摘要:

Plasma waves associated with the magnetopause, from the magnetosheath to the outer magnetosphere, are examined with an emphasis on high time resolution data and the comparison between measurements by using different antenna systems. An early ISEE crossing of the magnetopause region, including passage through two well‐defined flux transfer events, the magnetopause current layer, and boundary layer plasma, is studied in detail. The waves in these regions are compared and contrasted with the waves in the adjoining magnetosheath and outer magnetosphere. Four types of plasma wave emissions are characteristic of the nominal magnetosheath: (1) a very low frequency continuum, (2) short wavelength spikes, (3) ‘festoon‐shaped’ emissions below about 2 kHz, and (4) ‘lion roars.’ The latter two emissions are well correlated with ultra‐low frequency magnetic field fluctuations. The dominant plasma wave features during flux transfer events are (1) an intense low‐frequency continuum, which includes a substantial electromagnetic component, (2) a dramatic increase in the frequency of occurrence of the spikes, (3) quasi‐periodic electron cyclotron harmonics correlated with ∼1‐Hz magnetic field fluctuations, and (4) enhanced electron plasma oscillations. The plasma wave characteristics in the current layer and in the boundary layer are quite similar to the features in the flux transfer events. Upon entry into the outer magnetosphere, the plasma wave spectra are dominated by intense electromagnetic chorus bursts and electrostatic (n+ 1/2)fg−emissions. Wavelength determinations made by comparing the various antenna responses and polarization measurements for the different w

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02087

年代:1982

数据来源: WILEY

摘要:

The analysis of the dual magnetic field profile obtained by the ISEE mission provides a unique opportunity to study the earth's magnetospheric boundaries. A survey of the magnetopause thickness over the dayside magnetosphere is carried out by using the magnetic field measurements from the twin ISEE 1 and ISEE 2 magnetometers. Since reliable measurements are possible only for small separations (<1000 km) between ISEE 1 and 2 our data set is restricted to only thirty magnetopause crossings in the range of local time from 0800 to 1700 and at GSM latitude from 2° to 35°. We find that the magnetopause is in constant rapid and irregular motion with velocities ranging, in 80% of the cases, from 10 km/s to 80 km/s and with the current sheet thickness ranging from 400 to 1000 km. The thickness seems much better ordered by dipole mangetic latitudes than by GSM latitude. Near the magnetic equator the magnetopause current sheet is thinnest, about 500 km on average. This observation suggests that reconnection is initiated in the equatorial regions rather than in the polar cusp

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02108

年代:1982

数据来源: WILEY

摘要:

The fine structure of two magnetopause crossings observed on November 10, 1977, is studied in detail as representative of a class of magnetopause observations. A so‐called magnetopause layer is observed between the magnetosheath and the magnetosphere. Changes in the magnetic field indicate that there are current sheets on each side of this magnetopause layer, and therefore does not show the smooth features of a rotational discontinuity observed on other occasions. The magnetopause layer is characterized by an irregular and a magnetosheath‐like energy distribution, part of the time with increased flow and energy compared with the magnetosheath. The flow direction deviates considerably from that of the magnetosheath. No boundary layer plasma is observed on the magnetospheric field lines inside the magnetopause layer in the cases discussed. Electromagnetic energy is dissipated at the two edges of the magnetopause layer where the current layers are observed. The two crossings are tentatively interpreted to take place on the two sides of the X line that moved because of a change of the inclination of the magnetosheath magnetic fi

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02115

年代:1982

数据来源: WILEY

摘要:

