Link between the internal variability and the baroclinic instability in the Bohai and Yellow Sea

Abstract

A regional ocean ensemble simulation with slightly different initial conditions demonstrates that internal variability is formed (not only) in the Bohai and Yellow Sea. In this paper, we analyze the relationship between the internal variability and the baroclinic instability, (represented by the Eady predicted theoretical diffusivity $${K}_{t}$$ K t ; the larger the $${K}_{t}$$ K t , the stronger the baroclinic instability level). In the ensemble, with tidal forcing, the spatial correlation between the Eady predicted theoretical diffusivity $${K}_{t}$$ K t and the internal variability amounts to 0.80. Also, the time evolution trends of baroclinic instability and internal variability are similar. Based on this evidence, baroclinic instability may be a significant driver for internal variability. This hypothesis is validated using an additional ensemble of simulations, which is identical to the first ensemble, but this time, the tides are inactivated. This modification leads to an increase in internal variability, combined with the strengthening of baroclinic instability. In addition, the baroclinic instability level and internal variability variation co-vary consistently when comparing summer and winter seasons, both with and without tides. Our interpretation is that a stronger baroclinic instability causes more potential energy to be transformed into kinetic energy, allowing the unforced disturbances to grow.

Effects of tide induced dynamics on surface transport properties

“…Previously it was mentioned that tidal forcing could affect the already existing eddy field, but we could also consider that it could affect the formation of eddies. Lin et al (2023) found that with tidal forcing there is an increase in vertical mixing and thus a change of stratification that decreases baroclinic instabilities. Ajayi et al (2020) showed that for the North Atlantic baroclinic mixed layer instabilities are responsible for an increase of submesoscale eddies in Winter.…”

“…Since mesoscale eddies can retain floating material for several days (e.g., d 'