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Following the launch of the Global Precipitation Measurement (GPM) Core Observatory in early 2014, motivated from the successful Tropical Rainfall Measurement Mission (TRMM) satellite, an advanced and sophisticated global multi-satellite precipitation product-Integrated Multi-satellitE Retrievals for GPM (IMERG) was released at finer spatio-temporal scales. This precipitation product has been upgraded recently after several refinements and supposed to be superior to other existing global or quasi-global multi-satellite precipitation estimates. In the present study, IMERG precipitation is comprehensively evaluated for the first time against moored buoy observations over the north Indian Ocean at hourly scale for the study period of March 2014 to December 2015. IMERG precipitation performs considerably better over the Bay of Bengal than the Arabian Sea in both detection and estimation. The systematic error in IMERG is appreciably lower by about 14%; however, it generally overestimates in-situ precipitation and also exhibits noticeable false alarms. Furthermore, IMERG essentially shows an improvement over the TRMM Multi-satellite Precipitation Analysis (TMPA) at a daily scale over the north Indian Ocean. IMERG precipitation estimates show overall promising error characteristics, but there is still a need of substantial efforts for improvement in the satellite-based precipitation estimation algorithms especially over data sparse regions such as north Indian Ocean. [ABSTRACT FROM AUTHOR]

Over the past two decades, the Indian Ocean moored surface buoy observation networks have expanded in the spatiotemporal domain and technologically matured with system reliability, availability, cost optimization, and precision measurement of meteorological and oceanographic parameters as the key targets. Based on the return of experiences in the development, operation, and maintenance of the moored buoy observation networks over two decades, this paper for the first time summarizes the reliability metrics achieved by the National Institute of Ocean Technology (NIOT)-operated moored buoy networks, the healthiness monitoring interval implemented to achieve the highest level of on-demand reliability, the methodologies adopted to ensure highest possible system availability, and data returns. The tsunami buoy network with two buoys and the meteorological buoy with cyclone tracking sensors are found to have a mean time between failure of 1.27 years and 0.5 years, respectively. The identified performances provide a baseline for defining the technical improvement targets, identifying alternate technologies, incorporating redundancies, cost optimization, and maintenance planning. The approach serves as a reference for reliability assessment and integrity management of similar moored buoy ocean observation networks and for evolving standards for oceanographic systems. [ABSTRACT FROM AUTHOR]

A data analysis of 171 broadband vertical-component records of 62 shallow crustal distant events in the northern Indian Ocean region was undertaken to investigate the far-source geometric attenuation rate, high-frequency cutoff filter parameter (kappa), and apparent source characteristics. Event magnitude varied from 4.0 to 5.9 in the short-period body-wave magnitude (mb) scale, and hypocentral distance ranged between 2.3° (260 km) and 14.1° (1578 km) for the dataset. The far-source geometric attenuation rate was estimated by fitting data to a predefined attenuation equation at a frequency range of 0.5-8.5 Hz, using the multiple linear regression method. A secondary regression in the frequency domain on constants resulting from the main (first) regression was performed to find kappa and the second hinge point of the trilinear geometric attenuation function. Source characteristics (stress drop, comer frequency, and moment magnitude) of selected events were determined using the Brune (1970, 1971) model. The average far-source geometric attenuation rate was determined to be R-05 (R is hypocentral distance) for the selected frequency range, but at low frequencies (below about 2 Hz) slightly lower rates than the average were observed. Kappa was found to be 0.041 ± 0.009 s. The second hinge point of the geometric attenuation function was estimated to be 120 ± 30 km, and the complete form of the function, after considering compliancy G=1/551.3√120/R, R>120 km with actual records, was collated as Average static stress drops were found to be 9.5 and 16.0 MPa for the mb 4-5 and 5-6 magnitude bands, respectively. Corner frequencies approximately fell within 1.0-7.0 Hz for the dataset. Derived attenuation parameters were also validated using a ground-motion comparison between recorded and stochastically simulated events. [ABSTRACT FROM AUTHOR]

