Prediction of fog/visibility over India using NWP Model     

Aditi Singh  John P George  Gopal Raman Iyengar 《Journal of Earth System Science》2018,127(2):26

Frequent occurrence of fog in different parts of northern India is common during the winter months of December and January. Low visibility conditions due to fog disrupt normal public life. Visibility conditions heavily affect both surface and air transport. A number of flights are either diverted or cancelled every year during the winter season due to low visibility conditions, experienced at different airports of north India. Thus, fog and visibility forecasts over plains of north India become very important during winter months. This study aims to understand the ability of a NWP model (NCMRWF, Unified Model, NCUM) with a diagnostic visibility scheme to forecast visibility over plains of north India. The present study verifies visibility forecasts obtained from NCUM against the INSAT-3D fog images and visibility observations from the METAR reports of different stations in the plains of north India. The study shows that the visibility forecast obtained from NCUM can provide reasonably good indication of the spatial extent of fog in advance of one day. The fog intensity is also predicted fairly well. The study also verifies the simple diagnostic model for fog which is driven by NWP model forecast of surface relative humidity and wind speed. The performance of NWP model forecast of visibility is found comparable to that from simple fog model driven by NWP forecast of relative humidity and wind speed.  相似文献   

The absorption of soft X-rays from the Crab nebula     

V. S. Iyengar  S. Naranan  B. V. Sreekantan 《Astrophysics and Space Science》1975,32(2):431-446

The X-ray spectrum of the Crab nebula has been determined in the energy range 0.5 10 keV using thin window proportional counters carried aboard a Centaur IIA rocket launched from TERLS, India. The spectrum can be well represented by a power law with an exponent?2.1 beyond 2 keV. The absorption of the soft X-ray component below 2 keV is clearly seen in the experiment. Attempts to understand quantitatively the spectral features in terms of interstellar absorption lead to a column density of hydrogen in the iirection of the Crab nebula of 3.5×10²¹ H atoms cm^?2, if we adopt a revised version of the interstellar absorption coefficients of Brown and Gould to include the contributions of heavier elements, especially of iron. This value of density is a factor of 2 higher than the density obtained from 21 cm radio observations, but falls well within the range of values for atomic and total hydrogen deducible from UV measurements with satellites and the measured visual extinction coefficients for the Crab nebula. It is concluded that it is not necessary to consider anomalous abundance of elements like carbon or neon either in the source or in the interstellar medium as suggested by some authors. The absorption of X-rays in the interstellar dust in the light of current dust models is presented.  相似文献   

Is IRAS 03134 + 5958 a Herbig-Haro object?     

K. V. K. Iyengar  T. N. Rengarajan 《Journal of Astrophysics and Astronomy》1986,7(3):237-240

The source IRAS 03134 + 5958 identified by Iyengar & Verma (1984) on the Palomar Observatory Sky Survey (POSS) prints with a nonstellar optical object with [P – R]≃ 5.3 ± 1.5 is near the edge of Lynds dark cloud No. 1384 and is either embedded in or behind the cloud. The galactic latitude of this source (b ^II = 2‡.3), its positionvis-a-vis the Lynds dark cloud, its nonstellar appearance, high [P – R] colour and its far-infrared spectrum, all suggest the possibility of its being a Herbig-Haro (HH) object. To test this possibility we undertook measurements of its proper motion and variability (two of the characteristic properties of HH objects). These yield μ_a = (3.6 ± 2.3) arcsec/century and μ_δ= (−1.2 ± 2.0) arcsec/century for its proper motion. The source reveals large variation in brightness between 1950 and 1954. Optical line studies of the source are required to confirm its classification as an HH object.  相似文献   

Identification of some of the unidentified EIC-1 sources     

R. P. Verma  K. V. K. Iyengar 《Astrophysics and Space Science》1983,97(1):157-159

We have identified 20 of the 75 unidentified Equatorial Infrared Catalogue Number-1 sources with stars in the BD Catalogue. Two of these are also found in the HD Catalogue.  相似文献   

Engineering source model for strong ground motion     

S.T.G. Raghu Kanth  R.N. Iyengar 《Soil Dynamics and Earthquake Engineering》2009

A new engineering source model consistent with seismological concepts for simulating strong-motion accelerograms (SMAs) is presented in this paper. The source region is modeled as a horizontally layered elastic medium to cater for site dependency. The moment field acting on the rupture plane is decomposed into space and time functions, which is a novel concept. The spatial and temporal components are determined for six well-recorded earthquakes using the corresponding recorded SMA. The obtained spatial variations indicate that they can be modeled as an anisotropic random field. The temporal components of all the six events are transients, with typical frequency spectra. Based on these results, a simplified source model is proposed for the synthesis of SMA during strong earthquakes. The model is validated by simulating strong-motion acceleration time histories at stations deliberately kept out of the modeling exercise. It is found that the present model is efficient in simulating observed time histories. The proposed model is also illustrated by simulating an ensemble of acceleration time histories for the Kutch earthquake of 26th January 2001 using only the few known source parameters.  相似文献   

