U. K. De

Identification of significant parameters for the prediction of pre-monsoon thunderstorms at Calcutta, India

In the present work, the well-known principal component analysis (PCA) technique has been applied to study the thunderstorm phenomenon (which evidently has a multivariate structure) at Calcutta (India) during the pre-monsoon season (i.e. March–May). Various parameters (both thermodynamic and dynamic) already identified by different scientists as responsible for thunderstorm occurrence have been considered here for different atmospheric layers. The purpose of the study is to reduce the number of parameters and hence identify the significant parameters linked up with various layers of the atmosphere for thunderstorm as well as for fair-weather days of Calcutta so that these may be used for parameterization. As the analysis reveals that there is a structural difference between the morning and the afternoon atmosphere at Calcutta, so the analysis has been performed separately for morning and afternoon on thunderstorm as well as fair-weather days. Originally, 20 parameters were included in the analysis. The final result shows that in the morning only four parameters out of the 20 and in the afternoon only five parameters out of the 20 are found to be significant (i.e. they are expected to be jointly responsible) for occurrence or non-occurrence of thunderstorms at Calcutta during the pre-monsoon season. The study has however been confined up to the 500 hPa level. Copyright

Simulation of CO 2 concentrations at Tsukuba tall tower using WRF-CO 2 tracer transport model

Simulation of carbon dioxide (CO2) at hourly/weekly intervals and fine vertical resolution at the continental or coastal sites is challenging because of coarse horizontal resolution of global transport models. Here the regional Weather Research and Forecasting (WRF) model coupled with atmospheric chemistry is adopted for simulating atmospheric CO2 (hereinafter WRF-CO2) in nonreactive chemical tracer mode. Model results at horizontal resolution of 27 × 27 km and 31 vertical levels are compared with hourly CO2 measurements from Tsukuba, Japan (36.05°N, 140.13 oE) at tower heights of 25 and 200 m for the entire year 2002. Using the wind rose analysis, we find that the fossil fuel emission signal from the megacity Tokyo dominates the diurnal, synoptic and seasonal variations observed at Tsukuba. Contribution of terrestrial biosphere fluxes is of secondary importance for CO2 concentration variability. The phase of synoptic scale variability in CO2 at both heights are remarkably well simulated the observed data (correlation coefficient >0.70) for the entire year. The simulations of monthly mean diurnal cycles are in better agreement with the measurements at lower height compared to that at the upper height. The modelled vertical CO2 gradients are generally greater than the observed vertical gradient. Sensitivity studies show that the simulation of observed vertical gradient can be improved by increasing the number of vertical levels from 31 in the model WRF to 37 (4 below 200 m) and using the Mellor–Yamada–Janjic planetary boundary scheme. These results have large implications for improving transport model simulation of CO2 over the continental sites.

Identification of a surface layer structure and analysis of humidity data in two weather situations at Jodhpur (26°18'N, 73°04'E), India, during MONTBLEX 1990

The Monsoon Trough Boundary Layer Experiment held in 1990 was a multi-institutional effort to probe the atmospheric boundary layer over the monsoon trough over northern India. For this experiment, four micrometeorological towers were set up at four different locations along the normal position of the trough. One such tower of 30m height was located at Jodhpur (26‡18′N, 73‡04′E), Rajasthan. The fast and slow response data available during the experiment have been used in the present study to determine a suitable layer-structure of the surface layer for evaluation of sensible heat flux using the multilayer hypothesis of Kramm (1989).

Surface sensible heat flux over a deep moist convective region and its interplay with synoptic and mesoscale features

The surface parameters are being evaluated using a methodology which considers the vertical temperature structure of MONTBLEX ’90. For this 30 metre micrometeorological tower data are utilised. In this process, a concept of isolated layers has been introduced. The parameters have been evaluated following two successive iterative processes to give a consistent value both in the flux-profile relation and the related similarity relation.The heat flux obtained using the present methodology, is then utilised to examine its interplay with the synoptic as well as mesoscale features. The existence of such an interplay is observed.

