频散效应对自由大气能量输送的影响

本文应用扩大的Ｐｒａｎｄｔｌ混合长理论分析自由大气中的Ｒｅｎｏｌｄｓ平均运动方程组，着重分析了频散效应对自由大气大迟度运动能量输送的影响。分析指出：频散效应的自由大气中能量由扰动动能向平均动能转换（即能量逆转）的根本原因；正压大气能量逆转只能在扰动的尺度小于临界迟度Ｌｃ时才能发生；斜压大气能量逆转主要在扰动的厚度小于临界厚度Ｄｃ时发生。不同尺度的扰动与包含和不包含频率散效应的简单模式结果验证了上面     

扰动近地层湍流互谱特征研究

运用国际能量平衡实验(EBEX-2000)的湍流、净辐射和温度梯度资料, 对近地层8.7 m和2.7 m两个高度的湍流互谱结构、温度廓线和湍流通量的特征进行了分析, 重点研究了逐块灌溉所致的扰动近地层内大涡与局地湍流的相互作用以及大涡对地表通量的影响。研究结果显示, 低频湍流互谱的峰值频率在两个高度趋于一致, 基本遵循外层标度律(OLS)模型; 高频湍流符合局地各向同性湍流理论。由于大涡的影响, 湍流互谱低频能量显著增强, 且该增强作用在8.7 m高度比2.7 m高度更为突出。湍流谱的低频部分出现多峰值, 峰值频率对应的涡旋尺度与热力非均匀性的尺度有较好的对应关系, 主要的3个涡旋尺度分别为800, 400和200 m。大尺度涡旋扰动对局地湍流的影响: 上层大于下层, 不稳定时大于稳定时。     

Circulation in the South China Sea in summer of 1998

Based on the CTD and meteorological data obtained by R/VXiangyanghong No. 14 in the South China Sea (SCS) in the summer of 1998, both current velocity and volume transport are calculated by using a modified inverse model. Circulation in the SCS is analyzed by combining the calculated results with ADCP data. The following results are obtained, (i) The most important feature of the circulation in the northeastern SCS is that a branch of the Kuroshio intrudes into the SCS with a small volume transport. It flows anticyclonically through the Bashi Strait and towards the southwest off the Taiwan Island, and it does not intrude into the inner SCS. (ii) The northern SCS is dominated mainly by a cyclonic circulation system with two cold eddies, (iii) The central and southwestern SCSs are mainly occupied by anticyclonic circulation systems, including three anticyclonic and one stronger cyclonic eddies. (iv) In the southeastern SCS, there is a large scope of cyclonic circulation extending in the SW-NE direction, (v) There is a “multi-eddy phenomenon” in the SCS, and a larger eddy contains several small eddies. (vi) There is western intensifying of the currents and eddies in the SCS.     

恒定有压扩散流的大涡模拟

采用大涡模拟（LES）方法对恒定有压扩散流进行了数值模拟，对大尺度漩涡直接求解Navier-Stokes方程，小尺度漩涡采用标准Smagorinsky亚格子模型模拟．针对不同雷诺数下扩散段内的水流进行数值模拟，得到了各雷诺数流动时的时均速度场，分析了不同流态下扩散段内恒定有压扩散流时均流动特性．通过对不同流态下扩散段内连续瞬态流场的分析，探讨了不同雷诺数流动时扩散段内瞬态流场结构特点以及分离区内漩涡的变化规律，指出在恒定流状态下扩散段内存在流动的局部不稳态现象（主流的非周期性摆动），并对此现象进行分析．计算结果和试验结果吻合较好．     

Progress of regional oceanography study associated with western boundary current in the South China Sea

