共查询到20条相似文献，搜索用时 968 毫秒
1.
本工作发展了一个用于研究热带海洋-大气系统相互作用和El Ni?o/Southern Oscillation动力过程的混合型(hybrid)耦合模式，其中的大气部分为一个由一阶斜压模表示的自由大气和混合行星边界层所组成的简单热带大气模式(区域为热带太平洋:120°E～80°W，30°N～30°S；水平分辨率为2°×2°)，海洋部分为大气物理研究所高分辨率自由表面热带太平洋环流模式(经纬圈方向水平分辨率分别为1°和2°，垂直方向分为不等距的14层)。两模式间的耦合是这样进行的:简单大气模式计算出海表风应力，热通量由松弛公式计算，淡水通量(蒸发与降水之差)由观测资料给定，它们一起作为海洋环流模式(OGCM)的强迫场；而OGCM计算出海表温度(SST)，在其以外地区给定观测到的气候海表温度或陆地温度，作为大气模式的边界条件。本文给出采用逐日、同步耦合方案时模式对热带太平洋气候态模拟结果，表明未采用任何通量修正(fluxes correction)，耦合模式未出现气候漂移(climate drift)现象，并且非常逼真地再现了热带太平洋气候态，特别是海表风场及相伴随的辐合带和降水、海表温度和流场及它们的季节变化。文中还进行了对耦合模式的比较研究，以验证其良好性能和对实际热带太平洋气候系统的模拟能力。 相似文献
2.
耦合模式热带太平洋云—气候反馈模拟误差评估 总被引：2，自引：2，他引：0
云—气候反馈是热带海气相互作用的重要过程, 同时也是气候模拟的难点。本文利用IPCC AR4提供的耦合模式20世纪模拟试验结果和观测资料, 通过滤波和经验正交展开 (EOF) 的方法将热带太平洋海表温度的年际变化和年代际变化信号分别提取出来, 然后再分别计算观测和模式在年际和年代际时间尺度上云—辐射和热通量反馈特征, 发现在上述两个时间尺度上, 耦合模式模拟的云—辐射和热通量的反馈都要比观测和再分析资料的偏弱。反馈偏弱的可能原因是模式中热带大气对流和云对海表温度变化的敏感性比真实大气要偏弱。值得注意的是, 尽管耦合模式热带太平洋年代际热力反馈偏弱, 但是耦合模式模拟的热带太平洋南北纬10°之间海表温度的年代际增温趋势与观测相当。进一步分析表明, 只用年代际热力反馈来解释热带太平洋的气候变化是不够的, 还必须考虑动力反馈对于海表温度变化的调节作用。 相似文献
3.
本工作发展了一个用于研究热带海洋大气系统相互作用和ＥｌＮｉｎ～ｏ／ＳｏｕｔｈｅｒｎＯｓ－ｃｉｌａｔｉｏｎ动力过程的混合型（ｈｙｂｒｉｄ）耦合模式，其中的大气部分为一个由一阶斜压模表示的自由大气和混合行星边界层所组成的简单热带大气模式（区域为热带太平洋：１２０°Ｅ～８０°Ｗ，３０°Ｎ～３０°Ｓ；水平分辨率为２°×２°），海洋部分为大气物理研究所高分辨率自由表面热带太平洋环流模式（经纬圈方向水平分辨率分别为１°和２°，垂直方向分为不等距的１４层）。两模式间的耦合是这样进行的：简单大气模式计算出海表风应力，热通量由松弛公式计算，淡水通量（蒸发与降水之差）由观测资料给定，它们一起作为海洋环流模式（ＯＧＣＭ）的强迫场；而ＯＧＣＭ计算出海表温度（ＳＳＴ），在其以外地区给定观测到的气候海表温度或陆地温度，作为大气模式的边界条件。本文给出采用逐日、同步耦合方案时模式对热带太平洋气候态模拟结果，表明未采用任何通量修正（ｆｌｕｘｅｓｃｏｒｒｅｃｔｉｏｎ），耦合模式未出现气候漂移（ｃｌｉｍａｔｅｄｒｉｆｔ）现象，并且非常逼真地再现了热带太平洋气候态，特别是海表风场及相伴随的辐合带和降水、海表温度和流场及它们的季节变化。文中还进行 相似文献
4.
