摘要:

Previous work indicates that coronal mass ejection (CME) events in the solar wind at 1 AU can be identified by the presence of a flux of counterstreaming solar wind halo electrons (above about 80 eV). Using this technique to identify CMEs in 1 AU plasma data, we find that most large geomagnetic storms during the interval surrounding the last solar maximum (Aug. 1978 – Oct. 1982) were associated with Earth‐passage of interplanetary disturbances in which the Earth encountered both a shock and the CME driving the shock. However, only about one CME in six encountered by Earth was effective in causing a large geomagnetic storm. Slow CMEs which did not interact strongly with the ambient wind ahead were particularly ineffective in a geomagnetic se

ISSN:0094-8276    

DOI:10.1029/GL017i007p00901

年代:1990

数据来源: WILEY

摘要:

Upstream waves have been postulated to be a major source of energy for the dayside magnetic pulsations within the magnetosphere. Thus it is of interest to determine over what frequency range in the ion foreshock the power of fluctuations in the solar wind is enhanced. We have examined the magnetic field data from pairs of spacecraft when they are on either side of the ion foreshock boundary. We find that the power of magnetic fluctuations is enhanced only at periods less than about two minutes, not at longer periods. Thus the upstream waves may contribute to Pc 3 and Pc 4 pulsations in the dayside magnetosphere, but they can not be directly responsible for the longer period waves.

ISSN:0094-8276    

DOI:10.1029/GL017i007p00905

年代:1990

数据来源: WILEY

摘要:

When the interplanetary magnetic field is northward, wave‐particle cross‐field transport may contribute to solar wind‐magnetosphere coupling. Such transport is studied here through the use of hybrid computer simulations (particle ions, fluid electrons with nonzero mass) carried out in thex‐yplane of a plasma with a density gradient in thexdirection, no average iow speed, and a magnetic field B =B(x)ž. At early times, the lower hybrid drift instability grows on the gradient. However, at times long compared to an ion gyroperiod, the fluctuations coalesce to longer wavelengths in they‐direction and nondiffusive densityx‐profiles emerge which exhibit “plateaus” and “inclusions” qualitatively similar to those observed by ISEE near the magnetopause. These results call into question critical assumptions of quasilinear theories of cross‐field transpo

ISSN:0094-8276    

DOI:10.1029/GL017i007p00909

年代:1990

数据来源: WILEY

摘要:

An examination of IMP‐8 tail lobe magnetic field measurements has been conducted to determine whether the traveling compression region (TCR) phenomena detected by ISEE‐3 in the distant geotail, and believed to be caused by tailward moving plasmoids, are present closer to the earth. The study produced 16 examples of TCRs at distances of X = −31 to −37 RE. For two events considered in detail TCRs were observed in close association with substorm growth phase signatures in the lobes. The lengths of these TCRs are estimated to be 8–12 RE. It is our conclusion that the IMP‐8 TCR observations provide new evidence that small plasmoids and, hence, multiple reconnection neutral lines can exist earthward of

ISSN:0094-8276    

DOI:10.1029/GL017i007p00913

年代:1990

数据来源: WILEY

摘要:

We apply a two‐dimensional, nonlinear hydromagnetic computer code to the problem of pure fast mode cavity resonances in a box model of the magnetosphere. The cavity modes are excited by a magnetopause compression and relaxation with maximum boundary velocityv0. The results show that significant mass transport of relatively low energy plasma by the wave fields may be possible forv0/A0∼ 0.2, whereA0is the Alfvén speed at the boundary. For a likely field‐aligned perturbatiou structure, the mass tends to accumulate at and near the equatorial plane. We interpret this mass transport as being driven by the ponderomotive force, which is finally limited by opposing pressure gradients in a finite β plasma. Heating by adiabatic compression of the plasma is al

ISSN:0094-8276    

DOI:10.1029/GL017i007p00917

年代:1990

数据来源: WILEY

摘要:

We present and analyze sounding rocket and HILAT satellite measurements of the low frequency (Σp−1, which we argue to be due to the presence of Alfvén waves incident from the magnetosphere and reflecting from the lower ionosphere, forming a standing wave pattern. These waves may represent an electromagnetic coupling mechanism between the auroral acceleration region

