The mean and turbulence structure simulation of the monsoon trough boundary layer using a one-dimensional model withe-l ande-ε closures     

Kusuma G. Rao  V. N. Lykossov  A. Prabhu  S. Sridhar  E. Tonkacheyev 《Journal of Earth System Science》1996,105(3):227-260

An attempt has been made here to study the sensitivity of the mean and the turbulence structure of the monsoon trough boundary layer to the choice of the constants in the dissipation equation for two stations Delhi and Calcutta, using one-dimensional atmospheric boundary layer model withe-ε turbulence closure. An analytical discussion of the problems associated with the constants of the dissipation equation is presented. It is shown here that the choice of the constants in the dissipation equation is quite crucial and the turbulence structure is very sensitive to these constants. The modification of the dissipation equation adopted by earlier studies, that is, approximating the Tke generation (due to shear and buoyancy production) in theε-equation by max (shear production, shear + buoyancy production), can be avoided by a suitable choice of the constants suggested here. The observed turbulence structure is better simulated with these constants. The turbulence structure simulation with the constants recommended by Aupoixet al (1989) (which are interactive in time) for the monsoon region is shown to be qualitatively similar to the simulation obtained with the constants suggested here, thus implying that no universal constants exist to regulate dissipation rate. Simulations of the mean structure show little sensitivity to the type of the closure parameterization betweene-l ande-ε closures. However the turbulence structure simulation withe-ε. closure is far better compared to thee-l model simulations. The model simulations of temperature profiles compare quite well with the observations whenever the boundary layer is well mixed (neutral) or unstable. However the models are not able to simulate the nocturnal boundary layer (stable) temperature profiles. Moisture profiles are simulated reasonably better. With one-dimensional models, capturing observed wind variations is not up to the mark.  相似文献   

Observational Procedure for the Prediction of Ultimate Swell     

Prakash  K.  Siddharth Prabhu  N.  Sridharan  A. 《Geotechnical and Geological Engineering》2021,39(6):4669-4676

Geotechnical and Geological Engineering - Montmorillonitic soils pose problems in the field as they are capable of exhibiting appreciable swelling when come in contact with water. In this context,...  相似文献   

A correlation between ellipticity and core-strength in extended radio galaxies     

T. P. Prabhu  R. K. Kochhar 《Astrophysics and Space Science》1984,102(1):29-39

We show that in the case extended radio sources a correlation exists between the fraction of the radio flux retained in the core component and the ellipticity of the underlying galaxy. The correlation is in the sense that stronger cores occur in flatter galaxies. It would seem that there exists a class of intrinsically rounder, redder, massive ellipticals with larger velocity dispersions and metallicities, that can form extended radio sources more efficiently. Thus the occurrence of a radio source appears to be related to the dynamical and chemical evolution of the Galaxy.  相似文献   

Urban Slum Detection Approaches from High-Resolution Satellite Data Using Statistical and Spectral Based Approaches     

R. Prabhu  R. A. Alagu Raja 《Journal of the Indian Society of Remote Sensing》2018,46(12):2033-2044

This paper proposes a new technique to detect the urban slums from urban buildings using very high resolution data. Many cities in the Global South are facing the development and growth of highly dynamic slum areas, but often lack detailed spatial information. Unlike buildings, vegetation and other features, urban slums lack in their unique spectral signatures. Thus, accurate detection of slums using remote sensing data poses real challenge to researchers and decision-makers. In this work, gray-level co-occurrence matrix, Tamura-based statistical feature extraction and wavelet frame transform-based spectral feature extraction techniques are proposed for detecting the urban slums from urban buildings. The very high resolution data of Madurai city, South India, acquired by Worldview-2 sensor (1.84 m) proved the ability of the proposed approaches to identify urban slums from urban buildings. Experimental results demonstrate that the proposed wavelet frame transform-based approach can generate higher classification accuracy than other approaches.  相似文献   

The Luminosity Function and Size Distribution of HII Regions in NGC 1365     

Swara Ravindranath  Tushar P. Prabhu 《Astrophysics and Space Science》2001,276(2-4):429-436

We present the HII region luminosity function and size distribution obtained for the HII regions in NGC 1365. The diameters were corrected for the effects of seeing using a Wiener image restoration procedure. The luminosities and sizes were calculated using the Cepheid distance of 18±2 Mpc, to NGC 1365. We find good correlation between the H_α luminosities and other properties, such as absolute magnitudes and sizes of the HII regions within this galaxy. We find that the HII region luminosity function can be fitted by a power law of slope α=–2.29$plusmn;0.11, which is consistent with what is expected for its Hubble type. Also, the size distribution of the HII regions can be represented by an exponential form. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Evolution of the optical spectrum of SN 1987a in the large magellanic cloud     

B. N. Ashoka  G. C. Anupama  T. P. Prabhu  S. Giridhar  K. K. Ghosh  S. K. Jain  A. K. Pati  N. Kameswara Rao 《Journal of Astrophysics and Astronomy》1987,8(2):195-209