GOALS/LASG模式对气候平均态的模拟 总被引：3，自引：2，他引：3
中国科学院大气物理研究所LASG最近发展了全球海洋 大气 陆面耦合气候模式系统 (GOALS)的新版本 ,实现了全球大气环流谱模式 (R42L9)与海洋环流模式 (T63L3 0 )在 40°S～ 40°N之间的开洋面上海 气通量交换的完全耦合。该模式系统已积分了 40a ,基本上不存在明显的气候漂移。文中通过对所模拟的后 3 0a平均的热带、副热带地区海温、海表风应力、洋面净通量和降水等的气候平均态与多种实测资料的对比分析 ,结果表明 ,GOALS模式基本上模拟再现了当今气候的一些主要特征 ,对热带气候平均态已具有一定的模拟能力 ,但也注意到 ,与观测相比 ,区域性差异是明显存在的 ,比如沿赤道西太平洋“暖池”区和靠近南美沿岸的东太平洋海域以及印度洋海表温度明显偏高约 2℃ ,所模拟的赤道东太平洋海温冷舌西伸明显 ,造成赤道中太平洋海温明显偏冷等偏差。这些模拟误差 ,与模式中海表风应力和洋面所得到或释放的净热通量有密切的关系。SST的模拟误差反过来也影响到对降水的模拟 相似文献
5.
一个大洋环流模式和相应的海气耦合模式的评估Ⅰ.热带太平洋年平均状态 总被引：4，自引：0，他引：4
评估了中国科学院大气物理研究所大气科学和地球流体动力学数值模拟国家重点实验室海洋环流模式L30T63和海气耦合模式FGCM-0模拟的热带太平洋年平均状态,资料取自L30T63由观测的大气强迫驱动的Control试验、由NCAR CCM3大气强迫驱动的Spinup试验、以及相应的海气耦合模式FGCM-0.主要的结论是:(1)在"准确"的海表强迫下,Control模拟的海面温度和温跃层与观测结果相当接近,模式的固有误差是赤道冷舌过分西伸和东南太平洋温跃层偏浅.(2)Spinup能模拟出合理的热带太平洋上层海洋环流,但存在两个问题,即:暖池区海面温度显著偏高、沿赤道的梯度过大;赤道温跃层偏浅、东西向坡度偏小,它们分别与CCM3提供的海表短波辐射通量和风应力的系统误差有关.这两个问题很可能是海气耦合模式FGCM-0运行初期误差迅速发展的重要原因.(3)FGCM-0模拟的赤道暖池区上层100 m的平均温度比观测低3℃.分析表明FGCM-0夸大了暖池区海洋动力过程的降温作用,使得模拟的"暖池"在一定程度上具有冷舌的属性.FGCM-0模拟的热带南太平洋温跃层比观测结果偏浅数十米到100 m,以致赤道两侧的上层海洋温度分布趋于对称,成为"double ITCZ"现象在上层海洋中的表现.风应力旋度的系统误差和垂直混合随深度衰减过快是温跃层偏浅的两个可能原因;FGCM-0中与北太平洋中高纬地区深厚冷偏差相关的经圈环流也有利于热带温跃层误差的维持. 相似文献
6.
评估了中国科学院大气物理研究所大气科学和地球流体动力学数值模拟国家重点实验室海洋环流模式L30T63和海气耦合模式FGCM 0模拟的热带太平洋年平均状态 ,资料取自L30T63由观测的大气强迫驱动的Control试验、由NCARCCM3大气强迫驱动的Spinup试验、以及相应的海气耦合模式FGCM 0。主要的结论是 :( 1 )在“准确”的海表强迫下 ,Control模拟的海面温度和温跃层与观测结果相当接近 ,模式的固有误差是赤道冷舌过分西伸和东南太平洋温跃层偏浅。 ( 2 )Spinup能模拟出合理的热带太平洋上层海洋环流 ,但存在两个问题 ,即 :暖池区海面温度显著偏高、沿赤道的梯度过大 ;赤道温跃层偏浅、东西向坡度偏小 ,它们分别与CCM3提供的海表短波辐射通量和风应力的系统误差有关。这两个问题很可能是海气耦合模式FGCM 0运行初期误差迅速发展的重要原因。 ( 3)FGCM 0模拟的赤道暖池区上层 1 0 0m的平均温度比观测低 3℃。分析表明FGCM 0夸大了暖池区海洋动力过程的降温作用 ,使得模拟的“暖池”在一定程度上具有冷舌的属性。FGCM 0模拟的热带南太平洋温跃层比观测结果偏浅数十米到 1 0 0m ,以致赤道两侧的上层海洋温度分布趋于对称 ,成为“doubleITCZ”现象在上层海洋中的表现。风应力旋度的系统误差和垂直混合随深度衰减过快 相似文献
7.
