OK, right up front, I’m not sure what to make of this.
I started with looking for an Airport and a non-Airport to compare, but in Wunderground (who make these nice graphs) the non-airport stations around here “cut off” just a couple of years back. So I’m stuck with two airports. Given that, I decided to take one that has had a large growth profile to an International Airport and one where there has been growth, but a whole lot less. Same “back from the ocean behind some hills with a view out a bay” geography. Same ocean influenced climate. (More wind in Salinas, though). But in a “Farm Town” that has not had as much “boom” at the airport.
To me, it looks like there is just some “cyclicality” showing in the graphs. I think there is more of a ‘hot tarmac’ signature at the SJC San Jose International Airport in the 1998 peak graph (and less in the present “cloudy a lot” graph) and it looks like Salinas has less of that. But the dominant feature looks like ocean cycling to me. Then again, it mostly looks like “things change a lot”.
I tried to make all the graphs the same. Jan 1 – April 30; but Wunderground has its own way about things, so it mutated some of them to end on May 1. The vertical scale also wanders around, so you must keep an eye on that and adjust for it. Properly, the daily data ought to be downloaded and the graphs made from that, all on the same page (and with the ‘delta’ between them calculated). Maybe if I can see enough reason to do it from these graphs I’ll take a look at that. (Or someone else could … hint hint…)
I’ve semi-randomly chosen some representative dates. Sometimes because that was about as early as I could reliably find. Sometimes, like 1998, because it was a ‘peak’ of some sort.
Back in 1953
San Jose is about 50 F in winter, popping up to 60 F in tiny peaks. Spring comes and we get some ‘rolling cycle’ to it with more time spent hanging out at 60 F (about 16 C) and less down at 50 F ( 10C )
How does Salinas compare?
Darned near the same graph, IMHO. The humidity shows up (why it’s missing from SJC is an interesting question…) but other than that, “wiggles match” is the dominant theme.
New Little Ice Age Scare 1976
By this time SJC has turned into a commercial airport. Significant traffic. Not the full scale Big Traffic Major Airport of now. Then you could park in “short term parking” for something like $4 a day, dash all of 100 yards across the street, pick up your ticket at the counter about 30 feet inside, then step out the door 10 feet behind the counter and onto the tarmac near the stairs up to your plane. But it WAS tarmac… Now much more space is paved. They’ve added huge parking areas. A giant new terminal (and the associated taxiways et.al. So how does it look then?
The San Jose scale is compressed compared to Salinas. You’ve still got that 50/60 rolling, but it looks to me like some of those winter lows have been lifted just a tad, and in the last half of March, that ‘dip between the peaks’ seems to hang a degree or two higher in SJC compared to Salinas. At the end, we “cruise out” with SJC hanging almost on top of the 16 C line while Salinas “cycles” a bit more and drops below the line. I think we’re seeing that tarmac effect.
That 1990 “warming not a peak” point?
Here, the two scales match again, so a direct visual compare works better. While barometric pressure is almost a twin (these two are not very far from each other) the temperatures have a persistent if subtile departure. From March 15 to the end, Salinas “hangs the 16 C line” pretty consistently. SJC, though, “pops up” from time to time almost to the 24 C line. IMHO, those are the first sunny days of spring making that tarmac warm. The first part of the graph continues to look very “twin like” to me. Some of the warm days may hang a bit longer, but it’s hard to tell. January just before the 16th, for example, drops faster at KSNS than at SJC. The end of February seems to “hang high” just a bit longer at SJC also. Both are times of dropping barometric pressure. As our dominant storm track is from the north east, clouds ought to arrive at SJC before Salinas, not after.
The Hot Peak of 1998
OK in 1998 we hit a peak and we’ve been falling ever since. How do these two look then?
Now it’s the barometric pressure scale that has shifted in one and not the other. Adjusting for that, they continue to look like substantially the same result.
