Through a further application of the condition for magnetospheric wave growth in the presence of anisotropic charged‐particle distributions, the Kennel‐Petschek theory that traditionally imposes an upper bound on the integral flux of charged particles at energies above a certain threshold is extended to provide a limit on the differential flux at any energy above this threshold. Thus, a modest reformulation of the nonrelativistic Kennel‐Petschek problem for electrons and protons enables a limiting energy spectrum to be derived, such that (for specified pitch‐angle anisotropy s of the energetic particle population) electromagnetic‐cyclotron waves at each frequency less than a fraction s/(s + 1) of the equatorial gyrofrequency are marginally stable against spontaneous generation. The limiting spectrum is given in closed form for integer values of s (>0) and computed numerically or by analytical interpolation for non‐integer values of s. Asymptotic expansions for energies E barely above and much greater than the minimum resonant energy E* provide estimates of the limiting energy spectrum J4π*(E) in these extremes, regardless of whether s is an integer. A reconsideration of the original Kennel‐Petschek problem, in which the differential energy spectrum is not calculated but specified as a certain power law (J4π ∝ E1‐l), enables both the wave frequency ω*/2π corresponding to maximum spatial growth rate and the limiting integral flux I4π* above the minimum resonant energy E* to be calculated in closed form as functions of l and s.
The spectral characteristics and fluorescent efficiencies for electron excitation of nitrogen and air at 600 Torr have been determined. Results are presented for the efficiency of conversion of electron energy to optical radiation in approximately one hundred resolved spectral components of air and nitrogen between 3200 and 10 800 Å when bombarded by 50-keV electrons. The total fluorescent efficiency under these conditions is (0.14±0.02)% for nitrogen and (6.7±1.0)×10—3% for air. In nitrogen the first positive (B 3Πg→A 3Σu+), second positive (C 3Πu→B 3Πg), Gaydon green, Herman infrared, and Goldstein—Kaplan (C′ 3Πu→B 3Πg) band systems of N2 and the first negative (B 2Σu+→X 2Σg+) band system of N2+ were observed. The (0–2) and (0–3) transitions of the Herman infrared system and [N I]32(2D—2P) forbidden doublet at 1.04 μ, previously unreported in the laboratory, were observed. In air the first positive and second positive band systems of N2 and the first negative band system of N2+ were observed as well as atomic spectra of nitrogen, oxygen, and argon.
A Monte Carlo method was used to compute the latitudinal dispersion in the auroral zone of 5‐ to 20‐kev protons injected on a magnetic field line with equatorial pitch angles less than 3°. Neutral hydrogen atoms resulting from charge exchange at altitudes of 300–500 km were found to travel large distances across field lines. An isotropic injection pitch angle distribution results in precipitation of protons and hydrogen atoms in the atmosphere over an area as wide as 600 km. The associated auroral Balmer α emission is also expected to originate in a region several hundred kilometers wide. The mechanism described here seems adequate to account for the diffuseness of observed auroral hydrogen emission.
A model is developed for self‐modulated pulsations in the outer trapped electron belts. The pulsations are a consequence of growth of VLF waves and removal of trapped electrons following an electron injection event. If too many electrons are removed by wave interactions, the system restores itself by building up the flux again to values exceeding the equilibrium flux, repeated through many cycles. Pulsations are shown to be possible for both broadband VLF wave generation and narrowband wave generation. The resulting electron precipitation pulses are consistent with observations of pulsating aurorae on the morningside following a substorm injection event. The conditions for pulsations are quite stringent and favor trapped particle fluxes near the stable trapping limit. Individual pulses may be in or near strong diffusion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.