热带太平洋年代际平均气候态变化与ENSO循环 总被引：20，自引：0，他引：20
文中用观测的热带太平洋海表温度资料、风应力资料和OLR资料，通过多时间尺度分析，将与ENSO有关的变化分为3个主要的分量，一是2～7a的ENSO循环尺度，二是8～20a的年代际尺度，三是20a以上的平均气候态变化。讨论了热带太平洋这种平均气候态变化的主要特征以及与ENSO循环的关系，并用耦合模式的数值试验来研究平均气候态的变化对ENSO循环的影响。结果表明热带太平洋的平均气候态在20世纪70年代后期发生了一次由冷态向暖态的变化，主要增暖区是沿赤道以及热带东太平洋的，海表温度变化最大中心可以达到0.6℃。伴随着海表温度的变化，赤道西太平洋的西风距平加强，赤道东太平洋的东风距平也加强，在赤道中太平洋形成了一个加强的辐合中心。年代际平均气候冷暖态的变化对ENSO最直接的线性影响是使ElNio位相增加，而形成ENSO冷位相和暖位相的不对称。另一方面较暖的平均气候态可能引起海洋和大气之间的耦合加强，导致ENSO循环振荡有所加强。 相似文献
8.
利用观测海温驱动NCAR CAM5模式进行了两组数值试验,对比分析了在CAM5模式海气湍流热通量参数化方案中引入阵风效应前后,模式对冬季NPO(North Pacific Oscillation,北太平洋涛动)年际变化模拟效果的差异。结果表明,考虑了阵风效应后,CAM5模式能较好地模拟冬季NPO的年际变化特征,模拟的1979—1999年冬季NPO指数序列与观测结果的相关系数由0.09提高到0.57;热带东太平洋海表温度异常通过影响海表湍流热通量异常,对冬季NPO年际变化产生影响;引入阵风效应后,模式对热带东太平洋海表湍流热通量异常的模拟结果更趋合理,从而使得模式可以较好地模拟出冬季NPO的年际变化。 相似文献
9.
利用观测海温资料和CMIP5模式模拟结果分析西北太平洋(120°E~120°W,20~60°N)海表温度的气候态和年代际变化特征。结果表明,所选22个模式可以较好地模拟出西北太平洋海表温度的气候特征及其年际、年代际变化特征;模式模拟的海表温度总体标准偏差在黑潮延伸体区域最大;绝大多数模式能模拟出海表温度的第一EOF模态;西北太平洋海表温度具有较明显的年代际振荡现象,13/22的模式模拟的海表温度存在明显的年代际振荡,同时海表温度气候态的模拟偏差对其周期振荡模拟的影响较大,尤其在黑潮延伸体区域。 相似文献
10.
热带太平洋对全球的气候有重要作用。然而,关于全球变暖背景下热带太平洋海温长期趋势的研究,迄今为止仍有争议。本文利用多套海表温度资料和次表层海温资料,基于无参的趋势估计方法（Theil-Sen趋势）,分析了热带太平洋海表温度长期趋势及赤道太平洋次表层海温长期趋势。多套资料的结果均表明在全球变暖背景下,热带太平洋冷舌区为长期冷趋势,而冷舌区之外的热带太平洋区域为长期暖趋势,即似La Ni?a（La Ni?a-like）海温长期趋势。此海温长期趋势是由热带太平洋冷舌模态所引起。当冷舌模态为正位相时,对应热带太平洋冷舌区为冷海温异常,而冷舌区之外的热带太平洋为暖海温异常。冷舌模态时间序列主要为长期趋势,而造成冷舌模态长期趋势的机制是全球变暖强迫下的海洋动力反馈过程。赤道太平洋的表层和次表层海温似La Ni?a型的长期趋势,是冷舌模态在表层海温和次表层海温上的不同体现。 相似文献
11.
