A strong decrease in Saturn's equatorial jet at cloud level

The atmospheres of the giant planets Jupiter and Saturn have a puzzling system of zonal (east-west) winds alternating in latitude, with the broad and intense equatorial jets on Saturn having been observed previously to reach a velocity of about 470 m x s(-1) at cloud level. Globally, the location and intensity of Jupiter's jets are stable in time to within about ten per cent, but little is known about the stability of Saturn's jet system. The long-term behaviour of these winds is an important discriminator between models for giant-planet circulations. Here we report that Saturn's winds show a large drop in the velocity of the equatorial jet of about 200 m x s(-1) from 1996 to 2002. By contrast, the other measured jets (primarily in the southern hemisphere) appear stable when compared to the Voyager wind profile of 1980-81.     

Moist convection as an energy source for the large-scale motions in Jupiter's atmosphere. Galileo Imaging Team

Jupiter's dominant large-scale weather patterns (dimensions approximately 10,000 km) are zonal jets and long-lived ovals. The jets have been flowing east and west at constant speeds of up to 180 m s(-1) for over 100 years. These jets receive energy from small-scale eddies, which pump eastward momentum into the eastward jets and westward momentum into the westward jets. This momentum transfer was predicted by numerical models before it was observed on Jupiter. The large ovals roll between the jets in an anticyclonic direction-clockwise in the northern hemisphere and counterclockwise in the southern hemisphere--where they regularly assimilate small anticyclonic eddies. But from where the eddies receive their energy has been an open question. Here we argue that the eddies, which ultimately drive both the jets and the ovals, receive their energy from moist convection. This hypothesis is consistent with observations of jovian lightning, which is an indicator of moist convection. It also explains the anticyclonic rotation and poleward drift of the eddies, and suggests patterns of upwelling and downwelling that resemble the patterns of large-scale axisymmetric overturning in the Earth's atmosphere.     

An intense stratospheric jet on Jupiter

The Earth's equatorial stratosphere shows oscillations in which the east-west winds reverse direction and the temperatures change cyclically with a period of about two years. This phenomenon, called the quasi-biennial oscillation, also affects the dynamics of the mid- and high-latitude stratosphere and weather in the lower atmosphere. Ground-based observations have suggested that similar temperature oscillations (with a 4-5-yr cycle) occur on Jupiter, but these data suffer from poor vertical resolution and Jupiter's stratospheric wind velocities have not yet been determined. Here we report maps of temperatures and winds with high spatial resolution, obtained from spacecraft measurements of infrared spectra of Jupiter's stratosphere. We find an intense, high-altitude equatorial jet with a speed of approximately 140 m s(-1), whose spatial structure resembles that of a quasi-quadrennial oscillation. Wave activity in the stratosphere also appears analogous to that occurring on Earth. A strong interaction between Jupiter and its plasma environment produces hot spots in its upper atmosphere and stratosphere near its poles, and the temperature maps define the penetration of the hot spots into the stratosphere.     

Deep winds beneath Saturn's upper clouds from a seasonal long-lived planetary-scale storm

Convective storms occur regularly in Saturn's atmosphere. Huge storms known as Great White Spots, which are ten times larger than the regular storms, are rarer and occur about once per Saturnian year (29.5 Earth years). Current models propose that the outbreak of a Great White Spot is due to moist convection induced by water. However, the generation of the global disturbance and its effect on Saturn's permanent winds have hitherto been unconstrained by data, because there was insufficient spatial resolution and temporal sampling to infer the dynamics of Saturn's weather layer (the layer in the troposphere where the cloud forms). Theoretically, it has been suggested that this phenomenon is seasonally controlled. Here we report observations of a storm at northern latitudes in the peak of a weak westward jet during the beginning of northern springtime, in accord with the seasonal cycle but earlier than expected. The storm head moved faster than the jet, was active during the two-month observation period, and triggered a planetary-scale disturbance that circled Saturn but did not significantly alter the ambient zonal winds. Numerical simulations of the phenomenon show that, as on Jupiter, Saturn's winds extend without decay deep down into the weather layer, at least to the water-cloud base at pressures of 10-12 bar, which is much deeper than solar radiation penetrates.     

室内空气流动过程的模型实验研究

为了分析在不同的进风位置、射流方向以及进风温度条件下,房间壁温对室内空气流动的影响,在缩小模型实验的基础上,利用流动可视化和定量测量相结合的办法测量了不同工况下室内的空气流动形态、速度以及模型整体换热情况。结果表明:壁温恒定时,进风温度的降低引起水平进风方式的自由射流区缩短;垂直进风方式下射流形成的涡的中心位置向壁面靠近;中间垂直进风方式下射流向左侧偏转;右侧垂直进风方式下射流向右侧壁面偏转;同时浮升力引起的自然对流作用增强,换热温差加大,提高了围护结构漏热量。     

Interannual atmospheric variability forced by the deep equatorial Atlantic Ocean

Climate variability in the tropical Atlantic Ocean is determined by large-scale ocean-atmosphere interactions, which particularly affect deep atmospheric convection over the ocean and surrounding continents. Apart from influences from the Pacific El Ni?o/Southern Oscillation and the North Atlantic Oscillation, the tropical Atlantic variability is thought to be dominated by two distinct ocean-atmosphere coupled modes of variability that are characterized by meridional and zonal sea-surface-temperature gradients and are mainly active on decadal and interannual timescales, respectively. Here we report evidence that the intrinsic ocean dynamics of the deep equatorial Atlantic can also affect sea surface temperature, wind and rainfall in the tropical Atlantic region and constitutes a 4.5-yr climate cycle. Specifically, vertically alternating deep zonal jets of short vertical wavelength with a period of about 4.5?yr and amplitudes of more than 10?cm?s(-1) are observed, in the deep Atlantic, to propagate their energy upwards, towards the surface. They are linked, at the sea surface, to equatorial zonal current anomalies and eastern Atlantic temperature anomalies that have amplitudes of about 6?cm?s(-1) and 0.4?°C, respectively, and are associated with distinct wind and rainfall patterns. Although deep jets are also observed in the Pacific and Indian oceans, only the Atlantic deep jets seem to oscillate on interannual timescales. Our knowledge of the persistence and regularity of these jets is limited by the availability of high-quality data. Despite this caveat, the oscillatory behaviour can still be used to improve predictions of sea surface temperature in the tropical Atlantic. Deep-jet generation and upward energy transmission through the Equatorial Undercurrent warrant further theoretical study.     

Depth of a strong jovian jet from a planetary-scale disturbance driven by storms

The atmospheres of the gas giant planets (Jupiter and Saturn) contain jets that dominate the circulation at visible levels. The power source for these jets (solar radiation, internal heat, or both) and their vertical structure below the upper cloud are major open questions in the atmospheric circulation and meteorology of giant planets. Several observations and in situ measurements found intense winds at a depth of 24 bar, and have been interpreted as supporting an internal heat source. This issue remains controversial, in part because of effects from the local meteorology. Here we report observations and modelling of two plumes in Jupiter's atmosphere that erupted at the same latitude as the strongest jet (23 degrees N). The plumes reached a height of 30 km above the surrounding clouds, moved faster than any other feature (169 m s(-1)), and left in their wake a turbulent planetary-scale disturbance containing red aerosols. On the basis of dynamical modelling, we conclude that the data are consistent only with a wind that extends well below the level where solar radiation is deposited.     

天山北麓一例黑风暴天气的成因

利用常规观测资料、地面气象自记记录和静止气象卫星云图资料对1998-04-18由南支冷锋爆发性发展生成的干飑线触发的天山北麓黑风暴天气过程进行了分析。结果表明：强沙尘暴和黑风暴过境时风、压、温、湿在短时间内出现突变,跃变幅度黑风暴远大于强沙尘暴,黑风暴嵌于强沙尘暴时变化幅度比强沙尘暴弱。沙尘壁具有等温性,水平厚度4～9km。影响黑风暴的天气因素中,地面大风形成主要源于冷锋的加强和锋后强冷平流,高空急流的加强及其形成的次级环流使高空动量有效下传到地面则是另一个重要原因。混合层是有利于黑风暴在干旱环境形成的大气层结特征,这次过程深厚混合层的形成是深厚干对流和黑风暴产生的主要原因,而它的形成则是长时间地面加热的结果。     

聚能射流长靶距下的侵彻仿真模型

提出了一个用于长靶距下聚能装药的断裂射流侵彻能力预测数值仿真模型.因聚能射流有很大的速度梯度,当它飞行数倍于标准炸高的距离后,射流被拉断为碎段,其穿甲能力大为降低.基于非线性瞬态动力学程序AUTODYN,研究了聚能装药射流的形成和大靶距下的断裂射流对不同靶体的侵彻和贯穿模拟.通过与实验结果比较,给出了一个用于预测长靶距下聚能装药射流侵彻能力的计算模型.与实验数据比较,所给模型可给出准确的预测结果.     

