How to Destroy the Universe Read Online Free PDF

moisture to condense into rain clouds. The cool, dry air then falls back down to sea level where the cycle repeats. The physics responsible for this process is known as convection. It happens because gases expand as they are heated up. This lowers the gas’s density, causing it to rise—in just the same way that an object with a density lower than that of water will float on the surface of the sea. Convection is also the reason why hot-air balloons are able to fly.
    If only convection were involved, hurricanes wouldn’t be much to write home about. But there’s another process going on that stirs things up—quite literally. It’s called the Coriolis effect, named after the 19th-century French scientist Gustav Coriolis, who first wrote down the mathematics describing it. It makes the air in Earth’s northern hemisphere swirl in an anti-clockwise direction (as viewed from above), while air in the south swirls clockwise.
    The Coriolis effect is caused by the planet’s rotation. Imagine taking a series of horizontal slices through Earth from the North Pole down to the equator. As the planet turns all the slices rotate in lockstep, each slice completing one whole revolution per day. But the diameter of each slice gets bigger as you head south, so the actual straight-line speed of the slice’s outer edge increases. For example, while Earth’s surface at thelatitude of New York (40.74°N) is traveling east at 1,260 km/h (783 mph), at the equator it’s moving much quicker, at 1,670 km/h (1,038 mph). Someone in between the two, say on the island of Cuba (21.5°N) will be moving east at 1,554 km/h (966 mph). But here’s the crucial thing. In this island dweller’s own point of view, the equator is moving east relative to them at 116 km/h (72 mph), but New York actually appears to be going west, at 294 km/h (183 mph). The net result is to set up a turning effect that makes convection cycles, and other cloud masses in the northern hemisphere, swirl in an anti-clockwise direction. And this is why hurricanes and other cyclones spin. The Coriolis effect tends to produce a rising column of warm air that cools and spirals outward at high altitude before it falls back to sea level, gets warmed once more by the ocean and then sucked back to the center where it rises again. As the air rises and cools it releases its heat energy and this is what powers the hurricane.
Hurricane hotspots
    Creating a sufficient thermal updraft to form a cyclone requires ocean temperatures of over 26°C (80°F). Generally the sea is only this warm within the tropics, which is why cyclones are sometimes known as “tropical cyclones.” Cyclones can form in all the world’s equatorial ocean basins. Each area has its own cycloneseason, corresponding to the time of year when the difference between the temperature at sea level and at high altitude is greatest—driving the strongest convection currents. For the North Atlantic, this is June to November with most hurricanes occurring in August and September. In the southern Indian Ocean, the season runs from December until April. Once formed, a cyclone tends to migrate westward, driven by the equatorial trade winds, which blow from east to west. Like hurricanes, the trade winds are caused by a combination of convection and the Coriolis effect. Warm air at the equator rises due to convection, cools and migrates outward to latitudes of +/-30°, where it falls back to sea level. The low pressure that the convection causes then sucks this cooled air back down to the equator where the process repeats. If Earth did not rotate, this air would simply move in a straight line toward the equator, but the Coriolis effect changes that.
    Again, it’s rather like the situation in a hurricane. Here a patch of low pressure draws air currents radially inwards. But the Coriolis effect makes the currents form a swirling anti-clockwise vortex—in other words,