This study considers 28 geomagnetic storms with Dst $\leq-50$ nT driven by high-speed streams (HSSs) and associated stream interaction regions (SIRs) during 2010-2017. Their impact on ionospheric horizontal and field-aligned currents (FACs) have been investigated using superposed epoch analysis of SuperMAG and AMPERE data, respectively. The zero epoch ($t_0$) was set to the onset of the storm main phase. Storms begin in the SIR with enhanced solar wind density and compressed southward oriented magnetic field. The integrated FAC and equivalent currents maximise 40 and 58 min after $t_0$, respectively, followed by a small peak in the middle of the main phase ($t_0$+4h), and a slightly larger peak just before the Dst minimum ($t_0$+5.3h). The currents are strongly driven by the solar wind, and the correlation between the Akasofu $\varepsilon$ and integrated FAC is $0.90$. The number of substorm onsets maximises near $t_0$. The storms were also separated into two groups based on the solar wind dynamic pressure p_dyn in the vicinity of the SIR. High p_dyn storms reach solar wind velocity maxima earlier and have shorter lead times from the HSS arrival to storm onset compared with low p_dyn events. The high p_dyn events also have sudden storm commencements, stronger solar wind driving and ionospheric response at $t_0$, and are primarily responsible for the first peak in the currents after $t_0$. After $t_0+2$ days, the currents and number of substorm onsets become higher for low compared with high p_dyn events, which may be related to higher solar wind speed.

We present a statistical investigation of the effects of interplanetary magnetic field (IMF) on hemispheric asymmetry in auroral currents. Nearly six years of magnetic field measurements from Swarm A and C satellites are analyzed. Bootstrap resampling is used to remove the difference in the number of samples and IMF conditions between the local seasons and the hemispheres. Currents are stronger in Northern Hemisphere (NH) than Southern Hemisphere (SH) for IMF B$y^+$ in NH (B$y^-$ in SH) in most local seasons under both signs of IMF B$z$. For B$y^-$ in NH (B$y^+$ in SH), the hemispheric difference in currents is small except in local winter when currents in NH are stronger than in SH. During B$y^+$ and B$z^+$ in NH (B$y^-$ and B$z^+$ in SH), the largest hemispheric asymmetry occurs in local winter and autumn when the NH/SH ratio of field-aligned current (FAC) is 1.18$\pm$0.09 in winter and 1.17$\pm$0.09 in autumn. During B$y^+$ and B$z^-$ in NH (B$y^-$ and B$z^-$ in SH), the largest asymmetry is observed in local autumn with NH/SH ratio of 1.16$\pm$0.07 for FAC. We also find an explicit B$y$ effect on auroral currents in a given hemisphere: on average B$y^+$ in NH and B$y^-$ in SH causes larger currents than vice versa. The explicit B$y$ effect on divergence-free (DF) current during IMF B$z^+$ is in very good agreement with the B$y$ effect on the cross polar cap potential (CPCP) from the Super Dual Auroral Radar Network (SuperDARN) dynamic model except at SH equinox and NH summer.

We present a new analysis technique for estimating 2D neutral wind pattern using data from a single Scanning Doppler Imager (SDI) or a combination of SDIs, incoherent scatter radars (ISR) and Fabry-Perot interferometers (FPI) within overlapping field-of-views. Neutral wind plays an important role in ionospheric electrodynamics and Ionosphere-Thermosphere coupling, by for example affecting the Joule heating rates and plasma transport. However, reliable and extensive measurements of the neutral wind are rather difficult to obtain. Pointwise measurements can be obtained with ISRs or FPIs, but these measurements can not provide 2D latitude-longitude maps of the neutral wind pattern needed in mesospheric studies. A Scanning Doppler Imager can measure the line-of-sight (LOS) component of the neutral wind in dozens of directions simultaneously. However, further modeling is needed to convert the LOS velocities into 2D velocity maps. Unfortunately these maps are far from unique, as perpendicular velocities (e.g. rotation around the measurement site) are not visible in the LOS data. This can be mitigated by combining data from several nearby SDIs, or a combination of SDIs, FPIs and ISRs. Our analysis technique is based on fitting the LOS data with special vector basis functions called Spherical Elementary Current Systems (SECS). In this approach the wind is naturally divided into curl-free and divergence-free components, and there is no need to provide any explicit boundary conditions on the wind pattern. We present several synthetic test scenarios as well as first results using data from SDIs located in Alaska. Using the synthetic test scenarios we further estimate optimal locations for 2 or 3 SDIs that could be located around the future EISCAT_3D radar system in northern Scandinavia.

We present a statistical investigation of the seasonal effect on hemispheric asymmetry in the auroral currents during low (Kp $<$ 2) and high (Kp $\geq$ 2) geomagnetic activity. Five years of magnetic data from the Swarm satellites has been analysed by applying the spherical elementary current system (SECS) method. Bootstrap resampling has been used to remove the seasonal differences between the hemispheres in the dataset. In general, the currents are larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Asymmetry is larger during low than high Kp, and during winter and autumn than summer and spring. The NH/SH ratio for FACs in winter, autumn, spring and summer are 1.17 $\pm$ 0.05, 1.14 $\pm$ 0.05, 1.07 $\pm$ 0.04 and 1.02 $\pm$ 0.04, respectively. The largest asymmetry is observed during low Kp winter, when the excess in the NH currents is 21$\pm$5\% in FAC, 14 $\pm$ 3\% in curl-free (CF), and 10$\pm$3\% in divergence-free (DF) current. We also find that evening sector (13-24 MLT) contributes more to the high NH/SH ratio than the morning (01-12 MLT) sector. The physical mechanisms producing the hemispheric asymmetry are not presently understood. We calculated the background ionospheric conductances during low Kp conditions from the IRI, NRLMSISE and CHAOS models. The results indicate that only a small part of the hemispheric asymmetry can be explained by variations in the solar induced conductances.