Temperatures? Also a divergent scale. That right there tells you they were different enough for the software to choose different scalings. But let’s try to pick some points to compare “datum for datum”. The last two peaks in SJC are about 21 C. For KSNS, it’s closer to 19-20 C. The “dip” at the start of April is about 10 C for both, but that mid April “pip” goes higher at SJC. Hardly showing at all in KSNS. That warm spell each side of March 15… it’s about 16C with a pip to about 18 C at the end in SJC. For KSNS, it’s more like 15 C and the “pip” struggles to get over the 16 C line, even then not holding hardly at all. January continues to be 50 F / 60 F cycling for both, with a sporadic drop to 45 F or so on cold dips. Then it looks like at the start of February on another plunge of barometric pressure SJC “hangs high” a bit longer compared to KSNS. KSNS drops to 50 F and lays there, cycling a little each side in just a couple of days. SJC takes a week or so, finally matching in Mid February. To me, it looks like it just took a while to cool down all the cement and tarmac.
By this point, SJC is a major international airport. It’s had acres and acres of paving added. Flight schedules are much more often and much larger aircraft. All around, it’s just a more paved, more solar collecting, and warmer place.
Now, in 2011
OK, time passes. The Pacific Decadal Oscillation shifts. This winter and spring has been very overcast and it has rained a lot. There have been some sunny days, but not nearly as many as in the last couple of decades. It’s been too cold to plant tomatoes even at the start of April ( I’ve sometimes put them in end of March ) and the sun has been gone for weeks at a time. We have had a “couple of weeks rain / couple of weeks not” pattern of alternating warm and cold. So any evidence of differential solar heating? (Again, note that the scales are quite different, so we do this one “by the numbers” as well…) Barometric pressures look like a substantial match to me.
At about Jan 10th, Salinas does a plunge to about 40 F that SJC doesn’t follow. Hanging up closer to 44 F. It looks like “cold spikes” get clipped at SJC. (Perhaps those 20 miles of homes and factories in all directions… and the incessent traffic…) Mid January, we pop up to that usual 60 F “warm time”, but KSNS is more prone to cooling dips, while SJC just goes to the warm line and hugs it.
It looks to me like on that rising barometric pressure in Feb start, SJC warms up quickly in the sun while KSNS takes a bit longer to “come along”. Due to the differing scales, it’s hard to see if temperatures are much different in the end of February. The biggest thing I see is that SJC is much more “steady”. Excursions are dampened.
Mid March, we’re back near that 60 F line, but with Salinas just a bit lower, on average, than SJC. April looks to start about the same at both places to me. Again, the different scales make it harder to see for sure, but that “end of the graph” month or two looks very similar in both places. I guess being under clouds most of the time does that… The very start of April “dip” looks deeper at KSNS, but it would be better to use the numbers than trying to back out the distortion of the graph visually.
Not much new. It looks to me like you can see the UHI impact in the dead of winter, and a solar / tarmac impact during the springtime (that is exacerbated by a PDO shift from “cloudy spring” to “sunny spring” and back on a 30 year basis). I think it’s pretty clear that compared to 1953 when these were “near twins” that SJC is now a degree or two warmer AND with much reduced volatility, especially downward volatility looks dampened to me.
IMHO, this kind of comparison needs to be done for each and every one of the Airport thermometers in the GHCN. It needs to be done at the “month by month” and preferably even “weather regime by weather regime” basis.
There is a significant UHI visible, and a significant Solar Tarmac effect seems to be evidenced at well.
To me, this all just shows that averaging it all together and hoping it comes out better is a gross error. Averaging is just hiding the important details of what really is happening. And that is not “Global Warming”, it is “Airport Tarmac”.
OK, that’s what I’m seeing; but this is pulling a lot of “vision” out of some pretty thin tea leaves and I could just be putting a load of “confirmation bias” into it. So if more folks could take a look and see what you see… So, you seeing something else?
Salinas Airport has a photo gallery here, so you can look around:
It starts with a Blue Angels show, so you need to scroll in a ways to see the grounds.
The SJC site has a photo montage on the top page:
These two places are about 60 miles from each other ( or about 100 km).