Hurricanes: Their Nature and Impacts on Society - Climate Science ...

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HURRICANES: THEIR NATURE AND IMPACT ON SOCIETY
BEFORE
Figure 4.11 Hypothesized vertical cross-sections through a hurricane eye wall <strong>and</strong> rain
b<strong>and</strong>s before <strong>and</strong> after seeding. Dynamic growth of seeded clouds in the inner rain
b<strong>and</strong>s provides new conduits for conducting mass to the outflow layer <strong>and</strong> causes decay
of the old eye wall. Source: Simpson et al. (1978)
iodide outside the eye wall, clouds with liquid water colder than O°C (referred
to as "supercooled water") could be converted to ice crystals. This change of
phase of water would release the heat of fusion, thereby enhancing the growth
of the cumulus clouds <strong>and</strong> establishing the eye wall at a greater radius from
the center of the storm circulation. Without the silver iodide, it is hypothesized
that the cloud droplets would remain liquid. Just as ice skaters slow their
rotation when their arms are spread out, the hypothesis is that a larger radius
of the eye wall will cause a reduction in wind strength. The hypothesis is
sketched schematically in Figure 4.11.
This program of tropical storm modification was called Project Stormfury.
Robert <strong>and</strong> Joanne Simpson were the original source of the Stormfury
hypothesis in 1960. <strong>Their</strong> insight was inspired by an observation of Hurricane
Donna (1960) by Professor Herbert Riehl, who noted that nearly all of the
outflow cloudiness stemmed from an aggregation of thunderstorms in the
front right quadrant of the eye wall. <strong>Hurricanes</strong> Esther (1961), Beulah (1963),
<strong>and</strong> Debbie (1969) were seeded as part of this project, although only the
Debbie experiments closely followed the most recent Stormfury hypotheses.