Signature of atmospheric oscillations in GPS-measured tropospheric delay     

C. Suresh Raju  Korak Saha  K. Parameswaran 《Journal of Atmospheric and Solar》2009,71(17-18):1784-1793

Ground-based GPS finds potential applications in many atmospheric studies such as spatial distribution of columnar water vapor as well as the tidal oscillations in the atmosphere. The zenith tropospheric delay (ZTD) derived from GPS data at two Indian IGS stations are used to establish its potential for studying the atmospheric tidal, intra-seasonal and planetary oscillations. The major tidal oscillations observed in ZTD data are diurnal, semi-diurnal and their harmonics. Prominent intra-seasonal oscillations observed in ZTD are reported for the first time in this context. These intra-seasonal oscillations are Madden–Julian Oscillation (30–70 days, 60–90 days, 100–120 days) and planetary waves (like 27, 16 and 5–10 days periodicities). Quantification of these periodicities will provide a useful handle to improve the empirical models employed in the estimation of tropospheric delay.  相似文献   

Assessment of the Present State and Future Fate of River Saraswati,India: Water Quality Indices and Forecast Models as Diagnostic and Management Tools     

Sasanka Pramanik  Jayanta Kumar Biswas  Anilava Kaviraj  Subrata Saha 《洁净——土壤、空气、水》2023,51(4):2200321

Water quality assessment is key to the conservation and management of rivers. River Saraswati, a distributary of the river Ganga, serves as a lifeline to many villages in the district Hooghly in West Bengal, India. As the river is gradually dying due to diverse man-made pollution, ten water quality parameters in two sampling spots (PR-1 and PR-2) in the river are monitored month-wise from March 2017 to February 2020,  and these are compared with those from a reference pond. The water quality index (WQI) is determined for the two riverine spots and the reference pond based on the Canadian Council of Ministers of Environment WQI (CCMEWQI) and weighted arithmetic WQI, respectively. In addition to actual observations, three different forecasting methods, exponential smoothing, autoregressive integrated moving average, and artificial neural network, are used to predict WQI for the next two years. This study indicates that free CO₂, dissolved oxygen, and turbidity are the key parameters to evaluate this river's anthropogenic stress and health. The actual and forecasted results reflect the precipitous degradation of CCMEWQI in PR-2. Therefore, the immediate intervention of all stakeholders is required to adopt an integrated and comprehensive river management plan to save the river from utter obliteration.  相似文献   

Polynomial friction pendulum isolators (PFPIs) for seismic performance control of benchmark highway bridge     

Arijit Saha  Purnachandra Saha  Sanjaya Kumar Patro 《地震工程与工程振动(英文版)》2017,16(4):827-840

The seismic response of a benchmark highway bridge isolated with passive polynomial friction pendulum isolators (PFPIs) is investigated and subjected to six bidirectional ground motion records. The benchmark study is based on a lumped mass finite-element model of the 91/5 highway overcrossing located in Southern California. The PFPI system possesses two important parameters; one is horizontal flexibility and the other is energy absorbing capacity through friction. The evaluation criteria of the benchmark bridge are analyzed considering two parameters, time period of the isolator and coefficient of friction of the isolation surface. The results of the numerical study are compared with those obtained from the traditional friction pendulum system (FPS). Dual design performance of the PFPI system suppressed the displacement and acceleration response of the benchmark highway bridge. The dual design hysteresis loop of the PFPI system is the main advantage over the linear hysteresis loop of the FPS. The numerical result indicates that the seismic performance of the PFPI system is better than that of the traditional FPS isolated system. Further, it is observed that variations of the isolation time period and coefficient of friction of the FPS and PFPI systems have a significant effect on the peak responses of the benchmark highway bridge.  相似文献   

The Stellar Populations in Local Group Dwarf Galaxies     

Abhijit Saha 《Astrophysics and Space Science》1999,267(1-4):193-199

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A study of earthquake-induced vibration on laminated composite plates using finite element method     

Saha  Prithwish  Mandal  Kalyan Kumar 《Natural Hazards》2021,106(3):2251-2277

Natural Hazards - This study presents the dynamic response of an eight-noded composite plate under earthquake excitation. Koyna earthquake excitation frequency is considered for the present study....  相似文献   

Angular power spectrum of CMB anisotropy from WMAP     

Tarun Souradeep  Rajib Saha  Pankaj Jain   《New Astronomy Reviews》2006,50(11-12):854

The remarkable improvement in the estimates of different cosmological parameters in recent years has been largely spearheaded by accurate measurements of the angular power spectrum of cosmic microwave background (CMB) radiation. This has required removal of foreground contamination as well as detector noise bias with reliability and precision. Recently, a novel model-independent method for the estimation of CMB angular power spectrum from multi-frequency observations has been proposed and implemented on the first year WMAP (WMAP-1) data by Saha et al. [Saha, R., Jain, P., Souradeep, T., 2006. ApJL, 645, L89]. We review the results from WMAP-1 and also present the new angular power spectrum based on three years of the WMAP data (WMAP-3). Previous estimates have depended on foreground templates built using extraneous observational input to remove foreground contamination. This is the first demonstration that the CMB angular spectrum can be reliably estimated with precision from a self contained analysis of the WMAP data. The primary product of WMAP are the observations of CMB in 10 independent difference assemblies (DA) distributed over five frequency bands that have uncorrelated noise. Our method utilizes maximum information available within WMAP data by linearly combining DA maps from different frequencies to remove foregrounds and estimating the power spectrum from the 24 cross-power spectra of clean maps that have independent noise. An important merit of the method is that the expected residual power from unresolved point sources is significantly tempered to a constant offset at large multipoles (in contrast to the l² contribution expected from a Poisson distribution) leading to a small correction at large multipoles. Hence, the power spectrum estimates are less susceptible to uncertainties in the model of point sources.  相似文献   

