|Green Flashes of two kinds ~ Two types of green flash captured from the Californian coast by Jim Grant. ©Jim Grant, shown with permission.
|The flash of the top image is well above the horizon and largely above a still visible sun sliced into ever changing layers. This is a ‘mock-mirage’ green flash.
Contrast with the lower image. A brilliant green flash blazes forth as the last sliver of sun slips beneath the waves. This is the much sought classical (Jules Verne) flash – an ‘inferior-mirage’ flash.
Opposite temperature gradients produce the two mirages. The mock-mirage results from one or more temperature inversions where cooler air is trapped beneath warmer. Inferior-mirages are produced when abnormally warm air is beneath cooler.
Both flashes need mirage conditions to vertically magnify the otherwise small separation of colours produced by differential refraction.
Mock-mirage flashes are hard to see visually and they are more easily photographed. An inferior mirage flash is unforgettable.