MT-index – a possible new index to characterize the magnetic configuration of magnetotail

Sergeev, V. A.; Gvozdevsky, B. B.

doi:10.1007/s005850050249

Cited by 17 publications

(48 citation statements)

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“…Increases in tail stretching increase b2i and vice versa. Therefore b2i can be used to slightly modify the T89 magnetic model so the stretching of its field lines agrees with observations [Sergeev and Gvozdevsky, 1995].…”

Section: Discussionsupporting

confidence: 60%

“…These indices, although useful in many applications, do not indicate the instantaneous magnetotail magnetic field configuration very well, that is, the stretching of the field lines, which is crucial for field line mapping [e.g., Fairfield, 1991' Tsyganenko, 1990Sergeev et al, 1993]. Sergeev and Gvozdevsky [1995] demonstrated that the latitude of the equatorward isotropic boundary has a high correlation, r --0.9, with the magnetic field inclination, that is, the degree of stretching, measured simultaneously at the geomagnetic equator (approximately the same correlation holds true for b2i as determined from DMSP by the algorithm of Newell et al [1996b]). Sergeev and Gvozdevsky proposed a new magnetic index (MT) which is based on the invariant latitude of the isotropic boundary.…”

Section: Introductionmentioning

confidence: 99%

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Central plasma sheet ion properties as inferred from ionospheric observations

Wing¹,

Newell²

1998

J. Geophys. Res.

164

197

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Abstract. A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantage of this method over in situ measurements is that the CPS can be studied in its entirety, rather than only in fragments. As a result, for the first time, comprehensive two-dimensional equatorial maps of CPS pressure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) particle instruments onboard DMSP F8, F9, F10, and Fll satellites during the entire year of 1992. Ion spectra occurring in conjunction with electron acceleration events are specifically excluded. Because of the variability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) adjusted to agree with the actual magnetotail stretch at observation time. The latter is inferred with a high degree of accuracy (correlation coefficient -0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temperature, pressure, and density all exhibit dawn-dusk asymmetries unresolved with previous measurements. The ion temperature peaks near the midnight meridian. This peak, which has been associated with bursty bulk flow events, w.idens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increases with decreasing distance from the Earth. In contrast, the density is higher at dawn than at dusk, and there appears to be a density enhancement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with increasing distance from the Earth and may even reverse so that at distances X < --10 to -12 Roe, depending on magnetic activity, the dawn sector has slightly higher pressure. The temperature and density asymmetries in the near-Earth region are consistent with the ion westward gradient/curvature drift as the ions ExB convect earthward. When the solar wind dynamic pressure increases, CPS density and pressure appear to increase, but the temperature remains relatively constant. Comparison with previously published work indicates good agreement between the inferred pressure, temperature, and density and those obtained from in situ data. This new method should provide a continuous mechanism to monitor the pressure, temperature, and density in the magnetotail with unprecedented comprehensiveness.

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Section: Discussionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Central plasma sheet ion properties as inferred from ionospheric observations

Wing¹,

Newell²

1998

J. Geophys. Res.

164

197

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“…Recently this precipitation attracted much attention because of its potential importance for evaluation of magnetotail magnetic con®guration. As has been shown by Sergeev et al (1993) and Sergeev and Gvozdevsky (1995), on the nightside this isotropic precipitation is formed by particle pitch-angle scattering in the tail plasma sheet where the adiabatic motion is violated in the weak and curved magnetic ®eld regions. This ever present and eective scattering mechanism provides the isotropic precipitation if the ratio of magnetic ®eld curvature radius to the proton gyroradius q is <8 (see also Delcourt et al, 1996).…”

Section: Introductionmentioning

confidence: 85%

“…A remarkable feature of energetic proton precipitation is their isotropic precipitation (with¯uxes being isotropic over the loss cone) which exists at any local time in any disturbance conditions (Hauge and Soraas, 1975;Lundblad et al, 1979) and forms the oval-shaped isotropic precipitation zone (Sergeev and Gvozdevsky, 1995). Recently this precipitation attracted much attention because of its potential importance for evaluation of magnetotail magnetic con®guration.…”

Section: Introductionmentioning

confidence: 99%

Dayside isotropic precipitation of energetic protons

1997

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Abstract.Recently it has been shown that isotropic precipitation of energetic protons on the nightside is caused by a non-adiabatic eect, namely pitch-angle scattering of protons in curved magnetic ®eld lines of the tail current sheet. Here we address the origin of isotropic proton precipitation on the dayside. Computations of proton scattering regions in the magnetopheric models T87, T89 and T95 reveal two regions which contribute to the isotropic precipitation. The ®rst is the region of weak magnetic ®eld in the outer cusp which provides the 1±2°wide isotropic precipitation on closed ®eld lines in a $2±3 hour wide MLT sector centered on noon. A second zone is formed by the scattering on the closed ®eld lines which cross the nightside equatorial region near the magnetopause which provides isotropic precipitation starting %1.5±2 h MLT from noon and which joins smoothly the precipitation coming from the tail current sheet. We also analyzed the isotropic proton precipitation using observations of NOAA low altitude polar spacecraft. We ®nd that isotropic precipitation of >30 to >80 keV protons continues around noon forming the continuous oval-shaped region of isotropic precipitation. Part of this region lies on open ®eld lines in the region of cusp-like or mantle precipitation, its equatorward part is observed on closed ®eld lines. Near noon it extends $1±2°below the sharp boundary of solar electron¯uxes (proxy of the open/closed ®eld line boundary) and equatorward of the cusp-like auroral precipitation. The observed energy dispersion of its equatorward boundary (isotropic boundary) agrees with model predictions of expected particle scattering in the regions of weak and highly curved magnetic ®eld. We also found some disagreement with model computations. We did not observe the predicted split of the isotropic precipitation region into separate nightside and dayside isotropic zones. Also, the oval-like shape of the isotropic boundary has a symmetry line in 10±12 MLT sector, which with increasing activity rotates toward dawn while the latitude of isotropic boundary is decreasing. Our conclusion is that for both dayside and nightside the isotropic boundary location is basically controlled by the magnetospheric magnetic ®eld, and therefore the isotropic boundaries can be used as a tool to probe the magnetospheric con®guration in dierent external conditions and at dierent activity levels.

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“…The magnetic field at geostationary orbit evaluated with this method was in good agreement (correlation coefficient r∼0.9) with the real magnetic field observed at the geostationary GOES spacecraft (Sergeev et al, 1993); (Newell et al, 1998), showing that the IB latitude is effectively controlled by the tail magnetic field. A simple index of magnetotail stretching (MT-index) was proposed for tail current monitoring to perform the accurate mapping from the ionosphere to the magnetosphere (Sergeev et al, 1995, later referred to as SG95). The global IB shape (its CGLat dependence on MLT), as well as its dependences on the solar wind dynamic pressure Pd and magnetic activity index AE was first evaluated in SG95, although the available database was rather small (one month of data obtained from 2 spacecraft).…”

Section: Introductionmentioning

confidence: 99%

Statistical study of the proton isotropy boundary

2005

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Abstract. Based on a large data set of polar NOAA-type satellite observations we studied the latitude-MLT shape of the 80 keV proton isotropy boundary (IB) as a function of the solar wind parameters and magnetic activity. Using "snapshots" of isotropy boundaries near-simultaneously crossed at four points we found that its equatorward expansion, as well as its dawn-dusk shift, depends mostly on the AEindex and on the corrected D st *, whereas the amplitude of the IB daily variation is mostly controlled by the solar wind dynamic pressure. Applying a nonlinear, multi-parametric, least-square regression procedure, the empirical relationship describing the IB latitude as a function of MLT and AE, Pd, D st * parameters was obtained. Comparing it with the predictions from the Tsyganenko-2001 model we found a good agreement during the quiet time but some important differences during the disturbed periods. Interpretation of these results in terms of the properties of the magnetospheric configuration is briefly discussed.

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MT-index – a possible new index to characterize the magnetic configuration of magnetotail

Cited by 17 publications

References 0 publications

Central plasma sheet ion properties as inferred from ionospheric observations

Central plasma sheet ion properties as inferred from ionospheric observations

Dayside isotropic precipitation of energetic protons

Statistical study of the proton isotropy boundary

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