Monsoon activity and coupling between low-latitude and high-latitude stratospheric activities

From a Fourier analysis of the monthly mean values of the northern hemispheric geopotential heights at 30 and 50 mb levels, for the period 1972–1979, the transports of momentum and of sensible heat, and the energy conversion terms,C(K _E ,K _Z ) andC(A _Z ,A _E ), have been computed along 30°N and 60°N latitutudes. The variation in these dynamical parameters at 60°N, in relation to monsoon activity in low latitudes and the easterly and westerly phases of the QBO over Gan Island, suggest that a coupling may exist between the high-latitude stratospheric changes and low-latitude monsoon activity and that the low-latitude stratospheric activity modulates high-latitude circulation, confirming the results obtained byHolton andTan (1980) and byLabitzke (1983). The study of the low-latitude stratospheric changes in relation to the high-latitude warmings also indicates a linkage between the low- and high-latitude features     

Estimation of source function and medium response function by autoregressive method

By modelling seismograms as “low” and “high” order autoregressive (AR) processes, the source function and the medium response function are separated from a single channel seismogram. Akaike's final prediction error is used as a statistic to select the appropriate “low” and “high” AR order of the process. Case studies of synthetic data show that the recovered source and reflectivity functions compare very well with the input functions. Using this method, arrivals of the surface reflected P phases of five explosions from the Soviet region and of two earthquakes from Kamchatka, recorded at Gauribidanur Seismic Array (GBA), India, are identified. Certain features of the source and source region of these events are also inferred.     

Dynamics of the stationary eddies in the lower stratospheric circulation in the wavenumber domain and monsoon activity

Meridional transports of momentum and sensible heat have been computed using the Fourier coefficients of the geopotential heights at 50 mb and 30 mb levels for each month during the years 1972 to 1979. Seasonal variations in these transports and in the energy conversionsC (K _E ,K _Z ) andC (A _z ,A _E ) in the contrasting years of monsoon activity have been discussed. The transport and the conversion terms undergo annual variations only with winter maxima and summer minima. Large northward transport of momentum and of sensible heat in the low latitude summer and in the high latitude preceeding winter suggests a linkage between monsoon activity and high latitude stratosphere. Seasonal variations in the energy conversion termsC (K _E ,K _Z ) andC (A _Z ,A _E ) conform with the changes in the system in the years of widely differing monsoon activity both in low and high latitudes. Large conversion of energy fromA _Z toA _E in low latitude summer indicates weakening of the existing meridional temperature gradient, in bad monsoon years.     

Repeated load tests on geosynthetic reinforced unpaved road sections

This paper presents the experimental results from laboratory repeated plate load tests on unreinforced and reinforced model sections of unpaved road constructed in a steel test tank. Different types of geosynthetics, namely, geotextile, two types of biaxial geogrids and geocells were used to reinforce the road sections in different tests. The effect of type and form of reinforcement on the stress-strain hysteresis of unpaved road sections is discussed in the light of experimental results. Model tests were also conducted with varying heights and positions of geocell layer to study the effect of these parameters on deformations and surface profiles. It was observed that at higher settlements, the reinforced systems developed less permanent settlements and more elastic settlements compared to unreinforced systems. Increasing the height of the geocell layer resulted in improved performance up to a certain height, beyond which, further increase in the height reduced the load resistance because of the inadequate granular overlay thickness.     

Prediction of gas hydrate saturation throughout the seismic section in Krishna Godavari basin using multivariate linear regression and multi-layer feed forward neural network approach

Stepwise linear regression, multi-layer feed forward neural (MLFN) network method was used to predict the 2D distribution of P-wave velocity, resistivity, porosity, and gas hydrate saturation throughout seismic section NGHP-01 in the Krishna-Godavari basin. Log prediction process, with uncertainties based on root mean square error properties, was implemented by way of a multi-layer feed forward neural network. The log properties were merged with seismic data by applying a non-linear transform to the seismic attributes. Gas hydrate saturation estimates show an average saturation of 41 % between common depth point (CDP) 600 and 700 and an average saturation of 35 % for CDP 300–400 and 700–800, respectively. High gas hydrate saturation corresponds to high P-wave velocity and high resistivity except in a few spots, which could be due to local variation of permeability, temperature, fractures, etc.     

Differential Alteration of Ilmenite in a Tropical Beach Placer, Southern India: Microscopic and Electron Probe Evidences

Abstract. The study based on microscopic and microprobe techniques reveals that ilmenite of Manavalakurichi deposit has generally reached the alteration phase of 'leached ilmenite'. The XRD and bulk chemical analysis confirm the limited alteration undergone by ilmenite grains. Ilmenite alteration has been found to be a process of continuous leaching of iron from the mineral lattice and hydroxylisation. The enrichment of trace elements with progressive alteration is discussed. Si and Al are enriched by more than 100 fold. The prevalence of reducing environment at present in the deposit indicates that the oxidation of ferrous iron leading to pseudorutile formation would have occurred during transportation of sediments.     

Dynamics of urban boundary layer over São Paulo associated with mesoscale processes

Summary Examination of the Doppler SODAR data from Sao Paulo, Brazil, has given valuable information on the coupling between planetary boundary layer (PBL) and the free atmosphere above, which is reported here. In this communication a case study, on the dynamics of the urban boundary layer over the Metropolitan Area of Sao Paulo (MASP), Brazil, is examined for July 27, 1999 when a multiple gravity wave (GW), a low-level jet (LLJ) and a cold front (CF) all occurred in one single day in succession, making use of data from Doppler SODAR, surface meteorological instruments, satellite imageries and model derived values. The experimental findings are compared to provide validations of ground truth with the model-derived profiles based on the mesoscale analysis of Regional Atmospheric Modelling System (RAMS).It is seen that the multiple GW, the LLJ and the CF have different types of nonlinear coupling between the PBL and the free atmosphere. However, there is convincing matching between Doppler SODAR derived features, those of mesoscale analysis from RAMS and satellite view of cloud dynamics. The study provided valuable information on (i) the very nature of these events, (ii) the nonlinear hydrodynamical coupling between the PBL and the free atmosphere above, during such events, and (iii) the possible mechanism of CF influencing the formation of GW and LLJ.     

Observations of the atmospheric surface layer parameters over a semi arid region during the solar eclipse of August 11th, 1999

This paper discusses the observations of the Atmospheric Surface Layer (ASL) parameters during the solar eclipse of August 11th, 1999. Intensive surface layer experiments were conducted at Ahmedabad (23‡21′N, 72‡36′E), the western part of India, which was close to the totality path. This rare event provided by nature is utilised to document the surface layer effects during the eclipse period using measurements of high frequency fluctuations of temperature, tri-axial wind components as well as mean parameters such as temperature, humidity, wind speed and subsoil temperature. Analysis showed that during the eclipse period, the turbulence parameters were affected leading to the suppression of the turbulence process, the main dynamic process in the atmospheric boundary layer, while the mean parameters showed variations within the natural variability of the observational period. The spectra of the wind components and temperature indicated decrease in spectral power by one order in magnitude during the eclipse period. The rate of dissipation of turbulent kinetic energy is found to decrease by more than one order during the eclipse period. The stability parameter showed a change from unstable to stable condition during the period of eclipse and back to unstable condition by the end of eclipse