6.4: Cyclonic and Anticyclonic flow in real life.
- Page ID
- 44404
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Now that we have learned how winds behave around low- and high-pressure systems, we can use wind direction to estimate the air pressure at a location. Figure \(\PageIndex{1}\) is a map of surface observations at 1900 UTC on August 30, 2017. Remember that the long poles extending from the station model point in the direction from which the wind is coming. There is a “mystery” pressure system over Eastern Louisiana, indicated by a green “?” Your mission, should you choose to accept it, is to identify the type of pressure system.
- In general, winds on the western side of the “mystery” pressure are blowing from the:
- northwest, and northeast.
- west, and southwest
- south and southeast
- east, and northeast
- In general, winds on the eastern side of the “mystery” pressure are blowing from the:
- northwest, and northeast.
- west, and southwest
- south and southeast
- east, and northeast
Draw arrows indicating the motions you selected for questions 18 and 19 on Figure \(\PageIndex{1}\) to help you visualize the wind directions.
- Putting these two findings together, the motion around this mysterious pressure is generally:
- clockwise
- counter-clockwise
You should also notice that the center circle of the station model shows cloud conditions, while the symbols on the left-hand side of the center show precipitation. You can reference the National Weather Service page for the station model to refresh your memory.
- Thus, based on the direction of the rotation, the presence of clouds, and precipitation data, the conditions indicate that this mystery pressure system is indeed a:
- high-pressure system
- low-pressure system.
Convergence and Divergence
The previous situation demonstrates Convergence. It occurs when air flows toward a center of pressure from different directions. Once it reaches the center, it has nowhere to go but rise upwards. When air rises, it cools, forms clouds, and often produces precipitation, such as showers or thunderstorms.
- Thus, convergence must occur in a ________ pressure system.
- low
- high
On the other hand, Divergence occurs when surface air is moving away from a center of pressure. In this case, air from above must sink to fill the space previously occupied by the escaping surface air. This causes sinking motion over an area of divergence, inhibiting cloud formation and leading to clear skies.
- Thus, divergence must occur in a _________ pressure system.
- low
- high