caa a22 4500 469077131 CHVBK 20180323132938.0 cr unu---uuuuu 170328e19920901xx s 000 0 eng 10.1007/BF02507839 doi (NATIONALLICENCE)springer-10.1007/BF02507839 Magnetohydrodynamic instabilities at Comet P/Halley: Giotto observations [Elektronische Daten] [G. Bellucci, V. Formisano, E. Amata] Summary: We examine the plasma parameters observed by the ion mass spectrometer of the Giotto JPA experiment, downstream the bow shock and up to the closest approach of comet P/Halley. From the analysis of the observations we have identified two regions where the ΔV between the proton and water group ion bulk velocities is first parallel and later perpendicular, respectively, to the magnetic-field direction. In the parallel region, a strong MHD turbulence is observed that we suppose to be generated by a firehose instability mechanism driven by the velocity difference. At about 5·105 km from closest approach, the center of mass switches from solar-wind protons to the cometary ions, while the velocity difference becomes perpendicular to the magnetic field, causing the quenching of the isstability and the disappearing of the plasma fluctuations. Società Italiana di Fisica, 1992 Interplanetary space nationallicence Comets nationallicence Plasma instabilities nationallicence Bellucci G. Istituto di Fisica dello Spazio Interplanetario, CNR, Via Galileo Galilei, C.P. 27, 00044, Frascati, Italia aut Formisano V. Istituto di Fisica dello Spazio Interplanetario, CNR, Via Galileo Galilei, C.P. 27, 00044, Frascati, Italia aut Amata E. Istituto di Fisica dello Spazio Interplanetario, CNR, Via Galileo Galilei, C.P. 27, 00044, Frascati, Italia aut Il Nuovo Cimento C Kluwer Academic Publishers 15/5(1992-09-01), 665-673 0390-5551 15:5<665 1992 15 11543 https://doi.org/10.1007/BF02507839 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF02507839 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Bellucci G. Istituto di Fisica dello Spazio Interplanetario, CNR, Via Galileo Galilei, C.P. 27, 00044, Frascati, Italia aut NATIONALLICENCE 700 1- Formisano V. Istituto di Fisica dello Spazio Interplanetario, CNR, Via Galileo Galilei, C.P. 27, 00044, Frascati, Italia aut NATIONALLICENCE 700 1- Amata E. Istituto di Fisica dello Spazio Interplanetario, CNR, Via Galileo Galilei, C.P. 27, 00044, Frascati, Italia aut NATIONALLICENCE 773 0- Il Nuovo Cimento C Kluwer Academic Publishers 15/5(1992-09-01), 665-673 0390-5551 15:5<665 1992 15 11543 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer