Looming, Towering, Mock Mirage, Green Flash ~ Jim Grant�s sequence of sunset images from north of San Diego show all these atmospheric refraction effects. Notably, San Clemente Island some 70 miles away is visible with a definitely non-realistic mountain profile. ©Jim Grant, shown with permission.

The distorted sun and the green flash at its upper limb result from refraction by several stacked temperature inversion layers � kinks in the normal fall in air temperature with height with abnormally warmer air above cooler. There are at least two inversion layers.

Looming is an old sailors' term. Distant objects that sometimes should be below the horizon appear raised up. Here the appearance of 70 mile distant San Clemente is due to the combination of relatively cool (and normal temperature gradient) air beneath the lowest inversion layer.

Looming does not distort a distant object, it merely raises it. But something more is apparently happening to San Clemente because the island does not have such steep conical peaks! Sailors called this
towering. The island image is distorted - stretched vertically. The towering is probably a result of the lowest temperature inversion which reduces or even inverts the vertical temperature gradient towards the top of the island profile. In effect the island image is stretched by more looming at its top than at its lower part.

Looming and towering are distortions from atmospheric refraction but not mirages. They lack the inverted or multiple images necessary for them to be called mirages.


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