Drift rate in a dipole field

Abstract. The Polar Ionospheric X-ray Imaging Experiment (PIXIE) and the ultraviolet imager (UVI) onboard the Polar satellite have provided the first simultaneous global-scale views of the patterns of electron precipitation through imaging of the atmospheric X-ray bremsstrahlung and the auroral ultraviolet (UV) emissions. While the UV images respond to the total electron energy flux, which is usually dominated by electron energies below 10 keV, the PIXIE, 9.9-19.7 keV X-ray images used in this study respond only to electrons of energy above 10 keV. Previous studies by ground-based, balloon, and space observations have indicated that the patterns of energetic electron precipitation differ significantly from those found in the visible and the UV auroral oval. Because of the lack of global imaging of the energetic electron precipitation, one has not been able to establish a complete picture. In this study the development of the electron precipitation during the different phases of magnetospheric substorms is examined. Comparisons are made between the precipitation patterns of the high-energy (PIXIE) and low-energy (UVI) electron populations, correlated with ground-based observations and geosynchronous satellite data. We focus on one specific common feature in the energetic precipitation seen in almost every isolated substorm observed by PIXIE during 1996 and which differs significantly from what is seen in the UV images. Delayed relative to substorm onsets, we observe a localized maximum of X-ray emission at 5-9 magnetic local time. By identifying the location of the injection region and determining the substorm onset time it isfound that this maximum most probably is caused by electrons injected in the midnight sector drifting (i.e., gradient and curvature drift) into a region in the dawnside magnetosphere where some mechanism effectively scatters the electrons into the loss cone.

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Global‐scale electron precipitation features seen in UV and X rays during substorms

Østgaard¹,

Stadsnes²,

Bjordal³

et al. 1999

“…In Figure 3 the Universal Time at which the large flux gradient was observed is plotted for each of the measured energy bands for the nose structure of Orbit 314. The calculated longitudinal drift times (Lew, 1961) for protons at these energies, injected near midnight and gradient drifting around to the point of the satellite observation, are shown as the solid line. This line is normalized to 13.5 keV to correspond to the earliest proton flux increase.…”

Section: Characteristic Features Of Ring Current Enhancementsmentioning

confidence: 99%

Direct observations in the dusk hours of the characteristics of the storm time ring current particles during the beginning of magnetic storms

Smith¹,

Hoffman²

1974

196

136

The characteristic features of the initial enhancement of the storm time ring current particles in the evening hours are consistent with flow patterns resulting from a combination of inward convection, gradient drift, and corotation, which carries plasma sheet protons into low L values near midnight and the higher‐energy proton component into the plasmasphere and through the evening hours. Data from four magnetic storms during the early life of S³‐A (Explorer 45) when the local time of apogee was in the afternoon and evening hours show that protons with lower magnetic moments penetrate deeper into the magnetosphere until a lower limit, determined by the corotation and gradient drift forces, is reached. Such particle motions produce the stable energy‐dependent inner boundary of the ring current protons inside the plasmapause in the dusk sector and also provide the mechanism for energy injection into the ring current region. From the analyses of the pitch angle distributions it is evident that charge exchange and wave‐particle interactions are not the dominant causes of this inner boundary. Observations of plasma sheet protons and electrons at altitudes just beyond the measured plasmapause are also consistent with the resulting flow patterns.

“…electric field [ Volland, 1973;Stern, 1974]. As for the off-90° pitch angle particle motions at the equator, several approximation methods to compute particle bounce period, second invariant and bounce average drift velocity have been investigated [Lew, 1961, Hamlin et al , 1961Lenchecic et al , 1.961;Schultz, 1971;Chen and Stern, 1975] . But the off-90° particle trajectories in the magnetospheric equatorial plane have not been intensively studied yet.…”

mentioning

confidence: 99%

Trajectory traces of charged particles in the magnetosphere

Ejiri¹

1978

220

188

The characteristic enhancements of ring current particles with energies of about 1–100keV, associated with magnetospheric substorms, were observed by Explorer 45 (S³‐A) around the plasmapause in the afternoon to midnight region and showed the characteristic structure called a ‘nose’ in the proton spectrograms. This paper examines the time‐developing characteristics of newly injected particles in the magnetosphere under a recently proposed convection electric field and a dipole magnetic field. Approximate equations of a bounce period, a second adiabatic invariant, and a bounce‐averaged azimuthal velocity are given with an error of less than about 10−3 for all pitch angles. The complete set of flow patterns of 90° pitch angles is also described by means of inflection lines through which radial and/or azimuthal drifts change their directions and where particle velocities show their local minima, i.e., the flow becomes sluggish. These particle tracings in the magnetosphere, from which time dependent particle fronts can be constructed, give the basic concept and mechanics to explain the complex and dynamical properties of the magnetic storm time particle enhancements.