摘要:

At the time of a sudden commencement or even of a sudden impulse, very‐low‐frequency waves can be excited. In turn, the wave turbulence drives the pitch‐angle diffusion of energetic electrons trapped in the magnetosphere, causing them to be precipitated into the lower ionosphere. The distribution of this precipitation as a functon of geomagnetic latitude and local time is shown to be directly related to the characteristics of the magnetic disturb

ISSN:0148-0227    

DOI:10.1029/JA077i001p00101

年代:1972

数据来源: WILEY

摘要:

The absolute intensity of geomagnetically trapped protons in the energy ranges 0.52 ≤Ep≤ 4.0 Mev and 0.90 ≤Ep≤ 1.8 Mev has been measured with the solid‐state proton detector on the University of Iowa low‐altitude (initial apogee 2502 km, perigee 527 km) high‐latitude (inclination 81°) satellite Injun 4 for the period from March 1 to May 31, 1965. A study of the temporal variations of these fluxes associated with the April 17, 1965, magnetic storm (sc 1313 UT April 17, main phase onset ∼0200 UT April 18) shows a general redistribution of these protons forL≳ 2.5 and all sampled |B| ranges, which persisted for at least 36 days after the storm. The effect of the sudden commencement was a general depression in the intensities and a hardening of the energy spectrums, although the intensities recovered to their prestorm level during the initial phase. The major redistribution was apparently initiated by the polar substorm that began at ∼0620 UT on April 18 and continued long after (to 1100 UT) the substorm had subsided (∼0800 UT). During the recovery phase, a secondary peak developed in the intensity profile atL∼ 3.5 for 0.52‐Mev protons that had no counterpart at this energy at the equator (L. R. Davis, private communication, 1971). No such peak was observed for 0.9‐Mev protons. The over‐all effect of the storm on the steady‐state distribution was a nonadiabatic one with an increase in intensities atL≲ 3 and a decrease atL≳ 3. The loss and/or gain of particles appears to be fractionally the same at all |B| values sampled here. The post‐storm dependence of the spectral parameterE0onLgenerally follows the relationE0∝L−3, although the prestorm dependence cannot be described by a simple function at allLvalues. The appearance of a secondary peak and the behavior of the prestorm and post‐storm spectrums are in qualitative agreement with the predictions of the bimodal diffusion model ofTheodoridis et al.[1969], whereby the sola

ISSN:0148-0227    

DOI:10.1029/JA077i001p00112

年代:1972

数据来源: WILEY

摘要:

Independent measurements of the plasmapause and associated thermal plasma structure from Ogo 3 are compared with ground‐based Pc 1 observations from the period 1966‐67. Substantial agreement between the plasmapause crossings identified on the satellite and the Pc 1 occurrence positions observed on the ground at midlatitudes during the nighttime (including dawn and dusk) indicates that these nighttime Pc 1 events are closely associated with the plasmapause. A correlation of selected closely spaced events obtained in the nighttime under quiet to moderate activity (Kpequal to or less than 4) provides good agreement in the proton concentrations near the plasmapause boundary. Examination of plasma fine structure reveals distinct plasma irregularities near the plasmapause in the afternoon‐dusk local‐time sector and at the other locations during the recovery phase of a magnetic storm. Preliminary results indicate Pc 1 excitation is associated with plasma irregularities near the plasmapause and is particularly favorable in the region of ‘post‐storm recovery’ and in the region of diurnal ‘plasma bulge’ in the afte

ISSN:0148-0227    

DOI:10.1029/JA077i001p00131

年代:1972

数据来源: WILEY

摘要:

Quasi‐sinusoidal magnetic‐field oscillations (micropulsations) are regularly observed at ATS 1 during geomagnetic storms. The wave events typically occur during the main phase and tend to be confined to the afternoon sector. All observed events have been closely correlated with magnetospheric substorm activity. Power spectral analysis shows that the observed oscillations are composed of harmonically related components. Twenty‐six wave events were observed in 1967; the analysis of three typical Pc 5 events is presented here. The observations are compared with the predictions of theory for a hot (β ≳ 1) inhomogeneous plasma. It is suggested that the observed micropulsations can be understood as the occurrence of either an Alfvén wave instability, or a drift instability, of the enhanced storm‐time ring current. However, it is concluded that the proposed models require further refinement for a definitive explanation of the o

