Lack of Westerly Wind Bursts in Unmaterialized El Niño Years

The lack of westerly wind bursts (WWBs) when atmospheric intraseasonal variability (ISV) events occur from boreal spring to autumn is investigated by comparing two types of El Niño years with unmaterialized El Niño (UEN) years. Although high ocean heat content buildup and several ISV events propagat...

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Bibliographic Details
Published in:Journal of climate 2018-01, Vol.31 (2), p.593-612
Main Authors: Seiki, Ayako, Takayabu, Yukari N., Hasegawa, Takuya, Yoneyama, Kunio
Format: Article
Language:English
Subjects:
Annual variations
Anomalies
Bursts
Convection
Cooling
Earth science
Eddies
Eddy kinetic energy
El Nino
El Nino phenomena
Energy budget
Enthalpy
Equatorial regions
Heat content
Kinetic energy
Lower troposphere
Noise
Ocean currents
Ocean-atmosphere interaction
R&D
Research & development
Sea surface
Sea surface temperature
Sea surface temperature anomalies
Studies
Surface temperature
Temperature anomalies
Troposphere
Vortices
Westerlies
Westerly wind bursts
Wind
Winds
Zonal winds
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Summary:The lack of westerly wind bursts (WWBs) when atmospheric intraseasonal variability (ISV) events occur from boreal spring to autumn is investigated by comparing two types of El Niño years with unmaterialized El Niño (UEN) years. Although high ocean heat content buildup and several ISV events propagating eastward are observed in all three types of years, few WWBs accompany these in the UEN years. The eddy kinetic energy budget analysis based on ISV shows that mean westerly winds in the lower troposphere facilitate the development of eddy disturbances, including WWBs, through convergence and meridional shear of zonal winds. In the UEN years, these westerly winds are retracted westward and do not reach the equatorial central Pacific mainly as a result of interannual components. In addition, positive sea surface temperature anomalies in the western Pacific, which are conducive to active convection, spread widely in a meridional direction centered on 15°N. Both westward-retracted mean westerlies and off-equatorial warming enhance off-equatorial eddies, which result in a reduction in equatorial eddies such as WWBs. The characteristics of the UEN years are significantly different from those observed during the eastern Pacific El Niño (EP-EN) years, which are characterized by anomalous cooling (warming) and suppressed (enhanced) convective eddies in the off-equatorial (equatorial) western Pacific. The central Pacific El Niño years show mixed features during both EP-EN and UEN years. Different background states not only in the equatorial region but also in the off-equatorial region can be a reason for the lack of WWBs in the UEN years.
ISSN:0894-8755
1520-0442
DOI:10.1175/jcli-d-17-0291.1