But I think we’re losing the object of this. The issue here is just because lights=0, that doesn’t mean the site is really “rural” or that the site doesn’t suffer from the same contamination issues that the urban sites do.

In addition, the purpose of this all is to gather information on sites meeting standards or not, so in the future we can audit the trends between the sites that meet standards and those that don’t, and how the adjustments in and between sites affect the whole. Of course, we need all or most of the stations categorized in order to do that. So what one station is doing in any particular way is not really important; we don’t want exact detailed information, just overall trends.

I think trying to figure out the exact effect at any one place is a distraction and a waste of time. Just knowing it doesn’t meet the standards and is probably contaminated “in some way” is enough.

http://www.flomerics.com/

(I had not looked at that site in a long time …. they now have S/W that seems perfectly tailored for evaluating microsite issues)

I do not know if any of you have used the Computational Fluid Dynamics modelling tool FLUENT? It is a common student package in UK universities. It will simulate many aspects of airflow in complex conditions, including temperatures.

I suspect it would be easy for an engineering undergraduate to model the Happy Ranch buildings and run the package to find out where the air goes. It sounds like a typical project. Pehaps you could find a tame student and try it?

I agree with you that what goes on in the country is not necessarily what goes on in the city, but this is a federal gov’t installation – I expect they could get the power upgraded if they wanted.

On the other hand, A/C units are often undersized – not b/c any competent HVAC installer would ever think about putting in undersized units, but b/c internal thermal loads change over the years. People add coffee pots and copy machines, they hire a new employee and move from a 19″ TV to a 60″ plasma screen. Some of these units could easily be undersized, but we have no data that any are or are even operational.

#125, Reid Simpson
Will the duty cycle matter for a single Tmax measurement ? Probably not, If the algorithm allows a single 10 sec reading to represent Tmax for the whole day. Even on cool Spring days the A/C will be on for 45 sec or so before cycling off. And the danger here, of course, is that w/o more detailed records of the time series, it will be impossible to resolve the cycling of the A/C to look for an effect in the temp signal. [Unless one shuts all of the A/C units down for a week or so, periodically, and records the fact in notes for the site, so a step function could be sought. Call it macro-cycling.]

#131: Sam Urbanito,
An A/C unit draws in ambient air, often mixed with a small amount of condenser discharge air that circles around in a vortex. It can’t bring in air cooler than ambient into the area unless there’s a nearby source of sub-ambient air. It’s possible that a very large unit that pulls in a lot of ambient air could ‘flush out’ the warming effects of concrete, say, but I doubt it. If possible, I wouldn’t call that a “spurious cooling trend.”

I agree with your general take that A/C is likely to have some effect, but we don’t have to quantify the contamination

I also agree with TCO’s prior comment that small A/C units don’t appear to be covered by the standards listed by Steve M. in #5, above. Even though A/C isn’t a large industrial heat source, it shouldn’t be near the measurement station. Perhaps the standards need to be updated, now that everybody has air conditioning.

Tom replies by noting that The National Weather Service guidelines for thermometer exposure are stringent and that failure to adhere to them will result in erroneous readings. He says “Unfortunately, the criteria are practically impossible to satisfy in an urban setting”. He relates that “A thermometer (or its sensor) should be located over grass in a white, ventilated shelter 4-6 feet off the ground, at least 100 feet from all paved surfaces and at least 500 feet from any building”. He suggests to Olson that the high day time readings could result from the thermometer’s exposure to heat radiated from a nearby sunlit surface or from heat released from an air conditioner.

here is the link to the PDF

“A technique to detect microclimatic inhomogeneities in historical records of screen-level air temperature”

Runnalls K. E. and T. R. Oke

JOURNAL OF CLIMATE 19 (6): 959-978 MAR 15 2006