摘要:

The existence of a second ion population in addition to (mostly) protons and electrons is a common signature of laboratory and space plasmas, and even a small admixture may modify the plasma properties significantly. A bi-ion fluid approach is used to describe the collisionless coupling between the two ion populations. It is shown that the appearance of additional wave modes leads to new types of stationary nonlinear structures, such as bi-ion solitons and a magnetic pile-up boundary (or ion composition boundary). We highlight effects observed at comets and Mars. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324957

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Broadband ULF waves are routinely observed throughout the magnetosheath. These waves may be of solar wind origin or they might be generated closer to Earth, for instance, in the foreshock. Magnetohydrodynamic (MHD) wave mode conversion is a mechanism capable of delivering the energy flux carried by these ULF MHD waves to the plasma at the magnetopause. We present numerical simulations for typical subsolar magnetopause configurations. Resonant coupling to Alfve´n and slow-mode waves can occur. Energy is fed to the plasma in the resonant sheets, which can explain the enhanced ULF fluctuation level observed at the magnetopause. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324958

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Many space plasmas have an excess of superthermal particles and can be modelled by a &kgr;-distribution. While&kgr;→∞yields the Maxwellian, a low value of &kgr; describes a power-law distribution with a strongly accelerated, hard spectrum. Wave studies require the generalized plasma dispersion function, which may be expressed in terms of a hypergeometric function, making it easily usable. We review studies of waves in &kgr;-distribution plasmas, focusinginter aliaon applications to space plasmas. Wave behavior for low-&kgr; plasmas is significantly different from that found for Maxwellian plasmas. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324959

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Perturbations of electric and magnetic fields with periods of the order of 1 second are commonly observed in the auroral region by satellites and sounding rockets. The events are often accompanied by magnetic field aligned electron precipitation. The observations have been interpreted as inertial Alfve´n mode waves. A variety of theories, some of which are surveyed here, have been suggested to describe such events. Recent observations of Alfve´nic activity by sounding rockets and satellites are presented and their implications for the theoretical models are discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324960

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Preliminary results from an investigation of the helicon instability in a plasma composed of protons, electrons and singly charged oxygen ions, are presented. The velocity distribution function for each plasma component is modeled by a bi-Lorentzian distribution, which allows each particle species to possess a power law tail of arbitrary spectral index. This permits us to model accurately the shape of the power law tails observed on particle species in the plasma sheet region, where the helicon mode is believed to play an important role. The presence of a hard power law tail on the oxygen component is found to dramatically enhance the maximum growth rate of the instability when the oxygen ions possess a smallT∥>T⊥anisotropy. Above a certain value ofT∥/T⊥,however, this behavior is reversed. The growth rate decreases as the spectral index of the protons is decreased. The relevance of these effects to the central plasma sheet region is briefly discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324961

出版商:AIP    

年代:1900

数据来源: AIP