Based on the Van Allen Probe A observations from 1 October 2012 to 31 December 2014, we develop two empirical models to respectively describe the hiss wave normal angle (WNA) and amplitude variations in the Earth's plasmasphere for different substorm activities. The long‐term observations indicate that the plasmaspheric hiss amplitudes on the dayside increase when substorm activity is enhanced (AE index increases), and the dayside hiss amplitudes are greater than the nightside. However, the propagation angles (WNAs) of hiss waves in most regions do not depend strongly on substorm activity, except for the intense substorm‐induced increase in WNAs in the nightside low L‐region. The propagation angles of plasmaspheric hiss increase with increasing magnetic latitude or decreasing radial distance (L‐value). The global hiss WNAs (the power‐weighted averages in each grid) and amplitudes (medians) can be well reproduced by our empirical models.
[1] In the quasi-linear approximation, we study electron acceleration process generated by whistler-mode and compressional ULF (fast mode waves) turbulences near the Earth's synchronous orbit. The results show that the whistler-mode turbulence (0.1f ce f 0.75f ce ) can accelerate substorm injection electrons with several hundreds of keV through wave-particle gyroresonant interaction and hence may play an important role in the electron acceleration during substorms. The compressional ULF turbulence (2-15 mHz) can accelerate both lower-energy background electrons (<30 keV) and substorm injection electrons ($30-300 keV) through the transit-time damping mechanism. So the compressional ULF turbulence acceleration mechanism is important during both substorms and quiet times. The compressional ULF turbulence accelerates substorm injection electrons more effectively than whistler-mode turbulence. The combined electron acceleration by whistler-mode and ULF turbulences is most effective and can cause the number density of the relativistic electrons increase largely within about 8 hours. Substorms can offer both substorm injection electrons and strong turbulences, and therefore large flux enhancement events of relativistic electrons (!1 MeV) always occur during substorm time. For magnetic storms that are composed of a series of substorms, extremely large flux enhancement events of the relativistic electrons can thus occur.Citation: Li, L., J. Cao, and G. Zhou (2005), Combined acceleration of electrons by whistler-mode and compressional ULF turbulences near the geosynchronous orbit,
[1] Since storms/substorms can lead to flux enhancements of relativistic electrons (E > 500 keV) in one region of the outer zone (L $ 2-7) and simultaneously to flux decreases in another region, the final effects of storms/substorms on changing the entire outer zone relativistic electron population are indicated by the total flux variation of the entire outer zone relativistic electrons. The total flux of the relativistic electrons is the summation of their omnidirectional integral fluxes over the entire outer zone. By analyzing the total flux variations of relativistic electrons in the entire outer zone during about 18 storms from August 1990 to March 1991, this paper investigates the statistical relationships between the total flux variations of the entire outer zone relativistic electrons and the intensities of storms/substorms. The statistical results indicate that the primary impact of a storm development is the net loss of relativistic electrons from the entire outer zone via the main phase losses of relativistic electrons, whereas the continuous intense substorm activity (average AE > 200 nT) can lead to the net increases of the relativistic electrons in the entire outer zone. Furthermore, the more intense the substorm activity, the larger the increases of the relativistic electrons, indicating that the continuous intense substorm activity can effectively supply relativistic electrons for the entire outer zone. Since the net increases of the relativistic electrons usually occur during the continuous intense substorm activity, the effective acceleration of the relativistic electron is correlated with the continuous intense substorm activity, e.g., the stochastic acceleration of electron by whistler mode chorus waves.
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