Studies of some diatomic molecules in the F- and early G-type dwarf stars

A critical analysis of CH, NH, OH, C₂, and CN molecules/radicals has been made in twenty-four F- and early G-type dwarfs at different effective temperature as well as in new constructed model atmosphere. Molecular indices of bandheads ofA-X system of CH, NH, OH, C₂, and CN have been obtained by using the data available in the literature (thirteen-colour and eight-colour photometry).Besides, some interesting plots of the molecular indices vs _eff, molecular abundances and molecular indices vs dissociation energy, reduced equivalent widths and FCF's vs dissociation energy for respective molecules have also been enumerated. It is found that the molecular indices at bandheads ofA-X system of CH, NH, OH, C₂, and CN are approximately constant (5810–6570 K). It is to be noted that the molecular indices decrease in the order OH, NH, CH, C₂, and CN at a given temperature.The dissociation equilibrium of CH, NH, OH, C₂, and CN is considered at 5810, 6570, and 7160 K phases in model atmosphere. At standard scale of abundance the molecular abundance and molecular index decrease in the order OH, NH, CH, C₂, and CN at any given phase, however, CN abundance and index increase (_eff=0.867-0.767). The amplitude of abundance and index variation decrease in the order NH, OH, CH, C₂, and CN (_eff=0.767-0.704).The reduced equivalent width decrease in the order OH, NH, CH, and C₂ and FCF's decrease in the order CH, OH, NH, CN, and C₂.The confrontation of models and observations of spectra of F- and early G-type dwarfs of parent molecules is of primary importance to investigate the physical conditions within atmospheres. Reliable excitation models are also requisite for interpreting spectroscopic observations of parent molecules and deriving molecular abundances.     

Numerical modeling of tide-surge interaction along Orissa coast of India

The Orissa coast of India is one of the most vulnerable regions of extreme sea levels associated with severe tropical cyclones. There was extensive loss of life and property due to the October 1999 super cyclone, which devastated large part of the Orissa coast. The shallow nature of the head bay, presence of a large number of deltas formed by major rivers of Orissa such as Mahanadi and Dhamra, and high tidal range are responsible for storm surge flooding in the region. Specifically, rising and falling tidal phases influence the height, duration, and arrival time of peak surge along the coast. The objective of the present study is to evaluate the tide-surge interaction during the 1999 Orissa cyclone by using nonlinear vertically integrated numerical models. The pure tidal solution for the head bay region of the Bay of Bengal provides the initial condition for the fine resolution nested grid Orissa model. However, the feedback from the Orissa model does not affect the head bay model as the study provides a one-way interaction. Numerical experiments are performed to study the tide-surge interaction by considering various relative phases of the tidal waves with the surge-wave produced by 1999 Orissa cyclone. The comparison, although utilizing only the limited estimates of tidal data, appears adequate to assert that the principal features are reproduced correctly.     

Variations in wave direction estimated using first and second order Fourier coefficients

In most design applications such as alignment of the berthing structure and breakwater alignment, it becomes necessary to determine the direction of design wave. There are two different approaches to determine wave direction. One involves the use of first order Fourier coefficients (mean wave direction) while the other uses second order Fourier coefficients (principal wave direction). Both the average wave direction over the entire frequency range (0.03–0.58 Hz) and the direction corresponding to the peak frequency are used in practice. In the present study, comparison is made on wave directions estimated based on first and second order Fourier coefficients using data collected at four locations in the west and east coasts of India. Study shows that at all locations, the mean and principal wave directions for frequencies ranging from 0.07 to 0.25 Hz (±0.5 times peak frequency) co-vary with a correlation coefficient of 0.99 but at lower and higher frequencies, difference between the parameters is large. Average difference between the mean wave direction at peak frequency and the average over the frequency related to spectral energy more than 20% of maximum value is less, around 13°. Study shows that average difference in the sea and swell directions is around 39°.     

Radioelement distribution in river,beach, and offshore areas and their significance to Chavara placer deposit,Southern Kerala Coast of India

The radioelement and heavy mineral distribution in river, beach and innershelf areas of the southern Kerala coast is related to placer mineral concentration on the beaches at Chavara. Southern Kerala rivers—Neyyar, Karamana and Vamanapuram—transport higher amounts of radioactive elements than the larger Kallada River due to higher radioactive minerals in the hinterland rocks. Coastal configurations and the seasonal longshore current pattern seems to control along-shore distribution of minerals. The proposed model for placer concentration suggests that the energy difference and seasonal current direction along this coast is important.     

Some vibrational bands of theC-X system of V0 molecules in the umbral spectrum of the Sun

Vibrational transition probabilities namely Franck-Condon factors and r-centroids have been evaluated using an approximate analytical method for theC-X system of V0. Morse potential energy curves forX _{4 –} andC _{4 –} states of V0 have been constructed using the latest spectroscopic data. The value of r-centroids for the band have been found to increase linearly with the corresponding wavelength. We show results for new transition and ten new bands in the umbral spectrum of the Sun.     

Variability of surface roughness and turbulence intensities at a coastal site in India

Surface-layer features with different prevailing wind directions for two distinct seasons (Southwest Monsoon and Northeast Monsoon) on the west coast of India are studied using data obtained from tower-based sensors at a site located about 500 m from the coast. Only daytime runs have been used for the present analysis. The surface boundary-layer fluxes have been estimated using the eddy correlation method. The surface roughnessz ₀ obtained using the stability-corrected wind profiles (Paulson, 1970) has been found to be low for the Southwest monsson season. For the other season,z ₀ is relatively high. The drag coefficientC _D varies with height in the NE monsoon season but not in the season with lowz ₀. This aspect is reflected in the wind profiles for the two seasons and is discussed in detail. The scaling behaviour of friction velocityu _* and the turbulence intensity of longitudinal, lateral and vertical winds _u, _v and _w, respectively) are further examined to study their dependence on fetch. Our study shows that for the non-dimensional case, _u/u_* and _v/u_* do not show any surface roughness dependence in either season. On the other hand, for _w/u_* for the season with lowz ₀, the values are seen to agree well with that of Panofskyet al. (1977) for homogeneous terrain whereas for the other season with highz ₀, the results seem to conform more to the values observed by Smedman and Högström (1983) for coastal terrain. The results are discussed in the light of observations by other investigators.     

Incoherent Cerenkov process as a source of low-latitude VLF emissions

Employing a realistic ionospheric model and a suitable energetic electron spectra, detailed power calculations are carried out to confirm the generation mechanism of low-latitude VLF emissions observed both in the satellites and on the ground. Raypaths of the radiated waves are also calculated to account for the attenuation and spreading losses. It is shown that 100 eV?1 keV electrons radiating incoherently in the Cerenkov mode are the main sources of these emissions.     

YO molecule in the sun

Vibrational transition probabilities, namely Franck—Condon factors and -centroids have been evaluated by an approximate analytical method for the (A–X), (A–X), and (A–X) system of YO molecule. Morse potential energy curves forX ²⁺,A ²₂,A²₂, andA²₂, states of YO have been constructed using the latest spectroscopic data. The value of -centroids for the band have been found to decrease linearly with the corresponding wavelengths. We show results for two new transitions of (A–X) and (A–X) and five new bands of (A–X) of YO in the umbral spectrum of the Sun.