共查询到20条相似文献，搜索用时 688 毫秒
1.
In this paper, the coupling schemes of atmosphere-ocean climate models are discussed with one-dimensional advection equations.
The convergence and stability for synchronous and asynchronous schemes are demonstrated and compared.
Conclusions inferred from the analysis are given below. The synchronous scheme as well as the asynchronous-implicit scheme
in this model are stable for arbitrary integrating time intervals. The asynchronous explicit scheme is unstable under certain
conditions, which depend upon advection velocities and heat exchange parameters in the atmosphere and oceans. With both synchronous
and asynchronous stable schemes the discrete solutions converge to their unique exact ones. Advections in the atmosphere and
ocean accelerate the rate of convergence of the asynchronous-implicit scheme. It is suggusted that the asynchronous-implicit
coupling scheme is a stable and efficient method for most climatic simulations. 相似文献
2.
Asynchronous and periodically-synchronous schemes for coupling atmosphere and ocean models are presented. The performance of the schemes is tested by simulating the climatic response to a step function forcing and to a gradually increasing forcing with a simple zero-dimensional non-linear energy balance model. Both the initial transient response and the asymptotic approach of the equilibrium state are studied. If no annual cycle is allowed the asynchronous coupling technique proves to be a suitable tool. However, if the annual cycle is retained, the periodically synchronous coupling technique reproduces the results of the synchronously coupled runs with smaller bias. In this case it is important that the total length of one synchronous period and one ocean only period is not a multiple of 6 months. 相似文献
3.
Z. Liu R. G. Gallimore J. E. Kutzbach W. Xu Y. Golubev P. Behling R. Selin 《Climate Dynamics》1999,15(5):325-340
The use of the equilibrium asynchronous coupling (EAC) scheme is proposed as a strategy to better understand long-term climate
changes in a fully coupled ocean-atmosphere general circulation model. The EAC scheme requires each component model to be
integrated to its equilibrium before being coupled to the other component. Use of this scheme has the distinct advantage of
being able to clarify the nature of the coupling between the ocean and atmosphere, because each asynchronous iteration takes
the form of a sensitivity experiment. Basic features of the EAC scheme are first studied in an energy balance model. It is
found that the convergence rate of the EAC scheme is proportional to the damping rate in the atmosphere or surface ocean,
but is inversely proportional to the coupling strength between the ocean and atmosphere. Furthermore, the seasonal cycle response
converges much faster than the annual mean response. Using realistic parameters, the seasonal cycle response should converge
in a few iterations. The EAC scheme is further applied to a coupled ocean-atmosphere general circulation model to study the
tropical monsoon climate of the early Holocene. The convergence behavior of the sea surface temperature is found to agree
with the theory derived from the energy balance model study. The EAC scheme is further used to investigate the role of ocean-atmosphere
feedback in modifying the response of monsoons to orbital forcings in the early Holocene. It is found that the ocean exerts
a positive feedback on the North African monsoon, but a negative feedback on the Indian monsoon.
Received: 16 March 1998 / Accepted: 24 December 1998 相似文献
4.
Simulations of long-term climatic variations require the use of coupled oceanic and atmospheric models. Given their different
scales in space and time and present computing limitations, asynchronous coupling schemes are often used. Comparing the evolutions of simple dynamic systems which we couple alternatively with synchronous
and asynchronous schemes, we show that the behaviour can be modified, not only in minute details, but drastically, if asynchronous
coupling is used with insufficient care. We study how it happens, then suggest methods to insure that the average behaviour
of more realistic models is not modified with asynchronous schemes. Other branches of physics with coupled non-linear systems
could make use of these remarks.
Received: 19 February 1997 / Accepted: 17 June 1998 相似文献
5.
A coupled atmosphere/mixed-layer ocean energy balance model of intermediate complexity is used to examine the feasibility of a technique to accelerate the model's convergence rate while using equilibrium asynchronous coupling (EAC). EAC consists of an iterative sequence of integrations of an atmospheric model driven to equilibrium with fixed SSTs, the output of which is used to drive an ocean model to equilibrium. In an attempt to accelerate a radiatively perturbed climate to its final equilibrium state, we superimpose on the EAC scheme a mixed-flux condition, in which a portion of the turbulent air-sea heat flux from the most recent atmospheric leg is used in the present oceanic integration. In sensitivity tests using enhanced insolation, this mixed-flux approach strongly hastens the model's convergence rate, whose acceleration is regionally dependent: the tropics show the strongest sensitivity to the mixed-flux condition, while polar regions are least affected. This geographic variation stems from the presence of polar sea-ice, which promotes a temperature inversion and thereby causes a seasonal change in the sign of the total turbulent air-sea heat flux. Potential applications and limitations of this accelerated EAC method are also discussed. 相似文献
6.
