Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ) electric field variations with the post sunset F-region electrodynamics

The paper is based on a detailed observational study of the Equatorial Spread F (ESF) events on geomagnetically quiet (<I>A<sub>p</sub></I>≤20) days of the solar maximum (2001), moderate (2004) and minimum (2006) years using the ionograms and magnetograms from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat ~0.5° N) in India. The study brings out some interesting aspects of the daytime Equatorial Electrojet (EEJ) related electric field variations and the post sunset F-region electrodynamics governing the nature of seasonal characteristics of the ESF phenomena during these years. The observed results seem to indicate a plausible linkage of daytime EEJ related electric field variations with pre-reversal enhancement which in turn is related to the occurrence of ESF. These electric field variations are shown to be better represented through a parameter, termed as "E", in the context of possible coupling between the E- and F-regions of the ionosphere. The observed similarities in the gross features of the variations in the parameter "E" and the F-region vertical drift (<I>V<sub>z</sub></I>) point towards the potential usage of the EEJ related parameter "E" as an useful index for the assessment of <I>V<sub>z</sub></I> prior to the occurrence of ESF

Role of gravity wave like seed perturbations on the triggering of ESF - a case study from unique dayglow observation

First observational evidence, from the Indian longitudes, for the presence of gravity wavelike perturbations with periods of 20-30 min, acting as probable seeds for Equatorial Spread F (ESF) irregularities is described. The study is based on the daytime optical measurements of the mesopause temperature and the intensity of the thermospheric O(1D) 630.0 nm dayglow emissions using the unique MultiWavelength Dayglow PhotoMeter from Trivandrum (8.5° N; 77° E; dip lat ˜0.5° N), a dip equatorial station. Measurements during the equinoctial months of a solar maximum (2001) and a solar minimum year (2006) have been used in this study. It is shown that under identical background ionospheric conditions within a solar epoch, the power of the gravity waves have a deterministic role in the generation of ESF. The mesopause temperature simultaneously observed, indicate that possible source regions for these perturbations lie in the lower atmosphere

The new 130-cm optical telescope at Devasthal, Nainital

A modern Ritchey-Chretien Cassegrain 130-cm diameter optical telescope has been successfully installed at Devasthal, Nainital in the central Himalayan region. This location was chosen after carrying out extensive site surveys. The first images obtained with the telescope indicate that atmospheric seeing and sky darkness at Devasthal are nearly at values as measured during the site survey. The values of seeing and sky darkness are comparable to some of the best astronomical sites in the world. The 130-cm telescope is functional and observations can be carried out from the control centre at Devasthal or from the Manora Peak in Nainital. This telescope has started providing valuable data for a number of research projects and is expected to help meet part of the national requirement in optical observational astronomy from small-aperture ground-based telescopes

Plausible explanation for the equatorial temperature and wind anomaly (ETWA) based on chemical and dynamical processes

It has been proposed earlier through independent studies that either 'chemical heating' or 'ion drag' might be responsible for the generation of a large-scale low-latitude process, namely the Equatorial Temperature and Wind Anomaly (ETWA). The present study based on simultaneous measurements of ionospheric and thermospheric parameters by DE-2 satellite alongwith some of the standard models shows that both the processes are important and necessary for the generation of ETWA. A proper quantification has been attempted with reasonable success by taking into account both the chemical heating and ion drag. The chemical heating which operates irrespective of the time of the day, has been shown to account for 25-30 K (˜30%) of the neutral temperature enhancements in ETWA. On the other hand, the ion-drag associated heating, which is operative only during daytime conditions could raise the temperature by 60-80 K. Thus the relative importance of ion drag and chemical heating have been evaluated in arriving as a plausible explanation of ETWA

IMPROVED SEARCH MECHANISM IN ABC AND ITS APPLICATION IN ENGINEERING DESIGN PROBLEMS

ABC (Artificial Bee Colony) is one of the most recent nature inspired algorithm (NIA) based on swarming metaphor. Proposed by Karaboga in 2005, ABC has proven to be a robust and efficient algorithm for solving global optimization problems over continuous space. In this paper, we propose a modified version of the ABC. In modified version called Dichotomous ABC (DABC), the idea is to move dichotomously in both directions to generate a new trial point. The results of a trade study carried out on three classical structural optimization problems taken from literature indicate the validity of the proposed algorithm

Parameterisation of the local and non-local processes in the thermospheric energy budget based on DE-2 satellite data

Though the mechanism redistributing the energy and momentum between the neutral and ionised species of the upper atmosphere i.e. thermosphere and ionosphere system (TIS) over low and equatorial latitudes are understood reasonably well, only few individual processes could be modeled so far. As a result, the most widely used thermospheric model (MSIS) is found to fall short of the true prediction of low latitude thermospheric temperatures and its variabilities. Large scale local processes like equatorial ionisation anomaly (EIA) and equatorial temperature and wind anomaly (ETWA) do affect the thermal structure of this region significantly. Apart from that, the effect of the processes which are essentially non-local in origin like the one that could be represented by the variabilities in earth's ring currents, also contribute to the thermal structure and its variabilities. The present paper deals with parameterisation of these local and non-local processes and suggests ways of incorporating the same in the existing MSIS model. It has been demonstrated that the whole exercise leads to a significant improvement in the MSIS which is now able to make very good predictions, with regard to the variabilities and in terms of absolute magnitudes on more than 50-60% of the events studied. The present results take us closer towards a realistic model for low/equatorial latitudes