Change of river channel and bank erosion of the burhi dihing river (assam), assessed using remote sensing data and gis   总被引：1，自引：0，他引：1  

J. N. Sarma  D. Borah  U. Goswami 《Journal of the Indian Society of Remote Sensing》2007,35(1):93-100

The Burhi Dining river flows in a meandering course for about 220 km through alluvial plains of Assam including a short rocky and hilly tract in between. Sequential changes in the position of banklines of the river due to consistent bank erosion have been studied from Survey of India topographic maps of 1934 and 1972, and digital satellite data of 2001 and 2004 using GIS. Two broad kinds of changes have been observed, e.g. alteration of direction of flow due to neck cut-off and progressive gradual change of the meander bends that accounts for translational, lateral, rotational, extensional and other types of movement of the meander bends. Study of bankline shift due to the bank erosion has been carried out for the periods 1934–1972, 1972–2001, 2001–2004 and 1934–2004 at 13 segments spaced at 5′ longitude interval (average 15 km) as the river course trends nearly east to west. The amounts of the bank area lost due to erosion and gained due to sediment deposition are estimated separately. The total area eroded in both banks during 1934–1972 was more (26.796 km²) as compared to sediment deposition (19.273 km²), whereas total sediment deposition was more (34.61 km²) during 1972-2001 as compared to erosion (23.152 km²). Erosion was again more in 2001–2004 (7.568 km²) as compared to sediment deposition (2.493 km²). During the entire period (1934–2004) of study the overall erosion on the both banks was 31.169 km² and overall sediment deposition was 30.101 km². The highest annual rates of bank erosion as well as bank building of the river are 21055.47 m²/km in 2001–2004 and 9665.81 m²/km in 1972-2001, respectively. Similarly the highest average annual rates of erosion as well as sediment deposition in both banks are observed during 2001–2004 and 1972–2001, respectively. The hard rocks of the hilly tract situated in between result in development of entrenched meandering and this tract has suffered minimum bank erosion.  相似文献   

Nier Prize Citation for Gopalan Srinivasan     

Jitendra Nath Goswami 《Meteoritics & planetary science》1998,33(Z4):A4-A4

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Foreword     

P. Goswami 《Journal of Earth System Science》1998,107(1):1-2

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Role of barotropic,baroclinic and combined barotropic-baroclinic instability for the growth of monsoon depressions and mid-tropospheric cyclones     

B. N. Goswami  R. N. Keshavamurty  V. Satyan 《Journal of Earth System Science》1980,89(1):79-97

A detailed barotropic, baroclinic and combined barotropic-baroclinic stability analysis has been carried out with mean monsoon zonal currents over western India, eastern India and S.E. Asia. The lower and middle tropospheric zonal wind profiles over western India are barotropically unstable. The structure and growth rate of these modes agree well with the observed features of the midtropospheric cyclones. Similar profiles over eastern India and S.E. Asia, however, are barotropically stable. This is attributed to weak horizontal shear, inherent to these profiles. The upper tropospheric profiles, on the other hand, are barotropically unstable throughout the whole region. The features of these unstable modes agree with those of observed easterly waves. The baroclinic and combined barotropic-baroclinic stability analyses show that the baroclinic effects are not important in tropics. Though the barotropic instability of the mean zonal current seems to be res ponsible for the initial growth of the mid-tropospheric cyclones, neither barotropic nor baroclinic instability of the mean zonal current seem to explain the observed features of the monsoon depressions.  相似文献   

Effect of land–ocean contrast on the structure of anomaly tropical circulation     

Binson Joseph  Prashant Goswami 《Dynamics of Atmospheres and Oceans》1998,28(3-4)

