PG Thesis
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Item Influence of Indian ocean on structure and variability of monsoon low level jet in the present and future climate perspectives(College of climate change and environmental science, Vellanikkara, 2023-11-30) Neha Johnson.; Ruchith , R DThe Monsoon Low-Level Jet (MLLJ) is a crucial synoptic feature of the Indian summer monsoon, responsible for a significant portion of moisture transport to the Indian subcontinent. The present study focuses on analyzing the variability and vertical structure of the Monsoon Low-Level Jet (MLLJ) during the Southwest Monsoon season from 1979 to 2022. To conduct in-depth analysis, the total MLLJ path was divided into five regions: the Southern Indian Ocean, Equatorial Indian Ocean, Arabian Sea, Indian subcontinent, and the Bay of Bengal. The mean jet core height for these selected regions was found to be 588.84 ± 37.81, 874 ± 16.9, 849.62 ± 24.11, 830 ±39.85, 832 ± 41.25 and mean jet speed were found to be 2.96 ± 2.78, 10.49 ± 1.07, 15.79 ± 3.1, 11.43 ± 3.4 and 9.857 ± 3.09 respectively. Monthly variation in the jet properties were also analysed. To consider the impact of global warming on MLLJ characteristics, the analysis was conducted by dividing the study period into two epochs: pre-20 (1979 – 2000) and post-20 (2001 – 2022). The properties of the jet exhibit remarkable differences between these two epochs. Trend analysis also indicates a significant change between these epochs. Jet properties show robust interconnections with sub-seasonal ocean processes, including Somali, Oman, and South Eastern Arabian Sea upwellings in the Indian Ocean. The Arabian Sea Mini Warm Pool exhibits a significant correlation with jet properties, especially Arabian Sea core height.Extensive research was conducted to deeply investigate the pivotal influence of MLLJ characteristics on cloud and precipitation processes. The association of Convective Available Potential Energy (CAPE) and convective precipitation with core height exhibited similarities in the Arabian Sea (AS) and Indian subcontinent (IS) regions, while the Bay of Bengal (BB) region displayed notable differences. The Jet speed exhibits same pattern. In the study, MLLJ characteristics were examined in relation to ocean-atmospheric processes, including the IOD, ENSO, and SIOD indices, with a focus on notable variations in the SIOD index. The MLLJ characteristics also correlate with Indian summer rainfall, showing significant relationships. To assess future prospects, historical (1850-2014) and projection (2015-2096) data from IITM ESM were analyzed in conjunction with jet properties.Item Assessment of blue carbon pool in the sediments of selected mangrove stands of vembanad lake, kerala(College of Cimate Change and Environmental Science, Vellanikkara, 2023-11-20) Lakshmi Asokan.; Shelton PaduaThis study investigates the pivotal role of mangroves in climate change mitigation by assessing their capacity to sequester substantial carbon stocks, thereby reducing greenhouse gas concentrations and contributing to sustainable environmental solutions. The study quantified the total organic carbon, mineral associated organic carbon, particulate organic carbon and 6 other sediment characteristics at 1 meter depth sediment core in the selected eleven locations of Vembanad Lake, Kerala during Pre Monsoon and Monsoon seasons. The findings of this study indicate that during the pre monsoon period, the average carbon storage in the sediments of A. officinalis in the selected locations was measured to be 177.56 Mg C ha-1and during monsoon season, it was 171.1 Mg C ha-1 . Both of these values exhibit a lower magnitude when compared to the average global soil organic carbon storage (386 Mg C ha-1) found in the mangrove ecosystem. This result suggests that there is significant potential for increased carbon sequestration in the selected mangrove habitats in Vembanad Lake through implementation of appropriate management strategies. The sediment characteristics showed variations between two seasons and along the soil depths. A comprehensive understanding of the distribution of organic carbon in sediment, with a specific focus on distinguishing between particulate organic carbon (POC) and mineral associated organic carbon (MAOC), is necessary in order to facilitate efficient mitigation of climate change. MAOC has garnered significant attention