The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed

Power to the magnetosphere: May 4, 1998

An extraordinary powering of the magnetosphere by the solar wind occurred in a 3-hour burst early on May 4 when the IMF was very intense and pointed south (≈-35 nT; “erosion phase”). Examining solar wind streams over 3 months, we found that May 4 represented a very fast, hot, non-corotating stream overtaking an interplanetary coronal mass ejection (ICME), thus forming a compound stream. By integrating the “epsilon” parameter over time, we find that the energy deposited in the magnetosphere during the erosion phase on May 4 (of order 7.5 J m−2) was higher to that deposited during the previous 3-day period, itself a very geoeffective interval. We compare the energy and power supply to the magnetosphere on May 4 with 13 other events, mainly ICMEs and magnetic clouds, during the period 1995–2000. Specifically, we examine (a) the total energy input over 3 days, and (b) the average power over a 3-hour period near maximum power of the respective configurations. As regards (a), we find the energy of the May 4 stream to be comparable to that of the strong events observed during the 6-year period. As regards (b), we find May 4 to represent a large fluctuation from the norm, exceeded only by the Bastille Day event (July 15, 2000). The ability to predict a concentration of electromagnetic power and energy such as that in the May 4 fast stream poses a challenge to our ability to predict space weather

Large-scale geomagnetic effects of May 4, 1998

We study large-scale magnetospheric disturbances elicited by the May4, 1998 high speed stream by modeling the Dst and studying records from 4 meridional magnetometer chains covering key local time sectors. The quasi-sequential episodes of Bz < < 0 and high dynamic pressure (10–50 nPa) allow a clean separation of their respective geoeffects. Ring current evolution is followed by the kinetic model of Jordanova et al. (1998), which includes both charge exchange and Coulomb collisions of ring current ions H+, He+ and O+ drifting in a Volland-Stern convection electric field. The overall agreement with the temporal variation of the Dst is very good, but the strength of the great storm (min Dst = -280 nT) with its rapid main phase is not reproduced fully. A very asymmetric ring current forms near minimum Dst with maximum energy density located at dusk for all ion species. The data show evidence of (a) a great geomagnetic storm; (b) large enhancements of magnetopause currents; (c) substorm onsets, some of which were triggered; (d) a convection reversal boundary at relatively low latitudes (60–65°); and (e) what might be omega bands at morning local times associated with substorm recovery. An unprecedented measurement at Halley Bay station of an approximately 10% change in the ambient magnetic field strength is related to a sharp 5-fold increase in the dynamic pressure and to a large (≈50 nT) variation in IMF B

The Earth: Plasma Sources, Losses, and Transport Processes

International audienceThis paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed