Lauri Pänkäläinen

Dipolarization fronts (DFs) are transient structures occurring in Earth's magnetotail, characterized in spacecraft observations by sudden enhancements of the dipolar magnetic field component. Often linked to transient channels of fast earthward plasma flow, DFs are responsible for energy conversion, particle acceleration and magnetic flux transport. We investigate a DF event identified in a global hybrid-Vlasov simulation and study how it converts energy from electromagnetic fields to plasma flow and heat. We analyze velocity distribution functions associated with the event and trace test particles sampled from them. Our results indicate that non-compressional effects can be important to DF dissipation processes. Test particle tracing reveals that the DF actively replaces the local plasma population by transporting new particles into the region and displacing the pre-existing plasma, leading to a decoupling between the plasma properties before and after the front. The results may explain atypical temperature decreases reported in spacecraft observations of DFs.

We investigate ion velocity‐space features within the exhaust of magnetopause reconnection using a global hybrid‐Vlasov simulation. The Hermite transform and Gaussian Mixture Model (GMM) are applied to quantify the complexity of velocity‐space structures that arise during the mixing of magnetospheric and magnetosheath ion populations. Using the Hermite transform, we calculated the enstrophy metric to quantify available free energy. From the GMM multi‐beam decomposition we obtained pseudothermal energy. We find that pseudothermal energy appeared due directed beam motion accounts for nearly half of the apparent thermal energy within the exhaust. The enstrophy evolves similarly to the pseudothermal energy estimate selected via the optimal number of Gaussian components. These results revise ion energy partitioning during magnetopause reconnection and suggest an approach for defining thermal energy in non‐Maxwellian plasmas.

The dynamics of the inner magnetosphere and magnetotail are determined by a number of factors such as magnetic reconnection, plasma instabilities, and large-scale plasma motion. We use the global hybrid-Vlasov simulation Vlasiator to study these dynamics as well as their signatures in the ionosphere. We observe magnetic reconnection, fast flows, and vorticity in the transition region between the Earth's dipolar field and the magnetotail. In our simulation, reconnection is first triggered at the dawn and dusk sides of the magnetotail current sheet. It then spreads across the current sheet. Concurrently, an azimuthally periodic, wave-like density structure develops in the transition region along with fast Earthward flows and enhanced vorticity patterns. The Earthward flows and vorticity induce field-aligned currents, which map onto the ionospheric simulation domain, creating a patchy current distribution. We find that the event is driven by the combination of reconnection-induced fast flows and the ballooning/interchange instability.

The interaction between localized fast plasma jets, called bursty bulk flows (BBF) or flow bursts and ambient magnetic field plays an important role in the complex chain of solar wind-magnetosphere-ionosphere coupling processes. In particular the transition region, where the magnetic field configuration changes from dipolar-like configuration to tail-like configuration and where near-Earth flow braking/bouncing processes take place, is a key region of fundamental processes such as the particle energization and wave-particle interaction. These processes, associated with magnetic and pressure disturbances, drive enhanced energy and momentum transfer from the nightside outer magnetosphere along Earth’s magnetic field lines down to the ionosphere. Across the field lines, particle injections further affect the inner magnetosphere dynamics, constituting a source population for the radiation belt and the ring current.In this presentation we stress the importance of observations of BBFs and dipolarization fronts by multi-point measurements in an extensive region covering both equatorial and off-equatorial locations, and simultaneously at ion and fluid scales for understanding the energy transport processes. These allows us to monitor both the field-aligned and perpendicular evolution of the flux tube and enable to study the coupling with the ionosphere. By showing several examples of observations from previous studies of different scales of disturbances and fortuitous multi-spacecraft configuration at different scales, the 3D nature of the interaction between the BBF and ambient plasma, and its relationship to ionosphere including field-aligned current and aurora will be discussed.

Magnetic reconnection and plasma instabilities in Earth's magnetotail can lead to dipolarisation fronts (DFs), rapid enhancements of the magnetic field component aligned with Earth's magnetic dipole axis. DFs are often associated with channels of fast plasma flow, and they accelerate particles and transport magnetic flux to the inner magnetosphere. Satellite observations suggest that DFs propagate Earthward until they decelerate and either vanish, rebound or deflect as they reach the transition region between tail-like and dipole-like magnetic field configurations.We study the evolution and characteristics of DFs in a global magnetospheric simulation conducted using Vlasiator, a 3D hybrid-Vlasov code that solves ion dynamics by evolving the ion distribution functions explicitly. Events are identified using a magnetic field time derivative threshold, and individual fronts are tracked from their formation to their termination. Preliminary results show how magnetic forces affect the propagation of DFs and how energy is converted as the fronts develop. Tracking the evolution of DFs in global simulations offers a complementary point of view to satellite observations, where following individual fronts is often impossible.

