Reflection Subsun and the Yolo Bypass

As I walked out of the building on the end of the workday on January 25, 2017 I noticed a bright patch on the clouds in the western sky that I immediately recognized as a reflection subsun. I had previously been fortunate enough to observe this phenomenon on Feb. 1, 2008, which I photographed and submitted to Spaceweather.com. Soon after the original observation I was contacted by Ágnes Kiricsi, who informed me what it was that I had seen as well as its rarity.



Upon seeing this phenomenon again I immediately took a few photos on the spot and then began traveling down the road, stopping to take more photos when the view to the west became less obstructed by foreground objects. I also noticed that the effect seemed to be intensifying as the minutes passed. I decided to head to a hilltop a little over a mile north of my location and had hopes that I would have a better view from there. Once I arrived I was amazed at how much the reflection subsun had brightened and I took several more pictures. I wanted to continue to observe the spectacle until it disappeared but I had obligations that I needed to meet and could not stay any longer.



The conditions under which I observed this phenomenon were nearly identical for both occasions. These included the time of year, the hour of day, the clouds and their positions, and very importantly, a very wet winter leading up to the observing date. This last factor adds uniqueness to the reflection subsun occurances that I witnessed due to the fact that the required reflective body of water is normally not even in existence! Approximately 60 miles west of my observing location in Auburn, California is a long north-south flood plain called the Yolo Bypass. It is normally dry but during periods of excessive precipitation it floods (by design) with water that the Sacramento River cannot contain safely. My local winter in 2008 was sufficiently rainy to fill this region with water but then the Bypass remained mostly dry every successive year until it flooded again in 2017. I will be sure to be looking for the reflection subsun on afternoons whenever the Bypass is full and the sun is obscured by altocumulus clouds.

By Steve Sumner