Sensitivity of Tropical Tropospheric Temperature to Sea Surface Temperature Forcing
Sensitivity of Tropical Tropospheric Temperature to Sea Surface Temperature Forcing
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DOI：
10.1175/1520-0442-16.9.1283
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发表时间：
2003-05
影响因子：
4.9
通讯作者：
-J.;D. Neelin;Joyce;-E.;Meyerson
中科院分区：
文献类型：
--
作者：
-J.;D. Neelin;Joyce;-E.;Meyerson
厄尔尼诺期间，整个热带地区都有相当大的对流层温度异常，这与中、东太平洋海面温度(SSTs)变暖有关。利用准平衡热带环流模式研究了热带对流层温度对海温强迫的响应机制。在观测和模式模拟中，对于观测到的T9海温强迫，热带平均三层温度距平Tˆ9&与热带平均海温距平^&近似成线性关系。利用区域海温异常实验来估计区域敏感性指标，并量化其非线性程度。例如，中太平洋38C的海温异常将给出一个非线性的Tˆ9响应，比实验所预测的小海温异常的线性拟合大约15%，但对于该地区观测到的最大海温异常，响应与线性仅相差5%。即使在局地降水响应高度非线性的情况下，^Tˆ9&响应的非线性也是适度的。当温度异常具有较大的空间尺度时，降水异常主要集中在海温异常区。热带平均降水异常P9&不一定与热带平均对流层温度异常或海温强迫有简单的关系。^Tˆ9响应的近似线性是由于两个因素：1)局地出现的强非线性倾向于与输送项有关，而在大区域平均中，输送项变小；2)大气顶部和地面通量对温度的依赖在^Tˆ9及变化范围内只有微弱的非线性。对QTcm的分析近似表明，气候SST通过通量项的直接影响对^T9&对^&的敏感性a的区域差异有一定的贡献。风速对α有较强的影响，但倾向于与T9 S海温的直接影响相反，因为寒冷的海温区往往有较强的气候风，从而产生较大的坡度。降水区和非降水区的水汽对海温异常的不同反应是对a区域差异的重要贡献。尽管气候温暖水域上空的区域敏感性稍高，但即使在较冷的东太平洋，厄尔尼诺海温异常的次区域对对流层温度异常也有很大贡献。
During El Nino, there are substantial tropospheric temperature anomalies across the entire tropical belt as- sociated with the warming of sea surface temperatures (SSTs) in the central and eastern Pacific. The quasi- equilibrium tropical circulation model (QTCM) is used to investigate the mechanisms for tropical tropospheric temperature response to SST forcing. In both observations and model simulations, the tropical averaged tro- pospheric temperature anomaly ^T ˆ9& is approximately linear with the tropical mean SST anomaly ^& for observed T9 SST forcing. Regional SST anomaly experiments are used to estimate regional sensitivity measures and quantify the degree of nonlinearity. For instance, SST anomalies of 38C in the central Pacific would give a nonlinear ^T ˆ9& response about 15% greater than a linear fit to small SST anomaly experiments would predict, but for the maximum observed SST anomaly in this region the response differs by only 5% from linearity. Nonlinearity in ^T ˆ9& response is modest even when local precipitation response is highly nonlinear. While temperature anomalies have large spatial scales, the main precipitation anomaly tends to be local to the SST anomaly regions. The tropical averaged precipitation anomalies ^P9& do not necessarily have a simple relation to tropical averaged tropospheric temperature anomalies or SST forcing. The approximate linearity of the ^T ˆ9& response is due to two factors: 1) the strong nonlinearities that occur locally tend to be associated with the transport terms, which become small in the large-area average; and 2) the dependence on temperature of the top-of-atmosphere and surface fluxes has only weak nonlinearity over the range of ^T ˆ9& variations. Analytical approximations to the QTCM suggest that the direct impact of climatological SST, via flux terms, contributes modestly to regional variations in the sensitivity a of ^T9& to ^& . Wind speed has a fairly strong effect on a but tends to oppose T9 s the direct effect of SST since cold SST regions often have stronger climatological wind, which would yield larger slopes. A substantial contribution to regional variation in a comes from the different reaction of moisture to SST anomalies in precipitating and nonprecipitating regions. Although regions over climatologically warm water have a slightly higher sensitivity, subregions of El Nino SST anomalies even in the colder eastern Pacific contribute substantially to tropospheric temperature anomalies.