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排序方式: 共有218条查询结果,搜索用时 109 毫秒
1.
Erman Şentürk Muhammad Arqim Adil Mohd Saqib 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(6):1937-1947
The effects of physical events on the ionosphere structure is an important field of study, especially for navigation and radio communication. The paper presents the spatio-temporal ionospheric TEC response to the recent annular solar eclipse on June 21, 2020, which spans across two continents, Africa and Asia, and 14 countries. This eclipse took place on the same day as the June Solstice. The Global Navigation Satellite System (GNSS) based TEC data of the Global Ionosphere Maps (GIMs), 9 International GNSS Service (IGS) stations and FORMOSAT-7/COSMIC-2 (F7/C2) were utilized to analyze TEC response during the eclipse. The phases of the TEC time series were determined by taking the difference of the observed TEC values on eclipse day from the previous 5-day median TEC values. The results showed clear depletions in the TEC time series on June 21. These decreases were between 1 and 9 TECU (15–60%) depending on the location of IGS stations. The depletions are relatively higher at the stations close to the path of annular eclipse than those farther away. Furthermore, a reduction of about ?10 TECU in the form of an equatorial plasma bubble (EPB) was observed in GIMs at ~20° away from the equator towards northpole, between 08:00–11:00 UT where its maximum phase is located in southeast Japan. Additionally, an overall depletion of ~10% was observed in F7/C2 derived TEC at an altitude of 240 km (hmF2) in all regions affected by the solar eclipse, whereas, significant TEC fluctuations between the altitudes of 100 km ? 140 km were analyzed using the Savitzky-Golay smoothing filter. To prove TEC depletions are not caused by space weather, the variation of the sunspot number (SSN), solar wind (VSW), disturbance storm-time (Dst), and Kp indices were investigated from 16th to 22nd June. The quiet space weather before and during the solar eclipse proved that the observed depletions in the TEC time series and profiles were caused by the annular solar eclipse. 相似文献
2.
Paul Morgan Suzanne E. Smrekar Ralph Lorenz Matthias Grott Olaf Kroemer Nils Müller 《Space Science Reviews》2017,211(1-4):277-313
The HP3 instrument on the InSight lander mission will measure subsurface temperatures and thermal conductivities from which heat flow in the upper few meters of the regolith at the landing site will be calculated. The parameter to be determined is steady-state conductive heat flow, but temperatures may have transient perturbations resulting from surface temperature changes and there could be a component of thermal convection associated with heat transport by vertical flow of atmospheric gases over the depth interval of measurement. The experiment is designed so that it should penetrate to a depth below which surface temperature perturbations are smaller than the required measurement precision by the time the measurements are made. However, if the measurements are delayed after landing, and/or the probe does not penetrate to the desired depth, corrections may be necessary for the transient perturbations. Thermal convection is calculated to be negligible, but these calculations are based on unknown physical properties of the Mars regolith. The effects of thermal convection should be apparent at shallow depths where transient thermal perturbations would be observed to deviate from conductive theory. These calculations were required during proposal review and their probability of predicting a successful measurement a prerequisite for mission approval. However, their uncertainties lies in unmeasured physical parameters of the Mars regolith. 相似文献
3.
4.
Jie Jiang Robert H. Cameron Dieter Schmitt Manfred Schüssler 《Space Science Reviews》2013,176(1-4):289-298
To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations. 相似文献
5.
Ontological Modularity and Spatial Diversity 总被引:1,自引:1,他引:0
6.
The calculation of particle trajectories in the Earth's magnetic field has been a subject of interest since the time of Störmer. The fundamental problem is that the trajectory-tracing process involves using mathematical equations that have `no solution in closed form'. This difficulty has forced researchers to use the `brute force' technique of numerical integration of many individual trajectories to ascertain the behavior of trajectory families or groups. As the power of computers has improved over the decades, the numerical integration procedure has grown more tractable and while the problem is still formidable, thousands of trajectories can be computed without the expenditure of excessive resources. As particle trajectories are computed and the characteristics analyzed we can determine the cutoff rigidity of a specific location and viewing direction and direction and deduce the direction in space of various cosmic ray anisotropies. Unfortunately, cutoff rigidities are not simple parameters due to the chaotic behavior of the cosmic-ray trajectories in the cosmic ray penumbral region. As the computational problem becomes more manageable, there is still the issue of the accuracy of the magnetic field models. Over the decades, magnetic field models of increasing complexity have been developed and utilized. The accuracy of trajectory calculations employing contemporary magnetic field models is sufficient that cosmic ray experiments can be designed on the basis of trajectory calculations. However, the Earth's magnetosphere is dynamic and the most widely used magnetospheric models currently available are static. This means that the greatest uncertainly in the application of charged particle trajectories occurs at low energies. 相似文献
7.
