Observed Strengthening of the Zonal Sea Surface Temperature Gradient across the Equatorial Pacific Ocean
Observed Strengthening of the Zonal Sea Surface Temperature Gradient across the Equatorial Pacific Ocean
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DOI：
10.1175/2009jcli2936.1
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发表时间：
2009-08-15
影响因子：
4.9
通讯作者：
Cane, Mark A.
中科院分区：
文献类型：
--
作者：
Karnauskas, Kristopher B.;Seager, Richard;Cane, Mark A.
热带太平洋是厄尔尼诺-南方涛动 (ENSO) 现象的发生区，其十年来的微小幅度变化（海面温度 (SST) 类似于 0.3 摄氏度）已被证明对全球气候产生强大影响。不同气候模型的未来预测对于这一关键特征在人为强迫的影响下将如何变化并不一致。为了解决这个问题，人们做出了许多尝试，通过研究从 1880 年代至今（大气中温室气体浓度不断上升的时期）观察到的趋势。最近的一次尝试得出的结论是，三大数据集对海温赤道梯度的趋势存在分歧。使用这些数据集之一的校正版本，并将分析扩展到季节周期，这里显示，所有人都同意赤道太平洋纬向海表温度梯度从 1880 年到 2005 年北方秋季期间有所加强，此时该梯度通常最强。这一结果似乎支持基于海洋动力学的未来变化理论，而不是基于大气能量考虑的理论。这两种理论都基于 ENSO 理论的预期，即热带太平洋的纬向海平面压力 (SLP) 梯度与海表温度耦合，因此应随着海表温度梯度而增强。虽然海平面气压梯度并未加强，但发现它似乎仅在北春季节减弱，这与海温季节性趋势一致。政府间气候变化专门委员会（IPCC）第四次评估报告中包含的大多数耦合模型都低估了北方秋季海温梯度的增强，并且显示任何季节的海平面气压梯度几乎没有变化。本文的观察分析表明，这两种理论都起作用，但相对强度随季节变化，并且这两种理论不必相互矛盾。
Decadal variations of very small amplitude [similar to 0.3 degrees C in sea surface temperature (SST)] in the tropical Pacific Ocean, the genesis region of the interannual El Nino-Southern Oscillation (ENSO) phenomenon, have been shown to have powerful impacts on global climate. Future projections from different climate models do not agree on how this critical feature will change under the influence of anthropogenic forcing. A number of attempts have been made to resolve this issue by examining observed trends from the 1880s to the present, a period of rising atmospheric concentrations of greenhouse gases. A recent attempt concluded that the three major datasets disagreed on the trend in the equatorial gradient of SST. Using a corrected version of one of these datasets, and extending the analysis to the seasonal cycle, it is shown here that all agree that the equatorial Pacific zonal SST gradient has strengthened from 1880 to 2005 during the boreal fall when this gradient is normally strongest. This result appears to favor a theory for future changes based on ocean dynamics over one based on atmospheric energy considerations. Both theories incorporate the expectation, based on ENSO theory, that the zonal sea level pressure (SLP) gradient in the tropical Pacific is coupled to SST and should therefore strengthen along with the SST gradient. While the SLP gradient has not strengthened, it is found that it appears to have weakened only during boreal spring, consistent with the SST seasonal trends. Most of the coupled models included in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report underestimate the strengthening SST gradient in boreal fall, and show almost no change in the SLP gradient in any season. The observational analyses herein suggest that both theories are at work but with relative strengths that vary seasonally, and that the two theories need not be inconsistent with each other.