Intraseasonal oscillations and interannual variability of surface winds over the Indian monsoon region     

B. N. Goswami  D. Sengupta  G. Suresh Kumar 《Journal of Earth System Science》1998,107(1):45-64

The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalyses for the period 1987–1996. Two dominant ISOs are found in all years, with a period between 30–60 days and 10–20 days respectively. Although the ISOs themselves explain only about 10–25% of the daily variance, the spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances), indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics of the two modes and their interannual variability are studied in detail. The synoptic structure of the 30–60 day mode is similar in all years and is shown to be intimately related to the strong (‘active’) or weak (‘break’) phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of Bengal corresponds to the ‘active’ (‘break’) phase of monsoon strengthening (weakening) the entire large scale monsoon circulation. The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough). The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The vorticity pattern associated with the 30–60 day mode has a bi-modal meridional structure similar to the one associated with the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30–60 day mode is consistent with fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10–20 day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30–60 day mode. Elsewhere in the Indian Ocean, this mode is almost always weaker than the 30–60 day mode. In the Bay of Bengal region, the wind curl anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay. On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite structure of the 30–60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual scales.  相似文献   

Methane emissions from rice fields amended with biogas slurry and farm yard manure     

Goutam Debnath  M. C. Jain  Sushil Kumar  K. Sarkar  Suresh K. Sinha 《Climatic change》1996,33(1):97-109

In an experiment on methane-emission measurements from rice fields amended with urea, biogas spent slurry (BSS) + urea, and farm yard manure (FYM) + urea, three distinctive peaks in the methane emissions were observed at 15, 46, and 69 days after transplanting (DAT) due to the availability of readily degradable C-sources. In all cases, the highest peak was at 69 DAT. The steepest Eh drop to a minimum of -320 mV was reached within two weeks of submergence. pH ranged between 7.5 and 8.5. The combined fertilization (FYM + urea) plot showed the maximum emission rate of 4.86 mg m^–2 h^–1 with a total load of 49.44 kg ha^–1 and was 2.3 times higher than (BSS + urea)-treated plot (22.08 kg ha^–1). Grain yields in urea, (BSS + urea) and (FYM + urea) plots were 3.34, 2.94, and 2.85 t ha^–1 respectively, suggesting that biogas slurry is a preferred source over FYM causing lesser environmental pollution without any significant reduction in grain yield.  相似文献   

Forest site quality assessment by aerial photo-interpretation case study of sal forests     

M. D. Shedha  Suresh Kumar 《Journal of the Indian Society of Remote Sensing》1984,12(2):13-25

93 black & white panchromatic aerial photographs of 1972 on 1:20,000 scale were used for assessing the site quality of Sal forest of part of West Dehradun Forest Division, by both direct and indirect methods. The forests were stratified into 5 height and 5 density classes and according to species composition. For necessary data for the assessment of growing stock, field measurements were made on 54 sample plots of 0.1 hectare each. This provided direct indication of actual productive capacity of a particular site. According to indirect method, ground vegetation was sampled in 54 quadrats of 5m x 5m each and has been classified into statistically sound vegetation groupings by normal association analysis technique. These groups facilitated the standardisation of their photo perameters. The indicator value of the plants in a grouping was used to assess the suitability of the site. This was substantiated by super-imposing growing stock, present at that site. By combination of the direct and indirect methods, sites have been classified into 3 categories i.e., suitable, conditionally suitable and unsuitable. Suggestions have been made for management of conditionally suitable sites and the cause for unsuitability of sites are explored. Hence, interpretation of qualitative attributes of vegetation alongwith the measurements of quantitative parameters on aerial photographs have proved to be useful for site quality assessment.  相似文献   

