SST日变化对西太平洋暖池海表热通量季节内变化的影响

基于利用日最大太阳辐射、日平均海面风和日降水量近似计算海表温度(SST)日变化的振幅的方法，发展了一个计算SST日循环的参数化方案。利用周平均SST强迫美国国家大气研究中心(NCAR)的CCM3大气模式进行了有、无考虑SST日变化的比较试验。热带海洋与全球大气计划之耦合海气响应实验(TOGA COARE)的强化观测期间IMET浮标的逐时海表观测资料不仅验证了该参数化方案的合理性，也表明了利用参数化方案对强迫场SST迭加日变化使CCM3较真实地模拟出西太平洋暖池海表热通量的季节内变化的位相结构。     

东太平洋冷舌区海表面温度日变化特征的模拟研究

本文通过分辨太阳辐射日变化, 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/IAP) 气候系统海洋环流模式 (LICOM), 模拟了东太平洋冷舌区海表面温度 (SST) 的日变化特征并研究了弱混合对其影响。采用理想的太阳辐射日变化强迫上层垂向分辨率为10 m的海洋模式LICOM, 模拟出了SST日变化一些特征, 同时海洋的上层流场也产生明显日变化。模拟的SST日变化振幅水平分布与观测接近, 且受太阳辐射日变化振幅水平分布调制。在赤道中东太平洋区, 模拟的SST日变化振幅 (约为0.3～0.4℃) 比观测偏小约0.1～0.2℃。模拟的SST日变化峰值出现在15～16 时 (当地标准时间), 落后于太阳辐射峰值2～3个小时, 接近观测。进一步减弱混合后, 模拟的日变化振幅增加约0.1℃, 更接近观测。这说明在东太平洋冷舌区SST日变化主要受太阳辐射日变化和垂直混合影响。此外, 混合减小后, 在太阳辐射日变化调制下, 平均态 (如混合层、温度和流场) 也出现明显变化。在赤道东太平洋冷舌区北侧, 弱混合导致混合层变浅, 变浅使热量堆积进而使平均SST升高约0.3℃; 在赤道东太平洋冷舌南侧, 经向平流加强导致平均SST降低约0.2℃。     

基于信息流理论的因果分析在辨析大西洋多年代际振荡物理机制中的应用

大西洋多年代际振荡（AMO）是指发生在北大西洋的海表温度（SST）冷暖异常多年代际（50～80年）振荡的现象。通常AMO被认为是受大西洋经向翻转环流（AMOC）及其对应的海洋动力过程（经向热量输运）的影响。近年来有观点认为,AMO是大气随机热力强迫的产物,大气主导了海气间的热量交换进而影响AMO。弄清AMO和北大西洋海表热通量的因果关系是辨析AMO动力和热力驱动机制的关键。本文利用基于信息流理论的因果分析方法,研究了1880年以来观测的AMO与北大西洋海表热通量间的因果关系。结果表明,在多年代际尺度上,从AMO到海表热通量的信息流要远大于二者相反方向的信息流,这说明AMO是北大西洋海表热通量异常的因,海洋主导了海气间的热量交换。大气随机热力强迫机制无法解释AMO与热通量两者因果分析的结果。对泛大西洋地区的陆地气温和AMO指数进行分析,进一步表明由于海洋主导了海气热量交换,AMO的海温异常加热/冷却控制了绝大多数地区气温的多年代际变化。利用海温驱动的大气环流模式的模拟结果验证了AMO的海温异常对周边陆地气温强迫作用。本文的结果为辨析AMO的动力和热力驱动机制提供了新线索,进一步表明AMO并非是大气随机热力强迫的产物,海洋环流可能是AMO的主要驱动因子。     