While the important role of land–ocean contrast (LOC) in the mean atmospheric circulation is well-known, an intriguing question remains as to whether LOC can also significantly influence the anomaly circulation. This question is particularly important in the tropics, where a large part of the variabilities is known to be due to convective internal dynamics, which in turn can be significantly affected by LOC. In the present work, we investigate this question using a model of convectively driven anomaly circulation in the tropics. Emphasizing the lower tropospheric flow, we adopt a model describing the horizontal dynamics of the first baroclinic mode on an equatorial β-plane, in the presence of moist feedbacks. We introduce LOC in both latitudinal and longitudinal directions. Land surface dryness is taken into account in the moisture budget through the control of evaporative flux. A constant non-latent heating term is used over land in order to represent radiative and sensible heating effects. First, a control run is performed, numerically, without any LOC using random initial perturbations. The gravest mode that emerges from the control run, which is a wave-2 feature with a period around 20 days, is then used as the initial field for the model runs with LOC. The results show that LOC can significantly influence even the tropical variabilities. A latitudinal LOC, with a land mass in the northern hemisphere (north of 10°N), tends to shift the region of maximum precipitation slightly north of the equator with accompanying steeper gradients near the land–ocean boundary. The implications of this result for our understanding of Asian summer monsoon conditions are discussed. When LOC is only in the longitudinal direction, the dominant wave structure that emerges from the model run has wavenumber one and a period of about 35 days, very similar to the observed 30–60 day oscillation. In our final experiment, which is nearer to the realistic land–ocean configuration in the tropics, it is found that both latitudinal and longitudinal effects of LOC are important aspects of the tropical anomaly circulation. It is suggested that some of the patterns in the precipitation distribution, observed in the tropics and simulated using general circulation models are results of convectively induced internal dynamics, modulated by LOC.  相似文献   

Use of SARAL/AltiKa Observations for Modeling River Flow     

Praveen Gupta  Amit Kumar Dubey  Nandita Goswami  Raghvendra Pratap Singh  Prakash Chauhan 《Marine Geodesy》2015,38(3):614-625

In the absence of many gauging stations in the major and mighty river systems, there is a need for satellite-based observations to estimate temporal variations in the river water storage and associated water management. In this study, SARAL/AltiKa application for setting up hydraulic model (HEC-RAS) and river flow simulations over Tapi River India has been discussed. Waveform data of 40 Hz from Ka band altimeter has been used for water levels retrieval in the Tapi river. SARAL/AltiKa retrieved water levels were converted to discharge in the upstream location (track-926) using the rating curve available for the nearby gauging site and using linear spatial interpolation technique. Steady state simulations were done for various flow conditions in the upstream. Validation of river flow model was done in the downstream location (track-367) by comparing simulated and altimeter retrieved water levels (RMSE 0.67 m). Validated model was used to develop rating curve between water levels and simulated discharge for the downstream location which enables to monitor discharge variations from satellite platform in the absence of in situ observations. It has been demonstrated that SARAL/AltiKa data has potential for river flow monitoring and modeling which will feed for flood disaster forecasting, management and planning.  相似文献   

Analysis and quantification of contrasts in observed meteorological fields for foggy and non-foggy days   总被引：1，自引：0，他引：1  

Prashant Goswami  Sumana Sarkar 《Meteorology and Atmospheric Physics》2015,127(5):605-623

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Effects of atmospheric dynamics and ocean resolution on bi-stability of the thermohaline circulation examined using the Grid ENabled Integrated Earth system modelling (GENIE) framework     

T. M. Lenton  R. Marsh  A. R. Price  D. J. Lunt  Y. Aksenov  J. D. Annan  T. Cooper-Chadwick  S. J. Cox  N. R. Edwards  S. Goswami  J. C. Hargreaves  P. P. Harris  Z. Jiao  V. N. Livina  A. J. Payne  I. C. Rutt  J. G. Shepherd  P. J. Valdes  G. Williams  M. S. Williamson  A. Yool 《Climate Dynamics》2007,29(6):591-613

