ISSN:0048-6604    

DOI:10.1029/RS008i011p00891

年代:1973

数据来源: WILEY

摘要:

Harbingers of significant magnetospheric motions consist of the interactions of interplanetary discontinuities with the standing bow shock. The most common discontinuity is the tangential discontinuity. Less frequent in occurrence, but of major significance to subsequent magnetospheric dynamics, is the flare‐generated interplanetary shock wave and its initiation of bow shock and magnetopause motion toward Earth. Early studies utilized the ordinary gas‐dynamic analogy of the well‐known Riemann splitting of an initial discontinuity (i.e., bow shock) into a reflected shock (the moving bow shock) and the transmitted shock (the inward‐moving interplanetary shock). It was shown that order‐of‐magnitude pressure increases at the subsolar point of the magnetopause are readily found for typical shock‐on‐shock studies. Phenomenological studies also demonstrated, in agreement with observations, that the magnetopause motion could be predicted on the basis of quasi‐static variation of the solar wind dynamic pressure. Recent hydromagnetic studies (for the simplified case of perpendicular shocks) have extended the theory to predict bow shock and magnetopause velocities which appear to be observed by spacecraft. Such one‐dimensional studies provide upper limits for all average plasma parameters within the region of the Sun‐Earth axis. The general case of the time‐dependent interaction in three dimensions has, as yet, not been done. Nevertheless, the general configurational and plasma details are, in principle, amenable to examination with the use of multiple spacecraft measurements during the interaction and the ensuing dynamic motions on a time scale of tens of min to the several hr required for the magnetopause to move to smaller geocentric distances. The physical processes of various energy transfers from kinetic to thermal and magnetic as predicted by the hydromagnetic theory could then be assessed by study of the plasma average velocity, direction of flow, magnetic field, temperature, and density.The magnetosheath plasma properties following such interactions could, on a more speculative note, provide new boundary conditions (associated with appropriate magnetosheath and magnetosphere magnetic field polarities) which could, in turn, initiate and drive the reconnection process

ISSN:0048-6604    

DOI:10.1029/RS008i011p00893

年代:1973

数据来源: WILEY

摘要:

To the present date only the reconnection process for exactly antiparallel fields has been discussed in detail. In magnetospheric terms this restricts us to the consideration only of southward interplanetary fields. The qualitative study presented here shows how reconnection takes place between arbitrarily oriented fields in infinite and finite geometries. The process may best be thought of as a continuous exchange of field‐line partners during the time a field line maps into the diffusion region. In a finite geometry the diffusion regions lie on field lines which connect neutral points of the field configuration, and along which a potential drop is imposed. Although the discussion here centers principally on the magnetosphere, the described reconnection process and field topology should also be applicable to other astrophysical problem

ISSN:0048-6604    

DOI:10.1029/RS008i011p00903

年代:1973

数据来源: WILEY

摘要:

The three‐dimensional problem of magnetopause merging has been analyzed using an extension of Alfvén's neutral‐sheet field annihilation model. That model has been generalized for an arbitrary magnitude and direction of the interplanetary magnetic field. The analysis provides a quantitative prediction of the merging rate that is consistent with the observed dependence of geomagnetic activity on the direction and magnitude of the interplanetary magnetic f

ISSN:0048-6604    

DOI:10.1029/RS008i011p00915

年代:1973

数据来源: WILEY

摘要:

We briefly review the results of a laboratory field‐line reconnection experiment. In doing so the flux transfer rate is defined and contrasted with magnetic Mach numbers as measures of the reconnection rate. We examine the origin of the reconnection electric field to determine some of the requirements of nonsteady versus steady reconnection. The dependence of various measures of the reconnection rate on electrical conductivity is discussed as well as some experimental features which may relate to previous theory. Finally, we present some approximate scaling between laboratory events and the geomagnetic substorm. We reach three major conclusions: (a) The flux transfer rate as a measure of the reconnection rate is different from a magnetic Mach number. (b) The early reconnection process is quasi‐steady state or “Petschek‐like” and we associate this phase with magnetic energy storage. A later rapid flux transfer event is more energetic and is associated with storm events. The flux transfer event is triggered by a change in resistivity. (c) The laboratory event scales reasonably well to the duration and energy of a

ISSN:0048-6604    

DOI:10.1029/RS008i011p00917

年代:1973

数据来源: WILEY

摘要:

The magnetospheric morphology is reviewed using the method of the ΔBtopology. Typical examples of ΔBprofiles along individual passes of OGO‐5 in the morning hours and near noon are given, supplementing similar data presented earlier. These results demonstrate the significance of the equatorial current system in the distortions of the magnetospheric field in its quiet state. A preliminary study of the differences between the observed inclination,I, andIcalculated from a reference field, and the corresponding differences in declination,D, shows that ΔIand ΔDare larger than expected from the existing models. The magnitudes of ΔIat low latitudes are larger in the dusk sector than in the dawn sector, suggesting that the equatorial inner magnetosphere is more inflated near dusk than near dawn. The ΔDdata show that the bending of the field lines toward the tail is greater in the dusk than in the dawn sector. To account for the large ΔDvalues at midlatitudes it is suggested that they are caused by field‐aligned currents flowing from the dusk end of the cross‐tail current to the ionosphere and returning to the tail from the ionosphere on the

