Spatial distribution of near-surface CO over bay of Bengal during winter: role of transport

As part of Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), cruise-based measurements of near-surface CO were carried out over Bay of Bengal (BoB) covering the latitude–longitude sector 3.5°N–21.0°N and 76.0°E–98.0°E, during winter months of December 2008 to January 2009. These in-situ measured CO mixing ratio varied in the range of 80–480 ppbv over this marine environment with the distinct spatial pattern. The highest mixing ratios were measured over southeast-BoB with mean value of 379±58 ppbv. CO mixing ratios were high over north-BoB compared to southern BoB. These in-situ measurements were compared with the satellite-measured surface CO obtained from Measurements of Pollution in the Troposphere (MOPITT) onboard TERRA and found to be in good agreement over most of the regions, except at southeast-BoB. Surface CO and column CO from MOPITT data showed a similar spatial pattern. Based on the analysis of airmass back-trajectories, satellite-based spatial map of CO distribution over Asian region and Potential Source Contribution Function analysis, different pathways of transport of CO were identified. Transport from northern landmass as well as from south-east Asia has a significant influence in the spatial variation of CO over BoB. Winter-time mixing ratio of CO was found to be higher compared to those measured during other campaigns conducted during February–March 1999, 2001 (pre-monsoon) and September–October, 2002 (post-monsoon).     

First results of convectively generated long-period Kelvin waves in the low-latitude mesosphere during Indian summer monsoon

Spectral analysis of Tirunelveli (8.7°N, 77.8°E) MF radar winds for the year 2007 indicate the presence of long-period Kelvin waves with periods ～23 and ～16 days in the low-latitude mesosphere during Indian summer monsoon months. The dominant presence of these slow-phase speed waves at mesospheric altitudes motivated us to investigate their origin and vertical propagation characteristics. Space-time Fourier analysis of NCEP winds and OLR show the presence of these periodicities with zonal wavenumber 1 indicating that tropical convection is the potential source for these waves and westward phase of stratospheric QBO winds might have favoured these waves to reach the mesosphere.     

Estimation of sedimentary layer shear wave velocity using micro-tremor H/V ratio measurements for Bangalore city

For assessing earthquake hazard of metro cities, knowledge of soil amplification, thickness and properties of sedimentary layer are essential. In order to map the soil thickness using microtremor survey method, in Bangalore city, it is required to calibrate the relation between fundamental resonance frequency of the soil layer and its thickness for the region. For this purpose microtremor survey was carried out at 34 locations in the city where borehole log was available. The resonance frequency of the soil is evaluated from the microtremor recordings using the H/V ratio technique. A nonlinear regression relation between the thickness of sedimentary layer h (m), from the borehole logs, and the resonance frequency f_r (Hz), was derived as h=(58.3±8.8)f_r^{−(0.95)±0.1}. Using the model of shear wave velocity increasing with depth at these locations, the derived average shear wave velocity and the corresponding soil thickness were used, to get an empirical relation between V_S (m/s) and depth z(m), as V_s=(174±28)(1+z)^0.16±0.07. This relation also compares reasonably with the fit obtained between simulated V_S and depth from borehole logs for Bangalore city. The calibrated relations can be used at locations in Bangalore city where borehole logs are not available, for finding the thicknesses and shear wave velocities of the local soil layers at the survey locations.     

Algorithms for time synchronization of wireless structural monitoring sensors

Dense networks of wireless structural health monitoring systems can effectively remove the disadvantages associated with current wire‐based sparse sensing systems. However, recorded data sets may have relative time‐delays due to interference in radio transmission or inherent internal sensor clock errors. For structural system identification and damage detection purposes, sensor data require that they are time synchronized. The need for time synchronization of sensor data is illustrated through a series of tests on asynchronous data sets. Results from the identification of structural modal parameters show that frequencies and damping ratios are not influenced by the asynchronous data; however, the error in identifying structural mode shapes can be significant. The results from these tests are summarized in Appendix A. The objective of this paper is to present algorithms for measurement data synchronization. Two algorithms are proposed for this purpose. The first algorithm is applicable when the input signal to a structure can be measured. The time‐delay between an output measurement and the input is identified based on an ARX (auto‐regressive model with exogenous input) model for the input–output pair recordings. The second algorithm can be used for a structure subject to ambient excitation, where the excitation cannot be measured. An ARMAV (auto‐regressive moving average vector) model is constructed from two output signals and the time‐delay between them is evaluated. The proposed algorithms are verified with simulation data and recorded seismic response data from multi‐story buildings. The influence of noise on the time‐delay estimates is also assessed. Copyright © 2004 John Wiley & Sons, Ltd.     