热通量和风应力影响北太平洋SST年际和年代际变率的数值模拟 总被引：2，自引：0，他引：2
利用一个大洋环流模式LICOM, 通过1958～2001年风应力 (ERA40) 和热通量驱动下的两组模拟试验, 检验了二者在北太平洋年际和年代际变率形成中的作用。结果表明, 尽管在年际尺度上热带太平洋变率主要受风应力影响, 但合理考虑热通量异常的强迫作用能够显著改进模式对El Niño的模拟效果, 包括对El Niño周期非规则性的成功模拟; 北太平洋SST的年际和年代际异常主要受热通量异常的影响, 合理考虑热通量强迫的年代际变化能够改善模式对北太平洋年代际变率的模拟效果。在北太平洋海盆的不同区域, 导致SST变率异常的因子不同: 在加利福尼亚沿岸, 冬季平均海温的变率异常主要由热通量的异常决定; 在北太平洋中部, 温度趋势异常主要受热通量和水平平流的作用影响; 在黑潮及其延伸体区域, 对温度趋势异常起主导作用的是热通量和海洋非线性作用, 与此同时, 水平平流和扩散的作用亦不容忽视。 相似文献
12.
印度洋对ENSO事件的响应:观测与模拟 总被引：11，自引：3，他引：8
观测事实显示,在El Ni(n～)o期间,伴随着赤道中东太平洋表层海温(SST)的升高,热带印度洋SST出现正距平.作者利用海气耦合模式模拟了印度洋对ENSO事件的上述响应,并进而讨论了其物理机制.所用模式为法国国家科研中心Pierre-Simon-Laplace 全球环境科学联合实验室(IPSL)发展的全球海气耦合模式.该模式成功地控制了气候漂移,能够合理再现印度洋的基本气候态.观测中与ENSO相关的热带印度洋SST变化,表现为全海盆一致的正距平,并且这种变化要滞后赤道中东太平洋SST变化大约一个季度,意味着它主要是对东太平洋SST强迫的一种遥响应,模式结果也支持这一机制,尽管模式中的南方涛动现象被夸大了,使得模拟的与ENSO相关联的SST正距平的位置南移,阿拉伯海和孟加拉湾被负距平(而不是正距平)所控制.研究表明,东太平洋主要通过大气桥影响潜热释放来影响印度洋SST变化.赤道东太平洋El Ni(n～)o事件的发展,导致印度洋上空风场异常自东而西传播;伴随着风场的变化,潜热发生相应变化,并最终导致SST异常的发生.非洲东海岸受索马里急流控制的海域,其SST的变化不能简单地利用热通量的变化来解释.证据显示,印度洋的增暖是ENSO事件发生的结果而不是其前期信号. 相似文献
13.
Recent climatic trends in the tropical Atlantic 总被引：1，自引：1，他引：0
Jacques Servain Guy Caniaux Yves K. Kouadio Michael J. McPhaden Moacyr Araujo 《Climate Dynamics》2014,43(11):3071-3089
A homogeneous monthly data set of sea surface temperature (SST) and pseudo wind stress based on in situ observations is used to investigate the climatic trends over the tropical Atlantic during the last five decades (1964–2012). After a decrease of SST by about 1 °C during 1964–1975, most apparent in the northern tropical region, the entire tropical basin warmed up. That warming was the most substantial (>1 °C) in the eastern tropical ocean and in the longitudinal band of the intertropical convergence zone. Surprisingly, the trade wind system also strengthened over the peirod 1964–2012. Complementary information extracted from other observational data sources confirms the simultaneity of SST warming and the strengthening of the surface winds. Examining data sets of surface heat flux during the last few decades for the same region, we find that the SST warming was not a consequence of atmospheric heat flux forcing. Conversely, we suggest that long-term SST warming drives changes in atmosphere parameters at the sea surface, most notably an increase in latent heat flux, and that an acceleration of the hydrological cycle induces a strengthening of the trade winds and an acceleration of the Hadley circulation. These trends are also accompanied by rising sea levels and upper ocean heat content over similar multi-decadal time scales in the tropical Atlantic. Though more work is needed to fully understand these long term trends, especially what happens from the mid-1970’s, it is likely that changes in ocean circulation involving some combination of the Atlantic meridional overtuning circulation and the subtropical cells are required to explain the observations. 相似文献
14.
