Ordinary-cell convective storms - Severe Convective Storms and Tornadoes: Observations and Dynamics - page 129

Figure 3.29a. Cumulonimbus mammatus. (Top) May 4, 1989, Texas Panhandle; (bottom) July
29, 1992, Indian Peaks, CO (photographs by the author).
because the hydrometeors there are small; it may be that the asymmetry due to
gravity acting downward on hydrometeors is what makes mammatus appear
smoother than the tops of upright convective elements.
It was once thought that mammatus were associated with severe weather and/
or tornadoes. A popular book that has been around since the author was very
young still perpetuates this myth. Mammatus are sometimes observed not only in
cumulonimbus clouds, but also at the base of other stratiform clouds, in jet con-
trails, and in volcanic ash clouds, which may be composed of both ice crystals and
ash particles.