摘要:

The effect of charge transfer between solar wind alpha‐particles and hydrogen atoms of interstellar origin is revisited. Singly‐charged helium ions born in the charge transfer carry important information on processes in the solar wind and the heliosphere. The velocity distribution of such He+ions is substantially different from that of He+pick‐up ions due to ionization of the interstellar helium atoms. Estimates of the expected abundances of the charge‐exchange born He+in the solar wind are presented, and the possibility of measuring this plasma component on deep space missions is di

ISSN:0094-8276    

DOI:10.1029/92GL01277

年代:1992

数据来源: WILEY

摘要:

The curious bursts of hot ions in the inner coma of comet Halley detected by plasma instruments on the Giotto probe remain unexplained. In the present paper we discuss the possible contribution from current sheet acceleration in the near‐tail region of this comet. If the transformation of the tear‐drop shape of the magnetic field free boundary of the ionospheric contact surface to an elongated current sheet is accompanied by the formation of a magnetic neutral line, the introduction of a cross‐tail electric field could be effective in generating keV ions near the neutral line and the current sheet. The beaming of these accelerated ions towards the inner coma will likely result in the production of a secondary hot ion component with degraded energies from collisional thermalization. Such an “auroral” activity could play an important role in the energetics, ionization and dynamics of cometary io

ISSN:0094-8276    

DOI:10.1029/92GL01021

年代:1992

数据来源: WILEY

摘要:

Linear and nonlinear properties of waves excited by the mirror instability in high beta, low anisotropy (β⟂>β‖≥ 1) plasmas characteristic of the magnetosheath are investigated using linear theory and one‐dimensional hybrid simulations. The mechanisms for wave growth and saturation at low amplitudes are discussed. A new method is considered for generating the large amplitude mirror waves observed in the magnetosheath based on external compression of magnetic flux tubes. Simulations in which the anisotropy is maintained by recycling the ions shows this process can inhibit the growth of ion cyclotron waves and enhances the growth of mir

ISSN:0094-8276    

DOI:10.1029/92GL01282

年代:1992

数据来源: WILEY

摘要:

The kinetic structure of rotational discontinuities (RDs) in anisotropic plasmas withT⟂/T‖>1 is investigated by using a one‐dimensional electromagnetic hybrid code. To form the RD, a new approach is used where the plasma is injected from one boundary and reflected from the other, resulting in the generation of a traveling fast shock and an RD. Unlike the previously used methods, no a priori assumptions are made regarding the initial structure (i.e. width or sense of rotation) of the rotational discontinuity. The results show that across the RD both the magnetic field strength and direction, as well as the plasma density change. Given that such a change can also be associated with an intermediate shock, the Rankine‐Hugoniot relations are used to confirm that the observed structures are indeed RDs. is found that the thickness of RDs is a few ion inertial lengths and is independent of the rotation angle. Also, the preferred sense of rotation is in the electron sense; however, RDs with a rotation angle larger than 180° are found to be unstable, changing their rotation to a stable i

ISSN:0094-8276    

DOI:10.1029/92GL01127

年代:1992

数据来源: WILEY

摘要:

We present heretofore unreported Viking observations of sporadic AKR bursts occurring well above the electron gyrofrequency together with spiky electrostatic emissions recorded just above the lower hybrid frequency, which exhibit a high degree of correlation in time. Both types of waves show simultaneous large amplitude variations of the order of 30‐40 dB on time scales of a few hundreds of ms. Possible interpretations which may account for the observed correlation are investigated. Arguments are given which suggest that such events could be the signature of small scale non‐linear structures in the pla

ISSN:0094-8276    

DOI:10.1029/92GL01154

年代:1992

数据来源: WILEY

摘要:

