Modeling the Effects of the Factors Affecting IGF in Coastal Areas and Variation of IGF in Jiaodong Peninsula of China Based on Finite Element Method

Based on finite element method, we develop a model of the induced geoelectric field (IGF) occurring in land-sea boundary regions during large geomagnetic field disturbances. The model is used first to study the effects of the changes in the lithospheric conductivity, ionospheric current, and ocean depth on the distribution of IGF in a typical land-sea boundary region. The results show that the changes in the lithospheric conductivity and ionospheric current (frequency, magnitude and direction) have major effects and ocean depth has minor effect on IGF in coastal areas. Then by incorporating a realistic 3-D conductivity variation of Jiaodong Peninsula (JDP) in China obtained from measured data, the model is used to simulate the IGF variation in JDP covering its land-sea boundaries for east-west and north-south ionospheric currents. The results show a new aspect that extremely large IGF development on the land side of the coastal bay areas perpendicular to the currnet compared to plane coastal areas. The results can stimulate detailed investigations of IGF (and GIC, geomagnetically induced current) in coastal areas.

Reproducibility of the Geomagnetically Induced Currents at Middle Latitudes During Space Weather Disturbances

Watari et al. (Space Weather, 2009, 7) found that the geomagnetically induced current (GIC) in Hokkaido, Japan (35.7° geomagnetic latitude (GML)), is well correlated with the y-component magnetic field (By) (correlation coefficients >0.8) and poorly correlated with Bx,z and dBx,y,z/dt. The linear correlation with By would help predict the GIC, if we have capabilities of reproducing the magnetosphere–ionosphere currents during space weather disturbances. To validate the linear correlation with By for any periods (T) of disturbances, we made correlation analyses for the geomagnetic sudden commencements and pulsations (T = 1–10 min), quasi-periodic DP2 fluctuations (30 min), substorm positive bays (60 min), geomagnetic storms (1–20 h), and quiet-time diurnal variations (8 h). The linear correlation is found to be valid for short periods (cc > 0.8 for T < 1 h) but not for long periods (cc < 0.3 for T > 6 h). To reproduce the GIC with any periods, we constructed one-layer model with uniform conductor and calculated the electric field (IEF) induced by By using the convolution of dBy/dt and the step response of the conductor. The IEF is found to be correlated with the GIC for long periods (cc > 0.9), while the GIC-By correlation remains better for short periods. To improve the model, we constructed a two-layer model with highly conductive upper and less conductive lower layers. The IEF is shown to reproduce the GIC with cc > 0.9 for periods ranging from 1 min to 24 h. The model is applied to the GIC measured at lower latitudes in Japan (25.3° GML) with strong By dependence. The mechanism of the strong By dependence of the GIC remains an issue, but a possible mechanism for the daytime GIC is due to the zeroth-order transverse magnetic (TM0) mode in the Earth-ionosphere waveguide, by which the ionospheric currents are transmitted from the polar to equatorial ionosphere.

Network community structure of substorms using SuperMAG magnetometers

Geomagnetic substorms are a global magnetospheric reconfiguration, during which energy is abruptly transported to the ionosphere. Central to this are the auroral electrojets, large-scale ionospheric currents that are part of a larger three-dimensional system, the substorm current wedge. Many, often conflicting, magnetospheric reconfiguration scenarios have been proposed to describe the substorm current wedge evolution and structure. SuperMAG is a worldwide collaboration providing easy access to ground based magnetometer data. Here we show application of techniques from network science to analyze data from 137 SuperMAG ground-based magnetometers. We calculate a time-varying directed network and perform community detection on the network, identifying locally dense groups of connections. Analysis of 41 substorms exhibit robust structural change from many small, uncorrelated current systems before substorm onset, to a large spatially-extended coherent system, approximately 10 minutes after onset. We interpret this as strong indication that the auroral electrojet system during substorm expansions is inherently a large-scale phenomenon and is not solely due to many meso-scale wedgelets.

