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    <title>DRS Collection: Physical Sciences</title>
    <link>http://drs.nio.org/drs/handle/2264/10</link>
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      <title>Yanai waves in the western equatorial Indian Ocean</title>
      <link>http://drs.nio.org/drs/handle/2264/4289</link>
      <description>Title: Yanai waves in the western equatorial Indian Ocean
&lt;br/&gt;
&lt;br/&gt;Authors: Chatterjee, A.; Shankar,  D.; McCreary, J.P.; Vinayachandran, P.N.
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&lt;br/&gt;Abstract: Observations and models have shown the presence of intraseasonal fluctuations in 20-30-day and 10-20-day bands in the equatorial Indian Ocean west of 60 degrees E (WEIO). Their spatial and temporal structures characterize them as Yanai waves, which we label low-frequency (LFYW) and high-frequency (HFYW) Yanai waves, respectively. We explore the dynamics of these intraseasonal signals, using an ocean general circulation model (Modular Ocean Model) and a linear, continuously stratified model. Yanai waves are forced by the meridional wind tau sup(y) everywhere in the WEIO most strongly during the monsoon seasons. They are forced both directly in the interior ocean and by reflection of the interior response from the western boundary; interference between the interior and boundary responses results in a complex surface pattern that propagates eastward and has nodes. Yanai waves are also forced by instabilities primarily during June/July in a region offshore from the western boundary (52-55 degrees E). At that time, eddies, generated by barotropic instability of the Southern Gyre, are advected southward to the equator. There, they generate a westward-propagating, cross-equatorial flow field, v sub(eq), with a wave number/frequency spectrum that fits the dispersion relation of a number of Yanai waves, and these waves are efficiently excited. Typically, Yanai waves associated with several baroclinic modes are excited by both wind and eddy forcing; and typically, they superpose to create beams that carry energy vertically and eastward along ray paths. The same processes generate LFYWs and HFYWs, and hence, their responses are similar; differences are traceable to the property that HFYWs have longer wavelengths than LFYWs for each baroclinic mode.</description>
      <pubDate>Mon, 29 Oct 2012 22:58:59 GMT</pubDate>
    </item>
    <item>
      <title>Influence of winds on temporally varying short and long period gravity waves in the near shore regions of the eastern Arabian Sea</title>
      <link>http://drs.nio.org/drs/handle/2264/4280</link>
      <description>Title: Influence of winds on temporally varying short and long period gravity waves in the near shore regions of the eastern Arabian Sea
&lt;br/&gt;
&lt;br/&gt;Authors: Glejin, J.; SanilKumar, V.; Nair, T.M.B.; JaiSingh
&lt;br/&gt;
&lt;br/&gt;Abstract: Wave data collected off Ratnagiri, west coast of India, during 1 May 2010 to 30 April 2012 are used in this study. Seasonal and annual variations in wave data controlled by the local wind system such as sea breeze and land breeze, and remote wind generated long period waves are also studied. The role of sea breeze on the sea state during pre- and postmonsoon seasons is studied and it is found that the maximum wave height is observed at 15:00 UTC during the premonsoon season, with an estimated difference in time lag of 1-2 h in maximum wave height between premonsoon and postmonsoon seasons. Observed waves are classified in to (i) short waves (T sub(p) less than 8 s), (ii) intermediate waves (8 less than T sub(p) less than 13 s), and (iii) long waves (T sub(p) more than 13 s) based on peak period (T sub(p)) and the percentages of occurrence of each category are estimated. Long period waves are observed mainly during the pre- and the postmonsoon seasons. During the southwest monsoon period, the waves with period more than 13 s are a minimum. An event during 2011 is identified as swells propagated from the Southern Ocean with an estimated travelling time of 5-6 days. The swells reaching the Arabian Sea from the south Indian Ocean and Southern Ocean, due to storms during the pre- and postmonsoon periods, modify the near surface winds due to higher phase wave celerity than the wind speed. Estimation of inverse wave age using large-scale winds such as NCEP (National Centers for Environmental Prediction) reflects the presence of cyclonic activity during pre- and postmonsoon seasons but not the effect of the local sea breeze/land breeze wind system.</description>
      <pubDate>Mon, 29 Oct 2012 22:58:59 GMT</pubDate>
    </item>
    <item>
      <title>Observational Evidence of Summer Shamal Swells along the West Coast of India</title>
      <link>http://drs.nio.org/drs/handle/2264/4274</link>
      <description>Title: Observational Evidence of Summer Shamal Swells along the West Coast of India
&lt;br/&gt;
&lt;br/&gt;Authors: Glejin, J.; SanilKumar, V.; Nair, T.M.B.; JaiSingh; Mehra, P.