It is well established that the prolonged and thorough mixing of numerous nucleosynthetic components that constitutes the
matter in the solar nebula resulted in an essential isotopic homogeneity of the solar system material. This may or may not
be true for the short-lived radionuclides which were injected into or formed within the solar nebula just prior to or during
solar system formation. Distinguishing between their heterogeneous or homogeneous distribution is important because the short-
lived radionuclides are now widely used for the relative chronology of various objects and processes in the early solar system
and as constraints for models of nucleosynthesis. The recent studies of the 53Mn-53Cr isotope system (half life of 53Mn is 3.7 Ma) in various solar system objects have shown that the relative abundance of radiogenic 53Cr is consistent with essentially homogeneous distribution of 53Mn in the asteroid belt. Thus, the relative 53Mn-53Cr chronometer can be directly used for dating samples which originated in the asteroid belt. Importantly, however, all meteorite
groups studied so far indicate a clear excess of 53Cr as compared to Earth and to a lunar sample, which exhibits also a terrestrial 53Cr/52Cr ratio. The results from the Martian (SNC) meteorites show that their 53Cr excesses are less than half of those found in the asteroid belt bodies. Thus, the characteristic 53Cr/52Cr ratio of Mars is intermediate between that of the Earth-Moon system and those of the other meteorites. If these 53Cr variations are viewed as a function of the heliocentric distance, the radial dependence of the relative abundances of radiogenic
53Cr is indicated. This observed gradient can be explained by either an early, volatility controlled, Mn/Cr fractionation within
the nebula or by an initial radial heterogeneous distribution of 53Mn. Although model calculations of the Mn/Cr ratios in the bulk terrestrial planets seem to be inconsistent with the volatility
driven scenario, the precision of these calculations is inadequate for eliminating this possibility. In contrast, recent studies
of the 53Mn-53Cr system in the enstatite chondrites indicate that, while their bulk Mn/Cr ratios are essentially the same as in ordinary
chondrites, the 53Cr excess in bulk enstatite chondrites is three times lower than that in the bulk ordinary chondrites. This difference cannot
be explained by a Mn/Cr fractionation and, thus, strongly suggests that a radial heterogeneous distribution of 53Mn must have existed in at least the early inner solar system. Using the observed gradient and the 53Cr/52Cr ratio of the bulk enstatite chondrites, their parent body(ies) formed at ∼1.4 AU or somewhat closer to the Sun.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Markus J. Aschwanden Felix Scholkmann William Béthune Werner Schmutz Valentina Abramenko Mark C. M. Cheung Daniel Müller Arnold Benz Guennadi Chernov Alexei G. Kritsuk Jeffrey D. Scargle Andrew Melatos Robert V. Wagoner Virginia Trimble William H. Green 《Space Science Reviews》2018,214(2):55
Self-organization is a property of dissipative nonlinear processes that are governed by a global driving force and a local positive feedback mechanism, which creates regular geometric and/or temporal patterns, and decreases the entropy locally, in contrast to random processes. Here we investigate for the first time a comprehensive number of (17) self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous “order out of randomness”, during the evolution from an initially disordered system to an ordered quasi-stationary system, mostly by quasi-periodic limit-cycle dynamics, but also by harmonic (mechanical or gyromagnetic) resonances. The global driving force can be due to gravity, electromagnetic forces, mechanical forces (e.g., rotation or differential rotation), thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational (Balbus-Hawley) instability, the convective (Rayleigh-Bénard) instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or a loss-cone instability. Physical models of astrophysical self-organization processes require hydrodynamic, magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical formulations of self-organizing systems generally involve coupled differential equations with limit-cycle solutions of the Lotka-Volterra or Hopf-bifurcation type. 相似文献
9.
利用简化的飞机模型,通过改变尾翼的迎角及展弦比,试图建立一种能加速自我消亡的尾流涡系统.该实验在拖曳水槽中进行,运用SPIV(体视粒子图像测速技术)系统进行测量,获得了一系列空间切面的2D/3C(二维/三分量)数据,给出了三种不同尾翼情况(两种有尾翼情况及一种无尾翼情况)下的SPIV观测结果,并将这几种情况作了对比. 相似文献
10.
Experimental investigation of hot and cold side jet interaction with a supersonic cross-flow 总被引:2,自引:0,他引:2
This paper reports on experimental aerodynamic investigations on a high-speed missile with side jet control especially with regard to the interaction of cold and hot side jets with supersonic cross-flow. The hot jets were generated with solid propellants. To analyze the effect of the hot jet in relation to side jet control, wall pressure distributions were measured in the area of jet interaction. As a test parameter, the jet pressure ratio was varied and schlieren images were taken to visualize the shocks. In addition, the development of large-scale vortex structures on hot gas jets was detected with high-speed videos. The frame sequences show periodical turbulent jet structures and permit the manual evaluation of their spatial distribution. Analyzing the images, the convection velocities of the large-scale structures and their convection angles were determined. The convection velocities reach the magnitude of cross-flow velocity shortly behind the hot jet exit. 相似文献