The average global characteristics of precipitating auroral ions were determined using the data from the SSJ/4 detectors on the F6 and F7 satellites of the Defense Meteorological Satellite Program (DMSP). For this study the high-latitude region was divided into spatial elements in magnetic local time (MLT) and corrected geomagnetic latitude (CGL). One such spatial matrix was created for each of seven levels of magnetic activity as defined by Kp. Approximately 26.5 million, individual, 1-s spectra were used to determine the average ion spectrum over the energy range from 30 eV to 30 keV in each spatial zone and at each level of activity. Where appropriate, the spectra were extrapolated to 100 keV to provide a more complete estimate of the total integral energy flux, number flux, and average energy. The global patterns of the integral energy flux, integral number flux, and average energy derived from the average spectra vary smoothly with latitude, MLT, and activity. For a given Kp value the higher levels of integral energy flux occur in C-shaped regions symmetric about a meridian running prenoon to premidnight. The maximum integral energy flux is found premidnight; the minimum peak integral energy flux in latitude is found prenoon. Except in the prenoon region, the overall level of integral energy flux increases with Kp with the premidnight maximum increasing by a factor of 6.1 from Kp = 0 to Kp ≥ 6−. The maximum integral number flux is centered at noon and is taken to be the center of the cusp. The maximum value does not vary significantly with activity, although its location moves to lower latitude with increasing Kp. A minimum in the average energy also occurs in the noon meridian, several degrees poleward of the integral number flux maximum. The separation in latitude between the integral flux maximum and the average energy minimum of the cusp increases with Kp. The maximum average energy occurs on the eveningside of the oval near the equatorward boundary of the ion precipitation and shifts toward noon with increasing activity. The average integral number flux for the precipitating auroral ions is 1-2 orders of magnitude less than that for the precipitating auroral electrons at all latitudes, MLTs, and activities. The integral energy flux of the ions, on the eveningside of the oval, can equal or exceed that for the electrons near the equatorward edge of the auroral region. Integrated globally, the ratio of the ion to electron number flux varies from 0.024 to 0.015 over the range of activity from Kp = 0 to Kp ≥ 6−. The ratio for the integral energy flux ranges from 0.11 to 0.17 with no trend in activity.

A statistical model of auroral ion precipitation

Considerable information on the state of the magnetosphere is embedded in the structure of nightside charged particle precipitation. To reduce ambiguity and maximize the geophysically significant information extracted, a detailed scheme for quantitatively classifying nightside precipitation is introduced. The proposed system, which includes operational definitions and which has been automated, consists of boundary 1, the “zero-energy” convection boundary (often the plasmapause); boundary 2e, the point where the large-scale gradient dEe/dλ switches from positive to ≤0 (the start of the main plasma sheet); boundary 2i, the ion high-energy precipitation cutoff (the ion isotropy boundary or the start of the tail current sheet); boundaries 3a,b, the most equatorward and poleward electron acceleration events (spectra with “monoenergetic peaks”) above 0.25 erg/cm2 s; boundary 4s, the transition of electron precipitation from unstructured on a ≥10-km spatial scale (spectra have 0.6–0.95 correlation coefficients with neighbors) to structured (correlation coefficient usually 0.4 and below); boundary 5, the poleward edge of the main auroral oval, marked by a spatially sharp drop in energy fluxes by a factor of at least 4 to levels below those typical of the auroral oval; and boundary 6, the poleward edge of the subvisual drizzle often observed poleward of the auroral oval.

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Morphology of nightside precipitation

A detailed analysis of the ULF noise observed on the GEOS magnetic antennas in the frequency range ∼0.2'12 Hz has revealed the properties of structured emissions occurring just above the proton gyrofrequency whose existence was reported by Russell et al. (1970) and Gurnett (1976). These waves are observed in the vicinity of the geomagnetic equator at all L values between ∼4 and ∼8. They propagate in a direction perpendicular to the dc magnetic field. The waves consist of harmonically related monochromatic emissions. The fundamental frequency is generally of the order of the local proton gyrofrequency. Sometimes the fundamental and first harmonics are missing. If there is more than one fundamental frequency present, nonlinear coupling often occurs between the different emissions. The amplitudes of individual events vary from some tens of milligammas to some hundreds. Their duration ranges from some tens of minutes to some hours. Within the range of sensitivity of the detectors (10−2 γ Hz−1/2 at 1 Hz, 10−3 γ Hz−1/2) at 8 Hz the average probability of emission occurrence during a given hour is 12%, this number increases to ∼30% during the afternoon and in the pre-midnight sectors. Simultaneous observations of proton fluxes, as obtained from the two GEOS particle experiments show that these waves are often associated with distribution functions peaking at some energy (5 ≲ E ≲ 30 keV) for 90° pitch angle particles. This ring-like distribution provides the energy source for the excitation of non-resonant (k∥ = 0) instabilities near nFH+ (n = running number). A theoretical model is presented that qualitatively explains the main characteristics of the observed waves.

