Circumzenithal arc in NZ
© Simon O'Connor/Stuff
The circumzenithal arc, or smile in the sky, seen above the Wind Wand on Saturday afternoon.
It's known as a smile in the sky, and somebody up there must be happy because there were two grinning down on New Plymouth during Saturday afternoon.

The upside down rainbows - captured here above the Wind Wand by photographer Simon O'Connor - are officially known as circumzenithal arcs, or Bravais arcs.

They are formed by sunlight refracting off ice crystals in the air high above, rather than light hitting raindrops, which is what causes an ordinary rainbow.

According to Physics.org, upside down rainbows are more common in cold climates, but still fairly rare.

Still, after the stormy weather that hit New Plymouth this week, complete with a 3.8 metre king tide at the lee breakwater and residents evacuated from homes near the sea at Waitara, hopefully this smile above is a happy sign of warm days to come.