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Seasonal Behaviour of Mesoscale Eddy Trajectories in the North Indian Ocean Based on Satellite Altimetry

International Journal of Geosciences 2022年第2期13卷 93-114页

作者： shailesh mohan pednekar Ocean Science Group National Centre for Polar & Ocean Research Ministry of Earth Sciences Headland Sada Vas-co-da-Gama Goa India

In the north Indian Ocean (NIO), maps of sea level anomaly from satellite altimetry were analysed from January-1995 to December-2000. The study attempted to trace the trajectories of the individual mesoscale anomalies manually and to understand seasonal changes in terms of phase speed. Mesoscale anomalies are detected as concentric circular shapes and diameters of ~90 km to 600 km and the minimum 30 days life cycle. Relatively higher eddy kinetic energy was noticed in the northwestern region of the NIO. Individual mesoscale anomalies, namely positive (warm, anticyclonic eddies) and negative (cold, cyclonic eddies) showing travelling direction westward in the NIO basins. In autumn, the number of negative anomalies detected is more than positive anomalies and vice versa during summer. The westward propagating positive (negative) anomalies in the Arabian Sea start appearing in winter (spring) along (away from) the west coast of India and west of 65°E;individual anomalies move to the west in spring/summer/autumn and collide along Somalia’s & Arabian coast. A group of positive (negative) anomalies trajectories appears as a tail at the southern tip of India are located west of the Laccadive ridge in winter (summer to autumn) associated with LH (LL). The Bay of Bengal (BB) trajectories show southwestward in northern BB, westward in central BB and northwestward in southern BB;individual anomalies are appearing along the west coast of Andaman & Nicobar ridge. The zonal phase speed decreases away from the equator, and the magnitude varies longitudinally in each season in the form of a wave-like pattern propagating westward from autumn to summer;the life cycle of the wave is almost 365 days (a year). The theoretical phase speed of the first mode of the baroclinic Rossby waves is quite similar to that of averaged zonal speed. Therefore mesoscale anomalies (eddies) are embedded into the large waves like phenomenon (Rossby waves), responsible for creating high variability and EKE

关键词： Remote Sensing Satellite Altimetry North Indian Ocean Circulation MSLA Mesoscale Eddy Seasonal Variability Positive and Negative Anomalies

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Trends and Interannual Variability of Satellite-Based Wind and Sea Surface Temperature over the Southern Ocean in the Recent Decade

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International Journal of Geosciences 2015年第2期6卷 145-158页

作者： shailesh mohan pednekar Earth System Sciences Organization (ESSO) Ministry of Earth Sciences (MoES) Government of India National Centre for Antarctic and Ocean Research (NCAOR) Vasco-da-Gama India

Using satellite-based 10-m surface wind (SW), wind stress (WS) and sea surface temperature (SST) anomalies, trends and inter-annual variability during 1993 and 2008 over the Southern Ocean (SO) are addressed. The climatological mean (16 years average) indicates that negative wind stress curl diminished (enhanced) between 40°S and 60°S zonal strap region coincide with weak (strong) SW and warm (cold) SST anomaly during January (July). Annual climatology indicates that strong region of SW divides warmer waters northward with positive wind stress curl (WSCL) and colder waters southward with negative WSCL. The time series anomalies are smoothened with a 12-month running mean filter. The filtered area-mean time series anomalies of zonal and meridional component of SW and SST have linear trends of -0.0005 ± 0.0003 m/s/decade, 0.0012 ± 0.0002 m/s/decade and -0.00005°C ± 0.0001°C/decade, respectively. The SW anomalies show an increasing trend of 0.0013 ± 0.0002 m/s/decade, with the meridional (zonal) component exhibiting an increasing (decreasing) trend. The meridional component plays a critical role in heat transfer through atmospheric circulation. The WS and wind stress divergence exhibit increasing trends whereas wind stress curl shows a decreasing trend. The SST fluctuates close to zero with repeated high and low peaks at an interval of 2 - 3 years. We address the interannual variability by performing EOF analysis on SW, WS, WSCL and SST anomalies which have been passed through a 12-month running mean filter. EOF-1 spatial pattern portrays low variances south of 40°S in SW between 25°E and the Drake Passage whereas in WS it is confined to Pacific Ocean sector of the SO. EOF-2 pattern exhibits high variability along the ACC, which is pronounced in the central Indian sector of the SO in SW and Pacific Ocean sector of the SO in WS. The time coefficient (SW, WS and WSCL) of EOF-1 (EOF-2) is correlated with reversed (actual) Antarctic Oscillation (AAO) index. The EOF-1 of SS

关键词： Southern Ocean Trends Interannual Variability

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Plant Community and Nutrient Status of the Soils of Schirmacher Oasis,East Antarctica

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Chinese Journal of Polar Science 2008年第1期19卷 63-76页

作者： Shiv mohan Singh Jagdev Sharma Rasik Ravindra Purnima Singh National Centre for Antarctic and Ocean research National Research Centre for grapes Purvanchal University Jaunpur India

Investigations on plant community and micronutrient status of Schirmacher Oasis, East Antarctica have been presented in this paper. The dominant plant communities include moss and lichen. The frequency of species occurrence and changes in species composition at different location varied. Thirty-four soil samples were ana- lyzed for chemical properties of the soils of Schirmacher Oasis and Nunatak, East Antarctica. The most common plant species growing throughout the areas of Sehirmacher Oasis and Nunataks are： Candelariella tiara （ lichen ） and Bryum pseudotriquetrum （moss）. Large variations were observed among different soil samples in all the nutri- ents and other measured soil chemical parameters. The soils are characterized by a-cidic pH ranging from 4.42 - 6.80. The mean organic carbon content was 0.62 and ranged from 0. 06 - 1.29%. The electrical conductivity in 1 ： 2 soil water ratio ranged from 0.06 - 1.29. The average content of macronutrient cation, which are ammonium acetate extractable was in the order of Ca 〉 K 〉 Na 〉 Mg. The average content of DTPA extractable micronutrient cations was in the order of Fe 〉 Mn 〉 Cu 〉 Zn. Thirty one out of 34 samples contained less than 0.80 ppm DTPA extractable Zn. Correlation studies revealed that content of macronutrient cations significantly and positively correlated to that of chlorides. Electrical conductivity exhibited significant and positive relationship with pH, K, Ca, Mg, Na and chloride content. Sodium （r =0.876 ＊＊） exhibited highest correlation followed by K （r =0. 831 ＊＊） with chlo- ride content. The correlation coefficient for chlorides was higher with electrical conductivity （r=0.732＊＊） than pH （r =0. 513 ＊＊）. Organic carbon content of the soil was positively correlated with Fe （ r = 0. 442 ＊）. The nutrient status did not appear to be a limiting factor in growth of plants. Lichen and moss community structure and composition in the study area were not related with fertility status of soil. Terres

关键词： Antarctica Schirmacher Oasis Nutrient Lichen Moss.

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