一类计算稳定性好的显式平流差分格式 总被引：1，自引：0，他引：1
通常的显式平流差分格式，如迎风格式，Lax-Wendroff格式等，均是有条件稳定的,其稳定条件与差分网格的时、空步长有关。本文对线性和拟线性平流方程分别构造了一种计算稳定性好的显式差分格式。对前一格式，本文严格证明了它的无条件稳定性及收敛性，并具有一阶精度；对后一格式，由于非线性方程的限制，本文用数值试验研究了它的计算稳定性。 相似文献
7.
比较Morcrette辐射方案和Fu_Liou辐射方案对NCC/IAP T63海气耦合模式云和辐射模拟的影响, 结果表明:两种方案模拟的大气顶入射辐射存在明显的差异; 晴空大气Fu_Liou方案的短波吸收能力在全球普遍较Morcrette方案低; 在60°S~60°N之间, Fu_Liou方案模拟的行星反照率更接近于ERBE卫星观测; 在对大气顶净辐射的模拟上, 除了冬季的太平洋和大西洋东岸云量明显减少的部分地区外, Fu_Liou方案对大气顶净辐射的模拟总体上较Morcrette方案有了较为明显的改善; Fu_Liou方案模拟的海洋低层云显著减少, 而热带地区高云的模拟明显增加; 由于采用了“二元云量”算法, 尽管云量有所减少, Fu_Liou方案模拟的云短波吸收作用仍有所增强, 一定程度上改进了Morcrette方案云的短波吸收作用偏弱的现象。 相似文献
8.
A periodically synchronous scheme suitable for coupling atmosphere and ocean models with high internal variability is presented. The performance of the scheme is tested by means of a simple zero-dimensional non-linear energy balance model with stochastic forcing. The equilibrium behaviour and the response to changes in the model parameters are analysed. The response experiments are similar to CO2 doubling and transient CO2 experiments. The best results are obtained using a method with weighted means of the air-sea fluxes which are calculated during the synchronously coupled periods. 相似文献
9.
Performance assessment of three convective parameterization schemes in WRF for downscaling summer rainfall over South Africa 总被引：2，自引：1，他引：1
Satyaban B. Ratna J. V. Ratnam S. K. Behera C. J. deW. Rautenbach T. Ndarana K. Takahashi T. Yamagata 《Climate Dynamics》2014,42(11-12):2931-2953
Austral summer rainfall over the period 1991/1992 to 2010/2011 was dynamically downscaled by the weather research and forecasting (WRF) model at 9 km resolution for South Africa. Lateral boundary conditions for WRF were provided from the European Centre for medium-range weather (ECMWF) reanalysis (ERA) interim data. The model biases for the rainfall were evaluated over the South Africa as a whole and its nine provinces separately by employing three different convective parameterization schemes, namely the (1) Kain–Fritsch (KF), (2) Betts–Miller–Janjic (BMJ) and (3) Grell–Devenyi ensemble (GDE) schemes. All three schemes have generated positive rainfall biases over South Africa, with the KF scheme producing the largest biases and mean absolute errors. Only the BMJ scheme could reproduce the intensity of rainfall anomalies, and also exhibited the highest correlation with observed interannual summer rainfall variability. In the KF scheme, a significantly high amount of moisture was transported from the tropics into South Africa. The vertical thermodynamic profiles show that the KF scheme has caused low level moisture convergence, due to the highly unstable atmosphere, and hence contributed to the widespread positive biases of rainfall. The negative bias in moisture, along with a stable atmosphere and negative biases of vertical velocity simulated by the GDE scheme resulted in negative rainfall biases, especially over the Limpopo Province. In terms of rain rate, the KF scheme generated the lowest number of low rain rates and the maximum number of moderate to high rain rates associated with more convective unstable environment. KF and GDE schemes overestimated the convective rain and underestimated the stratiform rain. However, the simulated convective and stratiform rain with BMJ scheme is in more agreement with the observations. This study also documents the performance of regional model in downscaling the large scale climate mode such as El Niño Southern Oscillation (ENSO) and subtropical dipole modes. The correlations between the simulated area averaged rainfalls over South Africa and Nino3.4 index were ?0.66, ?0.69 and ?0.49 with KF, BMJ and GDE scheme respectively as compared to the observed correlation of ?0.57. The model could reproduce the observed ENSO-South Africa rainfall relationship and could successfully simulate three wet (dry) years that are associated with La Niña (El Niño) and the BMJ scheme is closest to the observed variability. Also, the model showed good skill in simulating the excess rainfall over South Africa that is associated with positive subtropical Indian Ocean Dipole for the DJF season 2005/2006. 相似文献
10.
