The wall-layer dynamics in a weakly stratified tidal bottom boundary layer

The application of the classical logarithmic layer model for wall-bounded shear flows to marine bottom boundary layer (BBL) usually leads to an overestimation of the friction velocity u* due possibly to the influence of form drag, stratification, and rotation of the flow vector. To gain insights on the BBL velocity scaling, acoustic Doppler current profiler (ADCP) measurements taken in the East China Sea were analyzed (a total of 270 sixteen-minute averaged velocity profiles). Single and double log-layer models, a log-wake model, and a modified log-layer (MLL) model that accounts for stratification in the upper part of the BBL (Perlin, Moum, Klymak, Levine et al. 2005) were explored. Although the first three models fit well for a majority of the profiles, the friction velocities appeared to be substantially overestimated, leading to unreasonably high drag coefficients. The friction velocity u*ml inferred from a slightly modified MLL, however, is half of that estimated using the classical log-layer assumption u*l. In a weakly stratified extended BBL, the dissipation rate ε decreases with the height from the seafloor ζ much faster than that in a homogeneous stationary BBL. This observation could be well approximated (in terms of r2) by an exponential ε (ζ) = ε0e–ζ/Lm or a power law decrease. The mixing length scale Lm = cLhBL, where hBL = 19–20 m is the BBL height and cL = 0.17, as well as the characteristic dissipation ε0, should vary in time, depending on the tidal currents and stratification in the BBL. The eddy diffusivity KN = 0.2ε/N2 showed an inverse dependence on the Richardson number Ri according to KN = K0/ (1 + Ri/Rc), where Rc is a constant and the diffusivity in nonstratified flow near the seafloor K0 = u*κζ is specified using u* = u*ml

ASIRI : an ocean–atmosphere initiative for Bay of Bengal

Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 97 (2016): 1859–1884, doi:10.1175/BAMS-D-14-00197.1.Air–Sea Interactions in the Northern Indian Ocean (ASIRI) is an international research effort (2013–17) aimed at understanding and quantifying coupled atmosphere–ocean dynamics of the Bay of Bengal (BoB) with relevance to Indian Ocean monsoons. Working collaboratively, more than 20 research institutions are acquiring field observations coupled with operational and high-resolution models to address scientific issues that have stymied the monsoon predictability. ASIRI combines new and mature observational technologies to resolve submesoscale to regional-scale currents and hydrophysical fields. These data reveal BoB’s sharp frontal features, submesoscale variability, low-salinity lenses and filaments, and shallow mixed layers, with relatively weak turbulent mixing. Observed physical features include energetic high-frequency internal waves in the southern BoB, energetic mesoscale and submesoscale features including an intrathermocline eddy in the central BoB, and a high-resolution view of the exchange along the periphery of Sri Lanka, which includes the 100-km-wide East India Coastal Current (EICC) carrying low-salinity water out of the BoB and an adjacent, broad northward flow (∼300 km wide) that carries high-salinity water into BoB during the northeast monsoon. Atmospheric boundary layer (ABL) observations during the decaying phase of the Madden–Julian oscillation (MJO) permit the study of multiscale atmospheric processes associated with non-MJO phenomena and their impacts on the marine boundary layer. Underway analyses that integrate observations and numerical simulations shed light on how air–sea interactions control the ABL and upper-ocean processes.This work was sponsored by the U.S. Office of Naval Research (ONR) in an ONR Departmental Research Initiative (DRI), Air–Sea Interactions in Northern Indian Ocean (ASIRI), and in a Naval Research Laboratory project, Effects of Bay of Bengal Freshwater Flux on Indian Ocean Monsoon (EBOB). ASIRI–RAWI was funded under the NASCar DRI of the ONR. The Indian component of the program, Ocean Mixing and Monsoons (OMM), was supported by the Ministry of Earth Sciences of India.2017-04-2

Inscribing the Victor’s Land: Nationalistic Authorship in Sri Lanka’s Post-war Northeast

This article examines the nationalistic authorship of space in Sri Lanka’s post-conflict Northeast as part of the state’s nation-building strategy and as a continuation of a post-colonial process of Sinhala-Buddhist nationalistic revival. Exploring issues of historiography, conflict resolution, physical vehicles of ideology and collective memory, the article demonstrates how land policies, development and the tourism industry in a post-conflict context can go hand-in-hand with dispossession, militarisation and the humiliation of a ‘defeated’ minority community

