On the Dynamics of the Jovian Ionosphere and Thermosphere: III. The Modelling of Auroral Conductivity

Recent work has been concerned with calculating the three-dimensional ion concentrations and Pedersen and Hall conductivities within the auroral region of Jupiter for varying conditions of incident electron precipitation. Using the jovian ionospheric model, we present results that show the auroral ionospheric response to changing the incoming flux of precipitating electrons (for constant initial energy) and also the response to changing the initial energy (for both constant flux and constant energy flux). The results show that, for expected energy fluxes of precipitating particles, the average auroral integrated Pedersen conductivity attains values in excess of 1 mho. In addition, it is shown that electrons with an initial energy of around 60 keV are particularly effective at generating auroral conductivity: Particles of this energy penetrate most effectively to the layer of the jovian ionosphere at which the auroral conductivity is at a maximum.     

Evidence for periodicities in the auroral occurrence frequency since 300 AD and their implications

Spectral analyses of the Chinese auroral records dating from 300 AD using maximum entropy, Fourier and autocorrelation methods have revealed significant periods. The power spectral density of the auroral records has a strong multiplet of spectral lines centered on the median period. The prominent period is 200 years followed by enveloping bands of 80–130, 40–60 and 20–30 years. Nonstationarity is found for periods less than 120 years.The similarity of these periods with intervals between sunspot minima and other solar-terrestrial parameters is noted     

On the Dynamics of the Jovian Ionosphere and Thermosphere: II. The Measurement of H3 Vibrational Temperature, Column Density, and Total Emission

We present the first reported measurements of the intensity of a “hotband” transition for the H₃⁺ molecular ion in the northern auroral/polar region of Jupiter. This transition is identified as the R(3, 4⁺) line of the (2v₂(l=0)→v₂) hotband, with a wavelength of 3.94895 μm. This is the first time such a transition has been measured outside the laboratory, and the wavelength as measured on Jupiter is within the experimental accuracy of the lab measurement. This detection makes it possible to investigate H₃⁺ transitions that simultaneously originate from different vibrational levels. We use the intensity ratio between this line and the Q(1, 0⁻) fundamental transition to derive effective vibrational temperatures, column densities, and total emission parameters as a function of position across the auroral/polar region. Effective temperatures range from ∼900 to ∼1250 K; an increase in average temperature during our observing run of ∼100 K is noted. The derived temperatures are toward the high end or in excess of the auroral temperature range that has been reported in the literature to date. The relationship among emission intensity, temperature, and density is shown to be complex. This may reflect the nonthermalization of the vibrational levels at the gas densities prevailing in the jovian thermosphere. An alternative analysis allowing for this effect is presented. But this approach requires thermospheric temperatures to be ∼1500 K at the level that the majority of H₃⁺ is being produced, higher than has previously been proposed.     

Auroral research

An auroral substorm, unique in that it occurred at the relatively low latitude of SANAE, is described based on the full range of observational techniques at SANAE together with satellite data. Some features fit the generally accepted picture of substorms, others do not. From ground-based television imagery of Giant Undulations the temporal evolution of their dynamics is obtained and possible theories for their extistence examined. Super fast auroral waves, with speeds of up to 1200 km s^–1, have been observed for the first time. Their characteristics can not, as yet, be accounted for by a single generation mechanism. The potential value of simultaneous recordings of aurorae by television and riometer is discussed