基于Prata晴空大气下行长波辐射参数化方案,针对其在高原地区及可降水量较小地区理论精度较差的缺点,考虑不同高度的大气柱发射的长波辐射量不同,提出了三种考虑气压的大气下行长波辐射参数化方案,通过全球ERA-5再分析数据进行最小二乘拟合确定经验常数并在全球不同区域对其适用性进行了分析。模拟结果表明,考虑气压的参数化方案有效地改善了可降水量减小时Prata方案大气发射率收敛过快的不足,三种新方案在青藏高原安多地区和南美洲圣路易斯地区的下行长波辐射模拟结果相对于观测值和ERA-5再分析数据的平均偏差和均方根误差均更小,模拟精度相对Prata方案均有提高,适用性更强。 相似文献
11.
12.
13.
Xiaolong Jia Chongyin Li Ningfang Zhou Jian Ling 《Dynamics of Atmospheres and Oceans》2010,49(2-3):141-163
The Madden–Julian oscillation (MJO) is simulated using an AGCM with three different cumulus parameterization schemes: a moist convective adjustment (MCA) scheme, the Zhang–McFarlane (ZM) mass-flux scheme, and the Tiedtke scheme. Results show that the simulated MJO is highly dependent on the cumulus parameterization used. Among the three cumulus parameterizations, only the MCA scheme produces MJO features similar to observations, including the reasonable spatial distribution, intraseasonal time scales and eastward propagation. Meanwhile, the amplitude is too large and the eastward propagation speed too fast than observations and the relationship between precipitation and low-level wind anomaly is unrealistic with enhanced convection occurring within easterly anomalies instead of westerly anomalies as in observations. The over-dependence of precipitation on boundary convergence produced by the MCA scheme is presumably responsible for this unrealistic phase relation in the simulation. The other two schemes produce very poor simulations of the MJO: spectral power of westward propagation is larger than that of eastward propagation in zonal wind and precipitation, indicating a westward propagation of the intraseasonal variability.The mean state and vertical profile of diabatic heating are perhaps responsible for the differences in these simulations. The MCA scheme produces relatively realistic climate background. When either ZM or Tiedtke scheme is used, the observed extension of westerly winds from the western Pacific to the dateline is missing and precipitation over the equatorial region and SPCZ is dramatically underestimated. In addition, diabatic heating produced by both ZM and Tiedtke schemes are very weak and nearly uniform with height. The heating profile produced by the MCA scheme has a middle-heavy structure with much larger magnitude than those produced by the other two schemes. In addition, a very unrealistic boundary layer heating maximum produced by the MCA scheme induces too strong surface convergence, which perhaps contributes to the too strong intraseasonal variability in the simulation. 相似文献
14.
A numerical experiment of an asynchronous coupled ocean-atmosphere model has been described in this paper.A two-layer global atmosphere general circulation model(OSU/IAP-AGCM)and a two-layer North Pacific Ocean general circulation model(NPOGCM) developed by Liu et al.(1992)are used in numerical experiment.The sea surface temperature anomaly(SSTA) corresponding to the meander of the Kuroshio is treated as the initial perturbation in the Pacific Ocean and the abnormal phenomena caused by the disturbance and the interaction between atmosphere and ocean,have been studied.The numerical experiment showed that the SST anomaly in the North Pacific could induce a new 30-60 day osciltation through the coupling between atmosphere and ocean and the interaction between the meander of the Kuroshio and atmosphere circulation is a positive feedback process. 相似文献
15.
16.
J. Egger 《Climate Dynamics》1997,13(4):285-292
Flux correction schemes are used in order to suppress the drift of coupled ocean atmosphere models. This technique is tested
for a simple box model of the climate system. Two “perfect” models of the ocean and the atmosphere are available. These are
coupled to form an ocean-atmosphere model representing the true climate system. This climate system is simulated by a climate
model which is also constructed by coupling those two perfect models. This time, however, both models are run first separately
as models of the atmosphere and the ocean. In that case, “observations” from the climate system are prescribed at the ocean
surface in the uncoupled models. It is assumed that these observations are imperfect. A drift results, when these models are
coupled to form an ocean-atmosphere stimulation model. A flux adjustment scheme is implemented to remove this drift. It is
argued that the merits and shortcomings of the flux correction technique can be assessed more clearly this way than by coupling
imperfect models as is done normally. Sensitivity tests are performed where either radiation parameters are changed or a salt
anomaly is implanted. Model parameters are chosen such that the ocean has a thermally direct circulation in the unperturbed
climate state. It is found that the flux correction technique is performing satisfactorily as long as the imposed perturbations
are small enough so that the ocean circulation does not change its sense. If, however, the model climate is close to the transition
to an indirect circulation, then the flux correction technique is unreliable. The predictions of the coupled model with flux
correction may deviate substantially from the response of the climate system in that case.
