National Centre for Earth Science Studies

The Southwestern Shelf Sea (SWSS) of India has a distinct wave pattern, which makes it different as compared to the adjoining regions. Wave directional spectra during the monsoon season are comparatively broader and double peaked in contrast to that of the western shelf sea. The well-defined directional bi-modality is observed during the south west monsoon which is attributed to the coexistence of the south Indian Ocean swells and the southwest monsoon swells. The shamal swells generated by the shamal wind blowing from the Arabian Peninsula are found to have a significant influence on the wave pattern of the SWSS. In addition, the local sea breeze/land breeze also contributes significantly to the observed changes, particularly to the diurnal variation. A distinct phase lag in occurrence of the maximum significant wave height for the wind sea component is also observed in the northern region of the SWSS during the fair seasons.

Bibliographic Info: Anoop, T. R., Sheela Nair, L., Prasad, R., Reji Srinivas, Ramachandran, K. K., Prakash, T. N., Balakrishnan Nair, T.M. [2020]. Locally and remotely generated wind waves in the southwestern shelf sea of India. Journal of Coastal Research, Special Issue 89, pp. 77-83. https://doi.org/10.2112/SI89-014.1

Submarine groundwater discharge (SGD) is an important process driven by marine and terrestrial forces. Low tide affects SGD the most, therefore the ideal time to detect SGD is the low tide, especially during spring tide. Techniques to detect and quantify SGD along with the understanding of the related aquifer characteristics is discussed in this study. Scientific community across the world is realizing the importance of studying and mapping SGD because in the scenario of climate change, this part of the global hydrological cycle is an important process and is known to have a significant effect on the marine ecosystem due to nutrient and metal inputs around the region of discharge. Therefore, understanding the processes governing SGD becomes very important. In this review, various components and processes related to SGD (e.g., Submarine Groundwater Recharge, Deep Porewater Upwelling, Recirculated Saline Groundwater Discharge), along with detailed discussion on impacts of SGD for marine ecosystem is presented. Also, it highlights the future research direction and emphasis is put on more research to be done keeping in mind the changing climate and its impacts on SGD.

Bibliographic Info: Suresh Babu, D. S., Ashwini Khandekar, Chandrashekhar Bhagat, Ashwin Singh, Vikrant Jain, Mithila Verma, Brijesh K. Bansal, Manish Kumar [2020]. Evaluation, effect and utilization of submarine groundwater discharge for coastal population and ecosystem: A special emphasis on Indian coastline. Journal of Environmental Management, Vol. 277, Art. 111362. https://doi.org/10.1016/j.jenvman.2020.111362

In the present study, seven-year-long observations of rain microphysical properties are presented using a ground-based disdrometer located at Braemore; a site on the windward slope of the Western Ghats (WG) over the Indian Peninsula. The annual cycle of rainfall shows a bimodal distribution with a primary peak during summer monsoon and secondary peak during pre-monsoon. Pre-monsoon rain events are less in number but are with high intensity and characterize large raindrops and low number concentration. During summer monsoon, short and less intense rain events with small drops are noticed. Post-monsoon rain is having a long duration less intense events with lower concentration of large raindrops compared to the summer monsoon. In the seasonal variation of mean diameter (D_m) and raindrop concentration (N_T ) with Rain Intensity (RI), winter and pre-monsoon rains exhibit higher values of D_m and lower values of N_T compared to the summer and post-monsoon seasons for all the RI ranges. The mean features of the rain microphysical parameters are also supported by the case studies of rain events. RI, D_mand N T are categorized into different range bins for all the seasons to identify their variation and relative rainfall contribution to the total seasonal rainfall. Heavy drizzle/Light rain has maximum rain duration, and the relative contribution to the rainfall is high from heavy rain type. Winter and pre-monsoon rains are mostly contributed from the larger raindrops (>D_m 3), and during summer and post-monsoons it is from D_m 2 onwards. The distribution of occurrence frequency of N_T and rainfall are similar during all four seasons. N_T 2 recorded rainfall percentage nearly the same as N_T 1 in summer monsoon and this also supports large number of raindrops in this season. In RI-Duration analysis, all seasons showed similar distribution, and 90% of total duration is contributed from RI with less than 20 mm h^-1.

 Bibliographic Info: Sreekanth, T. S., Hamza Varikoden, Mohan Kumar, G., Resmi, E. A. [2019]. Microphysical features of rain and rain events during different seasons over a tropical mountain location using an Optical Disdrometer. Scientific Reports, Vol. 9 (1), Art. 19083. https://doi.org/10.1038/s41598-019-55583-z

A methodology was invented to detect the unknown API gravity of oils/oils in HCFIs/oil condensates using fluid inclusion techniques coupled with microscope-based fluorescence emission spectroscopy. The API gravity (American Petroleum Institute’s gravity) is a commercial value indicator of petroleum (HCFIs). A diode laser emitting at 405 nm was used for the study. We have derived an arithmetic equation y = y0 (x0−x)t ± 1 for determining the unknown API gravity based on fluorescence emission ratio at F620/F560. With the use of a laser as an excitation source it is possible to specifically target the fluorophores that have absorption at this wavelength within the HCFIs. The precise determination of API gravity of oils in HCFIs at the time of drilling itself leads to the estimation of the quality of oils in a basin that gives an impetus for further exploration activities in petroleum industry. In general, 40% of the exploratory wells may end up as a dry well and the patented invention can help to determine the quality of minute quantities of oil detected by means of fluid inclusion studies and determination of API gravity values using a non-destructive micro-spectrometric technique could lead to further exploration in adjoining areas areas of such dry & abandoned wells...
Patentee Info: Dr. V. Nandakumar, Dr. J. L. Jayanthi

National Centre for Earth Science Studies

Patent No. 315456 dated 03/07/2019

The challenge with Raman spectral studies on natural hydrocarbon-bearing fluid inclusions (HCFIs) is the common presence of fluorescence emission from minerals and aromatic compounds in HCFIs leading to the masking of Raman signals. Selection of optimum excitation wavelength is another challenge. To overcome these hurdles, special wafer preparation techniques, along with the use of fluorescence quenchers, were employed in our study to obtain Raman signals from natural HCFIs. The present study is a demonstration of how best the Raman signals from natural hydrocarbon-bearing fluid inclusions could be detected using an excitation wavelength of 785 nm with suitable optical parameters and with special wafer preparation techniques to negate the background fluorescence. Using the laser Raman technique we were able to detect peaks corresponding to cyclohexane, benzene and bromobenzene, carbon monoxide, nitrogen, ethylene, sulphur oxide, carbonyl sulphide, hydrogen sulphide in liquid form along with the presence of a broad peak of liquid water, peaks of calcium carbonate and calcium sulphate. The chemical constituents in natural HCFIs from the same basin identified using laser Raman spectrometric methods with a 785 nm laser excitation agrees well with the GC-MS results of oil in the same basin, which again supports the utility of the laser Raman technique with 785 nm laser for the chemical constituents identification in natural HCFIs. The present study elucidates the potential of Raman spectroscopic methods using a 785 nm laser excitation for detecting the chemical constituents of HCFIs..
Bibliographic Info: JL Jayanthi, V. Nandakumar and S. S. Anoop [2017]. Feasibility of a 785 nm diode laser in Raman spectroscopy for characterizing hydrocarbon-bearing fluid inclusions in Mumbai Offshore Basin, India. Petroleum Geoscience, 23 (3), 2017, 369-375. doi: https://doi.org/10.1144/petgeo2016-071