The moored data buoys deployed by the National Institute of Ocean Technology (NIOT) are floating platforms designed to carry a specific suit of sensors to measure wave parameters. Waves are measured by the Motion Reference Unit (MRU), which outputs roll, pitch, compass, and heave. These data are recorded at a rate of 1 Hz for 17 minutes every three hours. For this study, wave measurements were carried out at two locations (deep and shallow water) over the same period. The wave spectra were generated from the hard disk data (roll, pitch, heave, and compass) of the moored buoys. A Matrix Laboratory (MATLAB) program was developed for generating the wave spectrum using the hard disk data. The spectrum exhibits significant features for deep- and shallow-water buoys. In a single peak spectrum the dominant peaks are observed at 0.08 and 0.1 Hz and the multi-peak spectrum energy is distributed over a wide range, from 0.05 to 0.25 Hz. The buoy spectra were compared to the Joint North Sea Wave Project (JONSWAP) spectrum in deep- and shallow-water locations in the Bay of Bengal, and also the deep-water buoy spectrum was compared to the wave model (WAM) output spectrum in the Arabian Sea. The JONSWAP spectrum mostly conforms to the buoy spectrum in regard to marine wind conditions. [ABSTRACT FROM AUTHOR]

The Bay of Bengal, the northeastern limb of the tropical Indian Ocean is a region strongly coupled with summer and winter monsoons and tropical cyclones. The Bay is also a region of strong vertical stratification near the surface due to large inputs of freshwater through rainfall and river run-off. In situ subsurface ocean measurements are quite sparse both in space and time in this region. The National Institute of Ocean Technology (NIOT), Chennai deployed instrumented moored buoys in the Bay since 1997 to provide continuous time-series measurements of surface meteorological and oceanographic parameters at selected locations. In the recent years several studies have shown the important role of variability of heat storage in the near-surface layers on the intraseasonal and interannual evolution of monsoons and cyclones. Hence a strong need was felt to augment some of these buoys with subsurface temperature, salinity and current sensors to continuously record the temporal evolution of their vertical structures. Under a new initiative, NIOT has deployed six moored buoys attached with sensors to collect subsurface oceanographic parameters on real-time basis in the Bay. These are coded as the OMNI (Ocean Moored buoy Network for Northern Indian Ocean) buoy system. The time-series of vertical profiles of temperature and salinity in 500 m water column from the surface and currents in the topmost 100 m water column are monitored at discrete depths in the Bay. The OMNI buoy programme addresses a long-standing need to understand the observed variability of upper ocean thermohaline and current structures on several timescales that has important bearing on the evolution of seasonal monsoons and cyclones. This article presents an account on the evolution, status and usefulness of the OMNI buoy programme. [ABSTRACT FROM AUTHOR]

Recent sediments of the Andaman Backarc Basin, Indian Ocean, between the Andaman Nicobar islands and the Malay Peninsula have been analyzed for biomarker lipids. Three cores were selected: one each from the fault zone in a deep basin (a graben between two fault systems), another from a location adjacent to the fault, and the third from the topographic high in the rift valley. The molecular composition of the lipid classes (n-alkanes, isoprenoids, alkylbenzenes, alkylcyclohexanes, hopanoids, polycyclic aromatic hydrocarbons, steranes, alcohols, sterols and fatty acids) was examined by gas chromatography (GC) and GC/mass spectrometry to understand the nature and source of the hydrocarbons present and the processes of maturation of organic matter. The data show that the hydrocarbons are of hydrothermal origin, derived from thermal alteration of sedimentary organic matter, consisting of a mixture predominantly of marine-derived components with some terrestrial inputs. Normal alcohols and fatty acids also corroborate the distribution of n-alkanes. The distribution profiles and various parameters computed from the concentration of the target compounds suggest that oxidative reactions and microbial degradation in this environment are insignificant. Triterpane and PAH compositions indicate that the thermal maturity of the bitumen in the samples is comparable to or lower than that found at other hydrothermal regions such as the Northern Juan de Fuca Ridge, Guaymas Basin and Escanaba Trough. [Copyright &y& Elsevier]