Global ENA IMAGE Simulations

Fok, M.‐C.; Moore, T. E.; Wilson, G. R.; Perez, J. D.; Zhang, X. X.; Brandt, P. C.; Mitchell, D. G.; Roelof, E. C.; Jahn, J.; Pollock, C. J.; Wolf, R. A.

doi:10.1007/978-94-010-0027-7_5

Cited by 53 publications

(76 citation statements)

References 42 publications

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“…In contrast, the plasma at auroral latitudes, where the lower electrical conductivity and the strong field-aligned current systems allow for fast convection to the dayside, has rapid transport from the nightside to the dayside and the reconnecting magnetopause. This suggestion is in accord with the work of Fok et al (2003), who pointed out that different electric field models resulted in very different local time distribution for the ring current ions in modeling the stormtime ion drift trajectories. The classical picture where the partial ring current occurs in the afternoon sectors is associated with a strong electric field in the duskside, such as that in the Weimer electric field model (Weimer, 1995).…”

Section: Discussionsupporting

confidence: 90%

Morphology of the ring current derived from magnetic field observations

2004

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Abstract. Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ∼3 R E and a main westward ring current at ∼4-7 R E for all levels of geomagnetic disturbances. In general, the insitu observations show that the ring current varies as the D st index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (∼0.5 MA) and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ∼3 MA, whereas the total symmetric ring current is ∼1 MA. Thus, the partial ring current contributes dominantly to the decrease in the D st index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in the sense of region-2 field-aligned currents, downward into the ionosphere near the dusk and upward out of the ionosphere near the dawn.

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Section: Discussionsupporting

confidence: 90%

Morphology of the ring current derived from magnetic field observations

2004

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“…Accordingly, ENA intensities are drastically enhanced during 2005-2036 UT [Brandt et al, 2002;Fok et al, 2003] in the nightside but ceased by 2259 UT. This is a general consequence of the southward IMF due to enhanced convection.…”

Section: Image Observationsmentioning

confidence: 97%

“…[75] This scenario must assume a strong electric field [e.g., Brandt et al, 2002;Fok et al, 2003;Ebihara and Fok, 2004;Jordanova, 2005], and such a strong field is indeed inferred from the IMAGE/HENA data in Figure 7. The inferred electric field in the postmidnight sector for the 21 October 2001 event is strong enough to drive $10 keV ions quickly to the morning sector.…”

Section: Source Location and Mechanismmentioning

confidence: 99%

Source location of the wedge‐like dispersed ring current in the morning sector during a substorm

et al. 2006

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[1] Source of wedge-like dispersed sub-keV ring current ions (wedge-like structure) is investigated using Cluster CIS data. Statistics from nearly 550 traversals show that the wedge-like structure with upper energy extending to ordinary energy of ring current is found mostly in the morning sector whereas those limited within sub-keV range are found mostly in the noon-to-afternoon sector. The former is most likely the original form of the latter. With this knowledge, the Cluster traversal on 21 October 2001 turned out to be a unique observation that reveals the formation of the wedge-like structure. Spacecraft 1 and 4 detected a wedge-like structure of 0.1 $ 10 keV protons at 2350 UT, while spacecraft 3 did not detect it 10 min before in the same magnetic flux tube. With the observed electric field of less than 3 mV/m, this fact indicates that the dispersion started within half an hour. Pitch angle distributions of the wedge-like structure is in most cases double conic-like butterfly distributions, but the wedge-like dispersed oxygen ions during the 21 October 2001 event flow mainly from one direction (from Northern Hemisphere) without a loss cone. With its characteristic energy of 0.05 $ 0.3 keV, these oxygen ions originate from the Northern Hemisphere about 20 $ 30 min before the observation. Both the dispersion analysis and the oxygen ion tracing suggest that the observed wedge-like structure is formed in the late morning sector during the latest substorm that started at 2310 UT. Possible mechanisms of the morning source are discussed.Citation: Yamauchi, M., et al. (2006), Source location of the wedge-like dispersed ring current in the morning sector during a substorm,

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“…[17] The RCM has successfully been used to explicate major magnetospheric phenomena such as the development of region-2 Birkeland currents which shield the magnetosphere [e.g., Jaggi and Wolf, 1973;Harel et al, 1981b], the buildup and evolution of the storm-time ring current [e.g., Wolf et al, 1982;Spiro and Wolf, 1984;Sazykin et al, 2002;Fok et al, 2003;Garner, 2003], formation and evolution of the plasmasphere and plasmapause [e.g., Spiro et al, 1981;Wolf et al, 1986], the penetration of convection electric fields to low ionospheric latitudes [e.g., Spiro et al, 1988;Fejer et al, 1990;Sazykin, 2000], the Harang discontinuity [Erickson et al, 1991], and coupling to the thermosphere [e.g., Forbes and Harel, 1989;Wolf et al, 1986].…”

Section: Description Of the Rcmmentioning

confidence: 99%

Coupling of a global MHD code and an inner magnetospheric model: Initial results

Zeeuw¹

2004

J. Geophys. Res.

215

278

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[1] This paper describes the coupling of BATS-R-US (Block Adaptive Tree Solar-wind Roe-type Upwind Scheme), a magnetohydrodynamics (MHD) code representing the Earth's global magnetosphere and its coupling to the ionosphere and solar wind, and the Rice Convection Model (RCM), which represents the inner magnetosphere and its coupling to the ionosphere. The MHD code provides a time-evolving magnetic field model for the RCM as well as continuously updated boundary conditions for the electric potential and plasma. The RCM computes the distribution functions of inner magnetospheric particles, including transport of inner plasmasheet and ring current particles by gradient/curvature drifts; it thus calculates more accurate inner magnetospheric pressures, which are frequently passed to the MHD model and used to nudge the MHD values. Results are presented for an initial run with the coupled code for the case of uniform ionospheric conductance with steady solar wind and southward interplanetary magnetic field (IMF). The results are compared with those for a run of the MHD code alone. The coupled-code run shows significantly higher inner magnetospheric particle pressures. It also exhibits several well-established characteristics of inner magnetospheric electrodynamics, including strong region-2 Birkeland currents and partial shielding of the inner magnetosphere from the main force of the convection electric field. A sudden northward turning of the IMF causes the ring current to become more nearly symmetric. The inner magnetosphere exhibits an overshielding (dusk-to-dawn) electric field that begins about 10 min after the northward turning reaches the magnetopause and lasts just over an hour.

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Global ENA IMAGE Simulations

Cited by 53 publications

References 42 publications

Morphology of the ring current derived from magnetic field observations

Morphology of the ring current derived from magnetic field observations

Source location of the wedge‐like dispersed ring current in the morning sector during a substorm

Coupling of a global MHD code and an inner magnetospheric model: Initial results

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