A systematic study of ULF Waves Above FH+ from GEOS 1 and 2 Measurements and Their Relationships with proton ring distributions

Detection of ultra-low-frequency emissions connected with the Spitak earthquake and its aftershock activity, based on geomagnetic pulsations data at Dusheti and Vardzia observatories

The departure of the aurora from quiet levels in a dynamic manner constitutes some type of auroral “breakup” event. Research into the auroral breakup predates the International Geophysical Year (1957/1958). This feature of the aurora, and the later, more global concept of the auroral substorm, has become a focus for much of the auroral research that occurs today. New instrumentation and global collaborations continue to refine our knowledge of the substorm process and how it proceeds in the ionosphere. In particular, global auroral imaging has advanced our understanding of the dynamics of the process and has given us the ability to put localized observations into a global perspective. Fundamentally new cycles of auroral activity are now understood to exist, and this has provided a means by which auroral activity can answer questions about magnetospheric substorm dynamics. Along with this wealth of observations has come a wide range of theories purporting to explain the mechanism of the onset of this phenomenon. There is, however, no single theory which stands out as clearly explaining the wide range of active auroral phenomena. A synthesis which combines these theories and allows them to each explain individual aspects of the problem appears to be required. This has led to a new way of understanding the active aurora as a set of processes or modules which occur either coupled together or independent of one another to form a particular event. This view represents a fundamental departure from the view of the substorm as a single unchanging entity. Auroral activity can rather be thought of as the earthward end of a diverse set of ionospheric and magnetospheric processes which couple together to form different cyclical patterns. A symbolic representation of this modularization is presented to simplify future schematics of large-scale auroral dynamics.

What is a global auroral substorm

The auroral ion measurements (0.4–30 keV) made from the polar satellite Aureol 1 have revealed two types of precipitation with different energy characteristics in the auroral and subauroral nighttime zone: (1) In the entire nighttime auroral zone a proton precipitation with an average energy ranging from ≃5 keV to at least 25 keV, which coincides with the region of auroral Balmer series lines emission as observed from the ground (Crasnier et al., 1974). The large scale characteristics of this precipitation reflect the adiabatic acceleration of the protons in the plasma sheet and their drift motions in the outer magnetosphere (Galperin et al., 1976, 1978). (2) A subauroral precipitation of ions with energy less than 12 to 15 keV limited to the morning sector between approximately 0000 and 0500–0600 MLT. This newly observed structure is sporadic and takes place in the hours following the injections of plasma sheet particles into the inner magnetosphere at the onset of magnetospheric substorms. The ionospheric region affected by this precipitation corresponds, in the equatorial plane, to the zone in which Alfven layers result from the ion drift pattern (from the added effects of convection and corotation electric fields and from magnetic field gradient). It is shown that the electric and magnetic field models derived by McIlwain (1972) from the energy dispersion of the particles injected at 6.6 RE at the substorm onset accounts for the main spatial and energy characteristics of these low-energy ion subauroral precipitation. This result is obtained by extending the logic used to study the proton ‘noses’ (Smith and Hoffman, 1974; Konradi et al., 1976) from the evening side to the morning side of the inner magnetosphere, and this makes it possible to obtain, from the injection boundary concept, a coherent approach to the substorm injection features at different local time sectors.

Morning sector ion precipitation following substorm injections

A study of the average energy and temperature of ions precipitated in the nocturnal auroral zone during periods of low magnetic activity is presented. On the basis of this study, carried out using the Aureole 1 satellite, it can be concluded that the characteristics of ions at auroral altitudes well reflect their convection in the distant plasma sheet and the betatron and Fermi type acceleration accompanying it.

Adiabatic acceleration induced by convection in the plasma sheet

Non-linear Alfven wave generator of auroral particles and ELF/VLF waves

Detection of suprathermal ionospheric o~ ions inside the plasmasphere

Very low frequency and ELF effects in the upper ionosphere caused by large-scale acoustic waves in the lower ionosphere observed from AUREOL-3 satellite

N. V. Jorjio

Papers

Morning sector ion precipitation following substorm injections

Adiabatic acceleration induced by convection in the plasma sheet

Non-linear Alfven wave generator of auroral particles and ELF/VLF waves

Detection of suprathermal ionospheric o~ ions inside the plasmasphere

Very low frequency and ELF effects in the upper ionosphere caused by large-scale acoustic waves in the lower ionosphere observed from AUREOL-3 satellite