Mountain Climate - Mountain Geography: Physical and Human Dimensions - page 105

cumulus cloud, although often streamlined, or with streamers of cirrus forms. They sit
near or just below the summit level, appearing like a hat atop the peak. Banner clouds
are cap clouds which extend downwind from the peak like a flag waving in the wind,
and are sometimes difficult to distinguish from streamers of snow blowing from sum-
mits. Lenticular clouds are lens-shaped clouds formed in regular spaced bands parallel
to the mountain barrier on the lee side. These streamlined cloud features form through
the interaction of high-velocity winds with the mountain barriers. Stratification of hu-
midity in the atmosphere can result in multistoried lenticular clouds, forming a “pile
of plates” or “pile of pancakes.” These sometimes eerie-looking clouds might be re-
sponsible for the “flying saucer” scare of the 1950s, which originated from a sighting
of “a disc-shaped craft skimming along the crest of the Cascades Range in Washington”
(Arnold and Palmer 1952).
FIGURE 3.18 Contribution of fog drip to precipitation during 28-week study period (October
1972-April 1973) on the forested northeast slopes of Mauna Loa, Hawai'i. Numbers show precip-
itation totals in millimeters. Those in parentheses indicate fog drip. Percentages are the relative
amounts contributed to the total by fog drip at each station. (After Juvik and Perreira 1974: 24.)
FOG (CLOUD) DRIP Fog drip is most significant in areas adjacent to oceans with relatively
warm, moist air moving across the windward slopes. The moisture yield from fog drip
may exceed that of mean rainfall by as much as 462 percent (Juvik et al. 2011). The po-
tential of clouds for yielding fog drip depends primarily upon their liquid content, the
size of the cloud-droplet spectrum, and the wind velocity (Vermeulen et al. 1997). The
amount depends upon the nature of the obstacles encountered and their exposure to the
clouds and wind. For example, a tree will yield more moisture than a rock, and a needle-
leaf tree is more efficient at “combing” the moisture from the clouds than a broadleaf
tree (Vermeulen et al. 1997). A tall tree will yield more moisture than a short one, and a
tree with frontline exposure will yield more than one surrounded by other trees (Juvik et