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
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Between heat island effect from more blacktop, cement and building reflecting and then add the dimension of wind farms sucking cooler air to the lowest strata, what a global warming world we will be living in. Not created by coal plants but by human habitation and green energy. Wow!
Interesting. Just submitted a letter to “Earth” magazine related to this very issue.
This is a terrific paper: it is a empirically motivated advance in modeling. I would like to have seen some scatterplots of model values vs data for at least some actual column, but maybe we’ll get some of those in the future.
I forgot, with the new green wind turbines we get to kill more eagles. It will be easier then for natives applying for eagle feathers for pow wows because there will be MORE dead eagles. Yippee!
This is not new. In 2003, a ppaer suggested that 10% of warning downwind of urban centers is a product of UHI.
sigh…its getting late. Spelling errors, and not posting a reference…
http://web.archive.org/web/20031230234647/http://greeningearthsociety.org/wca/2003/wca_3b.html
As a Reno, Nevadan, living NW and approx. 400ft higher than the airport weather station, I see significant differences in “official” numbers and my own. (I’ve calibrated my outdoor sensor, btw)..
Daytime temps are within reasonable ranges for mine and the official, but nighttime temps are very often 5 degrees cooler, sometimes more. I get a lot of down-canyon drafts off of Peavine, so that’s taken into consideration. Interesting to note that our very own Mike Alger is one of the few knowledgable weather people here that does not even mention nighttime lows very often, knowing that they’re skewed. Nice to see one in the craft that doesn’t fall for the media push to subscribe us all to AGW.
I don’t really see the motivation. We already know that cities are warmer at night, and we camn see why intuitively.
This doesn’t need to be used in models. If we’re going to have models (which we shouldn’t anyway!) they should simply be based on good long-term non-urban observations.
Basic metrology. When there’s a choice between a measurement that has to be adjusted vs a measurement that doesn’t need adjusting, skip the adjusted one and use the ‘clean’ one. Only use adjusted or inferred measurements when good ones are physically unavailable, as in temperatures on Jupiter.
I’ve said it several times before. There was massive urbanisation from 1970’s to 2000’s and until they actually go out and see what the historical changes have taken place ANY WHERE NEAR weather stations, I have suspected that people responsible for doing the calculations have GREATLY UNDERESTIMATED the effect of urban warming on the so-called global average land temperature.
If we remove all the “adjustments”, and take proper accounting of urban heat effects, I wonder if there has really been that much warming at all !!
I think we were here in April but just with windmills as an example:
Supreme irony: wind farms can cause atmospheric warming, finds a new study
Posted on April 30, 2012 by Anthony Watts
http://wattsupwiththat.com/2012/04/30/supreme-irony-wind-farms-can-cause-atmosphereic-warming-finds-a-new-study/
@polistra.
The problem is that the land temperature calculations, during the 1970’s -2000’s, became much more heavily weighted towards urban and semi-urban weather stations partly because of the massive loss of remote station (why did that happen, anyone know?) and partly because many station would have been slowly influenced by the expanding urban areas.
If just raw land based tempertures are used, there is going to be an upward trend in the calculation if correct accounting for these warming effects isn’t made. And with the likes of GISS and CRU actually adjustiung things upwards while cooling the past record, a much larger trend has been manufactured.. just to suit the AGW agenda.
So what is the justification for lowering past temperature records? All the flap claiming this decade is the warmest in the U.S. does not add up to reports from the 1930’s.
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.
Tmin generally occurs in the daytime. Some time after dawn depending on latitude and season (which determine the amount of solar irradiance). And is particularly sensitive to factors that affect early morning insolation (clouds and aerosols).
Here in Australia, it correlates poorly with night time temperatures and is not a good proxy.
With all due respect, while you may not see the motivation there are those with advanced degrees heavily steeped in the last war’s ideas and commonly accepted premises who must brought forward in the climate change arguments kicking and screaming every inch of the way (it is and will be cathartic for them) through demonstrable ‘trvth’ [sic] by way of measurement (observational data) and ‘proof’ (theoretical exercise taking into account all known factors and their associated parameters, modeled even!), hence, papers like this are not written so much for thee as they are for thy antagonists …
.
There appears to be an important environment missing from the diagram. That being “airport”. Where you’d need to factor in the effect of the planes moving air around.
On the subject of boundary layer mixing, Starting around 1970 in parts of western Europe, including England there were 2 significant land use trends. Removal of hedgerows and installing field drainage. The first would reduce near ground turbulence and hence boundary layer mixing. The second reduce evaporation and hence humidity.
A post at Pielke Snr’s website documents how in western Europe humidity has decreased since the 1970s and diurnal temperature range has increased (which decreased turbulence and decreased humidity would contribute to), the opposite to the global average, which has seen DTR decrease and humidity increase.
http://pielkeclimatesci.wordpress.com/2011/05/13/guest-post-european-diurnal-temperature-range-dtr-is-increasing-not-decreasing-by-francis-massen/
Demonstrating once again that change in a global average isn’t evidence of a global effect.
Further to my previous comment (lost?) -not just road traffic, but airport traffic- would prop wash and wing tip vortices stir up the air enough (e.g. early morning departures)?
My previous comment was lost by me!
This has long been recognised in Australia by the BOM (bless ’em) who show that very minor land form changes (e.g. an earth bank or levee, or longer grass) can affect minimum temperatures. Trees or shrubs growing taller, or even very small buildings, alter air flow. Slightly windier conditions will raise minima. Here in tropical Queensland, a very still, clear night is needed for frost to settle in winter. Very small air movement ill prevent a frost. Has increased road traffic near weather stations been considered? Just another reason not to rely on surface temperatures.