轧辊冷却用扇形喷嘴的射流性能

扇形喷嘴是轧辊冷却系统中的核心元件,但目前对扇形喷嘴的射流速度和流量分布的研究尚不够深入。在对轧辊冷却用喷嘴理论研究的基础上,建立了喷口的数学模型,并利用成熟的圆形湍流自由射流理论分析确定了射流边界和射流流量分布计算模型。以GYQ 1981B1型扇形喷嘴为例,进行了具体的计算。利用自行设计的扇形喷嘴实验台对该喷嘴各项射流指标进行了试验测试,试验结果与理论分析结果具有良好的一致性。     

考虑固体颗粒的自由喷流噪声的数值研究

研究固体颗粒对喷流流场和声场的影响.选取6种不同的湍流模型，对自由喷流进行稳态计算分析，对比发现RNG k-ε模型最适合用于稳态喷流数值模拟；采用LES模型计算喷流的非稳态结果，并结合FW-H方程进行了喷流声场分析，与试验数据进行对比，验证了数值模型的正确性；在此模型的基础上，添加固体颗粒研究其对自由喷流流场和声场的影响，仿真结果表明固体颗粒的存在减小了喷流流场的超音速段长度，显著提高了喷流温度；增大了喷流下游区域噪声，减小了中上游区域噪声.      

合成喷形成的机理分析

合成喷是一种新型喷 ,了解它的形成机理对其设计和应用起着重要的作用。该文讨论了液体合成喷和气体合成喷的形成特点并建立了各自相应的数学物理模型。利用小扰动模型解释了大空间液体合成喷形成的原因 ,通过一个简单的热力学模型探讨了气体合成喷的形成机理。分析认为 :液体合成喷的产生主要是空化效应的结果 ,而气体合成喷的形成机制类似于微型压缩机。与他人实验结果的对比表明 :上述二种合成喷的机理分析是合理的     

基于合成射流的高空飞艇分离流控制

采用数值模拟方法研究了基于合成射流技术的高空飞艇流动控制方法。将合成射流装置安放在飞艇表面,靠近分离线处,并沿分离线布置,通过合成射流口吹吸空气产生涡流,并将其注入边界层内来达到延缓流动分离,进而达到减阻和大迎角阵风减缓的目的。研究首先利用对原始飞艇进行仿真,找到分离线的位置,进而研究了合成射流口出射速度幅值不同时飞艇阻力系数的变化,并以此来分析合成射流的流动控制效果。结果表明,射流口吹吸速度幅值越大,时均减阻效果越好,但射流的能量消耗也越大,气动力的脉动幅值也大。在扣除合成射流本身的能量消耗影响以后,最优的时均控制效果发生在迎角30°左右。研究结果显示,合成射流可以用来降低飞艇小迎角下的巡航阻力,也可以用来控制大迎角情况下的瞬态气动力,从而作为阵风减缓措施。     

圆形喷嘴内部结构对射流冲击换热性能的影响

研究了内部结构分别为柱状和锥状喷嘴的射流冲击换热性能.在初始条件和边界条件相同的情况下,利用计算流体力学软件Fluent对两种喷嘴的冲击换热过程进行了热流耦合模拟.对流固交界面的压力、剪切力、湍流强度、对流换热系数等流场和温度场数据进行对比分析.模拟结果表明,锥状结构喷嘴的射流冲击换热性能明显优于柱状结构的喷嘴.所得结论对热轧钢超快速冷却设备喷嘴的设计具有指导意义.     

