一个简单陆气耦合模式中的绿洲-荒漠化效应

发展了一个简单的地气相互作用模式 ,讨论了不同气候和植被条件对绿洲消长的影响。结果表明 ,能使绿洲扩大的主要条件是低纬度、小尺度 ,并具有低水汽、较高温度的环境以及较小气孔阻力的植被。这一简单的理论分析对发展复杂的数值模式和对观测的布局有参考意义 ,对治理荒漠也有一定的启示。     

Numerical simulation of the critical scale of oasis maintenance and development in the arid regions of Northwest China

Oasis is a special geographic landscape among the vast desert/Gobi in Northwest China (NWC). The surface sensitive heat flux and latent heat flux at Zhangye Oasis during 1 to 11 August 1991 are simulated using the NCAR nonhydrostatic mesoscale model MM5 Version 3. The horizontal grid resolution is set as 1km. By comparing the simulation results with HEIFE observations, it is proved that the model can be used to simulate the surface energy and water mass exchange of arid and semiarid regions in NWC.Based on the above results, the influence of different oasis scales on the local atmospheric field near the ground surface, and the critical scale of oasis maintenance, in NWC are studied dynamically. The following conclusion is obtained: the local thermal circulation between the oasis and the desert/Gobi is formed in the oasis downstream if the oasis scale is larger than 4 km. This local thermal circulation between the oasis and the desert adjacent to the oasis helps to conserve water vapor over the oasis. At the sametime, it transfers the abundant water vapor from the oasis into the desert/Gobi near to the oasis to supply relatively plentiful water vapor for desert crops to grow on the fringe of the oasis. So, it is advantageous for oasis extension. However, if the scale of the oasis is smaller than 4 km, it is not easy for the local thermal circulation between the oasis and the desert/Gobi to take shape. This study provides a new standpoint for oasis maintenance and development.     

Ensemble data assimilation in a simple coupled climate model: The role of ocean-atmosphere interaction

A conceptual coupled ocean-atmosphere model was used to study coupled ensemble data assimilation schemes with a focus on the role of ocean-atmosphere interaction in the assimilation. The optimal scheme was the fully coupled data assimilation scheme that employs the coupled covariance matrix and assimilates observations in both the atmosphere and ocean. The assimilation of synoptic atmospheric variability that captures the temporal fluctuation of the weather noise was found to be critical for the estimation of not only the atmospheric, but also oceanic states. The synoptic atmosphere observation was especially important in the mid-latitude system, where oceanic variability is driven by weather noise. The assimilation of synoptic atmospheric variability in the coupled model improved the atmospheric variability in the analysis and the subsequent forecasts, reducing error in the surface forcing and, in turn, in the ocean state. Atmospheric observation was able to further improve the oceanic state estimation directly through the coupled covariance between the atmosphere and ocean states. Relative to the mid-latitude system, the tropical system was influenced more by ocean-atmosphere interaction and, thus, the assimilation of oceanic observation becomes more important for the estimation of the ocean and atmosphere.     

Self-generated aperiodic behaviour in a simple climate model

Climatic variability arising from the coupling between ocean temperature and sea-ice extent is studied in a spatially distributed system. A spatial degree of freedom is crudely introduced by the coupling, through energy transfer, of two box models each of which describes a different space region. The evolution equations are cast into a normal form and some qualitative features of this general class of models are predicted. It is shown, both analytically and numerically, that internally generated complexity in the form of aperiodic behaviour can be a natural consequence of spatially distributed systems.     

A study of abrupt climate change in a simple nonlinear climate model

We use a seasonal energy balance climate model to study the behavior of the snowline cycle as a function of external parameters such as the solar constant. Our studies are confined in this study to cases with zonally symmetric land-sea distributions (bands or caps of land). The model is nonlinear in that the seasonally varying snow/sea ice line modifies the energy receipt through its different albedo from open land or water. The repeating steady-state seasonal cycle of the model is solved by a truncated Fourier series in time. This method is several thousand times faster than a time stepping approach. The results are interesting in that a number of bifurcations in the snowline behavior are found and studied for various geographies. Polar land caps and land bands positioned near the poles exhibit a variety of discontinuous summer snow cover behaviors (abrupt transitions as a parameter such as solar constant is slowly varied), which may be relevant to the inception and decay of continental ice sheets.     

