变分同化方法反演海气耦合模型参数的研究

采用变分资料同化技术,结合最优控制思想,对一个海气耦合模型的模式参数和强迫项进行了反演。结果表明,采用该方法对模式进行优化,既可以补偿模式参数不准确性给预报带来的误差,又可以对模式参数本身进行修正和估计,为将来在实际应用中改善更复杂的预报模式、提高预报准确率提供了一个可借鉴的思路。

基于遗传算法的海气耦合模型参数反演

为了提高模型参数反演效率和精度,基于遗传算法和系统优化思想,从一个简单的海气耦合模式出发,反演模式参数和强迫项。试验结果表明:遗传算法和系统优化结合的方法,可以有效优化模式参数和强迫项,进而修正模式的预报误差。同时,该方法具有参数反演过程不与模型结构发生耦合,计算量小和操作性强、反演效率高等优点,为在实际应用中改善模式参数和初值、提高预报准确率提供了一个可借鉴的方法和途径。

简单热带海气耦合模型中不同扰动形式间的耦合作用

在局地热平衡情况下研究了简单热带海气耦合模式中不同扰动形式间的耦合，依次讨论了由大气准定常Ｋｅｌｖｉｎ波与海洋Ｒｏｓｓｂｙ波、大气准定常Ｒｏｓｓｂｙ波与海洋Ｋｅｌｖｉｎ波、大气准定常 Ｋｅｌｖｉｎ波与海洋 Ｋｅｌｖｉｎ波、大气准定常 Ｒｏｓｓｂｙ波与海洋 Ｒｏｓｓｂｙ波组成的耦合系统的性质，并研究了存在于其中的耦合扰动的特征。

简单热带海气耦合模型中不同扰动形式的作用

在局地热平衡情况下，将物理量先用韦伯函数展开，然后去掉相应分量的滤波方 法，讨论了简单热带海气耦合模型中不同形式扰动的作用和贡献，结果表明，在热带海气耦合 系统中，大气准定常 Ｒｏｓｓｂｙ波和海洋 Ｒｏｓｓｂｙ波对于耦合系统贡献较大，它们决定着耦合系统 与耦合扰动的性质，而大气准定常Ｋｅｌｖｉｎ波和海洋Ｋｅｌｖｉｎ波对于耦合系统贡献相对较小．

关于二阶伴随模型的理论研究

Ｈｅｓｓｅ矩阵－目标函数关于控制变量的二阶偏导数形成的矩阵，在变分数据同化过程中以及敏感性分析等方面起着重要的作用；它可以通过建立数学模型的一阶和二阶伴随模型求得．以浅水方程模型为例，利用泛函的Ｇａｔｅａｕｘ微分和Ｈｉｌｂｅｒｔ空间上伴随算子的概念，导出了一阶和二阶伴随模型并由此得到Ｈｅｓｓｅ矩阵．改进了 Ｚｈｉ Ｗａｎｇ等（ １９９２）建立的二阶伴随模型理论．

简单热带海气耦合模式中的海洋低频扰动

讨论简单热带海气耦合模式中的低频海洋扰动。研究结果表明，挟卷对海洋Ｒｏｓｂｙ波的发展起抑制作用，而平流有利于海洋Ｒｏｓｓｂｙ波的发展；

基于地面气象测量的蒸发波导预测系统设计

为了获取蒸发波导特征参数,考虑到舰船无线电系统的实际环境和架设条件,建立了一种基于地面气象测量的蒸发波导预测系统。首先,在船尾后边的船舷上架设非接触式红外温度传感器测量海表温度。然后,在船尾平台上架设高6 m的高精度气象传感器,获取温度、气压、湿度和风速风向等气象参数。最后,利用蒸发波导预测的P-J模型和海气通量模型预测出蒸发波导高度。实验结果表明:该系统能够达到较高精度预测蒸发波导特征参数的目的,且具有性价比高、布设方便的特点。

厄尔尼诺和南方涛动海气耦合模型中参数估计的变分方法

提出一种基于变分原理估计厄尔尼诺和南方涛动海气耦合模型中未知参数的方法.首先将所研究的非线性海气耦合动力方程引入到目标泛函中;接着利用变分方法导出伴随方程和待辨识参数泛函梯度的公式;然后设计了估计未知参数的算法.数值试验结果表明变分方法是一种能有效估计海气耦合非线性系统未知参数的方法.