The influence of mean climate on the seasonal cycle and the El Ni?o-Southern Oscillation (ENSO) in the tropical Pacific climate is investigated using the Climate Community System Model Version 3 (CCSM3). An empirical time-independent surface heat flux adjustment over the tropical ocean is applied to the oceanic component of CCSM3. In comparison with the control run, the heat flux-adjusted run simulates a more realistic mean climate not only for the sea surface temperature (SST) but also for wind stress and precipitation. Even though the heat flux adjustment is time-independent, the seasonal cycles of SST, wind stress and precipitation over the equatorial eastern Pacific are more realistic in the flux-adjusted simulation. Improvements in the representation of the ENSO variability in the heat flux-adjusted simulation include that the Nino3.4 SST index is less regular than a strong biennial oscillation in the control run. But some deficiencies also arise. For example, the amplitude of the ENSO variability is reduced in the flux-adjusted run. The impact of the mean climate on ENSO prediction is further examined by performing a series of monthly hindcasts from 1982 to 1998 using CCSM3 with and without the heat flux adjustment. The flux-adjusted hindcasts show slightly higher predictive skill than the unadjusted hindcasts with January initial conditions at lead times of 7?C9?months and July initial conditions at lead times of 9?C11?months. However, their differences during these months are not statistically significant. 相似文献
15.
The Kuroshio Extension region is characterized by energetic oceanic mesoscale and frontal variability that alters the air–sea fluxes that can influence large-scale climate variability in the North Pacific. We investigate this mesoscale air-sea coupling using a regional eddy-resolving coupled ocean–atmosphere (OA) model that downscales the observed large-scale climate variability from 2001 to 2007. The model simulates many aspects of the observed seasonal cycle of OA coupling strength for both momentum and turbulent heat fluxes. We introduce a new modeling approach to study the scale-dependence of two well-known mechanisms for the surface wind response to mesoscale sea surface temperatures (SSTs), namely, the ‘vertical mixing mechanism’ (VMM) and the ‘pressure adjustment mechanism’ (PAM). We compare the fully coupled model to the same model with an online, 2-D spatial smoother applied to remove the mesoscale SST field felt by the atmosphere. Both VMM and PAM are found to be active during the strong wintertime peak seen in the coupling strength in both the model and observations. For VMM, large-scale SST gradients surprisingly generate coupling between downwind SST gradient and wind stress divergence that is often stronger than the coupling on the mesoscale, indicating their joint importance in OA interaction in this region. In contrast, VMM coupling between crosswind SST gradient and wind stress curl occurs only on the mesoscale, and not over large-scale SST gradients, indicating the essential role of the ocean mesocale. For PAM, the model results indicate that coupling between the Laplacian of sea level pressure and surface wind convergence occurs for both mesoscale and large-scale processes, but inclusion of the mesoscale roughly doubles the coupling strength. Coupling between latent heat flux and SST is found to be significant throughout the entire seasonal cycle in both fully coupled mode and large-scale coupled mode, with peak coupling during winter months. The atmospheric response to the oceanic mesoscale SST is also studied by comparing the fully coupled run to an uncoupled atmospheric model forced with smoothed SST prescribed from the coupled run. Precipitation anomalies are found to be forced by surface wind convergence patterns that are driven by mesoscale SST gradients, indicating the importance of the ocean forcing the atmosphere at this scale. 相似文献
16.
中尺度海-气耦合模式GRAPES_OMLM对台风珍珠的模拟研究 总被引：1，自引：0，他引：1
利用全球/区域同化与预报系统GRAPES(Global/Regional Assimilation and Prediction System)和改进的Mellor-Yamada型海洋混合层模式OMLM(Ocean Mixed Layer Model),建立了一个新的中尺度海-气耦合模式GRAPES_OMLM,并利用该模式对发生于南海的台风珍珠(0601)进行了模拟研究,检验了GRAPES_OMLM对台风的模拟性能,并分析了局地海-气相互作用对台风的影响。结果表明,GRAPES_OMLM基本能模拟出台风天气过程中的主要物理过程。考虑了海-气相互作用的耦合试验所模拟出的台风强度、近台风中心最大风速以及台风后期移动路径,相对于两组控制试验(单独大气模式)的模拟结果都有较大的改进。而且,采用逐日变化海表温度作为下边界条件的控制试验2的模拟结果相对于SST不变的控制试验1更接近观测。耦合模式GRAPES_OMLM能较好地模拟出台风过境海表温度的变化,台风珍珠在其路径右侧有超过4.0℃的降温。SST的变化和海表风应力的变化呈反相关系,风应力的增大伴随着海洋近表层湍流动能(TKE)的加强,大风动力作用是SST降低的主要原因。SST的降低致使海洋向台风输送的热通量减少,进而削弱了台风的强度并改变台风环流结构,同时通过改变位势涡度趋势的一波结构(WN-1)来影响台风的移动路径。 相似文献
17.
