then the thin layer is blown away, and our body is exposed to the ambient air temperature.

[gsn]

(sonoranfans @ Mar. 13 2008,18:06)

QUOTE

Yes we are not all scientists, but we can discuss these things as adults and not get our egos bruised when we are ignorant.  Overcoming ignorance is a part of every day life for everyone.  Those who persevere will overcome, those who dont ...  will remain as they are.

I looked in the mirror I didn't see any bruises on my EGO! But I might have been looking in the wrong PLACE, everything looked pretty much the same as usual    :laugh:

I didn't miss that wind blowing on an object is the most important factor ,at least in MY definition. The actual temperature ,combined with the wind speed,creates a perceived APPARENT temperature. Well that along with other things ,like barometric pressure,humidity,ect!

Trust me I beleive VERY little of what my weatherman tells me! ::

Please continue the disscussion re:WIND CHILL and PALMS without me , stick a FORK in me, I am DONE! :cool:

[_Keith]

(elHoagie @ Mar. 13 2008,17:17)

QUOTE

At night, wind will make the temperature of a palm leaf warmer. If it's calm, the typical temperature of a leaf is 1-2C below the temperature of the ambient air. This is mainly because leaves are much more efficient at radiating energy than the atmosphere is. But, if it's windy the temperature of the leaf will be almost the same as the ambient air temperature...

The only reason wind chill applies to humans is because our body temperature is typically warmer than the surrounding air. If it's calm, then there's a thin layer of warmer air around us, and we don't have to work as hard to maintain our body temperature. But, if it's windy then the thin layer is blown away, and our body is exposed to the ambient air temperature.

So, something like Wilt-pruf applied to the leaves of a palm could indeed improve cold hardiness up to maybe 2C?

That is a question, by the way.  I know we are down to picking nits, but sometimes 2 degrees is the difference between life and death for a palm.

[Neofolis]

Jack, I agree that at night the wind can be beneficial.  What about as temperatures drop, as night approaches?  The palm would have stored heat, which it would start to lose.  The wind would increase that rate of cooling.  If the wind then stops during that increased rate of cooling, will the palm then cool further than the usual 1-2 degrees below the air temperature, due to the increased rate of cooling?