Interplanetary type II radio bursts and their association with CMEs and flares     

A. Shanmugaraju  K. Suresh  V. Vasanth  G. Selvarani  S. Umapathy 《Astrophysics and Space Science》2018,363(6):126

We study the characteristics of the CMEs and their association with the end-frequency of interplanetary (IP)-type-II bursts by analyzing a set of 138 events (IP-type-II bursts–flares–CMEs) observed during the period 1997–2012. The present analysis consider only the type II bursts having starting frequency \(< 14~\mbox{MHz}\) to avoid the extension of coronal type IIs. The selected events are classified into three groups depending on the end-frequency of type IIs as follows, (A) Higher, (B) Intermediate and (C) Lower end-frequency. We compare characteristics of CMEs, flares and type II burst for the three selected groups of events and report some of the important differences. The observed height of CMEs is compared with the height of IP type IIs estimated using the electron density models. By applying a density multiplier (\(m\)) to this model, the density has been constrained both in the upper corona and in the interplanetary medium, respectively as \(m= 1 \mbox{ to } 10\) and \(m = 1 \mbox{ to } 3\). This study indicates that there is a correlation between the observed CME height and estimated type II height for groups B and C events whereas this correlation is absent in group A. In all the groups (A, B & C), the different heights of CMEs and type II reveal that the type IIs are not only observed at the nose but also at the flank of the CMEs.  相似文献   

Sea-breeze-initiated rainfall over the east coast of India during the Indian southwest monsoon   总被引：1，自引：0，他引：1  

Matthew Simpson  Hari Warrior  Sethu Raman  P. A. Aswathanarayana  U. C. Mohanty  R. Suresh 《Natural Hazards》2007,42(2):401-413

Sea-breeze-initiated convection and precipitation have been investigated along the east coast of India during the Indian southwest monsoon season. Sea-breeze circulation was observed on approximately 70–80% of days during the summer months (June–August) along the Chennai coast. Average sea-breeze wind speeds are greater at rural locations than in the urban region of Chennai. Sea-breeze circulation was shown to be the dominant mechanism initiating rainfall during the Indian southwest monsoon season. Approximately 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to convection initiated by sea-breeze circulation.  相似文献   

Excitation equilibrium for low lying levels in Cii,Niii, Oiv,Nevi, Mgviii,Six, and Siii     

Suresh Chandra 《Solar physics》1978,58(2):291-297

The populations of the excited state ² P _3/2 relative to the ground state ² P _1/2 have been investigated in C ii, N iii, O iv, Ne vi, Mg viii, Si x, and Si ii by considering all the radiative and collisional processes including the collisional transitions to the higher states which cascade to the upper level. The relative populations are used for the calculation of the line emissivities. The intensities of 76 320, 30 258 and 14 302 lines of Nevi, Mgviii, and Six ions respectively in the chromosphere-corona transition region are also calculated.  相似文献   

Bending–buckling interaction as a failure mechanism of piles in liquefiable soils     

Suresh R. Dash  Subhamoy Bhattacharya  Anthony Blakeborough 《Soil Dynamics and Earthquake Engineering》2010,30(1-2):32-39

This paper investigates the importance of bending–buckling interaction in seismic design of piles in liquefiable soils using numerical techniques. A pseudo-static analysis has been performed using a well documented case history, where the pile–soil interaction is modelled as a beam on nonlinear winkler foundation (BNWF). Six possible analytical methods, three force based and three displacement based, are performed in which the pile is subjected to both lateral and axial load. Three out of six analysis cases did not predict the failure of the piles when analysed only for bending (i.e., lateral loads only). The buckling analysis showed that the pile was also safe against pure buckling during full liquefaction. Further, two out of those three cases which did not predict failure in bending were reanalysed for bending–buckling interaction (i.e., lateral and axial loads acting simultaneously). These combined analyses showed a more realistic behaviour of pile response and did predict the pile failure. Hence, it can be concluded that if a pile is designed for bending and buckling criteria separately and safe for these individual design criteria, it may fail due to their combined effect.  相似文献   

The delicate balance between soil production and erosion,and its role on landscape evolution     