Recent progress of physical oceanography in the South China Sea (SCS) associated with the western boundary current (WBC) and eddies is reviewed in this paper. It includes Argo observations of the WBC, eddy detection in the WBC based on satellite images, cross-continental shelf exchange in the WBC, eddy-current interaction, interannual variability of the WBC, air-sea interaction, the SCS throughflow (SCSTF), among others. The WBC in the SCS is strong, and its structure, variability and dynamic processes on seasonal and interannual time scales are yet to be fully understood. In this paper, we summarize progresses on the variability of the WBC, eddy-current interaction, air-sea interaction, and the SCSTF achieved in the past few years. Firstly, using the drifting buoy observations, we point out that the WBC becomes stronger and narrower after it reaches the central Vietnam coast. The possible mechanisms influencing the ocean circulation in the northern SCS are discussed, and the dynamic mechanisms that induce the countercurrent in the region of northern branch of WBC in winter are also studied quantitatively using momentum balance. The geostropic component of the WBC was diagnosed using the ship observation along 18°N, and we found that the WBC changed significantly on interannual time scale. Secondly, using the ship observations, two anti-cyclonic eddies in the winter of 2003/2004 in the northern SCS, and three anti-cyclonic eddies in the summer of 2007 along 18°N were studied. The results show that the two anti-cyclonic eddies can propagate southwestward along the continental shelf at the speed of first Rossby wave (～0.1 ms-1 ) in winter, and the interaction between the three anti-cyclonic eddies in summer and the WBC in the SCS is preliminarily revealed. Eddies on the continental shelf of northern SCS propagated southeastward with a maximum speed of 0.09 ms-1 , and those to the east of Vietnam coast had the largest kinetic energy, both of which imply strong interaction between eddy activity and WBC in the SCS. Thirdly, strong intraseasonal variability (ISV) of sea surface temperature (SST) near the WBC regions was found, and the ISV signal of SST in winter weakens the ISV signal of latent heat flux by 20%. Fourthly, the long-term change of SCSTF volume transport and its connection with the ocean circulation in the Pacific were discussed.     

An initial note on quasistationary, cold-core Lanyu eddies southeast off Taiwan Island

Drifting buoys,satellite altimetry and satellite-derived sea surface thermal images are used to identify the existence of a large cold-core,cyclonic Kuroshio fontal eddy between Hengchun Peninsula and Lanyu,southeast off Taiwan Island around March 1996.The cold eddy accompanies an offshore meander of the Kuroshio near Lanyu,about 70 km and 100 km in horizontal zonal and meridional scales,respectively.The cold eddy is different from normal Kuroshio frontal eddies for its persisting of about 2 months near Lanyu.Supporting evidence suggests that the Kuroshio intruded into the South China Sea(SCS,hereafter) forming a loop-like structure during the persisting period of the cold eddy and that similar eddies occur occasionally in the same location.Compared with the corresponding studies in the Gulf of Mexico,it is suggested that Lanyu cold eddies are SCS analogues of Tortugas eddies found in the southern Straits of Florida.Overshooting of the meandering Kuroshio when it leave the SCS and effects from conservation of potential vorticity are the possible mechanism of eddy genesis.     

Observational evidence for an ocean heat pump induced by tropical cyclones

Ocean mixing affects global climate and the marine biosphere because it is linked to the ocean's ability to store and transport heat and nutrients. Observations have constrained the magnitude of upper ocean mixing associated with certain processes, but mixing rates measured directly are significantly lower than those inferred from budget analyses, suggesting that other processes may play an important role. The winds associated with tropical cyclones are known to lead to localized mixing of the upper ocean, but the hypothesis that tropical cyclones are important mixing agents at the global scale has not been tested. Here we calculate the effect of tropical cyclones on surface ocean temperatures by comparing surface temperatures before and after storm passage, and use these results to calculate the vertical mixing induced by tropical cyclone activity. Our results indicate that tropical cyclones are responsible for significant cooling and vertical mixing of the surface ocean in tropical regions. Assuming that all the heat that is mixed downwards is balanced by heat transport towards the poles, we calculate that approximately 15 per cent of peak ocean heat transport may be associated with the vertical mixing induced by tropical cyclones. Furthermore, our analyses show that the magnitude of this mixing is strongly related to sea surface temperature, indicating that future changes in tropical sea surface temperatures may have significant effects on ocean circulation and ocean heat transport that are not currently accounted for in climate models.     