ISSN:0148-0227    

DOI:10.1029/JA077i001p00143

年代:1972

数据来源: WILEY

摘要:

The magnetic field in the tail region observed by the Imp 1 satellite was compared with geomagnetic‐micropulsation activities detected by ground‐based observations at Ralston, Alberta, Canada. The tail field strength was found to decrease, typically by one to a few gammas, in simultaneity with the onset of a Pi 2 micropulsation activity detected on the ground. Several tens of such examples were obtained during continuous rapid‐run micropulsation observations for about a week. During the same time interval, four Pc 3 micropulsation events took place with clearly identifiable onsets—an unusual feature for Pc 3. The tail field followed a characteristic pattern of evolution in each of the four events. In a period of about one‐half hour to one and one‐half hours before a Pc 3 onset the tail field strength gradually built up, and with the onset it abruptly decreased by several gammas. Whereas a sudden onset‐time decrease in the tail field strength is common to Pi 2 and Pc 3, Pc 3 activity is found to diminish in sympathy with a gradual tail field decrease over a time of about twenty minutes or more, provided that the tail field decrease exceeds abo

ISSN:0148-0227    

DOI:10.1029/JA077i001p00159

年代:1972

数据来源: WILEY

摘要:

This paper presents a study of auroral‐zone VLF hiss and low‐energy charged‐particle observations with the Injun 5 satellite. The results of this study provide a direct verification of the association between auroral‐zone VLF hiss and intense fluxes, 104to 107electrons (cm² sec ster ev)−1, of low‐energy electrons with energies on the order of 100 ev to several kev. On the dayside of the magnetosphere, these low‐energy electrons are identified with the dayside polar‐cusp region observed at higher latitudes with the Imp 5 satellite. At other local times, through the dawn and dusk regions and into the nightside of the magnetosphere, the VLF hiss and low‐energy electron precipitation regions are believed to correspond to the extension of the dayside polar cusp into the distant plasma sheet and downstream magnetosheath on the nightside of the magnetosphere. Intense fluxes of upgoing electrons are often observed in a narrow latitudinal band near the low‐energy electron precipitation bands. These upgoing electrons are believed to be associated with another type of VLF emission called a saucer, which is frequently observed with Injun 5. On the basis of present models, the observed VLF hiss intensities cannot be accounted for by incoherent Cerenkov radiation from the observed electron fluxes, thus indicating that a coherent plasma instability mechanism is involved in some, if not all, of the VLF hiss generation. A model for the generation regions of VLF hiss and saucer em

ISSN:0148-0227    

DOI:10.1029/JA077i001p00172

年代:1972

数据来源: WILEY

摘要:

A sounding rocket was launched in the early evening into an auroral display during a 50‐γ positive bay. The flight path carried the rocket over the two most northerly arcs in a band of parallel east‐west oriented arcs, into a region of low activity to the north of the band, and then into a large fold northeast of the launch site. Several times during the flight, intense field‐aligned electron pitch‐angle distributions (i.e., peaked near 0°) were observed; these regions were found to be coincident with the northern boundary of the band of auroral precipitation. No equivalent distributions were observed between arcs to the south. Electron intensities of about 1011(cm² sec ster kev)−1peaked near β = 0 were observed at 0.55 kev, and electrons near this energy were conservatively estimated to carry a current of 2 × 10−4amp/m². This electron current sheet was estimated to have a large east‐west extent and a north‐south thickness of 10 km, and under certain conditions would produce a transverse magnetic field of 10³ γ. Field‐aligned 7.8‐kev electrons were also observed in the boundary region with intensities (∼3 × 109(cm² sec ster kev)−1), a factor of 10 larger than that observed at any other time in the flight. Energetic electron (E>25 kev) pitch‐angle distributions were found to be generally antisotropic peaked near 90°; however, at times of maximum intensities, the distributions approached isotropy. Energetic proton (E>30 kev) intensity profiles obtained during the flight were featureless, and pitch‐angle distributions were anisotropic, peaked near 90°. No correlation with electron intensities was apparent; however, the proton pitch‐angle distributions gradually shifted toward isotropy on two occasions of intense electron precipitation (near the center of the arc). This minor correlation wag not considered statistically significant. Low‐energy ion precipitation was below the limit of detectability, and an upper limit on the primary ion beam was set at 5 × 105(cm² sec ster kev)−1and the 1‐ to 20‐kev energy range. Most characteristics of particle precipitation observed in the boundary region are shown to be consistent with a local acceleration from a parallel ele

