This upside-down “question mark” in the clouds photographed by the 51-J crew is something of a teaser. Such clouds have only been observed from above on rare occasions and a clear explanation is not readily available. Experiments with aircraft have produced a similar effect but on a much smaller scale — this “question mark” is some 200 miles long. From time to time, tornados in very intense storms have been observed lying horizontally in the cloud mass, rather than funneling to the ground, but this is only likely to happen over land and this photograph was taken over sea. Comparison with the satellite weather data for the day in question, October 5, 1985, suggests that this roll cloud lies along the margin of a long cold front located over the ocean off the east coast of Japan. Confrontation between the front and the air beyond it causes the roll effect. Exactly why this roll cloud should be sitting distinctly above the remainder of the cloud mass (as evidenced by the shadow running along the right edge) is not presently understood, although a wind shear downburst along the leading edge of the low pressure front squall line is a possibility.
STS 51-J, October 1985. Picture #51J-48-022.