Ken
Entirely logical but it raises a question in my mind. 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? I’m guessing that the average pilot (and I’m really guessing here I have no idea) would want the airport upwind of the urban setting to minimize how much turbulence has to be dealt with when landing and taking off. If there is a bias in terms of airport siting that in turn biases the impact implied by this study to the weather stations located at airports, might it imply a bias to the temperature record as a whole?
1. If Tmin rises faster than Tmax, how long before day & nite temps are equal? ;>)
I expect the Tmin rise to slow down at some point, unless Global Cooling sets in.
2. The Tmax rise should be closer to the CO2 effect without any of the forcing stuff. (Is it above, below, or “exact?” Anybody know?)
Attempts to measure the height and shape of the Heat Island day and night was going on over 40 years ago. We were measuring the heat island effect of Winnipeg, Manitoba in the late 1960s. We were also attempting to measure the boundary layer but it was limited by the poor instrumentation of the day.
We put instruments on high buildings as well as air samplers there and throughout the city for some measure of dispersion. We put instruments every 200 feet up a 1000 foot radio tower right on the edge of the city and discovered the amount of layering and its variation.
Others were trying to measure the height of the Heat Island with tethered balloons, helicopters and one study I recall was a tower within the city of Tokyo.
We measured and mapped the dispersion effect depending on the various isobaric and measured wind directions and speeds. The downstream impact of an urban area was first identified in the La Porte Indiana anomaly identified by Stanley Changnon.
http://adsabs.harvard.edu/abs/1980BAMS…61..702C
This is why I have always argued that the amount of heat island is a function of the prevailing winds and the location of the weather station relative to the urban area.
Hmm a few issues.
1. using GHCN adjusted to look at diurnal changes. rather than using adjusted monthly data
they should have used un adjusted daily data. The answer you get about changes in diurnal range over the 20th century changes if you use the right data and the right method for computing trends. There is a significant change in regime post 1985, but again, you have to
use a more complete dataset than GHCN adjusted to see that.
2. The paper is nearly silent in its description of how trends for Tmin and Tmax were calculated, how uncertainty was calculated and how the relatively sparse network of GHCN was compared with the spatially complete results of models.
3. I see no links to the code or the data. Show your work or it isnt science. maybe they gave their work to Lonnie Thompson to archive.. or maybe its at the journal.. when folks find it, please provide a link.
That said, it is interesting to see the theory about the effect of winds, especially downwind of an urban area. As Oke noted UHI max can be heavily modulated by the regional wind speed and direction. It should be interesting to test these models..
REPLY: “Show your work or it isnt science. maybe they gave their work to Lonnie Thompson to archive…” Mr. Mosher, while I agree, that’s really an unfair comparison, and I’m disappointed in you. Have you asked? No, you haven’t…you want others to find those for you while you bask in snark.
Ask and ye shall receive, but until then, please don’t compare Dick McNider to Lonnie Thompson without doing your own due diligence first. – Anthony
Some actual data:
At about 10PM here in Sacramento (day before yesterday), currently having a mini heat wave, the temperatures were:
Official temp 76 (reported on http://www.intellicast.com/Local/Weather.aspx?location=USCA0967 ).
Indoor temp measured in suburbs about 10 mi. from city Center 74.
Felt temp outdoors, 5-10 degrees (F) cooler than that.
Conclusion, the official temp is actually measuring a mini-climate, the actual temp is far different than that. The official temp is probably from an area surrounded by concrete, like the airport, or from some area surrounded by buildings. The official temp is probably measured at similar micro climate locations across the country and world. The official temp is therefor wrong. Officials measuring that temp get kudos and money if they report warming, so they keep the location where it will report warming.
An example of this officialdom effect, the reported increase in autism. When there is any hint that it might be present (like when the child acts up due to the boring drone bureaucrat teacher), the parents want autism to be true because they get money if it is true, and the school also wants it to be true because they also get money, hence the reported increase. Somehow, I don’t think human genes could have changed that much in so short a period of time to create so much more autism, do you?
So… are airports more likely to be built upwind of urban centres? Or downwind?
Good question. The answer appears (from some google searches) to be neither. Because airport runways are oriented to the prevailing winds, in order to avoid airplanes overflying the nearby city, airports are located at right angles to the prevailing wind. If the prevailing winds are from the west, the airport would generally, be north or south of the city.
Bob Shapiro;
2. The Tmax rise should be closer to the CO2 effect without any of the forcing stuff. (Is it above, below, or “exact?” Anybody know?)
>>>>>>>>>>>>
Nobody in my opinion “knows” because there are just too many factors that all affect each other. But if one was to eliminate all of those and just ask what the forcing effect of CO2 would be over the course of a day from Tmin to Tmax, even that isn’t a simple answer. My observations would be that:
1. P=5.67*10^-8*T^4 which is Stefan-Boltzmann Law with P in w/m2 and T in degrees K. So the first issue which makes the discussion less than straight forward is that the amount of P(w/m2) required to raise the temperature 1 degree at Tmin is LESS than the amount of P(w/m2) required to raise the temperature 1 degree at Tmax.
2. The CO2 forcing can only work with the radiance that is provided to it in the first place. Back to SB Law. The amount of radiance emitted at earth surface is a function of SB Law. If less watts are emitted, then there’s less watts to be absorbed and re-radiated by CO2. So…at Tmin, there are less watts than there are at Tmax.
Now I’m pretty certain that this doesn’t answer your question. My point is that though the question is simple, the answer is not. Beware the simple answer.