A study of long-term climate change in a simple seasonal nonlinear climate model

Solar radiation cycles, earth-orbital changes, and continental drift drive long to very long term (10³–10⁶ years) climatic changes. Lin and North used the stationary solutions of a simple energy balance model (EBM) to study the equilibrium climatic stages. In this paper, we study time dependent solutions and, in particular, transition processes. We make use of two time scales: a seasonal cycle (fast variation) and a long term time change (slow variation). Variations over short time scales are solved using a Fourier transform in time and long term variations are studied using a 4th order Runge-Kutta method. The energy balance equation is a parabolic type equation and it is well posed. Climate changes depend mainly on external forcing and the state of the climate is determined by the slow time scale forcing. In other words, transitions from one climate stage (snow-covered) to another (snow-free) at bifurcation points are monotonic, despite 20% to 50% shortperiod random fluctuations in the solar energy. This smooth transition is especially noticeable when the land bands lie close to the north pole (70° N to 90° N) or at high latitudes (50° N to 75° N).Now at Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20723, USA     

A coupled simple climate model and its global analysis

Summary An atmosphere-land coupled simple climate model is constructed and its climatic properties are analyzed by introducing a global analysis method, cell mapping. The simple model is a nonlinear six order simplified climate model featured with chaotic dynamics, dissipation, and forcing source, which are the main features of the real climate system. The cell mapping method is applied with this coupled system. Numerical experiments are carried out for investigating the interactions between the fast-changing atmospheric variables and slow-changing underlying surface variables. The predictability of the system is also investigated via the global analysis, with which the evolution of the system is translated to the evolution of probability transition on a Markov Chain. An effective scheme is proposed for computing the probability transition matrix for the coupled system. Predictions can be made based on the combination of dynamics and statistics. The importance of constructing the coupled model is shown by globally analyzing the predictability of the coupled system. The coupling mechanism prolongs the memorization of initial information, and then the predictability as well.     

Continuous versus discontinuous albedo representations in a simple diffusive climate model

A one-dimensional annually and zonally averaged energy-balance model, with diffusive meridional heat transport and including icealbedo feedback, is considered. This type of model is found to be very sensitive to the form of albedo used. The solutions for a discontinuous step-function albedo are compared to those for a more realistic smoothly varying albedo. The smooth albedo gives a closer fit to present conditions, but the discontinuous form gives a better representation of climates in earlier epochs.     

干旱区典型绿洲热场分布规律研究——以渭干河-库车河三角洲绿洲为例

利用Landsat 7 ETM+遥感资料热红外波段定量反演晴空状态下夏季干旱区典型绿洲地表真实温度,运用影像叠加分析、直方图比对、缓冲区分析和空间自相关分析及剖面线分析等方法,分析其热场分布规律.结果表明:绿洲热场分布具有显著正空间自相关特性,Moran's值为0.5489,z值为48.44,同时呈现出显著的局部空间集...     

