High-level warmings and total ozone over a tropical region

The rocketsonde data obtained from the launchings made at Thumba (8°3215N, 76°5148E) during the winter period 1970–71, as already reported, have indicated that warmings of noticeable magnitude occurred at high levels (upper stratosphere and mesosphere) over this tropical station during the period mentioned. The mean monthly radiosonde temperatures of 50, 100 and 300 mb levels at Thumba (Trivandrum) and Delhi (28°35N, 77°12E) during the same period have also pointed out certain anomalies consistent with the warmings referred to above at Thumba. The radiosonde temperatures of the two stations, Thumba (Trivandrum) and Delhi, have now been examined, along with the values of total ozone, for the ten winter periods commencing from 1961–1962. The analysis has pointed out the possibility of high-level warmings also having occurred in the past over the Indian region during the winters of 1963–1964 and 1967–1968, which are also the periods when prominent warmings are definitely known to have occurred at higher latitudes. The behaviour of total ozone has been found to be different in the different years of the warmings. The features noticed have been presented and discussed.     

Marine Boundary-Layer Variability Over The Indian Ocean During Indoex (1998)

The variability in boundary-layerstructure over the Indian Ocean during a north-eastmonsoon and the factors influencing it areinvestigated. This study was made possible as acomponent of the Indian Ocean Experiment (INDOEX),conducted from February 19 to March 30, 1998. The dataused are, surface-layer mean and turbulencemeasurements of temperature, humidity and wind, andvertical soundings of temperature and humidity.Significant spatio-temporal variability was observedin the boundary-layer structure throughout the cruise.The ITCZ was characterized as the region withstrongest winds and maximum surface turbulent fluxesof momentum and heat. One of the important findingsfrom this study was a strong influence of continentalair masses on the boundary-layer structure in theNorthern Hemisphere, even at a distance of 600 km offthe Indian coast. This was generally evident in theform of an elevated plume of dry continental airbetween altitudes of 1500 m and 2700 m. Advection ofcontinental aerosols in this layer presents potentialfor significant entrainment into shallow clouds inthis region, which eventually feed deeper clouds atthe ITCZ. This finding provides an explanation foranomalous higher aerosol concentrations found duringprevious studies. The structure of the marineboundary layer was influenced by various factors suchas proximity to land, an anomalous warm pool in theocean and the ITCZ. In the southern hemisphere, theboundary-layer height was primarily governed bysurface-layer sensible heat flux and was found to behighest in the vicinity of the ITCZ. North of theequator it was strongly influenced by land-air-seainteractions. In addition to this synoptic modulation,there was also a significant diurnal variability inthe boundary-layer height.     

Radar Observations of Leonid Meteor Shower 2003

Observations carried out during Leonid meteor shower 2003, by using Indian MST radar (13.46^N, 79.18^E; dip 12.5^N) are used to determine the number density of meteoroids through the cross section of the meteor streams. Cross sections are calculated for a number of classes of echo duration (particle size). They are also used to determine the relative flux of the shower in particle size ranges producing radar meteor echoes having durations <0.4 s, 0.4–1 s and >1 s. Mean activity profiles along the Earth's passage through the stream show a systematic change of the peak activity and the width of the stream depending on the distribution of echo durations across the stream. The patterns of mass distribution index s are presented and discussed.     

Application of wave transformation models for estimation of morphological changes at Vellar estuary,southeast coast of India

Assessment of the wave climate at near coast is vital for estimation of morphological changes, such as growth of sand spit and associated siltation of tidal inlets. Vellar (bar-built) estuary is one of the prominent estuaries along the southeast coast of India, located at 11°30′N and 79°46′E, less studied in terms of its morphological features. The inlet of Vellar is exposed to high energetic waves, inducing large sediment transport rates and shoreline changes. Local wave characteristics are not accurately defined and the available wave information at near coast is limited (point based observations). In the present study, three decoupled numerical models are employed to derive the monthly nearshore wave climate at Vellar by transforming waves from deep water to nearshore. These models are independently validated with buoy observations in deep water and wave gauge data at nearshore. Based on the nearshore wave data, littoral drift along the coast was estimated and compared with the spit growth at Vellar inlet. The estimated average littoral drift along this coast from February to October is 1.93 × 10⁶ m³ toward north and from November to January it is 1.52 × 10⁶ m³ toward south, resulting in a net northerly drift. Results indicated that increase in the wave energy during the period of July to September is responsible for the maximum growth of the sand spit observed in the field.     

Evaluation of atmospheric corrections on hyperspectral data with special reference to mineral mapping

Hyperspectral images have wide applications in the fields of geology, mineral exploration, agriculture, forestry and environmental studies etc. due to their narrow band width with numerous channels. However, these images commonly suffer from atmospheric effects, thereby limiting their use. In such a situation, atmospheric correction becomes a necessary pre-requisite for any further processing and accurate interpretation of spectra of different surface materials/objects. In the present study, two very advance atmospheric approaches i.e. QUAC and FLAASH have been applied on the hyperspectral remote sensing imagery. The spectra of vegetation, man-made structure and different minerals from the Gadag area of Karnataka, were extracted from the raw image and also from the QUAC and FLAASH corrected images. These spectra were compared among themselves and also with the existing USGS and JHU spectral library. FLAASH is rigorous atmospheric algorithm and requires various parameters to perform but it has capability to compensate the effects of atmospheric absorption. These absorption curves in any spectra play an important role in identification of the compositions. Therefore, the presence of unwanted absorption features can lead to wrong interpretation and identification of mineral composition. FLAASH also has an advantage of spectral polishing which provides smooth spectral curves which helps in accurate identification of composition of minerals. Therefore, this study recommends that FLAASH is better than QUAC for atmospheric correction and correct interpretation and identification of composition of any object or minerals.     

