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  • 1.
    Gunell, Herbert
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nesbit-Östman, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Krämer, Eva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nilsson, Hans
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Magnetosheath jets at Mars2023Ingår i: Science Advances, E-ISSN 2375-2548, Vol. 9, nr 22, artikel-id eadg5703Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Plasma entities, known as magnetosheath jets, with higher dynamic pressure than the surrounding plasma, are often seen at Earth. They generate waves and contribute to energy transfer in the magnetosheath. Affecting the magnetopause, they cause surface waves and transfer energy into the magnetosphere, causing throat auroras and magnetic signatures detectable on the ground. We show that jets exist also beyond Earth's environment in the magnetosheath of Mars, using data obtained by the MAVEN spacecraft. Thus, jets can be created also at Mars, which differs from Earth by its smaller bow shock, and they are associated with an increased level of magnetic field fluctuations. Jets couple large and small scales in magnetosheaths in the solar system and can play a similar part in astrophysical plasmas.

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  • 2.
    Hamrin, Maria
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Opgenoorth, Hermann J.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nesbit-Östman, Sara
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Krämer, Eva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Araújo, Juan Carlos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för naturvetenskapernas och matematikens didaktik.
    Baddeley, Lisa
    Department of Arctic Geophysics, University Centre in Svalbard, Longyearbyen, Norway.
    Gunell, Herbert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Pitkänen, Timo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Institute of Space Sciences, Shandong University, Weihai, China.
    Gjerloev, Jesper
    Johns Hopkins University, Laurel, MD, USA.
    Barnes, R. J.
    Johns Hopkins University, Laurel, MD, USA.
    Space weather disturbances in non-stormy times: occurrence of dB/dt spikes during three solar cycles2023Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, nr 10, artikel-id e2023JA031804Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spatio-temporal variations of ionospheric currents cause rapid magnetic field variations at ground level and Geomagnetically Induced Currents (GICs) that can be harmful for human infrastructure. The risk for large excursions in the magnetic field time derivative, “dB/dt spikes”, is known to be high during geomagnetic storms and substorms. However, less is known about the occurrence of spikes during non-stormy times. We use data from ground-based globally covering magnetometers (SuperMAG database) from the years 1985–2021. We investigate the spike occurrence (|dB/dt| > 100 nT/min) as a function of magnetic local time (MLT), magnetic latitude (Mlat), and the solar cycle phases during non-stormy times (−15 nT ≤ SYM-H < 0). We sort our data into substorm (AL < 200 nT) intervals (“SUB”) and less active intervals between consecutive substorms (“nonSUB”). We find that spikes commonly occur in both SUBs and nonSUBs during non-stormy times (3–23 spikes/day), covering 18–12 MLT and 65°–80° Mlat. This also implies a risk for infrastructure damage during non-stormy times, especially when several spikes occur nearby in space and time, possibly causing infrastructure weathering. We find that spikes are more common in the declining phase of the solar cycle, and that the occurrence of SUB spikes propagates from one midnight to one morning hotspot with ∼10 min in MLT for each minute in universal time (UTC). Finally, we discuss causes for the spikes in terms of spatio-temporal variations of ionospheric currents.

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  • 3.
    Krämer, Eva
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Gunell, Herbert
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Karlsson, T.
    Division of Space and Plasma Physics, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden.
    Steinvall, K.
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Goncharov, O.
    Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic.
    André, Mats
    Swedish Institute of Space Physics, Uppsala, Sweden.
    Waves in Magnetosheath Jets—Classification and the Search for Generation Mechanisms Using MMS Burst Mode Data2023Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, nr 7, artikel-id e2023JA031621Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetosheath jets are localized dynamic pressure enhancements in the magnetosheath. We make use of the high time resolution burst mode data of the Magnetospheric Multiscale mission for an analysis of waves in plasmas associated with three magnetosheath jets. We find both electromagnetic and electrostatic waves over the frequency range from 0 to 4 kHz that can be probed by the instruments on board the MMS spacecraft. At high frequencies we find electrostatic solitary waves, electron acoustic waves, and whistler waves. Electron acoustic waves and whistler waves show the typical properties expected from theory assuming approximations of a homogeneous plasma and linearity. In addition, 0.2 Hz waves in the magnetic field, 1 Hz electromagnetic waves, and lower hybrid waves are observed. For these waves the approximation of a homogeneous plasma does not hold anymore and the observed waves show properties from several different basic wave modes. In addition, we investigate how the various types of waves are generated. We show evidence that, the 1 Hz waves are connected to gradients in the density and magnetic field. The whistler waves are generated by a butterfly-shaped pitch-angle distribution and the electron acoustic waves by a cold electron population. The lower hybrid waves are probably generated by currents at the boundary of the jets. As for the other waves we can only speculate about the generation mechanism due to limitations of the instruments. Studying waves in jets will help to address the microphysics in jets which can help to understand the evolution of jets better.

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  • 4.
    Pitkänen, Timo
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China.
    Chong, Ghai Siung
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hamrin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kullen, A.
    Space and Plasma Physics, School of Electrical Engineering and Computer Science, Royal Institute of Technology, Stockholm, Sweden.
    Vanhamäki, H.
    Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland.
    Park, J.-S.
    Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China.
    Nowada, M.
    Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China.
    Schillings, Audrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Krämer, Eva
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Fast Earthward Convection in the Magnetotail and Nonzero IMF By: MMS Statistics2023Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, nr 12, artikel-id e2023JA031593Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We statistically investigate convective earthward fast flows using data measured by the Magnetospheric Multiscale mission in the tail plasma sheet during 2017–2021. We focus on “frozen in” fast flows and investigate the importance of different electric field components in the Sun-Earth (V⊥x) and dusk-dawn (V⊥y) velocity components perpendicular to the magnetic field. We find that a majority of the fast flow events (52% of 429) have the north-south electric field component (Ez) as the most relevant or dominating component whereas 26% are so-called conventional type fast flows with Ey and Ex as the relevant components. The rest of the flow events, 22%, fall into the two ’mixed’ categories, of which almost all these fast flows, 20% of 429, have Ey and Ez important for V⊥x and V⊥y, respectively. There is no Y-location preference for any type of the fast flows. The conventional fast flows are detected rather close to the neutral sheet whereas the other types can be measured farther away. Typical total speeds are highest in the mixed category. Typical perpendicular speeds are comparably high in the conventional and mixed categories. The slowest fast flows are measured in the Ez category. Most of the fast flow events are measured in the substorm recovery phase. Prevailing interplanetary magnetic field By conditions influence the V⊥y direction and the influence is most efficient for the Ez-dominated fast flows.

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