The distribution of ion beams and conics below 8000 km

Abstract

Measurements from electrostatic analyzers aboard the polar-orbiting S3-3 satellite have been tabulated to form a synoptic picture of the occurrence of upgoing 90eV to 3.9keV auroral ions. In this survey, a distinction is made between ion distributions having peak fluxes along B (beams) and those exhibiting flux maxima that are not field-aligned (conics). It is shown that both beams and conics are common auroral phenomena, whose frequencies of occurrence in latitude, local time, and altitude have a marked dependence on magnetic activity. During quiet conditions (Kp • 3) conical ion distributions are observed with constant frequency in altitude above 1000 km and appear to be associated with the daytime polar cusp region. In contrast, quiet time ion beams have a maximum occurrence frequency in the premidnight sector. Ion beams are observed primarily above 5000 km, with a frequency increasing with altitude up to the satellite apogee at 8000 km. During disturbed times, ion beams are a persistent phenomenon, mainly confined to the dusk sector, while conical distributions are observed uniformly in local time with a frequency that increases steadily in altitude. The results of this study, which are shown to be consistent with previous surveys of upward flowing ions if no distinction is made between conical and field-aligned distributions, provide information relating to auroral ion acceleration processes.

Acceleration from Field-Aligned Potential Drops

“…Unfortunately, cp^ is usually distributed over several 1000 km, and E l is difficult to measure directly. However, particle distributions measured immediately above or below, but also inside the parallel potential drop reflect the experienced acceleration and allow in many cases a derivation of the magnitude of 4> l (Gorney et al 1981). The transverse electric field, on the other hand, is strong and has been measured extensively.…”

“…Acceleration from magnetic field-aligned potential drops is known to occur at several 1000 km altitudes above auroral arcs (e.g., Mozer et al 1977;Sharp, Johnson, & Shelley 1977;Gorney et al 1981). It is thus the closest realization of a powerful cosmic acceleration process, easy to probe, and, indeed, documented by a wealth of data (a good collection of papers with data from the Swedish Viking satellite can be found in the May issue [no.…”

The relationship between suprathermal heavy ion outflow and auroral electron energy deposition: Polar/Ultraviolet Imager and Fast Auroral Snapshot/Time‐of‐Flight Energy Angle Mass Spectrometer observations

“…Regardless of what other processes are involved, the escape of heavy ions from Earth's gravity undoubtedly requires either parallel acceleration or perpendicular heating to gain the 10 eV or more of energy needed. In the low-altitude region pertinent to this study (_< 4000 km), conic distributions dominate over beams [Gorney et al, 1981;Miyake et al, 1996], so that perpendicular heating is the most important process. Recent statistical studies using Freja data at 1700 km ] and Fast Auroral Snapshot (FAST) data between 2000 and 4000 km [Lund et al, 2000] suggest that broadband extremely low frequency (BBELF) waves are the dominant heating agent in this region, eclipsing electromagnetic ion cyclotron waves and lower hybrid waves.…”

Modeling of occurrence frequencies of ion conics as a function of altitude and conic angle

“…There have been several reports on occurrence frequencies of ion conics based on satellite observations (Gorney et al, 1981;Yau et al, 1984;Kondo et al, 1990;Thelin et al, 1990;Peterson et al, 1992;Miyake et al, 1993Miyake et al, , 1996. Most of them, however, did not examine the quantitative relationship of the observed occurrences between ion conics with di erent conic angles and at di erent altitudes.…”