B.S.N. Prasad

Vertical structure of mesospheric echoes from the Indian MST radar

An experiment has been carried out using the Indian MST Radar located at Gadanki (13.5degreesE, 79.2degreesN) to investigate the radio wave (53 MHz) scattering characteristics from mesospheric region and associated dynamical phenomena. The main objective is to study the temporal variation of the vertical structure of the radar return echo power and the dynamics of the scattering regions within the mesosphere based on the observations conducted during the period March 1998-July 1999 with radar time provided for 2 days per month. The results presented here show general agreement with those obtained earlier using the Jicamarca radar. However, some of the new features brought out by the analysis of data include (a) significant height variation of the main scattering field/layer occurring between 68 and 76 km with lowest in winter and highest in summer months, (b) the intensity of radar return echo shows periodic variations indicating generation and decay of major scattering centres caused by neutral turbulence and (c) the absolute magnitudes of the fine-of-sight velocities are found to be anti-correlated with the strength of the return echo power. The mechanisms leading to the fluctuations in the refractive indices responsible for mesospheric echoes are discussed and a synthesised view is presented for possible explanations to these results

The Electrical Conductivity as an Index of Air Pollution in the Atmosphere

Air is never perfectly clean. Many natural sources of air pollution have always existed. Ash from volcanic eruptions, salt particles from breaking waves, pollen and spores released by plants, smoke from forest and brushfires, and windblown dust are all examples of natural air pollution. Human activities, particularly since the industrial revolution, have added to the frequency and intensity of some of these natural pollutants. Air pollution has considerable effects on many aspects of our environment: visually aesthetic resources, vegetation, animas, soils, water quality, natural and artificial structures, and human health. The effect of air pollution on vegetation include damage to leaf tissue, needles, or fruit, reduction in growth rates or suppression of growth, increased susceptibility to a variety of diseases, pests, and adverse weather. Air pollution can affect human health in several ways. The effects on an individual depend on the dose or concentration of exposure and other factors, including individual susceptibility. Some of the primary effects of air pollutants include toxic poisoning, causing cancer, birth defects, eye irritation and irritation of the respiratory system, viral infections causing pneumonia and bronchitis, heart diseases, chronic diseases, etc. The consequences of air pollution reach beyond health and agriculture, and they influence the weather as well. There is strong evidence that increased atmospheric contamination reduces visibility, modifies electrical conductivity, alters precipitation, and changes the radiation balance. The very presence of a city affects the local climate, and as the city grows, so does its climate changes. Now-a-days, cities are warmer than the surrounding areas. The temperature increase is a result of the enhanced production of heat energy, may be the heat emitted from the burning of fossil fuels and other industrial, commercial, and residential sources, and the decreased rate of heat loss since the dust in the urban air traps and reflects back into the city as long wave radiation. In addition, particulates in the atmosphere over a city are often at least 10 times more abundant than in rural areas. Although the particulates tend to reduce incoming solar radiation by up to 30% and thus cool the city, this cooling effect of particulates is small in relation to the effect of processes that produce heat in the city. Particulate matter encompasses the small particles of solid or liquid substances that are released into the atmosphere by many activities and are referred to as aerosols. Modern farming adds considerable amounts of particulate matter to the atmosphere, as do

A simplified D-region ion chemistry scheme and its possible use for IRI lower ionosphere modelling

Abstract Ion composition of the D region is principally characterized by the existence of two distinct regions of predominant molecular ions and predominant cluster ions, separated from each other by a rather sharp ‘transition height’, which is proposed to be included in the IRI as an additional parameter, supplementing the electron density models. It is possible to predict the position of this ‘transition height’ at a given place and time with the aid of a simplified ion chemistry scheme which is shown to be satisfactorily compatible with experimental ion composition data available in the literature. Our suggested method of this prediction makes use of the (IRI or experimental) electron density profile at the location and season in question, together with an effective clustering rate coeeficient calculated from corresponding temperature and density profiles taken from a suitable reference model of the neutral atmosphere.