Date:29 August 2017
A hurricane is one of nature’s most powerful events. Here’s how a big one is born and the climate conditions that feed it.
By Douglas Fox
Hurricane Harvey is this week devastating large parts of the Texas. But to us here in South Africa they’re not that common. So here’s a look at how hurricanes are born and become powerful.
How a hurricane works:
1 | Heat Engine
Hurricanes are massive dynamos powered by the evaporation of water and its subsequent recondensation into clouds and rain. Each gallon of water that evaporates and condenses carries about as much thermal energy into the atmosphere as that contained in 1 cup of gasoline.
2 | Hotspot
Hurricanes spawn over patches of ocean where the surface water has warmed to at least 80 F down to a depth of at least 160 feet. Ocean water evaporates in these hotspots and the moist air rises.
3 | Updraft
The rising of warm, moist air creates a low-pressure zone, pulling in more air from nearby areas, which also moistens and rises. The continued updraft is fed by condensation of evaporated water into clouds and rain. The condensation dumps energy back into the air, warming it and making it more buoyant.
4 | Spiral
Surrounding air flows into the low-pressure zone in a spiral pattern. This inward-spiraling air forms the hurricane’s destructive winds. The direction of the spiral is determined by the Coriolis effect—a byproduct of the Earth’s rotation.
5 | Sinking
Air is ejected from the top of the storm at an altitude of about 40,000 feet. This cooled, dried air sinks through the eye of the storm or else flows out and sinks in the outer bands of the storm, forming areas without rain.
6 | Magnitude
At its peak, a hurricane can dump 5 cubic miles of rain per day and unleash thermal power (freed by condensation of that water) at a rate of 6 x 1014 watts—equal to 200 times the amount of electricity generated by humans worldwide. Only about 0.25 percent of this power is converted to wind.
7 | Effects
In addition to destructive winds, hurricanes can pile up sea surges higher than 20 feet (which are responsible for most deaths). Even after winds dissipate inland, rain can cause flooding for days—as happened with Hurricane Mitch, whose floods and mudslides killed nearly 20,000 people in Central America in 1998.
From: PM USA