Empirical modeling of the quiet time nightside magnetosphere

Lui, A. T. Y.; Spence, H. E.; Stern, David P.

doi:10.1029/93ja02647

Cited by 57 publications

(65 citation statements)

References 39 publications

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“…During storm late recovery and quiet times the model reproduces a pressure maximum near local midnight, consistent with the region 2 current generation mechanism described by Lui et al [1994] for an earthward pointing pressure gradient.…”

Section: Discussionsupporting

confidence: 78%

Computational analysis of the near‐Earth magnetospheric current system during two‐phase decay storms

Liemohn¹,

Kozyra²,

Clauer³

et al. 2001

J. Geophys. Res.

104

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Abstract. Several two-phase decay magnetic storms are examined using a kinetic transport model to find the spatial and temporal distribution of the perpendicular and field-aligned currents in the inner magnetosphere. The global morphology of these currents in the calculational domain (inside of geosynchronous orbit) is discussed as a function of storm epoch, obtaining good comparison between the numerically derived features and observed values of stormtime currents in this region. The model results are also consistent with quiet time plasma observations showing an increasing pressure in to L=3 or 4, including a pressure maximum near midnight for the generation of region 2 Birkeland currents in the proper direction. A detailed analysis of the characteristic features of these currents is also presented and discussed. It is found that most of the ring current (>90%) during the main phase and early recovery phase is partial rather than symmetric, closing mostly (up to 90%) through field-aligned currents into the ionosphere. Conversely, the quiet time ring current is largely (>60%) symmetric, with most of the asymmetry produced by minor injections of near-Earth plasma sheet material. In general, the peak asymmetric current (which occurs during the main phase) is 2-3 times larger than the peak symmetric current (which occurs during the recovery phase) for any particular two-phase decay event. This is the case for all of the events studied, regardless of storm size, solar wind parameters, or solar cycle. The maximum azimuthal current (integrated over a local time slice) reaches 5 to 20 MA, compared with <2 MA of symmetric current at quiet times.

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Section: Discussionsupporting

confidence: 78%

Computational analysis of the near‐Earth magnetospheric current system during two‐phase decay storms

Liemohn¹,

Kozyra²,

Clauer³

et al. 2001

J. Geophys. Res.

104

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“…In particular, it will be useful to extend the previous study of Lui et al [1994] to obtain an empirical quiet time magnetic field model which takes into account the presence of an inner eastward ring current and the occurrence of anisotropy plasma pressure. In fact, as underlined by Lui et al [1994], a better assessment of the variation of pressure as a I•nction of local time could be incorporated in their model to provide a better description of the magnetospheric field by assuming a magnetohydrodynamic momentum balance.…”

Section: Discussionmentioning

confidence: 99%

An average image of proton plasma pressure and of current systems in the equatorial plane derived from AMPTE/CCE‐CHEM measurements

Michelis¹,

Daglis²,

Consolini³

1999

J. Geophys. Res.

110

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Abstract. The present study attempts to visualize the global equatorial current systems and the proton pressure in the near-Earth magnetosphere based on AMPTE/CCE-CHEM measured proton distributions, which were sorted by the AE index ( "quiet": AE < 100 nT, "active": 100 nT < AE < 600 nT). The data were averaged over 2 years (from January 1985 to June 1987) in order to obtain the necessary spatial resolution with statistical significance. The results provide an average image of proton plasma pressure, proton plasma anisotropy, and current systems as a function of geomagnetic activity. In particular, the changes of pressure anisotropy with local time and the noon-midnight pressure asymmetry are studied and correlated to the current systems out of the equatorial plane that generate the closure circuits. Moreover, we identify and spatially locate two different current systems for the quiet period (the ring current and the inner portion of the quiet thne cross-tail current) and three different current structures for the active period (the ring current, the partial ring current, and the region 2 current).

