Nitrogen sources for new production in the NE Arabian Sea

New productivity measurements using the ¹⁵N tracer technique were conducted in the north-eastern (NE) Arabian Sea during six expeditions from 2003 to 2007, mostly in winter. Our results indicate that the NE Arabian Sea has a potential for higher new productivity during blooms. Nitrate uptake by plankton is the highest during late winter. New productivity and f-ratios in the NE Arabian Sea are mainly controlled by hydrodynamic and meteorological parameters such as wind strength, sea surface temperature (SST), mixed layer depth (MLD) and mixed layer nitrate. Deepening of the mixed layer supplies nitrate from below, which supports the observed nitrogen uptake. Higher f-ratios during blooms indicate the strong coupling between surface layers and sub-surface layers. Deepening of mixed layer below 100 m (from its inter-monsoon value between 30 and 40 m) transferred often more than 100 mmol N–NO₃ m^? 2 into the surface layers from below. The observed winter blooms in the region are supported by such input and are sustained for more than a month. Higher new productivity has been found in late winter, whereas transport of nitrate is maximum in early winter. In general, new production varies progressively during winter. Diurnal cycling of the mixed layer could be the reason for the under utilization of entrained nitrate during early winter. New productivity values and wind strength show significant differences during Feb–Mar 03 and Feb–Mar 04. These differences indicate that the winter cooling and parameters related the biological productivity also vary inter-annually. However, the difference between the new productivity values between Feb–Mar 03 and Feb–Mar 04 is much lower than the difference between Jan 03 and Feb–Mar 03. The results suggest that amplitude of seasonal variation is higher than the inter-annual variation in the region. During spring, Fickian diffusive fluxes of nitrate into the surface layer range from 0.51 to 1.38 mmol N–NO₃ m^? 2 day^? 1, and can account for 67% and 78% of the observed nitrogen uptake in the coastal and open ocean regions, respectively. We document the intra-seasonal and inter-annual variations in new productivity during winter and identify sources of nitrate which support the observed productivity during spring.     

Delineating and defining the boundaries of an active landslide in the rainforest of Puerto Rico using a combination of airborne and terrestrial LIDAR data

Light detection and ranging (LIDAR) is a remote sensing technique that uses light, often using pulses from a laser to measure the distance to a target. Both terrestrial- and airborne-based LIDAR techniques have been frequently used to map landslides. Airborne LIDAR has the advantage of identifying large scarps of landslides covered by tree canopies and is widely applied in identifying historical and current active landslides hidden in forested areas. However, because landslides naturally have relatively small vertical surface deformation in the foot area, it is practically difficult to identify the margins of landslide foot area with the limited spatial resolution (few decimeters) of airborne LIDAR. Alternatively, ground-based LIDAR can achieve resolution of several centimeters and also has the advantages of being portable, repeatable, and less costly. Thus, ground-based LIDAR can be used to identify small deformations in landslide foot areas by differencing repeated terrestrial laser scanning surveys. This study demonstrates a method of identifying the superficial boundaries as well as the bottom boundary (sliding plane) of an active landslide in National Rainforest Park, Puerto Rico, USA, using the combination of ground-based and airborne LIDAR data. The method of combining terrestrial and airborne LIDAR data can be used to study landslides in other regions. This study also indicates that intensity and density of laser point clouds are remarkably useful in identifying superficial boundaries of landslides.     

Diurnal variability of upper ocean temperature and heat budget in the southern Bay of Bengal during October–November, 1998 (BOBMEX-Pilot)

Time-series data on upper-ocean temperature, Vessel-Mounted Acoustic Doppler Current Profiler (VM-ADCP) measured currents and surface meteorological parameters have been obtained for the first time in the southern Bay of Bengal at 7‡N, 10‡N, and 13‡N locations along 87‡E during October–November, 1998 under BOBMEX-Pilot programme. These data have been analysed to examine the diurnal variability of upper oceanic heat budget and to estimate the eddy diffusivity coefficient of heat in the upper layer. Diurnal variation of near-surface temperature is typical at northern location (13‡N) with a range of 0.5‡C while the diurnal range of temperature is enhanced to 0.8‡C at the central location (10‡N) due to intense solar radiation (1050 W/m²), clear skies and low wind speeds. At the southern location (7‡N), the diurnal variation of temperature is atypical with the minimum temperature occurring at 2000 hrs instead of at early morning hours. In general, the diurnal curve of temperature penetrated up to 15 to 20 m with decreasing diurnal range with depth. The VM-ADCP measured horizontal currents in the upper ocean were predominantly easterly/northeasterly at southern location, north/northerly at central location and northwesterly at northern location, thus describing a large-scale cyclonic gyre with the northward meridional flow along 87‡E. The magnitudes of heat loss at the surface due to air-sea heat exchanges and in the upper 50 m layer due to vertical diffusion of heat are highest at the southern location where intense convective activity followed by overcast skies and synoptic disturbance prevailed in the lower atmosphere. This and the estimated higher value (0.0235 m²/s) of eddy diffusivity coefficient of heat in the upper ocean (0–50 m depth) suggest that 1-D processes controlled the upper layer heat budget at the southern location. On the other hand, during the fair weather conditions, at the central and northern locations, the upper layer gained heat energy, while the sea surface lost (gained) heat energy at northern (central) location. This and lower values of eddy diffusivity coefficient of heat (0.0045 and 0.0150 m²/s) and the northward intensification of horizontal currents at these locations suggest the greater role of horizontal heat advection over the 1-D processes in the upper ocean heat budget at these two locations.     