CCM3模式中LSM积雪方案的改进研究（I）：修改方案介绍及其单点试验

为了改进美国NCAR CCM3全球模式中LSM陆面模型中的积雪方案的模拟效果，在Sun等SAST积雪模型的基础上，作了部分修改后，加进CCM3模式LSM模型中。该方案根据格点区域平均积雪深度的不同，把地面雪盖划分为1到3层不等，能在积雪表层和中间层更好地描述温度的日变化和季节变化；较详细地考虑了雪的热传导、太阳辐射的穿透吸收、雪的融化、液态水的储存、渗透和再冻结等积雪内部的主要物理过程；根据Nimbus-7卫星实测雪深资料修改了积雪覆盖度和雪面反照率的计算方案。利用前苏联6个台站1978—1983年的实测积雪资料和大气强迫数据，进行了单点模拟试验，结果表明，新的积雪参数化方案能够较好地再现积雪深度和雪水当量的逐日和季节变化特征，部分提高了积雪参数化方案对积雪的模拟能力。     

副热带东太平洋低云对LASG耦合环流模式FGCM-0中"双ITCZ"的影响

与其他耦合环流模式一样,LASG耦合模式FGCM-0也存在虚假的“双ITCZ”。为了认识FGCM-0中“双ITCZ”,首先研究了FGCM-0的大气分量模式,剧INCAR(美国国家大气研究中心)的公用气候模式CCM3对秘鲁和加利福尼亚沿岸低云以及低层大气整体稳定度的模拟能力。发现：尽管CCM3模拟的低层大气整体稳定度与利用NCEP(美国国家环境预报中心)再分析资料分析的结果较一致,但模拟的低云量比ISCCP(国际卫星云气候计划)观测值显偏少。利用ISCCP低云量与由NCEP再分析温度场分析的低层整体稳定度之间的回归关系,修改了CCM3中低云参数化方案,并用于敏感性试验,以研究副热带东太平洋低云对FGCM-0中“双ITCZ”的影响。结果发现,修改的方案能显增强对低云量的模拟,秘鲁沿岸冷海域低云量增加能显减弱赤道以南热带东太平洋海表面温度(SST)的暖偏差,但同时也将使赤道冷舌增强、向西伸展更远;加利福尼亚沿岸低云量增加可以有效减弱赤道以北ITCZ区SST暖偏差。为了检验秘鲁沿岸SST与低云间的正反馈,又实施了一个控制秘鲁沿岸SST的敏感性试验,结果表明：控制秘鲁沿岸SST抑制其增暖,对自东南太平洋向西北至中、西赤道太平洋广大区域产生的影响,与增加秘鲁沿岸低云量产生的影响相似。     

热带太平洋海表温度年际变化对降水季节内振荡的影响

根据 １９８２—１９９２年期间的日平均 ＭＳＵ（Ｓｐｅｎｃｅｒ, １９９３）海洋降水和 ５天平均的ＣＭＡＰ（Ｘｉｅ＆ Ａｒｋｉｎ, １９９７）降水观测资料,分析了热带太平洋大气季节内振荡（ＭＪＯ）的年际变化特征。在太平洋海表温度（ＳＳＴ）年际变化的正常年份（１９８２—８３年, １９８６—８８年, １９９１—９２年）,均有明显的ＭＪＯ信号传到日界线以东并在中、东太平洋维持数月。热带ＭＪＯ活动强度的年际变化与局地ＳＳＴ的变化存在正相关。中、东太平洋降水的季节内振荡的年际变化与热带太平洋ＳＳＴ的最强正相关在Ｎｉｎｏ３区附近。以观测ＳＳＴ场强迫ＣＣＭ３大气模式的数值试验基本上真实地再现了１１年期间热带太平洋降水季节内振荡的年际变化总趋势,但模拟季节内振荡的强度较观测平均偏弱。对比分别采用周平均和月平均ＳＳＴ强迫场的积分结果,发现在中、东太平洋,二个积分模拟的降水季节内振荡强度的年际变化接近并且趋势与观测基本一致,而在西太平洋二个积分的模拟结果差别较大。这表明在热带中、东太平洋,ＳＳＴ强迫的年际变化对ＭＪＯ强度的变化有强的制约。而在ＭＪＯ总体活跃的热带西太平洋,ＳＳＴ强迫场的季节变化对模拟ＭＪＯ活动也有较大影响。ＣＣＭ３模拟     

GAMIL模式海气湍流通量参数化方案的改进及其对大气环流年际变率模拟效果的影响

通过引人中尺度对流运动对海表湍流通量的贡献,改进了大气环流模式GAMIL1.0的海气湍流通量参数化方案.利用1979年1月至2000年12月的观测海温资料驱动GAMIL1.0模式,研究了海气湍流通量参数化改进对大气环流年际变化模拟效果的影响.结果表明:采用改进的海气湍流通量参数化方案,模拟的热带海表湍流热通量得到增强,...     

