From Dr. Roger Pielke Sr. comes word of an important new paper that shows how the air near the ground (boundary layer) is highly affected by sensitive nighttime dynamics, which show up in the Tmin of weather station data (GHCN stations in this case) but are not captured by climate models. The paper also showed that the stable nocturnal boundary layer was very sensitive to the turbulent parameterization and surface characteristics such as roughness, and land surface heat capacity and conductivity. That (bold mine) is the sorts of heat sinks/siting issues pointed out in the surfacestations project which showed that 90% of the stations in the USHCN (many of which are also part of GHCN) don’t meet siting specifications (NOAA’s 100 foot rule for example) and have been compromised by urbanization. There will be more coming on this issue in the future.
The authors also found that mixing of air aloft was the biggest contributor to nightime warming, and this may be due to surface roughness causing increased turbulence, and thus vertical mixing. I’ve added this graphic to give you an idea of how this works. A weather station downwind of the city, even in rural areas, would get more mixed air that is a composite of naturally striated warmer air aloft as well as air that was warmed from the heat sink effect of the city releasing LWIR at night into the boundary layer.
This is a very significant finding and may explain why we see things like the UHI temperature bubble in Reno Nevada, where there is a strong measured nighttime UHI effect at the surface, and it manifests itself in the USHCN/GHCN weather station at the airport. The Tmin at that station is rising faster than the Tmax. – Anthony
New JGR – Atmosphere Article “Response And Sensitivity Of The Nocturnal Boundary Layer Over Land To Added Longwave Radiative Forcing”
By Richard McNider, University of Alabama in Huntsville
We have just had a paper published in JGR entitled
McNider, R. T., G.J. Steeneveld, B. Holtslag, R. Pielke Sr, S. Mackaro, A. Pour Biazar, J. T. Walters, U. S. Nair, and J. R. Christy (2012). Response and sensitivity of the nocturnal boundary layer over land to added longwave radiative forcing, J. Geophys. Res.,doi:10.1029/2012JD017578, in press. [for the complete paper, click here]
The paper addresses the diurnal asymmetry in warming that has occurred in the observed temperature trends in the last century in which minimum temperatures have warmed at a substantially greater rate than maximum temperatures. While the paper goes into considerable detail on the response of the stable boundary layer to radiative forcing that perhaps only a stable boundary layer junkie can appreciate, the implications of the paper ,I believe, are critical to interpreting both the historical temperature data set and global modeling over the last century. For those who do not want to be overwhelmed with details, I believe the introduction and conclusions are tractable for non-boundary layer specialists.
Here let me summarize and at the end editorialize on the key points of the paper. In the last century minimum temperatures have warmed nearly three times more than maximum temperatures as captured by the NOAA Global Historical Climate Network. In fact this asymmetry is one of the most significant signals in the climate record and has been the subject of many papers.
Our paper shows that the CMIP3 climate models only capture about 20% of this trend difference.
This is consistent with other studies. Because climate models have not captured this asymmetry, many investigators have looked to forcing or processes that models have not included such as jet contrails, cloud trends, aerosols, and land use change to explain the lack of fidelity of models. However, our paper takes an alternative approach that explores the role of nonlinear dynamics of the stable nocturnal boundary layer that may provide a general explanation of the asymmetry.
This was first postulated in a nonlinear analysis of a simple two layer model we carried out a few years ago (Walters et al. 2007) that indicated that slight changes in incoming longwave radiation from greenhouse gases might result in large changes in the near surface temperature as the boundary is destabilized slightly due to the added downward radiation. This produced a mixing of warmer temperatures from aloft to the surface as the turbulent mixing was enhanced just as an increase in wind speed can destabilize the nighttime boundary and mix warm air from aloft to the surface.
…
Most of the warming at shelter height was due to the warm air mixed from aloft. This is illustrated in figure 10 in the paper. Thus, this process is a highly sensitive positive feedback to surface warming.
Figure 10: (top) Expanded view of the difference in potential temperature profile between the case of added GHG energy and base case for a geostrophic wind of 8 m s-1(top). (bottom) Expanded view of profile difference.
