NOPR Collection:

Dependence of Whistler Activity on Geomagnetic Latitude

Thu, 01 Jun 1972 00:00:00 GMT

Title: Dependence of Whistler Activity on Geomagnetic Latitude Authors: Rao, Manoranjan; Lalmani; Somayajulu, V. V.; Tantry, B. A. P. Abstract: It is shown that the coupling between the ordinary and extraordinary magneto-ionic waves in the lower ionospheric regions should also be considered as one of the factors which control the dependence of whistler activity on the geomagnetic latitude. Page(s): 192-194

Ground Riser Whistlers at Low Latitudes

Thu, 01 Jun 1972 00:00:00 GMT

Title: Ground Riser Whistlers at Low Latitudes Authors: Singh, Birbal; Misra, S. N.; Tantry, B. A. P. Abstract: An attempt has been made to explain theoretically the characteristics of ground risers reported by Dikshit et al. [Nature, Lond., 230 (1971), 114]. From computations employing Haselgrove two-dimensional ray tracing equations and the diffusive equilibrium model for electrons and ions in the magnetosphere, a riser whistler having all the characteristics of the reported ground risers was computed. The riser waves, radiated from lightning discharge, with frequencies lying between 2.8 and 7 kHz and penetrating the ionosphere at different entry points, are found to reflect at different heights during their quasi-transverse propagation but form, alter reflection, a bunch of waves to be received as a ground riser. The upper cutoff frequency (7 kHz) of the ground riser is explained in terms of the non-reflection of vlf waves in the same hemisphere as that of the originating atmospherics and crossing over the equatorial plane to be propagated in the opposite hemisphere; the lower cutoff frequency (2.8 kHz) of the whistler is explained in terms of deviation, after reflection, from the arrival latitude of the riser waves. Page(s): 188-191

Study of OH Bands at Mt Abu, India

Thu, 01 Jun 1972 00:00:00 GMT

Title: Study of OH Bands at Mt Abu, India Authors: Rao, V. Ramachandra; Kulkarni, P. V. Abstract: The intensities of two hydroxyl bands, OH (7-2) band origin at 6861 A, and OH (8-3) band origin at 7273 A, are recorded on all clear moonless nights at Mt Abu, during the period November 1966-May 1969. Both the bands show striking similarities in their behaviour showiel1 very high positive correlation. The hydroxyl night glow exhibits different types of nocturnal variation. Continuous decay till midnight followed by an increase in intensity towards dawn is the most common type of variation. The possible, causes of the different types of variation exhibited by OH are discussed in view of the two excitation mechanisms proposed for the OH night glow, considering the possible contribution from the two reactions. It is concluded that ozone-hydrogen mechanism is the main reaction as far, as nocturnal variation is concerned. The OH night glow shows maximum intensity in winter months and minimum intensity in April. This variation is more or less opposite to that of 5577 A radiation. There is an apparent increase of OH intensity with solar activity, the intensity being more in the high active period. The OH intensity also increases following magnetic storms. Page(s): 181-187

Role of Molecular Nitrogen Column Density in Controlling the Intensity of Spectral Emission in Day-glow due to Photoelectronic Impact

Thu, 01 Jun 1972 00:00:00 GMT

Title: Role of Molecular Nitrogen Column Density in Controlling the Intensity of Spectral Emission in Day-glow due to Photoelectronic Impact Authors: Singh, Raghubir; Sharma, V. N.; Tolpadi, S. K. Abstract: Intensity-height profiles for a number of day-glow spectral emissions of molecular nitrogen arising from the impact of photoelectrons produced in the photoionization of the various atmospheric species due to solar ultraviolet radiations have been theoretically calculated using the column number density instead of mere number densities. The results show that the maximum intensity for a particular emission would be observed at a particular height in agreement with the rocket measured data. The intensity-height profiles have been computed under different conditions of solar activity for some molecular nitrogen emissions expected to be observed in day-glow. The results of the present study are discussed in the light of earlier experimental results. Page(s): 178-180