A new DRP-4DVar-based coupled data assimilation system for decadal predictions using a fast online localization technique

Climate Dynamics - A new coupled data assimilation (CDA) system based on dimension-reduced projection four-dimensional variational data assimilation (DRP-4DVar) for decadal predictions is developed...     

Simulated impacts of afforestation in East China monsoon region as modulated by ocean variability

Using the National Center for Atmospheric Research Community Climate System Model Version 3.5, this paper examines the climatic effects of afforestation in the East China monsoon region with a focus on land–atmosphere interactions and the modulating influence of ocean variability. In response to afforestation, the local surface air temperature significantly decreases in summer and increases in winter. The summer cooling is attributed to enhanced evapotranspiration from increased tree cover. During winter, afforestation induces greater roughness and weaker winds over the adjacent coastal ocean, leading to diminished latent heat flux and increased sea-surface temperature (SST). The enhanced SST supports greater atmospheric water vapor, which is accompanied by anomalous wind, and transported into the East China monsoon region. The increase in atmospheric water vapor favors more cloud cover and precipitation, especially in the eastern afforestation region. Furthermore, the increase in atmospheric water vapor and cloud cover produce a greenhouse effect, raising the wintertime surface air temperature. By comparing simulations in which ocean temperature are either fixed or variable, we demonstrate that a significant hydrologic response in East China to afforestation only occurs if ocean temperatures are allowed to vary and the oceanic source of moisture to the continent is enhanced.     

2010年6月中下旬南方暴雨过程变形场作用分析

利用常规原始报文资料,采用基于Lanczos窗口滤波器的合成分析方法,对2010年6月13-27日的形势场、物理量进行合成分析,计算并分析了低空合成风场的总变形.结果表明:500 hPa大陆中、高纬地区存在一“Ω”形类阻塞高压,西北冷空气从其东部源源不断向长江及以南地区输送,与副热带高压西北侧的西南暖湿气流在我国南方地区交汇.700、850 hPa大陆高压与西太平洋副热带高压之间形成的鞍型场,位于长江以南地区,鞍型场鞍点附近及其东部膨胀轴是暴雨发生的主要区域.在南方地区上空200 hPa西北气流辐散产生的抽吸作用,对这次长时间、高强度的降水起了重要作用.发生在鞍型场和切变线上的低空中尺度气旋,是造成暴雨的重要天气系统.鞍型场膨胀轴附近,总变形最大,其位置、走向均与雨带基本一致,有利于锋生和中尺度气旋形成.低空冷暖气流交汇区域形成低空强θse梯度,在垂直剖面图上,等θse线呈现十分倾斜状态,该区域强θse水平梯度与低空总变形、正涡度区一致,可能是特大暴雨发生的重要因素.     

Oceanic climatology in the coupled model FGOALS-g2: Improvements and biases

The present study examines simulated oceanic climatology in the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2) forced by historical external forcing data. The oceanic temperatures and circulations in FGOALS-g2 were found to be comparable to those observed, and substantially improved compared to those simulated by the previous version, FGOALS-g1.0. Compared with simulations by FGOALS-g1.0, the shallow mixed layer depths were better captured in the eastern Atlantic and Pacific Ocean in FGOALS-g2. In the high latitudes of the Northern Hemisphere, the cold biases of SST were about 1°C–5°C smaller in FGOALS-g2. The associated sea ice distributions and their seasonal cycles were more realistic in FGOALS-g2. The pattern of Atlantic Meridional Overturning Circulation (AMOC) was better simulated in FGOALS-g2, although its magnitude was larger than that found in observed data. The simulated Antarctic Circumpolar Current (ACC) transport was about 140 Sv through the Drake Passage, which is close to that observed. Moreover, Antarctic Intermediate Water (AAIW) was better captured in FGOALS-g2. However, large SST cold biases (>3°C) were still found to exist around major western boundary currents and in the Barents Sea, which can be explained by excessively strong oceanic cold advection and unresolved processes owing to the coarse resolution. In the Indo-Pacific warm pool, the cold biases were partly related to the excessive loss of heat from the ocean. Along the eastern coast in the Atlantic and Pacific Oceans, the warm biases were due to overestimation of shortwave radiation. In the Indian Ocean and Southern Ocean, the surface fresh biases were mainly due to the biases of precipitation. In the tropical Pacific Ocean, the surface fresh biases (>2 psu) were mainly caused by excessive precipitation and oceanic advection. In the Indo-Pacific Ocean, fresh biases were also found to dominate in the upper 1000 m, except in the northeastern Indian Ocean. There were warm and salty biases (3°C–4°C and 1–2 psu) from the surface to the bottom in the Labrador Sea, which might be due to large amounts of heat transport and excessive evaporation, respectively. For vertical structures, the maximal biases of temperature and salinity were found to be located at depths of >600 m in the Arctic Ocean, and their values exceeded 4°C and 2 psu, respectively.     

CINRAD/CC型雷达数据传输系统故障分析与改进方案

对甘肃省3部CINRAD/CC型雷达近4年的雷达故障进行统计分析,作为雷达系统的主要故障部件,随着使用年限的增加,雷达数据传输系统的故障有明显的增多趋势.对引起故障的主要因素进行统计分析,提出了改进方法:基于标准网络的数据传输方式舍弃了原来的光纤系统;取消了基于光端机和复分接的通信方式,代以采用标准网络传输的通信方式;采用四创电子研发的终端软件(2.0版本),新增了集成的网络功能、用户权限功能、数据产品和图像产品全自动生成、数据文件的检索能力、语音报警等功能.改进后的雷达数据传输系统运行情况表明:网络型光纤通信系统减少了雷达数据传输故障,增强了系统的可靠性和稳定性;雷达数据的传输率和有效性也得到一定的提高,确保了新一代天气雷达的正常业务观测.     

Bimodality of the South Asia High simulated by coupled models

The observed South Asia High (SAH) center is characterized by two distinctive equilibrium modes during boreal midsummer, namely the center of SAH is located between 82.5^o--92.5^oE for the Tibetan Plateau mode and between 55^o--65^oE for the Iranian Plateau mode, respectively. The present study describes the ability of 15 coupled general circulation models (CGCM) used in the Intergovernmental Panel on Climate Changes (IPCC) 4th Assessment Report to reproduce the observed bimodality of the SAH. These models reveal a wide range of skill in simulating this bimodality. Nearly half of the models reproduced the bimodality, while the other half of the models did not simulate well these two modes whereas usually preferring one mode. The models that reproduced the bimodality of the SAH present similar horizontal and vertical circulations as those features from the NCEP reanalysis data. The results from these models identify the warm characteristics of the SAH and indicate that these two modes have different dynamic and thermodynamic properties. Different characteristics of the simulated sensible heat and latent heat related to precipitation partly contribute to the difference in the simulations of the SAH bimodality. The majority of these models that prefer to simulate the Tibetan Plateau mode produce a small sensible heat flux difference between the Iranian Plateau and the Tibetan Plateau, and also generally simulate a very strong false precipitation center over the east of the Tibetan Plateau, which indicates strong latent release and thereby contributes to the preference of the SAH center on the Tibetan Plateau. Whereas, the models that reproduce the bimodality of the SAH tend to simulate large precipitation over the southern Himalayas and no obviously false precipitation is produced over the east of the Tibetan Plateau. In addition, the models resolution may also have important impacts on the simulations of precipitation.     

A View of Earth System Model Development

This paper gives a definition of earth system model and shows three development phases of it, including physical climate system model, earth climate system model, and earth system model, based on an inves- tigation of climate system models in the world. It provides an expatiation on the strategic significance of future development of earth system model, an introduction of some representative scientific research plans on development of earth system model home and abroad, and a review of its status and trends based on the models of the fourth assessment report （AR4） ofthe Intergovernmental Panel on Climate Change （IPCC）. Some suggestions on future development of earth system model in China are given, which are expected to be helpful to advance the development.     