Read the entire post here at Dr. Roger Pielke Sr.’s website: “Response And Sensitivity Of The Nocturnal Boundary Layer Over Land To Added Longwave Radiative Forcing”
The full paper is available here: http://pielkeclimatesci.files.wordpress.com/2012/07/r-371.pdf
The paper is important, but there is nothing new in the boundary layer/turbulence diagram. Discussion, and (less elegant) versions of this appear in publications and studies related to tropical climate design going back to the early 70’s.
Noted that Steven Mosher gets a slap on the wrist above, but ” … UHI max can be heavily modulated by the regional wind speed and direction .. ” is certainly correct. We are aware of this here at 19°S 146°E. The knowledge is largely empirical.
” … It should be interesting to test these models … ” could be a problem.
Boundary layer wind tunnel tests are expensive to set up, but can produce meaningful results for estimating airflow effects. (Su San Lee, PhD Thesis, Natural Ventilation and Medium Density House Forms in the Tropics, 1998, Institute of Tropical Architecture, James Cook University).
Temperature data logging should be easier these days, but would need to be done at high resolution and in the real world. (No point measuring the air temperature in a wind tunnel, on the ground, inside a building, electric fan, cables everywhere.)
Subject is touched on here:
http://people.aapt.net.au/jclark19/designing-for-climate.pdf
(Originating from 1993 course notes, some of it outdated, no implied warranty of fitness etc.)
Let’s compare the old analog data (+/- a half degree) to todays digital temperatures. Everything still falls in the range of slope! Except for heat island and other man made Unnatural effects. Kill the eagles and save the polar bears.
Meant SLOP!
Moshpit is at it again. Clearly he’s a bright bloke but that doesn’t mean he’s always correct. He too, just like ‘scientists’ and ‘intellectuals’ everywhere is suffering from the same sickness as me; hubris!
He’s looked at the ‘Best Data’, given it his best shot and come up with ‘.. and this is what it means’ Stats without Science.
In comes a new study; it may be right, wrong or irrelevant but it challenges his from-high prognostications.
The result is that he bristles and defends his declared position. And with snark as Anthony suggests,
A very human failing that, however understandable, places him squarely within the arena occupied by Mann, Jones et al.
Less snark and snipe, Mosh. Just take a lead from SMc and do it without anything to prove other than integrity and an unselfcentred need to be honest!
But I’m a know-nothing so easy to swat aside.
As to aircraft moving air, I concur. i sat behind DC-10s and 747’s back in my airfrieght days
at say, Oakland in my twin cessna waiting for the runway viz to increase(fog) as the Jumbo took off
had to have min 1800ft viz and the jumbos were usually good for 2400 or better..
One point about airports that I don’t recall anyone making is snow removal. When it snows, airports remove all the snow from concrete areas as soon as possible. I recall being at Chicago airport in a snowstorm and watching bulldozers and trucks dump snow into a large hole, and I could see flames coming out of the hole. I assume from gas flames used to melt the snow.
Snow has a high albedo and keeps the air above it substantially cooler than concrete. In places where it snows, snow removal will have a significant warming effect on airport temperatures. And increases in the area covered with concrete will introduce a trend.
Thinking about night time temperatures, time of measurements, and what may be assumed.
A couple years ago I decided to reduce the temperature in my house. It had an asbestose roof and fibro walls. The inside of the house in summer would hit 43deg C.
So for two weeks beforehand I measured temperatures in 3 rooms, the roof, outside and under the house. I found a significantly different temperature profile for each day and in each location. (Most impressive was was 33degC outside and 53degC in the roof).
Doing a 24hour temp chart with measurements every half hour; The lowest temperature ouside is steady between 4am and 6am. The sun came up at 6am and the temperature climed steady till 12:30pm. At 2pm the temperature stared an almost linear decline till 7pm, then slowly leveled out and hit bottom at 4am (sun went down at 5:30 [I’m behind a hill]).
Just for interest; I installed vents in the roof to see what impact that would have. It delayed the temperature rise in the roof, and it cooled quicker, but made zero impact on the maximum temperature reached inside the roof. Pink bats raised the temperature inside the roof nearly 10 deg C, but reduce the temp in the house 4deg C.
