Bar (tropical cyclone)

The bar of a mature tropical cyclone is a very dark gray-black layer of cloud that appears to be near to the horizon as seen from an observer preceding the approach of the storm, and is composed primarily of dense stratocumulus clouds.[1] Cumulus and cumulonimbus clouds bearing precipitation follow immediately after the passage of the wall-like bar.[2] Altostratus, 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 William Dampier while observing a typhoon in the South China Sea during a circumnavigation 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

The basic vertical structure of a mature tropical cyclone. The bar appears as the storm's main disk of initially the upper storm clouds followed by the lower clouds as viewed from a distance, and gaps exist in the rainbands after the bar passes over.

When the bar of the storm approaches an observer, it appears stationary in azimuthal position, whereas a storm moving toward the observer at an angle or perpendicular to the observer will appear to drift along the horizon.[1] A reddish tint sometimes appears toward the top of the bar,[3] while the darkness often varies depending on the storm's intensity. Tints of indigo, green, yellow or violet may also be present depending on the time of day due to the prismatic effect of water droplets in the cloud. Cumulus clouds first appear at the outflow boundary of the lower part of the bar.[2] As the bar passes overhead, barometric pressure at the observer's location falls steadily. The first rainband arrives, the clouds moving from left to right roughly along isobar lines, but this is often followed by short periods of relative calm. During the onset of the bar's arrival, winds continuously increase in intensity leading toward the 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 Beaufort scale while waves become drastically higher when the bar reaches overhead and squall lines begin to arrive.[1]

## References

1. ↑ 1.0 1.1 1.2 1.3 Bowditch, Nathaniel. "Tropical Cyclones". I'd Rather Be Sailing. The American Practical Navigator. pp. 513–515. http://www.irbs.com/bowditch/pdf/chapt36.pdf.
2. ↑ 2.0 2.1 2.2 2.3 Longshore, David (2008). Encyclopedia of Hurricanes, Typhoons, and Cyclones.. Checkmark Books. pp. 468. ISBN 978-0-8160-7409-9.
3. ↑ Sheets, Bob; Jack Williams (2001). "Early History and Science". Hurricane watch: Forecasting the deadliest storms on earth. Random House. p. 12. ISBN 0-375-70390-X.

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Cyclones and anticyclones of the world (Centers of action)

Concepts|

* Anticyclonic storm
* Storm
* High-pressure area
* Low-pressure area
* Rapid intensification
* Central dense overcast
* Annular tropical cyclone
* Bar (tropical cyclone)
* Superstorm
* Hypercane

Anticyclone|

| Northern Hemisphere|

* North Polar High
* Siberian High
* Azores High
* North American High
* North Pacific High
* Ridiculously Resilient Ridge
* Subtropical ridge

|

Southern Hemisphere|

* South Polar High
* South Atlantic High
* South Pacific High
* Kalahari High
* Subtropical ridge

Cyclone|

| Synoptic scale|

| Surface-based|

| Polar|

* North Polar low
* South Polar low

|

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Extratropical cyclones

Concepts|

* Anticyclonic storm
* Storm
* Cyclone
* Post-tropical cyclone
* Low-pressure area
* Weather bomb
* Sting jet
* List
* Rainband

Northern Hemisphere|

| North America|

| Continental|

| Lee Cyclone|

* Alberta clipper
* Colorado low
* Great basin low

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Other|

* Panhandle hook
* Witch of November

Oceanic|

* Aleutian Low
* Hatteras low
* Nor'easter
* Gulf low
* Pacific Northwest windstorm

Europe|

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European windstorms

Historical|

* Grote Mandrenke
* Burchardi flood
* Great Storm of 1703
* Great Storm of 1824
* Night of the Big Wind
* Moray Firth fishing disaster
* Tay Bridge disaster
* Eyemouth disaster

20th century|

* Iberia 1941
* North Sea flood of 1953
* Hurricane Debbie 1961
* North Sea flood of 1962
* 1968 Scotland storm
* Quimburga 1972
* Gale of January 1976
* December 1981 windstorm
* Ex-Hurricane Charley 1986
* Great Storm of 1987
* Burns' Day storm 1990
* New Year's Day Storm 1992
* Braer Storm of January 1993
* Christmas Eve storm 1997
* Boxing Day Storm of 1998
* Anatol 1999
* Lothar and Martin 1999

2000s|

* Oratia 2000
* Jeanett 2002
* Gudrun 2005
* Per 2007
* Kyrill 2007
* Emma 2008
* Klaus 2009
* Xynthia 2010
* Berit 2011
* Friedhelm/Bawbag 2011
* Joachim 2011
* Dagmar 2011
* Andrea 2012
* St Jude 2013
* Xaver 2013
* Dirk 2013
* Tini 2014
* Elon and Felix 2015
* Niklas 2015
* Egon 2017
* Thomas (Doris) 2017
* Zeus 2017
* Xavier 2017
* Ophelia 2017
* Herwart 2017
* Eleanor (Burglind) 2018
* Friederike (David) 2018

2015–present|

* 2015–16
* 2016–17
* 2017–18
* 2018–19
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See also|

* List of European windstorms
* List of atmospheric pressure records in Europe

Other|

* Black Sea storms
* Icelandic Low
* Genoa low

Asia|

* Western Disturbance
* Continental North Asian storms
* East Asian-northwest Pacific storms

Other areas|

* Arctic
* Kona storm

Southern Hemisphere|

| Australia|

* Australian east coast low
* Black nor'easter

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Other areas|

* Southern Ocean cyclone
* Sudestada

Subtropical|

* Kona storm
* Australian east coast Low
* Lake Huron cyclone
* Mediterranean tropical-like cyclone
* Thermal

Tropical
(List)|

| Northern Hemisphere|

* Atlantic hurricane
* Cape Verde hurricane
* Pacific hurricane
* Typhoon
* North Indian Ocean tropical cyclone
* Mediterranean tropical-like cyclone

|

Southern Hemisphere|

* South-West Indian Ocean tropical cyclone
* Australian region tropical cyclone
* South Pacific tropical cyclone
* South Atlantic tropical cyclone

Upper level|

* Cold-core low
* Polar vortex
* Upper tropospheric cyclonic vortex

Mesoscale|

| Mesoscale ocean eddies|

* Catalina eddy
* Haida Eddies

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Mesoscale convective system|

* Wake Low
* Mesohigh
* Mesoscale convective vortex
* Line echo wave pattern

Whirlwind|

| Major|

* Mesocyclone
* Supercell
* Low-topped supercell
* Wall cloud
* Funnel cloud
* Tornado
* Multiple-vortex tornado
* Satellite tornado
* Anticyclonic tornado
* Landspout
* Waterspout

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Minor|

* Gustnado
* Dust devil
* Steam devil
* Fire whirl

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