DSpace Collection:
https://hdl.handle.net/10356/79186
2024-03-19T02:32:53ZSeasonal and spatial variations in spice generation in the South Indian Ocean salinity maxima
https://hdl.handle.net/10356/174098
Title: Seasonal and spatial variations in spice generation in the South Indian Ocean salinity maxima
Authors: Kaundal, Madhu; Raju, Nadimpalli Jithendra; Samanta, Dhrubajyoti; Dash, Mihir Kumar
Abstract: Spiciness anomalies generated in the salinity maxima region are important for several atmospheric and oceanic factors as they move along the geostrophic pathways towards the equator and resurface. Subduction and injection mechanisms are responsible for the spiciness generation in the South Indian Ocean (SIO) salinity maxima region. Using ECCO data from 1992 to 2017, here we study monthly variations of spiciness associated with both of these mechanisms in the SIO salinity maxima region. Using a Lagrangian approach, we estimated the monthly evolution of the subduction rate. A maximum subduction rate of 35–38 m/mon occurs during September and consequently decreases towards the end of the year. The effective subduction rate in the salinity maxima region shows the dominance of temporal induction (mixed layer tendency) term, with a sharp gradient in total subduction rate along the 30∘S associated with large mixed layer depth variation. Further, a high Turner angle (> 66∘) to the south of 30∘S confirms the generation of spiciness by injection mechanism. We found that the decrease in mixed layer salt (MLS) coincides with the increase in salinity below the mixed layer. To explore the significance of MLS changes in spiciness generation, we further addressed the monthly evolution of spiciness through MLS budget. Our results suggest that the entrainment and meridional advection terms are key to monthly variations in MLS changes and thus the spiciness.2022-01-01T00:00:00ZReducing systematic biases over the Indian region in CFS V2 by dynamical downscaling
https://hdl.handle.net/10356/174097
Title: Reducing systematic biases over the Indian region in CFS V2 by dynamical downscaling
Authors: Hari Prasad, K. B. R. R.; Ramu, Dandi A.; Rao, Suryachandra A.; Hameed, Saji N.; Samanta, Dhrubajyoti; Srivastava, Ankur
Abstract: The usefulness of dynamical downscaling of seasonal reforecasts of Indian Monsoon is explored to address the seasonal mean biases in the reforecasts. Almost all the current generation global coupled models, including the Climate Forecast System version 2 (CFSv2, T126 ∼110 km), exhibit systematic mean dry bias over the central Indian region during the summer monsoon season. Cold sea surface temperature (SST) biases in the Indian Ocean and a weak monsoon circulation due to a colder tropospheric temperature contribute to this dry bias. Such systematic biases restrict the use of skillful forecasts from these models in climate applications (such as agriculture or hydrology). Dynamical downscaling of seasonal forecasts (∼110 km resolution) using the Weather Research and Forecasting (WRF) model coupled to a simple ocean mixed layer model (OML; WRFOML) at 38 km resolution significantly reduces the majority of the systematic biases reported earlier. The seasonal mean dry bias reduces to 16% in WRFOML as compared to 44% (33%) in the CFSv2-T126 (WRFCTL) over the Indian land region. Warmer SSTs in the Indian Ocean and a more robust monsoon circulation emanating from a realistic simulation of the tropospheric temperature reduced the systematic biases in WRFOML compared to CFSv2-T126 and WRFCTL. Additionally, category-wise rainfall distributions are also improved drastically in the downscaled simulations (WRFOML). Downscaled reforecasts with reduced systematic biases have better suitability for climate applications.2021-01-01T00:00:00ZThe CoralHydro2k database: a global, actively curated compilation of coral δ18O and Sr/Ca proxy records of tropical ocean hydrology and temperature for the Common Era
https://hdl.handle.net/10356/174096
Title: The CoralHydro2k database: a global, actively curated compilation of coral δ18O and Sr/Ca proxy records of tropical ocean hydrology and temperature for the Common Era