I am currently in rural Montana and it is 100 F at 6:30 pm. We have two banks in town. The larger of the two banks has the thermal sensor hanging on a pipe and the wire runs about 150 feet to the digital reader and posts it at 100. The bank down the block has the sensor mounted in a metal sign and it reads 96 degrees. Why is there a 4 degree differential with two digital thermameters located only 4 blocks apart? How is that for slanting the readings.
davidmhoffer,
construction of airports are secondarily based on engineering or technical issues. Primary issues are political!!! Whose land will be bought for how much and where will it be convenient to the people contributing to the politicians making the decisions. Who will benefit from the increase in land values around the airport etc.
Philip Bradley you have missed another change in Europe. In 1967, virulent strain of Dutch Elm disease arrived in Britain. More than 25 million trees have died in the UK alone, very few mature elms were left in Britain or much of continental Europe. The English elm, which grew to more than 45 m high,are almost all gone; they died between 1970 and 2000.
So, I understand UHI but this paper tells me I must be wary of night temps because of UHI? Well, color me not surprized.
So, Steven Mosher, are you trying to say something about Dr. Pielke’s integrity in promoting this study???
http://washingtonexaminer.com/conservative-think-tank-aei-hosted-secret-meeting-with-liberal-groups-on-carbon-taxation/article/2502017
this is a report on AEI having a meeting with enviros to conjure up a carbon tax during the lame duck after the elections this year
one of the people seems to have been affiliated with HI
has anyone heard anything about this?
(i know this is OT, but if the political machine is moving on this it means that the momentum will trump any further science)
“Show your work or it isnt science.” — Steven Mosher
That pegged the irony meter so hard that the dang thing busted. I’ll need your address so I can send you the bill for repair and recalibration.
I am a non scientist. My observation of this and similar papers is that obtaining meaningful temperature data for the entire earth is probably impossible. Satellites seem to offer a far better approximation of anomolies but ground stations have far too many variables, some I suspect yet to be identified, to be of much use. The best that can be said of the AGW scam is that it has increased research and interest in climate and by doing so has rendered the original hypothesis falsified on many counts.
The full paper access link doesn’t work for me, but I see no mention of localized phase changes of water. I would have guessed that freeze/thaw or dew/evapo-transpiration might have a greater effect on the minimum than the maximum. Is this observed in practice, and is humidity data also collected at the weather stations?
Tim, having trouble with the link in your post above; it goes to the site but the far right side of the link looks to be ‘malformed’ and results in this error message on the site: “No valid record indentifier specified” … searching for “Stanley Changnon” didn’t seem to yielded four papers and none close to ‘urban heat island’ or related.
TIA, _Jim
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Steven Mosher-I think the reason the paper doesn’t go into detail about the calculation of the diurnal temperature range trends is because that is not the new work that this paper is doing: diurnal trends are a well tread area of the literature. The majority of the paper-and all the novel work in the paper-is in the particular boundary layer model used to assess the potential for redistribution of heat in the boundary layer as an explanation for the asymmetrical temperature trends in min and max.
I’ve seen many references to thermometers in the ground to take soil temperatures, but apart from some brief data i took with a colleague, I have not seen any results tabulated – not that I have looked so hard. This related to the header mention of land surface heat capacity and conductivity. If radiation is going to happen at night, the heat from the day has to get to the surface. How slow is this?
While I’m here, might I please go completely OT and ask if anyone has data from thermometers of various types exposed to specific windows in the spectrum, fromUV through vis to near IR to far IR about 100 microns out? Some potentially significant errors could arise if thermomenters were wavelength sensitive. WE know the spectrum reasonably well in terms of absorbance, but I’ve seen next to nothing about how this affects mercury, for example.
davidmhoffer says:
We know that over the course of the last number of decades, a lot of weather stations have moved from random locations where they were no longer practical for one reason or another to airports. So… are airports more likely to be built upwind of urban centres? Or downwind?
It doesn’t really matter whether an airport was originally built upwind or downwind of urban centers. Eventually the urban center encroaches upon and surrounds the airport. Wouldn’t it be more important that airports originally didn’t have paved runways but now have sprawling tarmacs or that they’re now more likely to host jets than propeller planes?
