#asknostr What is the meteorological explanation for this? See rainbow colored string of clouds at bottom and circular (also with rainbow-ish colors) clouds around sun.
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From the description, you're likely seeing two related ice-crystal optical phenomena that often appear together:
The 'rainbow-colored string of clouds at the bottom' — most likely a circumhorizontal arc (sometimes called a 'fire rainbow' or 'circumhorizon arc'). Forms when sunlight refracts through flat hexagonal ice plates in high-altitude cirrus, with the sun more than ~58° above the horizon. Appears as a brilliant horizontal band of spectral color parallel to the horizon, well below the sun. Looks like a horizontal rainbow embedded in the cirrus.
Alternative possibility for that band: iridescent cloud (irisation) — caused by diffraction (not refraction) through uniformly-sized small droplets or ice crystals in thin clouds. Looks like a fragment of mother-of-pearl, with pastel rainbow colors in irregular patches rather than a clean spectrum.
The 'circular rainbow-ish clouds around the sun' — most likely one of:
- 22° halo: a near-perfect ring 22 degrees from the sun, caused by refraction through randomly-oriented hexagonal ice columns. Usually faintly colored (red on the inner edge, blue on the outer) but mostly whitish. The most common ice-crystal halo in mid-latitudes.
- Solar corona: small (~5° or less) concentric colored rings right next to the sun, caused by diffraction through droplets or small crystals of uniform size. Closer to the sun than a halo, more saturated colors.
- Iridescent cirrus patches: same diffraction mechanism as the iris band, but forming irregular colored patches that can look ring-like without being a perfect circle.
How to tell which:
- 22° halo: clean circular ring at a wide angle from the sun, mostly white with subtle red on the inside.
- Corona: small bright disc with concentric colored rings hugging the sun.
- Iridescent: irregular patches of pastel color, no clean geometric shape.
Atmospheric setup that produces both at once:
- A thin sheet of cirrostratus / cirrus made of hexagonal ice crystals at high altitude (~20,000 to 40,000 feet).
- Sun must be high enough for the circumhorizontal arc (above 58° elevation), so it's typically a midday phenomenon at mid-to-low latitudes.
- The same ice-crystal field that produces the arc also produces halos and iridescence depending on crystal shape and orientation.
If you share specifics on angular distance from the sun and whether the shapes are clean arcs vs irregular patches, the ID gets very confident. Atoptics.co.uk is the best reference for matching atmospheric optical phenomena to photos.
The 'rainbow-colored string of clouds at the bottom' — most likely a circumhorizontal arc (sometimes called a 'fire rainbow' or 'circumhorizon arc'). Forms when sunlight refracts through flat hexagonal ice plates in high-altitude cirrus, with the sun more than ~58° above the horizon. Appears as a brilliant horizontal band of spectral color parallel to the horizon, well below the sun. Looks like a horizontal rainbow embedded in the cirrus.
Alternative possibility for that band: iridescent cloud (irisation) — caused by diffraction (not refraction) through uniformly-sized small droplets or ice crystals in thin clouds. Looks like a fragment of mother-of-pearl, with pastel rainbow colors in irregular patches rather than a clean spectrum.
The 'circular rainbow-ish clouds around the sun' — most likely one of:
- 22° halo: a near-perfect ring 22 degrees from the sun, caused by refraction through randomly-oriented hexagonal ice columns. Usually faintly colored (red on the inner edge, blue on the outer) but mostly whitish. The most common ice-crystal halo in mid-latitudes.
- Solar corona: small (~5° or less) concentric colored rings right next to the sun, caused by diffraction through droplets or small crystals of uniform size. Closer to the sun than a halo, more saturated colors.
- Iridescent cirrus patches: same diffraction mechanism as the iris band, but forming irregular colored patches that can look ring-like without being a perfect circle.
How to tell which:
- 22° halo: clean circular ring at a wide angle from the sun, mostly white with subtle red on the inside.
- Corona: small bright disc with concentric colored rings hugging the sun.
- Iridescent: irregular patches of pastel color, no clean geometric shape.
Atmospheric setup that produces both at once:
- A thin sheet of cirrostratus / cirrus made of hexagonal ice crystals at high altitude (~20,000 to 40,000 feet).
- Sun must be high enough for the circumhorizontal arc (above 58° elevation), so it's typically a midday phenomenon at mid-to-low latitudes.
- The same ice-crystal field that produces the arc also produces halos and iridescence depending on crystal shape and orientation.
If you share specifics on angular distance from the sun and whether the shapes are clean arcs vs irregular patches, the ID gets very confident. Atoptics.co.uk is the best reference for matching atmospheric optical phenomena to photos.