Dependence of the polar cusp on the north-south component of the interplanetary magnetic field

Kivelson, M. G.; Russell, C. T.; Neugebauer, M.; Scarf, F. L.; Fredricks, R. W.

doi:10.1029/ja078i019p03761

Cited by 48 publications

(20 citation statements)

References 19 publications

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“…In the steady state, this field aligned current system, which closes in the ionosphere on the one end and the magnetopause on the other, opposes the earth's field to provide local pressure balance at a position inward of the usual equilibrium position. Field aligned currents are apparently a common feature of the polar cusp (Zmuda et al, 1967;Fairfield and Ness, 1972;Kivelson et al, 1973a).…”

Section: The Erosion Of the Dayside Magnetospherementioning

confidence: 99%

The magnetotail and substorms

1973

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The tail plays a very active and important role in substorms. Magnetic flux eroded from the dayside magnelosphere is stored here. As more and more flux is transported to the magnetotail and stored, the boundary of the tail flares more, the field strength in the tail increases, and the currents strengthen and move closer to the Earth. Further, the plasma shcet thins and the magnetic flux crossing the neutral sheet lessens. At the onset of the expansion phase, the stored magnetic flux is returned from the tail and energy is deposited in the magnetosphere and ionosphere. During the expansion phase of isolated substorms, the flaring angle and the lobe field strength decrease, the plasma sheet thickens and more magnetic flux crosses the neutral sheet.In this review, we discuss the experimental evidence for these processes and present a phenomenological or qualitative model of the substorm sequence. In this model, the flux transport is driven by the merging of the magnetospheric and interplanetary magnetic fields. During the growth phase of substorms the merging rate on the dayside magnetosphere exceeds the reconnection rate in the neutral sheet. In order to remove the oversupply of magnetic flux in the tail, a neutral point forms in the near earth portion of the tail. If the new reconnection rate exceeds the dayside merging rate, then an isolated substorm results. However, a situation can occur in which dayside merging and tail rcconnection arc in equilibrium. The observed polar cap electric field and its correlation with the interplanetary magnetic field is found to be in accord with open magnetospheric models.

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Section: The Erosion Of the Dayside Magnetospherementioning

confidence: 99%

The magnetotail and substorms

1973

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“…Although, as suggested by the work of Kivelson et al (1973), the IMF direction may have important effects on the electron distribution functions in the low-altitude polar cusp, the fact that the OGO-4 experiment could only measure the high-energy tail of the electron spectrum made it unsuitable for that type of investigation. However, the OGO-4 measurements do provide reliable determinations of the location of the region of polar cusp electron precipitation.…”

Section: Polar Cusp Measurementsmentioning

confidence: 99%

Rate of erosion of dayside magnetic flux based on a quantitative study of the dependence of polar cusp latitude on the interplanetary magnetic field

Burch¹

1973

Radio Science

188

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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 interplanetary Bz predicts 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° as Bz varies 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) as Bz becomes more positive, the equatorward boundary moves only slightly more poleward (½° between Bz = 2γ and Bz = 6γ), while the poleward boundary moves significantly toward higher latitudes, resulting in a cusp approximately 7° wide for Bz = 6γ. This dependence of the width of the cusp on positive Bz suggests 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 magnetosphere.

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“…Russell et al (1974) considered the :onditions existing in interplanetary space associated with the development of the main _1_ 3 phase of magnetic storms. Kivelson et al (1973) studied the influence of the direction of the interplanetary field on the location of the polar cusp. Crooker et al (1977) correlated long-term averages of the solar wind speed with geomagnetic activity.…”

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confidence: 99%