In general the inclusion of turbulent mixing and Rayleigh convection would seem to be very enlightened in atmospheric modelling. However why would nocturnal LWIR be the major driver of ground level turbulence – would not winds be a greater driver?
In consideration of Mosher above, curiosity gets the best of me. I wonder if anyone has filtered out urban data as best it can be, and focused only on rural station data, in its many flavors (T-whatever). Papers, charts etc.?
Would this not shed light on a better-mixed thermal anthropogenic atmospheric elixir? Consider wind directions, station geometry to urban centers and downwind stations within given range envelopes developing the long-term radial influence picture for urban density effects.
We would need the simply un-messed around with data, wouldn’t we? Does such exist?
In juxtaposition to a model, measurement times, readings diurnally vetted for T-min/max, the results might be an indirect measurement of UHI and overall thermal mixing downrange averaged over time and distance.
A step further, the stations within a given range of observed historical downrange UHI could be additionally removed such that the data from stations not known to be indicative of modern UHI might represent the well-mixed continental windswept mean. Such a conservative approach would not consider urban growth, opting for present-day urban footprints, further limiting stations that might be used to construct the “rural mean and variance”.
Has this already been done? (Apologies if so)
If not, Willis, would you be interested? Steven?
Or is it just not that simple?
It would be nice to know the trends of whatever the uncontaminated but well-mixed natural/anthropogenic means might turn out to be at this point in the probable evolution of the most recent end extreme interglacial. At the best resolutions we continue to prize out of the paleoclimate recordings, climate chaos seems to attend the ends of the extremes. To even tell we were here, now, we must generate a signal clearly discernible over such historic climate noise.
Veritable treasure-trove of articles on the topic under discussion –
Go here: http://www.adsabs.harvard.edu/
enter: ‘urban heat island’ as the search words (don’t use the single quotes though)
Note that several returned results mention “Nocturnal …” in the title. Unfortunately, some (all?) seem to be located behind paywalls ultimately …
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Katherine;
Wouldn’t it be more important that airports originally didn’t have paved runways but now have sprawling tarmacs or that they’re now more likely to host jets than propeller planes?
>>>>>>
I think that’s a given, I was looking for an induced trend over and above that. Philip Bradley burst my bubble though by pointing out (correctly) that airports tend to be located at right angles to the prevailing wind, which I think would result in them being neutral from the perspective of this paper.
Found an abstract of the Changon paper mentioned by Dr. Tim Ball above:
Abstract of BAMS 1980 paper by Stanley Changnon, Jr.
Title: More on the La Porte Anomaly: A Review.
Authors: Changnon, Stanley A., Jr.
Publication: Bulletin of the American Meteorological Society, vol. 61, Issue 7, pp.702-702
Publication Date: 07/1980
Origin: AMS
DOI: 10.1175/1520-0477(1980)0612.0.CO;2
Bibliographic Code: 1980BAMS…61..702C
Abstract
“The anomalous behavior of the precipitation in northwestern Indiana (the La Porte anomaly) since the late 1930s has been extensively studied and debated. Local records suggested an upward shift in warm season rainfall, thunderstorms, and hail during the 1935-65 period. The possible causes for this included changed station exposure, a poor observer, urban influences on the atmosphere due to nearby Chicago, and/or shifts in the general circulation patterns. Most debate has centered on the observer error versus urban effects explanation, but the La Porte anomaly has become a cause célèbre in the interwoven areas of climate change, air pollution, weather modification, and the quality of climatic records. A variety of recent studies of rainfall conditions and their areas of impact (streamflow, crop yields, and hail losses) show that the anomaly in the La Porte area began to shift locale in the 1950s and then disappeared in the 1960s. Taken in totality, it seems likely that the anomalous precipitation at La Porte was due to urban influences on the atmosphere, but the anomaly either ended or shifted into Lake Michigan (where it cannot now be detected) as the general circulation pattern changed, leading to fewer cyclonic passages and a more southward position of the Polar Front in the Midwest since 1960.”