与热带印度洋系统海表温度误差相关的北方冬季大气偏置遥相关

Yuan-Bing Zhao, Nedjeljka Žagar, Frank Lunkeit, Richard Blender
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引用次数: 0

摘要

摘要耦合气候模式在热带印度洋(TIO)受到明显的海表温度(SST)偏差的影响,导致全球气候预测出现误差。在本研究中,我们研究了TIO海温偏置对模拟大气环流和时空变率的局地和远程影响。在一个中等复杂的大气模式下进行了一组由理想化海温扰动强迫的长达一个世纪的模拟,这些模拟类似于耦合气候模式中的各种(单极或偶极,正或负)TIO海温偏差。使用正态函数(NMF)分解分析了北方冬季的偏置遥相关,该函数可以区分空间尺度上的平衡和不平衡流。结果表明,由TIO海温偏置引起的大气环流偏置在热带地区具有gill - matsuno型,在温带地区具有ross - by-波列结构,与热带加热扰动的稳态响应相似。热带偏压和温带偏压之间的遥相关是由来自副热带的罗斯比波活动通量建立的。超过90%的偏置方差(即偏置振幅的平方)包含在纬向波数k≤5中。远离赤道的海温偏北移减弱了振幅,但没有改变大气响应的空间结构。此外,在相同大小和幅度的情况下,海温正偏压比负偏压产生更强的偏压遥相关。在NMF框架中,时间平均状态(即能量)的空间方差变化等于偏置方差和环流偏置与参考状态之间的协方差之和(即偏置协方差)。由于TIO海温偏置,全球不平衡纬向平均(k=0)流能减少,而平衡流能增加。这些变化主要由强偏倚协方差引起。对于k>0,在单极海温偏置情况下,全球不平衡和热带平衡能量均增加,而在偶极海温偏置情况下则减少。增加主要表现为偏差方差,而减少则与k=1和2时强烈的负偏差协方差相关。而当TIO SST偏置为正(负)时,温带平衡波能量减小(增大),主要与k=1时的偏置协方差有关。年际方差(IAV)的变化取决于TIO海温偏倚的标志。平衡和不平衡流动中的IAV均为正偏压减小,而负偏压增大。从地理上看,背景IAV较强的热带印度洋-西太平洋地区、澳大利亚、南亚和东北亚、太平洋-北美地区和欧洲的IAV变化较大。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Atmospheric bias teleconnections in boreal winter associated with systematic sea surface temperature errors in the tropical Indian Ocean
Abstract. Coupled climate models suffer from significant sea surface temperature (SST) biases in the tropical Indian Ocean (TIO), leading to errors in global climate predictions. In this study, we investigate the local and remote effects of the TIO SST bias on the simulated atmospheric circulation and spatio-temporal variability – bias teleconnections. A set of century-long simulations forced by idealized SST perturbations, which resemble various (monopolar or dipolar, positive or negative) TIO SST biases in coupled climate models, are conducted with an intermediate-complexity atmospheric model. Bias teleconnections with a focus on boreal wintertime are analysed using the normal-mode function (NMF) decomposition, which can differentiate between balanced and unbalanced flows across spatial scales. The results show that the atmospheric circulation biases caused by the TIO SST bias have the Gill–Matsuno-type pattern in the tropics and Rossby-wave-train structure in the extratropics, similar to the steady-state response to tropical heating perturbations. The teleconnections between the tropical and extratropical biases are set up by Rossby wave activity flux emanating from the subtropics. Over 90 % of the bias variance (i.e. the square of the bias amplitude) is contained in zonal wavenumbers k≤5. The northward shift of the SST bias away from the Equator weakens the amplitude but does not change the spatial structure of the atmospheric response. Besides, the positive SST bias produces stronger bias teleconnections than the negative one of the same size and magnitude. In the NMF framework, the change in the spatial variance of the time-mean state (i.e. energy) is equal to the sum of the bias variance and the covariance between the circulation bias and the reference state (i.e. bias covariance). Due to the TIO SST biases, the global unbalanced zonal-mean (k=0) flow energy decreases, whereas its balanced counterpart increases. These changes primarily arise from the strong bias covariance. For k>0, both the global unbalanced and the tropical balanced energies increase in the case of a monopolar SST bias and decrease in the case of a dipolar SST bias. The increase appears mainly as the bias variance, whereas the decrease is associated with a strong negative bias covariance at k=1 and 2. In contrast, the extratropical balanced wave energy decreases (increases) when the TIO SST bias is positive (negative), which is mainly associated with the bias covariance at k=1. The change in the interannual variance (IAV) is contingent upon the sign of the TIO SST bias. A positive bias reduces, whereas a negative one increases, the IAV in both balanced and unbalanced flows. Geographically, large IAV changes are observed in the tropical Indo-West Pacific region, Australia, South and Northeast Asia, the Pacific-North America region, and Europe, where the background IAVs are strong.
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