Category Archives: Phenomena

Has there been a sudden stratospheric warming this year?

The stratosphere, which begins approximately 6 miles above the cold poles and 10 miles above the tropics, is where the temperature increases with altitude. Temperatures increase because ozone molecules in the stratospheric ozone layer absorb solar ultraviolet energy within the stratosphere. Air flow in the stratosphere is much less turbulent than in the troposphere. For this reason, jet aircraft pilots like to cruise at stratospheric altitudes so the flight is less bumpy. In polar regions, the top of the stratosphere extends upward to around 30 miles.

The polar vortex is a band of strong winds high in the atmosphere that spins counterclockwise around the North Pole. At the southern edge of the vortex is the polar jet stream, which separates warm air to its south from increasingly colder air to its north. Continue reading

Category: Phenomena, Severe Weather

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Why is the wind often calmer at night than during the day?

The cycle of daytime heating and night time cooling explains why, under most circumstances, calm winds are near the surface at night.

The wind usually increases with height above Earth’s surface. The wind several thousand feet above the ground is almost always stronger than that experienced near the ground. Friction causes the wind close to the ground to move more slowly. Friction decelerates the wind in the same way a rough road surface slows down a bicycle. Continue reading

Category: Meteorology, Phenomena

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How can there be frost on the ground when my thermometer reads 36 degrees?

This set of circumstances does not mean that her thermometer is faulty and in need of replacement. Instead, it reflects a nearly daily reality that goes undetected for most of the year until the cold season. It turns out that the air does not radiate heat away nearly as well as the solid ground beneath it. As a consequence of this difference, given 13 hours of nighttime with clear skies, the ground radiates a lot more energy away (and cools rapidly) while the air above struggles to cool as efficiently. Over those many hours, this difference results in a big difference between the ground temperature and the air temperature even as little as 5 or 6 feet above the ground. Continue reading

Category: Meteorology, Phenomena

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Are hurricanes intensifying more quickly?

Hurricane intensities are classified using the Saffir–Simpson scale, which rates hurricanes on a scale of 1 to 5 based on the damage their winds would cause upon landfall. Major hurricanes are those classified as Category 3 and higher on this … Continue reading

Category: Meteorology, Phenomena, Tropical

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What are the trade winds?

On the morning of August 3, 1492, Christopher Columbus set sail on his first voyage to the Americas. He sailed south along the west coast of Africa, searching for the easterly “trade winds,” discovered earlier by the Portuguese, that would propel his fleet westward toward what he thought was India.

The trade winds are a component of a global-scale tropical circulation feature known as the Hadley cell. This cell is driven by the fact that the equator is heated more intensely than latitudes to its north and south, resulting in the production of collections of thunderstorms girdling the globe roughly along the equator. Continue reading

Category: Meteorology, Phenomena, Tropical

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