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331.
The forecast of the terrestrial ring current as a major contributor to the stormtime Dst index and a predictor of geomagnetic storms is of central interest to ‘space weather’ programs. We thus discuss the dynamical
coupling of the solar wind to the Earth's magnetosphere during several geomagnetic storms using our ring current-atmosphere
interactions model and coordinated space-borne data sets. Our model calculates the temporal and spatial evolution of H+, O+, and He+ ion distribution functions considering time-dependent inflow from the magnetotail, adiabatic drifts, and outflow from the
dayside magnetopause. Losses due to charge exchange, Coulomb collisions, and scattering by EMIC waves are included as well.
As initial and boundary conditions we use complementary data sets from spacecraft located at key regions in the inner magnetosphere,
Polar and the geosynchronous LANL satellites. We present recent model simulations of the stormtime ring current energization
due to the enhanced large-scale convection electric field, which show the transition from an asymmetric to a symmetric ring
current during the storm and challenge the standard theories of (a) substorm-driven, and (b) symmetric ring current. Near
minimum Dst there is a factor of ∼ 10 variation in the intensity of the dominant ring current ion specie with magnetic local time, its
energy density reaching maximum in the premidnight to postmidnight region. We find that the O+ content of the ring current increases after interplanetary shocks and reaches largest values near Dst minimum; ∼ 60% of the total ring current energy was carried by O+ during the main phase of the 15 July 2000 storm. The effects of magnetospheric convection and losses due to collisions and
wave-particle interactions on the global ring current energy balance are calculated during different storm phases and intercompared.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
332.
We use a simplified atmospheric general circulation model (AGCM) to investigate the response of the lower atmosphere to thermal
perturbations in the lower stratosphere. The results show that generic heating of the lower stratosphere tends to weaken the
sub-tropical jets and the tropospheric mean meridional circulations. The positions of the jets, and the extent of the Hadley
cells, respond to the distribution of the stratospheric heating, with low latitude heating displacing them poleward, and uniform
heating displacing them equatorward. The patterns of response to the low latitude heating are similar to those found to be
associated with solar variability in previous observational data analysis, and to the effects of varying solar UV radiation
in sophisticated AGCMs. In order to investigate the chain of causality involved in converting the stratospheric thermal forcing
to a tropospheric climate signal we conduct an experiment which uses an ensemble of model spin-ups to analyse the time development
of the response to an applied stratospheric perturbation. We find that the initial effect of the change in static stability
at the tropopause is to reduce the eddy momentum flux convergence in this region. This is followed by a vertical transfer
of the momentum forcing anomaly by an anomalous mean circulation to the surface, where it is partly balanced by surface stress
anomalies. The unbalanced part drives the evolution of the vertically integrated zonal flow. We conclude that solar heating
of the stratosphere may produce changes in the circulation of the troposphere even without any direct forcing below the tropopause.
We suggest that the impact of the stratospheric changes on wave propagation is key to the mechanisms involved. 相似文献
333.
Gerhard Haerendel 《Space Science Reviews》2006,124(1-4):317-331
Three types of processes, occurring in the weakly ionized plasmas of the Earth’s ionosphere as well as in the solar chromosphere,
are being compared with each other. The main objective is to elaborate on the differences introduced primarily by the grossly
different magnitudes of the densities, both with respect to the neutral and, even more so, to the plasma constituents. This
leads to great differences in the momentum coupling from the plasma to the neutral component and becomes clear when considering
the direct electric current component transverse to the magnetic field, called “Pedersen current”; in the ionosphere, which
has no quasi-static counterpart in the chromosphere. The three classes of processes are related to the dynamical response
of the two plasmas to energy influx from below and from above. In the first two cases, the energy is carried by waves. The
third class concerns plasma erosion or ablation in the two respective regions in reaction to the injection of high Poynting
and/or energetic particle fluxes. 相似文献
334.
耦合电感对多路输出电源输出纹波的影响 总被引:1,自引:1,他引:0
输出电液脉动是多路输出电源的一个重要性能指标,而耦合电感又是影响多路输出电源输出电流动的关键部件,因此需要研究耦合电感对输出电路脉动的影响,本文以两路输出电源为例,深入分析了耦合电感对输出电流脉动的影响,首先相入简单有效的数学模型,在此基础上给出了耦合电感匝比关系的一般选取原则。然后进一步分析了耦合电感各参数对输出电流脉动的影响,并提出新的调整输出纹波的方法,实验结果验证了所提方法的有效性。 相似文献
335.
研究弹性飞行器的动态耦合问题,首先导出了非定常气动力作用下的弹性飞行器的纵向运动方程。就简化的非定常气动力数学模型提出了分析气动弹性飞行器稳定性的影响方法,而后对弹性飞行器的动态耦合特性提出了定性的分析方法。并从有效抑制飞行器的弹性振动角度,研究了主动反馈控制、操纵面及陀螺位置的合适选择的协同设计问题。 相似文献
336.
主要研究了压电网络系统针对薄板的振动抑制特性,在对压电网络复合板机电耦合动力学方程分析的基础上,通过设计模拟电感电路解决了压电网络复合板振动实验中最优电感值过大的问题,从理论和实验上分析比较了电阻型和电感电阻并联型压电网络复合板振动控制效果及其特点。实验证明采用均匀化处理方法建立的机电耦合动力学方程能够正确预测压电网络复合板的动力学特性,同时实验验证了压电网络的电路模态和压电复合板的机械模态的耦合关系,明确了最优电学参数选取原则,为压电网络复合板的最优参数设计提供了依据。 相似文献
337.
基于非谐振节点理论,提出了一种改进的直接耦合矩阵综合方法。通过将非谐振节点看作谐振点,采用经典耦合矩阵综合方法得到耦合矩阵,再对矩阵作相似变换,使非谐振节点位置相对应的元素不含传输零点信息,并对其所在行列作比例变换,使其还原为非谐振节点,直接综合得到可用于设计含非谐振节点滤波器的耦合矩阵。这种综合方法简化了含非谐振节点滤波器的综合、拓扑重构和性能仿真,Matlab和HFSS仿真结果验证了这种综合方法的合理性和可行性。 相似文献
338.
对不同耦合方式下产生的电磁干扰,从其耦合机理出发,分别探析了干扰形成的过程及防护措施与实现方法,在此基础上提出了按照功能分层进行综合设计来实现系统电磁防护的有效方法。 相似文献
339.
340.