Incidence of Alfvenic SC Pulse Onto the Conjugate Ionospheres

Pilipenko, Vyacheslav; Fedorov, E. N.; Xu, Zhonghua; Hartinger, M.; Engebretson, M. J.; Edwards, Thom R.

doi:10.1029/2019ja027397

Cited by 3 publications

(4 citation statements)

References 17 publications

(24 reference statements)

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“…(2021), the southern hemisphere auroral oval is generally more in darkness in comparison to the northern hemisphere auroral oval, which may affect conductances and auroral electrojets more weakly in the southern hemisphere. Although not investigated in this paper, ionospheric conductances, seasons, and IMF B y may also play a role in determining inter‐hemispheric asymmetries in ground magnetic field response (Hartinger et al., 2017; Oliveira et al., 2023; Pilipenko et al., 2020; Weygand et al., 2022). Similar inter‐hemispheric asymmetries in AMPERE Birkeland currents were also reported by Shi et al.…”

Section: Discussionmentioning

confidence: 98%

Substorm‐Time Ground dB/dt Variations Controlled by Interplanetary Shock Impact Angles: A Statistical Study

Oliveira,

Weygand,

Coxon

et al. 2024

Space Weather

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In this study, we investigate the effects caused by interplanetary (IP) shock impact angles on the subsequent ground dB/dt variations during substorms. IP shock impact angles have been revealed as a major factor controlling the subsequent geomagnetic activity, meaning that shocks with small inclinations with the Sun‐Earth line are more likely to trigger higher geomagnetic activity resulting from nearly symmetric magnetospheric compressions. Such field variations are linked to the generation of geomagnetically induced currents (GICs), which couple to artificial conductors on the ground leading to deleterious consequences. We use a sub‐set of a shock data base with 237 events observed in the solar wind at L1 upstream of the Earth, and large arrays of ground magnetometers at stations located in North America and Greenland. The spherical elementary current system methodology is applied to the geomagnetic field data, and field‐aligned‐like currents in the ionosphere are derived. Then, such currents are inverted back to the ground and dB/dt variations are computed. Geographic maps are built with these field variations as a function of shock impact angles. The main findings of this investigation are: (a) typical dB/dt variations (5–10 nT/s) are caused by shocks with moderate inclinations; (b) the more frontal the shock impact, the more intense and the more spatially defined the ionospheric current amplitudes; and (c) nearly frontal shocks trigger more intense dB/dt variations with larger equatorward latitudinal expansions. Therefore, the findings of this work provide new insights for GIC forecasting focusing on nearly frontal shock impacts on the magnetosphere.

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Section: Discussionmentioning

confidence: 98%

Substorm‐Time Ground dB/dt Variations Controlled by Interplanetary Shock Impact Angles: A Statistical Study

Oliveira,

Weygand,

Coxon

et al. 2024

Space Weather

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“…As a proxy of N e in the upper ionosphere TEC maps can be used. Nonetheless, the expected correction factor would hardly exceed a few tens of percent (Pilipenko et al., 2020). In a realistic magnetosphere‐ionosphere system, the plasma distribution along a field line is inhomogeneous, so it can be characterized by a single value such as Σ A only qualitatively, but demands numerical calculations of field‐aligned eigenfunction.…”

Section: Discussionmentioning

confidence: 99%

“…This last approach was applied to find the driver characteristic of travelling convection vortices (Kim et al., 2015) and storm sudden commencements (Pilipenko et al., 2020). The examination of conjugacy properties may be an effective tool to comprehend the physics of magnetospheric ULF waves (Obana et al., 2005).…”

Section: Introduction: Current/voltage Dichotomy Of Ulf Wavesmentioning

confidence: 99%

Conjugate Properties of Magnetospheric Pc5 Waves: Antarctica‐Greenland Comparison

