摘要:

Measurements of the neutral wind in the polar F‐region from Dynamics Explorer‐2 (DE‐2) have been used to illustrate asymmetries in the Northern hemisphere neutral circulation that are dependent on the sign of the By(East‐West) component of the interplanetary magnetic field (IMF). Individual DE‐2 orbits and averaged data sets from different Universal times are presented. The data are categorized according to the sign of the hourly averaged IMF Bycomponent measured by ISEE‐3 for the hour preceding the DE‐2 measurement. The major features observed are: 1), an asymmetry in the polar cap neutral flow velocity with the region of most rapid anti‐sunward flow shifting from the dawn‐side to the dusk‐side of the polar cap as Bychanges from positive to negative; 2), a shift in magnetic local time of the region of entry of neutral gas into the polar cap from a location on the dawn‐side of the noon‐midnight meridian for Bypositive to one more biased towards the dusk‐side for Bynegative; 3), an enhancement in the velocities associated with the dawn, anti‐clockwise neutral vortex for Bynegative relative to those observed for Bypositive. The Byneutral wind asymmetries can be explained by similar asymmetries, previously observed, in the polar ion convection pattern. They imply a direct causal relationship between solar wind/magnetosphere coupling and neu

ISSN:0094-8276    

DOI:10.1029/GL012i004p00155

年代:1985

数据来源: WILEY

摘要:

On 24th November, 1982, The North‐South (Bz) component of the Interplanetary Magnetic Field (IMF) became positive for a period of about 11 hours reaching a relatively large and steady value of ∼25 nT. During this rare occurrence, the Dynamics Explorer‐2 (DE‐2) spacecraft was in a configuration that enabled the dynamics of both ionic and neutral species of the high‐latitude F‐region to be measured simultaneously along the track of the polar‐orbiting satellite. Results from two Northern (winter) polar passes of DE‐2, extracted from a larger data set, are shown to illustrate the response of the neutral F‐region to ion drag forcing arising from a configuration of ion convection characteristic of strongly northward IMF. The measured neutral winds differ appreciably from those more commonly observed for periods of southward IMF. The multi‐cellular ion drift pattern associated with positive Bzis observed to drive a similar but less structured and weaker neutral wind configuration in the winter polar cap. Major features of the ion drift pattern are mimicked by the neutral circulation but smaller‐scale and more irregular structures of ion flow are not. This is ascribed to the relatively long time constant (few hours) for momentum exchange between the ion and neutral gases. The results demonstrate that sunward flow of neutral gas can be established and maintained by ion drag in the central pola

ISSN:0094-8276    

DOI:10.1029/GL012i004p00159

年代:1985

数据来源: WILEY

摘要:

It is shown that isolated dipole vortices can exist in the F‐region of the ionosphere. These are associated with the Rayleigh‐Taylor and gradient drift instabilities. The vortices may be responsible for the rapid structuring of barium clouds as well as other phenomena observed in the upper ionosph

ISSN:0094-8276    

DOI:10.1029/GL012i004p00163

年代:1985

数据来源: WILEY

摘要:

The coupled time dependent continuity, momentum and energy equations of a two ion (O+and H+) quasineutral plasma were solved in order to extend our understanding of polar wind behavior. This numerical code allows studies of the time dependent behavior of polar wind‐type flows into and out of the ionosphere. Initial studies indicate that the typical time constants for electron and ion temperature changes are of the order of minutes and tens of minutes, respectively. The response time of the minor high altitude ion O+is less than an hour, whereas that of the major ion, H+, is many hours. The initial test runs also demonstrate the fact that temporary supersonic flows ofbothO+and H+are possible, especially in the presence of significant ion heatin

ISSN:0094-8276    

DOI:10.1029/GL012i004p00167

年代:1985

数据来源: WILEY

摘要:

The differential excitation cross section of O(¹D) from the ground state has been measured at 20 eV electron impact by a crossed‐beam method. The angular range covered was from 30 to 150 degrees. Atomic oxygen was generated by a thermal dissociation method (iridium oven). The measured total excitation cross section is (1.5±0.7)×10−17cm² which agrees, within the accuracy of the measurement, with the theoretical value (1.7 × 10−17cm²) calculated by Henry et

