Friday morning’s sunrise featured a few atmospheric phenomena over the Metro Atlanta area: A sun halo, with both sundogs on each side of the sun.
According to EarthSky.org, “Halos are a sign of high thin cirrus clouds drifting 20,000 feet or more above our heads.”
“These clouds contain millions of tiny ice crystals. The halos you see are caused by both refraction, or splitting of light, and also by reflection, or glints of light from these ice crystals.”
According to the site Atmospheric Optics, the halo remains the same diameter no matter what position the sun is found in the sky. However, portions of the ring may be missing -- either due to terrain or other atmospheric conditions -- so at times, a segment of the halo can be seen.
A sun halo is also referred to as a 22-degree halo because the ring has a radius of approximately 22 degrees around the sun or moon.
How Sundogs Form
Sundogs are also known as parhelion when one is in view, parhelia when both are visible in the sky; the term is Ancient Greek for “beside the sun”. They are also known as “mock suns” because they resemble the true sun in the middle.
Sundogs occur when sunlight refracts in the ice crystals within the high, thin clouds in the sky. The ice crystals are oriented so that their faces are parallel to the ground, allowing the light to pass through the edges at a 22-degree angle.
The sunlight enters the ice crystal and exits from a different edge, refracting again at the exit point. Red light refracts more than blue light, so the reddish hues will be on the side facing the true sun, while blueish hues will be on the outer sides of the sundog.
But it takes more than a single ice crystal to produce a sundog! In fact, the sun halo and sundogs are produced when large amounts of ice crystals are present in the atmosphere.
You may have heard the phrase “ring round the moon means rain soon”. Of course, a ring around the sun also means rain soon!
This is meteorologically correct, since the ice crystals in these clouds are associated with an advancing rain or storm system. Sun halos and sun dogs often form when thin, wispy cirrus clouds are present in the sky. These clouds arrive a few days before rain, storms or even snow, and they can also occur when a storm system is leaving the area.
In fact, I am tracking rain showers and a few thunderstorms for Easter Weekend!
Below is a Futurecast Radar animation for Saturday morning. Rain showers and a few thunderstorms will move from the north to the south between 4am and 11am, but Metro Atlanta should dry out by 12pm Saturday.
I am tracking more rain again for Easter Sunday, mainly from 9am through the afternoon and evening hours.
Did You Spot a Sun Halo or a Sundog? Share Your Photo With Me!
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