Reading Frost

The last few days I’ve been up and awake at about 6 am. (Shocking, I know ;-) We have a car in the shop, so I’ve been driving the spouse to work. Since the 300 TD Diesel Wagon died, her ‘backup car’ doesn’t exist. While she can drive a stick shift, it is more of an ’emergency only’ skill.

The 300 TD, for any who missed the footnote, has a ‘spun #2 rod bearing’. I inspected the crank and bearing inserts yesterday. Rough gall and smear where their ought to be polished metal. I suspect that “spun” is not an accurate term. The little notch / tabs on the ends that key the bearing material into place are intact, so the material didn’t ‘spin’. It looks to me more like some oil interruption or bit of ‘junk’ in the oil caused a lube failure and overheat / melt of the material, then an abraded and seized bearing. The engine is now in pieces as the mechanic decides what to do; boat or house payment for the year …. sarc;> ?

In any case, I’m driver while her primary car gets the suspension fixed and tires done.

Which means I’ve been up at the crack of dawn, and looking at frost on the windshield of my car (that is parked outside).

Frost. Condensed frozen water.

Water that came out of the air.

Water that, as a GHG, ought to cause a spike in cooling when it has left the air, and a spike in warming when it has evaporated back into the air the next morning. IFF the GHG thesis is correct, there ought to be some kind of evidence as we have grams / sq.meter of water coming out of the air, then going back into the air. Fairly well defined in time as well. For the morning frost, it looks like it starts melting when the sun hits it and is largely done by 10 am. So a 2 hour band from 8 am to 10 am mostly. (It varies a little bit as some places are more shaded than others).

We’ve had nearly no air flow / wind. Nice for having a stable comparison window. Also clear sky, no clouds, and no precipitation. Just air, sun, water vapor / frost cycling. Pretty clean ‘test case’.

The only “odd bit” is that the San Jose temperature is measured at the airport some distance away. I don’t know if they get frost on the grounds there. Still, the local urban bubble is pretty much one air space. SJC air slides over my head not too long after it leaves the airport on most days. (We are downwind for the normal wind patterns).

So lets look at ‘the week so far’ graphs from Wunderground:

San Jose Airport weekly 18 Jan 2013

San Jose Airport weekly 18 Jan 2013

Looking at this, even knowing that the last three mornings have had frost ( Wed, Thur, Fri); I’m not seeing much / anything in the way of a change of slope at frost evaporation / condensation times. Looks substantially directly tied to sun angle during the day and decaying heat loss at night.

Lets look at a close up of just one day, yesterday:

SJC 17Jan2013 Temp Humidity Wind

SJC 17Jan2013 Temp Humidity Wind

I was scraping frost off the windshield at 7 am. Roofs were covered with it, so were lawns. All the way over a 20 mile drive, lots of frost. This wasn’t just a local one block or two kind of thing. The regional air was significantly reduced in the largest GHG of water vapor during the late night, then it rushed back in between about 8 am and 10 am. Is there any clear indication of MORE and more rapid heat loss / cooling at the ‘after 2 am’ times? How about a break in the smooth heating increase with sun angle as the GHG floods the local air around 9 am? Not seeing it? Me neither.

In fact, the rate of cooling slows as the frost covers the surfaces later in the night. The rate of warming slows as the GHG is at it’s peak and we move past noon. There is a great deal of evidence for a “directly proportional to sunshine” temperature curve, and negative evidence for the large flux of the largest GHG.

It would likely be better to repeat this test with other areas. Find a place where the frost can be observed AT the temperature measuring site. But frankly, having looked at some stations almost in my back yard (not posting that graph as it gives more location information that I want published ;-) they are not significantly different from this graph. No ‘step functions’ with frost formation or evaporation. Solar profile not water vapor.

So IMHO, the frost is saying that there is no visible effect from having grams / sq.meter changes in the major GHG. As the air freezes and the water vapor level drops, it just doesn’t do much. What does the dew do? Not much to heat loss to space. Nor heat gain in the mornings. The sun cranks the temperature profile in a cycle. Everything else is just along for the ride. When the sun is gone, we cool, but with ever more slow heat loss even as the GHG of water vapor is dropping and forming a layer of frost. You could make the case that there is enough water vapor that stays in the sky, high overhead, so that we’re pretty stable at the surface to heat loss. But that same case would hold for adding / removing the same grams of CO2 as are cycling in the frost.