冬季北太平洋海表热通量异常和海气相互作用——基于一个全球海气耦合模式长期积分的诊断分析

利用一个全球海气耦合模式长期积分所给出的资料,分析了冬季北太平洋海表湍流热通量（潜热和感热）异常及其对海表温度（SST）异常的影响,并比较了海表热通量诸分量和海洋内部的动力学过程对SST变化的相对重要性。结果表明,冬季热带外海洋上的湍流热通量是影响SST的主要因子,但在北太平洋中部海水的平流作用也不可忽视。冬季热带外海洋向大气释放的潜热和感热通量与SST倾向（而不是SST本身）之间存在着显著的相关,这同Cayan和Reynolds等利用COADS资料和NCEP资料同化模式分析的结果是一致的。模式诊断的结果支持这样一种看法：和热带海洋不同,冬季热带外海洋上的海气相互作用主要地表现为大气对海洋的强迫作用,而不是相反。模式给出的SST倾向的第一个EOF分量及其与海平面气压场的相关特征同Wallace等从观测资料分析所得到的结果是一致的;进一步的分析表明：在冬季北太平洋的大部分区域（特别是西太平洋）,大尺度大气环流异常在很大程度上决定着SST的异常,而这种决定作用正是通过它对湍流热通量的强烈影响来实现的。     

不同海温强迫的月动力延伸集合预报试验

利用全球谱模式T106L19和增长模繁殖法（BGM）建立了月动力延伸集合预报系统,基于气候海表面温度（SST）和预测海表面温度,设计了三组集合预报试验,一组为气候SST作为模式下边界条件的集合预报试验（CSST试验）,另一组为预测SST作为模式的下边界条件的集合预报试验（FSST试验）,第三组为前两组试验的集合预报结果之和（AVE30试验）,对两种海温强迫分别进行了48个月的试验,并对预报结果进行了检验和分析。结果表明：相对于单一的控制预报,不管是CSST试验还是FSST试验,利用BGM方法制作的初值集合预报能显著提高月平均环流的预报技巧,集合预报对PNA区域的预报技巧改进显著,特别是预测SST强迫有正的贡献;同时考虑初值和边值不确定性影响的集合预报试验（AVE30试验）,其全球预报技巧不仅高于控制预报,也分别高于FSST试验和CSST试验,这说明要提高月延伸预报技巧,必须同时考虑初值和边值的影响;大气对SST强迫的响应在模式积分10天开始显著,SST对第二旬和第三旬的作用直接影响月平均环流的预报效果,而SST对第二旬和第三旬预报的影响不仅与SST本身变化有关,还与初值有关,不同的初值其作用不同;集合预报对我国夏季月平均温度分布具有较强预报能力,采用预报海温强迫的预报结果,总体上优于气候海温强迫的结果。     

CCM3模式中LSM积雪方案的改进研究(Ⅰ):修改方案介绍及其单点试验

为了改进美国NCARCCM3全球模式中LSM陆面模型中的积雪方案的模拟效果,在Sun等[1]SAST积雪模型的基础上,作了部分修改后,加进CCM3模式LSM模型中.该方案根据格点区域平均积雪深度的不同,把地面雪盖划分为1到3层不等,能在积雪表层和中间层更好地描述温度的日变化和季节变化;较详细地考虑了雪的热传导、太阳辐射的穿透吸收、雪的融化、液态水的储存、渗透和再冻结等积雪内部的主要物理过程;根据Nimbus-7卫星实测雪深资料修改了积雪覆盖度和雪面反照率的计算方案.利用前苏联6个台站1978-1983年的实测积雪资料和大气强迫数据,进行了单点模拟试验,结果表明,新的积雪参数化方案能够较好地再现积雪深度和雪水当量的逐日和季节变化特征,部分提高了积雪参数化方案对积雪的模拟能力.     