ISSN:0148-0227    

DOI:10.1029/JA077i001p00191

年代:1972

数据来源: WILEY

摘要:

A model of theF1layer is set up with a basic structure essentially the same as anE‐layer model recently published by Keneshea, Narcisi, and Swider. The models yield almost identical results for the same input parameters. Using the model in this form, observed and calculated diurnal variations of electron density at Sanae (70°S, 2°W,L= 4) are compared for heights from 120 to 200 km for selected days during the 6‐month period June to December 1966. The first continuous solution of the ion concentrations O+, O2+, NO+, and N2+for a high‐latitude station is presented. It is found that fair agreement in electron plasma frequency (within a factor of 2) is obtained after about November 4. The agreement becomes steadily worse as one draws nearer to winter, and the model is totally inadequate to explain the bulk of ionization observed in theF1layer in winter. Because several recent papers have reported large fluxes of low‐energy electrons both at middle and high latitudes, an estimate is made of the electron fluxes and energy spectra that would be required to explain the diurnal densities observed on 1 day in June (29) and on 1 day in November (4). Energy fluxes are of the same magnitude as observed by Schield and Frank. The energy spectrum is also of the form exp (−E/Eo), becoming harder towards midday. In winterEo≈ 0.25 kev and in summer ≈1 kev. This hardening of the spectrum from winter to summer is consistent with observations. It is found that the total energy flux at midday and midnight does not change with season. These results are consistent with N2+emissions ob

ISSN:0148-0227    

DOI:10.1029/JA077i001p00203

年代:1972

数据来源: WILEY

摘要:

A rocket‐borne vector magnetometer has been used to infer the current magnitude, direction, and distribution of midlatitude ionospheric currents near sporadicE. The payload, comprising a scalar magnetometer with bias coil and a solar aspect sensor for determining vehicle attitude, was launched via a Nike‐Apache sounding rocket from Wallops Island, Virginia, at 0705 local time (1205 UT) on August 7, 1968. Complete vector information returned throughout the flight indicates that a southward equivalent surface current (vertically integrated current) of 0.15 amp/m was encountered between the altitudes of 104 and 118 km in both ascending and descending portions of the flight. Vertical distribution of the current within the layer was approximately uniform, and the layer was found to be horizontal within the accuracy of the experiment. The data are consistent with the assumption that a sporadic‐Elayer observed by Wallops Island ionosondes significantly altered the usualSqcurrent flow pattern by concentrating the current into a narrow altitude range, and by horizontally focusing the current flow into the sporadic‐Eregion with attendant reduction of current density outside the region. Such an effect is discussed in relation to previous theoretic

ISSN:0148-0227    

DOI:10.1029/JA077i001p00212

年代:1972

数据来源: WILEY

摘要:

Consideration is given to a low‐frequency mode of instability that can arise in a partly ionized plasma as a result of an electron temperature gradient aligned perpendicular to a magnetic field. The irregularities so produced are essentially thermal in nature but are associated with related electron density fluctuations. The unstable mode propagates at approximately the electron drift velocity in a direction essentially perpendicular to the magnetic‐field lines. An additional requirement for instability is that there should exist an electron density gradient having a component in the direction of and of the same sign as the electron temperature gradient. It is also necessary that the scale for the electron density variation should be roughly a factor of 7/3 greater than the scale of the electron temperature variation. Application of this instability to the ionosphere is considered. It is found that the energy loss from the electron gas by virtue of collisions with ionized and neutral particles prevents the occurrence of this instability under most ionospheric conditions. However, if electron temperature variations on the scale of about a kilometer were to exist in the auroral ionosphere, for example, field‐aligned irregularities of size 10–100 meters could be produced as a result of this instability at altitudes above about

ISSN:0148-0227    

DOI:10.1029/JA077i001p00224

年代:1972

数据来源: WILEY