Basically, we’re pretty well saturated in that whole IR heat loss band effect and adding / removing marginal amounts just doesn’t do much. The temperature profile is dominated by solar heating of surfaces directly during the warming cycle, then direct cooling of those surfaces down to a nearly stable temperature between about 3 am and 7 am when the water vapor GHG is at its lowest. When heat flow out of the surface is balanced against heat loss to space, at no net temperature change. Solar heat storage and extraction from surface materials dominates. Not the gas / IR dynamic. (At least at times like these where the ‘wind’ is essentially nil and convection is very-low other than mid afternoon when it is simply low.)

So that’s what frost is telling me. It’s telling me ‘never mind’ about radiative changes from GHG flux. “He’s saturated, Jim”.


In looking at several cities in the ‘select location’ tab, I keep seeing the same thing. Dew point just below min-temp. Even as far south as Salinas (about an hour or less south on 101 a farm town not near anything large). There are two possible interpretations (that I can think of). 1) That’s the way the physics works and frost forms of exposed surfaces before the temp gets that low in ‘free air’ and the heat of fusion is keeping them a degree apart in the race condition between lowering moisture in the air and temperature. 2) The automated measuring things have a high value for the low temp and frost is demonstrating the ‘problem’. One would need to ‘decorate’ a station with surface thermometers to figure out which.

But here is the graph for Salinas (that looks a lot like Lincoln – near airport – and Santa Clara and a couple of other neighborhoods around).

Salinas temperature and dew point graph

Salinas temperature and dew point graph

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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18 Responses to Reading Frost

  1. Tim Clark says:

    Am I correct in stating the graph you show appears to indicate that the temperature never drops below the dewpoint. If so, is the guage near the jetblast of the redeye flights?

  2. E.M.Smith says:

    @Tim Clark:

    Yeah, I noticed that too. The local sites are similar. Not sure why. I basically noted it, and figure it was a ‘for later’ thing… Frost can form above the dew point as some surfaces get colder than free air.

    But the low temperature was only 35°F, How did frost form?

    What is important is not what the temperature was at the thermometer but what the temperature was where the frost formed, and if frost formed the local temperature was below freezing.

    A thermometer indicates the temperature where the thermometer is, usually a few feet above the ground. Because cold air sinks relative to warmer air and because the ground can cool very quickly the temperature at ground level can be cooler than a few feet higher where the thermometer is, eventhough the thermometer indicates a temperature that is above freezing, it can easily be below freezing a few feet lower
    But some areas had dew, others had frost….some areas nothing at all!…How can that happen?

    In the same way temperature varies in very areas in close proximity to one another, the amount of water vapor varies too. An exposed parking lot may have less vapor in the air than a nearby garden because the a plant canopy traps water vapor and plants transpire (emit) water vapor.

    In the garden there may be enough vapor so the condensation temperature is a dew point temperature, while in the parking lot the condensation temperature is a frost point temperature. If the air over each cools to the condensation temperature dew would be found in the garden and frost on cars in the parking lot.

    Perhaps all those tons of kerosene being turned into water vapor changing the relative humidity…

    What’s clear is that the frost was on surfaces all over here. The temperature curves are smooth (feel free to check other stations near S.J. airport at wunderground) during the phase transition times and after.

  3. agimarc says:

    Perhaps the higher temps at the airport are more reflective of the UHI effect of tarmac and physical location of the sensor site. Looks like the site sits at the center of the airport. There are micro climates all over the place, even within the UHI. We have a cold spot up here that averages 5-7 deg F below what the rest of town is reporting. Need to consider that delta when layering up to ski when cold. Cheers –

  4. adolfogiurfa says:

    Frozen water? Was it not that water was disappearing from the earth, according to your most venerated ecological saints?
    And why is it so that so many zillions of tons of water dare to violate the sacred law of the most revered science holy saint Newton and float over our heads?
    And not to count those pesky CME´s from the Sun, pouring zillions of tons of hydrogen nucleii running toward their virginal counterparts, ozone and oxygen, and ready to engage in a loving embrace to make up a lot of little babies, called water molecules…
    Never it´s too late to realize cosmological truths, at least not when we are closer to the end, 24 hours closer each day.

  5. E.M.Smith says:


    Yes, 24 hours closer each day… but the journey is a few billion years….


    I’ve added a graph for Salinas, more south and rural. It, too, has a small gap between dewpoint and temperature. Something odd to figure out. Temperature clearly hit freezing on Tuesday at a minimum, so they would have been ‘frosted’. (Air from here drifts down that way so there is enough water in the air to make frost.)