Impact of resolving the diurnal cycle in an ocean–atmosphere GCM. Part 1: a diurnally forced OGCM

The diurnal cycle is a fundamental time scale in the climate system, at which the upper ocean and atmosphere are routinely observed to vary. Current climate models, however, are not configured to resolve the diurnal cycle in the upper ocean or the interaction of the ocean and atmosphere on these time scales. This study examines the diurnal cycle of the tropical upper ocean and its climate impacts. In the present paper, the first of two, a high vertical resolution ocean general circulation model (OGCM), with modified physics, is developed which is able to resolve the diurnal cycle of sea surface temperature (SST) and current variability in the upper ocean. It is then validated against a satellite derived parameterization of diurnal SST variability and in-situ current observations. The model is then used to assess rectification of the intraseasonal SST response to the Madden–Julian oscillation (MJO) by the diurnal cycle of SST. Across the equatorial Indo-Pacific it is found that the diurnal cycle increases the intraseasonal SST response to the MJO by around 20%. In the Pacific, the diurnal cycle also modifies the exchange of momentum between equatorially divergent Ekman currents and the meridionally convergent geostrophic currents beneath, resulting in a 10% increase in the strength of the Ekman cells and equatorial upwelling. How the thermodynamic and dynamical impacts of the diurnal cycle effect the mean state, and variability, of the climate system cannot be fully investigated in the constrained design of ocean-only experiments presented here. The second part of this study, published separately, addresses the climate impacts of the diurnal cycle in the coupled system by coupling the OGCM developed here to an atmosphere general circulation model.     

Westerly wind events,diurnal cycle and central Pacific El Niño warming

In the past three decades, the strongest central Pacific (CP) El Niño event was observed in 2009–2010 by satellites. When intensity of this CP El Niño reached its maximum, large diurnal variations of sea surface temperature (SST) were also observed from tropical atmosphere ocean moorings in the central equatorial Pacific. Solar radiation in the equatorial central Pacific is larger than 140 W/m², which leads to the amplitude of diurnal cycle of SST primarily determined by large-scale wind patterns. Intraseasonal westerly wind events (WWEs) can lead to an eastward displacement of the warm pool and also can weaken the trade winds in central Pacific. When the occurrence of equatorial WWEs is more than 20 days in a month, monthly mean wind speed in central equatorial Pacific has high possibility of wind speed less than 3 m/s, thus has pronounced diurnal cycle of SST. The diurnal cycle of SST will rectify daily mean SST. Reduced mixing at the base of the mixed layer and suppression of entrainment due to the accumulated effect of diurnal cycle may lead to warmer SST in the following month. This study suggests the occurrence of more diurnal SST events may contribute to the increasing intensity of the CP El Niño events.     

外强迫对热带季节内振荡影响的模拟研究

应用经过修改的NCAR CCM3模式和CAM2模式进行的数值实验结果以及NCEP的GFS模式的输出结果讨论了海温等外强迫作用对热带季节内振荡的影响.结果表明,热带季节内振荡是热带大气固有的内部变率.它是由大气内部过程的相互作用决定的.但外强迫对热带季节内振荡的强度、传播方向等有明显的影响.当外强迫没有变化时,模式可以模拟出与观测近似的低频振荡.当作为外强迫的海温和太阳辐射有年内季节变化时,模式模拟的季节内振荡则明显减弱.当海温与辐射不仅有季节变化而且有年际变化时,模式模拟的季节内振荡会进一步减弱.具有长周期的外强迫还会削弱季节内振荡中东移波动的能量而增加静止波的强度.在与海洋模式耦合的状态下,模式不受来自海洋的外强迫影响,而是与海洋构成一个耦合系统,可以产生最强的季节内振荡.     