ISSN:0094-8276    

DOI:10.1029/GL012i004p00171

年代:1985

数据来源: WILEY

摘要:

Recent rocket and space shuttle experiments have demonstrated the capability to launch electron beams of moderate power (100 W to 10 kW) into the earth's ionosphere and magnetosphere. In this letter we describe how such beams, when fired from rockets or satellites, can create significant ionization in the E and F‐regions of the ionosphere. Through proper selection of beam‐related parameters, an interesting variety of plasma density structures, including plasma sheets and plasma filaments, can be created and studied over periods of 30 minutes to 1 hour, depending on the rate of plasma recombination and the density of the ambient plasma. Observations of these structures can give new information relating to the physics of plasma density structures in the ionosphere and the effects these features have upon the scattering of radio waves. It is also possible that observations of the density structures will provide a new means for studying neutral winds and electrodynamic phenomena in the ionosph

ISSN:0094-8276    

DOI:10.1029/GL012i004p00175

年代:1985

数据来源: WILEY

摘要:

Certain jovian radio emissions seem to be triggered from outside, by much weaker radio waves from the sun. Recently found in the Voyager observations near Jupiter, such triggering occurs at hectometric wavelengths during the arrival of solar radio bursts, with the triggered emissions lasting sometimes more than an hour as they slowly drifted toward higher frequencies. Like the previous discovery of similar triggered emissions at the earth, this suggests that Jupiter's emissions might also originate from natural radio lasers.

ISSN:0094-8276    

DOI:10.1029/GL012i004p00179

年代:1985

数据来源: WILEY

摘要:

High time resolution (60 ms) Voyager magnetometer and plasma wave measurements of a strong (fast Mach number 16), quasi‐perpendicular Jovian bow shock reveal an abrupt change in the plasma wave spectrum at the leading edge of the shock foot. Upstream electron plasma waves terminate at the leading edge, and are replaced by a lower‐frequency broadband spectrum of ion‐acoustic‐like waves, which terminates at the main shock ramp. The clear association with the foot region of the lower frequency component suggests that it is generated by reflected ions. If the upstream plasma waves are generated by an escaping electron heat flux, their termination at the leading edge suggests that electrons are heated by the low‐frequency waves in the s

ISSN:0094-8276    

DOI:10.1029/GL012i004p00183

年代:1985

数据来源: WILEY

摘要:

We study the characteristics of a series of disturbances observed on February 10‐11, 1982 by the plasma analyzer and the magnetometer on the Pioneer Venus Orbiter (PVO) obtained in the solar wind upstream of Venus. We conclude that the events were associated with the propagation of a solar wind disturbance of coronal origin and not with an encounter with a comet or other local outgassing object (Russell et al., 1983). The plasma analyzer spectra clearly show the presence of increases in He++and they argue strongly against Russell et al.'s interpretation. The peak in magnetic field magnitude on February 11 is identified as the magnetic signature of a thin, trailing "filament" at the end of a series of solar initiated events. Corresponding increases in He++and magnetic field fluctuations were observed near earth by ISEE‐3 about a day later, and this strongly supports the concept of a solar ori

ISSN:0094-8276    

DOI:10.1029/GL012i004p00187

年代:1985

数据来源: WILEY

摘要:

During the recent ISEE‐3 Geotail Mission three events have been identified from the magnetometer data which are consistent with a spacecraft crossing of a magnetotail flux rope. We present energetic electron and proton observations obtained by the Max‐Planck‐Institut/University of Maryland sensor system during two of the possible flux rope events. During one event remote sensing of the flux rope with energetic protons reveals that the flux rope is crossed by the spacecraft from south to north. This allows determination of the handedness of the magnetic field twist and of the flux rope velocity relative to the spacecraft. A minimal flux rope radius of 3 REis derived. Energetic proton intensity is highest just inside of the flux rope and decreases towards the core. Energetic electrons are streaming tailward near the outer boundary indicating openess of the field lines and are isotropic through the inner part of the flux

ISSN:0094-8276    

DOI:10.1029/GL012i004p00191

年代:1985

数据来源: WILEY