Received: 4 December 1995/Accepted: 15 October 1996 相似文献
17.
通过分析发现地形坐标系中气压梯度力差分格式的计算误差应分为二类，其中，第二类误差在水平坐标面倾斜时出现。这种误差可理解为将水平坐标面上的气压(或位势高度)插回到等高面(或等压面)上的插值误差。 构造气压梯度力差分格式的目的正是为了减小这种第二类误差，而不是其他误差。 误差分析表明静力扣除法和Corby 格式的第二类误差都很小，比一般方法的误差小约一个量级。分析还表明第二类误差产生的主要原因是由于气压随高度非线性变化。依据这一分析思路，本文改进了#As(z)#a坐标系中的静力扣除法。 改进后的方法比改进前的误差小约一个量级。 相似文献
18.
新一代天气雷达网资料的三维格点化及拼图方法研究 总被引：31，自引：6，他引：31
文中研究了几种把球坐标系下的雷达网反射率体扫资料插值到统一的笛卡尔坐标系下的经纬度网格上以及用多个雷达的反射率网格资料进行三维拼图的方法,并对多个雷达同步观测的反射率因子的空间一致性、系统误差以及雷达等距离线上回波的水平和垂直结构进行了分析。结果发现:在雷达资料格点化过程中,径向和方位上的最近邻居法和垂直方向的线性内插法的结合(NVI方法)是一种有效的雷达资料分析方法,它既能得到空间比较连续的反射率分析场,同时也较好地保留了体扫资料中原有的反射率结构特征;广州雷达和梅州雷达同步观测的空间一致性比较好;在多个雷达资料合成拼图的过程中,距离指数权重平均法能提供空间连续的三维反射率拼图数据,拼图也减轻了由雷达波束几何学引起的各种问题。 相似文献
19.
模式的不同参数化方案会对模拟的天气和气候产生影响,但如何影响陆气耦合还不是很清楚。利用WRF 4.0模式设计了一组16种不同参数化方案组合的集合试验,对华北地区2013年夏季气候进行模拟。结果表明,不同积云对流参数化方案对模拟的降水平均态影响较大,其次是短波辐射方案,而微物理方案影响较小。进一步利用潜热通量(LH,Latent Heat flux)和土壤湿度(SM,Soil Moisture)、抬升凝结高度(LCL,Lifting Condensation Level)的相关系数R(SM,LH)和R(LH,LCL)表征陆气耦合过程,评估了陆气耦合对不同参数化方案的敏感性。模式模拟的R(SM,LH)在不同区域随着平均降水、相对湿度的增加以及平均短波辐射的减少而减小,而R(LH,LCL)的变化正好相反。它们内在的物理机制类似,与气候态的干湿变化密切相关,即随着土壤湿度趋于饱和,蒸散发过程逐渐受太阳辐射的限制,陆面对大气的影响减弱。另外,陆气耦合强度受积云对流方案、微物理方案和短波辐射方案的影响而产生差别,这与不同参数化方案模拟的气候态的不同密切相关,因此本研究对于WRF 4.0模式中参数化方案特别是积云对流方案的选择同样有着重要的指导意义。 相似文献
20.
利用WRF-Chem模式,采用3种边界层参数化方案 (YSU, MYJ和ACM2),针对1个晴空、静稳日 (2013年8月26日20:00—27日20:00(北京时)) 进行模拟,着重分析不同边界层参数化方案对夜间残留层形成及日出前后O3浓度垂直分布形式的模拟效果,并与固城站地面及垂直同步观测资料进行对比。结果表明:3种边界层参数化方案均能够模拟出温度及风速的区域分布形式以及风温垂直结构的变化特征;相比之下,MYJ方案模拟的夜间边界层高度较YSU方案和ACM2方案明显偏高,该对比结果可能是导致近地面污染物浓度模拟差异的重要原因;在夜间稳定层结至日出后稳定状态打破的边界层结构演变过程中,采用YSU方案和ACM2方案模拟的温度和风速垂直扩线形式与观测结果更为接近;同样采用非局地闭合的YSU方案和同时考虑局地和非局地闭合的ACM2方案,对于边界层高度内O3浓度垂直分布形式的模拟效果具有明显优势。 相似文献