共查询到20条相似文献，搜索用时 384 毫秒
1.
DH Hathaway PA Gilman JW Harvey F Hill RF Howard HP Jones JC Kasher JW Leibacher JA Pintar GW Simon 《Science (New York, N.Y.)》1996,272(5266):1306-1309
Doppler velocity observations obtained by the Global Oscillation Network Group (GONG) instruments directly measure the nearly steady flows in the solar photosphere. The sun's differential rotation is accurately determined from single observations. The rotation profile with respect to latitude agrees well with previous measures, but it also shows a slight north-south asymmetry. Rotation profiles averaged over 27-day rotations of the sun reveal the torsional oscillation signal-weak, jetlike features, with amplitudes of 5 meters per second, that are associated with the sunspot latitude activity belts. A meridional circulation with a poleward flow of about 20 meters per second is also evident. Several characteristics of the surface flows suggest the presence of large convection cells. 相似文献
2.
The Sun's rotation profile and lithium content have been difficult to understand in the context of conventional models of stellar evolution. Classical hydrodynamic models predict that the solar interior must rotate highly differentially, in disagreement with observations. It has recently been shown that internal waves produced by convection in solar-type stars produce an asymmetric, shear layer oscillation, similar to Earth's quasi-biennial oscillation, that leads to efficient angular momentum redistribution from the core to the envelope. We present results of a model that successfully reproduces both the rotation profile and the surface abundance of lithium in solar-type stars of various ages. 相似文献
3.
Helioseismology is probing the interior structure and dynamics of the sun with ever-increasing precision, providing a well-calibrated laboratory in which physical processes can be studied under conditions that are unattainable on Earth. Nearly 10 million resonant modes of oscillation are observable in the solar atmosphere, and their frequencies need to be known with great accuracy in order to gauge the sun's interior. The advent of nearly continuous imaged observations from the complementary ground-based Global Oscillation Network Group (GONG) observatories and the space-based Solar and Heliospheric Observatory instruments augurs a new era of discovery. The flow of early results from GONG resolves some issues and raises a number of theoretical questions whose answers are required for understanding how a seemingly ordinary star actually operates. 相似文献
4.
The sun's differential rotation has a cyclic pattern of change that is tightly correlated with the sunspot, or magnetic activity, cycle. This pattern can be described as a torsional oscillation, in which the solar rotation is periodically sped up or slowed down in certain zones of latitude while elsewhere the rotation remains essentially steady. The zones of anomalous rotation move on the sun in wavelike fashion, keeping pace with and flanking the zones of magnetic activity. It is uncertain whether this torsional oscillation is a globally coherent ringing of the sun or whether it is a local pattern caused by and causing local changes in the magnetic fields. In either case, it may be an important link in the connection between the rotation and the cycle that is widely believed to exist but is not yet understood. 相似文献
5.
Sromovsky LA 《Science (New York, N.Y.)》1991,254(5032):684-686
Voyager observations suggest that three of Neptune's major cloud features oscillate in latitude by 2 degrees to 4 degrees and that two of them simultaneously oscillate in longitude by 7.8 degrees and 98 degrees about their mean drift longitudes. The observations define most convincingly the two orthogonal oscillations of the second dark spot (near 53 degrees south). These oscillations have similar periods near 800 hours and approximately satisfy a simple advective model in which a latitudinal oscillation produces a phase-shifted longitudinal oscillation proportional to the local wind shear. The latitudinal motion of the Great Dark Spot can be fit with an oscillation period of about 2550 hours, whereas its dominant longitudinal motion, if oscillatory at all, has such a long period that it is not well constrained by the Voyager data. 相似文献
6.
高寒冷凉区马铃薯地膜栽培生态效应研究 总被引：7，自引：0，他引：7
2001～2002年连续两年在方山县马坊镇对马铃薯覆膜后气候生态效应进行了试验研究,结果表明,地膜覆盖有明显的增温效应,苗期增温效应最为明显,随着马铃薯的生长发育,覆盖增温效应逐渐降低;表层增温显著,且随土层向下延伸,增温趋向递减;缩短了生育期,提早成熟上市;拓展了品种推广领域,打破了高寒冷凉区不能种晚熟品种的禁区;增产率达25.63%～36.05%,对提高高寒冷凉区马铃薯产量效益有重要的意义。 相似文献
7.
