Simulation of a Weak Mock-mirage Green Flash

Introduction

Here's a magnified view (3 times larger) of 8 seconds of this mock-mirage sunset, showing how the “plume” separates from the disk and turns green as it vanishes.

animation of a mock-mirage green flash

The green flash produced here as the neck of the hourglass breaks is hardly ever seen in practice, because it is so dim. The neck is usually drowned out by the bright main image below it, and the bright yellow “plume” above; so only the final green of the disappearing plume is well enough separated from the brighter main image to be noticed. The brightness of the flash is exaggerated in this simulation; I have more realistic simulations of such flashes, but they are not animated.

The green flash seen as the plume vanishes is actually a magnified image of the green rim, produced at the bottom of the thermal inversion. The simple model shown here illustrates the formation of these common mock-mirage flashes. Notice how far below the astronomical horizon the flash is; this is typical of a mock-mirage flash.

This flash was produced by a weak thermal inversion. If the inversion is much stronger, so that the observer looks down through a duct, quite a different set of phenomena can be seen.

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