I looked at the photosynthetically active radiation (PAR) in Corvallis and Ithaca for each day of 2015, and there was something strange in the data. I didn't think anyone would notice, but someone caught it right away:
@asianturfgrass Interesting how Corv. hangs around 1,750 all summer while Ithica blasts through to 2,000.— turfstuf (@turfstuf) March 12, 2016
The station -- I've used data from the U.S. Climate Reference Network -- latitudes at Corvallis (44.4°N) and Ithaca (42.4°N) are similar, so I expect the maximum radiation to be similar. In fact, on average during summer I'd expect Corvallis to receive more radiation, and Ithaca less, because of the climate differences between those two locations.
What's going on? Are my calculations wrong? Is it sensor error? Were there forest fires producing smoke over Corvallis through the summer of 2015? Was it exceptionally sunny in Ithaca, and cloudy in Corvallis? I decided to look at more years, getting data from every year since 2007 for comparison. I looked at the daily totals.
Something strange happened with the data for Corvallis in 2015. In all the previous years, there were some days with global solar radiation above 27 megajoules per square meter per day (27 MJ m-2 d-1). In 2015, nothing. At first I'd thought that the Ithaca data were abnormally high. But in looking at the data from 2007 to 2015, it seems that Ithaca is within a normal range of global solar radiation, but Corvallis data are abnormally low.
I counted the days with global solar radiation greater than or equal to 27 MJ m-2.
In the 8 years prior to 2015, Corvallis had 4 years with more than 40 days above 27 MJ m-2, and only 1 year (2011) with less than 20 days reaching that level. Then in 2015, 0 days.
I'm guessing this was an undetected sensor problem or other data error. The photosynthetic photon flux density (PPFD) in Corvallis probably should not be hanging around 1750 all summer. It was in 2015, because of the data I was working with. But after a closer look, those data seem abnormally low. I'd expect the PPFD in Corvallis to be blasting through to 2000 in early summer. Can anyone with a quantum meter in the Willamette Valley confirm this?