We have used the Grid ENabled Integrated Earth system modelling (GENIE) framework to undertake a systematic search for bi-stability of the ocean thermohaline circulation (THC) for different surface grids and resolutions of 3-D ocean (GOLDSTEIN) under a 3-D dynamical atmosphere model (IGCM). A total of 407,000 years were simulated over a three month period using Grid computing. We find bi-stability of the THC despite significant, quasi-periodic variability in its strength driven by variability in the dynamical atmosphere. The position and width of the hysteresis loop depends on the choice of surface grid (longitude-latitude or equal area), but is less sensitive to changes in ocean resolution. For the same ocean resolution, the region of bi-stability is broader with the IGCM than with a simple energy-moisture balance atmosphere model (EMBM). Feedbacks involving both ocean and atmospheric dynamics are found to promote THC bi-stability. THC switch-off leads to increased import of freshwater at the southern boundary of the Atlantic associated with meridional overturning circulation. This is counteracted by decreased freshwater import associated with gyre and diffusive transports. However, these are localised such that the density gradient between North and South is reduced tending to maintain the THC off state. THC switch-off can also generate net atmospheric freshwater input to the Atlantic that tends to maintain the off state. The ocean feedbacks are present in all resolutions, across most of the bi-stable region, whereas the atmosphere feedback is strongest in the longitude–latitude grid and around the transition where the THC off state is disappearing. Here the net oceanic freshwater import due to the overturning mode weakens, promoting THC switch-on, but the atmosphere counteracts this by increasing net freshwater input. This increases the extent of THC bi-stability in this version of the model. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Evidence for structural discordance in the inverted metamorphic sequence of Sikkim Himalaya: Towards resolving the Main Central Thrust controversy     

Saibal Gupta  Aditi Das  Sudipta Goswami  Ananda Modak  Suman Mondal 《Journal of the Geological Society of India》2010,75(1):313-322

Inverted metamorphism in the Himalayas is closely associated with the Main Central Thrust (MCT). In the western Himalayas, the Main Central Thrust conventionally separates high grade metamorphic rocks of the Higher Himalayan Crystalline Sequence (HHCS) from unmetamorphosed rocks of the Inner sedimentary Belt. In the eastern Himalayas, the Inner sedimentary Belt is absent, and the HHCS and meta-sedimentary Lesser Himalayan Sequence (LHS) apparently form a continuous Barrovian metamorphic sequence, leading to confusion about the precise location of the MCT. In this study, it is demonstrated that migmatitic gneisses of the sillimanite zone in the higher structural levels of the HHCS are multiply deformed, with two phases of penetrative fabric formation (S_1HHCS and S_2HHCS) followed by third folding event associated with a spaced, NW-SE trending, north-east dipping foliation (S_3HHCS). The underlying LHS schists (kyanite zone and lower) are also multiply deformed, with the bedding S₀ being isoclinally folded (F_1LHS), and subsequently refolded (F_2LHS and F_3LHS). The contact zone between the HHCS and LHS is characterized by ductile, top-to-the southwest shearing and stabilization of a pervasive foliation that is consistently oriented NW-SE and dips northeast. This foliation is parallel to the S_3HHCS foliation in the HHCS, and the S_2LHS in the LHS. Early lineations in the HHCS and LHS also show different dispersions across the contact shear zone, implying that pre-thrusting orientations of the two units were distinct. The contact shear zone is therefore interpreted to be a plane of structural discordance, shows a shear sense consistent with thrust movement and is associated with mineral growth during Barrovian metamorphism. It may well be considered to represent the MCT in this region.  相似文献   

Verification of cloud cover forecast with INSAT observation over western India     

Shivani Shah  B. M. Rao  Prashant Kumar  P. K. Pal 《Journal of Earth System Science》2010,119(6):775-781

Since the beginning of the summer monsoon 2009, experimental mesoscale weather forecasts in real time are being generated using WRF model by the Meteorology and Oceanography Group at the Space Applications Centre (ISRO) and are disseminated through MOSDAC () to various users. To begin with, the 12 h, 24 h and 48 h forecasts for the western India region are made available. A study is undertaken to comprehensively assess the cloudiness prediction performance of WRF model. The evaluations have been made over the three months period during monsoon 2009. INSAT cloud imagery data has been used as a reference for these evaluations. The verification strategy includes computation of various skill scores. It is seen that probability of detection (POD) of cloud is 84% and the false alarm rate (FAR) is around 18%. It is hoped that this assessment will provide information on the use of these forecasts in various applications.  相似文献