南京夏季城郊湍流特征对比分析

利用2010年南京夏季城市热岛三维观测试验资料,对比分析了南京夏季城市和郊区下垫面的湍流特征。结果表明:①郊区大气层结呈现规律性的日变化特征,而城市大气几乎全天处于不稳定层结状态;②不稳定层结下,城市、郊区三个方向无量纲风速标准差与稳定度参数均呈1/3幂次关系;城市无量纲水平风速标准差小于郊区,而在垂直方向无明显差异,郊区略小于城市;③城、郊下垫面归一化风速谱曲线在高频段随无因次频率满足-2/3幂次律;低频段谱曲线集中在相对狭窄范围内;郊区风速谱曲线要比城市开阔且平缓;城市风速谱有明显拐点,水平风速谱和垂直风速谱拐点对应的无因次频率分别为0.007和0.01;④南京城、郊的垂直风速脉动含能涡区的特征尺度均小于水平风速脉动含能涡区,湍流动能在垂直方向上主要分布于小尺度湍涡。     

旋风分离器分离空间流场的理论分析

针对旋风分离器内流场特点，运用代数涡粘模式，给出了描述分离器内流体运动的简化方程。用假设轴向或径向速度分布函数形式的方法，求得了与测量结果较为一致的三维速度半理论解。边壁速度和内外旋流分界面化置分别用入口收缩系数和最小压降原理确定。分析了湍流特征尺度——普朗特混合长度和柯莫格罗夫尺度的分布规律。结果表明，湍流特征尺度的理论计算结果与实验结果吻合较好。     

2003 vs 2002: A large amplitude wintertime temperature anomaly reversion event and its anomalous atmospheric circulation

It is revealed that there happened a large amplitude wintertime temperature anomaly reversion event (LTAR) in Northern Hemisphere high latitude regions and South Australia for the year 2003 versus 2002, with the most notable change in Eurasia, eastern North America, North Pacific, and South Australia. The accompanying atmospheric general circulation anomalies are analyzed and the dominant changes in the circulation are found out. The anomalous cyclonic eddies over the north Pacific and the anomalous anticyclonic eddies over North Europe that cooperate each other are mostly linked with the event. Both anomalous eddy systems are connected with the remote teleconnection patterns respectively. The research also suggests the existence of a cross-equator teleconnection pattern, namely, the Northern Pacific-Western Pacific-Australia teleconnection pattern (NPWPA). It is not only related to LTAR, but also associated with the temperature transition from cold episode to warm episode in the year 2003 versus 2002 during December-January-February.     

Intraseasonal interaction between the Madden-Julian Oscillation and the North Atlantic Oscillation

Bridging the traditional gap between the spatio-temporal scales of weather and climate is a significant challenge facing the atmospheric community. In particular, progress in both medium-range and seasonal-to-interannual climate prediction relies on our understanding of recurrent weather patterns and the identification of specific causes responsible for their favoured occurrence, persistence or transition. Within this framework, I here present evidence that the main climate intra-seasonal oscillation in the tropics-the Madden-Julian Oscillation (MJO)-controls part of the distribution and sequences of the four daily weather regimes defined over the North Atlantic-European region in winter. North Atlantic Oscillation (NAO) regimes are the most affected, allowing for medium-range predictability of their phase far exceeding the limit of around one week that is usually quoted. The tropical-extratropical lagged relationship is asymmetrical. Positive NAO events mostly respond to a mid-latitude low-frequency wave train initiated by the MJO in the western-central tropical Pacific and propagating eastwards. Precursors for negative NAO events are found in the eastern tropical Pacific-western Atlantic, leading to changes along the North Atlantic storm track. Wave-breaking diagnostics tend to support the MJO preconditioning and the role of transient eddies in setting the phase of the NAO. I present a simple statistical model to quantitatively assess the potential predictability of the daily NAO index or the sign of the NAO regimes when they occur. Forecasts are successful in approximately 70 per cent of the cases based on the knowledge of the previous approximately 12-day MJO phase used as a predictor. This promising skill could be of importance considering the tight link between weather regimes and both mean conditions and the chances of extreme events occurring over Europe. These findings are useful for further stressing the need to better simulate and forecast the tropical coupled ocean-atmosphere dynamics, which is a source of medium-to-long range predictability and is the Achilles' heel of the current seamless prediction suites.     