Authors: Walter, Rachel M.; Sayani, Hussein R.; Felis, Thomas; Cobb, Kim M.; Abram, Nerilie J.; Arzey, Ariella K.; Atwood, Alyssa R.; Brenner, Logan D.; Dassié, Émilie P.; Delong, Kristine L.; Ellis, Bethany; Emile-Geay, Julien; Fischer, Matthew J.; Goodkin, Nathalie Fairbank; Hargreaves, Jessica A.; Kilbourne, K. Halimeda; Krawczyk, Hedwig; Mckay, Nicholas P.; Moore, Andrea L.; Murty, Sujata A.; Ong, Maria Rosabelle; Ramos, Riovie D.; Reed, Emma V.; Samanta, Dhrubajyoti; Sanchez, Sara C.; Zinke, Jens; PAGES CoralHydro2k Project Members
Abstract: The response of the hydrological cycle to anthropogenic climate change, especially across the tropical oceans, remains poorly understood due to the scarcity of long instrumental temperature and hydrological records. Massive shallow-water corals are ideally suited to reconstructing past oceanic variability as they are widely distributed across the tropics, rapidly deposit calcium carbonate skeletons that continuously record ambient environmental conditions, and can be sampled at monthly to annual resolution. Climate reconstructions based on corals primarily use the stable oxygen isotope composition (δ18O), which acts as a proxy for sea surface temperature (SST), and the oxygen isotope composition of seawater (δ18Osw), a measure of hydrological variability. Increasingly, coral δ18O time series are paired with time series of strontium-to-calcium ratios (Sr/Ca), a proxy for SST, from the same coral to quantify temperature and δ18Osw variability through time. To increase the utility of such reconstructions, we present the CoralHydro2k database, a compilation of published, peer-reviewed coral Sr/Ca and δ18O records from the Common Era (CE). The database contains 54 paired Sr/Ca-δ18O records and 125 unpaired Sr/Ca or δ18O records, with 88% of these records providing data coverage from 1800CE to the present. A quality-controlled set of metadata with standardized vocabulary and units accompanies each record, informing the use of the database. The CoralHydro2k database tracks large-scale temperature and hydrological variability. As such, it is well-suited for investigations of past climate variability, comparisons with climate model simulations including isotope-enabled models, and application in paleodata-assimilation projects. The CoralHydro2k database is available in Linked Paleo Data (LiPD) format with serializations in MATLAB, R, and Python and can be downloaded from the NOAA National Center for Environmental Information's Paleoclimate Data Archive at 10.25921/yp94-v135 (Walter et al., 2022).2023-01-01T00:00:00ZThe role of anthropogenic forcings on historical sea-level change in the Indo-Pacific warm pool region
https://hdl.handle.net/10356/174095
Title: The role of anthropogenic forcings on historical sea-level change in the Indo-Pacific warm pool region
Authors: Samanta, Dhrubajyoti; Vairagi, Vedant; Richter, Kristin; McDonagh, Elaine L.; Karnauskas, Kristopher B.; Goodkin, Nathalie Fairbank; Chew, Lock Yue; Horton, Benjamin Peter
Abstract: Detecting and attributing sea-level rise over different spatiotemporal scales is essential for low-lying and highly populated coastal regions. Using the Detection and Attribution Model Intercomparison Project (DAMIP) from the Coupled Model Intercomparison Project Phase 6, we evaluate the role of anthropogenic forcing in sea-level change in the historical (1950–2014) period in the Indo-Pacific warm pool region. We use three models that have at least 10 ensemble members, corresponding to different DAMIP simulations. We determined the changes in regional sea level from both natural and anthropogenic forcings. Our results demonstrate: (a) the emergence of an anthropogenic footprint on regional sterodynamic sea-level change has a large spatiotemporal diversity over the Indo-Pacific warm pool region with the earliest emergence in the western Indian Ocean; (b) a significant rise in dynamic sea level (DSL) (up to 25 mm) and thermosteric (up to 40 mm) sea level over the western Indian Ocean due to greenhouse gas forcing; (c) a positive Indian Ocean Dipole-like pattern in the DSL changes over the tropical Indian Ocean; (d) a significant increase in the halosteric contribution to sea-level rise in the Indo-Pacific warm pool region, and (e) a pronounced rise of manometric sea level (up to 20 mm) over shallow oceans and coastal regions in recent decades. These results provide a comprehensive spatiotemporal analysis of the attribution of anthropogenic factors to sea-level changes in the Indo-Pacific warm pool region.2024-01-01T00:00:00Z