NOPR Collection:

Long-term analysis of waves off Mangaluru coast

Fri, 01 May 2020 00:00:00 GMT

Title: Long-term analysis of waves off Mangaluru coast Authors: Upadhyaya, S K; Rao, Subba; Manu Abstract: A competent coastal engineer should have adequate knowledge with regard to wave analysis. Long-term analysis is being effectively used worldwide to predict wave heights based on extreme wave statistics. The objective here is to analyze the ocean waves off Mangaluru coast, India. Long-term analysis is initially performed based on probability distributions like Log-normal distribution, Gumbel distribution, Fretchet distribution, Exponential distribution, and Weibull distributions on the in-situ wave data recorded at coastal waters off Mangaluru coast. The Extreme wave analysis is performed based on Peak Over Threshold method from which the best-fit probability distribution is obtained. Further, the best performing distribution is applied on the simulated wave heights obtained from MIKE 21 numerical model forced with ERA-interim wind speed data of 38-years. From the analysis, amongst the five different distributions considered Weibull distribution with α = 1.3 gave the best-fit for the wave dataset considered. Long-term analysis is then performed on 38-years hindcast data for 10, 50 and 100 year return periods for the Mangaluru coast region. Page(s): 717-723

Responses of dissolved oxygen to Deep Depression BOB 04 based on satellite and Bio-Argo observations in the Bay of Bengal

Fri, 01 May 2020 00:00:00 GMT

Title: Responses of dissolved oxygen to Deep Depression BOB 04 based on satellite and Bio-Argo observations in the Bay of Bengal Authors: Xu, H B; Tang, D L Abstract: This work explores the responses of subsurface dissolved oxygen (DO) to “Wind Pump” impacts of Deep Depression (DD) BOB 04 (2014) with a pre-existing cyclonic eddy based on satellite and Bio-Argo observations in the central Bay of Bengal. Results show the combined influence of the pre-existing cyclonic eddy and DD BOB 04 shoaled the oxycline from 48 m to the shallowest depth 32 m two days after the DD BOB 04. With the pre-existing cyclonic eddy, BOB 04 induced DO decrease in the subsurface for a long time of 18 days. The strong saline stratification suppressed the chlorophyll enhancement along the DD track after its passage. However, this weak DD caused the significant subsurface DO decrease owing to the upwelling. This hovered DD with a pre-existing cyclonic eddy played an important role in governing the boundary of oxygen minimum zone. Page(s): 724-731

Spatial variability of north east monsoon rainfall over Peninsular India during strong, weak and normal NEMR years

Fri, 01 May 2020 00:00:00 GMT

Title: Spatial variability of north east monsoon rainfall over Peninsular India during strong, weak and normal NEMR years Authors: Simon, E K; Sajeev, R; Mathew, Basil Abstract: North East Monsoon Rainfall (NEMR) is classified as strong, weak and normal depending on the strength of the NEM rainfall using Peninsular India (PI) monthly rainfall data and its behavior is examined during contrasting NEMR years. The sub divisions Kerala, Tamil Nadu and Coastal Andhra Pradesh contribute maximum rainfall to the cumulative PI NEMR and South Interior Karnataka and Rayalseema contribute the least, whether it is a strong or weak NEM. Analysis shows that the rainfall pattern is substantially different in all six sub divisions between strong and weak NEMR years and the difference is statistically significant as confirmed by the Wilcoxon Mann-Whitney rank sum test. Composite analysis shows that more rainfall is received in all the six sub divisions in comparison to the Long Period Average (LPA) during years of strong NEMR, and vice-versa during years of weak NEMR. Correlation analysis between PI NEMR and the sub divisional NEMR indicates that the sub divisions Tamil Nadu (TLN), Rayalseema (RLS), South Interior Karnataka (SIK) and Coastal Andhra Pradesh (CAP) have strong positive correlation whereas Kerala (KER) and Coastal Karnataka (COK) rainfall shows moderate correlation. Page(s): 732-739

Exploration of N2 fixation and denitrification processes in the Sundarban mangrove ecosystem, India

Fri, 01 May 2020 00:00:00 GMT

Title: Exploration of N2 fixation and denitrification processes in the Sundarban mangrove ecosystem, India Authors: Das, S; Ganguly, D; Mukherjee, A; Chakraborty, S; De, T K Abstract: Seasonal variations in nitrogen (N₂) fixation and denitrification rates were estimated in the sediment of Sundarban mangrove ecosystem, India. The mean rate of microbial N₂ fixation (16.53 ηmol N fixed/ hr/ g dry wt of sediment) was relatively higher than the mean rate of denitrification (14.72 ηmol N₂O-N /hr/dry wt of sediment) in the mangrove sediment throughout the study, suggesting satisfactory fertility of this ecoregion in terms of sediment nitrogen. Sediment from the deeper parts of this ecosystem showed higher N₂ fixation rate (18.23 ηmol N fixed/ hr/ g dry wt of sediment) than the surface sediment (10.17 ηmol N fixed/ hr/ g dry wt of sediment). Similar trend was observed for the denitrification rate in all the seasons. The ratio of N₂fixation to denitrification rate showed an increasing trend with depth. The results depicted that under higher anoxic condition bacteria would prefer N₂ fixation over denitrification and would ultimately enhance the nitrogen storage capacity of this mangrove ecosystem. Although population of free living N₂ fixing bacteria decreased with increase in depth, the rate of N₂ fixation showed a reverse trend, during the study period. These results suggested that anoxic condition and low level of nitrate-nitrogen content could stimulate the enzyme activity responsible for N₂ fixation in this particular ecosystem. Page(s): 740-747