North/South Asymmetry of sc/si Magnetic Variations Observed along the 210.DEG. Magnetic Meridian.

Yumoto, K.; Matsuoka, Hitoshi; Osaki, Hiroshi; Shiokawa, K.; Tanaka, Yoshihito; Kitamura, Toshio; Tachihara, H.; Shinohara, Masanao; Solovyev, S. I.; Makarov, G. A.; Vershinin, E. F.; Buzevich, A. V.; Manurung, S. L.; Sobari, Obay; Ruhimat, Mamat; Sukmadradjat,; Morris, R. J.; Fraser, B. J.; Menk, F. W.; Lynn, K. J. W.; Cole, David; Kennewell, J. A.; Olson, John V.; Akasofu, S.‐I.

doi:10.5636/jgg.48.1333

Cited by 15 publications

(12 citation statements)

References 10 publications

(8 reference statements)

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“…Mere magnetopause currents cannot explain the enhancement in the summer hemisphere, and hence it may indicate a contribution due to the enhanced ionospheric conductivities. This observation is in agreement with the findings of Yumoto et al (1996), who examined hemispheric differences in the MI amplitude of positive impulses at middle and low latitudes. They attributed these observed hemispheric differences to enhanced twinvortex type ionospheric currents in the summer hemisphere.…”

Section: Magnetic Field Variations After Maximum Deviationsupporting

confidence: 82%

Ionospheric current contribution to the main impulse of a negative sudden impulse

Vichare

Rawat

Bhaskar

et al. 2014

Earth, Planets and Space

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The geomagnetic field response to a moderate-amplitude negative sudden impulse (SI − ) that occurred on 14 May 2009 at 10:30 UT was examined at 97 geomagnetic observatories situated all over the globe. The response signature contains a contribution from magnetospheric as well as ionospheric currents. The main impulse (MI) is defined as the maximum depression in the observed geomagnetic field. It is observed that for low-to-high latitudes, the amplitude of the MI is larger in the afternoon to post-dusk sector than in the dawn-noon sector, indicating asymmetry in the MI amplitude. We estimated the contribution at various observatories due to the Chapman-Ferraro magnetopause currents using the Tsyganenko model (T01) and subtracted this from the observed MI amplitude to obtain the contribution due to ionospheric currents. It is found that the ionospheric currents contribute significantly to the MI amplitude of moderate SI − even at low-to-mid latitudes and that the contribution is in the same direction as that from the magnetopause currents near dusk and in the opposite direction near dawn. The equivalent current vectors reveal a clockwise (anticlockwise) ionospheric current loop in the afternoon (morning) sector during the MI of the negative pressure impulse. This evidences an ionospheric twin-cell-vortex current system (DP2) due to field-aligned currents (FACs) associated with the dusk-to-dawn convection electric field during the MI of an SI − . We also estimated the magnetic field variation due to prompt penetration electric fields, which is found to be very small at low latitudes in the present case. The studied SI − is not associated with shock, and hence no preliminary reverse impulse was evident. In addition, the summer hemisphere reveals larger MI amplitudes than the winter hemisphere, indicating once again the role of ionospheric currents.

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Section: Magnetic Field Variations After Maximum Deviationsupporting

confidence: 82%

Ionospheric current contribution to the main impulse of a negative sudden impulse

Vichare

Rawat

Bhaskar

et al. 2014

Earth, Planets and Space

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“…11. On the other hand, the amplitude relationship of SC between the summer and the winter hemispheres in the 210°meridian (Yumoto et al, 1995;Yumoto et al, 1996) are roughly consistent with the results of the 12±18 LT block of the voltage generator (Fig. 12).…”

Section: Asymmetry Of Ionospheric Current System In Solsticesupporting

confidence: 78%

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

Tsunomura¹

1999

Ann. Geophys.