夏季厄尔尼诺-Modoki和东部型ENSO海表温度异常分布型特征及其与海洋性大陆区域气候异常的联系

2007年,Ashok等揭示了赤道太平洋区域存在一种三极型分布海表温度异常并称之为厄尔尼诺-Modoki,同时定义了相应的海表温度异常指数EMI（记为I_EM）。在此基础上,利用英国哈得来中心逐月海表温度资料、美国NCEP/NCAR月平均再分析数据集、美国国家海洋和大气管理局（NOAA）逐月降水资料（CMAP）,通过在太平洋海表温度异常中扣除厄尔尼诺-Modoki信号后,在Nino1+2区域上定义了东太平洋型海表温度异常指数EPNI（I_EPN）。据此,由I_EPN和I_EM可构成描述热带太平洋海表温度异常变化的一对指数。分析了两个指数相应的海气状态及对海洋性大陆区域气候异常的影响。结果表明,厄尔尼诺-Modoki和东太平洋型海表温度异常及其影响存在显著差异。在北半球夏季,当I_EM处于正位相时,热带太平洋海表温度异常呈现“负-正-负”的结构,海洋性大陆大部分区域海表温度异常为负,此时对流层低层太平洋地区辐合,海洋性大陆地区辐散,对流层高层太平洋地区辐散,海洋性大陆地区辐合。对应于辐合辐散中心,存在着自赤道中太平洋分别向赤道东太平洋和海洋性大陆中东部地区的异常垂直环流圈,同时也存在自海洋性大陆西部向印度洋西部的垂直环流。大气在海洋性大陆区域北部加热,南部冷却;在太平洋地区西部加热而东部冷却;在海洋性大陆区域10°N以南降水偏少,而10°N以北降水偏多。当I_EPN处于正位相时,热带太平洋海表温度异常呈现“西负东正”分布型,海洋性大陆区域海表温度异常呈现“西正东负”分布,对流层低层海洋性大陆地区辐散中心范围偏大、位置偏东、强度偏强,太平洋地区辐合中心范围偏小、位置偏东,热带环流异常在垂直方向上呈斜压结构,海洋性大陆区域北部大气加热而南部冷却,太平洋地区大气均呈加热正异常,海洋性大陆大部分区域降水均偏少,赤道太平洋降水偏多。以上这些结果有利于深刻理解热带太平洋海表温度异常的特征及其对海洋性大陆区域气候的影响。     

夏季厄尔尼诺-Modoki和东部型ENSO海表温度异常分布型特征及其与海洋性大陆区域气候异常的联系

2007年,Ashok等揭示了赤道太平洋区域存在一种三极型分布海表温度异常并称之为厄尔尼诺-Modoki,同时定义了相应的海表温度异常指数EMI（记为I_EM）。在此基础上,利用英国哈得来中心逐月海表温度资料、美国NCEP/NCAR月平均再分析数据集、美国国家海洋和大气管理局（NOAA）逐月降水资料（CMAP）,通过在太平洋海表温度异常中扣除厄尔尼诺-Modoki信号后,在Nino1+2区域上定义了东太平洋型海表温度异常指数EPNI（I_EPN）。据此,由I_EPN和I_EM可构成描述热带太平洋海表温度异常变化的一对指数。分析了两个指数相应的海气状态及对海洋性大陆区域气候异常的影响。结果表明,厄尔尼诺-Modoki和东太平洋型海表温度异常及其影响存在显著差异。在北半球夏季,当I_EM处于正位相时,热带太平洋海表温度异常呈现“负-正-负”的结构,海洋性大陆大部分区域海表温度异常为负,此时对流层低层太平洋地区辐合,海洋性大陆地区辐散,对流层高层太平洋地区辐散,海洋性大陆地区辐合。对应于辐合辐散中心,存在着自赤道中太平洋分别向赤道东太平洋和海洋性大陆中东部地区的异常垂直环流圈,同时也存在自海洋性大陆西部向印度洋西部的垂直环流。大气在海洋性大陆区域北部加热,南部冷却;在太平洋地区西部加热而东部冷却;在海洋性大陆区域10°N以南降水偏少,而10°N以北降水偏多。当I_EPN处于正位相时,热带太平洋海表温度异常呈现“西负东正”分布型,海洋性大陆区域海表温度异常呈现“西正东负”分布,对流层低层海洋性大陆地区辐散中心范围偏大、位置偏东、强度偏强,太平洋地区辐合中心范围偏小、位置偏东,热带环流异常在垂直方向上呈斜压结构,海洋性大陆区域北部大气加热而南部冷却,太平洋地区大气均呈加热正异常,海洋性大陆大部分区域降水均偏少,赤道太平洋降水偏多。以上这些结果有利于深刻理解热带太平洋海表温度异常的特征及其对海洋性大陆区域气候的影响。      

