Assessing water renewal time scales for marine environments from three-dimensional modelling: a case study for Hervey Bay, Australia

We apply the three-dimensional Coupled Hydrodynamical Ecological model for Regional Shelf Seas (COHERENS) to compute water renewal time scales for Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia. Water renewal time scales are not directly observable but are derived indirectly from computational studies. Improved knowledge of these time scales assists in evaluating the water quality of coastal environments and can be utilised in sustainable marine resource management. Results from simulations with climatological September forcing are presented and compared to cruise data reported by Ribbe (2006). A series of simulations using idealised forcing provides detailed insight into water renewal pathways and regional differences in renewal timescales. We find that more than 85 % of the coastal embayment’s water is fully renewed within about 50-80 days. The eastern and western shallow coastal regions are ventilated more rapidly than the central, deeper part of the domain. The climatological simulation yields temperature and salinity patterns that are consistent with the observed situation and water renewal times scales in the range of those derived from idealised model studies. While the reported simulations involve many simplifications, the global assessment of the renewal time scale is in the range of a previous estimate derived for this coastal embayment from a simpler model and observational data

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Impact of climate variability on the circulation of an East-Australian bay

The climate along the subtropical east coast of Australia is changing significantly. Rainfall has decreased about by 50 mm per decade and temperature increased by about 0.1 °C per decade during the last fifty years. These changes are likely to impact upon episodes of hypersalinity and the persistence of inverse circulations which are often characteristic features of the coastal zone in the subtropics. These conditions are controlled by the balance between evaporation, precipitation and freshwater discharge. In this study, we use observations and results from an ocean model to investigate the circulation pattern and water renewal of Hervey Bay, a subtropical bay off the central east coast of Australia. The investigation of this shallow coastal environment (mean depth 15 m) showed how current climate trends have impacted upon the physical characteristics of the bay. The observed hypersalinity zone and inverse circulation, which are climatological features, are caused by the high evaporation rate, solar heat fluxes and the water renewal timescales of the bay. The region therefore acts as an effective source for an accumulation of salt. Over the last two decades the outflow of this salt has increased by about 25 % in direct consequence of recent climate trends. Further the manifestation of this salt export, in form of gravity currents, has also increased in frequency and strength. With the help of Lagrangian particle techniques, we could track these plumes on their way along/down the continental shelf to depths up to 220 m, to form a 'Hervey Bay' water mass. These outflow events, when integrated over the time they occur, have a volume comparable to the volume of the bay and have broad implications for the local biology, sediment dynamics but also for pollutant transport. The study further indicates that hypersalinity conditions are more persistent and reversal of these conditions is less frequent in the last decade due to the reduced supply of freshwater

Stability of an Australian inverse bay

[Abstract]: Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia, is a shallow tidal area (average depth = 15 m), close to the continental shelf. It shows features of an inverse estuary, due to the high evaporation rate (approx. 2 m/year), low precipitation (less than 1 m/year) and on average almost no freshwater input from three rivers that drain into the bay. We applied an ocean general circulation model to compute the temperature, density and salinity distribution within the bay and surroundings. The numerical studies are performed with the COupled Hydrodynamical Ecological model for REgioNal Shelf seas (COHERENS). A model validation and calibration was carried out after recent field campaigns. The investigations showed that the bay is almost vertically well mixed throughout the year and that the horizontal distribution of properties follows the bathymetry. As in other inverse/negative estuaries, the year-round salinity increases toward the shore to form a nearly persistent salinity gradient. This leads especially in the transition from summer to autumn to the formation of dense water mass thereby establishing gravity currents. The high saline water can sink beyond 200 m, flow over the continental shelf to form a ‘Hervey Bay’ water mass that is advected with the East Australian Current. The investigation further showed that air temperature, wind direction and tidal regime are mainly responsible for the stability of the inverse circulation and strength of the salinity gradient across the bay

On the Circulation in t5he East Frisian Wadden Sea: Numerical Modelling and Data Analysis.

Abstract not availableJRC.H-Institute for environment and sustainability (Ispra

Search for direct top squark pair production in final states with two leptons in s=13\sqrt{s} = 13 TeV pppp collisions with the ATLAS detector

International audienceThe results of a search for direct pair production of top squarks in events with two opposite-charge leptons (electrons or muons) are reported, using $36.1~\hbox {fb}^{-1}$ of integrated luminosity from proton–proton collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark $\tilde{t}$ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay $\tilde{t} \rightarrow b \tilde{\chi }_{1}^{\pm }$ into a b-quark and the lightest chargino with $\tilde{\chi }_{1}^{\pm } \rightarrow W \tilde{\chi }_{1}^{0}$ , the decay $\tilde{t} \rightarrow t \tilde{\chi }_{1}^{0}$ into an on-shell top quark and the lightest neutralino, the three-body decay $\tilde{t} \rightarrow b W \tilde{\chi }_{1}^{0}$ and the four-body decay $\tilde{t} \rightarrow b \ell \nu \tilde{\chi }_{1}^{0}$ . No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the $\tilde{t}$ and $\tilde{\chi }_{1}^{0}$ masses. The results exclude at 95% confidence level $\tilde{t}$ masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches

Searches for the ZγZ\gamma decay mode of the Higgs boson and for new high-mass resonances in pppp collisions at s=13\sqrt{s} = 13 TeV with the ATLAS detector

International audienceThis article presents searches for the Zγ decay of the Higgs boson and for narrow high-mass resonances decaying to Zγ, exploiting Z boson decays to pairs of electrons or muons. The data analysis uses 36.1 fb$^{−1}$ of pp collisions at $\sqrt{s}=13$ recorded by the ATLAS detector at the CERN Large Hadron Collider. The data are found to be consistent with the expected Standard Model background. The observed (expected — assuming Standard Model pp → H → Zγ production and decay) upper limit on the production cross section times the branching ratio for pp → H → Zγ is 6.6. (5.2) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125.09 GeV. In addition, upper limits are set on the production cross section times the branching ratio as a function of the mass of a narrow resonance between 250 GeV and 2.4 TeV, assuming spin-0 resonances produced via gluon-gluon fusion, and spin-2 resonances produced via gluon-gluon or quark-antiquark initial states. For high-mass spin-0 resonances, the observed (expected) limits vary between 88 fb (61 fb) and 2.8 fb (2.7 fb) for the mass range from 250 GeV to 2.4 TeV at the 95% confidence level