Study On The Characteristics Of The West-Subarctic Front And Its Fine Structure Of Underwater Three-dimensional Temperatur

The western subarctic front has attracted attention due to its seasonal variability and significant impact on the local oceanic dynamic environment and air-sea interaction.High resolution multi-source satellite merged sea surface temperature data is adopted in this study,and an algorithm that combines the advantages of histogram analysis and Sobel edge detection method is employed to detect the western subarctic front.The spatiotemporal variation of various front features is analyzed and quantified.The vertical characteristics of the western subarctic front are unclear,therefore a data-driven empirical modeling method is proposed to reconstruct the 3D temperature field of the front using the detected front features.A physical structure model of the front is also established to simulate the evolution of the 3D temperature field during the frontogenesis process,and the results of the two models are validated and evaluated.The main conclusions are as follows:(1)The combined algorithm has advantages in retaining the front strength represented by the SST gradient and reducing the level of detection noise,which helps to extract features such as strength,frequency,location,and coverage area of the western subarctic front.The front appears as a southwest-northeast band in shape,with a seasonal variation of high intensity in winter and low intensity in summer.In winter,its location is generally at 40 °N,while in summer,it moves northward to around 41 °N.The coverage area only exhibits a pattern of being wider in winter and smaller in summer in some individual years.(2)The data-driven empirical modeling method can effectively reconstruct the vertical temperature field in the western subarctic front region.Compared to ARMOR3 D data,the maximum difference between the two thermal fields is lower than 1 ℃,and the mean temperature difference exhibits significant fluctuations in the depth range of 0–450 m,with a maximum value of approximately 0.8 ℃.In this study,sensitivity experiments were conducted on the polynomial fitting order of sea surface temperature in the empirical model,and it was found that a fourth-order polynomial fit produced the best reconstruction result for the front.(3)The physical structure model of the western subarctic front is driven by perturbed field,and during frontogenesis process,a high thermal gradient band with increasingly dense isotherms forms over time in the depth range of 0–100 m at the center of the front.In the depth range of 100–200 m,there is a gradual appearance of a phenomenon of mixing of warm and cold seawater masses.Compared to HYCOM reanalysis datasets,the temperature field difference between the two models is within ±1 ℃,with errors mainly arising from the thermal inversion layer and the influence of anomalously warm water mass on the cold side of the front.