Browsing by Author "Santolik, O."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item EMIC waves converted from equatorial noise due to M/Q = 2 ions in the plasmasphere: Observations from Van Allen Probes and Arase(American Geophysical Union, 2019-06-07) Miyoshi, Y.; Matsuda, S.; Kurita, S.; Nomura, K.; Keika, K.; Shoji, M.; Kitamura, N.; Kasahara, Y.; Matsuoka, A.; Shinohara, I.; Shiokawa, K.; Machida, S.; Santolik, O.; Boardsen, S. A.; Horne, R. B.; Wygant, J. F.Abstract Equatorial noise (EN) emissions are observed inside and outside the plasmapause. EN emissions are referred to as magnetosonic mode waves. Using data from Van Allen Probes and Arase, we found conversion from EN emissions to electromagnetic ion cyclotron (EMIC) waves in the plasmasphere and in the topside ionosphere. A low‐frequency part of EN emissions becomes EMIC waves through branch splitting of EN emissions, and the mode conversion from EN to EMIC waves occurs around the frequency of M/Q = 2 (deuteron and/or alpha particles) cyclotron frequency. These processes result in plasmaspheric EMIC waves. We investigated the ion composition ratio by characteristic frequencies of EN emissions and EMIC waves and obtained ion composition ratios. We found that the maximum composition ratio of M/Q = 2 ions is ~10% below 3,000 km. The quantitative estimation of the ion composition will contribute to improving the plasma model of the deep plasmasphere and the topside ionosphere. Plain Language Summary Equatorial noise (EN) emissions are whistler mode waves. Using Van Allen Probe and Arase (ERG) plasma wave data, we found that EN emissions propagate toward the Earth and are converted to electromagnetic ion cyclotron (EMIC) waves in the deep plasmasphere and the topside ionosphere. We suggest that minor ions with a mass per charge (M/Q) = 2, that is, deuteron or alpha particles, play an important role in this process. The processes reported here are a new generation process of plasmaspheric EMIC waves. Moreover, we determined the ion composition ratio using characteristics of wave dispersion. We derived the altitude profile of the ion composition ratio and identified the maximum ratio of M/Q = 2 ions of about 10% in the deep plasmasphere.Item SHEDDING NEW LIGHT ON SOLITARY WAVES OBSERVED IN SPACE(European Space Agency, 2006-01) Pickett, J.S.; Chen, L.-J.; Gurnett, D.A.; Swanner, J.M.; Santolik, O.; Décréau, P.M.E.; Géghin, C.; Sundkvist, D.; Lefebvre, B.; Goldstein, Melvyn; Lavraud, B.; Lucek, E.; Kessel, R.; Lakhina, G.S.; Singh, S.V.; Reddy, R.V.; Tsurutani, B.T.; Rème, H.; Fazakerley, A.Electrostatic solitary waves are routinely observed by the Cluster Wideband (WBD) plasma wave receiver as the Cluster spacecraft cross boundary layers and regions of turbulence. These solitary waves are observed in the electric field waveform data as isolated pulses of various shapes, but primarily in the bipolar and tripolar forms. The amplitudes of the solitary waves appear to follow a somewhat general trend of increasing amplitude with increasing background magnetic field strength. Thus, the largest amplitude solitary waves are usually found closer to Earth as Cluster crosses magnetic field lines at about 4.5-6.5 RE that map to the auroral acceleration region and the smallest amplitudes farthest from Earth in the plasmasheet, magnetosheath and solar wind at 18-19.5 RE. Bow shock crossings are particularly interesting as there are significant differences in the number, amplitude and time duration of solitary wave pulses detected which probably indicate a dependence on the upstream environment and configuration of the interplanetary magnetic field. Continuing closer to earth into the magnetosheath we find that on the dayside, solitary waves are almost always present and the characteristics of them do not change appreciably from the bow shock to the magnetopause. This suggests that the solitary waves observed in the magnetosheath are being locally produced in the magnetosheath through one or more generation mechanisms. As we explore the properties of these solitary waves in the various regions, as well as the methods by which they could be produced, we hope to determine if and how these solitary waves are involved in more fundamental macroscale plasma processes.Item Statistical survey of the terrestrial bow shock observed by the Cluster spacecraft(American Geophysical Union, 2019-02-13) Kruparova, O.; Krupar, V.; Šafránková, J.; Němeček, Z.; Maksimovic, M.; Santolik, O.; Soucek, J.; Němec, F.; Merka, J.The terrestrial bow shock provides us with a unique opportunity to extensively investigate properties of collisionless shocks using in situ measurements under a wide range of upstream conditions. Here we report a statistical study of 529 terrestrial bow shock crossings observed between years 2001 and 2013 by the four Cluster spacecraft. By applying a simple timing method to multipoint measurements, we are able to investigate their characteristic spatiotemporal features. We have found a significant correlation between the speed of the bow shock motion and the solar wind speed. We have also compared obtained speeds with time derivatives of locations predicted by a three‐dimensional bow shock model. Finally, we provide a list of bow shock crossings for possible further investigation by the scientific community. Plain Language Summary The Sun is continuously emitting a stream of charged particles—called the solar wind—from its upper atmosphere. The terrestrial magnetosphere forms the obstacle to its flow. Due to supersonic speed of the solar wind, the bow shock is created ahead of the magnetosphere. This abrupt transition region between supersonic and subsonic flows has been frequently observed by the four Cluster spacecraft. Using a timing analysis, we have retrieved speed and directions of the bow shock motion for a large number of crossings. We have correlated the bow shock speed with the solar wind speed and predictions of the bow shock locations by the empirical model. A better understanding of the bow shock kinematics may bring new insights to wave‐particle interactions with applications in laboratory plasmas.