Browsing by Subject "PLASMA TRANSPORT"

Sort by: Order: Results:

Now showing items 1-5 of 5
  • Lakka, Antti; Pulkkinen, Tuija I.; Dimmock, Andrew P.; Kilpua, Emilia; Ala-Lahti, Matti; Honkonen, Ilja; Palmroth, Minna; Raukunen, Osku (2019)
    We study the response of the Earth's magnetosphere to fluctuating solar wind conditions during interplanetary coronal mass ejections (ICMEs) using the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4). The two ICME events occurred on 15-16 July 2012 and 29-30 April 2014. During the strong 2012 event, the solar wind upstream values reached up to 35 particles cm(-3), speeds of up to 694 km s(-1), and an interplanetary magnetic field of up to 22 nT, giving a Mach number of 2.3. The 2014 event was a moderate one, with the corresponding upstream values of 30 particles cm(-3), 320 km s(-1) and 10 nT, indicating a Mach number of 5.8. We examine how the Earth's space environment dynamics evolves during both ICME events from both global and local perspectives, using well-established empirical models and in situ measurements as references. We show that on the large scale, and during moderate driving, the GUMICS-4 results are in good agreement with the reference values. However, the local values, especially during high driving, show more variation: such extreme conditions do not reproduce local measurements made deep inside the magnetosphere. The same appeared to be true when the event was run with another global simulation. The cross-polar cap potential (CPCP) saturation is shown to depend on the Alfven-Mach number of the upstream solar wind. However, care must be taken in interpreting these results, as the CPCP is also sensitive to the simulation resolution.
  • Osmane, Adnane; Dimmock, Andrew P.; Pulkkinen, Tuija I. (2019)
    In this study we determine whether auroral westward currents can be characterized by low-dimensional chaotic attractors through the use of the complexity-entropy methodology developed by Rosso et al. (2007, https:// and based on the permutation entropy developed by Bandt and Pompe (2002, . Our results indicate that geomagnetic auroral indices are indistinguishable from stochastic processes from time scales ranging from a few minutes to 10 hr and for embedded dimensions d <8. Our results are inconsistent with earlier studies of Baker et al. (1990,, Pavlos et al. (1992), D. Roberts et al. (1991,, D. A. Roberts (1991, https://doLorg/10.1029/91JA01088), and Vassiliadis et al. (1990, p01841, 1991, indicating that auroral geomagnetic indices could be reduced to low-dimensional systems with chaotic dynamics.
  • Pulkkinen, T. I.; Dimmock, A. P.; Lakka, A.; Osmane, A.; Kilpua, E.; Myllys, M.; Tanskanen, E. I.; Viljanen, A. (2016)
    We examine the role of the magnetosheath in solar wind-magnetosphere-ionosphere coupling using the Time History of Events and Macroscale Interactions during Substorms plasma and magnetic field observations in the magnetosheath together with OMNI solar wind data and auroral electrojet recordings from the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain. We demonstrate that the electric field and Poynting flux reaching the magnetopause are not linear functions of the electric field and Poynting flux observed in the solar wind: the electric field and Poynting flux at the magnetopause during higher driving conditions are lower than those predicted from a linear function. We also show that the Poynting flux normal to the magnetopause is linearly correlated with the directly driven part of the auroral electrojets in the ionosphere. This indicates that the energy entering the magnetosphere in the form of the Poynting flux is directly responsible for driving the electrojets. Furthermore, we argue that the polar cap potential saturation discussed in the literature is associated with the way solar wind plasma gets processed during the bow shock crossing and motion within the magnetosheath.
  • Dimmock, A. P.; Osmane, A.; Pulkkinen, T. I.; Nykyri, K.; Kilpua, E. (2017)
    The magnetosheath contains an array of waves, instabilities, and nonlinear magnetic structures which modify global plasma properties by means of various wave-particle interactions. The present work demonstrates that ion-scale magnetic field structures (similar to 0.2-0.5 Hz) observed in the dayside magnetosheath are statistically correlated to ion temperature changes on orders 10-20% of the background value. In addition, our statistical analysis implies that larger temperature changes are in equipartition to larger amplitude magnetic structures. This effect was more pronounced behind the quasi-parallel bow shock and during faster solar wind speeds. The study of two separate intervals suggests that this effect can result from both local and external drivers. This manuscript presents two separate case studies, one from using THEMIS (Time History of Events and Macroscale Interactions during Substorms) data and another from Magnetospheric Multiscale; these measurements are then supported by extensive THEMIS statistical observations. These results could partly explain the 10-20% dawn-favored asymmetry of the magnetosheath ion temperature seed population and contribute to the dawn-favored asymmetry of cold component ions in the cold dense plasma sheet.
  • Lakka, Antti; Pulkkinen, Tuija I.; Dimmock, Andrew P.; Osmane, Adnane; Honkonen, Ilja; Palmroth, Minna; Janhunen, Pekka (2017)
    We investigate the effects of different initialisation methods of the GUMICS-4 global magnetohydrodynamic (MHD) simulation to the dynamics in different parts of the Earth's magnetosphere and hence compare five 12 h simulation runs that were initiated by 3 h of synthetic data and followed by 9 h of solar wind measurements using the OMNI data as input. As a reference, we use a simulation run that includes nearly 60 h of OMNI data as input prior to the 9 h interval examined with different initialisations. The selected interval is a high-speed stream event during a 10-day interval (12-22 June 2007). The synthetic initialisations include stepwise, linear and sinusoidal functions of the interplanetary magnetic field with constant density and velocity values. The results show that the solutions converge within 1 h to give a good agreement in both the bow shock and the magnetopause position. However, the different initialisation methods lead to local differences which should be taken into consideration when comparing model results to satellite measurements.