Search

The Indian Ocean significantly influences the global carbon cycle but it is one of the undersampled regions with reference to surface ocean pCO2. As a part of the Regional Carbon Cycle Assessment and Processes‐2 (RECCAP2) project, several approaches, such as interpolated observational climatology, hindcast model, observation‐based surface CO2 (empirical models), and atmospheric inversion models have been employed for estimating net sea‐to‐air CO2 fluxes between 1985 and 2018. The seasonal, spatial and long‐term variability in sea‐to‐air fluxes of CO2 were compared with observational climatology. The mean value of CO2 in the Indian Ocean (north of 37.5°S) for the period of 1985–2018 using all models is estimated to be −0.19 ± 0.1 PgC yr−1 and it is consistent with the observational climatology (−0.07 ± 0.14 PgC yr−1). The Indian Ocean north of 18°S is found to be the mean annual source (0.04 ± 0.05 PgC yr−1) whereas a net sink (−0.23 ± 0.11 PgC yr−1) in the south of 18°S. All models captured observed spatial patterns but underestimated the net source of CO2 in the Oman/Somalia upwelling, the Equatorial Indian Ocean and the Bay of Bengal whereas CO2 sink is overestimated in the South Indian Ocean. Overall, all models captured the seasonality in pCO2 levels and CO2 fluxes but overestimated the amplitude of their variability. All models suggested the strengthening of the sink over the period between 1985 and 2018 by 0.02 PgC yr−1 decade−1. A significant increase in the collection of surface ocean pCO2 and atmospheric CO2 measurements improves the model simulations in the Indian Ocean. Plain Language Summary: The Indian Ocean is under‐sampled with reference to pCO2 levels and CO2 fluxes. We evaluated the CO2 fluxes simulated by different models based on observational CO2 flux climatology. The CO2 fluxes estimated by all models are close to climatological value; however under and/or overestimation of fluxes are noticed in several regions. Due to weaker monsoon mixing, accurate river discharge data and atmospheric deposition of pollutants in the model, they failed to reproduce actual CO2 fluxes. Inclusion of such processes in the model improves their performance in future. Key Points: Northern Indian Ocean is a source whereas South Indian Ocean (SIO) is a sink for CO2Mean uptake of CO2 using all models comes to −0.18 ± 0.1 PgC yr−1Net CO2 flux is underestimated off Somalia, Bay of Bengal and Equatorial Indian Ocean whereas sink is over estimated in SIO [ABSTRACT FROM AUTHOR]

This study examines the impact of two very severe tropical cyclonic events, Phailin (over the Bay of Bengal) and Ockhi (over the Arabian Sea), on surface ocean pCO2 and the associated changes in the upper ocean structure using a coupled biogeochemical ROMS model. The primary productivity averaged over the mixed layer is increased from 6.9 to 12.0 (7.2–45.6) mgCm−3d−1 in response to Phailin (Ockhi). A decomposition analysis reveals that the mean contribution of temperature‐driven changes in inducing pCO2 variability in response to pre‐ and post‐cyclonic conditions, in case of Phailin (Ockhi), are 5.4 (−8.8) and −7.6 (−58.8) μatm whereas dissolved inorganic carbon (DIC) driven changes are 23.6 (19.5) and 27.8 (78.0) μatm. Although salinity and total alkalinity have a relatively lesser control in inducing pCO2 variability, salinity's response to the post‐Phailin conditions is significant owing to strong salinity stratification in the Bay of Bengal. The enhancement of DIC is more in the near‐surface waters than its removal by net biological processes resulting in the dominance of cyclone‐induced upwelling and associated vertical mixing driven changes over the enhanced biology‐driven changes in controlling pCO2 variability during both cyclones. Despite comparable magnitudes of environmental forcing during both cyclones, the oceanic response to Phailin is comparatively short‐lived and subdued due to stronger stratification in the Bay of Bengal. A relatively large ratio of DIC to total alkalinity in the upper layers of Arabian Sea facilitates a higher pCO2 response to Ockhi. This makes Ockhi a greater source of CO2 to the atmosphere. Plain Language Summary: Tropical cyclones dissipate large amounts of energy into the upper ocean, enhancing vertical mixing under the influence of strong winds. The enrichment of nutrients and carbon due to upwelling of deeper waters enhance pCO2 levels making a favorable environment for biological productivity eventually utilizing the CO2, and decreasing the net pCO2 level. This study examines the impact of two very severe cyclones on surface pCO2 variability in two contrasting basins of the northern Indian Ocean. In both the basins, physical processes like heat, water fluxes, air‐sea exchanges of inorganic carbon and mixing are largely controlling pCO2 variability during tropical cyclones. Biological processes like carbonate production/dissociation and organic matter cycling have a considerable control on pCO2 variability but not comparable with pCO2 variability driven by the physical processes. The strong upper ocean stratification in the Bay of Bengal and the vertical distribution of the inorganic carbon inventory inherent to both basins result in differential oceanic response to tropical cyclones. The Arabian Sea (Ockhi) acts as a greater source of CO2 to the atmosphere in comparison to the Bay of Bengal (Phailin) during tropical cyclones. Key Points: Cyclone‐induced upwelling and associated vertical mixing driven pCO2 variability dominate over the enhanced biology‐driven variabilityRelatively large ratio of DIC to total alkalinity in the upper layers of Arabian Sea facilitates a higher pCO2 response during cyclonesProportion of variance explained by ocean pCO2 on air‐sea CO2 flux is 53% (69%) whereas wind speed explained 57% (62%) for Phailin (Ockhi) [ABSTRACT FROM AUTHOR]