ISSN:0048-6604    

DOI:10.1029/RS008i011p00921

年代:1973

数据来源: WILEY

摘要:

From geomagnetic records of sixteen observatories distributed about the earth, a spectral analysis of the geomagnetic field was prepared for each day of 1965, a year of relatively quiet solar‐terrestrial activity. Field amplitudes were found to increase almost linearly with periods in the 5 min to 2 hr range of study. The northward and eastward components of field are about equal at all latitudes with slightly larger vaues ofHin the auroral and equatorial electrojet region. The vertical component of field is less than the others at all but the auroral zones. Seasonal changes in the amplitude appear at all locations but are more pronounced in the polar cap. Summer solstitial field strengths are about twice those of the winter period. On most quiet days of a month the amplitudes vary from about 0.5 to 0.1 times that of the monthly average levels. On most active days of the month the fields are between 4 to 10 times the size of the average monthly level amplitudes. The greatest variations in these levels occur at the equatorial and auroral zones. The lowest field values occur between 10° and 35° geomagnetic latitude with a minimum near 20° to 25°. Maximum values of the field are found at 65° to 75° geomagnetic latitude. Allowing for induced currents within the earth and for the global area of the distribution, about 91% of the magnetic energy is found between 60° and 80° geomagnetic latitude, about 4% in the higher latitude polar cap, and only 1% between the equato

ISSN:0048-6604    

DOI:10.1029/RS008i011p00929

年代:1973

数据来源: WILEY

摘要:

The meaning and characteristics of basic and average convection (i.e., electric field) patterns are described. The continuous existence of the basic convection pattern argues against treating magnetic field merging mechanisms as the fundamental cause of magnetospheric convection. However, whether related to merging or to some other mechanism, interplanetary magnetic field conditions significantly modulate the distribution, magnitudes, and boundaries of the convection pattern. A previous correlation between azimuthal, ф, angles of the inter‐planetary magnetic field and asymmetries in polar cap electric field distributions as seen by OGO‐6 is reviewed. A new approach is taken to reveal correlations with the north‐south, θ, angle and magnitude,B, of the interplanetary field as well as additional features which correlate with the ф angle. Both significant correlations and conditions which show a lack of correlation are found. Several aspects of the correlations appear to be particularly important. One is that for a given ф angle, correlations exist relative to θ independent ofBand relative toBindependent of θ. A second is that shifts in the latitude of the low altitude limit of the auroral belt convection are strongly correlated with all paramete

ISSN:0048-6604    

DOI:10.1029/RS008i011p00933

年代:1973

数据来源: WILEY

摘要:

The guiding center equations are solved numerically to follow 200 ev protons with pitch angles near the loss cone from the dayside magnetosheath on the noon meridian to their mirror height in a model open magnetosphere. We examine the effect of magnetic field line curvature and electric field strength upon proton mirror heights. We find that when the magnetic field has dipole‐like curvature along a dayside proton trajectory an increase in the strength of the dawn‐dusk electric field will result in an increase of the proton mirror height. When there exists significant nondipole‐like magnetic field curvature along a dayside proton trajectory an increase in the dawn‐dusk electric field strength can result in lower proton mirror heights. In our model, when the interplanetary magnetic field is directed northward or southward the latitude dependence of changes in proton mirror height resulting from changed dawn‐dusk electric field strength is the same along the noon‐midnight meridian over the northern and southern polar caps, but when the interplanetary magnetic field vector lies in the noon‐midnight meridian plane at an angle to the earth dipole axis, proton mirror height behavior in response to electric field strength changes is different over the northern and southern polar caps. Proton drift perpendicular to the magnetic field but having a component parallel to the electric field can result in kinetic energy changes of up to 25% as a proton moves from the magnetosheath to its

ISSN:0048-6604    

DOI:10.1029/RS008i011p00949

年代:1973

数据来源: WILEY

摘要:

By considering only those periods when the delay time from the interplanetary observing position to the magnetosphere is less than about 5 min, it is found that irrespective of substorm activity: (a) the 45‐min average value of interplanetaryBzpredicts the latitudes of the poleward and equatorward boundaries of polar cusp electron precipitation with rms errors of 1.34° and 1.16° respectively; (b) both boundaries move equatorward by about 5° asBzvaries from 0 to −6γ, the cusp remaining about 4° wide; (c) the amount of flux added to the polar cap is about 9.2% of the total southward flux impingent on the magnetosphere in the previous 45 min; and (d) asBzbecomes more positive, the equatorward boundary moves only slightly more poleward (½° betweenBz= 2γ andBz= 6γ), while the poleward boundary moves significantly toward higher latitudes, resulting in a cusp approximately 7° wide forBz= 6γ. This dependence of the width of the cusp on positiveBzsuggests that reconnection between the IMF (interplanetary magnetic field) and open geomagnetic field lines (which are southward near the dayside magnetopause) is facilitated when the IMF is northward, allowing deeper penetration of magnetosheath plasma into the high latitude

ISSN:0048-6604    

DOI:10.1029/RS008i011p00955

年代:1973

数据来源: WILEY