MHD simulations of magnetospheric response to a strong solar wind density pulse

<p>On 16-17 June 2012, an interplanetary coronal mass ejection with an extremely high solar wind density (~100 cm<sup>-3</sup>) and mostly strong northward (or eastward) interplanetary magnetic field (IMF) interacted with the Earth’s magnetosphere. We have simulated this event using global MHD models. We study the magnetospheric response to two solar wind discontinuities. The first is characterized by a fast drop of the solar wind dynamic pressure resulting in rapid magnetospheric expansion. The second is a northward IMF turning which causes reconfiguration of the magnetospheric-ionospheric currents. We discuss variations of the magnetopause position and locations of the magnetopause reconnection in response to the solar wind variations. In the second part of our presentation, we present simulation results for the forthcoming SMILE (Solar wind Magnetosphere Ionosphere Link Explorer) mission. SMILE is scheduled for launch in 2024. We produce two-dimensional images that derive from the MHD results of the expected X-ray emission as observed by the SMILE Soft X-ray Imager (SXI). We discuss how SMILE observations may help to study events like the one presented in this work.</p>

Electrojet poleward boundary variations with IMF By and season

<p>By utilising measurements from twenty ground magnetometer stations in Fennoscandia, divergence-free ionospheric currents above this region are modelled using spherical elementary currents (SECS). New modelling techniques are implemented that coerce the model to find a solution that resembles the resolvable ionospheric currents. The divergence-free currents are evaluated along the 105<sup>o</sup> magnetic meridian covering a period of almost 20 years with a resolution of 1 minute, as a result of the magnetometers chosen. From these sheet current density latitude profiles, the boundaries of the auroral electrojet are identified. After performing a large statistical analysis it is found that there is a significant IMF B<sub>y</sub> effect on the poleward boundary of the electrojets during the Summer but not during the Winter. We suggest that this seasonal effect can be attributed to the effects of lobe reconnection on the extent of currents in the auroral electrojets. Further work is done to compare the SECS derived electrojet boundaries with particle precipitation data from low orbit satellites.</p>

Dusk side clockwise vortex generation and aurora intensity decrease after Solar Wind Dynamic Pressure Decrease

<p>A solar wind dynamic pressure increase/decrease leads to the compression/expansion of the Earth’s magnetosphere. In response, field-aligned currents, which are carried by precipitating or escaping plasma particles, are generated in the magnetosphere and in lead to variations in the auroral intensity. In this study, we investigate magnetospheric and ionospheric responses (including magnetospheric plasma vortex, ionospheric currents and aurorae) to a sudden decrease in solar wind dynamic pressure (SW P<sub>dyn</sub>), which is critical for further understanding of the solar wind-magnetosphere-ionosphere coupling. We focused on a SW P<sub>dyn</sub> decrease event that monitored by OMNI. A counter-clockwise plasma vortex was generated in the dusk side magnetosphere uncovered by using MHD simulation method and a clockwise equivalent ionospheric currents (EIC) vortex was generated in the dusk side ionosphere within about ten minutes after the pressure pulse arrival. Simultaneously, the observation results of Spherical Elementary Currents (SECs) showed that the EIC vortex region is dominated by downward field-aligned currents and the ground-based All-Sky Imager (ASI) observations in the vicinity of this EIC vortex showed that the aurorae diminished. These observations are consistent with the scenario proposed by Shi et al. (2014) that flow vortices in the magnetosphere generated by SW P<sub>dyn</sub> sudden decrease carry downward field-aligned currents into the dusk side ionosphere, generating ionospheric current vortex and thereby modulating auroral activity on the dusk side.</p>

Polar cap patches, GPS TEC variations, and atmospheric gravity waves

<p>The southward pointing field of view of the Canadian component of the Resolute Bay Incoherent Scatter Radar (RISR-C) is well suited for observing the ionospheric signatures of flux transfer events and subsequent polar patch formation in the cusp.  The fast azimuthally oriented flows and associated density depletions often show an enhanced ion temperature from Joule heating caused by the sudden change in plasma flow direction. The newly formed polar patches are then observed as they propagate through the field-of-views of both RISR-C and RISR-N. In the ionosphere, the electron density gradients imposed in the cusp, and small-scale irregularities resulting from gradient-drift instability, particularly in the trailing edges of patches, cause GPS TEC and phase variations, and sometimes amplitude scintillation. The neutral atmosphere is affected by ionospheric currents resulting in Joule heating. The pulses of ionospheric currents in the cusp launch atmospheric gravity waves (AGWs) causing traveling ionospheric disturbances, as they propagate equatorward and upward. On the other hand, the downward propagating AGW packets can impact the lower atmosphere, including the troposphere. Despite significantly reduced wave amplitudes, but subject to amplification upon over-reflection in the upper troposphere, these AGWs can trigger/release existing moist instabilities, initiating convection and latent heat release, the energy leading to intensification of storms.</p>