Studies of Variational Assimilation for the Inversion of the Coupled Air-sea Model

For the prediction of ENSO, the accuracy of the model including the parameters, initial value and others of the model is important, which can be retrieved by the variational data assimilation methods developed in recent years. However, when the nonlinearity of the model is quite strong, the effect of the improvement made by the 4-D variational data assimilation may be poor due to the bad approximation of the tangent linear model to the original model. So in the paper the ideas in the optimal control is introduced to improve the effect of 4-DVAR in the inversion of the parameters of a nonlinear dynamic ENSO model. The results indicate that when the terminal controlling term is added to the cost functional of 4DVAR, which originated from the optimal control, the effect of the inversion may be largely improved comparing to the traditional 4DVAR, as can be especially obvious from the phase orbit of the model variables. The results in the paper also suggest that the method of 4DVAR in combination with optimal control cannot only reduce the error resulting from the inaccuracy of the model parameters but also can correct the parameters itself. This gives a good method in modifying the model and improving the quality of prediction of ENSO.

当前美国计算机在水文中应用的若干进展

1989年4月赴美考察期间,看到了计算机在水文中应用的某些进展。现介绍如下。一、超级计算机正在成为解决某些重大和基本科学问题的有力工具美国国家大气研究中心(NCAR)1977年安装了世界上第二台CRAY-1A超级机,速度达每秒1.

INTERCOMPARISON OF THE INTERDECADAL VARIATIONS OF SUMMER PRECIPITATION IN CHINA SIMULATED BY AOGCMS FROM THE IPCC-DDC

Simulations of the interdecadal variations of summer rainfall over China are assessed from 5 coupled AOGCMs from the Data Distribution Center (DDC) of the Intergovernmental Panel in Climate Change (IPCC) under the IPCC-Special Report in Emission Scenarios (SRES) A2 and B2 scenario. We examined their ability in simulating the interdecadal variations of summer precipitation over China from 1951 to 1990. The difference before and after the mid-1960’s and the late 1970’s is given respectively to check the capability of the models, especially in reproducing the rainfall jump in North China. We also investigated the interdecadal variations simulated by the models in the 1990’s and the average of 2001-2020 in the future under the scenario A2 and B2. The analysis shows that the current AOGCMs is not good enough in simulating the interdecadal variations of summer precipitation in China. The interdecadal variations of summer rainfall simulated by most of the models cannot reproduce the observation in North China. Higher resolution models are suggested to well simulate the interdecadal variability in regional scale.

THE IMPACT OF INITIAL FORCED WIND ON THE PREDICTABILITY OF THE ZEBIAK-CANE COUPLED OCEAN-ATMOSPHERE MODEL

With simultaneous observed sea surface temperature anomaly （SSTA）, the difference between NCEP/NCAR 925hPa reanalysis wind stress anomaly （NCEPWSA） and FSU wind stress anomaly （FSUWSA） is analyzed, and the prediction abilities of Zebiak-Cane coupled ocean-atmosphere model （ZC coupled model） with NCEPWSA and FSUWSA serving respectively as initialization wind are compared. The results are as follows. The distribution feature of NCEPWSA matches better with that of the observed SSTA than counterpart of FSUWSA both in 1980s and in 1990s; The ZC ocean model has a better skill under the forcing of NCEPWSA than that of FSUWSA, especially in 1990s. Meanwhile, the forecast abilities of the ZC coupled model in 1990s as well as in 1980s have been improved employing NCEPWSA as initialization wind instead of FSUWSA. Particularly, it succeeded in predicting 1997/1998 E1 Nino 6 to 8 months ahead, further analysis shows that on the antecedent and onset stages of the 1997/1998 E1 Nino event, the horizontal cold and warm distribution characteristics of the simulated SSTA from ZC ocean model, with NCEPWSA forcing compared to FSUWSA forcing, match better with counterparts of the corresponding observed SSTA, whereby providing better predication initialization conditions for ZC coupled model, which, in turn, is favorable to improve the forecast ability of the coupled model.

Recent Observations and Modeling Study About Sea Fog over the Yellow Sea and East China Sea

This review presents some of the latest achievements in sea fog research,including fog climatology,fog structure in the marine atmospheric boundary layer,and numerical simulations and forecasting of fog.With the development of atmospheric observational techniques and equipments,new facts about sea fog are revealed.The mechanisms involved in the formation,development and dissipation of sea fog are further explored with the help of advanced atmospheric models.