Bastnaesite from Kanigiri granite, Prakasam district, Andhra Pradesh

For the first time we report bastnaesite and hydroxyl bastnaesite (lanthanum cerium fluoro-carbonate) from the Kanigiri granite. The host granitoids are of A-type and vary in composition from quartz syenites to peralkaline granites. Rare metal and rare earth-bearing minerals identified by X-ray diffraction (XRD) studies in Kanigiri granite are bastnaesite and hydroxyl bastnaesite, besides columbite-tantalite, monazite, fergusonite, thorite and euxenite. Petromineralogical studies have also revealed the presence of bastnaesite. The presence of bastnaesite in Kanigiri granite suggests that the host felsic rocks may also form a potential source for light rare earth mineral, bastnaesite, apart from the already known rare-metal minerals.     

Numerical simulation and optimization of CO2 sequestration in saline aquifers for vertical and horizontal well injection

With heightened concerns on CO₂ emissions from pulverized-coal (PC) power plants, there has been major emphasis in recent years on the development of safe and economical geological carbon sequestration (GCS) technology. Saline aquifers are considered very attractive for GCS because of their large storage capacity in U.S. and other parts of the world for long-term sequestration. However, uncertainties about storage efficiency as well as leakage risks remain major areas of concern that need to be addressed before the saline aquifers can be fully exploited for carbon sequestration. A genetic algorithm-based optimizer has been developed and coupled with the well-known multiphase numerical solver TOUGH2 to optimally examine various injection strategies for increasing the CO₂ storage efficiency as well as for reducing its plume migration. The optimal injection strategies for CO₂ injection employing a vertical injection well and a horizontal injection well are considered. To ensure the accuracy of the results, the combined hybrid numerical solver/optimizer code was validated by conducting simulations of three widely used benchmark problems employed by carbon sequestration researchers worldwide. The validated code is then employed to optimize the proposed water-alternating-gas injection scheme for CO₂ sequestration using both the vertical and the horizontal injection wells. The results suggest the potential benefits of CO₂ migration control and dissolution. The optimization capability of the hybrid code holds a great promise in studying a host of other problems in GCS, namely how to optimally enhance capillary trapping, accelerate the dissolution of CO₂ in water or brine, and immobilize the CO₂ plume.     

Nitrification in Kochi backwaters

Nitrification rates, as oxidation of ¹⁵N-labelled ammonium and loss of nitrite from N-Serve treated samples, were measured in Kochi backwaters during three seasons. Nitrification rates ranged from undetectable to 166 nmol N L⁻¹ h⁻¹ in the water column and up to 17 nmol N (g wet wt)⁻¹ h⁻¹ in sediments. Nitrification rates were higher in intermediate salinities than in either freshwater or seawater end. Within this salinity range, nitrification rates could be related to ammonium concentrations. As shown by the relation between ammonification and nitrification rates, it is also likely that nitrification is more regulated by renewal rates, rather than by in situ concentrations, of substrate. Among other environmental parameters, temperature and pH may have an influence on nitrification. Potential nitrification rates calculated from loss of nitrite from N-Serve treated, nitrite-enriched samples were about 800 nmol N L⁻¹ h⁻¹ in the water column and 40 nmol N (g wet wt)⁻¹ h⁻¹ in sediments. While these rates are in balance with those of biological ammonium production they may be inadequate to mitigate ammonium pollution in this estuary.     

