You may recall a couple of weeks ago I did an investigation of a COOP weather station in Santa Ana, CA prompted by front page article in the Orange County Register titled Urbanization Raises The Heat in Orange County. It was front page news that day, on Friday, August 8th.
The story focused on the 7.5 degree average temperature increase in Santa Ana in the past century. Most of the focus was on UHI, some was on AGW, but one thing that wasn’t mentioned was station siting.
A little bit of investigation on my part showed that the official climate station for Santa Ana was not only on the roof of the fire station there, but also near several A/C unit exhausts, and the station shelter door was facing the wrong way, west instead of north which would allow sunlight into the shelter, potentially biasing the thermometer at the times readings were taken. NOAA and the World Meteorological Organization both have specs that the shelter does must face North.
And as we see from this photo, direct sunlight does indeed enter the screen when the door is opened. At certain times of the day and year it likely strikes the thermometer directly.:
The reporter that wrote the original story, Gary Robbins, also has a blog called “sciencedude”. I asked him to review the Santa Ana COOP station, and he reported again on it on Friday September 12th in a story titled:
In that story, he enlists the help of the local NWS office to check out the issues I’ve uncovered. As a result, there is a quote from Noel Isla, from the NWS in San Diego, who is responsible for the Santa Ana COOP station:
“The weather station was moved from the ground to the roof,” Isla later told me. “And for an undetermined period, the door of the weather station wasn’t facing in the right direction. But I compared the Santa Ana data with other nearby stations (Fullerton, Yorba Linda and John Wayne Airport) and the data is consistent. The affect of the air vents and the relocation of the station appears to be negligible, if they had any affect at all. The temperature readings are good.”
I was curious about the three used for comparison, so I did a cursory check of the three stations Fullerton, Yorba Linda and John Wayne Airport using the tools available to me today.
First I logged into the station database at the National Climatic Data Center using the “Guest Login” button.
Then I got the latitude, longitude, and equipment type for each station, so I knew what to look for.
Then I did Google Earth/Maps searches and Microsoft Live Maps (closeup aerial views) to actually locate the stations and their surroundings.The airports were easy to spot, because they use the ASOS system, and that is easily visible from the air by the presence of the anemometer and wind vane towers, which are painted FAA regulation hazard red/white stripes.
Here is a ground level ASOS photo from NOAA for comparison:
Now lets look at the three stations cited by Mr. Isla.
John Wayne Airport ASOS
You can spot the ASOS station on this live Google Maps view
And here is a closeup aerial view from Microsoft Live Maps:
John Wayne Airport ASOS click for a larger interactive image.
Note that this ASOS station is not only surrounded by asphalt runways and tarmac, it’s actually ON the asphalt access road to it. That would introduce a positive bias to the temperature. What is puzzling is why they did not place it in one of the grassier areas at the airport. Perhaps it is due to the primary mission being aviation, and not climate monitoring.
Fullerton Airport ASOS
You can spot the ASOS station on this live Google Earth View
Fullerton Airport ASOS click for a larger interactive image.
This station is just a few feet away from a large airport tarmac, which will of course add heat during the day to nearby air and retain heat at night, resulting in a higher than average temperature than if it were in a grassfield for example.
Yorba Linda (Nixon Presidential Library)
This one is a but more difficult, because the temperature sensor is much smaller than an ASOS. It is listed in the NCDC database as a “NIMBUS” which is the newer model of the MMTS (Max-Min Temperature System). The MMTS looks like a beehive mounted on a pole about 5.5 feet high. Here is a photo from NOAA:
I believe I can see the MMTS unit in the NW corner of the photo, near the A/C plant, look for the circle driveway with a grass center in this Google Maps View, there is a white dot on the grass, which appears to be the MMTS unit.
Here is a close up aerial view, looking south, from Microsoft Live Maps:
While it is over grass, it’s still within 100 feet of asphalt and the building and the HVAC plant. Since this aerial photo lacked the closeup detail needed to absolutely identify the MMTS, I called upon surfacestations.org volunteer Frank Perdicaro, who lives in Orange County. He was able to get photos today. Thanks Frank!
Note that in addition to the MMTS proximity to the HVAC plant and the parking lot, as shown in the additional photos, construction is going on, altering the albedo and eventually the character of the area around the temperature sensor.
So with all the three stations the NWS used for comparison (to Santa Ana Fire Station on the roof) also being out of compliance for station siting, is it any wonder that they’d be in agreement since they all have similar sorts of positive biases?
The NWS staffer, Mr. Noel Isla, probably isn’t aware of the placement issues with these stations and the potential for bias effects.
To get an idea of how these effects manifest themselves, here is a peer reviewed paper on the subject of placing temperature sensors over concrete and other surfaces:
Yilmaz et al (2008 ) Heat over grass/soil/concrete
Since we can’t rule out positive bias in the three stations cited by Mr. Isla, they may not be useful for comparison. So the issue remains, is Santa Ana reading higher because of it’s rooftop placement near A/C exhaust vents? Only a nearby parallel measurement in a proper siting venue over time will tell for sure.
In the meantime, how much of Santa Ana’s temperature increase is from UHI, AGW, station siting or natural causes? Before this investigation, station siting wasn’t considered, now I think in light of what is presented above, siting should be given strong consideration as a factor.