Engineering aspects of obtaining clear seawater from the muddy shores     

G.L. Natu  D.M. Patel  E.R.R. Iyengar  R.V. Vyas 《Ocean Engineering》1980,7(1):49-53

On some shores the seawater is muddy, contaminated with fine silt and clay in suspension. If it became necessary to use such seawater it would be essential either to resort to filtration or to allow for settling of soil sediments. The present scheme was undertaken with a view to providing clear seawater for experimentation in growing crops and plants with seawater. The system consisted of a filtration unit embedded in the shore over which the tidal water passes. The clear water is run through a conveying assembly and is stored in a sump for end uses. The design, construction materials and construction operation of such a device on coastal sand dunes has been described in detail. The precautions to be taken under such circumstances are also given.  相似文献   

Simultaneous infrared and H-alpha measurements of Be stars     

Krishna M. V. Apparao  S. P. Tarafdar  R. P. Verma  K. V. K. Iyengar  K. K. Ghosh 《Journal of Astrophysics and Astronomy》1993,14(3-4):131-134

The observed infrared excess in Be stars is usually interpreted as free-free and free-bound emission from a hot gas envelope around the Be star. This hot gas should also emit H-alpha line radiation. Earlier observations had suggested that the infrared excess and Hα radiation were not consistent with models in which they arise from the same ionized region; however the observations were made at different times. We have made simultaneous observation of infrared and H-alpha line radiation. Our observations imply that either both these radiations cannot arise from the same hot gas or additional processes have to be invoked to account for the observed excess infrared radiation.  相似文献   

Trapezoidal footings on non-linear subgrades     

S. Chandra  M. R. Madhav  N. G. R. Iyengar 《国际地质力学数值与分析法杂志》1984,8(6):519-529

The pressure versus settlement response is highly non-linear for soils, in general. In the present study, a cubic equation of the type p = K₁w ? K₂w³ is suggested to incorporate the non-linear behaviour. A trapezoidal footing with constant depth resting on a subgrade having non-linear response is analysed. The resulting fourth order non-linear differential equation with variable coefficients is solved by using the Galerkin technique and beam characteristic functions are employed to obtain faster convergence. The results are presented in the form of non-dimensional charts for valid ranges of footings and soil parameters.  相似文献   

Far infrared emission from three new planetary nebulae     

K. V. K. Iyengar 《Journal of Astrophysics and Astronomy》1985,6(4):227-231

As dust emission in the far infrared (FIR) is a characteristic property of planetary nebulae we searched the Infrared Astronomical Satellite (IRAS) point-source catalogue for confirmatory evidence on the two new possible planetary nebulae S 68 and 248 - 5 identified by Fesen, Gull & Heckathorn (1983) and the high-excitation planetary nebula 76 + 36 detected by Sanduleak (1983). We identify the nebulae 248 - 5 and 76 + 36 with IRAS sources 07404 - 3240 and 17125 + 4919, respectively and have determined their dust temperature, total FIR emission and optical depth. We also set a lower limit ranging in value from 1.2 × 10^-6 to 3.7 × 10^-5 forM _dust /M _bd of the nebula 248 - 5 depending on whether its grain material is silicate or graphite. S 68 could not be identified with an IRAS source.  相似文献   

Energy spectrum and time variations of hard X-rays from Cyg X-1     

P. C. Agrawal  G. S. Gokhale  V. S. Iyengar  P. K. Kunte  R. K. Manchanda  B. V. Sreekantan 《Astrophysics and Space Science》1972,18(2):408-424

Experimental results on the intensity, energy spectrum and time variations in hard X-ray emission from Cyg X-1 based on a balloon observation made on 1971, April 6 from Hyderabad (India) are described. The average energy spectrum of Cyg X-1 in the 22–154 keV interval on 1971 April 6 is best represented by a power law dN/dE=(5.41±1.53)E ^{–(1.92±0.10)} photons cm^–2s^–1 keV^–1 which is in very good agreement with the spectrum of Cyg X-1 derived from an earlier observation made by us on 1969 April 16 in the 25–151 keV band and given by dN/dE=(3.54±2.44)E ^{–(1.89±0.22)} photons cm^–2s^–1 keV^–1. A thermal bremsstrahlung spectrum fails to give a good fit over the entire energy range for both the observations. Comparison with the observations of other investigators shows that almost all balloon experiments consistently give a spectrum of E ^–2, while below 20 keV the spectrum varies fromE ^–1.7 toE ^–5. There is some indication of a break in the Cyg X-1 spectrum around 20 keV. Spectral analysis of data in different time intervals for the 1971 April 6 flight demonstrates that while the source intensity varies over time scales of a few minutes, there is no appreciable variation in the spectral slope. Analysis of various hard X-ray observations for long term variations shows that over a period of about a week the intensity of Cyg X-1 varies upto a factor of four. The binary model proposed by Dolan is examined and the difficulties in explaining the observed features of Cyg X-1 by this model are pointed out.  相似文献