二维射流混合层中的相干声源

通过二维射流混合层中相干时间尺度的测量，对声激励不稳定波增长过程及破碎点后的相干特性进行研究。实验结果表明，相干时间尺度在基波和第一亚谐波增长区较大，在破碎点后突然下降并在下游呈逐渐减小趋势。增加声激励强度可使不稳定波增长区的相干时间尺度增大，并对小游的流动结构有明显影响。     

Study and case simulation of a regional dust model coupled with a nonhydrostatic dynamics model

A new regional dust model suitable for simulation and forecasting of dust storms over northern China was described. The dust model was developed by coupling the mesoscale dynamics model MM5 (the Fifth-Generation NCAR/Penn State Mesoscale Model) with a set of mass conservation equations for the particles. The model includes all the atmospheric physical processes of dust storms including occurrence, lifting, transport, and dry and wet deposition. It considers the parameterization of dry and wet deposition, the dust size distribution and microphysical processes in detail. The dust flux from the surface is parameterized based on the friction velocity, which is provided by the mesoscale nonhydrostatic dynamics model, which takes account of the vegetation coverage, land use, soil category, and soil moisture. This new dust model is used to simulate the dust storm that occurred on 19--21 March, 2002 in North China. The results show that there is high dust concentration and its movement is consistent with the surface weather record and satellite monitoring images of the observed dust storm. The simulated dust concentration coincides with the observation data of the particulate concentration of PM10 (dust particles smallerthan 10 μm in diameter). The new numerical model also successfully simulates the formation and migration of the dust storm of 6-8 April, 2002 in North China.     

水球世界气候态与经向热量输送的数值模拟试验

利用完全耦合的气候模式(FOAM), 通过两组理想的水球试验, 研究水球气候系统中的平均气候态和经向热量输送。两组水球试验分别是Aqua和Ridge, 前者整个星球完全被水覆盖, 没有任何陆地, 后者与前者的唯一区别是从南极到北极有一道连续的地脊。相比于现实世界, 水球世界的气候更加温暖, 极地几乎没有海冰。北半球的经向温度梯度较现实世界弱, 导致北半球的大气经向热量输送较小。这些差别主要来源于海陆分布改变造成的行星反照率的改变, 而云量的增加部分抵消了这种改变。尽管在两个水球试验中海洋环流和平均温度场差别很大, 但大气平均气候态差别不大。不同于Ridge, 在Aqua中赤道区域出现“反”哈德雷环流, 使得低纬度大气向赤道方向输送热量。尽管水球世界的海洋环流与现实世界相比发生了巨大改变, 但总的经向热量输送及其在大气和海洋之间的分配依然保持稳定。中小尺度的涡旋和扩散引起的经向热量输送部分抵消了大尺度环流引起的经向热量输送, 尤其在中纬度起着重要作用。     

Weak response of the Atlantic thermohaline circulation to an increase of atmospheric carbon dioxide in IAP／LASG Climate System Model

Response of the Atlantic thermohaline circulation (THC) to global warming is examined by using the climate system model developed at IAP/LASG. The evidence indicates that the gradually warming climate associated with the increased atmospheric carbon dioxide leads to a warmer and fresher sea surface water at the high latitudes of the North Atlantic Ocean, which prevents the down-welling of the surface water. The succedent reduction of the pole-toequator meridional potential density gradient finally results in the decrease of the THC in intensity. When the atmospheric carbon dioxide is doubled, the maximum value of the Atlantic THC decreases approximately by 8%. The associated poleward oceanic heat transport also becomes weaker. This kind of THC weakening centralizes mainly in the northern part of the North Atlantic basin, indicating briefly a local scale adjustment rather than a loop oscillation with the whole Atlantic “conveyor belt” decelerating.     

