MỘT SỐ NHẬN ĐỊNH BAN ĐẦU VỀ HIỆN TƯỢNG SÓNG NỘI XẢY RA Ở VÙNG BIỂN MIỀN TRUNG VIỆT NAM

Internal waves often occur in the East Vietnam Sea and have been determined mainly based on RADAR images. By means of dataset of VNREDSAT-1 satellite images and other imagery sources, for the first time, internal waves in the East Vietnam Sea have been identified by multispectral images; Also the formation mechanism of internal wave in the nearshore waters of Central Vietnam has been found. The analytical results show that the phenomenon of internal wave occurs in the nearshore waters of Central Vietnam mainly in the Southwest monsoon season (from June to September every year) and is located along the edge of the continental shelf. Internal waves formed along the waters of Central Vietnam mainly include the signals that have been generated at the shelf by large waves, through the basin from Luzon Strait. The study results have discovered a new applied aspect of VNREDSAT-1 satellite images in oceanographic research in general and detailed studies on internal waves in particular.Sóng nội thường xuyên xuất hiện ở Biển Đông và đã được các học giả nước ngoài xác định chủ yếu dựa trên tư liệu ảnh RADAR. Bằng sử dụng nguồn ảnh viễn thám đa phổ, đa nguồn, đa thời gian bao gồm cả các ảnh viễn thám đa phổ VNREDSAT-1 (do Việt Nam bay chụp) thu thập trong thời gian gần đây, lần đầu tiên đã nhận dạng hiện tượng sóng nội ở Biển Đông bằng tư liệu ảnh đa phổ cũng như phát hiện ra quy luật hình thành sóng nội ở vùng biển miền Trung Việt Nam. Kết quả phân tích cho thấy, hiện tượng sóng nội xuất hiện ở vùng biển miền Trung Việt Nam, chủ yếu xuất hiện vào mùa gió Tây Nam (từ tháng 6 đến tháng 9 hàng năm) và nằm ở ven rìa của thềm lục địa. Sóng nội hình thành dọc theo vùng biển miền Trung Việt Nam chủ yếu là các tín hiệu được sinh ra tại vùng thềm bởi các sóng lớn, xuyên qua lưu vực từ eo biển Luzon. Kết quả nghiên cứu đã phát hiện ra một khía cạnh ứng dụng khác của ảnh viễn thám VNREDSAT-1 trong lĩnh vực hải dương học nói chung và nghiên cứu chi tiết sóng nội nói riêng

Abnormal features of oceanographic characteristics in upwelling Vietnam waters under impact of El Niño events

The summer upwelling that occurs in coastal waters of South Central Vietnam is one of the major hydrographic features in the South China Sea. A weakening of the upwelling after major El Niño events was observed in the literature for previous El Nino events and was verified here from the analysis of new satellite image data sets of sea surface temperature (SST) and surface wind. The analysis of empirical orthogonal function (EOF) from of monthly SST as well as of temporal and spatial variations of SST and wind force allow us to identify abnormal characteristics in ocean surface water that happened after El Niño episode, in agreement with previous studies. Those abnormal characteristics in Vietnam upwelling waters appeared mainly during the summers of 1998, 2003, 2010 and 2016 years for the El Niño decline phase. The upwelling weakening during El Niño decline episodes is associated with the following signals: (1) Wind force and Ekman pump are very weak; (2) the cold  and high chlorophyll-a  tongue is shifted northward but not extended eastward; (3) for years when El Nino occurs, SST strongly increases and reaches a peak in May or early June of next year, during the declining phase of El Niño episode; (4) upwelling phenomenon typically occurs during August and not July. Using a reanalysis dataset derived from the HYCOM/NCODA system coupled with a local Finite Element Model (FEM) allow us to complete our knowledge about the abnormal oceanographic characteristics of deeper water layers after El Niño episodes. The analysis of spatial variations of oceanography fields derived from HYCOM/NCODA/FEM system along zonal and meridional sections and vertical profiles as well as the results obtained from water mass analysis allow us to identify in details the abnormal oceanic characteristics of deeper water layers during the declining  El Niño phase. Those are; (5) Sea water in both surface and deeper water layers were transported dominantly northward  but not eastward; (6) The thermo-halocline layer in South Vietnam upwelling center was deeper (about 90 -100m), compared with previous El Nino and normal years (50-60 m and 35-40 m, respectively); (7) Extreme global warming in recent years (2012-2016) pressed the thermo-halocline layer in upwelling center deeper (90-100 m) during summer. Under the influence of the ocean global warming, this process should progress continuously, the depth of thermo-halocline layer should become therefore deeper and deeper in next years.References Barthel, K., R. 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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