Some features of winter aerosol and water vapor characteristics over Agra, a semi-arid location in India     

S. K. Saha  P. C. S. Devara 《Meteorology and Atmospheric Physics》2010,109(3-4):139-147

Reported in this article are the results of the analysis of extensive observations of aerosol optical, micro-physical characteristics, and precipitable water content (PWC) that have been carried out using compact, multi-band solar radiometers, over a semi-arid station, Agra (27°10′N, 78°05′E, 169 m AMSL) during winter 2004. The aerosol optical depth (AOD), Angstrom wavelength exponent (α), and PWC show, higher values on hazy- and foggy-days and lower values on clear-days. The turbidity coefficient (β) shows higher values for smaller values of α and vice versa. The aerosol size spectra exhibit bi-modal distribution with abundance of accumulation-mode particles during fog and haze occasions, and relatively coarse-mode particles on clear-days. The above features have been explained with co-located PWC and surface-level meteorological parameters. The NOAA HYSPLIT five-day back trajectories indicate the influence of trans-boundary pollution transport over the experimental station during the study period.  相似文献   

Signals of statistical anisotropy in WMAP foreground-cleaned maps     

Pramoda Kumar Samal  Rajib Saha  Pankaj Jain  John P. Ralston 《Monthly notices of the Royal Astronomical Society》2009,396(1):511-522

Recently, a symmetry-based method to test for statistical isotropy of the cosmic microwave background was developed. We apply the method to template-cleaned 3- and 5-years Wilkinson Microwave Anisotropy Probe - Differencing Assembly maps. We examine a wide range of angular multipoles from  2 < l < 300  . The analysis detects statistically significant signals of anisotropy inconsistent with an isotropic cosmic microwave background in some of the foreground-cleaned maps. We are unable to resolve whether the anomalies have a cosmological, local astrophysical or instrumental origin. Assuming the anisotropy arises due to residual foreground contamination, we estimate the residual foreground power in the maps. For the W -band maps, we also find a highly improbable degree of isotropy we cannot explain. We speculate that excess isotropy may be caused by faulty modelling of detector noise.  相似文献   

ENSO, IOD and Indian Summer Monsoon in NCEP climate forecast system     

Samir Pokhrel  H. S. Chaudhari  Subodh K. Saha  Ashish Dhakate  R. K. Yadav  Kiran Salunke  S. Mahapatra  Suryachandra A. Rao 《Climate Dynamics》2012,39(9-10):2143-2165

El Ni?o-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Indian Summer Monsoon rainfall features are explored statistically and dynamically using National Centers for Environment Prediction (NCEP) Climate Forecast System (CFSv1) freerun in relation to observations. The 100?years of freerun provides a sufficiently long homogeneous data set to find out the mean state, periodicity, coherence among these climatic events and also the influence of ENSO and IOD on the Indian monsoon. Differences in the occurrence of seasonal precipitation between the observations and CFS freerun are examined as a coupled ocean–atmosphere system. CFS simulated ENSO and IOD patterns and their associated tropical Walker and regional Hadley circulation in pure ENSO (PEN), pure IOD (PIO) and coexisting ENSO-IOD (PEI) events have some similarity to the observations. PEN composites are much closer to the observation as compared to PIO and PEI composites, which suggest a better ENSO prediction and its associated teleconnections as compared to IOD and combined phenomenon. Similar to the observation, the model simulation also show that the decrease in the Indian summer monsoon rainfall during ENSO phases is associated with a descending motion of anomalous Walker circulation and the increase in the Indian summer monsoon rainfall during IOD phase is associated with the ascending branch of anomalous regional Hadley circulation. During co-existing ENSO and IOD years, however, the fate of Indian summer monsoon is dictated by the combined influence of both of them. The shift in the anomalous descending and ascending branches of the Walker and Hadley circulation may be somewhat attributed to the cold (warm) bias over eastern (western) equatorial Indian Ocean basin, respectively in the model. This study will be useful for identifying some of the limitations of the CFS model and consequently it will be helpful in improving the model to unravel the realistic coupled ocean–atmosphere interactions for the better prediction of Indian Summer Monsoon.  相似文献   

Vanadium bearing titaniferous magnetite ore bodies of Ganjang,Karbi-Anglong District,Northeastern India     

Abhishek Saha  Sohini Ganguly  Jyotisankar Ray  Avik Dhang 《Journal of the Geological Society of India》2010,76(1):26-32

A new occurrence of (syenite-hosted) Vanadium bearing titaniferous magnetite ore body has been reported from Ganjang (26°09′35″ N: 93°20′ E), Karbi-Anglong, Northeastern India. The magnetite ore bodies have lumpy and sporadic occurrences within the host syenite pluton intrusive into gneissic country rocks. Ore microscopic studies reveal that magnetite is often associated with haematite and ilmenite depicting different textural patterns. Critical consideration of several elemental patterns suggests magmatic differentiation to be main ore-forming process. The ore body is suggested to have been formed as late stage segregation from a differentiating alkaline magma in a fluid enriched milieu.  相似文献