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“…Another series of approaches actually goes further than using empirical model fields for mapping observed plasma pressure distributions and try to infer the pressure from the empirical model itself, by attempting to calculate the pressure values that would be in force balance with the model fields in 1-D along the Sun-Earth axis [e.g., Spence et al, 1987;Lui et al, 1994] or in 2-D in the equatorial plane [Horton et al, 1993;Cao and Lee, 1994]. One important question poses itself with regard to this approach, and the question is "Can the empirical model fields be equilibrated by plasma pressure of a certain pressure tensor form ?"…”

Section: Plasma Pressure and Empirical Field Models; Lack Of Force Bamentioning

confidence: 99%

“…In the computation we use observation-based pressure profiles and realistic boundary conditions as input. The results we present in this paper are obtained using plasma pressure in the plasma sheet from GEOTAIL observations [e.g., Hori et al, 2000], or along the midnight meridian in the equatorial plane, from the so-called Spence-Kivelson formula [Spence and Kivelson, 1993], as well as anisotropic pressure closer to Earth obtained from AMPTE/CCE measurements [Lui , 1993;Lui et al, 1994;De Michelis et al, 1999]. The computation is performed inside a domain defined by magnetic flux boundaries obtained from Tsyganenko's T96 and T01 empirical field models [Tsyganenko, 1995;Tsyganenko and Stern, 1996;Tsyganenko, 2002].…”

Section: Possible Solutions To the Force Balance Problemmentioning

confidence: 99%

“…On the other hand, the degree of anisotropy is lowest at midnight and higher at other local times, but again with a maximum at noon. For this computation we use the polynomial empirical formula obtained by Lui et al [1994] for the degree of anisotropy on the midnight meridional line from AMPTE/CCE observations, and we add a simple dependence of the form 2 + cos φ to model its azimuthal variation, in accordance with the qualitative behavior found by De Michelis et al [1999]. With regard to the pressure values, the "average" pressure (defined as P = (2P ⊥ +P )/3) obtained from AMPTE/CCE on the nightside [Lui and Hamilton, 1992] has been shown [Zaharia and Cheng, 2002] to be very close to the isotropic P values of the SK formula.…”

Section: Anisotropic Pressure Input From Ampte/ccementioning

confidence: 99%

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3-D Force-balanced Magnetospheric Configurations

Zaharia

Cheng

Maezawa

2003

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Abstract. The knowledge of plasma pressure is essential for many physics applications in the magnetosphere, such as computing magnetospheric currents and deriving mag-netosphere-ionosphere coupling. A thorough knowledge of the 3-D pressure distribution has however eluded the community, as most in-situ pressure observations are either in the ionosphere or the equatorial region of the magnetosphere. With the assumption of pressure isotropy there have been attempts to obtain the pressure at different locations by either (a) mapping observed data (e.g. in the ionosphere) along the field lines of an empirical magnetospheric field model, or (b) computing a pressure profile in the equatorial plane (in 2-D) or along the Sun-Earth axis (in 1-D) that is in force balance with the magnetic stresses of an empirical model. However, the pressure distributions obtained through these methods are not in force balance with the empirical magnetic field at all locations. In order to find a global 3-D plasma pressure distribution in force balance with the magnetospheric magnetic field we have developed the MAG-3D code, that solves the 3-D force balance equation J × B = ∇P computationally. Our calculation is performed in a flux coordinate system in which the magnetic field is expressed in terms of Euler potentials as B = ∇ψ × ∇α. The pressure distribution, P = P (ψ, α), is prescribed in the equatorial plane and is based on satellite measurements. In addition, computational boundary conditions for ψ surfaces are imposed using empirical field models. Our results provide 3-D distributions of magnetic field, plasma pressure as well as parallel and transverse currents for both quiet-time and disturbed magnetospheric conditions.

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Empirical modeling of the quiet time nightside magnetosphere

Cited by 57 publications

References 39 publications

Computational analysis of the near‐Earth magnetospheric current system during two‐phase decay storms

Computational analysis of the near‐Earth magnetospheric current system during two‐phase decay storms

An average image of proton plasma pressure and of current systems in the equatorial plane derived from AMPTE/CCE‐CHEM measurements

3-D Force-balanced Magnetospheric Configurations

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