On the seasonal cycle of stratospheric planetary waves

Quasi-stationary planetary waves exhibit different seasonal behaviour in the two winter stratospheres. Whereas, in a climatological sense, wave amplitudes are large throughout northern winter, in the Southern Hemisphere there is a climatological minimum in midwinter. It is suggested here that the southern hemisphere behaviour is basically linear, the midwinter minimum arising from the opacity of the strong westerlies of southern midwinter to stationary wave propagation. On the other hand, it is further suggested that, in the northern hemisphere winter, the westerlies are prevented from becoming so strong (in a climatological sense) by the action of the waves themselves on the means state and that the penetration of large-scale waves into the midwinter northern stratosphere thus depends on a nonlinear feedback process. Preliminary tests of this hypothesis are conducted, using a highly truncated beta-plane model of the stratospheric flow.     

Styles of mantle convection and their influence on planetary evolution

Mantle convection is the method of heat elimination for silicate mantles in terrestrial bodies, provided they are not too small or too hot. Bodies that are small (～Moon or smaller, possibly even Mercury) may rely largely on conduction or melt migration, and bodies that are very hot (Io, very early Earth) may use massive melt migration (magma oceans) and heat pipes. In the standard, simple picture, we can use scaling laws to determine the secular cooling of a planet, likelihood and form of volcanism, and the possibility of a core dynamo. Contrary to popular belief, small planets do not cool faster than larger planets (provided they convect) but they do tend to have a slightly lower internal temperature at all times and thus may cease to be volcanically active at an earlier epoch. On the other hand, a larger volume fraction of a small planet may be involved in melt generation. However, our understanding of heat transfer by mantle convection is limited by three very important, largely unsolved problems: The complexities of rheology, the effects of compositional gradients, and the effects of phase transitions, especially melting. The most striking manifestation of the role of rheology lies in the difference between a mobile lid mode (plate tectonics for Earth) and a stagnant lid mode (other large terrestrial bodies). This difference may arise because of the role of water, but perhaps also because of melting, or size (gravity), or the vagaries of history. It has profound effects for the differences in history of Earth, Venus and Mars, including their surface geology, volatile reservoirs and magnetic fields. Since thermal convection is driven by small density differences, it can also be greatly altered or limited by compositional or phase effects. Melt migration introduces additional complications to the heat transport as well as being a source for the irreversible differentiation that might promote layering. Our limited understanding and ability to model these processes continues to limit the development of a predictive framework for the differences among the terrestrial planets.     

A New Power-Law Relation For The Vertical Distribution of Suspended Matter

Generally, the vertical distribution of suspendedmatter is described by a simplepower-law relation in which it is assumed that thefriction velocity is constant withheight. This is a simplification of the actual mechanismof turbulent transport, sinceturbulence will most likely be reduced in the presenceof suspended particles for avariety of reasons. Here we investigate analytically,by assuming a constant shearstress with height, how the increased density of thetwo-phase mixture reduces thefriction velocity. This reduces the upward turbulentflux of particles, which tends todecrease the drift density compared to a situation inwhich changes in friction velocityare neglected. A new power-law relation is derived,which in snowdrift predicts amaximum reduction in drift density of 25% (and 40%for Martian dust) over thestandard power-law relation. In other geophysicaltwo-phase flows, such as suspendedmatter in water, the effects are shown to be negligiblebecause of the small ratio of driftdensity and medium density. Generally, this and otherinteractions between the particlesand the flow should be taken into account to betterunderstand the vertical profile ofsuspended matter in geophysical two-phase flows.     

区域入境旅游业竞争力比较研究

为了分析和提高区域入境旅游业的市场竞争力 ,该文建立区域入境旅游业市场竞争态及其转移模型。运用此模型定量分析和比较了河北、新疆两地区入境旅游业的现实竞争状态以及它们各自在 1991— 2 0 0 0年的竞争态转移规律 ,为区域入境旅游业的发展规划提供参考。     

蒙语“12121”气象语音自动答询系统的实现

鄂尔多斯市蒙语"12121"气象语音自动答询系统是在汉语"12121"气象语音自动答询系统的基础上实现的,于2008年5月1日试运行,在运行期间,受到了社会各界的好评,为农牧区朋友提供了科学的生产依据。     

降海鲑渗透生理及入海窗口期的研究进展

在过去30年中,降海鲑的发育得到了大量关注,研究降海鲑的发育,特别是如何调控降海鲑发育的时间和品质,以便幼鲑移入海水网箱。洄游型鲑科鱼类幼鲑向降海鲑的转变包含了一系列的行为、形态、生理的改变,这都为降海洄游进入河口做准备。降海鲑发育受几种激素的促进,包括生长激素、胰岛素样生长因子-I、皮质醇、甲状腺素,而催乳素通常会抑制发育。鳃氯细胞中特殊的离子转运蛋白(NKA、Na+/K+/Cl-协同转运蛋白和Cl-通道)丰度的增加引起盐分泌能力的提高,从而有利于降海鲑在海水中生长、游泳和存活。具银化期的鲑科鱼类(如大西洋鲑(Salmo salar)、硬头鳟(Oncorhyunchus mykiss)、银大麻哈鱼(Oncorhynchus kisutch)至少在淡水中生活一年,达到临界最小规格之后才可改变其对光周期的响应。如果在银化前未达到这个最小规格,则需等到下一年(或更长)。鲑科鱼类如何在一年中合适的时间确定其规格或生长率,并增加对光周期的响应性,这一重要的领域还未得到大量的关注。因此,了解降海鲑渗透生理及入海窗口期,查明不同鱼类适宜生长盐度,入海时间和方式非常重要,可为鲑科鱼类(如虹鳟(Oncorhynchus mykiss)、硬头鳟等)在黄海冷水团规模化养殖提供理论支持。     

