Bar (tropical cyclone)
The bar of a mature
cirrostratus and cirrus clouds are usually visible in ascending order above the top of the bar, while the wind direction
for an observer facing toward the bar is typically from the left and slightly behind the observer.
History
The dark layer of clouds on the horizon seen prior to a tropical cyclone's passage over a location was first described in 1687 and the observed phenomenon later published in 1697 by
pirate ship. These observations led to an improved understanding of the nature of tropical cyclones. The use of "bar" as a term to describe this cloud layer first appeared in the 19th century.[2]
Inside the bar
When the bar of the storm approaches an observer, it appears stationary in
eyewall. Navigators of ships at sea often use the first appearance of a bar to steer clear of the approaching tropical cyclone.[1]
Closer to the center of tropical cyclone, the eyewall also exhibits the appearance of a bar, and high lightning activity occurs within this central bar. After the bar passes through, the strongest winds and often the heaviest precipitation abruptly changes to calmer conditions within the eye, before the eyewall passes over again and the strongest winds arrive from the opposite direction.[2]
At sea, wind speeds typically reach level 8 on the
waves become drastically higher when the bar reaches overhead and squall lines begin to arrive.[1]
References
- ^ a b c d Bowditch, Nathaniel. "Tropical Cyclones" (PDF). I'd Rather Be Sailing. The American Practical Navigator. pp. 513–515. Archived from the original (PDF) on 9 April 2011. Retrieved 7 November 2010.
- ^ ISBN 978-0-8160-7409-9.
- ISBN 0-375-70390-X.