A fogbow is something I’ve heard of, but have never seen before – until now. This morning I went for an early morning walk at the Eagleson Ponds, and was dismayed at first to see how foggy it was. It was only a couple of degrees above zero, with a low fog and an otherwise bright blue sky. I started walking south along the shoreline, and when I looked across the water, I saw it – a bright white patch resting on the water with a thin, pale arc reaching toward the sky like half of a rainbow. There was no colour within the arc – it appeared the same ghostly white colour as the mist.
I followed the direction of the arc with my eyes, and found another bright white patch of fog shining just at the water’s surface of the central pond, with a second arc curving toward the first. It was not a complete “bow”, but I knew what it must be – a fogbow.
Fogbows are created much in the same way as rainbows, with sunlight shining through the fog droplets and causing the light to refract at predictable angles. Fogbows can be found anywhere provided the conditions are right: thin fog and fairly bright sunshine. In addition, the the sun must be fairly low in the sky – less than 30-40° above the horizon unless you are on a hill or a ship where the mist and fogbow can be viewed from above. This is why they are most commonly seen from hills, mountains and on ships sailing through the sea mist. In fact, sea or river fog is an excellent source of fogbows. This fog forms quite frequently when warm air comes in contact with the cooler water and is chilled.
The smaller water droplets within the fog diffract light much more extensively than the rain droplets that create rainbows. Because of this, fogbows are usually white with faint reds on the outside and blues inside. They may also contain a glory at their center – a small, bright patch of colour containing the colours of the rainbow. Glories form directly opposite the sun whenever the mist or fog is below the observer, and are often photographed by mountain climbers.
I did not see a glory, and the fogbow itself was very faint. Some fogbows have very low contrast, so they are best found by looking for small bright patches in the misty background – this type of bow is brightest at the two points where it appears to meet the sea or ground. This is exactly how I managed to find it.
It didn’t last long, and disappeared as the sun climbed higher and the mist faded. I was happy to see it and add a new type of atmospheric phenomenon to my list.
On December 2nd I was returning home from shopping late in the afternoon. It was getting close to dusk, and the dark clouds in the west had already swallowed up the sun. As I turned down one road, heading west, I saw a brilliant rainbow-hued light in the sky: a sun dog. It was so bright I knew I had to photograph it, but needed a good spot with an open view of the sky. I was close to the Eagleson ponds so I figured I might as well stop in there before it disappeared. I pulled up to the entrance on Meadowbreeze Drive, got out, and started shooting.
Sun dogs are very common, but are seldom noticed. They appear twice a week in North America, on average, no matter what time of year it is. They are best seen when the sun is low in the sky, and since the sun rises and sets later in the winter than in the summer, most people tend to see them only in the winter months and associate them with cold weather. Sometimes they are so bright it appears as if there are three suns in the sky; at other times, only a smudge of colour is visible. Continue reading →
On December 18th I accompanied Jon Ruddy’s Eastern Ontario Birding trip to Algonquin Park. This was an early Christmas present to myself as it’s one of my favourite parks in Ontario and I don’t get to go that often – it’s been almost two full years since the last time I’ve been. As usual, the goal was to find winter finches and Algonquin specialties such as Spruce Grouse, Black-backed Woodpecker, Boreal Chickadees and Canada Jays (formerly known as Gray Jays); we were excited when Jon told us just a few days earlier three Spruce Grouse had been photographed right in the parking lot of the Spruce Bog Boardwalk.
The drive down was pleasant; notable birds seen along the way included an American Kestrel perching on a wire near the town of Douglas and a juvenile Bald Eagle soaring above the car just past Barry’s Bay. When we got to the park and paid for our permits, the East Gate was quiet; we heard only a single chickadee calling in the trees.
On May 20th I finished my morning birding and, after having lunch, decided to spend some time working on the garden in the backyard. At one point I happened to glance up and immediately stopped what I was doing when I saw this band of colour etched against the sky. I recognized what it was immediately – a type of ice halo known as a circumhorizontal arc – but I’ve only seen one once, and that was a long time ago. On July 20, 2009 I was at work in a downtown office highrise when I noticed a similar rainbow band in the southern sky outside our 26th floor window. I happened to have my camera with me, and managed to take a few pictures.
This phenomenon is similar to 22° halos and sundogs that are common in winter when the sun is low on the horizon, except the circumhorizontal arc only appears during the mid-summer when the sun is high in the sky and cirrus clouds are present. Tiny hexagon-shaped ice crystals in the atmosphere create halos by refracting or reflecting light. In this case, the hexagonal face of the crystals must be parallel to the ground, while the sun’s rays enter the vertical side of the crystal and exit via the lower horizontal side. The refraction of these rays produces the well-separated colours just as a prism does.
In order for this prism effect to occur, however, the sun must be at least 58° above the horizon. This means that these stunning ice halos are more commonly seen in latitudes close to the equator, and decrease in frequency the further north (or south) one travels due to the shorter amount of time the sun is sufficiently high enough. These charts shows the likelihood of circumhorizontal arcs forming at various cities in the northern hemisphere. In Ottawa – which shares the same latitude as Milan, Italy – circumhorizontal arcs are able to appear between late April and mid-August, with about 480 hours a year when it is possible.
Once I saw the beautiful band of colour I ran into the house to get my camera, then went out onto the street to take some pictures. It didn’t last long, as the cirrus clouds blew away only a few minutes later. Given how short-lived the blaze of colour turned out to be, it’s no wonder that it’s been nine years since I last saw one, and I realized how lucky I was to look up in time to see this one!
One of the most common atmospheric displays is the 22° circular halo, such as this one that I photographed in Kanata on Saturday. Created by sunlight refracting through hexagonal ice crystals suspended in the atmosphere, they are visible throughout the year and are easiest to spot when the sky is covered with a thin layer of high altitude cirrus clouds. The halo is always a distance of 22° from the sun, or about the distance between your thumb and pinkie finger when your arm is fully extended with all your fingers spread. Although the hexagonal ice crystals may be randomly-oriented, the diameters of the crystals are less than 20.5 micrometers.
The following day Deb and I spent the morning birding along the Ottawa River. There were only two weeks left until Christmas, and we wanted to make the most of our morning as we weren’t sure whether we’d be able to get out together again before the new year. We agreed to meet at 7:30, not realizing just how short the days had become; the sun had barely risen when I left, and a sun pillar was visible in the sky. The sunrise was gorgeous, but by the time I was able to pull over onto the shoulder in a safe place the sun pillar had become nearly invisible. One of the bonuses of winter birding is that the sun is so low in the sky in the morning, atmospheric phenomena such as sun dogs and other ice crystal halos are often visible. Continue reading →
After several days of gray, oppressive skies, Monday turned out to be beautiful and sunny. I decided to take my camera with me to work so I could go to Hurdman at lunch; however, even before I got to the bus stop that morning I found something interesting to photograph. A few thin, gauzy white clouds were spread across the sky, and in one of these I noticed the rainbow colours of a sun dog! Sun dogs are very common, but are seldom noticed. They appear twice a week in North America, on average, no matter what time of year it is, but are best seen when the sun is low in the sky. Sometimes they are so bright it appears as if there are three suns in the sky; at other times, only a smudge of colour is visible.