ISSN:0094-8276    

DOI:10.1029/GL017i007p00921

年代:1990

数据来源: WILEY

摘要:

Effects of temperature anisotropies on the early stage refilling of the outer plasmasphere are studied by solving an appropriate set of hydrodynamic equations. The anisotropies result from the supersonic outflows from the conjugate ionospheres and from the perpendicular ion heating in the equatorial region. The equatorial ion heating affected by wave‐particle interaction is included phenomenologically. Even for the equatorial heating associated with moderate wave levels, the mirror force on the flows severely limits the interhemispheric plasma exchange. The temporal evolution of the flow developing in an empty flux tube is characterized by: (1) supersonic plasma outflows from the conjugate ionospheres, (2) reflections of the flows by the mirror force as they begin to penetrate into the opposite hemispheres, (3) formation of shocks in the reflection region and (4) propagations of the shacks to the ionospheres of the origins of the flows. In the quasi‐steady state when flow completely subsides, the density distribution in the flux tube shows distinctive large‐scale features, determined by the balance between electric, pressure and anisotropy forces. The latter force becomes significant in a broad equatorial region where Tt>>Tpand also at relatively high geomagnetic latitudes where Tt<

ISSN:0094-8276    

DOI:10.1029/GL017i007p00925

年代:1990

数据来源: WILEY

摘要:

We describe a new two‐frequency lidar for measuring Na temperature profiles that uses a stabilized cw single‐mode dye laser oscillator (rms frequency jitter<1 MHz) followed by a pulsed‐dye power amplifier (140 MHz FWHM linewidth) which is pumped by an injection‐locked Nd: YAG laser. The laser oscillator is tuned to the two operating frequencies by observing the Doppler‐free structure of the Na D2fluorescence spectrum in a vapor cell. The lidar technique and our initial observations of the temperature profile between 82 and 102 km at Ft. Collins, CO (40.6°N,105°W) are described. Absolute temperature accuracies at the Na layer peak of better than ±3 K with a vertical resolution of 1 km and an integration period of approximately 5 min w

ISSN:0094-8276    

DOI:10.1029/GL017i007p00929

年代:1990

数据来源: WILEY

摘要:

A parameterization of the mechanisms believed to be responsible for the quasi biennial oscillation (QBO) in the zonal winds of the equatorial lower stratosphere has been added to a fully interactive dynamical radiative photochemical two dimensional model of the atmosphere. In addition to a well defined QBO in the zonal winds, temperature and column ozone, the model exhibits a strong QBO signal in many of the other modelled trace gases. Large year to year variations, in some cases up to 70 %, are predicted. The importance of taking this prediction into account when measuring and interpreting the distributions of these gases is emphasized.

ISSN:0094-8276    

DOI:10.1029/GL017i007p00933

年代:1990

数据来源: WILEY

摘要:

The historic trend of the levels of gaseous H2O2during 1960's–1980's in Los Angeles was assessed from field date and numerical simulations. The results indicate that during 1960's–1970's concentrations of H2O2, as well as O3, were likely to have been higher than those during 1980's, For the period 1969–1987, predicted summer peak concentrations of H2O2and O3in the ground level atmosphere were in a range of 6–10 ppb and 200–350ppb, respectively. Also H2O2and 03concentrations decreased by about 35% and 42% respectively from the levels of 1975 to 1987. Model simulations indicated that the reduction of NMHC and CO emissions from industrial and automotive sources have resulted in the decrease in H2O2levels during the late 1970's–1980's, whereas the reduction of NMHC, CO and NOxemissions have resulted in lower O3levels. The role of H2O2as an oxidant for SO2and as a possible toxin on trees in Los Angeles and surrounding mountains during the past decades are discussed. From the historic data of atmospheric levels of sulfate in Los Angeles, we suggest that the decrease in the levels of H2O2and O3may have contributed to the decrease in sulfite levels during

ISSN:0094-8276    

DOI:10.1029/GL017i007p00937

年代:1990

数据来源: WILEY