A New Ocean Mixed-Layer Model Coupled into WRF

A new mesoscale air-sea coupled model (WRF- OMLM-Noh) was constructed based on the Weather Research and Forecasting (WRF) model and an improved Mellor-Yamada ocean mixed-layer model from Noh and Kim (OMLM-Noh). Through off-line tests and a simulation of a real typhoon, the authors compared the performance of the WRF-OMLM-Noh with another existing ocean mixed-layer coupled model (WRF-OMLM-Pollard). In the off-line tests with Tropical Ocean Global Atmosphere Program's Coupled Ocean Atmosphere Response Experiment (TOGA-COARE) observational data, the results show that OMLM-Noh is better able to simulate sea surface temperature (SST) variational trends than OMLM -Pollard. Moreover, OMLM-Noh can sufficiently reproduce the diurnal cycle of SST. Regarding the typhoon case study, SST cooling due to wind-driven ocean mixing is underestimated in WRF-OMLM-Pollard, which artificially increases the intensity of the typhoon due to more simulated air-sea heat fluxes. Compared to the WRF- OMLM-Pollard, the performance of WRF-OMLM-Noh is superior in terms of both the spatial distribution and temporal variation of SST and air-sea heat fluxes.

A STUDY ON THE IMPACTS OF LATENT HEAT PARAMETERIZATION SCHEME ON PREDICTION SKILL OF ENSO WITH A SIMPLE OCEAN-ATMOSPHERE COUPLED MODEL

This study revises Weare＇s latent heat parameterization scheme and conducts an associated theoretic analysis. The revised Weare＇s scheme is found to present potentially better results than Zebiak＇s scheme. The Zebiak-Cane coupled ocean-atmosphere model, initialized by the National Centers for Environmental Prediction and the National Center for Atmospheric Research （NCEP/NCAR） reanalysis of wind stress anomaly at 925 hPa, is referred to as the ZCW coupled model. The atmosphere models of the ZCW coupled model that use Zebiak＇s scheme and the revised Weare＇s scheme are referred to as the ZCW0 and ZCWN atmosphere models, respectively. The coupled ocean-atmosphere models that use Zebiak＇s scheme and the revised Weare＇s scheme are referred to as the ZCWoand ZCWN coupled models, respectively. The simulations between the ZCW0 and ZCWN atmosphere models and between the ZCW0 and ZCWN coupled models are analyzed. The results include： （1） The evolution of heat, meridional wind and divergence anomalies simulated by similar ZCW0 and ZCWN atmosphere models, although the magnitudes of the former are larger than those of the latter; （2） The prediction skill of the Nino3 index from 1982 to 1999 by the ZCWN coupled model shows improvement compared with those by the ZCW0 coupled model; （3） The analysis of E1 Nino events in 1982/1983, 1986/1987, and 1997/1998 and La Nifia events in 1984/1985, 1988/1989, and 1998/2000 suggests that the ZCWN coupled model is better than the ZCW0 coupled model in predicting warm event evolution and cold event generation. The results also show the disadvantage of the ZCWN coupled model for predicting E1 Nino.

Modeling Surgery: A New Way Toward Understanding Earth Climate Variability

A new modeling concept, referred to as Modeling Surgery, has been recently developed at University of Wisconsin-Madison. It is specifically designed to diagnose coupled feedbacks between different climate components as well as climatic teleconnections within a specific component through systematically modifying the coupling configurations and teleconnective pathways. It thus provides a powerful means for identifying the causes and mechanisms of low-frequency variability in the Earth's climate system. In this paper, we will give a short review of our recent progress in this new area.

Assessing the Seasonal Predictability of Summer Precipitation over the Huaihe River Basin with Multiple APCC Models

Seasonal rainfall predictability over the Huaihe River basin is evaluated in this paper on the basis of 23-year(1981-2003) retrospective forecasts by 10 climate models from the Asia-Pacific Economic Cooperation(APEC) Climate Center(APCC) multi-model ensemble(MME) prediction system.It is found that the summer rainfall variance in this basin is largely internal,which leads to lower rainfall predictability for most individual climate models.By dividing the 10 models into three categories according to their sea surface temperature(SST) boundary conditions including observed,predicted,and persistent SSTs,the MME deterministic predictive skill of summer rainfall over Huaihe River basin is investigated.It is shown that the MME is effective for increasing the current seasonal forecast skill.Further analysis shows that the MME averaged over predicted SST models has the highest rainfall prediction skill,which is closely related to model's capability in reproducing the observed dominant modes of the summer rainfall anomalies in Huaihe River basin.This result can be further ascribed to the fact that the predicted SST MME is the most effective model ensemble for capturing the relationship between the summer rainfall anomalies over Huaihe River basin and the SST anomalies(SSTAs) in equatorial oceans.