Variability and teleconnections of South and East Asian summer monsoons in present and future projections of CMIP5 climate models

Coupled Model Inter-comparison Project Phase 5 (CMIP5) model outputs of the South and East Asian summer monsoon variability and their tele-connections are investigated using historical simulations (1861-2005) and future projections under the RCP4.5 scenario (2006-2100). Detailed analyses are performed using nine models having better representation of the recent monsoon teleconnections for the interactive Asian monsoon sub-systems. However, these models underestimate rainfall mainly over South Asia and Korea-Japan sector, the regions of heavy rainfall, along with a bias in location of rainfall maxima. Indeed, the simulation biases, underestimations of monsoon variability and teleconnections suggest further improvements for better representation of Asian monsoon in the climate models. Interestingly, the performance of Australian Community Climate and Earth System Simulator version 1.0 (ACCESS1.0) in simulating the annual cycle, spatial pattern of rainfall and multi-decadal variations of summer monsoon rainfall over South and East Asia appears to more realistic. In spite of large spread among the CMIP5 models, historical simulations as well as future projections of summer monsoon rainfall indicate multi-decadal variability. These rainfall variations, displaying certain epochs of more rainfall over South Asia than over East Asia and vice versa, suggest an oscillatory behaviour. Teleconnections between South and East Asian monsoon rainfall also exhibit a multi-decadal variation with alternate epochs of strengthening and weakening relationship. Furthermore, large-scale circulation features such as South Asian monsoon trough and north Pacific subtropical high depict zonal oscillatory behaviour with east-west-east shifts. Periods with eastward or westward extension of the Mascarene High, intensification and expansion of the upper tropospheric South Asian High are also projected by the CMIP5 models.     

Study on clean technology-assisted combustion behavior and NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> emission using thermal imager for alternate fuel blends

The correlation between oxides of nitrogen emission and in-cylinder temperature of diesel engine fueled with various alternative fuels has been investigated in this research paper. Experimentations were performed in engine without any modifications using pure high-speed diesel fuel, used cooking oil biodiesel (UCO20), animal fat residue biodiesel (AFR20) and camphor oil (CMR20) at 20% volume concentration of biodiesel each. From combustion analysis, the heat release rate and peak cylinder pressure of biodiesel blends were about 13.487% lower and 4.819% higher than those of diesel fuel on an average, respectively. Longer combustion duration has been observed for all biodiesel blends at all load conditions. Oxides of nitrogen emission level show 16.405, 10.352 and 7.524% increment for UCO20, AFR20 and CMR20, respectively. Noteworthy NO _x reduction of about 43.8% was recorded for diesel blended with camphor oil when compared to other biodiesel blends. The relationship between in-cylinder temperature and NO _x emission concentration was premeditated through thermal imager. The result depicted that the increase in NO _x concentration depends on augmented in-cylinder temperature for all test fuels.     

Role of intra-seasonal oscillations in modulating Indian summer monsoon rainfall

The day-to-day behavior of Indian summer monsoon rainfall (IMR) is associated with a hierarchy of quasi-periods, namely 3?C7, 10?C20 and the 30?C60?days. These two periods, the 10?C20?days and the 30?C60?days have been related with the active and break cycles of the monsoon rainfall over the Indian sub-continent. The seasonal strength of Indian summer monsoon rainfall may depend on the frequency and duration of spells of break and active periods associated with the fluctuations of the above intra-seasonal oscillations (ISOs). Thus the predictability of the seasonal (June through September) mean Indian monsoon depends on the extent to which the intra-seasonal oscillations could be predicted. The primary objective of this study is to bring out the dynamic circulation features during the pre-monsoon/monsoon season associated with the extreme phases of these oscillations The intense (weak) phase of the 10?C20 (30?C60) days oscillation is associated with anti-cyclonic circulation over the Indian Ocean, easterly flow over the equatorial Pacific Ocean resembling the normal or cold phase (La Nina) of El Nino Southern Oscillation (ENSO) phenomenon, and weakening of the north Pacific Sub-tropical High. On the other hand the weak phase of 10?C20?days mode and the intense phase of 30?C60?days mode shows remarkable opposite flow patterns. The circulation features during pre-monsoon months show that there is a tendency for the flow patterns observed in pre-monsoon months to persist during the monsoon months. Hence some indications of the behavior of these modes during the monsoon season could be foreshadowed from the spring season patterns. The relationship between the intensity of these modes and some of the long-range forecasting parameters used operationally by the India Meteorological Department has also been examined.     

Air-sea interaction over the tropical Indian Ocean during several contrasting monsoon seasons

Monthly mean anomaly fields of various parameters like sea surface temperature, air temperature, wind stress, effective radiation at the surface, heat gain over the ocean and the total heat loss between a good and bad monsoon composite and the evaporation rates over the Arabian Sea and southern hemisphere have been studied over the tropical Indian Ocean. The mean rates of evaporation on a seasonal scale over the Arabian Sea during a good and bad monsoon composites were equal (about 2·48 × 10¹⁰ tons/day). The evaporation rates over the southern hemisphere were greater during all the months. The mean evaporation rates over the southern hemisphere on a seasonal scale for the good and bad monsoon composites were 4·4 × 10¹⁰ and 4·6 × 10¹⁰ tons/day respectively. The maximum evaporation rates over the southern hemisphere were observed in August. The anomalies of wind stress, effective radiation at the surface and the heat gain over the ocean also exhibit large variations in August, as compared to other monsoon months.