Natural radioactivity distribution studies in Trivandrum district,Kerala, India

The distribution pattern of radioactive minerals in Trivandrum district of Kerala has been investigated. The surface radioactivity was measured employing a jeep-mounted four-channel gamma-ray spectrometer coupled to a high volume Na I (T1) crystal detector. The distribution of radioactivity has been correlated with the corresponding litho-units and major structures of the study area. The total countrate from sedimentaries including beach sands and pegmatite rich zones (～ 3,500 CPS) are significantly higher than that of the laterites and gneisses which are substantiated by laboratory studies.     

Estimating surface sensible heat flux using sodar and surface temperature measurements in the evolving convective boundary layer

A simple method is described for estimating the sensible heat flux by using a Doppler sodar system and a thermal probe. This method, which can be applied to a convective boundary layer in morning hours, is based on knowing the zero heat flux level from the reflectivity and the vertical wind speed.     

Terrain characteristics and longitudinal,land use and land cover profiles behavior—a case study from Vamanapuram river basin,southern Kerala,India

The morphology of Vamanapuram river basin (VRB), southern Kerala, India has been studied by preparing longitudinal profiles from the source of VRB at Chemmunji Mottai (1,717 m) to its mouth at Muthalapallipozhy (Lakshadweep Sea). Survey of India topographical maps, Geocoded Satellite Imageries, Microsoft Excel and GIS software ILWIS 2.1 are used in this study. The morphometric analysis reveals that there are 1,489, 347, 79, 21, 6, 2 and 1 first-, second-, third-, fourth-, fifth-, sixth- and seventh-order streams, respectively, in VRB, which are responsible for the present-day landform genesis. The mean bifurcation value of VRB is 3.49. The Ponmudi hills receive the highest rainfall in VRB in the Western Ghats Region and Attingal, the lowest in the Coastal Strand Plain. The six land use and land cover profile sections show the distribution of land use–land cover with respect to elevation and depth to water level. The study reveals that mid and high lands generally occupy lower order streams up to fourth order and generally originate from linear ridge, hill crest, rocky slope (scarp face), side slope (S3)/slope 10–15° and hilly terrain.     

Geochemistry of Vellayani lake sediments: Indicators of weathering and provenance

The Vellayani lake, located on the west coast, Kerala, South India, is a natural fresh water lake. In order to understand the source and nature of the sediments; thirteen lake floor sediment samples were collected from the Vellayani lake at different intervals along the S-N transects covering the entire surface area of the lake. Textural studies indicate that lake floor sediments are dominant in sand (55.39%) followed by clay (30.57%) and silt (14.04%) fractions. Coarse components are dominant at the inlet ofthe stream into the lake. The geochemical content of the sediments reveals low SiO₂, MnO, CaO, MgO, Na₂O, K₂O, and P₂O₅ content while TiO₂, Fe₂O₃ and Al₂O₃ are high when compared with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC) values. SiO₂ is high in coarse fractions while Al₂O₃ is strongly associated with fine sediments. Major oxide contents supported by Rare Earth Element (REE) data reveal a distinct negative Eu anomaly reflecting a dominant cratonic origin of the sediments. Detailed geochemical data indicate a mixed source, predominantly, the lateritic soils, sedimentary and metamorphic bedrocks exposed around the lake and in the catchment area.     

On the structure of sea-breeze fronts observed near the coastline of Thumba,India

An investigation has been made of the structure of sea-breeze fronts observed at Thumba mostly during the months of December to April using data from a Doppler SODAR and in situ measurements of wind components, humidity and temperature. The study shows that the vertical wind structure observed in the SODAR height range provides a distinct signature of the passage of a front and that the intensity of the front is decided by the intensity and direction of the prevailing winds as well as the amount of rotation of the wind vector during the onset of the sea-breeze. Spectral analyses of vertical winds during the passage of the front reveal a dominant periodicity of about 6 min for strong sea-breeze fronts.