An Easy Airport Heat Island Audit?

It is just now early dawn…

I’ve been out to say “Good Morning” to my bunnies and to assure all is well. Also took a ‘seed jar’ from my seed archive (freezer and fridge on the back patio) as I’m going to start some beans this weekend. Noticed it was “a bit cold” and looked at the patio thermometer… At that time, it was 41 F. BRRRRrrrrr (Hey, you folks in Canada, stop laughing! Now! I mean it!! Look, I’m a native Californian, OK? There are places in L.A. that don’t even HAVE heaters in the apartments… and if your Mocha drops below drinking temperature in under an hour, it’s, er, well, we call it cold…)

So I’m back in the house and I’m pondering what GISS or CRU or NOAA would call this, and thinking of the nearest airport… When I remember that we have Wonderful Wonderful Wunderground.com that takes airport codes as locations.

Type type typity type…

SJC is showing 46 F. Hmmm…..

Now my back patio is NOT an ideal measuring location, but the bias ought to be very much to the “warm” side, not the cool. And my thermometer is hardly calibrated worth a damn (about a 20 year old Big Round Dial job). So I get my “photography” thermometer and put it nearby. After a while, It’s reading about 47.x where it’s hard to tell exactly what the x is. A re-check of SJC shows it 48 F at that time.

But this one particular measurement is NOT the point of this article.

What’s The Point?

Each and every one of us can do a simple audit of Airport Heat Island Effect.

Get a good thermometer. Put it in a good location in your yard ( in a Stevenson screen if you can get one). Then compare to the nearest airport code at Wunderground.

Errors in thermometer siting are rarely to the low side. ( It is hard to make something artificially colder). So if you have an accurate thermometer (and I’m pretty sure Anthony Watts at WUWT has nice high / low recording thermometers for sale fairly cheaply) you can provide a “sanity check” on your nearest airport.

I’ll be getting a ‘thermometer upgrade’ for my place as soon as possible (and finding out the specs for a DIY Stevenson Screen ) and then plan to have a periodic check on my local airport. It is only a couple of miles away (same altitude and geography), and Hansen is sure you can compare and substitute temperatures ( with adjustment) from up to 1000 km away (and at different latitudes, geographies, and weather zones), so I’m pretty sure we can have useful information come from such an ‘Audit the Airport Heat Island’ project.

One would expect that the errors would have a more or less ‘bell normal’ distribution, so if we have a LOAD of readings that are lower than nearby airports, that would pretty much show that AHI is very real and give a rough magnitude. If there is little AHI, then there ought to be a more or less normal distribution about the airport temps from nearby observers.

Is there another way to do this study…

Sidebar on Airport Codes

When I first asked for local temperatures, Wunderground gave me the Santa Clara reading rather than SJC (even though I’d put in San Jose as the search term). I suspect it has some zip code info stored or that it ‘makes a good guess’ rather than jump immediately to the airport. When I put in the airport code, I got the airport, and it was a bit warmer.

SJC is presently 48 F while Santa Clara (PWS) is reporting 47.8 F so that’s 2/10 F in a few yards to small miles. (San Jose Airport is on the border of Santa Clara and San Jose). Gilroy is a semi-rural area about 10 – 15 miles south in the same valley. It is reporting 47.6 F at the moment. So as a ‘first estimate’, I’d say we’ve got about 0.4 F of Airport Heat Island. San Martin California, a bit closer, is at 47.7 F.

At times like sunrise, you do need to watch the time stamps. They do not all update at the same time and I expect the slew rate is pretty high at ‘first light’.

There is the very real possibility of identifying matched sets of airport code thermometers and “nearby” non-airport code thermometers and doing an AHI study from your living room or office without ever going outdoors (!) or owning a thermometer. This would take a bit more ‘desk work’ to find COOP or similar stations “near” each airport, but ought not to be too hard and is a lot less work than installing your own thermometer.

So, to be sure, you ought to use the actual airport code for getting the airport temperature. Then you can try putting in some nearby city names and see if there is a good reference set near your particular airport.

Also, FWIW, one study I saw on AHI said it was strongest on days with no wind (the idea being that the wind brings in fresh cooler air) so you might also want to pick stations in each major wind direction from the airport and compare them too. If the heat is drifting on the wind, there ought to be 3 cooler stations, and medium warm ones at the airport and just down wind, during modest breezes.

Why does this matter? Because the Global Historical Climate Network, GHCN, is presently 92%+ at airports in the USA and France is “all but one” airports (and one reader asserted the ‘not an airport’ was miscoded and really IS an airport…) so any AHI directly contributes to a bogus “Global Warming” factor. Many airports are also coded as “Rural” when they clearly are NOT a rural environment.

My Thermometer Location

Just so folks know, the ‘bias’ factors that might impact my thermometer are that it is over a flagstone patio (that is shaded) and under a white painted metal awning (but attached to the pole holding up the North edge of the awning, so right AT the edge). The awning itself tends to be shaded by the house from southern exposure; however, in the late afternoon, the sun shines directly in at a low angle onto the backside of the thermometer. Readings during that last 2 hours or so of sunshine are to be highly suspect of being high side. It hangs about 4 feet from the little office sized fridge and 3 foot tall mini-freezer that are my seed archive. They consume very little power and run intermittently, so I think that they are not much of an issue, but need to be assessed.

There is also a dark wood fence that DOES get some southern sun on it about 5 feet from the backside of the patio, so again we have a sunny bias to high side mid-day.

During the evenings / night, the proximity to the flagstone, and the house (stucco) ought to induce a mild warming bias. Basically, it takes a while to cool down masonry. There is also the obligatory BBQ (rarely used) about 20 feet away made of brick. This masonry might also slow the rise time in the morning. Also it is a fairly large and old ‘dial’ thermometer that may simply be wrong due to age, weathering, and the complete lack of calibration.

And I’m in the middle of a 20 mile wide basin that is Silicon Valley, so it’s a large UHI basin all by itself. Cars and pavement galore for a good long ways, then you reach the fringing mountains that keep it all in the bucket.

Given all that, I’d expect any reading I get to be biased high via the Urban Heat Island and specific locational issues.

San Francisco and SFO

Putting in “San Francisco, California” gave me SOMA San Francisco (South Of MArket street, near downtown San Francisco) while SFO gave the airport. SFO had a similar 6:53 AM reporting time as SJC, so I suspect there may be a ‘once an hour’ update near the hour. SOMA gave a current time. SFO is reporting 50 F (odd, another ‘whole degree F’, so I’m wondering if they always report whole F? And do they round up?) SOMA is reporting 49.8 F at 7:46 AM, so almost an hour later and much more ‘sun time’ and it’s still colder.

For those not familiar with the area, SFO is a few miles south of San Francisco and on the edge of the bay. (Some runway approaches are over water right up the end of the runway, so you used to get the ‘water ditch’ instructions on approach. But that seems to have mutated into a general ‘your seat is a floatation device’ nag recently.) SOMA is also near the water, just a bit further north, but much closer to a major urban area and generally down wind of it.

I would have expected SOMA to be warmer than SFO.

UPDATE: At 7:56 SFO updated to 52 F. SOMA is 50.7 at that same time. Monte Verde San Bruno (near SFO to the East) is 50.9 F so it’s looking to me like an easy way to spot about 1 F of AHI at SFO as the sun hits.