We present a detailed analysis of>24 keV ion data obtained from the ISEE 2 satellite on an inbound crossing of the magnetopause at 1130 LT on November 8, 1977, from 0200 to 0330 UT. Based on the technique presented by Williams (1979) of sounding the position of the magnetopause using energetic particle azimuthal asymmetries, we exploit the four second time resolution available on the ISEE 2 satellite to determine the location, structure, orientation, and temporal variation of the magnetopause region. We find that the trapping boundary for energetic ions is sharp and well defined for ∼35 keV ions and that it corresponds most of the time to the earthward edge of the plasma boundary layer. Usually magnetosheath plasma penetrated the trapping boundary only up to distances approximately that of the plasma (1 keV) ion gyroradius (∼100 km). On some occasions magnetosheath‐like plasma was observed up to 800 km inside the trapping boundary but these occurrences were usually associated with rapid trapping boundary movement with velocities exceeding 50 km/s. If the trapping boundary determines the position of the last closed field line, the occasional occurrence of magnetosheath plasma deep inside the trapping boundary is inconsistent with accepted merging theories. The determination of the position of the trapping boundary using five separate ion energy channels from 24 to 70 keV was internally consistent for the lowest three channels although the higher energy channels consistently indicated somewhat smaller values. Radial motion was present affecting the position of the trapping boundary on two scales; a wave‐like oscillation with a period of ∼105 s superimposed on a larger scale irregular ‘breathing’ motion. We argue that the wave nature of the trapping boundary was the cause of the slight difference between the higher and lower energy ion trapping bound

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02125

年代:1982

数据来源: WILEY

摘要:

The position of the trapping boundary for ≥24‐keV ions in the vicinity of the magnetopause has been determined using energetic particle three‐dimensional distributions observed by ISEE 1 and 2. These observations have been compared with simultaneous plasma magnetic field measurements for the 0130–0135 UT interval on November 20, 1977. The results show that for this interval the magnetosheath plasma penetration depth into the magnetosphere can be limited to a distance equal to the local plasma ion gryoradius of ≲100 km inside the position of the trapping boundary although penetration greater than 200 km was also observed. During this time the trapping boundary was in continual, rapid motion with velocities of up to ∼90 km/s. This motion could complicate the geometry and therefore explain the apparent deeper penetration of the magnetosheath plasma a few ion gyroradii inside the trapping region. If the trapping boundary, determined by this energetic particle sounding technique, is the last closed field line, then the observation of magnetosheath plasma a number of ion gyroradii earthward of the trapping boundary indicates that magnetosheath plasma is able to penetrate onto closed

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02133

年代:1982

数据来源: WILEY

摘要:

Energetic ion mass spectrometer data obtained on ISEE 1 have shown that the plasma in the subsolar magnetospheric boundary layer, magnetopause, and adjacent magnetosheath have an ionospheric component (He+and O+) in addition to the solar wind component (H+and He++). We have examined in detail nine intervals where the location of the subsolar magnetopause and boundary layer are well defined by the ISEE 1 fast plasma and magnetic filed measurements. In five of the identified boundary layer intervals, keV He+ions were observed; energetic O+ions were seen, above background, in two of the boundary layers where He+was observed. The temporal resolution of the ion mass spectrometer was too coarse to rule out the possibility of He+or O+ions being present in the four remaining intervals. Ionospheric He+ions were also observed in the magnetosheath in two (and O+in one) of the nine intervals studied.

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02139

年代:1982

数据来源: WILEY

摘要:

Several highly unusual encounters with the earth's magnetopause occurred during an ∼5‐hour period on November 22–23, 1979, when the ISEE 1 and 2 satellites were near orbit apogee (∼22.2RE) at ∼0900 local time. These distant magnetopause crossings corresponded to a subsolar earth‐magnetopause distance of ∼20.4REand were associated with a drop in solar wind dynamic pressure to a value (∼1.4×10−10dynes cm−2) ∼100 times lower than is typical. Accelerated plasma flows whose magnitude and direction were consistent with the predictions of reconnection theory were observed on each of several satellite encounters with the magnetopause and boundary layer during this 5‐hour period. Further, the field variations through the magnetopause layer suggest that the magnetopause had the structure of a rotational discontinuity as required by reconnection theory. These observations thus indicate that on occasion reconnection at the dayside magnetopause can be a quasi‐stationary process. Geomagnetic activity during this 5‐hour period, and for at least 9 hours thereafter, was extremely low. Thus dayside reconnection is certainly not a sufficient condition for e

