ALBERT

Description: Marine heatwaves (MHWs) are widely recognized as prolonged periods of significantly elevated sea surface temperatures, leading to substantial adverse impacts on marine ecosystems. However, a comprehensive understanding of their characteristics and potential changes under climate change in the South China Sea (SCS, 0 ∼ 25°N, 105 ∼ 125°E) remains insufficient. Here, utilizing the OISST V2.0 reanalysis dataset, our study first examines MHW characteristics and their trends in the SCS during the historical period (1982 ∼ 2014). Then, in accordance with the criteria established in this study, GFDL-ESM4, EC-Earth3-Veg, NESM3, EC-Earth3, and GFDL-CM4 are identified from the CMIP6 ensemble of 19 models for their enhanced simulations of historical MHW characteristics. Moreover, considering that the fixed and sliding threshold methods offer distinct perspectives on the future evolution of MHWs, we employ both approaches to evaluate MHW characteristics under projected scenarios for the future period (2015 ∼ 2100) and subsequently compare the disparities between the two methodologies. The outcomes obtained using these methods consistently indicate that MHWs in the SCS are anticipated to intensify and persist for longer durations in the future. Besides, addressing seasonal variability, the peak intensity of MHWs falls in May during both the historical period and the four projected future scenarios. This study provides valuable insights into the behavior of MHWs in the SCS within the context of climate change, underscoring the urgency of adopting effective mitigation strategies. Especially, the use of two definition methods provides a more comprehensive set of information for understanding the future changes of MHWs in the SCS.

Description: Highlights: • The interactions between vortices in a four-vortex flow field using a rotating water tank. • Driven by the strain field, non-ideal vortices stretch along the centerline, and manifest an asymmetric stretching pattern. • Non-ideal vortices disperse vorticity, accumulate filaments, and exhibit distinctive variations in anti-symmetric vorticity distribution, impacting respective merging efficiency. Abstract: Oceanic vortex merging is an important physical process for the vortex evolution and its impact on marine environment. However, limitation of the in-situ oceanic observational data of vortex merging inhabits its better understanding. This study investigates the interactions between non-ideal vortices in a four-vortex flow field in a rotating tank. We examine the merging stages of anticyclonic vortices, influenced by two other cyclonic vortices and their respective dynamical behaviors and quantify the effects of merging on vortex characteristics. The results indicate a strong shear flow between two counter-rotating vortices, which accelerates the motion of the anticyclonic vortex, while cyclonic ones exhibit greater stability. Subsequently, different stages of non-ideal vortex merging in a co-rotating framework are defined, primarily the encircling stage, rapid approaching stage, and merging vortex stage. In addition, we quantify and compare variations in morphological parameters and anti-symmetric vorticity distribution of non-ideal vortices across these stages. The stretching of vortices primarily occurs along the line connecting their centers due to the strain field exerted by neighboring vortices, resulting in an asymmetric stretching pattern in the interactions among non-ideal vortices. Furthermore, during the merging process, non-ideal vortices disperse vorticity outward and accumulate vortex filaments in the surrounding environment, leading to distinctive variations in anti-symmetric vorticity distribution, affecting their respective merging efficiency.