海洋环流对全球增暖趋势的调制：基于FGOALS-s2的数值模拟研究 总被引：1，自引：0，他引：1
在工业革命以来全球长期增暖趋势背景下,全球平均表面气温还同时表现出年代际变化特征,二者叠加在一起使得全球平均气温在某些年份增暖相对停滞(如1999～2008年)或者增暖相对较快(如1980～1998年).利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)发展的耦合气候模式FGOALS-s2历史气候和典型路径浓度(RCPs)模拟试验结果研究了可能造成全球增暖的年代际停滞及加速现象的原因,特别是海洋环流对全球变暖趋势的调制作用.该模式模拟的全球平均气温与观测类似,即在长期增暖趋势之上,还叠加了显著的年代际变化.对全球平均能量收支分析表明,模拟的气温年代际变化与大气顶净辐射通量无关,意味着年代际表面气温变化可能与能量在气候系统内部的重新分配有关.通过对全球增暖加速和停滞时期大气和海洋环流变化的合成分析及回归分析,发现全球表面气温与大部分海区海表温度(SST)均表现出几乎一致的变化特征.在增暖停滞时期,SST降低,更多热量进入海洋次表层和深层,使其温度增加;而在增暖加速时期,更多热量停留在表层,使得大部分海区SST显著增加,次表层海水和深海相对冷却.进一步分析表明,热带太平洋表层和次表层海温年代际变化主要是由于副热带—热带经圈环流(STC)的年代际变化所致,然后热带太平洋海温异常可以通过风应力和热通量强迫作用引起印度洋、大西洋海温的年代际变化.在此过程中,海洋环流变化起到了重要作用,例如印度尼西亚贯穿流(ITF)年代际异常对南印度洋次表层海温变化起到关键作用,而大西洋经圈翻转环流(AMOC)则能直接影响到北大西洋深层海温变化. 相似文献
18.
Warm sea-surface temperature (SST) biases in the southeastern tropical Atlantic (SETA), which is defined by a region from 5°E to the west coast of southern Africa and from 10°S to 30°S, are a common problem in many current and previous generation climate models. The Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble provides a useful framework to tackle the complex issues concerning causes of the SST bias. In this study, we tested a number of previously proposed mechanisms responsible for the SETA SST bias and found the following results. First, the multi-model ensemble mean shows a positive shortwave radiation bias of ~20 W m?2, consistent with models’ deficiency in simulating low-level clouds. This shortwave radiation error, however, is overwhelmed by larger errors in the simulated surface turbulent heat and longwave radiation fluxes, resulting in excessive heat loss from the ocean. The result holds for atmosphere-only model simulations from the same multi-model ensemble, where the effect of SST biases on surface heat fluxes is removed, and is not sensitive to whether the analysis region is chosen to coincide with the maximum warm SST bias along the coast or with the main SETA stratocumulus deck away from the coast. This combined with the fact that there is no statistically significant relationship between simulated SST biases and surface heat flux biases among CMIP5 models suggests that the shortwave radiation bias caused by poorly simulated low-level clouds is not the leading cause of the warm SST bias. Second, the majority of CMIP5 models underestimate upwelling strength along the Benguela coast, which is linked to the unrealistically weak alongshore wind stress simulated by the models. However, a correlation analysis between the model simulated vertical velocities and SST biases does not reveal a statistically significant relationship between the two, suggesting that the deficient coastal upwelling in the models is not simply related to the warm SST bias via vertical heat advection. Third, SETA SST biases in CMIP5 models are correlated with surface and subsurface ocean temperature biases in the equatorial region, suggesting that the equatorial temperature bias remotely contributes to the SETA SST bias. Finally, we found that all CMIP5 models simulate a southward displaced Angola–Benguela front (ABF), which in many models is more than 10° south of its observed location. Furthermore, SETA SST biases are most significantly correlated with ABF latitude, which suggests that the inability of CMIP5 models to accurately simulate the ABF is a leading cause of the SETA SST bias. This is supported by simulations with the oceanic component of one of the CMIP5 models, which is forced with observationally derived surface fluxes. The results show that even with the observationally derived surface atmospheric forcing, the ocean model generates a significant warm SST bias near the ABF, underlining the important role of ocean dynamics in SETA SST bias problem. Further model simulations were conducted to address the impact of the SETA SST biases. The results indicate a significant remote influence of the SETA SST bias on global model simulations of tropical climate, underscoring the importance and urgency to reduce the SETA SST bias in global climate models. 相似文献
19.
