Search Results

You are looking at 1 - 10 of 11 items for

  • Author or Editor: S. V. Venkateswaran x
  • Refine by Access: All Content x
Clear All Modify Search
S. K. Lew
and
S. V. Venkateswaran

Abstract

No abstract available.

Full access
Stephen K. Lew
and
S. V. Venkateswaran

Abstract

An attempt is made in this paper to formulate the transport of hydrogen in the earth's upper atmosphere as a Monte Carlo problem. The relevant details of the technique adopted are given. The capability of the technique to provide useful answers to the following questions is demonstrated. How is the flux of hydrogen atoms, possessing enough kinetic energy to escape from the earth's gravitational field, influenced by the fact that the escape takes place not from a particular atmospheric level (the critical level) but from a layer of finite thickness? What is the law of variation of hydrogen density in this finite layer? More specifically, does the hydrogen gas maintain a Maxwellian distribution while diffusing through the layer? If not, how does the distribution change with height inside the layer? The answers obtained are discussed with reference to their statistical validity, and compared with some of the conclusions of earlier investigations.

Full access
S. V. Venkateswaran
and
Anna Mani

Abstract

The paper describes the techniques developed at Poona for the measurement of electrical potential gradient in the free atmosphere and discusses the results of the observations made over Poona during 1953–1958. The day-to-day and diurnal variations of potential gradient in the troposphere as well as the seasonal variations are discussed. The variation of potential gradient with height follows the theoretical values only during the monsoon months, showing an increase above 300 mb in winter and steady values above 500 mb during summer.

Full access
Jae R. Ballif
and
S. V. Venkateswaran

Abstract

No abstract available.

Full access
Jae R. Ballif
and
S. V. Venkateswaran

Abstract

The hydroxyl bands in the glow emanating from the earth's upper atmosphere are chemically excited. The two possible precursor reactions are O3+H→OH*+O2 and O2 *+H→OH*+O. Arguments are advanced in this paper to show that the night-time variations of the emission intensifies stimulated by these two reactions might be characteristically different. The relative importance of the reactions can therefore be judged by a systematic observational study of the intensity variations.

Full access
Jae R. Ballif
and
S. V. Venkateswaran

Abstract

The chemiluminescent reaction responsible for the nightglow in the sodium D lines is embedded in the complex kinetics of an oxygen-hydrogen atmosphere. Various possibilities of identifying this reaction from observational studies are considered. It is suggested that an important clue may be found in the time-variations of the height-integrated glow-intensity.

Full access
R. L. Walterscheid
and
S. V. Venkateswaran

Abstract

A spectral theory is developed for the solar semidiurnal tides in an atmosphere with background zonal winds. According to this theory, the vertical structures of the spectral components of the tide are governed by a set of coupled second-order ordinary differential equations which have to be solved for appropriate lower and upper boundary conditions. The lower boundary condition, in particular, has to be properly formulated to take into account the latitudinal variation of the atmospheric basic-state parameters. While the solutions to the equations have to be obtained by numerical methods, several aspects of their behavior can be revealed by simpler mechanistic models and concepts which are introduced in this first part (Part I) of a two-part report. Discussion of the detailed numerical solutions and of the adequacy of their mechanistic interpretations is given in the companion paper (Part II).

Full access
R. L. Walterscheid
and
S. V. Venkateswaran

Abstract

Classical and nonclassical model calculations have been performed for the solar semidiurnal tidal oscillations in the earth's atmosphere, for prescribed basic-state parameters and heating functions appropriate for the solstitial seasons when the nonclassical effects associated with the mean zonal wind are expected to be maximum. It is found that the enrichment of the higher order spectral components characteristic of the nonclassical model is due to the cross-coupling rather than the self-coupling of the spectral components in the model. These cross-coupling effects are shown to be sufficiently well represented by a mode-coupling model described in Section 3 of Part I. As explained in Part I, the effect of cross-coupling may be considered as some kind of indirect forcing. Such indirect forcing, which can be applied either at the lower boundary or inside the medium, is obtained and compared for each spectral component with the direct thermal forcing.

It is demonstrated that the actual behavior of a particular spectral component (such as the m=4 component whose enrichment is an important aspect of the nonclassical model) in the progressive wave regime (where waves forced from below dominate) can be explained as the net result of forcings, both direct and indirect, at the lower boundary and from different altitude regions above. Results of our model calculations for wind, temperature and pressure oscillations are compared with available observations at various altitudes. While this comparison succeeds in exposing definite nonclassical influences in the observations, it also reveals significant inadequacies of our model.

Full access
F. M. Ralph
,
C. Mazaudier
,
M. Crochet
, and
S. V. Venkateswaran

Abstract

Observations from two Doppler sodars and a radar wind profiler have been used in conjunction with data from a rawinsonde station and a mesoscale surface observation network to conduct a case study of a gravity current entering into an environment containing a nocturnal inversion and an elevated neutral layer. On the basis of synoptic and mesoscale analyses, it is concluded that the gravity current might have originated either as a scale-contracted cold front or as a gust front resulting from thunderstorm outflows observed very near the leading edge of a cold front. Despite this ambiguity, the detailed vertical structure of the gravity current itself is well resolved from the data. Moreover, the vertical velocity measurements provided by the sodars and the radar wind profiler at high time resolution have given unique information about the height structure of gravity waves excited by the gravity current. Although only wave periods, and not phase speeds or wavelengths, are directly measured, it is possible to make reasonable inferences about wave excitation mechanisms and about the influence and control of ambient stratification on wave-field characteristics. Both Kelvin-Helmholtz waves generated in the regions of high wind shear found in association with the gravity current and lee-type waves forced by the gravity current acting as an obstacle to opposing prefrontal flow are identified. It is also found that the propagation speed of the gravity current and the relative depths of the prefrontal inversion and the postfrontal cold air were not favorable for the formation of either internal bores or solitary waves at the time of day at which the gravity current was being observed.

Full access
R. L. Walterscheid
,
J. G. DeVore
, and
S. V. Venkateswaran

Abstract

Calculations of the semidiurnal atmospheric tide at solstice using improved heating rates are presented. The heating rates for solar absorption by water vapor are based on a global water vapor distribution (Jenne, 1969, 1975; Jenne et al., 1974), the data of McClatchey et al. (1972), and an absorptivity parameterization of Lacis and Hansen (1974); rates for solar absorption by ozone are based on the midlatitude ozone distribution of the U.S. Standard Atmosphere (COESA, 1976) and detailed radiative calculations using the solar fluxes and absorption cross sections of Ackerman (1971) with the Schumann-Runge band cross sections of Kockarts (1971). The heating rates for solstice are quite similar to those reported by Forbes and Garrett (1978) and significantly different from those of Lindzen and Hong (1974), which were used in the previous study of Walterscheid and Venkateswaran (1979b) investigating the influence of mean zonal motion and meridional temperature gradients on the solar semidiurnal tide.

The basic conclusions of this study based on the present heating rates are as follows: 1) Although effects of mean-wind related (nonclassical) generation are clearly discernible, the improved agreement with observations of the present results over those with the earlier rates with respect to wave-lengths of the semidiurnal tidal oscillations in the lower thermosphere (100–115 km) and with respect to both their wavelengths and amplitudes in the region (80–100 km) is primarily attributable to the improved heating rates; 2) without nonclassical generation the calculations exhibit a phase shift below 30 km in disagreement with observations; and 3) without mean-wind related effects the amplitude of the surface pressure oscillation is significantly underpredicted.

Full access