    I suspect most likely it is just that a surface gets colder than free air. Secondarily, I suspect the device doing the measuring doesn’t get as cold as the free air… It would be interesting to compare charts pre MMTS back in the ’70s. But that will need to be ‘later’ or ‘another day’…

  6. R. Shearer says:

    Perhaps there is no significant change in atmospheric water concentration dew (pun) to this effect.

  7. pg. sharrow says:

    Water vapor condenses and freezes giving up huge amounts of energy that rises into the air above. Radiation freezing of the surface that gives up energy and prevents cooling of the air.
    Remember wind machines in the orchards. ;-) pg

  8. EM I may have read your piece wrong but it seems you have evaporation and condensation the wrong way around. It takes heat to evaporate so it actually cools a surface. That is what wind chill or chill factor is about. The wind evaporates moisture from the body causing the body surface (skin) to be cooler. Same thing in your swimming pool. Evaporation cools the water. Condensation results in increased temperature -like your bathroom when someone has had a hot shower. The condensing steam increases the air temperature. Condensation of water vapor is what drives cyclones and hurricanes through a) higher local temps increasing air movement and mechanical energy and b) reduced atmospheric volume (from condensation) causing lower pressures.(which in turn increases evaporation at the water surface)

  9. crosspatch says:

    The impact from water vapor would be seen at night, not during the day. Look to see how the rate of temperature change looks as it crosses the dew point. Looks like the temperature never actually crossed the dew point on the days in your graph so there was no wholesale loss of water vapor from the air, just a little condensation from where the grass was actually colder than the air due to radiational cooling (same with the car, it can actually get colder than the surrounding air temperature).

  10. crosspatch says:

    I don’t think the last few nights even got below freezing but your car windshield/roof certainly can.

  11. John F. Hultquist says:

    We call it “Silver Frost” and it covers everything. Our temperature is below freezing (~26 +/- 4) and stays below so the stuff doesn’t go away. When the sky clears and the sun makes everything sparkle it is quite picturesque. That is on day 1. On day 2, interesting is a better word. On day 3, enough already. Today was day 4, I think. Tomorrow will be the same. If the NWS knows anything, they think this (“Patchy freezing fog”) will last until Wednesday when it might rain or snow.

  12. E.M.Smith says:

    @P.G. Sharrow & CementaFriend:

    Notice that I didn’t ascribe anything to freezing and melting / evaporation enthalpy changes. This was ‘by design’. The GHG thesis is that all can be explained by GHG dynamics. They, too, ignore Enthalpy. So “their rules” ;-)

    Yes, the formation of frost will liberate heat ( though NOT raise the temperature…) and the melting then evaporation of water will absorb heat ( though NOT stop or reverse the temperature rise from sunshine…)

    So what you have found is that enthalpy swamps GHG effects and solar heat swamps enthalpy.

    Thus GHG is useless to the cycle, and the sun / enthalpy are both more important.

    (Which is also why there is usually a ‘plateau’ at 32 F / 0 C as the ambient water freezing slows temperature drops. At least near enough to plenty of water.)

    Thank you for illustrating my point!

    (Yes, it was hard for me to NOT mention enthalpy nor heat of fusion / vaporization in the article. Though I note that when I added the addendum it slipped in…)

    So it wasn’t so much that I ‘missed’ heat of fusion, it was that I was trying very very hard to ignore it, since that’s what the GHG theory does…

    Just like I’m seriously trying to ignore the pun by R. Shearer… ;-)


    Doesn’t matter if the frost only formed on the surfaces, we still have significant volumes of water vapor leave the air. Thus less GHG. And no visible change. BTW, given the lapse rate, at ‘not too far up’ the air is frozen anyway.

    @John F. Hultquist:

    My condolences. Yes, great to look at day one, but by the end of the week…

    I couldn’t use a place like that for this compare, as the GHG of water vapor doesn’t reenter the air each day …

    I probably ought to find a place where it’s going below freezing as a compare. But I really want to be able to say “Saw significant frost and it evaporated about FOO”…

  13. E.M.Smith says:

    I think this matters. Looks like frost point is normally above the dew point:

    The frost point is the temperature at which the air is saturated with respect to water vapor over an ice surface. It is more difficult more water molecules to escape a frozen surface as compared to a liquid surface since an ice has a stronger bonding between neighboring water molecules. Because of this, the frost point is greater in temperature than the dew point. This fact is important to precipitation growth in clouds. Since the vapor pressure is less over an ice surface as compared to a supercooled liquid surface at the same temperature, when the relative humidity is 100% with respect to water vapor the relative humidity over the ice surface will be greater than 100%. Thus, precipitation growth is favored on the ice particles.

