摘要:

Ultra‐low‐frequency modulation of ion fluxes is frequently observed by the NOAA low‐energy particle detector on the synchronous satellite ATS 6. This modulation is usually associated with simultaneous periodic variations in the magnetic field. During the first 8 months of operation, 14 ULF modulation events have been identified, all with the unusual property that maximum flux modulation occurs in the smallest pitch angle detector. This paper examines one of these events in detail to determine the properties of the flux and field variations and the phase relations between the magnetic field and the various energy channels of three differently oriented particle telescopes. For this event it is found that maximum flux modulation occurs in the 100‐ to 150‐keV detector at an angle of 32° to the ambient field. The ratio of maximum to minimum flux for this channel is 3.7 during the interval of largest magnetic perturbation. Spectral analysis of the magnetic field data shows that the magnetic perturbation had a 96‐s period and a 5‐γ rms amplitude and was right elliptically polarized, with the major axis tilted about 30° from the dipole meridian plane. The direction of propagation was in the dipole meridian at an angle of about 15° to both the ambient field and the dipole axis. Cross correlations between the principal magnetic field variation and the various proton flux measurements indicate that the lowest energy channel showing modulation in the field‐aligned detector (48–71 keV) lags the field by 180°. Higher energy channels lag by smaller amounts. Comparisons of the observation with three available wave modes, namely, the drift wave, the MHD slow wave, and the bounce resonant interaction associated with a transverse wave, are carried out in detail. It is found that none of the wave modes can explain all the correlated particle and field oscil

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00515

年代:1980

数据来源: WILEY

摘要:

It is shown that the flux increases of trapped ions and electrons observed by Explorer 45 atL≤4 during two large geomagnetic storms can be quantitatively explained by a 1–3REinward radial displacement of the preexisting trapped particle distribution. This proposed source for the storm time ring current atL≤4 requires only the acceleration of the previously existing trapped particle population via inward displacement under conservation of the first two adiabatic invariants. No source of new trapped particles atL≤4 is required. It was not possible to test whether such an inward radial displacement can account for storm time flux increases at any radial distances beyondL=4; however, the existence of particle losses implies that new particles are injected into the trapping region beyondL=4. The required inward radial displacements of the trapped particles can be explained by an equatorial electric field with an average azimuthal component of ∼0.3–1.0 mV/m, which is a factor of 2 or 3 greater than electric fields observed within the plasmasphere in association with typical, nonstorm time, substorm activity. It is suggested that a significant difference between large geomagnetic storms and typical substorm activity may be inward convection occurring over a large (≳270°) longitude range during storms but only over a small (≲90°) longitude range during

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00523

年代:1980

数据来源: WILEY

摘要:

The equatorward boundary of the diffuse auroral zone, as viewed via the 6300‐Å (O(¹D)) emission line, has been examined by using ground‐based photometer data. These observations are supplemented with in situ measurements of ionospheric parameters by satellite‐borne instrumentation within the photometer field of view. We find high spatial correlation among 6300‐Å emission, low‐energy (E<1 keV) electron precipitation, and the high‐latitude recovery of ambient electron density which constitutes the poleward cliff of the main ionospheric trough. Time resolution afforded by this ground‐based optical method is especially suited for monitoring the ionospheric signature of this low‐energy particle precipitation over broad longitudes. A model is developed of the statistical equatorward boundary of the diffuse aurora as a function of magnetic local time and magnetic activity (as monitored byKpindex). The local time dependence of this boundary exhibits a latitudinal morphology similar to that of the earthward equatorial plasma sheet—that is, asymmetric about local midnight and skewed toward lesser invariant latitude values withi

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00531

年代:1980

数据来源: WILEY

摘要:

Given auroral electron and ion distribution functions as observed with satellites in inverted V events, we construct a self‐consistent electrostatic field distribution (both parallel and perpendicular to the earth's magnetic field). This field distribution is determined by (1) magnetic mirror forces which cause charge separation for species with different pitch angle distributions; (2) Poisson's equation, which gives the electric field in terms of the charge separation; (3) the ionospheric physics of charge and current conservation, coupled with precipitation sources and recombination losses; and (4) particle distribution functions specified at the equator (and for thermal and backscattered plasma, at the ionosphere). We assume that equatorial particle distribution functions depend onLonly through the dependence of the electrostatic potential onL; an assumed factorized form for the potential allows thisLdependence to be simply parameterized. These ingredients combine to yield a self‐consistent latitudinal scale length of some tens of kilometers, typical for quiet arcs. A variety of particle and field data at and below S3‐3 altitude are fit semiquantitatively with the model. We do not consider in this paper physical processes which act in the equatorial magnetosphere, although they could well be connected to the processes we do consider through some sort of fee

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00543

年代:1980

数据来源: WILEY

摘要:

