Is it normal to be cloudy like this?
On 17 July 2016, I was in the Tokyo area with Jim Brosnan. The daily light integral (DLI) in Tokyo that day was 14.2 mol/m2. Jim asked me if it was exceptionally cloudy that day. Not really, I answered. I told him that the such cloudiness was normal.
Now that July 2016 is over, I looked at the DLI for every day in July at Tokyo and also at Batesville, Arkansas. Both are at about 35.7°N latitude, so the day lengths will be identical.
The lowest DLI at Batesville in July was 22.8 mol/m2 on July 29. In Tokyo, there were 10 days in July with a DLI less than 22.8 mol/m2, including 5 days with a DLI less than 10 mol/m2. In that context, the cloudiness on July 17 was not exceptional.
To see more, check out the average hourly PPFD and DLI values for
Tokyo in this chart and for