406 research outputs found
Sonic Layer Depth estimated from XBT temperatures and climatological salinities
Get PDFSonic layer depth (SLD) plays an important role in antisubmarine warfare in terms of identifying the shadow zones for submarine safe parking. SLD is estimated from sound velocity profiles (SVP) which is in turn obtained from temperature and salinity (T/S) profiles. Given the limited availability of salinity data in comparison to temperature, SVPs need to be obtained from alternate methods. In the present work, to make use of voluminous temperature data sets from XBT, CTD and other source for estimating SLD, we propose a method of utilizing XBT measurements and World Ocean Atlas climatological salinities to compute SVP and then extract SLD. This approach is demonstrated by utilizing T/S data from Argo floats in the Arabian Sea (40° – 80° E and 0 – 30° N). SLD is estimated from SVP obtained from Argo T/S profiles first and again by replacing the Argo salinity with climatological salinity. It is found that in more than 90% of cases, SLD matched exactly, with the root mean square deviation ranging from 3 – 12 m with an average of 7 m
Altimetry for the future: Building on 25 years of progress
Get PDFIn 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Seasonal and inter-annual variability of sea surface temperature in the North Indian ocean and associated climate change signatures
Full text linkRole of Coastal Upwelling in the Generation of Potential Fishing Zones in the South-western Bay of Bengal
No full text<p>Coastal Upwelling, the upward flux of nutrient-rich waters into the euphotic layer, is associated with remarkable phytoplankton blooms, which form the base of the marine food web. In addition this entrainment of cold deeper waters to the surface, leads to sea surface temperature (SST) cooling that can also be determined from satellite observations of coastal SST gradients (often resulting in thermal fronts). Thermal fronts, (especially in high chlorophyll regions of the ocean,) are typically associated with significant biological activity.Thus, the detection of potential fishing zones (PFZs) typically involves the identification of fronts from satellite or model SST and Chl-a data. The western Bay of Bengal region presents some unique challenges with regard to the characterization and detection of PFZs based on these satellite data alone. Namely, the presence of clouds during southwest monsoon, (the season associated with the largest fish catches) limits the availability of infrared and visible data necessary for the estimation of high resolution SST and Chl-a. This difficulty is usually circumvented by using modelled SST and Chl-a data, which unfortunately illustrate significant disagreements with the corresponding observational datasets, especially for fronts with low persistence. Coastal upwelling along the east coast of India is seasonal and driven by southwesterly winds in the pre-monsoon (March – May) and earlier half of monsoon (June – July.)  We have previously characterized the seasonal variability of this system based on the near-shore SST gradient (represented in terms of an SST based upwelling index UI<sub>SST</sub>.) In addition to this the second complex empirical orthogonal function of SSHA was also observed to consist of negative coastal anomalies that are strongly correlated with the local alongshore windstress (AWS) (which is considered the wind based proxy upwelling index), the driver of coastal upwelling (Ray et al, 2022.) This study includes a multiscale analysis of the association between the generation of SST fronts or PFZs and the proxies of coastal upwelling (such as UISST, AWS, SSHA reconstructed from the second EOF mode.) e.g. figure 1 illustrates the occurrence of high frontal probability indices (FPIs) along a part of the coast previously identified to be a local wind-driven coastal upwelling system (Ray et al, 2022,) while figure 2 illustrates a close agreement (correlation coefficient = 85%) between the seasonally filtered SST-based upwelling index and the FPI around one coastal point. An improved understanding of the role of coastal upwelling in the generation of PFZs is potentially of great societal importance as it can enable the development of methods of detecting/forecasting the probability of formation of PFZs based on surface wind and SSHA observations which are not affected by the presence of clouds.</p>
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<p><strong>Figure 1</strong></p>
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<p><strong>Figure 2</strong></p>
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<p><strong>Reference:</strong></p>
&lt;p&gt;Ray, S., Swain, D., Ali, M. M., &amp; Bourassa, M. A. (2022). Coastal Upwelling in the Western Bay of Bengal: Role of Local and Remote Windstress.&amp;#160;&lt;em&gt;Remote Sensing&lt;/em&gt;,&amp;#160;&lt;em&gt;14&lt;/em&gt;(19), 4703.&lt;/p&gt;</jats:p
Did COVID-19 Lockdown Brew &ldquo;Amphan&rdquo; into a Super Cyclone?
No full textThe world witnessed one of the largest lockdowns in the history of mankind ever, spread over months in an attempt to contain the contact spreading of the novel coronavirus induced COVID-19. As billions around the world stood witness to the staggered lockdown measures, a storm brewed up in the urns of the rather hot Bay of Bengal (BoB) in the Indian Ocean realm. When Thailand proposed the name &ldquo;Amphan&rdquo; (pronounced as &ldquo;Um-pun&rdquo; meaning &lsquo;the sky&rsquo;), way back in 2004, little did they realize that it was the christening of the 1st super cyclone (Category-5 hurricane) of the century in this region and the strongest on the globe this year. At the peak, Amphan clocked wind speeds of 168 mph (Joint Typhoon Warning Center) with the pressure drop to 925 h.Pa. What started as a depression in the southeast BoB at 00 UTC on 16th May 2020 developed into a Super Cyclone in less than 48 hours and finally made landfall in the evening hours of 20th May 2020 through the Sundarbans between West Bengal and Bangladesh. Did the impact of the COVID-19 induced lockdown drive an otherwise typical pre-monsoon tropical depression into a super cyclone?</jats:p
Relation between Sonic Layer and Mixed layer depth in the Arabian Sea
Get PDF1264-1271Seasonal evolution of the sonic layer depth and its relation to mixed layer depth in the Arabian Sea is studied. Monthly sonic layer depth climatology is constructed using Argo temperature and salinity and compared with mixed layer depth. Sonic layer depth showed semiannual variability with peaks during June – August and December – February and lows during pre and post monsoon season. Sonic layer depth is observed to be shallower than mixed layer depth over most of the Arabian Sea except in the southeastern Arabian Sea during winter owing to temperature inversions. Sonic layer and mixed layer depth is observed to have high correlation (> 0.85) over most of the Arabian Sea indicating a good relationship between them, except in south eastern Arabian Sea. SLD is found to be deeper than MLD only in the southeastern AS (SEAS) during the winter season due to the presence of temperature inversions (TI) which are common phenomenon during that period. Advection of cooler low-salinity water over warmer salty SEAS water leads to the formation of TI in SEAS. Sound velocity being sensitive to temperature, results in deepening of SLD in this region. This can be used to understand relation between them to a great degree of accuracy and estimate one from the other
Rapid urbanization and associated impacts on land surface temperature changes over Bhubaneswar Urban District, India
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