Investigation 7: Surface Winds
- Page ID
- 40380
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Wind is simply air in motion. The atmosphere is composed of countless molecules that are constantly in motion, creating the sensation of wind. Winds can be gentle like a warm summer breeze, or they can be gusty and cold like a winter gale. In 1805, Sir Francis Beaufort, an Irish hydrographer and naval officer, created the Beaufort Scale, a measure of wind speed and observed conditions at sea or on land. It classifies windy conditions according to wind speeds and names them from calm conditions (0 mph) to hurricane-level conditions (wind speeds exceeding 74 mph). Figure 7.1 shows a NASA satellite image of Hurricane Katrina before landfall in the Gulf of Mexico, where winds reached 175 mph! These high wind speeds can pack a significant punch. Figure 7.2 shows a 2x4 wood beam driven forcefully through a tree by strong winds during a Hurricane in Puerto Rico.
But what determines how strong the wind blows? What determines its direction? How do cyclonic and anticyclonic flows form? These are the questions that we aim to address in this investigation.
By the end of this investigation, you should be able to:
- Distinguish between surface winds and winds aloft.
- Identify the three forces that determine wind speed and direction.
- Determine the combined effect of all the forces on wind speed and direction on a map.
- 7.1: Surface vs Aloft
- The distinction between surface weather and upper air weather is a key concept in meteorology. Surface weather deals with conditions near the Earth's surface, while upper air weather refers to conditions above 1,000 meters. Knowledge of both is essential, as higher-altitude weather can impact surface conditions. Additionally, it introduces weather stations and weather balloons as tools for measuring atmospheric conditions at different heights.
- 7.2: Why the wind blows
- The forces affecting wind, as per Newton's laws of motion, consist of three key components: the Pressure Gradient Force, which moves wind from high to low pressure; the Coriolis Force, which affects wind direction; and Friction, which slows it down. The Pressure Gradient Force is linked to air pressure differences and wind speed, with examples from weather maps illustrating how these forces impact wind dynamics in the atmosphere.
- 7.3: Other forces acting on the wind
- The Coriolis Force, which influences air movement due to Earth's rotation, causes rightward deflection in the Northern Hemisphere and leftward deflection in the Southern Hemisphere. It depends on the size, speed, and latitude. The Coriolis force balances with the Pressure Gradient Force, leading to geostrophic balance and winds flowing parallel to isobars.
- 7.4: Alternative Text Descriptions for Investigation 7
- This page provides detailed text descriptions of images and charts used in Investigation 7
Thumbnail: Idealized depiction of large-scale atmospheric circulation on Earth. Earth Global Circulation by Kaidor is licensed under CC BY-SA 3.0