波流环境中多孔射流三维数值模拟

建立了波流环境中多孔射流的三维大涡数学模型,探讨了波流共同作用下多孔射流的扩散和稀释机制,分析了孔间距对双孔射流、射流与环境水体相互作用的影响,并给出了最优相对孔间距。模拟结果表明：在波谷相位时刻,由于横流与波浪相互作用强烈,流场内的三维涡旋结构丰富、尺度较大、数目众多,有利于射流与环境水体、射流与射流之间的掺混,这是波流环境比单一横流环境中多孔射流运动扩散效果更佳的主要原因;随着孔间距的增大,双孔射流之间的相互作用慢慢削弱,而射流与环境水体之间的相互作用却在不断增强;双孔射流在孔间距为7.0倍管口直径时扩散效果最好。     

潮流底部多孔垂向排放污染物影响区的计算

根据射流受力平衡关系建立了非恒定横流中垂向射流轴线的积分方程,在前人对恒定横流中射流研究成果的基础上求得了该方程的解析解。由平面激光诱发荧光（ＰＬＩＦ）和数字图像技术测得的多孔射流浓度分布实验资料,获得了射流宽度、横向扩展角度与射流和横流速度比及射流相对高度的关系,为潮流底部多孔排放污染物影响区的计算提出了一套较完整的方法。计算结果得到实验结果的良好验证。     

Direct detection of a magnetic field in the innermost regions of an accretion disk

Models predict that magnetic fields play a crucial role in the physics of astrophysical accretion disks and their associated winds and jets. For example, the rotation of the disk twists around the rotation axis the initially vertical magnetic field, which responds by slowing down the plasma in the disk and by causing it to fall towards the central star. The magnetic energy flux produced in this process points away from the disk, pushing the surface plasma outwards, leading to a wind from the disk and sometimes a collimated jet. But these predictions have hitherto not been supported by observations. Here we report the direct detection of the magnetic field in the core of the protostellar accretion disk FU Orionis. The surface field reaches strengths of about 1 kG close to the centre of the disk, and it includes a significant azimuthal component, in good agreement with recent models. But we find that the field is very filamentary and slows down the disk plasma much more than models predict, which may explain why FU Ori fails to collimate its wind into a jet.     

Deep convection in the Irminger Sea forced by the Greenland tip jet

Open-ocean deep convection, one of the processes by which deep waters of the world's oceans are formed, is restricted to a small number of locations (for example, the Mediterranean and Labrador seas). Recently, the southwest Irminger Sea has been suggested as an additional location for open-ocean deep convection. The deep water formed in the Irminger Sea has the characteristic temperature and salinity of the water mass that fills the mid-depth North Atlantic Ocean, which had been believed to be formed entirely in the Labrador basin. Here we show that the most likely cause of the convection in the Irminger Sea is a low-level atmospheric jet known as the Greenland tip jet, which forms periodically in the lee of Cape Farewell, Greenland, and is associated with elevated heat flux and strong wind stress curl. Using a history of tip-jet events derived from meteorological land station data and a regional oceanic numerical model, we demonstrate that deep convection can occur in this region when the North Atlantic Oscillation Index is high, which is consistent with observations. This mechanism of convection in the Irminger Sea differs significantly from those known to operate in the Labrador and Mediterranean seas.     

Relationship between East Asian winter monsoon, warm pool situation and ENSO cycle

Based on the observational data analyses and numerical simulations with the air-sea coupled model (CGCM), a new perspective on the occurrence mechanism of ENSO is advanced in this paper. The continuous strong (weak) East Asian winter monsoon will lead to continuous westerly (easterly) wind anomalies over the equatorial western Pacific region. The anomalous equatorial westerly (easterly) winds can cause eastward propagation of the subsurface ocean temperature anomalies (SOTA) in the warm pool region, the positive (negative) SOTA have been in the warm pool region for quite a long time. The eastward propagating of positive (negative) SOTA along the thermocline will lead to positive (negative) SSTA in the equatorial eastern Pacific and the occurrence of El Niño (La Niña) event. After the occurrence of ENSO, the winter monsoon in East Asia will be weak (strong) due to the influence of El Niño (La Niña).     

低密度材料用于串联战斗部可行性研究

为研究浮法玻璃、合成树脂和有机玻璃3种低密度材料用于串联战斗部前级药型罩的可行性,用Autodyn-2D对3种低密度射流的成型以及对爆炸反应装甲的引爆过程进行了数值模拟.结果表明,与铜射流相比,低密度射流在同等条件下具有更高的头部速度,更大的射流直径以及良好的延展性,并能够快速而且有效的引爆爆炸反应装甲内的装药.初步验证了3种低密度材料用作串联战斗部前级药型罩材料的可行性.