Vorontsov SV Christensen-Dalsgaard J Schou J Strakhov VN Thompson MJ 《Science (New York, N.Y.)》2002,296(5565):101-103
Bands of slower and faster rotation, the so-called torsional oscillations, are observed at the Sun's surface to migrate in latitude over the 11-year solar cycle. Here, we report on the temporal variations of the Sun's internal rotation from solar p-mode frequencies obtained over nearly 6 years by the Michelson Doppler Imager (MDI) instrument on board the Solar and Heliospheric Observatory (SOHO) satellite. The entire solar convective envelope appears to be involved in the torsional oscillations, with phase propagating poleward and equatorward from midlatitudes at all depths throughout the convective envelope. 相似文献
8.
Observations of solar p-mode frequency splittings obtained at Big Bear Solar Observatory in 1986 and during 1988-90 reveal small ( approximately 1 percent) changes in the sun's subsurface angular velocity with solar cycle. An asymptotic inversion of the splitting data yields the latitude dependence of the rotation rate and shows that the largest changes in the angular velocity, approximately 4 nanohertz, occurred between 1986 and the later years, at high ( approximately 60 degrees ) solar latitudes. Earlier helioseismic observations suggest that solar cycle changes in the ratio of magnetic to turbulent pressure in the solar convection zone are large enough to account for the magnitude of the observed angular velocity variations but a detailed model of the phenomenon does not exist. 相似文献
9.
Crisp D Sinton WM Hodapp KW Ragent B Gerbault F Goebel JH Probst RG Allen DA Pierce K Stapelfeldt KR 《Science (New York, N.Y.)》1989,246(4929):506-509
Near-infrared images of the Venus night side show bright contrast features that move from east to west, in the direction of the cloud-top atmospheric superrotation. Recently acquired images of the Venus night side along with earlier spectroscopic observations allow identification of the mechanisms that produce these features, their level of formation, and the wind velocities at those levels. The features are detectable only at wavelengths near 1.74 and 2.3 micrometers, in narrow atmospheric windows between the CO(2) and H(2)O bands. The brightest features have brightness temperatures near 480 Kelvin, whereas the darkest features are more than 50 Kelvin cooler. Several factors suggest that this radiation is emitted by hot gases at altitudes below 35 kilometers in the Venus atmosphere. The feature contrasts are produced as this thermal radiation passes through a higher, cooler, atmospheric layer that has horizontal variations in transparency. The 6.5-day east-west rotation period of the features indicates that equatorial wind speeds are near 70 meters per second in this upper layer. Similar wind speeds have been measured by entry probes and balloons at altitudes between 50 and 55 kilometers in the middle cloud layer. The bright features indicate that there are partial clearings in this cloud deck. The presence of these clearings could decrease the efficiency of the atmospheric greenhouse that maintains the high surface temperatures on Venus. 相似文献
10.
Radar observations of Mars with a surface resolution of 1.3 degrees in latitude and 0.8 degrees in longitude have been carried out during the opposition of 1971. With a precision in surface height measurement approaching 75 meters in regions of high reflectivity, it has been possible to measure the detailed characteristics of a number of craters. Many of these can be identified with craters shown in Mariner photographs of Mars. In addition, a scarp has been seen at 41 degrees west, 14 degrees south with an average slope of about 6 degrees extending over about 40 kilometers. 相似文献
11.
Radar observations of a narrow belt of the surface of Mars, centered at 16 degrees south latitude, show a very rugged terrain, with elevation differences greater than 13 kilometers from peak to valley. For nearby points, the relative altitude is measured to 40 meters at best; the precision is worse for points at different latitudes, or widely separated in longitude, because of orbital uncertainties. Some of the larger craters have been resolved, and their depth and, in some cases, the height of the raised rim have been measured. Where high resolution photographs, are available, the correlation is excellent. 相似文献
12.
The Mars Odyssey Thermal Emission Imaging System (THEMIS) has discovered water ice exposed near the edge of Mars' southern perennial polar cap. The surface H2O ice was first observed by THEMIS as a region that was cooler than expected for dry soil at that latitude during the summer season. Diurnal and seasonal temperature trends derived from Mars Global Surveyor Thermal Emission Spectrometer observations indicate that there is H2O ice at the surface. Viking observations, and the few other relevant THEMIS observations, indicate that surface H2O ice may be widespread around and under the perennial CO2 cap. 相似文献
13.
Reck RA 《Science (New York, N.Y.)》1976,192(4239):557-559
Calculated surface temperature changes, DeltaT(8), due to stratospheric ozone depletion (at 35 degrees N latitude in April) are less than previously estimated and range between -0.6 and +0.9 degrees K. The sign of DeltaT(8), is determined by the surface albedo and the presence or absence of a low-lying particulate layer (heating with particles, cooling without particles). The calculations indicate that a 90 percent stratospheric ozone depletion does not cause the temperature inversion at the tropopause to vanish, although it is weakened substantially. 相似文献
14.