Decadal-scale climate variability in the tropical and North Pacific during the 1970s and 1980s: observations and model results 总被引：32，自引：3，他引：32
N E Graham 《Climate Dynamics》1994,10(3):135-162
An abrupt change in the large-scale boreal winter circulation pattern over the North Pacific was observed during the mid-1970s. Most notably, this change was marked by a southward shift and intensification of the Aleutian Low and prevailing westerlies over the mid-latitude central and eastern Pacific. Associated changes in diverse North Pacific climatological, hydrological, and biological variables have been noted by numerous researchers. Intriguingly, the timing of these changes in the extra-tropical circulation was coincident with a shift in the background state of the coupled ocean-atmosphere system over the tropical Pacific. These changes include increases in SST over broad regions of the central and eastern tropical Pacific and an eastward displacement of the region of persistent convection in the western Pacific. This paper presents a variety of observed data and model results to describe the climate shift, and to understand some of the links within the coupled climate system that produced it. Five main findings are emphasized: (1) evidence of abrupt, simultaneous, and apparently related changes can be found in many fields and in many model results; the climate shift is not an artifact, (2) over the tropical Pacific the climate change represents a shift in the state of the coupled ocean-atmosphere system, some aspects of which resemble features associated with El Niño episodes. However, the shift in state is not well characterized as due to a change in the frequency of intensity of El Ni~no episodes; it is better described as a change in background mean state, (3) when forced with observed SSTs, both a very simple atmospheric model and a full general circulation model (GCM) qualitatively simulate aspects of the decadal-scale shift over the tropical Pacific, (4) when forced with observed surface wind stress, two ocean models of the tropical Pacific, in which surface heat fluxes are parameterized as Newtonian damping, reproduce some aspects of the near-equatorial decadal SST signal. However, the models do not reproduce the large changes in SST observed at higher latitudes of the tropical Pacific, suggesting that altered surface heat fluxes dominated in producing these changes, and (5) an important new finding of this study is the success of a GCM in reproducing important aspects of the observed mid-1970s shift in winter northern hemisphere circulation. Comparative analyses of the observed and GCM simulated circulation suggest the altered patterns of tropical Pacific SST and convection were important in forcing the changes in the mid-latitude circulation, a finding corroborated by recent GCM experiments. 相似文献
20.
You-Soon Chang Shaoqing Zhang Anthony Rosati Thomas L. Delworth William F. Stern 《Climate Dynamics》2013,40(3-4):775-803
The Geophysical Fluid Dynamics Laboratory has developed an ensemble coupled data assimilation (ECDA) system based on the fully coupled climate model, CM2.1, in order to provide reanalyzed coupled initial conditions that are balanced with the climate prediction model. Here, we conduct a comprehensive assessment for the oceanic variability from the latest version of the ECDA analyzed for 51 years, 1960–2010. Meridional oceanic heat transport, net ocean surface heat flux, wind stress, sea surface height, top 300 m heat content, tropical temperature, salinity and currents are compared with various in situ observations and reanalyses by employing similar configurations with the assessment of the NCEP’s climate forecast system reanalysis (Xue et al. in Clim Dyn 37(11):2511–2539, 2011). Results show that the ECDA agrees well with observations in both climatology and variability for 51 years. For the simulation of the Tropical Atlantic Ocean and global salinity variability, the ECDA shows a good performance compared to existing reanalyses. The ECDA also shows no significant drift in the deep ocean temperature and salinity. While systematic model biases are mostly corrected with the coupled data assimilation, some biases (e.g., strong trade winds, weak westerly winds and warm SST in the southern oceans, subsurface temperature and salinity biases along the equatorial western Pacific boundary, overestimating the mixed layer depth around the subpolar Atlantic and high-latitude southern oceans in the winter seasons) are not completely eliminated. Mean biases such as strong South Equatorial Current, weak Equatorial Under Current, and weak Atlantic overturning transport are generated during the assimilation procedure, but their variabilities are well simulated. In terms of climate variability, the ECDA provides good simulations of the dominant oceanic signals associated with El Nino and Southern Oscillation, Indian Ocean Dipole, Pacific Decadal Oscillation, and Atlantic Meridional Overturning Circulation during the whole analyzed period, 1960–2010. 相似文献