| Influence of Intraseasonal Oscillation on the Asymmetric Decays of El Ni?o and La Ni?a |
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| 作者姓名： | Xiaomeng SONG Renhe ZHANG Xinyao RONG |
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| 作者单位： | State Key Laboratory of Severe Weather;Department of Atmospheric and Oceanic Sciences and Institute of Atmospheric Sciences |
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| 基金项目： | supported by the China National 973 Project (Grant No.2015CB453203);the National Key R&D Program of China (Grant No.2016YFA0600602);the National Natural Science Foundation of China (Grant No.41661144017) |
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| 摘 要： | Warm and cold phases of El Nino–Southern Oscillation (ENSO) exhibit a significant asymmetry in their decay speed. To explore the physical mechanism responsible for this asymmetric decay speed, the asymmetric features of anomalous sea surface temperature (SST) and atmospheric circulation over the tropical Western Pacific (WP) in El Nino and La Nina mature-to-decay phases are analyzed. It is found that the interannual standard deviations of outgoing longwave radiation and 850 hPa zonal wind anomalies over the equatorial WP during El Nino (La Nina) mature-to-decay phases are much stronger (weaker) than the intraseasonal standard deviations. It seems that the weakened (enhanced) intraseasonal oscillation during El Nino (La Nina) tends to favor a stronger (weaker) interannual variation of the atmospheric wind, resulting in asymmetric equatorial WP zonal wind anomalies in El Nino and La Nina decay phases. Numerical experiments demonstrate that such asymmetric zonal wind stress anomalies during El Nino and La Nina decay phases can lead to an asymmetric decay speed of SST anomalies in the central-eastern equatorial Pacific through stimulating di erent equatorial Kelvin waves. The largest negative anomaly over the Nino3 region caused by the zonal wind stress anomalies during El Nino can be threefold greater than the positive Nino3 SSTA anomalies during La Nina, indicating that the stronger zonal wind stress anomalies over the equatorial WP play an important role in the faster decay speed during El Nino.
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| 关 键 词： | ENSO asymmetry ENSO DECAY INTRASEASONAL OSCILLATION OGCM |
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