Ground Rainbows

Marianne Gustafsson saw these exceptionally intense and sharp ground rainbows on farmland in south-western Sweden.   

Ground rainbows, dew bows, are usually indistinct and faint.   These ones have everything.  

The primary bow has sharp and intense colours.   Inside the bow, to the right, the ground is bright exactly mimicking the bright white sky seen inside an airborne bow where drops still refract light back to the eye.    

To the left of the bright primary there is a fainter and broader secondary bow.   Between the bows the soil is dark – a earthy version of Alexanders dark band.

Bright well-defined bows like these require large (say >1mm diameter) spherical water drops.    How they could be present in such huge numbers after a frosty night is something of a mystery.   The bows were seen between 10 and 11 in the morning in October. It might be that the sun warmed and sublimed the overnight frost in furrows to form water vapour that subsequently condensed into very large dew drops on cooler ground - or onto spider webs as suggested by Doug Wolf and other readers.

Images ©Marianne Gustafsson


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Residual frost patches are visible to the left of the bow. The ground is much brighter to the right because water droplets inside the primary bow always refract light back to the eye. They do not do so in Alexanders dark band to the left