The magnetic connection between the ionosphere and the magnetotail current sheet allows for couplings between ionospheric conditions and various phenomena in the magnetotail. Magnetic reconnection in the tail causes fast plasma flow channels that affect the field-aligned currents (FACs) flowing between the tail and the ionosphere. It is currently understood that these plasma flows in the tail result in ionospheric current channels that correspond predominantly to North-South aligned auroral structures called streamers. We investigate the effects to the FAC systems by making a comprehensive survey of fast plasma sheet flows in the magnetotail and mapping the events to the ionosphere above Fennoscandia, using the T89 magnetic field model. The survey is done for Cluster-, MMS-, and THEMIS-mission data archives between the years 2001 and 2025. The criteria for fast flows are those commonly used for bursty bulk flows; velocity over 400 km/s in the Earthward direction and plasma beta over 0.5 to ensure the satellite is within the plasma sheet. We then utilise the Spherical Elementary Current System (SECS) method with the IMAGE magnetometer network to obtain ionospheric equivalent current densities and estimates of changes to FACs. Where possible, we analyse optical data, and compare auroral structures to the ionospheric current patterns. Studying the signatures of plasma sheet flows from ground-based observations as well as satellite data helps in building a better understanding of the connection between the two domains.

The dynamics of the inner magnetosphere and magnetotail are determined by a number of factors such as magnetic reconnection, plasma instabilities, and large-scale plasma motion. We use the global hybrid-Vlasov simulation Vlasiator to study these dynamics as well as their signatures in the ionosphere. We observe magnetic reconnection, fast flows, and vorticity in the transition region between the Earth's dipolar field and the magnetotail. In our simulation, reconnection is first triggered at the dawn and dusk sides of the magnetotail current sheet. It then spreads across the current sheet. Concurrently, an azimuthally periodic, wave-like density structure develops in the transition region along with fast Earthward flows and enhanced vorticity patterns. The Earthward flows and vorticity induce field-aligned currents, which map onto the ionospheric simulation domain, creating a patchy current distribution. We find that the event is driven by the combination of reconnection-induced fast flows and the ballooning/interchange instability.

The dynamics of the inner magnetosphere and magnetotail are determined by a number of factors such as magnetic reconnection, plasma instabilities, and large-scale plasma motion. We use the global hybrid-Vlasov simulation Vlasiator to study these dynamics as well as their signatures in the ionosphere. We observe magnetic reconnection, fast flows, and vorticity in the transition region between the Earth's dipolar field and the magnetotail. In our simulation, reconnection is first triggered at the dawn and dusk sides of the magnetotail current sheet. It then spreads across the current sheet. Concurrently, an azimuthally periodic, wave-like density structure develops in the transition region along with fast Earthward flows and enhanced vorticity patterns. The Earthward flows and vorticity induce field-aligned currents, which map onto the ionospheric simulation domain, creating a patchy current distribution. We find that the event is driven by the combination of reconnection-induced fast flows and the ballooning/interchange instability.

Magnetic flux ropes are helical structures of magnetic field which form in a variety of magnetized plasmas. In near-Earth space, flux ropes are a manifestation of energy transfer at the magnetopause and in the magnetotail current sheet. We present a new method to detect magnetic flux ropes in large-scale simulations using only magnetic field line tracing. The method does not require prior identification of structures of interest such as current sheets or null lines and thus allows one to identify flux ropes of any size and orientation anywhere in the simulation domain. In this work, the new method is implemented in the hybrid-Vlasov model Vlasiator and demonstrated in global simulations of the terrestrial magnetosphere. We study the evolution of flux ropes forming during flux transfer events on the dayside magnetopause under a southward interplanetary magnetic field. It is found that flux ropes with an axial orientation along the dawn–dusk direction and propagating beyond the cusps will rapidly reconnect with the lobe magnetic field and vanish. In contrast, the flux ropes remaining near the equatorial plane and with an axial orientation along the flow direction – that is, tangential to the magnetopause – can maintain their structure and propagate tens of Earth radii down the tail in the absence of a reconnecting shear magnetic field component. These results are a step forward in the global characterization of flux ropes in and around the magnetosphere and may help in guiding the search for elusive far-tail flux ropes in satellite measurements.

The dynamics of the inner magnetosphere and magnetotail are determined by a number of factors such as magnetic reconnection, plasma instabilities, and large-scale plasma motion. We use the global hybrid-Vlasov simulation Vlasiator to study these dynamics as well as their signatures in the ionosphere. We observe magnetic reconnection, fast flows, and vorticity in the transition region between the Earth's dipolar field and the magnetotail. In our simulation, reconnection is first triggered at the dawn and dusk sides of the magnetotail current sheet. It then spreads across the current sheet. Concurrently, an azimuthally periodic, wave-like density structure develops in the transition region along with fast Earthward flows and enhanced vorticity patterns. The Earthward flows and vorticity induce field-aligned currents, which map onto the ionospheric simulation domain, creating a patchy current distribution. We find that the event is driven by the combination of reconnection-induced fast flows and the ballooning/interchange instability.