海表热通量反馈及海温变率

Surface heat flux feedback and SST variability

海气交界面的能量交换与海洋平流共同决定海表面温度(sea surface temperature,SST)异常的形成、维持与衰减。基于作者近期的研究,本文回顾了海表面热通量(surface heat flux,SHF)反馈以及SST方差与海表热通量及海洋热输送方差之间的关系。海表热通量异常可近似为一个与SST成正比的线性反馈项与一个大气强迫项之和。SHF的反馈参数取决于SST和SHF间的滞后交叉协方差以及SST自协方差。这种反馈总体上为负反馈,减弱SST异常,海表湍流部分起主导作用。最强的反馈可见于南北两半球的中纬度,最大值出现在大洋的西部和中部位置并延伸至高纬度地区。SHF反馈于北半球秋冬两季增强,春夏两季减弱。这些反馈特征在CMIP3耦合气候模式中得到合理的模拟。然而,多数模式中反馈的强度与再分析资料的估值相比略为偏弱。与再分析资料的估值相比,"平均模式"反馈参数比单一模式有更相似的空间形态以及较小的均方根差。基于海表面能量收支平衡,SST的方差可以表示为3个要素的积:1)海表面辐射和湍流通量以及海洋热输送的方差之和;2)一个衡量SST持续性的传输系数G;3)一个反映海表热通量以及海洋热输送之间协方差结构的有效因子e。SST方差的地理分布类似于海表热通量及海洋热输送的方差之和,但为G和e因子所修正。

Energy exchanges at the air-sea interface together with the ocean advection govern the formation,maintenance and decay of sea surface temperature（SST）anomalies.Several aspects of the surface heat flux（SHF）feedback and the relation between SST and heat flux/transport variability are reviewed in this paper,based primarily on some of our recent studies.The heat flux anomaly is approximated as a forcing term plus a feedback term which is linear in SST.The SHF feedback parameter is determined from the lagged cross-covariances between SST and the SHF together with the auto-covariance of SST.Feedback represented in this way is generally negative and acts to damp SST anomalies.It is dominated by the surface turbulent component.The strongest feedback is found at mid-latitudes in both hemispheres,with the largest values occurring in the western and central portions of the oceans with extensions to higher latitudes.SHF feedback strengthens in northern winter and fall and weakens in spring and summer.These feedback features are reasonably well simulated in the CMIP3 coupled climate models.Nevertheless,the strength of the feedback in most of the models is somewhat weaker than reanalysis-based estimates.The＂mean model＂feedback parameter has better pattern correlations and smaller mean square differences than individual models when compared to reanalysis-based values.Based on the surface energy budget,SST variance may be expressed as the product of three factors：the sum of the variances of surface radiative and turbulent fluxes and the ocean heat transport,a transfer factor G measuring the persistence of SST,and an efficiency factor e reflecting the covariance structure among the heat fluxes and heat transport.The geographical distribution of the SST variance follows that of the sum of the variances of surface heat fluxes and the ocean heat transport,but modified by the factors of G and e.