A method is proposed for obtaining the in‐track wind component by exploiting the different ways in which two satellite‐borne instruments interact with the airstream. It makes possible the completion of the three‐dimensional wind vector from measurements which yield at most two components. This is especially important during geomagnetic storms when winds can cause serious errors in density measurements made by a single instrument. The method can be used to retrieve valuable information from existing data bases which contain measurements by three‐axis accelerometers and chambered instruments such as closed‐source mass spectrometers or press

ISSN:0094-8276    

DOI:10.1029/92GL01114

年代:1992

数据来源: WILEY

摘要:

Upper‐mesosphere combined optical measurements of wind and temperature fields at Amundsen‐Scott Station (South Pole) and wind radar measurements at Scott Base (78°S, 167°E) show the presence of large‐scale waves in this region of the atmosphere. At Amundsen‐Scott the largest amplitude wave observed with sub‐diurnal periodicity appears with a frequency near 2.4/day (∼10.1 hour period), with a westward phase progression of wavenumber one. The presence of a wave with this periodicity is confirmed by the observations at Scott Base. The combination of the experimentally‐found period, phase progression, associated small‐temperature oscillations, and theoretical considerations lead to the interpretation of this wave as a Lamb wave. The present combination of spatially‐resolved optical measurements and radar measurements illustrates the value of multiple‐station and multiple‐technique observations in elucidating the upper‐mesosphere dynamical state, as well as the properties of the waves propagating through the medium where the ob

ISSN:0094-8276    

DOI:10.1029/92GL01281

年代:1992

数据来源: WILEY

摘要:

A bispectral approach for temperature determination of semitransparent clouds is taken to identify areas covered by Polar Stratospheric Clouds (PSCs). The method is based upon the information obtained from two satellite pixels and two spectral channels of the passive HIRS instrument onboard the NOAA satellites. Since PSCs form and emit in very cold stratospheric environments (<195 K) solutions of the bispectral method yield low temperatures in a range that clearly differs from those derived for a cold but cloudfree stratosphere. Application of the method to NOAA satellite data gained during the major PSC event on January 31 1989 demonstrates that large areas covered by dense PSCs are found with a horizontal distribution in very good agreement to independent airborne and satellite measurements.

ISSN:0094-8276    

DOI:10.1029/92GL01065

年代:1992

数据来源: WILEY

摘要:

Modelling surface adsorption of HCl on type II PSC's, we have performed computer simulations of adsorption of HCl on single crystal ice. For stratospheric conditions, the maximum surface coverage of ice by HCl is calculated to be 10−7monolayer. This value was obtained by taking surface disorder into account. It is much too low for the reaction of HCl with chloronitrate to proceed rapidly on ordinary ice in one step. The calculated value of the surface coverage is much lower than recent experimental values for the uptake of HCl by polycrystalline ice, and the validity of the interpretation of the uptake of HCl by polycrystalline ice as being due to surface adsorption is questione

ISSN:0094-8276    

DOI:10.1029/92GL01124

年代:1992

数据来源: WILEY

摘要:

We present room temperature photo‐absorption cross sections between 180 and 340 nm for potassium nitrate dissolved in sulfuric acid‐water solutions of 0, 80, and 96% sulfuric acid by mass. Other investigators have obtained ultraviolet absorption spectra for similar solutions above 220 nm, and there is a large literature on the spectra, species, and nitration reactions in sulfuric acid solutions. The predominant nitrogen‐containing species are the nitrate anion (NO3−) in pure water or dilute sulfuric acid solutions, molecular nitric acid (HNO3) in 80% sulfuric acid, and the nitronium ion (NO2+) in 96% sulfuric acid. Upon reviewing the literature involving these species, we consider elementary ionic and molecular reactions in mechanisms of stratospheric heterogeneous catalysis. We formulate a general mechanism for acid catalyzed reactions, with examples that convert inactive HCl and ClNO3into photochemically active ClNO2, ClNO, Cl2, HOCl, and ClO, and we show that reactions forming all of these products are thermodynamically

ISSN:0094-8276    

DOI:10.1029/92GL01115

年代:1992

数据来源: WILEY