Globally coherent oscillation modes were discovered in the sun about a decade ago, providing a unique seismological probe of the solar interior. Current observations detect modes that are phase-coherent for up to 1 year, with surface velocity amplitudes as low as 2 millimeters per second, and thousands of mode frequencies have been measured to accuracies as high as 1 part in 10(5). This article discusses the properties of these oscillation modes and the ways in which they are adding to our understanding of the structure and dynamics of the sun. 相似文献
15.
铜陵杨山冲尾矿库能源植物生产示范基地的特征化 总被引：6，自引：0，他引：6
对铜陵杨山冲尾矿库能源植物生产示范基地尾砂的基本理化性质和污染特征进行了研究,结果表明：基地表层尾砂pH空间变异很大（oH2．65～9．02）,基地西南端尾砂呈碱性,平均容重为1．82g／cm^3;东北端呈酸性,平均容重为1．17g／cm^3,酸化只发生在尾砂表层20cm。0．43mol／L HNO3提取态（吸附态）As、Cu、Zn、Pb、Cd以及0．1mol／LNaNO3提取态（有效态）Cu、Zn含量水平较高,不同提取态重金属空间分布存在较大差异。研究结果初步明确了尾矿库能源植物生长的限制因子,为下一步筛选尾砂改良剂奠定了基础。 相似文献
16.
Observations made from the Viking I orbiter show very little water vapor in the Mars atmosphere in the southern hemisphere (0 to 3 precipitable micrometers) with a gradual increase across the equator to northern latitudes. Maximum amounts between 20 and 30 micrometers have been observed in the short period covered by the observations to date. The season, northern midsummer, corresponds to the beginning of the water vapor cycle in that hemisphere. A strong repetitive diurnal cycling between the solid and vapor phases is observed at a site to the east of the Tharsis Ridge at 10 degrees north latitude; the vapor lies close to the martian surface and is most probably in saturation equilibrium with a surface haze or fog throughout much of the day. 相似文献
17.
[目的]木榫旋转焊接是木结构、家具中的一种新型绿色连接技术,国内外对于竹榫旋转焊接研究较少,其最佳焊接工艺参数未知,竹榫、木榫旋转焊接之间的差异也有待研究.[方法]使用毛竹榫旋转焊接云杉基材,通过测试焊接形成的连接节点的抗拉拔性能,探究竹榫旋转焊接较优的工艺参数.选取基材预钻孔与竹榫直径比值(孔径比)、竹榫转速、竹榫含... 相似文献
18.
利用常规高空和地面形势场资料对2012和2013年的2次春季暴雪过程进行对比分析,结果表明,中高纬脊前冷空气不断补充,促使浅槽加深东移,低空西南急流建立,均为丹东地区暴雪提供有利环流背景和动力、水汽条件;地面倒槽顶部暖切变以及蒙古低压槽前切变是暴雪直接影响系统;中低层温度的分析是春季降雪预报的关键点,前期冷空气波动以及各层温度的垂直变化,尤其是低层逆温层的分析,均可以为判断降雪相态预报提供依据。 相似文献
19.
Sunspots, dark magnetic regions occurring at low latitudes on the Sun's surface, are tracers of the magnetic field generated by the dynamo mechanism. Recent solar dynamo models, which use the helioseismically determined solar rotation, indicate that sunspots should form at high latitudes, contrary to observations. We present a dynamo model with the correct latitudinal distribution of sunspots and demonstrate that this requires a meridional flow of material that penetrates deeper than hitherto believed, into the stable layers below the convection zone. Such a deep material flow may have important implications for turbulent convection and elemental abundance in the Sun and similar stars. 相似文献
20.
Taylor FW Diner DJ Elson LS Hanner MS McCleese DJ Martonchik JV Reichley PE Houghton JT Delderfield J Schofield JT Bradley SE Ingersoll AP 《Science (New York, N.Y.)》1979,203(4382):779-781
Orbiter infrared measurements of the Venus atmosphere in the 60- to 140-kilometer region show very small diurnal temperature differences near the cloud tops, increasing somewhat at higher levels. The seasonal (that is, equator to pole) contrasts are an order of magnitude larger, and the temperatures unexpectedly increase with increasing latitude below 80 kilometers. An isothermal layer at least two scale heights in vertical extent is found near the 100-kilometer altitude, where the temperature is about 175 K. Structure is present in the cloud temperature maps on a range of spatial scales. The most striking is at high latitude, where contrasts of nearly 50 K are observed between a cold circumpolar band and the region near the pole itself. 相似文献