Topanga Cloud Coronae
March 02, 2010
The cloud photos above showing brilliant hues and lovely color blending were captured above Topanga, California on January 10, 2010. All day long, Mother Nature sent wavy altocumulus clouds across the sky, delicate ripples and wispy mare's tails dropping from the clouds. The mackerel sky was spectacular, punctuated by lacunosus, rafts of waves and fall streak holes. Best of all, as the altocumulus passed near the Sun, they lit up in a riot of colors, called cloud corona (e). These are not related to the solar corona.
Cloud coronae colors are due to diffraction of sunlight by microscopic water droplets. When the droplets are all about the same size, which is a rarity in clouds because there’s usually a large range of particle sizes, their colors can be relatively pure and bright. Most colors occur in circular rings around the Sun. But when different parts of the cloud have groups of droplets, each with its own size range, the color distribution in the sky can be somewhat chaotic, with reds and greens intermingled. This effect is called commonly called irisation and can be seen many degrees from the Sun.
Cloud coronae are the brightest and most colorful of sky phenomena, easily outshining the rainbow and circumzenithal and circumhorizontal arcs. They’re also very common, yet few people see them. Why? Because cononae are so close to the Sun, and most people don’t look in this direction. Be sure to block the Sun with your hand or something else and also wear sunglasses -- these coronae are bright. No color manipulation was performed on these photos; these are right out of the camera.
Pictures taken on January 10, 2010. Field of view is about eight degrees.