NOPR Collection:

Studies on the dynamics of Venus ionosphere: Effects of varying the ionopause height and the onset of turbulence

1991-04-01T00:00:00Z

Title: Studies on the dynamics of Venus ionosphere: Effects of varying the ionopause height and the onset of turbulence Authors: Singhal, R P; Whitten, R C Abstract: The conservation equations of plasma dynamics in the upper ionosphere of Venus have been solved by using a spectral method in the horizontal and finite differencing in the vertical direction. The effect of varying the ionoapause height on the computed nightside ion densities is investigated. These ion densities show a sharp decrease as the ionopause altitude is reduced to 300 km. The effect of viscous forces on the horizontal plasma flow is investigated for a wide range of values of the coefficient of viscosity. The Reynolds numbers characteristics of the flow are calculated and the conditions for the onset of the turbulence discussed. It is found that the Reynolds number can be large (>1000) in the subsolar region for a coefficient of viscosity of h₀ 1.6 x 10^-10 gcm^-1s^-1. The influence of magnetic fields on viscosity is also discussed. Page(s): 150-156

Proton energy deposition and EUV emission in the Jovian and the Saturnian atmospheres

1991-04-01T00:00:00Z

Title: Proton energy deposition and EUV emission in the Jovian and the Saturnian atmospheres Authors: Singh, Vir Abstract: A model of the interaction of energetic protons with the atmospheres of Jupiter and Saturn is developed to examine the possibility that the high latitude ultraviolet aurorae observed on both planets are at least partly excited by proton precipitation. The method is based on the continuous slowing down approximation and takes into account the partial conversion of protons into hydrogen atoms and the contributions of secondary electrons. Comparison with previous models of auroral electron degradation in hydrogen atmospheres indicated that the efficiency of both types of particles is fairly similar. However, the relative contribution of secondary electrons in the excitation of the ultraviolet H₂ band is found to depend on the energy of the primary protons. The H/H intensity ratio is also different for proton and electron precipitations and roughly independent of the proton energy. The range of proton energies compatible with the spectral composition of the ultraviolet auroral spectra of Jupiter and Saturn is found to be ~ 1-1000 keV. It is suggested that ~ 1 MeV protons are viable candidates to explain the secondary peak observed in the longitudinal distribution of the Jovian auroral intensity. It is also shown that the H₂ bands/H ratio calculated in the model is compatible with the intensity of the visible arcs observed at Jupiter’s high latitude limb with the voyager camera. Page(s): 140-149

Models for temperature distribution in the solar atmosphere

1991-04-01T00:00:00Z

Title: Models for temperature distribution in the solar atmosphere Authors: Alam, B Abstract: A temperature model for the transition region-inner corona is deduced by assuming a constant conductive flux from higher temperature region towards the lower temperature region. Moreover, using the observed temperatures, a general model (denoted by A) is also fitted, which appears to represent the whole temperature regime of the solar atmosphere. These models are then compared with our earlier models. Besides, a comparative study of all of our models (earlier and present ones ) with various sets of parameters is also presented. The temperature distribution given by all these models do not differ much from each other. Consequently, one from each region, i.e. TR2 for the transition region-inner corona and OC2 for the outer corona, may be chosen as representative models. The combination of these two models then represents the whole solar atmosphere. Page(s): 135-139

Global peak flux profile of proton precipitation in the equatorial zone

1991-04-01T00:00:00Z

Title: Global peak flux profile of proton precipitation in the equatorial zone Authors: Miah, M A Abstract: Particle precipitation near the equator within ±30° geomagnetic latitude was investigated by the Phoenix-1 instrumentation on board the S81-1 mission. The monitor telescope on board the mission was sensitive to protons in the energy range 0.6-91 MeV, to alpha particles in the energy range 0.4-80 MeV/nucleon and Z 3 particles (¹²C) of energy greater than 0.7 MeV/nucleon. The peak efficiency of the telescope was for particles of ~ 88° pitch angles at the line of minimum magnetic field. Careful separation of the magnetically quiet time equatorial particle data from global data coverage and subsequent analysis shows that the ML detector on board the mission detected mostly protons. The proton peak flux profile follows the line of minimum magnetic field. The full width at half maximum (FWHM) of the equatorial zone is ~ 13°, which is well within the EUV emission zone. Page(s): 127-134