A westerly wind burst (WWB) or westerly wind event (WWE)
[https://glossary.ametsoc.org/wiki/Westerly_wind_burst] is a phenomenon commonly associated with
El Niño
EL, El or el may refer to:
Arts and entertainment Fictional entities
* El, a character from the manga series ''Shugo Chara!'' by Peach-Pit
* Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things''
* El, fami ...
events, whereby the typical east-to-west
trade winds
The trade winds or easterlies are permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere ...
across the
equator
The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
ial Pacific shift to west-to-east.
Definition
A westerly wind burst is defined by Harrison and Vecchi (1997) as sustained winds of over a period of 5–20 days.
However, no concrete definition has been determined, with Tziperman and Yu (2007) defining them as having winds of and lasting "at least a few days".
On average, three of these events take place each year, but are significantly more common during El Niño years. They have been linked to various
mesoscale phenomena, including
tropical cyclones
A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its ...
, mid-latitude cold surges, and the
Madden–Julian oscillation. Their connection with
Kelvin wave
A Kelvin wave is a wave in the ocean, a large lake or the atmosphere that balances the Earth's Coriolis force against a topographic boundary such as a coastline, or a waveguide such as the equator. A feature of a Kelvin wave is that it is non-d ...
s also indicate a connection with the onset of El Niño events, with every major occurrence since the 1950s featuring a westerly wind burst upon their onset.
Studies
Recent studies, including Yu et al. (2003), have indicated some correlation between westerly wind bursts and the
El Niño–Southern Oscillation
El Niño–Southern Oscillation (ENSO) is a global climate phenomenon that emerges from variation in winds and sea surface temperatures over the tropical Pacific Ocean. Those variations have an irregular pattern but do have some semblance of cyc ...
(ENSO). These events occur more frequently when the equatorial Pacific warm pool is extended by ENSO events. A significant relationship exists between the frequency of westerly wind bursts and the central equatorial Pacific
sea surface temperature
Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...
s, with events commonly taking place when temperatures were present. The wind bursts also traveled along with the warm pool, propagating west to east.
Cyclones
A westerly wind burst event can often result in the formation of twin tropical cyclones in the Pacific, with events occurring annually on average. These events spur counter-clockwise rotation in the
Northern Hemisphere
The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
and clockwise rotation in the
Southern Hemisphere—a key component of
low pressure systems.
For example, during July 2015
Typhoon Chan-hom and
Cyclone Raquel developed simultaneously over the Northwestern and Southwestern Pacific, respectively, in conjunction with a westerly wind burst. This was also the only known instance of twin cyclones during July and attributed to the record strength of the
2014–16 El Niño event.
Another unusually strong wind burst led to the atypical formations of
Tropical Depression Nine-C and
Hurricane Pali
Hurricane Pali was the earliest-forming Pacific hurricane on record, being the first Pacific hurricane to occur in January since Hurricane Ekeka of 1992 Pacific hurricane season, 1992. The first tropical cyclone of the 2016 Pacific hurricane se ...
in late December 2015 and early January 2016, respectively along with the formation of
Cyclone Ula in the Central and Southwestern Pacific.
Similarly, the formation of twin cyclones along the equatorial Pacific can spur the formation of a westerly wind burst and enhance El Niño events.
In May 2002, a strong westerly wind burst moved from west to east across the Indian Ocean, producing two separate sets of twin cyclones. It first led to the development of
Cyclone Kesiny in the south-west Indian Ocean and a
storm
A storm is any disturbed state of the natural environment or the atmosphere of an astronomical body. It may be marked by significant disruptions to normal conditions such as strong wind, tornadoes, hail, thunder and lightning (a thunderstor ...
that struck Oman, and later spawned
a deep depression that struck Myanmar and
Tropical Storm Errol to the southwest of
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
.
See also
*
Trade winds
The trade winds or easterlies are permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere ...
References
{{reflist, 30em
Tropical meteorology
Tropical cyclone meteorology
Weather hazards