中国周边海域海面温度日变化对区域气候的影响

利用区域气候模式,分别以逐时海面温度(sea surface temperature, SST)数据及逐日SST数据作为模式的海表温度进行强迫,开展了1991～2010年共计20年的数值模拟,探讨SST日变化对中国区域气候变化的影响。对比结果表明,两组试验均能合理地再现中国区域气候的主要气候态特征。同时发现,两组试验模拟的气候特征在我国沿海区域以及近海洋面上存在明显差异:考虑SST日变化之后,2 m气温和感热通量差异呈现夏季(冬季)升高(降低)为主的趋势;潜热通量则与之相反;低层风场差异在夏季以海洋吹向大陆的东南风为主,冬季则以陆面吹向海洋的西北风差异为主;另外,水汽输送差异呈气旋式(反气旋式)时,降水出现正差异(负差异)。SST日变化对上述气候因子的影响在夏季更为显著。     

Impact of intra-daily SST variability on ENSO characteristics in a coupled model

This paper explores the impact of intra-daily Sea Surface Temperature (SST) variability on the tropical large-scale climate variability and differentiates it from the response of the system to the forcing of the solar diurnal cycle. Our methodology is based on a set of numerical experiments based on a fully global coupled ocean–atmosphere general circulation in which we alter (1) the frequency at which the atmosphere sees the SST variations and (2) the amplitude of the SST diurnal cycle. Our results highlight the complexity of the scale interactions existing between the intra-daily and inter-annual variability of the tropical climate system. Neglecting the SST intra-daily variability results, in our CGCM, to a systematic decrease of 15% of El Ni?o—Southern Oscillation (ENSO) amplitude. Furthermore, ENSO frequency and skewness are also significantly modified and are in better agreement with observations when SST intra-daily variability is directly taken into account in the coupling interface of our CGCM. These significant modifications of the SST interannual variability are not associated with any remarkable changes in the mean state or the seasonal variability. They can therefore not be explained by a rectification of the mean state as usually advocated in recent studies focusing on the diurnal cycle and its impact. Furthermore, we demonstrate that SST high frequency coupling is systematically associated with a strengthening of the air-sea feedbacks involved in ENSO physics: SST/sea level pressure (or Bjerknes) feedback, zonal wind/heat content (or Wyrtki) feedback, but also negative surface heat flux feedbacks. In our model, nearly all these results (excepted for SST skewness) are independent of the amplitude of the SST diurnal cycle suggesting that the systematic deterioration of the air-sea coupling by a daily exchange of SST information is cascading toward the major mode of tropical variability, i.e. ENSO.     

Sensitivity of the diurnal warm layer to meteorological fluctuations. Part 2: A new parameterisation for diurnal warming

A new diurnal warming parameterisation has been developed which allows the shape of the diurnal sea surface temperature (SST) signal to change in response to meteorological fluctuations during the day based on an extensive examination of over 300 diurnal cycles. The parameterisation estimates the diurnal variation in temperature at the surface and at 1 m over a local day based only on wind and insolation measurements averaged over several different periods of the day. The parameterisation is validated against independent data and is compared against other existing parameterisations. Results show that diurnal warming estimates are more accurate when daily fluctuations in wind and insolation are taken into consideration and the new parameterisation captures some of the variability of the shape of the diurnal SST cycle which other parameterisations are unable to achieve. The parameterisation is currently being trialled in the European Space Agency MEDSPIRATION project (a contribution to the Global Ocean Data Assimilation Experiment High Resolution SST - Pilot Project) as a possible method to account for the diurnal variability in satellite measurements.     