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Abstract. A modeling method is proposed to derive a two-dimensional ionospheric layer conductivity, which is appropriate to obtain a realistic solution of the polar-originating ionospheric current system including equatorial enhancement. The model can be obtained by modifying the conventional, thin shell conductivity model. It is shown that the modi®cation for one of the non-diagonal terms (S hu ) in the conductivity tensor near the equatorial region is very important; the term in¯uences the pro®le of the ionospheric electric ®eld around the equator drastically. The proposed model can reproduce well the results representing the observed electric and magnetic ®eld signatures of geomagnetic sudden commencement. The new model is applied to two factors concerning polar-originating ionospheric current systems. First, the latitudinal pro®le of the DP2 amplitude in the daytime is examined, changing the canceling rate for the dawnto-dusk electric ®eld by the region 2 ®eld-aligned current. It is shown that the equatorial enhancement would not appear when the ratio of the total amount of the region 2 ®eld-aligned current to that of region 1 exceeds 0.5. Second, the north-south asymmetry of the magnetic ®elds in the summer solstice condition of the ionospheric conductivity is examined by calculating the global ionospheric current system covering both hemispheres simultaneously. It is shown that the positive relationship between the magnitudes of high latitude magnetic ®elds and the conductivity is clearly seen if a voltage generator is given as the source, while the relationship is vague or even reversed for a current generator. The new model, based on the International Reference Ionosphere (IRI) model, can be applied to further investigations in the quantitative analysis of the magnetosphere-ionosphere coupling problems.

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“…Magnetic pulsations observed on the ground are affected by currents driven by the electric field of ULF waves that are incident from the magnetosphere. As a consequence, the amplitude of the pulsations should depend on the ionospheric conductivity [e.g., Yumoto et al , 1996; Motoba et al , 2002]. According to Nishida [1978], the ionospheric transmission coefficient for Alfvén waves has a factor Σ H /Σ P , where Σ H and Σ P are the height‐integrated Hall and Pederson conductivities, respectively.…”

Section: Discussionmentioning

confidence: 99%

Dependence of the amplitude of Pc5‐band magnetic field variations on the solar wind and solar activity

et al. 2012

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[1] We have studied the dependence of the amplitude of magnetic field variations in the Pc5 band (1.6-6.7 mHz) on the solar wind and solar activity. Solar wind parameters considered are the bulk velocity V sw and the variation of the solar wind dynamic pressure dP sw . The solar activity dependence is examined by contrasting observations made in 2001 (solar activity maximum) and 2006 (solar activity declining phase). We calculated hourly Pc5 amplitude using data from geostationary satellites at L = 6.8 and ground stations covering 1 < L < 9. The amplitude is positively correlated with both V sw and dP sw , but the degree of correlation varies with L and magnetic local time. As measured by the correlation coefficient, the amplitude dependence on both V sw and dP sw is stronger on the dayside than on the nightside, and the dependence on V sw (dP sw ) tends to be stronger at higher (lower) L, with the relative importance of the two solar wind parameters switching at L $ 5. We attribute the V sw control to the Kelvin-Helmholtz instability on the magnetopause, occurring both at high and low latitudes, and the dP sw control to buffeting of the magnetosphere by variation of solar wind dynamic pressure. The GOES amplitude is higher at the solar maximum at all local times and the same feature is seen on the ground in the dawn sector at L > 6. A radial shift of the fast mode wave turning point, associated with the solar cycle variation of magnetosphere mass density, is a possible cause of this solar activity dependence.

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North/South Asymmetry of sc/si Magnetic Variations Observed along the 210.DEG. Magnetic Meridian.

Cited by 15 publications

References 10 publications

Ionospheric current contribution to the main impulse of a negative sudden impulse

Ionospheric current contribution to the main impulse of a negative sudden impulse

Numerical analysis of global ionospheric current system including the effect of equatorial enhancement

Dependence of the amplitude of Pc5‐band magnetic field variations on the solar wind and solar activity

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