Behaviour of Coupled Modes in a Simple Nonlinear Air-Sea Interaction Model

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生态输水前后塔里木河下游绿洲特征分析

依据樊自立等人对人工绿洲、天然绿洲的定义及分类,对塔里木河下游人工绿洲、天然绿洲包含的要素进行提取,并根据前人对干旱区人工、天然绿洲适宜配比的研究,结合相应的遥感影像数据,对塔里木河下游1990—2000年、2000—2010年人工绿洲和天然绿洲的变化规律及其比例进行分析,探讨该区人工绿洲和天然绿洲的适宜配比。主要结果为:1990—2010年期间,塔里木河下游人工绿洲平均以19.09 km~2/a的速率增加,而天然绿洲平均以13.20 km~2/a的速率减少。输水前在生态系统的退化过程中,高覆盖草地面积减少了43.91%,湖泊面积100%消失,同时水库面积减少了45.28%;输水后,高覆盖草地面积减少量大有好转,10 a间只减少了6.79%,水库面积增加了392.44%。塔里木河下游流域在生态输水前,耕地增加了12.31%,生态输水后,耕地增加了30.37%。1990—2010年间,而绿洲总面积(人工+天然)不变,变化主要是发生在人工绿洲与天然绿洲之间的相互转化,天然绿洲逐渐被人工绿洲替代,平均每增加1份面积的人工绿洲就要失去1.1份天然绿洲。     

石河子绿洲棉区覆膜内5cm地温变化与气温的关系及膜内5cm地温预报分析

膜内5cm地温稳定通过10-12℃即可播种为棉花适宜播种温度指标,找出地膜内5cm地温与气温的定量关系并进行地温预报,同时确定对应的日平均气温的稳定界限指标值,就成为开展棉花适宜播种期预报的关键所在。以石河子绿洲覆膜栽培棉区为研究对象,分析了2008-2014年棉区春播期膜内5cm地温、气温的变化趋势以及气温与覆膜内、外地温的关系,并建立了膜内5cm地温预报模型。结果表明：近年来石河子棉区春播期内气温和膜内外5cm地温变化趋势一致,均有所上升,且膜内5cm地温显著高于膜外地温和日平均气温。棉田覆膜内外5cm地温与气温之间显著相关（P≤0.01）,石河子棉田覆膜内5 cm地温稳定通过10-12℃时,对应的日平均气温界限范围为6.3-8.2℃;利用逐日气温建立膜内5cm地温预报模型,回代检验绝对误差平均为1.01℃,2014和2015年预报检验绝对误差分别为0.5、0.7℃。预报模型可为更好地开展棉花播种期气象服务提供参考依据     

Incorporating organic soil into a global climate model

Organic matter significantly alters a soil’s thermal and hydraulic properties but is not typically included in land-surface schemes used in global climate models. This omission has consequences for ground thermal and moisture regimes, particularly in the high-latitudes where soil carbon content is generally high. Global soil carbon data is used to build a geographically distributed, profiled soil carbon density dataset for the Community Land Model (CLM). CLM parameterizations for soil thermal and hydraulic properties are modified to accommodate both mineral and organic soil matter. Offline simulations including organic soil are characterized by cooler annual mean soil temperatures (up to ∼2.5°C cooler for regions of high soil carbon content). Cooling is strong in summer due to modulation of early and mid-summer soil heat flux. Winter temperatures are slightly warmer as organic soils do not cool as efficiently during fall and winter. High porosity and hydraulic conductivity of organic soil leads to a wetter soil column but with comparatively low surface layer saturation levels and correspondingly low soil evaporation. When CLM is coupled to the Community Atmosphere Model, the reduced latent heat flux drives deeper boundary layers, associated reductions in low cloud fraction, and warmer summer air temperatures in the Arctic. Lastly, the insulative properties of organic soil reduce interannual soil temperature variability, but only marginally. This result suggests that, although the mean soil temperature cooling will delay the simulated date at which frozen soil begins to thaw, organic matter may provide only limited insulation from surface warming.     

一个用于气候模式的简单冻土过程参数化方案的建立和检验

在NCAR／LSM的基础上，发展了一个简单的冻土过程参数化方案，并使用苏联6个站的水气象观测资料考察了耦合了新方案模式的气候效应。在新方案中，加入了对含冰量的求解和在相变过程中的能量变化;并使用Johanson的方案替代了模式中原有的土壤导热率的参数化方案，考虑了含冰量对土壤水热性质的影响。原模式和改进后模式的模拟结果的比较得到，冻土过程方案能够合理的模拟土壤列中的能量收支及水热性质随含冰量的变化。随着入渗的减少和径流的增加，春季的土壤湿度减小。因此，热通量的分配和土壤温度也产生了相应的变化。     