Anthropogenic emissions have produced significant amount of carbon dioxide (CO2) in the atmosphere since the beginning of the industrial revolution. High levels of atmospheric CO2 increases global temperature as CO2 absorbs outgoing longwave radiation and re-emits. Though a well-mixed greenhouse gas, CO2 concentration is not uniform in the atmosphere across different altitudes and latitudes. Here, we uncover a region of high CO2 concentration (i.e. CO2 pool) in the middle troposphere (500–300 hPa) over the Indo-Pacific Warm Pool (IPWP, 40° E–140° W, 25° S–25° N), in which the CO2 concentration is higher than that of other regions in the same latitude band (20° N–20° S), by using CO2 satellite measurements for the period 2002–2017. This CO2 pool extends from the western Pacific to the eastern Indian Ocean. Much of the CO2 pool is over the western Pacific Ocean (74.87%), and the remaining lies over the eastern Indian Ocean (25.13%). The rising branch of Walker circulation acts as a "CO2 Chimney" that constantly transports CO2 released from the natural, human-induced and ocean outgassing processes to the middle and upper troposphere. The CO2 pool evolves throughout the year with an average annual trend of about 2.17 ppm yr−1, as estimated for the period 2003–2016. Our analysis further reveals that La Niña (El Niño) events strengthen (weaken) the CO2 pool in the mid-troposphere. The radiative forcing for the CO2 pool suggests more warming in the region and is a grave concern for global warming and climate change. [ABSTRACT FROM AUTHOR]

The present research work represents the numerical study of the device performance of a lead-free Cs2TiI6−XBrX-based mixed halide perovskite solar cell (PSC), where x = 1 to 5. The open circuit voltage (VOC) and short circuit current (JSC) in a generic TCO/electron transport layer (ETL)/absorbing layer/hole transfer layer (HTL) structure are the key parameters for analyzing the device performance. The entire simulation was conducted by a SCAPS-1D (solar cell capacitance simulator- one dimensional) simulator. An alternative FTO/CdS/Cs2TiI6−XBrX/CuSCN/Ag solar cell architecture has been used and resulted in an optimized absorbing layer thickness at 0.5 µm thickness for the Cs2TiBr6, Cs2TiI1Br5, Cs2TiI2Br4, Cs2TiI3Br3 and Cs2TiI4Br2 absorbing materials and at 1.0 µm and 0.4 µm thickness for the Cs2TiI5Br1 and Cs2TiI6 absorbing materials. The device temperature was optimized at 40 °C for the Cs2TiBr6, Cs2TiI1Br5 and Cs2TiI2Br4 absorbing layers and at 20 °C for the Cs2TiI3Br3, Cs2TiI4Br2, Cs2TiI5Br1 and Cs2TiI6 absorbing layers. The defect density was optimized at 1010 (cm−3) for all the active layers. [ABSTRACT FROM AUTHOR]