Some exact solutions of nonlinear chiral field equations

Some new exact solutions of the nonlinear field equations for the chiral invariant model of pion dynamics are presented here. These solutions are a further generalization of some previous works presented by one of the authors (Ray). It is interesting to note that equations in (3.2) obtained by Ray (1978) are conformally invariant. Hence from any solution of these equations one can immediately generate infinitely many other solutions of these equations simply by replacing (x 1, x 2) by ( y, z), where y and z are any two mutually conjugate solutions of Laplace’s equations. Further, a striking similarity in form of these equations with one of the two generalized Lund–Regge equations makes the study of the solutions of these equations more worthwhile with the view that the study of the solutions of these equations will eventually lead to the study of the solution of a larger class of equations that will include these equations and generalized Lund–Regge equations as special cases.

Investigation of dominant modes of monsoon ISO in the northwest and eastern Himalayan region

This study investigates the altitudinal variation of dominant modes of summer monsoon intra-seasonal oscillation (ISO) over the Northwest (NWH) and Eastern Himalayan (EH) region using (i) spatially scattered 133 number of station rainfall observations and (ii) latitudinal transect-wise (LT) rainfall variation, obtained from an observed interpolated gridded rainfall data for the period 1995–2004. The altitudinal variation of dominant modes of monsoon ISO were investigated by exploring the strong and weak phases of the principal components of 10–90 days bandpass rainfall data of June to September with respect to location specific station height. Investigation of frequency of days for light and moderate rainfall along with the occurrence of total seasonal rainy days has revealed existence of a rainfall maximum around 2100 m height for the NWH region. Similarly, the total seasonal rainy days of EH region was found to have maxima between 1100 and 1400 m height. Analyses of the spatially scattered station rainfall observation for the NWH region showed that the strong periods of ISO modes exist around 747.9 (±131.7) m and 2227.2 (±100.2) m heights. Over the EH region, the dominant modes of the monsoon ISO were found to be centred around 1200 m. Significant alterations of strong and weak phases of monsoon ISO as a response to altitudinal variation in the mountain surface were observed when latitudinal transect-wise variation of monsoon ISO modes were investigated.

Some observations from the data taken in and around Kharagpur during the onset of the monsoon, 1990

During MONTBLEX 1990, various observational platforms were operated at Kharagpur and the nearby Kalaikunda Air Base. Using the data from all the platforms, one can draw the following conclusions. The temperature and wind data obtained from various sensors have overall compatibility. Sodar wind data indicate the presence of a low level jet at around 300 m above ground. The inversion height may be evaluated from the vertical profile of the sodar back-scatter echo intensity. The sub-synoptic or synoptic scale convergence modulates the inversion height and the presence of cloud-base within the inversion height in turn modulates the sensible heat and momentum fluxes.

Study of horizontal scales of motion observed over Kharagpur during MONTBLEX-1990

Characteristic wavelengths for theu andv components of wind are studied using the Monsoon Trough Boundary Layer Experiment (MONTBLEX) data obtained from a Doppler Sonic Detection and Ranging System (sodar) over the land station Kharagpur (near sea-coast). The principal stability parameter (Zi/Lo) is used to infer the behaviour of the non-dimensional form of the characteristic wavelength (LH) within the entire stability range occurring during the sounding periods. This is compared with GATE - 1974 results (over the sea surface) published by Fitzjarrald (1978).

Plane symmetric charged dust distribution

An attempt is made to obtain the complete set of solutions of Einstein’s equations for a nonstatic charged dust distribution with a comoving system of coordinates and the most general plane symmetric metric, i.e., ds2=exp [2u(x,t)]dt2 −exp[2v(x,t)]dx2−exp [2w(x,t)](dy2+dz2). The field equations have been reduced to a single ordinary differential equation which is integrated in a particular case.

Some solutions for Yang's equations for self-dual SU(2) gauge fields

Abstract It is shown that a large class of solutions of Yangs equations for self-dual SU(2) gauge fields can be obtained from the solutions of two-dimensional and four-dimensional Laplace equations.