关键海区海温异常的变化与中国区域降水和气温的关系

利用 １９５１年到 １９９８年的月平均海温资料及同时期中国 １６０个测站的降水和气温的月平均资料,选用海温异常的变化趋势一变温,讨论了关键海区海温异常的变化与我国降水和气温的关系,旨在探讨变温因子与我国降水和气温的关系与海温距平与降水和气温的关系有什么不同,用变温因子能否降低降水预报的不确定性。结果表明：降水异常对海温异常两种变化趋势的响应不完全相同,说明分别讨论同一种海温异常态的两种变化趋势对降水的影响比单独讨论海温距平对降水的影响更有效一些,有助于降低预报的不确定性;除西太平洋海区外,气温异常对各海区海温异常两种变化趋势的响应较一致。降水异常对变温的响应与对海温异常的响应,有一致之处,也有不同之处。     

干旱区绿洲气候变化及影响——以新疆石河子为例

文章以新疆石河子气象局1961—2008年年均气温、年降水量和年均日照观测资料为研究对象,运用趋势拟合方法、Morlet小波和Yamamoto方法分析其趋势变化、周期及突变特性。结果表明:48年中,石河子年平均气温和年降水量呈递增趋势,年均日照呈微弱递减趋势,均有一定的周期性,在不同的年份发生了突变,最后分析了气候变化对农业生产的影响。     

The role of phase locking in a simple model for glacial dynamics

Glacial–interglacial oscillations are often described by simple conceptual models. Relatively few models, however, are accompanied by analytical solutions, though detailed analytical investigation of climate models often leads to deeper understanding of the climate system. Here we study a simple conceptual model for glacial dynamics, a simplified version of the sea-ice-switch mechanism of Gildor and Tziperman (Paleoceanography 15:605–615, 2000), and provide a detailed analytical treatment for this model. We show that when the model is forced by a simplified insolation forcing it exhibits rich dynamics and passes through a series of bifurcations before being completely phase-locked to the insolation forcing. Our model suggests that even when the glacial cycles are self-sustained, insolation forcing has a major role on the complexity of glacial cycles: (1) it is possible to obtain glacial–interglacial oscillations for a wider parameters range when the amplitude of the insolation forcing is larger; (2) in addition, the ice-volume becomes more periodic; (3) when the period of the ice-volume is minimal the ice-volume is symmetric and for larger period is more asymmetric; (4) the ice-volume can be either periodic, higher order periodic, or quasi-periodic.     

Sensitivity of the thermohaline circulation and climate to ocean exchanges in a simple coupled model

 A new simple, coupled climate model is presented and used to investigate the sensitivity of the thermohaline circulation and climate to ocean vertical and horizontal exchange. As formulated, the model highlights the role of thin, ocean surface layers in the communication between the atmosphere and the subsurface ocean. Model vertical exchange is considered to be an analogue to small-scale, diapycnal mixing and convection (when present) in the ocean. Model horizontal exchange is considered to be an analogue to the effects of the wind-driven circulation. For small vertical exchange in the ocean, the model exhibits only one steady-state solution: a relatively cold, mid-high-latitude climate associated with a weak, salinity-driven circulation (“off ” mode). For large vertical and horizontal exchange in the ocean, the model also exhibits only one steady-state solution: a relatively warm, mid-high-latitude climate associated with a strong, thermally-driven circulation (“on” mode). For sufficiently weak horizontal exchange but large enough vertical exchange, both modes are possible stable, steady-state solutions. When model parameters are calibrated to fit tracer distributions of the modern ocean-atmosphere system, only the “on” mode is possible in this standard case. This suggests that the wind-driven circulation in consort with diapycnal mixing suppresses the “off ” mode in the modern ocean-atmosphere system. Since both diapycnal mixing and the wind-driven circulation would be expected to increase in a cold climate with greater meridional temperature gradients and enhanced winds, vertical and horizontal exchange in the ocean are probably associated with strong negative feedbacks which tend to stabilize climate. These results point to the need to resolve ocean wind-driven circulation and to greatly improve the treatment of ocean diapycnal mixing in more complete models of the climate system. Received: 16 November 1999 / Accepted: 19 June 2000