&lt;br/&gt;
&lt;br/&gt;Abstract: Wave data collected off Ratnagiri, West coast of India, in 2010 and 2011 are used to examine the presence of the summer shamal swells. This study also aims to understand variations in wave characteristics and associated modifications in wind sea propagation at Ratnagiri. Wind data collected using an autonomous weather station (AWS), along with Advanced Scatterometer (ASCAT) and NCEP data, are used to identify the presence of summer shamal winds along the west coast of the Indian subcontinent and on the Arabian Peninsula. NCEP and ASCAT data indicate the presence of summer shamal winds over the Arabian Peninsula and northwesterly winds at Ratnagiri. This study identifies the presence of swells from the northwest that originate from the summer shamal winds in the Persian Gulf and that reach Ratnagiri during 30 percent of the summer shamal period. AWS data show the presence of northwest winds during May and southwest winds during the strong southwest monsoon period (June-August). Another important factor identified at Ratnagiri that is associated with the summer shamal events is the direction of wind sea waves. During the onset of the southwest monsoon (May), the sea direction is in the direction of swell propagation (northwest); however, during the southwest monsoon (June-August), a major part of the wind sea direction is from the southwest. The average occurrence of summer shamal swells is approximately 22 percent during the southwest monsoon period. An increase in wave height is observed during June and July at Ratnagiri due to the strong summer shamal event.</description>
      <pubDate>Mon, 29 Oct 2012 22:58:59 GMT</pubDate>
    </item>
    <item>
      <title>Ocean currents structuring the mesozooplankton in the Gulf of Mannar and the Palk Bay, southeast coast of India</title>
      <link>http://drs.nio.org/drs/handle/2264/4273</link>
      <description>Title: Ocean currents structuring the mesozooplankton in the Gulf of Mannar and the Palk Bay, southeast coast of India
&lt;br/&gt;
&lt;br/&gt;Authors: Jagadeesan, L.; Jyothibabu, R.; Anjusha, A.; Mohan, A.P.; Madhu, N.V.; Muraleedharan, K.R.; Sudheesh, K.
&lt;br/&gt;
&lt;br/&gt;Abstract: We hypothesis perceptible physical barriers that exist between the deep Gulf of Mannar and shallow Palk Bay located between India and Sri Lanka, and seasonally reversing surface circulation patterns in the region have a concerted effect on the ecology of these oceanographically important areas. Data collected from 30 locations in the Gulf of Mannar and the Palk Bay in March 2010 (Spring Intermonsoon), September 2010 (Southwest Monsoon) and January 2011 (Northeast Monsoon) were used to investigate the role of ocean currents in molding mesozooplankton community characteristics in these, geographically closer and ecologically important transitional zones. Spatial difference in salinity was evident in the area with consistently higher values in the Gulf of Mannar as compared to the Palk Bay. The surface salinity was maximal during the Southwest Monsoon followed by the Spring Intermonsoon, and the Northeast Monsoon. These variations in salinity were closely linked with the seasonally reversing ocean currents as revealed in MIKE 21 flow model results. The mesozooplankton community dominated by copepods showed significant difference in species richness between the Gulf of Mannar (81 species) and the Palk Bay (63 species). Non-metric Multidimensional Scaling (NMDS) and Agglomerative Hierarchical Cluster Analysis (AHCA) on Bray-Curtis copepod similarity clearly estranged the Gulf of Mannar and the Palk Bay waters during the Spring Intermonsoon, and the Northeast Monsoon, attributable to the truancy of durable mixing typical of these seasons. In contrast, aided by strong currents, the increased mixing resulted in a homogenous copepod population in the Gulf of Mannar and the Palk Bay during the Southwest Monsoon. Furthermore, the indicator and dominant species analysis for copepods divulged the spatial heterogeneity in species composition during the Spring Intermonsoon and the Northeast Monsoon periods. Multivariate Redundancy Analyses showed salinity as the most important variable accountable for the observed variance in copepod distribution. In general, the copepod community in the Gulf of Mannar was composed both of coastal and offshore species whereas, coastal species largely inhabited the Palk Bay. This kind of a study depicting zooplankton community organization as governed by seasonally reversing monsoon circulation patterns forms the first record from the Indian coastal waters. The findings attain absolute significance considering its ecological implications on oceanographically transitional systems like the Gulf of Mannar, and the Palk Bay.</description>
      <pubDate>Mon, 29 Oct 2012 22:58:59 GMT</pubDate>
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