An accurate and efficient SPH modeling of the water entry of circular cylinders

The present work is dedicated to the enhancement and application of the recently developed δ⁺-SPH scheme for two and three dimensional water entry problems. The cylinder surface presents a circular shape and therefore the position where the flow separation happens is tightly related to the implementation of the boundary condition. A special treatment for the particle shifting between fluid and solid wall is highlighted. Adaptive particle refinement (APR) is applied in this work to reduce the computational cost. It is found that, APR and the δ⁺-SPH scheme benefit to each other. That is to say the former reduces the computing cost of the latter while in return the latter solves the problem of particle disorder of the inactive particles of the former. Thanks to the combination of APR and δ⁺-SPH especially in three dimensional (3D) cases, the overall computational cost is significantly reduced while sufficiently fine particle resolution can be obtained in the flow region characterized by large pressure gradient close to the structure surface. The fairly good agreements between the SPH results and the experimental data prove the present SPH model to be a reliable tool in accurately solving the fluid–structure interacting problems in ocean engineering.     

Expectations for Cassini observations of ring material with nearby moons

This paper describes N-body simulations of two regions of the saturnian ring system and examines what we might expect the Cassini orbiter to see in those areas. The first region is the edge of the Encke gap in the A ring that is perturbed by the satellite, Pan. Our previous simulations of this region neglected particle self-gravity [Lewis and Stewart, 2000a, Bull. Am. Astron. Soc. 34, 883]. Here we examine the interactions of the wakes caused by Pan with the wakes that form from local gravitational instabilities. We find that the two phenomena do not normally coexist and predict that measurements of particle sizes between the moon wakes should reflect the true particle size distribution of the region and not what is caused by gravitational aggregation. The region between the Encke gap edge and the first wake peak is an exception to this rule because our simulations exhibit the formation of exceptionally large gravity-induced wakes in this region. We also describe simulations of the F ring and explain the nature of braid-like structures that form naturally when the ring is perturbed by a single moon on an eccentric orbit. Finally, we discuss the very dynamic nature of the F ring system and how this should be taken into account when interpreting observations and even when planning future observations of this system.     

风云三号气象卫星星地数据传输X频段链路干扰协调门限研究

风云三号系列气象卫星使用8025～8400 MHz频段将卫星探测数据传输给地面,该频段还有其它系统在使用,极易干扰风云三号气象卫星星地通讯,影响数据传输。目前,在该频段开展的兼容性分析研究工作中,所采取的系统关键特性参数和干扰保护限值大多数是直接引用国际电联相关建议书,没有对被干扰系统做干扰门限的精细计算,导致协调评估结果不准确,这也给该段频谱的协调使用和精细化管理等工作留下了很多潜在隐患。研究了卫星系统集总和单入干扰门限的计算方法,并根据风云三号卫星数据传输链路实际特性参数,分别得出其长期和短期集总干扰门限,并进一步研究得到来自空间长期和短期单入干扰协调门限,以及来自地面的长期和短期单入干扰协调门限,这些门限直接应用于风云三号气象卫星的频谱兼容性研究和频率协调,提高协调效率和协调精度。     

Survival of a proto-atmosphere through the stage of giant impacts: the mechanical aspects

When a giant impact occurs, atmosphere loss may occur due to global ground motion excited by a strong shock wave traveling in the planetary interior. Here, the relations between the ground motion and the amount of the lost atmosphere are systematically investigated through calculations of a spherically one-dimensional atmospheric motion for various initial atmospheric conditions. The fraction of the lost atmosphere to the total mass of the atmosphere is found to be controlled only by the ground velocity and, insensitive to the initial atmospheric conditions. Unlike the previous studies (Ahrens, 1990, Origin of the Earth, H.E. Newson, J.H. Jones (Eds.), pp. 211-227; Ahrens, 1993, Annu. Rev. Earth Planet. Sci. 21, 525-555; Chen and Ahrens, 1997, Phys. Earth Planet. Inter. 100, 21-26); the estimated loss fraction for the giant impact is only 20%. Significant escape occurs only when the ground velocity is close to the escape velocity. Thus, most of the atmosphere should survive the giant impact. The cause of the difference from previous estimates is discussed from energetic and dynamic points of view. Moreover, if our estimates are applied to the atmosphere of the impactor planet, a significant fraction of it is carried to the target planet. Survival of the proto-atmosphere has very important effects on the origin and evolution of the terrestrial planets' volatile budget.