et al. 2021

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An electric circuit analogy for magnetosphere‐ionosphere current systems has two extremes for their driver: a current generator and voltage generator. In the case of a magnetospheric current generator the ground magnetic effect must be nearly the same under low‐conductivity or high‐conductivity ionospheres, whereas in the case of a voltage generator the magnetic response must be larger under a high‐conductivity ionosphere. Theoretical consideration of the field‐aligned current generation by a magnetospheric driver within the framework of the magnetosphere “plasma box” model with asymmetric ionospheres showed that excitation of resonant Alfvenic oscillations should correspond rather to a current generator regime. The asymmetry of Pc5 waves (frequencies about several mHz) recorded at conjugate magnetometers in Greenland and Antarctica has been analyzed from the viewpoint of the voltage/current generator dichotomy. We have selected Pc5 events under contrasting ionospheric conditions, during summer and winter. For resonant frequencies, we have plotted the latitudinal profiles of spectral power and compared the amplitudes of spatial maxima in opposite hemispheres. Along the same profile, latitudinal dependences of the ionospheric height‐integrated conductivities have been reconstructed with the use of the OVATION‐prime (OP) and solar illumination models. During both winter and summer events, the amplitudes of the spectral power peak in Greenland and Antarctica have been found to be about the same, though the OP model predicts a contrast between ionospheric conductivities of 5–10 times. Thus, the interhemispheric properties of Pc5 waves correspond to the current generator regime, as predicted by the magnetospheric plasma box model.

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“…For example, the arrival time is affected by magnetospheric wave speeds (e.g., Chi et al, 2006) that vary from event to event and may themselves be asymmetric with respect to the dipole equator. As another example, the intensity of the initial ground magnetic response depends on ionospheric conductivity and should have a seasonal dependence due to the seasonal dependence on solar extreme ultraviolet (EUV)/conductivity (Equation 10in Pilipenko et al, 2020), perhaps leading to a seasonal dependence in the magnetic intensity ratio; this contributed at least in part to the intensity asymmetries seen in Figures 2 and 3, though it cannot explain the extremely symmetrical response seen in the frontal shock event as this event occurred near solstice when there should have been larger asymmetries (if conductivity was the primary factor controlling the asymmetry in this event).…”

Section: Discussionmentioning

confidence: 99%

Interhemispheric Asymmetries in the Ground Magnetic Response to Interplanetary Shocks: The Role of Shock Impact Angle

Hartinger

Oliveira

et al. 2020

Space Weather

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Interplanetary (IP) shocks drive magnetosphere‐ionosphere (MI) current systems that in turn are associated with ground magnetic perturbations. Recent work has shown that IP shock impact angle plays a significant role in controlling the subsequent geomagnetic activity and magnetic perturbations; for example, highly inclined shocks drive asymmetric MI responses due to interhemispherical asymmetric magnetospheric compressions, while almost head‐on shocks drive more symmetric MI responses. However, there are few observations confirming that inclined shocks drive such asymmetries in the high‐latitude ground magnetic response. We use data from a chain of Antarctic magnetometers, combined with magnetically conjugate stations on the west coast of Greenland, to test these model predictions (Oliveira & Raeder, 2015, https://doi.org/10.1002/2015JA021147; Oliveira, 2017, https://doi.org/10.1007/s13538-016-0472-x). We calculate the time derivative of the magnetic field ( ∂Bfalse/∂t) in each hemisphere separately. Next, we examine the ratio of Northern to Southern Hemisphere ∂Bfalse/∂t intensities and the time differences between the maximum ∂Bfalse/∂t immediately following the impact of IP shocks. We order these results according to shock impact angles obtained from a recently published database with over 500 events and discuss how shock impact angles affect north‐south hemisphere asymmetries in the ground magnetic response. We find that the hemisphere the shock strikes first usually has (1) the first response in ∂Bfalse/∂t and (2) the most intense response in ∂Bfalse/∂t. Additionally, we show that highly inclined shocks can generate high‐latitude ground magnetic responses that differ significantly from predictions based on models that assume symmetric driving conditions.

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Incidence of Alfvenic SC Pulse Onto the Conjugate Ionospheres

Cited by 3 publications

References 17 publications

Substorm‐Time Ground dB/dt Variations Controlled by Interplanetary Shock Impact Angles: A Statistical Study

Substorm‐Time Ground dB/dt Variations Controlled by Interplanetary Shock Impact Angles: A Statistical Study

Conjugate Properties of Magnetospheric Pc5 Waves: Antarctica‐Greenland Comparison

Interhemispheric Asymmetries in the Ground Magnetic Response to Interplanetary Shocks: The Role of Shock Impact Angle

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