In-situ pore pressure variations in Koyna-Warna — A promising key to understand triggered earthquakes

The filling of the Koyna reservoir in western India and the associated triggered earthquakes have been well documented. Several studies have suggested that earthquakes are triggered on pre-existing faults in the region due to changes in pore pressure caused by pore pressure diffusion. To study in-situ pore pressure variations twenty-one borewells were drilled in the Koyna-Warna region under an Indo-German research program during 1995–1998. In most of these wells tidal signals are observed in well level variations indicating sensitivity to small strain changes in hydraulically connected, confined aquifers. Those signals, hence, are suitable to reflect variations in the stress field of local rock formations. More than a decade of well level monitoring has shown four types of earthquake related changes. The pre- and post-earthquake changes are mostly interpretative in nature and difficult to substantiate. The co-seismic and transient changes which are observed for local and large teleseismic events are well established. Wells connected to unconfined aquifers also showed changes related to seismicity in case of large magnitude earthquakes at closer distances. Some anomalous water level fluctuations are seen which are not associated with local or teleseismic earthquakes. These changes are coherent in nature and reflect aseismic regional volume strain.     

Structural interpretation of the Konkan basin,southwestern continental margin of India,based on magnetic and bathymetric data

Magnetic and bathymetric studies on the Konkan basin of the southwestern continental margin of India reveal prominent NNW-SSE, NW-SE, ENE-WSW, and WNW-ESE structural trends. The crystalline basement occurs at about 5–6 km below the mean sea level. A mid-shelf basement ridge, a shelf margin basin, and the northern extension of the Prathap Ridge complex are also inferred. The forces created by the sea-floor spreading at Carlsberg Ridge since late Cretaceous appears to shape the present-day southwestern continental margin of India and caused the offsets in the structural features along the preexisting faults.     

Growth and photosynthetic rates of Chlamydomonas plethora and Nitzschia frustula cultures isolated from Kuwait Bay, Arabian Gulf, and their potential as live algal food for tropical mariculture

With a view to utilize local algae as food organisms in mariculture, the green alga Chlamydomonas plethora and the diatom Nitzschia frustula were isolated and studied from the unique coastal waters arid zone off Kuwait. Batch cultures of C. plethora and N. frustula had maximum division rates (μ_max) of 2.5 and 3.4 day^?1, respectively. Cultures grown for 36 h yielded comparable growth rates. Photosynthesis‐irradiance relationships in cultures harvested at various phases of growth showed that cultures attained log phase after 1‐day growth and yielded the highest assimilation numbers (P: μg C [μg Chl a]^?1 h^?1): 22.8 for C. plethora and 18.1 for N. frustula. Their initial slopes (α^B: ng C [μg Chl a]^?1 h^?1 [μmol m^?2 s^?1]^?1 were also the highest observed so far: 79.5 for C. plethora and 39.6 for N. frustula. Photoinhibition was low. Compared with these, assimilation numbers in senescent cultures of 20‐day growth were <8% of the maximum for both species, and the initial slope decreased to 17 and 13% in C. plethora and N. frustula, respectively. Two polyunsaturated fatty acids (20:5n‐3 eicosapentaenoic acid and 22:6n‐3 docosahexaenoic acid) that are essential in many marine animal diets constituted up to 24% and 1.9% of the total fatty acids, respectively. Of the two algae, N. frustula contained higher levels of 16:1n‐7, 20:5n‐3 and comparatively low levels of 22:6n‐3 fatty acids. Due to its rapid growth, high photosynthetic rate and presence of the amino acids leucine, lysine, glutamic acid and arginine N. frustula has good potential as a feed organism in mariculture applications. The capacity of these algae to produce a wide range of size groups (nano and net plankton) is an additional bonus for mariculture operations.     

Dynamic soil properties for microzonation of Delhi,India

Delhi, the capital of India, has experienced mild seismic shaking during several earthquakes in the past. The large variations of depth to bedrock and ground water table coupled with different soil types at different locations of Delhi necessitate a seismic microzonation study. Dynamic soil properties such as shear wave velocity, modulus reduction and damping characteristics of local soils are the basic and essential input parameters for conducting even a preliminary ground response analysis which is an essential input in microzonation studies. Shear wave velocity is not measured routinely due to its high cost and lack of the required expertise. Several researchers in the past developed correlations between shear wave velocity (V _s ) and routinely measured N values. In the present study, shear wave velocity profiles measured in the field at more than 80 borehole locations to a depth of about 20 to 32m using Spectral Analysis of Surface Waves (SASW) are presented and correlations between shear wave velocity and N values are also presented for use by engineers and designers. Results of strain and stress controlled cyclic triaxial tests on remoulded samples of sand-silt mixtures in the high strain range are used for generating the modulus reduction and damping curves and are compared with the well-known curves in the literature. The results presented in this article can be used for microzonation studies as well as site specific ground response analyses at Delhi.