Analysis of the Slab Ocean El Nino atmospheric feedbacks in observed and simulated ENSO dynamics
Analysis of the Slab Ocean El Nino atmospheric feedbacks in observed and simulated ENSO dynamics
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DOI：
10.1007/s00382-014-2057-0
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发表时间：
2014-06-01
期刊：
影响因子：
4.6
通讯作者：
Frauen, Claudia
中科院分区：
文献类型：
--
作者：
Dommenget, Dietmar;Haase, Sabine;Frauen, Claudia
最近的一项研究表明，在没有任何海洋动力学的情况下，厄尔尼诺南方涛动(ENSO)模式可以存在。这种振荡模式的存在正是大气热通量和海洋热容相互作用的结果。这项研究的主要目的是进一步探索这些大气板层海洋ENSO动力学，从而探讨大气正反馈在模式模拟和观测中的作用。太阳辐射对海表面温度(SST)的正反馈是SLAB海洋厄尔尼诺动力学的主要正反馈，这是由于异常暖SST云量减少所致。这种正向云反馈的强度与赤道冷舌的强度有很强的相关性。正异常西侧的正潜热和感热通量与东侧的负潜热通量共同作用，导致海温异常向西传播，使海温异常有较好的6-7年周期振荡行为。一些迹象表明，这些动力中的一部分确实在其他大气或耦合大气环流模式(AGCM或CGCM)中被观测和模拟。由13种不同的大气模式模拟的CMIP3AGCM-SPLE集合显示，赤道太平洋沿岸不稳定的海洋-大气相互作用与更强的冷舌有关。在观测和CMIP3和CMIP5 CGCM模式集合中，云反馈的强度和符号是冷舌强度的函数。总之，这表明板条海洋厄尔尼诺动力学确实是赤道太平洋气候的一个特征，只有在SST冷舌足够强的情况下，才是主导或显著促进ENSO动力学的特征。在观测中，只有在强烈的拉尼娜条件下才会出现这种情况。在观测和CGCM模式模拟中，Slab Ocean ENSO大气反馈的存在表明，物理ENSO模族确实有另一个成员，它完全由大气过程驱动，不需要与主要ENSO动力学具有相同的空间模式或相同的时间尺度。
In a recent study it was illustrated that the El Nino Southern Oscillation (ENSO) mode can exist in the absence of any ocean dynamics. This oscillating mode exists just due to the interaction between atmospheric heat fluxes and ocean heat capacity. The primary purpose of this study is to further explore these atmospheric Slab Ocean ENSO dynamics and therefore the role of positive atmospheric feedbacks in model simulations and observations. The positive solar radiation feedback to sea surface temperature (SST), due to reduced cloud cover for anomalous warm SSTs, is the main positive feedback in the Slab Ocean El Nino dynamics. The strength of this positive cloud feedback is strongly related to the strength of the equatorial cold tongue. The combination of positive latent and sensible heat fluxes to the west and negative ones to the east of positive anomalies leads to the westward propagation of the SST anomalies, which allows for oscillating behavior with a preferred period of 6-7 years. Several indications are found that parts of these dynamics are indeed observed and simulated in other atmospheric or coupled general circulation models (AGCMs or CGCMs). The CMIP3 AGCM-slab ensemble of 13 different AGCM simulations shows unstable ocean-atmosphere interactions along the equatorial Pacific related to stronger cold tongues. In observations and in the CMIP3 and CMIP5 CGCM model ensemble the strength and sign of the cloud feedback is a function of the strength of the cold tongue. In summary, this indicates that the Slab Ocean El Nino dynamics are indeed a characteristic of the equatorial Pacific climate that is only dominant or significantly contributing to the ENSO dynamics if the SST cold tongue is sufficiently strong. In the observations this is only the case during strong La Nina conditions. The presence of the Slab Ocean ENSO atmospheric feedbacks in observations and CGCM model simulations implies that the family of physical ENSO modes does have another member, which is entirely driven by atmospheric processes and does not need to have the same spatial pattern nor the same time scales as the main ENSO dynamics.