Coupled Model Simulations of Climate Changes in the 20th Century and Beyond

Several scenario experiments of the IPCC 4th Assessment Report （AR4） are performed by version g1.0 of a Flexible coupled Ocean-Atmosphere-Land System Model （FGOALS） developed at the Institute of Atmospheric Physics, Chinese Academy of Sciences （IAP/CAS）, including the ＂Climate of the 20th century experiment＂, ＂CO2 1% increase per year to doubling experiment＂ and two separate IPCC greenhouse gases emission scenarios AIB and B1 experiments. To distinguish between the different impacts of natural variations and human activities on the climate change, three-member ensemble runs are performed for each scenario experiment. The coupled model simulations show： （1） from 1900 to 2000, the global mean temper- ature increases about 0.5℃ and the major increase occurs during the later half of the 20th century, which is in consistent with the observations that highlights the coupled model＇s ability to reproduce the climate changes since the industrial revolution; （2） the global mean surface air temperature increases about 1.6℃ in the CO2 doubling experiment and 1.5℃ and 2.4℃ in the A1B and B1 scenarios, respectively. The global warming is indicated by not only the changes of the surface temperature and precipitation but also the temperature increase in the deep ocean. The thermal expansion of the sea water would induce the rise of the global mean sea level. Both the control run and the 20th century climate change run are carried out again with version g1.1 of FGOALS, in which the cold biases in the high latitudes were removed. They are then compared with those from version g1.0 of FGOALS in order to distinguish the effect of the model biases on the simulation of global warming.     

Sensitivity of Atlantic meridional overturning circulation to the dynamical framework in an ocean general circulation model

The horizontal coordinate systems commonly used in most global ocean models are the spherical latitude–longitude grid and displaced poles, such as a tripolar grid. The effect of the horizontal coordinate system on Atlantic meridional overturning circulation (AMOC) is evaluated by using an OGCM (ocean general circulation model). Two experiments are conducted with the model—one using a latitude–longitude grid (referred to as Lat_1) and the other using a tripolar grid (referred to as Tri). The results show that Tri simulates a stronger North Atlantic deep water (NADW) than Lat_1, as more saline water masses enter the Greenland–Iceland–Norwegian (GIN) seas in Tri. The stronger NADW can be attributed to two factors. One is the removal of the zonal filter in Tri, which leads to an increasing of the zonal gradient of temperature and salinity, thus strengthening the north geostrophic flow. In turn, it decreases the positive subsurface temperature and salinity biases in the subtropical regions. The other may be associated with topography at the North Pole, because realistic topography is applied in the tripolar grid while the latitude–longitude grid employs an artificial island around the North Pole. In order to evaluate the effect of the filter on AMOC, three enhanced filter experiments are carried out. Compared to Lat_1, an enhanced filter can also augment NADW formation, since more saline water is suppressed in the GIN seas, but accumulated in the Labrador Sea, especially in experiment Lat_2_S, which is the experiment with an enhanced filter on salinity.     

汉江上游黄土常量元素地球化学特征及区域对比

本文对汉江上游黄土的常量元素含量及相关地球化学参数CIA、Na/K、淋溶系数、退碱系数、残积系数等进行了系统分析。结果显示：① 汉江黄土的主要化学成分为SiO₂、Al₂O₃和Fe₂O₃,三者含量总和达767.3 g/kg;常量元素含量大小排序为SiO₂>Al₂O₃>Fe₂O₃>K₂O>MgO>Na₂O>CaO。风化成壤过程中Na、Ca、Mg、Si发生不同程度的迁移淋溶,而Fe、Al、K相对富集。② 其风化成壤强度呈现从马兰黄土L₁→过渡性黄土L_t→古土壤S₀逐渐升高、全新世黄土L₀又降低的规律,记录了该区域气候经历了末次冰期（55.0-15.0 ka BP）冷干、早全新世（15.0-8.5 ka BP）增温增湿、中全新世（8.5-3.1 ka BP）达到最暖湿,晚全新世（3.1-0.0 ka BP）降温变干的演变过程。③ 汉江黄土与洛川、巫山、下蜀黄土的元素组合特征高度一致,不同地区常量元素（CaO除外）含量十分接近且UCC标准化值变幅均小于0.25,这暗示了它们风化之初具有相似的风成沉积基础;但不同区域黄土的化学风化强度差异明显,大致呈现洛川黄土<汉江黄土<巫山黄土<下蜀黄土的趋势,与中国现代季风气候的空间变化规律相吻合,即不同地区黄土风化程度差异主要是东亚季风变化影响的结果。