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02147

年代:1982

数据来源: WILEY

摘要:

Plasma and magnetic field data from ISEE 1 and 2 are examined for 5 passes of the magnetopause region at 20°–40° northern latitudes and ∼0800 to 1215 hours local time. These intervals contained a total of 15 well‐defined magnetic flux transfer events, which occurred in the magnetosheath as well as the magnetosphere. In either case, flux transfer events are characterized by a mixture of magnetosheath and magnetospheric particles. This fact strongly supports the hypothesis that flux transfer events represent encounters of reconnected flux tubes. Inside all of the studied events, the magnetic field strength as well as the sum of plasma and magnetic pressures is strongly enhanced. This excess pressure appears to be balanced by the tension of the ambient magnetic field lines as they are draped around the reconnected flux tube. The different observed magnetic field signatures are consistent with expectations for encounters of the flux tubes at different relative locations. Only those events that appear to be crossings of the flux tube close to its magnetopause crossing show large (∼100 km s−1) plasma flow speed enhancements. These increased velocities are restricted to the trailing portion of the events and are directed at large angles with respect to the magnetic field. One hypothesis is that the increased flow speeds are caused by continued reconnection at the low‐latitude boundaries of t

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02159

年代:1982

数据来源: WILEY

摘要:

We have analyzed energetic proton, alpha particle, and electron measurements during two magnetopause crossings of ISEE 1 which show magnetic field signatures characteristic of flux transfer events. While the ions are streaming highly collimated along the magnetic field, the electrons show either isotropic distributions or distributions which are consistent with convected small‐scale structures. Fluxes and relative abundances of ions in flux transfer events are similar to the trapped particle values. We have also observed similar particle signatures when no change in the magnetic field normal component has been measured. During the occurrence of isotropic electron distributions, the absolute electron flux (above 75 keV) is greatly reduced when compared with the flux of the trapped electron population. Thus the electrons cannot be explained by simple leakage out of the magnetospher

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02169

年代:1982

数据来源: WILEY

摘要:

From ISEE 1 magnetopause crossings on November 10, 1977, three‐dimensional distribution functions for energetic ions (24–120 keV) are studied in the magnetosphere, through the magnetopause, and in the magnetosheath. The particle distributions are particularly examined at and near the times that Russell and Elphic (1978) identified as flux transfer events (FTE). Using a simple, one‐dimensional, quasi‐static model, particle orbits are followed numerically, from the magnetosphere into the sheath. The inner, trapped, distribution initializes the distribution function. Liouville's theorem allows the inner distribution to be mapped into the sheath following the orbits. It is found that the modeled distribution function agrees quite well with that of the observed FTE's for an inward‐pointing, normal magnetic field component and the magnitude of any reconnection‐like tangential electric field must be less than about ½ mV/m. A tangential field up to about this limit may supplement gradient and curvature drifting, repopulating freshly ‘opened’ flux tubes. Electric fields associated with tangentially convecting sheath plasma are mapped along a connected flux tube, but do little to change the distribution function of the energetic ions. A quasi‐trapped population in the sheath usually seems to ‘sandwich’ the FTE distributions. These quasi‐trapped distributions are probably due to slow, large pitch angle, outward moving particles, left behind by the outward rush of the ions more field aligned at the time the flux tube was ‘opened.’ If this interpretation is correct, the spatial extent of ‘open’ field lines near the boundary is broader, not quite as localized as previously thought, at least for this particular data. The higher energy, outflowing particles with small to large pitch angles penetrate the magnetopause several thousand kilometers from the low energy particles. This result of the model, combined with 2 of the FTE observations, gives qualitative support to the suggestion that localized tangential electric fields above our upper limi

ISSN:0148-0227    

DOI:10.1029/JA087iA04p02177

年代:1982

数据来源: WILEY