A study on air–sea interaction on the simulated seasonal climate in an ocean–atmosphere coupled model

This study investigates the effects of air–sea interaction upon simulated tropical climatology, focusing on the boreal summer mean precipitation and the embedded intra-seasonal oscillation (ISO) signal. Both the daily coupling of ocean–atmosphere and the diurnal variation of sea surface temperature (SST) at every time step by accounting for the ocean mixed layer and surface-energy budget at the ocean surface are considered. The ocean–atmosphere coupled model component of the global/regional integrated model system has been utilized. Results from the coupled model show better precipitation climatology than those from the atmosphere-only model, through the inclusion of SST–cloudiness–precipitation feedback in the coupled system. Cooling the ocean surface in the coupled model is mainly responsible for the improved precipitation climatology, whereas neither the coupling itself nor the diurnal variation in the SST influences the simulated climatology. However, the inclusion of the diurnal cycle in the SST shows a distinct improvement of the simulated ISO signal, by either decreasing or increasing the magnitude of spectral powers, as compared to the simulation results that exclude the diurnal variation of the SST in coupled models.     

Impact of resolving the diurnal cycle in an ocean–atmosphere GCM. Part 2: A diurnally coupled CGCM

Coupled ocean atmosphere general circulation models (GCM) are typically coupled once every 24 h, excluding the diurnal cycle from the upper ocean. Previous studies attempting to examine the role of the diurnal cycle of the upper ocean and particularly of diurnal SST variability have used models unable to resolve the processes of interest. In part 1 of this study a high vertical resolution ocean GCM configuration with modified physics was developed that could resolve the diurnal cycle in the upper ocean. In this study it is coupled every 3 h to atmospheric GCM to examine the sensitivity of the mean climate simulation and aspects of its variability to the inclusion of diurnal ocean-atmosphere coupling. The inclusion of the diurnal cycle leads to a tropics wide increase in mean sea surface temperature (SST), with the strongest signal being across the equatorial Pacific where the warming increases from 0.2°C in the central and western Pacific to over 0.3°C in the eastern equatorial Pacific. Much of this warming is shown to be a direct consequence of the rectification of daily mean SST by the diurnal variability of SST. The warming of the equatorial Pacific leads to a redistribution of precipitation from the Inter tropical convergence zone (ITCZ) toward the equator. In the western Pacific there is an increase in precipitation between Papa new guinea and 170°E of up to 1.2 mm/day, improving the simulation compared to climatology. Pacific sub tropical cells are increased in strength by about 10%, in line with results of part 1 of this study, due to the modification of the exchange of momentum between the equatorially divergent Ekman currents and the geostropic convergence at depth, effectively increasing the dynamical response of the tropical Pacific to zonal wind stresses. During the spring relaxation of the Pacific trade winds, a large diurnal cycle of SST increases the seasonal warming of the equatorial Pacific. When the trade winds then re-intensify, the increase in the dynamical response of the ocean leads to a stronger equatorial upwelling. These two processes both lead to stronger seasonal basin scale feedbacks in the coupled system, increasing the strength of the seasonal cycle of the tropical Pacific sector by around 10%. This means that the diurnal cycle in the upper ocean plays a part in the coupled feedbacks between ocean and atmosphere that maintain the basic state and the timing of the seasonal cycle of SST and trade winds in the tropical Pacific. The Madden–Julian Oscillation (MJO) is examined by use of a large scale MJO index, lag correlations and composites of events. The inclusion of the diurnal cycle leads to a reduction in overall MJO activity. Precipitation composites show that the MJO is stronger and more coherent when the diurnal cycle of coupling is resolved, with the propagation and different phases being far more distinct both locally and to larger lead times across the tropical Indo-Pacific. Part one of this study showed that that diurnal variability of SST is modulated by the MJO and therefore increases the intraseasonal SST response to the different phases of the MJO. Precipitation-based composites of SST variability confirm this increase in the coupled simulations. It is argued that including this has increased the thermodynamical coupling of the ocean and atmosphere on the timescale of the MJO (20–100 days), accounting for the improvement in the MJO strength and coherency seen in composites of precipitation and SST. These results show that the diurnal cycle of ocean–atmosphere interaction has profound impact on a range of up-scale variability in the tropical climate and as such, it is an important feature of the modelled climate system which is currently either neglected or poorly resolved in state of the art coupled models.