The evolution of the spectrum of SN1987a is traced from 1987 February 26 to March 31. Based on the low-resolution spectroscopic data we identify the lines of H, He I, Na I, Fe II, Sc II, Ca II which are known to be present in Type II Supernovae, and also present evidence for the existence of lines of Mg I, Ca_I, O I, and N I. We discuss the evolution of the Hα profile, and draw attention to its complex structure around March 30. Close to the rest wavelength of Ha a double-peaked structure appeared in the profile with a peak-to-peak separation of ∼ 1400 km s⁻¹, suggestive of an expanding shell or disc of gas. Using the available broadband photometric information, we also trace the evolution of the photosphere of SN1987a assuming that it radiates like a supergiant.  相似文献   

Spectroscopic evolution of nova LW serpentis 1978 during its early decline     

T. P. Prabhu  G. C. Anupama 《Journal of Astrophysics and Astronomy》1987,8(4):369-387

Optical spectroscopic data are presented on nova LW Serpentis 1978, obtained during its decline fromV 9.0 to ≃10.2 (compared to a value of ∼ 8.0 at recorded maximum). The spectrum and its evolution compare well with a typical nova, though the principal absorption (∼ −750 km s^−l) was very weak in comparison with the diffuse-enhanced absorption (∼ −1300 km s⁻¹). The principal absorption could be identified only in the lines of O I λλ7774, 8446, and in moderate-resolution observations of Hα. The salient features of spectral evolution follow: The near-infrared triplet of Ca n continuously weakened. O I λ8446 was always brighter than O I λ 7774, indicating continued importance of Lyman Β fluorescence. The lines due to [O I], [N II] and N n brightened considerably near the end of our observations (37 days from maximum). The Hα emission line was asymmetric all through with more emission towards the red. Its emission profile showed considerable structure. Based on the individual peaks in the Hα line profile, a kinematical model is proposed for the shell of LW Ser. The model consists of an equatorial ring, and a polar cone on the side away from the earth. The nearer polar cone did not show significant emission of Hα during our observations. The polar axis of the shell is inclined at a small angle (∼ 15‡) to the line of sight.  相似文献   

On the correlation between supernova occurrence and nuclear activity in elliptical galaxies     

R. K. Kochhar  T. P. Prabhu 《Astrophysics and Space Science》1984,100(1-2):369-379

We show that there is a correlation between the occurrence of supernovae and nuclear activity in elliptical galaxies. Both shun a canonical elliptical and occur only in those ellipticals which accrete gas. We also show that the hypothesis that all SNI come from short-lived stars is consistent with the colour observations of elliptical galaxies. We propose that there is a class of intrisically rounder, massive, dusty, metal-rich ellipticals which produce supernovae and are more likely to contain a radio source.  相似文献   

Double radio peak and non-thermal collimated ejecta in RS Ophiuchi following the 2006 outburst     

S. P. S. Eyres  T. J. O'Brien  R. Beswick  T. W. B. Muxlow  G. C. Anupama  N. G. Kantharia  M. F. Bode  M. P. Gawro&#;ski  R. Feiler  A. Evans  M. T. Rushton  R. J. Davis  T. Prabhu  R. Porcas  B. J. M. Hassall 《Monthly notices of the Royal Astronomical Society》2009,395(3):1533-1540

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Characterization of suspended sediment in Meltwater from Glaciers of Garhwal Himalaya          下载免费PDF全文

Deepak Srivastava  Amit Kumar  Akshaya Verma  Siddharth Swaroop 《水文研究》2014,28(3):969-979

Glacierised basins are significant sources of sediments generated by glacial retreat. Estimation of suspended sediment transfer from glacierised basins is very important in reservoir planning for hydropower projects in Himalaya. The present study indicates that storage and release of sediment in proglacial streams may categorise the pattern of suspended sediment transfer from these basins. Assessment of suspended sediment concentration (SSC), suspended sediment load (SSL) and yield has been undertaken for Dunagiri Glacier basin located in Garhwal Himalaya (30^o33'20”N, 79^o53'36”E), and its results are compared with the Gangotri and Dokriani glaciers sharing close proximity. Out of the total drainage basin area, about 14.3 % of the area is glacierised. Data were collected for five ablation seasons (1984–1989, barring 1986). The mean daily SSCs for July, August and September were 333.9, 286.0 and 147.15 mg/l, respectively, indicating highest concentration of mean daily suspended sediment in July followed by August. SSL trends were estimated to be 93.0, 57.0 and 21.3 tonnes. About 59% of the total SSL of the melt period was transported during the months of August and September. Sediment yield for the study basin was computed to be 296.3 t km^?2 yr ^?1. It is observed that the cumulative proportion of SSC precedes the discharge throughout the melt season except in the year 1987. Release of SSL in terms of total load is less in the early part of melt season than in the later stage as compared to that of discharge. Diurnal variations in SSC reach their maximum at 2400 h, and therefore, SSC was found to be high during night (2000–0400 h). There was a good relationship between SSC and SSL with discharge for the ablation seasons (1988 and 1989). Mean monthly SSC and mean monthly SSL provide a good exponentional relationship with mean monthly temperature. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献