Impact of moisture variations on the circulation of the south-west monsoon

The impact of moisture anomalies on the circulation of the south-west Indian monsoon has been studied with a general circulation model. Newtonian relaxation is adopted to subject the model atmosphere under sustained moisture anomalies. The impact of negative anomalies of moisture was seen as a divergent circulation anomaly, while the positive anomaly was a stronger convergent anomaly. Although the humidity fields display a resilient behaviour, and relax back to normal patterns 1–2 days after the forcing terms in humidity are withdrawn, the circulation anomalies created by the moisture variation keeps growing. A feedback between positive moisture anomalies and low level convergence exists, which is terminated in the absence of external forcings.     

Selection of optimum frequency of a wind scatterometer

The problem of selecting the optimum operating frequency of a scatterometer, used for remote sensing of sea surface wind speed has been addressed by applying the criteria of maximum sensitivity of backscattering coefficient to wind speed as well as its correlation with wind speed. The backscattering coefficient values for sea surface were computed by the two-scale scattering theory. To compute the atmospheric transmittance, 753 clear sky atmospheres over Indian Ocean were used. While the correlation coefficient was uniform (0.94) throughout the frequency range of 1 to 30GHz, only frequencies above 5GHz were found sensitive enough to yield a wind speed accuracy of ±2msec⁻¹ and better, the accuracy improving with frequency.     

Quasi-specular sea scatter with modified reflection coefficient

The paper deals with the relationship between the sea surface wind speed (U) and the backscattering coefficient (σ⁰) for microwave frequencies and quasi specular range of angles. Valenzuela’s effective reflection coefficient based on the theory of scattering of electromagnetic waves from rought dielectric surfaces has been introduced in the expression of backscattering coefficient and the final result compared with the σ⁰-U relationship derived fromSEASAT scatterometer and concurrent sea truth data.     

Analysis of WRCC of Fly Ash-Bentonite Mixes Based on Combined Shrinkage and Suction Measurement

Sand-Bentonite mixtures are used in landfill liner application in appropriate proportions. However, effort has been made to replace the sand by some waste materials like fly ash without compromising the required properties for liner construction. In recent years, many studies were carried out to determine the suitability of different fly ashes for using with bentonite based on different geotechnical parameters. On the other hand, limited studies were found in determining the unsaturated characteristics i.e. Water Retention Characteristics Curve (WRCC) of fly ash-bentonite mixes. The determination of WRCC in case of bentonite is very complexed compared to other types of clay soil due to its high shrinkage and swelling characteristics upon drying and wetting. In this study, a combined shrinkage and suction measurement was carried out in fly ash-bentonite mixes to accurately represent the WRCC under drying condition only. The shrinkage measurement was carried out using balloon method and suction measurement was carried out with the help of WP4 dew point potentiameter device. Both the shrinkage and suction results were finally used to obtain the WRCC for the different mixes. Further, the study on the variability of WRCCs for the different mixes indicates that WRCC can be represented by a generalized plot with 20% variation.

     

Seismic bearing capacity of strip footing on partially saturated soil using modal response analysis

The present study proposes a novel and simplified methodology to assess the seismic bearing capacity (SBC) of a shallow strip footing by incorporating strength non-linearity arising due to partial saturation of a soil matrix. Furthermore, developed methodology incorporates the modal response analysis of soil layers to assess SBC. A constant matric suction distribution profile has been considered throughout the depth of the soil. The Van Genuchten equation and corresponding fitting parameters have been considered to quantify matric suction in the analysis. SBC has been obtained for three different geomaterials; viz. sand, fly ash and clay, based on their predominant grain size and diverse soil water characteristics curve (SWCC) attributes. Variation of SBC with different modes of vibration and damping ratio are reported for ranges of matric suction pertinent to the geomaterials considered in the study. The relative significance of matric suction on SBC has been reported for suction values within the transition zone of each geomaterial. It is observed that the SBC of sand is drastically reduced, with matric suction reaching beyond the residual suction value. The SBC of fly ash remains constant beyond the residual suction value, whereas the SBC of clay shows an increasing trend toward the practical range of matric suction values.

     

Load transfer mechanism for connected and disconnected piled raft: a comparative study

Acta Geotechnica - This paper presents a comparative experimental study highlighting the differences in load transfer mechanism between the connected and disconnected piled raft systems. Scaled...     

Role of interannual equatorial forcing on the subsurface temperature dipole in the Bay of Bengal during IOD and ENSO events

Role of equatorial forcing on the thermocline variability in the Bay of Bengal (BoB) during positive and negative phases of the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) was investigated using the Regional Ocean Modeling System (ROMS) simulations during 1988 to 2015. Two numerical experiments were carried out for (i) the Indian Ocean Model (IOM) with interannual open boundary conditions and (ii) the BoB Model (BoBM) with climatological boundary conditions. The first mode of Sea Surface Height Anomalies (SSHA) variability showed a west-east dipole nature in both IOM and altimetry observations around 11°N, which was absent in the BoBM. The vertical section of temperature along the same latitude showed a sharp subsurface temperature dipole with a core at ~ 100 m depth. The positive (negative) subsurface temperature anomalies were observed over the whole northeastern BoB during NIOD (PIOD) and LN (EN) composites due to stronger (weaker) second downwelling Kelvin Waves. During the negative phases of IOD and ENSO, the cyclonic eddy on the southwestern BoB strengthened due to intensified southward coastal current along the western BoB and local wind stress. The subsurface temperature dipole was at its peak during October–December (OND) with 1-month lag from IOD and was evident from the Argo observations and other reanalysis datasets as well. A new BoB dipole index (BDI) was defined as the normalized difference of 100-m temperature anomaly and found to be closely related to the frequency of cyclones and the surface chlorophyll-a concentration in the BoB.