We show that the global nature of trapped particle motion in phase space makes it entirely plausible that particles with pitch angles near 90° are trapped for extremely long times, probably indefinitely. The long observed lifetimes of trapped particles can immediately be accounted for by this former population. For particles with low pitch angles an ‘overstability’ develops which serves to produce rapid variations in pitch angle and, presumably, random walk into the loss cone. Numerical calculations are needed to assess how this transition to overstability depends on particle rigi

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00557

年代:1980

数据来源: WILEY

摘要:

By combining data from the Stare auroral radar system and the Triad satellite, it has been possible to study the nature of field‐aligned current closure in the vicinity of the Harang discontinuity. For the 2 days studied the largest electric fields were directed predominantly in the north/south directions, and field‐aligned current closure was via north/south directed Pedersen currents. The concurrent electrojets were overlapping east/west directed Hall currents with the westward electrojet to the north. From the Stare‐Triad data, latitudinal profiles of the ionospheric Joule heating rate and the height‐integrated Pedersen conductivity have been calculated. The Joule heating rate maximized to the north and south of an auroral arc and had peak values of 2–4 mW/m². The height‐integrated Pedersen conductivity outside of the auroral arc was approximately 4Ω−1, whereas in the vicinity of the arc, it was in excess of 12Ω−1. These values are in good agreement with incoherent scatter and rocket measurements. The agreement is gratifying, since our technique for the calculation of the Pedersen conductivity does not require a model of the altitude‐dependent

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00563

年代:1980

数据来源: WILEY

摘要:

Satellite and rocket measurements of ion and electron density indicate that near the magnetic equator, in the nighttime (dusk) ionosphericF1region, NO+is often the dominant ion up to altitudes of 250 to 300 km. To study this region we theoretically calculate NO+, O2+, and O+ion densities by solving the coupled, time‐dependent, nonlinear ion continuity equations numerically and include the effects of production, loss and transport by diffusion and drift. Incorporation of a realistic vertical drift model which includes a prereversal enhancement in upward drift, produces NO+, O2+, and O+density profiles which are consistent with the observations. The chemical reaction O2++ N(4S) → NO++ O is an important one and acts as a sink for O2+ions and a source of NO+as theFlayer moves upward under the action of drift. Both the observations and calculations show that where NO+is the dominant ion, the electron and ion densities are nearly constant in altitude, i.e., the plasma scale height becomes very large. The implications of this on the growth of large scale irregularities are briefly discus

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00569

年代:1980

数据来源: WILEY

摘要:

In some ways the magnetosphere behaves as if merging occurs only when the interplanetary magnetic field (IMF) is southward, and in other ways it behaves as if merging occurs for all IMF orientations. An explanation of this duality is offered in terms of a geometrical antiparallel merging model which predicts merging for all IMF orientations but magnetic flux transfer to the tail only for southward IMF. This is in contrast to previous models of component merging, where merging and flux transfer occur together for nearly all IMF orientations. That the problematic duality can be explained by the model is compelling evidence that antiparallel merging should be seriously considered in constructing theories of the merging process.

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00575

年代:1980

数据来源: WILEY

摘要:

An equatorial sheet current deduced from Pioneer 10 magnetic field observations has been added to a planetary dipole field to construct a model of magnetic field due to sources inside the magnetopause. This internal field has then been used to calculate the magnetopause surface in a cyclic process to a fifth order, in cycles, at which the calculation converges. The resulting magnetopause is considerably flatter in shape than one resulting from a primarily dipole internal field source. The field internal and external to the magnetopause surface due to the currents on the surface has been computed by integrating over the entire magnetopause. A model for the total magnetospheric field of the inflated magnetosphere has been constructed by adding this latter contribution to the internal source fields to obtain a global model of an inflated Jovianlike magnetospheric field.

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00579

年代:1980

数据来源: WILEY

摘要:

High latitude riometer data from the Alaska meridian chain of stations are presented in the form of contour maps and are compared with the distribution of auroras derived from all‐sky camera observations for intervals of time during 3 days of 1973. From this comparison it has been shown that the signature of the various forms of the diffuse and discrete aurora can be readily identified in riometer data. In the early evening sector, frequently strong radio wave absorption has been observed in association with ‘trough region auroras,’ which are believed to be caused by quasi‐trapped particle populations situated equatorward of the normal diffuse aurora. Weak absorption (previously described as ‘prebay absorption’) is associated with the normal diffuse aurora. Very intense precipitation, often lasting for only a short time, accompanies westward traveling surges in the premidnight sector and is usually observed on the poleward edge of the auroral oval, although enhanced absorption may also occur equatorward of the surge in association with an enhancement of the diffuse aurora. In the midnight sector, intense absorption is coincident with the poleward expanding bulge observed after the substorm onset. Absorption events of this nature can occur simultaneously over a range of latitudes. In the morning sector, strong absorption events tend to occur near the equatorward edge of the auroral oval. These events are associated with torchlike structure or patches in the dif

ISSN:0148-0227    

DOI:10.1029/JA085iA02p00593

年代:1980

数据来源: WILEY