in the field of carbon storage due to its notable persistence. The findings of the present investigation indicate that the mean value observed for MAOC (251.52 Mg C ha-1 , 279.27 Mg C ha 1 ) is greater than POC (147.33 Mg C ha-1 , 76.14 Mg C ha-1) in pre-monsoon and monsoon respectively. This suggests that the mineral-bound organic carbon reservoir makes up a substantial fraction of the total organic carbon concentration in the soil. The results of the GAM analysis indicate that POC exhibits greater vulnerability to sediment parameters compared to MAOC. This study highlights the importance of MAOC fraction, which serves as a more enduring and secure carbon reservoir in soils. 83 Keywords: Mangrove sediment, Blue carbon, Climate Mitigation, Mineral associated organic carbon, Particulate Organic Carbon, Total Organic Carbon, Avicennia officinalis.Item Investigation of pre-monsoon to monsoon transition of atmospheric conditions as observed with a 205 MHZ wind profiling Radar over Cochin(College of Climate Change and Environmental Sciences, Vellanikkara, 2021) Sruthi, K P.; Manoj, M GItem Aerosol radiative forcing during the pre monsoon to monsoon transition over the Indian monsoon region(College of Climate Change and Environmental Sciences,Vellanikkara, 2021) Anagha, PS; Manoj, MGItem Trends in India summer monsoon distribution over the western ghats(Academy of Climate Change Education and Research Vellanikkara, 2016) Abhijit Asokan; Kurien, E KThe Western Ghats with its strategic position plays a great role in channelling the summer monsoon rain into the mainland. The natural ecosystems and human livelihoods of this region are highly dependent on the Indian Summer Monsoon rainfall and even the slightest change can trigger a change in these systems. The global climate changing scenario is having its toll in the monsoonal system over this region. The extreme events in the region have been analysed for trends using Mann Kendall method and the return periods of the one day maximum rainfall has been modelled using Generalized Extreme Value (GEV) theory. The mean annual monsoonal rainfall over the region is 1616.15 mm and the standard deviation is 242.966.It was observed that the mean annual monsoonal rainfall varied from 231.4mm in grid 117 to 3416 mm in grid 253. The one day maximum rainfall extracted from the 32 constituent grids for the entire period showed a variation from 118.63 mm in 1981 to 316.63 mm in 2005. The temporal variation in one day maximum rainfall for the time series had a significant trend. The values were seen to increase steadily and a profound increase was observed in the recent decades. When the One day maximum rainfall was analysed for different latitudes, two latitudes (14°N and 21°N) had significant positive trends in One Day Maximum Rainfall in the whole region. Out of the 32 grids, 7 grids (186, 359, 394, 428, 429, 497 and 498) showed a significant rising trend in one day maximum rainfall. It was also observed that during the recent years, the occurrence of One day maximum Rainfall has shifted to the far end of the season. The number of grids getting heavy, very heavy and extreme rainfall events was found to have increased during the later years of the study. No significant trend in the instances of occurrence of heavy rainfall over the years was observed. But a significant trend was observed in the occurrences of rainfall events of very heavy and extreme magnitudes. When Split period analysis of the contribution of moderate and high intensity rainfalls was carried out, it was observed that the share of high intensity rainfalls had increased and a decrease was observed in the share of moderate events over the years. The return period analysis of the one day maximum rainfall events was done and it was observed that the 2 year, 5 year, 10 year, 25 year, 50 year and 100 year return levels of rainfall as 186.2mm, 224.3 mm, 250.2 mm, 283.8 mm, 309.3 mm and 335.1 mm for the complete region. The return levels for the two year return period were seen to be over 100 mm for the grids of 184 (118mm), 219 (114.9mm), 253 (145.8mm), 285 (104.5mm), 357 (147.6 mm), 392 (144.2mm), 427 (129.9mm) and 462 (122.4mm). A significant rising trend in the extreme events of summer monsoon rainfall over the Western Ghats was observed. This calls for better planning in all areas of livelihoods and management strategies to contain the disasters of a changing climate.