This is actually not a rainbow at all. Read further ...
"Bright and multi-colored, it was visible from 10 a.m. until sunset," reports photographer Paolo Bardelli. ...
Circumzenithal arcs typically appear in late autumn and early winter when the air is icy and the sun is low. "The CZA forms only when sun is less than 32.3° high," notes Cowley. As winter solstice approaches, "upside down rainbows" will become increasingly common. Look for them!