Evidence That Sea State Bias is Different for Ascending and Descending Tracks

Jason-1 and TOPEX/Poseidon (T/P) measured sea-surface heights (SSHs) are compared for five regions during the verification tandem phase. The five regions are of similar latitude and spatial extent and include the Gulf of Mexico, Arabian Sea, Bay of Bengal, and locations in the Pacific and Atlantic Oceans away from land. In all five regions, a bias, defined as Jason SSH—TOPEX-B SSH, exists that is different for ascending and descending tracks. For example, in the Gulf of Mexico the bias for ascending tracks was ?0.13 cm and the bias for descending tracks was 2.19 cm. In the Arabian Sea the bias for ascending tracks was ?2.45 cm and the bias for descending tracks was ?1.31 cm. The bias was found to depend on track orientation and significant wave height (SWH), indicating an error in the sea state bias (SSB) model for one or both altimeters. The bias in all five regions can be significantly reduced by calculating separate corrections for ascending and descending tracks in each region as a function of SWH. The correction is calculated by fitting a second-order polynomial to the bias as a function of SWH separately for ascending and descending tracks. An additional constraint is required to properly apply the correction, and we chose to minimize the sum of the TOPEX-B and Jason-1 root-mean-square (rms) crossover differences to be consistent with present SSB models. Application of this constraint shows that the correction, though consistent within each region, is different for each region and that each satellite contributes to the bias. One potential source that may account for a portion of the difference in bias is the leakage in the wave forms in TOPEX-B due to differing altitude rates for ascending and descending tracks. Global SSB models could be improved by separating the tracks into ascenders and descenders and calculating a separate SSB model for each track.     

Analysis of the Tsunami of December 26, 2004, on the Kerala Coast of India—Part I: Amplitudes

The Indian Ocean tsunami of December 26, 2004, not only affected the Bay of Bengal coast of India but also part of the Arabian Sea coast of India. In particular, the tsunami caused loss of life and heavy damage on some parts of the Kerala coast in southwest India. The tsunami traveled west, south of Sri Lanka, and some of the tsunami energy was diffracted around Sri Lanka and the southern tip of India and moved northward into the Arabian Sea. However, tsunami, being a long gravity wave with a wave length of a few hundred kilometers, has to take a wide turn. In that process, it missed the very southern part of the Kerala coast and did not achieve large amplitudes there. However, further north, the tsunami achieved amplitudes of upto 5 m and caused loss of life and significant damage. Here we identify the physical oceanographic processes that were responsible for selective amplification of the tsunami in certain locations.     

Identifying Rocky Seabed Using GIS-Modeled Predictor Variables

Mapping the seabed along the Norwegian coast is costly and time consuming. Hence, finding a modeling method to separate rocky seabed from other substrate types will provide digital maps that may be used to develop cost-effective sampling designs to predict species and habitat distribution. Our approach was to use geophysical data that were quantitative and objectively defined, generalized additive models (GAMs), and Akaike information criterion (AIC) to develop statistical models and select among them. We found that slope, terrain curvature, wave exposure, and depth predicted rocky seabed occurrence with a high degree of certainty.     

Vulnerability Assessment at Village Level Due to Tides,Surges and Wave Setup

An assessment of cyclone risk and vulnerability at the village level has evolved, which is an important component of the information system for local level development action plans for preparedness and mitigation. Here, a case study for the Nellore district along the east coast of India is considered. Using maximum probable surges along the coast, total water level (TWL) due to the combined effect of surge, tide, and wind wave is computed for the most vulnerable coastal villages of the Nellore district due to any tropical cyclones. The computations suggest that the TWL along the Nellore coast varies from 2 m in the south to 4 m in the north.     

Contribution of Tides to Sea Level Variations Along Visakhapatnam,India

The sea level variations along Visakhapatnam coast are governed by astronomical tides and nontidal oscillations including atmospheric pressure, winds, coastal currents, Ekman Pumping, and river influx. Tidal and nontidal sea level oscillations are usually studied separately because of the vastly different ways in which they are forced. In this study the tidal oscillations along Visakhapatnam are analyzed using GOTIC2 tidal model. The correlation between monthly mean sea level and monthly mean tides is 47% (r = 0.68) and increases to 54% (r = 0.74) when applied for inverse-barometric effect. The major six partial tides are computed and presented. The tidal variations from Neap tide to Spring tide are studied.     

