Transcript Energy?
Warm trapped (plasmaspheric) ion plume at ≤keV energy confined near the equator M. Yamauchi1, I. Dandouras2, H. Reme2, F. El-Lemdani Mazouz3, S. Grimald2, J. Pickett4 (1) IRF, Kiruna, Sweden (2) CNRS and U. Toulouse, IRAP, Toulouse, France (3) LATMOS, IPSL, Paris, France (4) University of Iowa, USA EGU2012-353 (XY680, 2012-4-25) Analyses Where? ~4 RE, confined near the equator (Cluster perigee) Species? H+ and He+ of ten’s eV ~ keV (CIS energy range) Energy? Pancake-like trapped ions (cf. Olsen et al., 1987) In this work: First time to examine features for > 50 eV, together with waves, using traversals in 2001-2002 (nearly 200 traversals). New results: * Ion characteristics in energy-time domain (Fig. 1, 3) * Ion distribution (Fig. 2) * Ion composition at different energy (Fig. 1, 2, 3) * Advantage of Cluster : time scale (Fig. 3, 5) and statistics (Fig. 4) * Accompanying waves = future work (Fig. 5) Figure 1 Energy-time spectrograms of differential energy flux observed by CIS/CODIF. (a) Average of looking directions 1, 2, 7, and 8, which correspond to anti-parallel (1,2) and parallel (7,8) directions to the geomagnetic field. (b)-(e) Average of looking directions 4 and 5, which correspond to nearly perpendicular direction to the geomagnetic field. The vertical arrow at the bottom indicates the crossing of the equatorial plane defined by wave activities (cf. Figure 5). Intense signature of H+ & He+ Only in the direction equator Confined near the equator (a) and (b): Velocity-space distribution function of H+ for energy < 2 keV for onespin data starting 1751:00 UT. Scale is linear in velocity, and is converted to energy in the vertical axis. The data are integrated over (a) 200 km width and (b) 50 km width over the third axis. White void region of the central circle correspond to energy < 25 eV (=no data). distribution at equator Flattened gyrotropic distribution. (c) and (d): Differential energy flux observed by SC-4 and SC-1, averaged over 7-8 spins (about 1~2 min). To remove the contamination from the radiation belt particles, difference of the values between the parallel and perpendicular directions is plotted (below the noise level = plotted on the x axis). Center energy ≠0, i.e., Figure 2 The dashed lines assumed a ring distribution of form of ~ exp[-(E-E0)/∆E], Ring distribution but not pancake (new!) i.e., E0 is the center energy of the ring and ∆E is approximate width of the ring. He+ energy > H+ energy (new!) Figure 3 Same format as Figure 1, but for only H+ and He+ data in the looking directions 4 & 5 (perpendicular to the geomagnetic field) for SC-1, SC-4, and SC-3 Energy time dispersion (new!) equator Sudden appearance in 40 min (new!) The energy time dispersion indicates a drift from a remote source (dispersion comes from the energy dependent magnetic drift). The difference in the drift speed between 150 eV ions and 30 eV ions is ~0.04 MLT/h at 4 RE. Since the drift at 17 MLT is mainly determined by corotation, it takes about 3 min (time lag in the dispersion in SC-3) to travel 0.04 MLT. From this, the drift time is expected to be 1 hour. This agrees with the sudden appearance in 40 min. equator equator Statistics Figure 4 CODIF (>30 eV) is operated most often on SC-4. Severe contamination by the radiation belt after 2003. Remove traversals with severe contamination. Total 164 traversals. The observation probability ~ 35-45% (more in noon/dusk than night-dawn) He+ energy statistics: Selected all “intense” H+ signature (> 3·106 keV cm-2s-1str-1keV-1) in traversals when He+ channel is not severely contaminated. Total 29 traversals. * He+ energy >> H+ energy : 10 events (ratio varies up to 10) * He+ energy ~ H+ energy : 6 (3 of them might be H+ contamination) * Without He+ signature : 13 events Energy ratio between He+ and H+ varies (new!) Dominated by H+ with variable content of He+ (mostly < 5%) Energy-time dispersion: The same 29 events are used. * With clear dispersion: 5 events (not often) Summary (1) Non-thermal ring distribution rather than pancake distribution. (2) Energy ratio of the ring between He+ and H+ = 1~10. (3) Some events show energy-time dispersion, indicating the drift. (4) The time scale of the development ~ 1 h. (5) Pitch angle ~ 90° for also > 30 eV. (6) Observation probability at 4~4.5 RE is ~ 40-45% in noon and dusk sectors and about 20-25% in the night-to-dawn sector. (7) Dominated by tens eV H+ with variable content of He+. The He+/H+ ratio is much less than 5% for the majority of the cases. (8) Co-located with wave-defined equator comparison between the ion signature and wave activity. Future work Dynamical Co-located waves are (n+0.5)f bursts at ten’s kHz, lower hybrid Figure 5 ce bursts at 100~200 Hz (weak in 2002-1-3 event), and broadband bursts at ~10 Hz. Are (n+0.5)fce bursts generated as the result of ion event?