Browsing by Author "Kilpua, Emilia K.J."

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  • Alfvén Ion Cyclotron Waves in Sheath Regions Driven by Interplanetary Coronal Mass Ejections
    (2019-06-01) Ala-Lahti, Matti; Kilpua, Emilia K.J.; Souček, Jan; Pulkkinen, Tuija I.; Dimmock, Andrew P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We report on a statistical analysis of the occurrence and properties of Alfvén ion cyclotron (AIC) waves in sheath regions driven by interplanetary coronal mass ejections (ICMEs). We have developed an automated algorithm to identify AIC wave events from magnetic field data and apply it to investigate 91 ICME sheath regions recorded by the Wind spacecraft. Our analysis focuses on waves generated by the ion cyclotron instability. AIC waves are observed to be frequent structures in ICME-driven sheaths, and their occurrence is the highest in the vicinity of the shock. Together with previous studies, our results imply that the shock compression has a crucial role in generating wave activity in ICME sheaths. AIC waves tend to have their frequency below the ion cyclotron frequency, and, in general, occur in plasma that is stable with respect to the ion cyclotron instability and has lower ion β‖ than mirror modes. The results suggest that the ion beta anisotropy β⊥/β‖>1 appearing in ICME sheaths is regulated by both ion cyclotron and mirror instabilities.
  • BepiColombo Science Investigations During Cruise and Flybys at the Earth, Venus and Mercury
    (2021-02-11) Mangano, Valeria; Dósa, Melinda; Fränz, Markus; Milillo, Anna; Oliveira, Joana S.; Lee, Yeon Joo; McKenna-Lawlor, Susan; Grassi, Davide; Heyner, Daniel; Kozyrev, Alexander S.; Peron, Roberto; Helbert, Jörn; Besse, Sebastien; de la Fuente, Sara; Montagnon, Elsa; Zender, Joe; Volwerk, Martin; Chaufray, Jean Yves; Slavin, James A.; Krüger, Harald; Maturilli, Alessandro; Cornet, Thomas; Iwai, Kazumasa; Miyoshi, Yoshizumi; Lucente, Marco; Massetti, Stefano; Schmidt, Carl A.; Dong, Chuanfei; Quarati, Francesco; Hirai, Takayuki; Varsani, Ali; Belyaev, Denis; Zhong, Jun; Kilpua, Emilia K.J.; Jackson, Bernard V.; Odstrcil, Dusan; Plaschke, Ferdinand; Vainio, Rami; Jarvinen, Riku; Ivanovski, Stavro Lambrov; Madár, Ákos; Erdős, Géza; Plainaki, Christina; Alberti, Tommaso; Aizawa, Sae; Benkhoff, Johannes; Murakami, Go; Quemerais, Eric; Hiesinger, Harald; Mitrofanov, Igor G.; Iess, Luciano; Santoli, Francesco; Orsini, Stefano; Lichtenegger, Herbert; Laky, Gunther; Barabash, Stas; Moissl, Richard; Huovelin, Juhani; Kasaba, Yasumasa; Saito, Yoshifumi; Kobayashi, Masanori; Baumjohann, Wolfgang
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    The dual spacecraft mission BepiColombo is the first joint mission between the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) to explore the planet Mercury. BepiColombo was launched from Kourou (French Guiana) on October 20th, 2018, in its packed configuration including two spacecraft, a transfer module, and a sunshield. BepiColombo cruise trajectory is a long journey into the inner heliosphere, and it includes one flyby of the Earth (in April 2020), two of Venus (in October 2020 and August 2021), and six of Mercury (starting from 2021), before orbit insertion in December 2025. A big part of the mission instruments will be fully operational during the mission cruise phase, allowing unprecedented investigation of the different environments that will encounter during the 7-years long cruise. The present paper reviews all the planetary flybys and some interesting cruise configurations. Additional scientific research that will emerge in the coming years is also discussed, including the instruments that can contribute.
  • Cavitons and spontaneous hot flow anomalies in a hybrid-Vlasov global magnetospheric simulation
    (2018-08-08) Blanco-Cano, Xochitl; Battarbee, Markus; Turc, Lucile; Dimmock, Andrew P.; Kilpua, Emilia K.J.; Hoilijoki, Sanni; Ganse, Urs; Sibeck, David G.; Cassak, Paul A.; Fear, Robert C.; Jarvinen, Riku; Juusola, Liisa; Pfau-Kempf, Yann; Vainio, Rami; Palmroth, Minna
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this paper we present the first identification of foreshock cavitons and the formation of spontaneous hot flow anomalies (SHFAs) with the Vlasiator global magnetospheric hybrid-Vlasov simulation code. In agreement with previous studies we show that cavitons evolve into SHFAs. In the presented run, this occurs very near the bow shock. We report on SHFAs surviving the shock crossing into the downstream region and show that the interaction of SHFAs with the bow shock can lead to the formation of a magnetosheath cavity, previously identified in observations and simulations. We report on the first identification of long-term local weakening and erosion of the bow shock, associated with a region of increased foreshock SHFA and caviton formation, and repeated shock crossings by them. We show that SHFAs are linked to an increase in suprathermal particle pitch-angle spreads. The realistic length scales in our simulation allow us to present a statistical study of global caviton and SHFA size distributions, and their comparable size distributions support the theory that SHFAs are formed from cavitons. Virtual spacecraft observations are shown to be in good agreement with observational studies.
  • Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF
    (2019-06) Hoilijoki, Sanni; Ganse, Urs; Sibeck, David G.; Cassak, Paul A.; Turc, Lucile; Battarbee, Markus; Fear, Robert C.; Blanco-Cano, Xochitl; Dimmock, Andrew; Kilpua, Emilia K.J.; Järvinen, Riku; Juusola, Liisa; Pfau-Kempf, Yann; Palmroth, Minna
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This paper describes properties and behavior of magnetic reconnection and flux transfer events (FTEs) on the dayside magnetopause using the global hybrid-Vlasov code Vlasiator. We investigate two simulation runs with and without a sunward (positive) B x component of the interplanetary magnetic field (IMF) when the IMF is southward. The runs are two-dimensional in real space in the noon-midnight meridional (polar) plane and three-dimensional in velocity space. Solar wind input parameters are identical in the two simulations with the exception that the IMF is purely southward in one but tilted 45° toward the Sun in the other. In the purely southward case (i.e., without B x) the magnitude of the magnetosheath magnetic field component tangential to the magnetopause is larger than in the run with a sunward tilt. This is because the shock normal is perpendicular to the IMF at the equatorial plane, whereas in the other run the shock configuration is oblique and a smaller fraction of the total IMF strength is compressed at the shock crossing. Hence, the measured average and maximum reconnection rate are larger in the purely southward run. The run with tilted IMF also exhibits a north-south asymmetry in the tangential magnetic field caused by the different angle between the IMF and the bow shock normal north and south of the equator. Greater north-south asymmetries are seen in the FTE occurrence rate, size, and velocity as well; FTEs moving toward the Southern Hemisphere are larger in size and observed less frequently than FTEs in the Northern Hemisphere.
  • Statistical analysis of mirror mode waves in sheath regions driven by interplanetary coronal mass ejection
    (2018-05-24) Ala-Lahti, Matti M.; Kilpua, Emilia K.J.; DImmock, Andrew P.; Osmane, Adnane; Pulkkinen, Tuija; Souček, Jan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present a comprehensive statistical analysis of mirror mode waves and the properties of their plasma surroundings in sheath regions driven by interplanetary coronal mass ejection (ICME). We have constructed a semi-automated method to identify mirror modes from the magnetic field data. We analyze 91 ICME sheath regions from January 1997 to April 2015 using data from the Wind spacecraft. The results imply that similarly to planetary magnetosheaths, mirror modes are also common structures in ICME sheaths. However, they occur almost exclusively as dip-like structures and in mirror stable plasma. We observe mirror modes throughout the sheath, from the bow shock to the ICME leading edge, but their amplitudes are largest closest to the shock. We also find that the shock strength (measured by Alfvén Mach number) is the most important parameter in controlling the occurrence of mirror modes. Our findings suggest that in ICME sheaths the dominant source of free energy for mirror mode generation is the shock compression. We also suggest that mirror modes that are found deeper in the sheath are remnants from earlier times of the sheath evolution, generated also in the vicinity of the shock.
  • Transmission of an ICME Sheath Into the Earth's Magnetosheath and the Occurrence of Traveling Foreshocks
    (2021-12) Ala-Lahti, Matti; Dimmock, Andrew P.; Pulkkinen, Tuija I.; Good, Simon W.; Yordanova, Emilya; Turc, Lucile; Kilpua, Emilia K.J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The transmission of a sheath region driven by an interplanetary coronal mass ejection into the Earth's magnetosheath is studied by investigating in situ magnetic field measurements upstream and downstream of the bow shock during an ICME sheath passage on 15 May 2005. We observe three distinct intervals in the immediate upstream region that included a southward magnetic field component and are traveling foreshocks. These traveling foreshocks were observed in the quasi-parallel bow shock that hosted backstreaming ions and magnetic fluctuations at ultralow frequencies. The intervals constituting traveling foreshocks in the upstream survive transmission to the Earth's magnetosheath, where their magnetic field, and particularly the southward component, was significantly amplified. Our results further suggest that the magnetic field fluctuations embedded in an ICME sheath may survive the transmission if their frequency is below ∼0.01 Hz. Although one of the identified intervals was coherent, extending across the ICME sheath and being long-lived, predicting ICME sheath magnetic fields that may transmit to the Earth's magnetosheath from the upstream at L1 observations has ambiguity. This can result from the strong spatial variability of the ICME sheath fields in the longitudinal direction, or alternatively from the ICME sheath fields developing substantially within the short time it takes the plasma to propagate from L1 to the bow shock. This study demonstrates the complex interplay ICME sheaths have with the Earth's magnetosphere when passing by the planet.