关于湍流多尺度统计理论方法的论证

用黑河化音测站的实测风、温脉动资料对一种湍流多尺度统计理论方法进行了分析验证,并应用此方法通过对相关系数、湍流时间尺度、湍谱和扩散参数等湍流特征量的研究,分析了黑河戈壁地区的湍流微结构和扩散特征.结果表明:多尺度分析方法正适合研究具有多尺度特征的大气湍流现象,可以比传统方法提供更多的有关湍流属性的信息,能够更直观地表现出不同尺度湍涡对扩散作用的大小,是发展湍流统计理论的一种有效工具     

青藏高原对全球大气温度和水汽分布的影响

利用耦合的气候模式CESM, 定量研究青藏高原对全球大气温度和水汽分布的影响。通过对比采用真实地形的参考实验(Real)和去掉青藏高原的敏感性实验(NoTibet)发现, 去掉青藏高原会使北半球大气变冷、变干, 对南半球的影响不明显。北半球中高纬度从地表至平流层均有强烈降温, 地表的降温中心在北大西洋, 年平均降温幅度达5ºC, 高空的降温中心在100 hPa的平流层, 年平均降温幅度达2ºC。北大西洋和南亚地区湿度减少, 南大西洋和东非地区湿度增加。北半球变冷主要是海洋向北经向热量输送减少的结果, 一方面增强了北半球的经向温度梯度, 导致Hadley环流增强, 加强了中低纬地区向北的大气热量输送, 部分补偿了海洋向北减少的热量输送, 维持了北半球中低纬度的能量平衡; 另一方面, 使得北半球中高纬度蒸发作用减弱, 大气中水汽含量减少, 北半球变得寒冷干燥。初步的研究表明, 青藏高原对北半球气候有重大影响, 影响范围可达北半球高纬度地区。     

径向热管换热器壳程数值模拟及结构参数优化

利用FLUENT软件,对同轴径向热管换热器壳程进行模拟计算,分析烟气速度、温度及局部对流换热系数沿壳程的变化规律,并寻求换热器结构参数优化值。研究结果显示:换热器壳程,离热管管壁越近,温度梯度越大;烟气流经管束时,在管束尾部形成一个楔形的涡流区,速度在流体出现脱体的地方达到最大;湍流强度在涡流中心区域也达到最大值,中心区域的换热强度明显高于热管两侧边缘处,管束尾部的烟气温度低于管边缘处的烟气温度。将模拟结果与测试结果进行比较,误差在10%以内。通过改变换热器结构参数,对换热器壳程烟气对流换热进行分析研究,得到径向热管换热器结构优化参数:横向管距为114~120 mm;纵向管距为120~125 mm;翅片高度不应高于26.5 mm;翅片间距为6 mm。     

Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data

Through its ability to transport large amounts of heat, fresh water and nutrients, the ocean is an essential regulator of climate. The pathways and mechanisms of this transport and its stability are critical issues in understanding the present state of climate and the possibilities of future changes. Recently, global high-quality hydrographic data have been gathered in the World Ocean Circulation Experiment (WOCE), to obtain an accurate picture of the present circulation. Here we combine the new data from high-resolution trans-oceanic sections and current meters with climatological wind fields, biogeochemical balances and improved a priori error estimates in an inverse model, to improve estimates of the global circulation and heat fluxes. Our solution resolves globally vertical mixing across surfaces of equal density, with coefficients in the range (3-12) x 10(-4) m2 s(-1). Net deep-water production rates amount to (15 +/- 12) x 10(6) m3 s(-1) in the North Atlantic Ocean and (21 +/- 6) x 10(6) m3 s(-1) in the Southern Ocean. Our estimates provide a new reference state for future climate studies with rigorous estimates of the uncertainties.