  14. AndrewS says:

    As frost occurs mostly at or near the ground, this aspect of climatology(Climate near the Ground) must not be overlooked.
    Most of the frost forming vapor likely is from the soil itself.

    [Reply: As the frost here is mostly on roof tops and cars, I think the ground is not the source of the water. -E.M.Smith]

  15. crosspatch says:

    Frost will also form above the dewpoint because the things the frost is forming on have cooled below the dewpoint. Your car roof is, through radiative cooling, trying to reach the same temperature as whatever is directly perpendicular to that surface (the nighttime sky). It will reach equilibrium when the radiation leaving equals the radiation arriving. But it can’t quite reach the temperature of the nighttime sky because the surrounding air keeps trying to warm it up through conduction. On a very still night, it is quite common for the roof of a car to drop below the temperature of the surrounding air. A bed of a pickup truck would be a great example because it would trap a pocket of air that is even colder than the surrounding air outside the bed that gives up its heat to the truck bed by conduction and it is radiated into space by the bed.

    A thermometer inside any sort of shelter or shield, particularly one that is aspirated with a fan, would not have that problem. That is one reason why they run fans in orange groves. In a grove of Mandarins which are most sensitive to cold temperatures, they will turn on the fans at 34-35F because on a very still night, the fruit can cool to below the ambient air temperature.

    When the temperature does cool below the dew point, hoar frost, “snow mist”, and “freezing fog” will appear (I experienced this many times in Northern Germany) and then it gets VERY cold if it is not cloudy after this moisture falls out of the air.

  16. tckev says:

    The more I read the piece the more this echoed in my mind –

    Fire and Ice by Robert Frost

    Some say the world will end in fire,
    Some say in ice.
    From what I’ve tasted of desire
    I hold with those who favor fire.
    But if it had to perish twice,
    I think I know enough of hate
    To say that for destruction ice
    Is also great
    And would suffice.

  17. Chuckles says:

    We’ve had a corollary here for the last couple of days. The crystallised global warming has been falling at frequent intervals, and everythings covered with a 3 or 4 inch blanket. Over the whole period my external temp sensor has been absolutely nailed at 0.00 deg C, day and night. So much so that I checked to make sure it was plugged in, and hadn’t been moved into a pool of ice/water or similar.
    But no, it’s sitting in mid air, in a sheltered spot, 1m above the ground.

    Checking the Wunderground sites around here, Cambridge, Histon, St Ives, they all show that the daily min-max range has dropped from 4-6 degrees C to 1-2 deg C, all of it in a little blip between 1 and 4 in the afternoon. The rest of the graph looks like it has been drawn with a ruler.

  18. Gary says:

    Now this is what I thought you would be writing about when I saw the title of your post. Robert Frost knew frost and it’s quiet, patient, inevitable actions on nature and human alike.

    Something there is that doesn’t love a wall,
    That sends the frozen-ground-swell under it,
    And spills the upper boulders in the sun,
    And makes gaps even two can pass abreast.
    The work of hunters is another thing:
    I have come after them and made repair
    Where they have left not one stone on a stone,
    But they would have the rabbit out of hiding,
    To please the yelping dogs. The gaps I mean,
    No one has seen them made or heard them made,
    But at spring mending-time we find them there.
    I let my neighbor know beyond the hill;
    And on a day we meet to walk the line
    And set the wall between us once again.
    We keep the wall between us as we go.
    To each the boulders that have fallen to each.
    And some are loaves and some so nearly balls
    We have to use a spell to make them balance:
    ‘Stay where you are until our backs are turned!’
    We wear our fingers rough with handling them.
    Oh, just another kind of out-door game,
    One on a side. It comes to little more:
    There where it is we do not need the wall:
    He is all pine and I am apple orchard.
    My apple trees will never get across
    And eat the cones under his pines, I tell him.
    He only says, ‘Good fences make good neighbors’.
    Spring is the mischief in me, and I wonder
    If I could put a notion in his head:
    ‘Why do they make good neighbors? Isn’t it
    Where there are cows?
    But here there are no cows.
    Before I built a wall I’d ask to know
    What I was walling in or walling out,
    And to whom I was like to give offence.
    Something there is that doesn’t love a wall,
    That wants it down.’ I could say ‘Elves’ to him,
    But it’s not elves exactly, and I’d rather
    He said it for himself. I see him there
    Bringing a stone grasped firmly by the top
    In each hand, like an old-stone savage armed.
    He moves in darkness as it seems to me~
    Not of woods only and the shade of trees.
    He will not go behind his father’s saying,
    And he likes having thought of it so well
    He says again, “Good fences make good neighbors.”

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