An undercurrent off the east coast of Sri Lanka

The existence of a seasonally varying undercurrent along 8° N off the east coast of Sri Lanka is inferred from shipboard hydrography, Argo floats, glider measurements, and two ocean general circulation model simulations. Together, they reveal an undercurrent below 100–200 m flowing in the opposite direction to the surface current, which is most pronounced during boreal spring and summer and switches direction between these two seasons. The volume transport of the undercurrent (200–1000 m layer) can be more than 10 Sv in either direction, exceeding the transport of 1–6 Sv carried by the surface current (0–200 m layer). The undercurrent transports relatively fresher water southward during spring, while it advects more saline water northward along the east coast of Sri Lanka during summer. Although the undercurrent is potentially a pathway of salt exchange between the Arabian Sea and the Bay of Bengal, the observations and the ocean general circulation models suggest that the salinity contrast between seasons and between the boundary current and interior is less than 0.09 in the subsurface layer, suggesting a small salt transport by the undercurrent of less than 4 % of the salinity deficit in the Bay of Bengal

Aircraft observations in a tropical supercluster over the equatorial Indian Ocean during MISO-BOB field campaign

Abstract The Monsoon Intra-Seasonal Oscillations in the Bay of Bengal (MISO-BOB) field campaign was conducted in the Indian Ocean during the 2018 and 2019 summer monsoon seasons. WC-130J aircraft of the 53rd Weather Reconnaissance Squadron of the US Air Force participated in the campaign in June 2018. The dropsonde observations across a tropical supercluster showed zonal wind variations in association with the structure of the convectively coupled Kelvin wave (CCKW). Within the supercluster, easterlies (westerlies) were observed in the upper (lower) troposphere; this transformation occurred just below the 0 $$^{\circ }$$ ∘ C level. The cold pool had an easterly component throughout, and it was coldest (by 2.5 $$^{\circ }$$ ∘ C) at the center of the supercluster, deepest ( $$\sim$$ ∼ $$1000\,\hbox {m}$$ 1000 m ) at its rear/western end, and shallowest ( $$\sim$$ ∼ 300 m) at the front/eastern end. The level of free convection (LFC) at the front end was at $$897\,\hbox {m}$$ 897 m altitude. At the eastern flank of the supercluster, zonal convergence in the lower troposphere occurred between 500-1500 m levels above the surface between the westerlies within the supercluster and opposing ambient easterlies. Thus, the uplifting of conditionally unstable air parcels above LFC to the east of the supercluster was likely to occur due to this convergence rather than the cold pool influence. Conversely, the western flank of the supercluster had low-level zonal divergence. These observations support the notion of ‘self-similarity’ among the mesoscale convective systems and large-scale waves

Increasing the Bioavailability of Phosphate by Using Microorganisms

Phosphorous (P) is a nonrenewable and one of the most important macronutrients for all living organisms. The formation of complexes with cations such as Al, Fe, and Ca reduces the solubility of P leading to limiting the absorption of P by plants. Therefore, we need to apply excessive amounts of P through conventional fertilizers. However, plants can use only a small portion of P of these added fertilizers whenever those become unavailable. Therefore, utilizing excess amounts of phosphate as fertilizers can lead to various environmental issues like eutrophication. Phosphate-solubilizing microorganisms (PSM) have the ability to solubilize soil phosphate through the production of organic acids, inorganic acids, enzymes, protons, siderophores, and exopolysaccharides resulting in the absorption of P by plants. The application of PSM has the potential to be used as an efficient, eco-friendly, and sustainable approach that can replace traditional fertilizers. This review aimed to give an overview of the diversity of PSM, methods of P solubilization, current trends, and technological advances that can assist in using PSM to achieve Sustainable Development Goals (SDGs)

ASIRI: An ocean-atmosphere initiative for bay of Bengal

An observation and modeling campaign in the Bay of Bengal is aimed at studying upper-ocean and lower-atmosphere processes and interactions in relation to Indian Ocean monsoons