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nuclear detonations, heavy snowstorms, and large hurricanes.) Over 2000 thunderstorms
are in progress above Earth's surface at any one time, and they generate approximately 8
million lightning strikes each day, or about 100 cloud-to-ground discharges every second.
Understanding the life cycle of thunderstorms and the risks associated with them is essen-
tial. The basic ingredients required for a thunderstorm to develop are moisture, instability,
and a lifting mechanism. Each thunderstorm has three phases ( Fig. 29-1 ):
1. Growth
2. Maturation
3. Dissipation
During the development, growth, or towering cumulonimbus stage, the thunderstorm
cloud is dominated by updrafts that may carry it up to 20,000 feet (6 km) and create turbu-
lence around the periphery.
With maturation, the storm cell has both updrafts and downdrafts, and may rise as high
as 40,000 to 60,000 feet (12 to 18 km). This phase is the most dangerous for hail, flooding,
and damaging winds.
The dissolution phase heralds the death of the thunderstorm. This last stage is high-
lighted by downdrafts, and as the storm no longer has moisture uplifting, it begins to dis-
sipate. Light winds and rain dominate, and the cloud has a classic anvil top.
Figure 29-1. Growth, maturation, and dissipation of a thunderstorm 1
Lightning can strike well outside the rain area, miles away from the storm, even beyond
sight, and can also strike from debris clouds tens of minutes after the decay of the thunder-
storm. Safety requires time and distance before the storm, during the storm, and after the
storm's dissipation.
As ice and water particles within a cloud (hydrometeors) grow and interact, some be-
come charged, possibly through collisions. The smaller particles are thought to acquire
a positive charge, whereas the larger particles acquire a more negative charge. These
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