Luminescence chronology and age model application for the upper part of the Chumbur-Kosa loess sequence in the Sea of Azov, Russia

A reliable chronology is essentially critical for correlating loess records with other paleoenvironmental time series, as well as for continuing improvements in the reconstruction of paleoenvironment and paleoclimate changes. It is exactly that the scarcity of chronologies across the Sea of Azov has limited the interpretation of climatic and environmental information in the East European Plain. In view of this, this paper conducted an exploratory study to investigate whether the optically stimulated luminescence(OSL) dating of medium-grained quartz could be used to obtain a set of chronologies and the age models could be used to establish an independent time scale since the Late Pleistocene for the Sea of Azov loess. The results showed that an internally consistent set of optical ages for the Azov loess deposited up to ~76 ka. In addition, the ages developed based on magnetic susceptibility and grain size ages models showed good comparability with independent OSL ages at an acceptable range, suggesting that it might be practicable to establish an independent time scale using age models at the Sea of Azov loess, at least for the uppermost part of the Chumbur-Kosa section. Comparison with the ages based on two age models,the grain size ages using fine-grain fractions may provide a more reliable chronological sequence at the Azov loess since the Late Pleistocene. With the help of absolute ages and climate proxies(magnetic susceptibility and grain size), paleoclimatic change in the Sea of Azov have been traced for the Late Pleistocene.

Ocean Mixing with Lead-Dependent Subgrid Scale Brine Rejection Parameterization in a Climate Model

Sea ice thickness is highly spatially variable and can cause uneven ocean heat and salt flux on subgrid scales in climate models.Previous studies have demonstrated improvements in ocean mixing simulation using parameterization schemes that distribute brine rejection directly in the upper ocean mixed layer.In this study,idealized ocean model experiments were conducted to examine modeled ocean mixing errors as a function of the lead fraction in a climate model grid.When the lead is resolved by the grid,the added salt at the sea surface will sink to the base of the mixed layer and then spread horizontally.When averaged at a climate-model grid size,this vertical distribution of added salt is lead-fraction dependent.When the lead is unresolved,the model errors were systematic leading to greater surface salinity and deeper mixed-layer depth(MLD).An empirical function was developed to revise the added-salt-related parameter n from being fixed to lead-fraction dependent.Application of this new scheme in a climate model showed significant improvement in modeled wintertime salinity and MLD as compared to series of CTD data sets in 1997/1998 and 2006/2007.The results showed the most evident improvement in modeled MLD in the Arctic Basin,similar to that using a fixed n=5,as recommended by the previous Arctic regional model study,in which the parameter n obtained is close to 5 due to the small lead fraction in the Arctic Basin in winter.

PRELIMINARY STUDY OF THE ASSESSMENT OF METHODS FOR DISASTER-INDUCING RISKS BY TCs USING SAMPLE EVENTS OF TCs THAT AFFECTED SHANGHAI

Hazard factors, hazard-bearling objects, disaster-developing environment, and disaster-preventing capability play key roles in the formation of Tropical Cyclone （TC） disasters. Of all of these, the most important is the intensity of hazard factors （risk sources）. In this study, this intensity is uniformly defined by the probability of hazard factors; then a relationship is established between disaster risk intensity and hazard factors. The exceedance probability of various hazard factors, including frequency and timing, scope of wind and rain, and maximum wind and rain of impacting TC cases, are calculated using data from TCs that impacted Shanghai fi＇om 1959-2006. The relationship between disaster situation and risk probability of hazard factors is analyzed, and the indices and model of TC disaster assessment are established based on the results. The process maximum wind speed and maximum daily precipitation are very important in TC-related disaster formation in Shanghai. The results of disaster indices coordinate with the results of the assessment model, and both can show the extent of probability of a TC disaster. Tests using TC data in 2007 and 2008 show that disasters caused by TC Krosa （0716） would be more serious than those by TC Wipha （0713）, and that TC Fung Wong （0808） would have a weak impact. Real-life situations validate these results.