This study describes an assessment of an ocean-ecosystem model in simulating marine ecosystem dynamics in the Indian coastal waters. Long-term sustained in-situ observations of temperature, salinity, chlorophyll-a and dissolved oxygen (DO) collected in the coastal waters of India, and ship-based observations are used for this assessment. The model captures observed trend of temperature, salinity and chlorophyll-a with high correlation in both eastern and western shelf waters except for salinity and DO along west and DO along east coast. The model performs very well in simulating the Indian coastal shelf ecosystem dynamics. The seasonal occurrence of prominent phytoplankton bloom in the central-east coast during pre-monsoon, south-west coast during monsoon and north-west coast during post-monsoon is realistically reproduced by the model. The model also reproduces the seasonal presence of significantly low DO content in the upwelled water at a shallow depth leading to coastal hypoxia in the south-west and central-east coast of India during summer monsoon. A fine-tuned model is useful in understanding better Indian coastal shelf ecosystem and predicting future changes in time and space, like the occurrence of coastal hypoxia or anticipating phytoplankton blooms. Such information is useful for predicting potential fishing grounds in coastal waters and fisheries management. [ABSTRACT FROM AUTHOR]

Lead-free perovskite solar cells (PSCs) appear to be a great contender of thin film based photovoltaic (PV) technology as they solve two prime issues, toxicity and stability. Ti-based PSCs can be imperative in a high-performance PV device. The external quantum efficiency (EQE) or classical efficiency is often used to measure the optical performance of the solar cell device. This work has a scope in optimizing ETL/HTL and other interfaces to obtain the most efficient Cs2TiI6–xBrx PSC, and enhancement in Jsc will increase the Shockley-Read-Hall (SRH) recombination. In such circumstances, selection and optimization of electron transport layers (ETLs) and hole transport layers (HTLs) materials are the major factor to be considered effectively to achieve optimum PV performance. Among all ETLs, TiO2 is found to be the most suitable ETL for our proposed FTO/ETLs Cs2TiX6/HTL/Ag based n-i-p structured PSCs. The optimum thickness of ETL should be 150-200 nm and of HTL – 10-20 nm, with the following optimized PV performance: Voc = 1.23 V, Jsc = 19.378 mA/cm², PCE = 14.537 % (Cs2TiCl6); Voc= 1.09 V, Jsc = 23.213 mA/cm², PCE = 17.452 % (Cs2TiI6); Voc= 1.53 V, Jsc = 16.822 mA/cm², PCE = 12.578 % (Cs2TiCl6) and Voc= 8.53 V, Jsc = 10.079 mA/cm², PCE = 7.348 % (Cs2TiCl6). Thus, a detailed study of this class of materials containing halide perovskite is need of the hour. [ABSTRACT FROM AUTHOR]

The present research work represents the study of device modelling and simulation of lead-free cesium titanium (IV) mixed halide (Cs2TiI6–xBrx, where x = 1 to 5) based perovskite active layer. The active layer thickness, operating temperature and defect density are optimized for photovoltaic performance using SCAPS-1D (Solar Cell Capacitance Simulator – 1 Dimension) device simulator. The validity of the selection of appropriate physical and basic parameters for the proposed solar cell with cell architecture FTO/TiO2/Cs2TiI6 – xBrx/CuSCN/Ag was used for the study. The optimum cell performance of the proposed device was studied for different thicknesses of the active layer, device temperature and defect density of active materials. The numerical study using SCAPS-1D revealed optimum device performance for the thickness of perovskite materials Cs2TiI1Br5, Cs2TiI2Br4, Cs2TiI3Br3, Cs2TiI4Br2, Cs2TiI5Br1 at 1.0, 1.0, 0.4, 0.4, and 0.4 µm, respectively. The optimum device performance at temperatures of 10, 10, 20, 20, and 20 °C was numerically simulated for Cs2TiI1Br5, Cs2TiI2Br4, Cs2TiI3Br3, Cs2TiI4Br2, and Cs2TiI5Br1 perovskite materials, respectively. The optimized defect density for all seven perovskite materials was found to be at 1010 cm – 3. The device has time of response of 1.27 µs for Cs2TiI2Br4, Cs2TiI3Br3, Cs2TiI4Br2, and Cs2TiI5Br1 absorbing layers and 1.18 µs for the Cs2TiI1Br5 absorbing layer-based device. [ABSTRACT FROM AUTHOR]