A Dynamical Statistical Model for Prediction of a Tropical Cyclone

A dynamical statistical method is applied for operational forecasting of the Bay of Bengal tropical cyclone “Nargis” of April–May 2008. The method consists of three forecast components, namely (a) analysis of Genesis Potential Parameter (GPP) and maximum potential intensity, (b) track prediction, and (c) 12 hourly intensity prediction for forecasts up to 72 hours. The results of the study showed that GPP could provide necessary predictive signal at early stages of development on the further intensification of the low pressure system into a tropical cyclone. The landfall forecast position errors by different operational numerical models (NWP) showed landfall position errors ranging from 10 km to 150 km and landfall time error ranges from 6 hours early to 6 hours delay. The dynamical statistical model is capable to provide 12 hourly nearly realistic intensity forecasts up to 60 hours of forecast.     

Geotechnical Aspects of Clayey Sediments Off Badagara on the Kerala Coast,India

Offshore geotechnical surveys form part of an integrated investigation to rejuvenate a decrepit minor port at Badagara, Kerala on the southwestern coast of India. The sediments typify a fluvio-marine milieu ranging from silty clay, sand, silty sand, sandy silt and clayey silt. Geotechnical and sedimentological studies of shallow cores reveal the geotechnical aspects besides the depositional history of the sediments. Downcore geotechnical variations and regressive coefficients based on their inter-relationships highlight diverse factorial inferences. X-Ray Diffraction data indicate the prominent clay type.

A comparative evaluation of the geotechnical characteristics of clayey sediments off Badagara, with similar studies along various sectors of the Kerala coast, both on land as well as in the near shore, is broadly attempted. Geotechnical studies carried out earlier on the uplifted Cochin marine clays provide comparative data for evaluating the possible variations between present day marine clayey sediments occurring along the Kerala coast and uplifted marine clays which, besides their gross variations in levels with respect to the present sea-level, also obviously relate to a much older depositional environment and provenance during probable Holocene times.     

Interannual Variation of Eddy Kinetic Energy from TOPEX Altimeter Observations

Monthly mesoscale eddy kinetic energy (EKE) per unit mass has been computed for four years, 1993-1996, from TOPEX altimeter data in the Indian Ocean. It ranges from 50 cm²/s² to 2,700 cm²/s² (about 4,000 cm²/s² near the Somali region in a few months). In the Arabian Sea and the Bay of Bengal, regions of high energies associated with various current systems under the influence of monsoonal winds have been delineated. Monthly variation of EKE near the Somali region has been studied. In this region the maximum EKE per unit mass has been observed during August every year, with variations in magnitude from year to year. The mesoscale eddy kinetic energy computed from TOPEX altimeter-derived SSH during 1993-1996 is highest near the Somali region during the SW monsoon, due to formation of mesoscale eddies and also because of upwelling. In the Bay of Bengal, high eddy kinetic energy is seen toward the western side during nonmonsoonal months due to the western boundary current. In the South Indian Ocean, it is high at a few places in some of the months. A large part of the Indian Ocean exhibits low eddy kinetic energy (less than 300 cm²/s²) year-round.     

Waters of the western springs catchment,Auckland

Abstract

Aquifers occur in basalt deposits infilling valleys in the Western Springs catchment of Auckland City, and they discharge into small streams incised along the edges of major lava flows. Total run‐off from the area is >0.261 m³·s^?1. Analyses by standard methods of twelve subsurface and surface waters show that flowing groundwaters have a low level of pollution (dissolved oxygen x = 7.6 mg·l^?1, abuminoid nitrogen x = 0.038 mg·l^?1, and total solids x = 188 mg·l^?1). Surface waters and stagnant groundwater have high, but varying levels of biological activity. Although much of the dissolved solid content of all the waters (e.g., Ca²⁺, Mg²⁺, Na⁺, K⁺, SiO₂) is consistent with the chemistry of the rocks of the catchment, particularly the glassy volcanic tuffs, for surface waters various sources of pollution also make significant contributions (e.g., leaking sewers, sewage overflows, combustion of fossil fuels, fertilisers, zoo animals). Apart from its iron level, the moderate volume (～.0.13 m³·s^?1) of flowing groundwater is of suitable quality for domestic, industrial and irrigation needs.