A. Dosseto  Heather Buss  P.O. Suresh 《Applied Geochemistry》2011

The diversity in landscapes at the Earth’s surface is the result, amongst other things, of the balance (or imbalance) between soil production and erosion. While erosion rates are well constrained, it is only recently that we have been able to quantify rates of soil production. Uranium-series isotopes have been useful to provide such estimates independently of erosion rates. In this study, new U-series isotope are presented data from weathering profiles developed over andesitic parent rock in Puerto Rico, and granitic bedrock in southeastern Australia. The site in Australia is located on a highland plateau, neighbouring a retreating escarpment where soil production rates between 10 and 50 mm/kyr have been determined. The results show that production rates are invariant in these two regions of Australia with values between 15 and 25 mm/kyr for the new site. Andesitic soils show much faster rates, about 200 mm/kyr. Overall, soil production rates determined with U-series isotopes range between 10 and 200 mm/kyr. This is comparable to erosion rates in soil-mantled landscapes, but faster than erosion in cratonic areas and slower than in alpine regions and cultivated areas. This suggests that soil-mantled landscapes maintain soil because they can: there is a balance between production and erosion. Similarly, thick weathering profiles develop in cratonic areas because, despite slow erosion rates, soil production is still significant. Bare landscapes in Alpine regions are probably the result of the inability of soil production to catch up with fast erosion rates, although this needs testing by U-series isotope studies of these regions. Finally, the range of production rates is up to several orders of magnitude lower than erosion rates in cultivated areas, demonstrating quantitatively the fast depletion of soil resources with common agricultural practices.  相似文献   

On the Inclusion of Some Biological Impacts and Influences in Coupled Transport Phenomena in Unsaturated Soil     

Hywel Rhys Thomas  Suresh Channarayapatna Seetharam  Philip James Vardon 《Geotechnical and Geological Engineering》2011,29(2):181-191

This paper presents a first attempt at the inclusion of some biological impacts and influences in the authors’ continued research on coupled transport phenomena through unsaturated porous media. The work presented here forms an extension to an existing coupled Thermo-Hydraulic-Chemical–Mechanical Model (THCM) to include the biological aspects, as a first attempt towards a new THCMB framework. The biological model incorporates biodegradation kinetics of organic substrates and resultant effects in the inorganic geochemistry. In order to achieve this, the biological aspects of the model are coupled to an equilibrium geochemical model following a two-step partial equilibrium approach. Additionally, of concern in contaminant/pollutant transport studies, including the biological aspects, is the effect on human health. This paper therefore also presents some aspects of a health impact analysis model adopted in this study.  相似文献   

Numerical Modeling and Spatial Moment Analysis of Thermal Fronts in a Coupled Fracture-Skin-Matrix System     

N.?NatarajanEmail author  G.?Suresh Kumar 《Geotechnical and Geological Engineering》2011,29(4):477-491

In this study, the behavior of thermal fronts along the fracture is studied in the presence of fracture-skin in a coupled fracture-matrix system. Cold water is injected into the fracture, which advances gradually towards production well, while extracting heat from the surrounding reservoir matrix. The heat conduction into the fracture-skin and the rock-matrix from the high permeability fracture is assumed to be one dimensional perpendicular to the axis of fluid flow along the fracture. Constant temperature cold water is injected through an injection well at the fracture inlet. The fluid flow takes place along the horizontal fracture which ensures connectivity between the injection and production wells. Since the rock-matrix is assumed to be tight, the permeability of fracture-skin as well as the rock-matrix is neglected. The present study focuses on the heat flux transfer at the fracture-skin interface as against the earlier studies on fracture-matrix interface, and the sensitivity of additional heterogeneity in the form of fracture skin in a conventional fracture-matrix coupled system is studied. The behavior of thermal fronts for various thermal conductivity values of the fracture-skin and rock-matrix is analyzed. Spatial moment analysis is performed on the thermal distribution profiles resulting from numerical studies in order to investigate the impact on mobility and dispersion behavior of the fluid in the presence of fracture-skin. The presence of fracture skin affects the heat transfer significantly in the coupled fracture-matrix system. The lower order spatial moments indicate that the effective thermal velocity increases with increase in skin thermal conductivity and a significant thermal dispersion is observed at the inlet of the fracture owing to the high thermal conductivity of the fracture-skin at the early stages. Furthermore the higher spatial moments indicate that the asymmetricity increases with decrease in skin thermal conductivity unlike the case with half fracture aperture and fluid velocity and the kurtosis is maximum with higher skin thermal conductivity which implies enhanced heat extraction from the fracture-skin into the fracture. Results suggest that the amount of heat extraction by the circulating fluid within the fracture from the reservoir not only depends on the rock-matrix module of the reservoir characteristics but also the fracture-skin characteristics of the system and subsequently influence the reservoir efficiency.  相似文献