Proposed optical observations of Comet Halley

A comprehensive programme is proposed for optical observations of Comet Halley based on the wide range of available facilities such as photometers, monochromators, interferometers and a polarimeter. Feasibility study of the proposed investigations with reference to existing facilities is carried out for each technique and needs for additional instrumentation are established. Conclusions for optimum utilization of existing facilities are presented.     

Ring effect and sodium dayglow

A coordinated programme of simultaneous observations of sodium dayglow and Fraunhofer Filling In (FFI) was organised for obtaining diurnal variation of sodium dayglow, free from effects of FFI or ‘Ring Effect’. Radiative transfer calculations for the estimation of sodium intensity were extended to include the combined effects of ground reflection and FFI. Our two-fold approach shows that the Ring effect could account for 30% change in the observed diurnal variation of sodium dayglow. The residual sodium intensity variation, still indicates a small variation of sodium abundance.     

Tidal components in 5577Å nightglow

Intensity variations of 5577A nightglow observed in IQSY and MAP periods are analysd for the estimation of tidal components. The analysis involves the use of photochemical model with an assumed tidal wave for the estimation of solar tidal component. A straightforward harmonic analysis has also been carried out for the estimation of lunar tidal components.     

Gravity waves from sodium-dayglow observations

The sampling interval of sodium dayglow observations was progressively reduced from one hour to two minutes for investigation of mesospheric dynamics, especially for daytime detection of the periods of gravity waves in the mesosphere and the lower thermosphere. The observations were analysed by usual power spectrum technique. The prominent periods, observed for the present, vary between 5 to 27 minutes in general agreement with results obtained by other techniques.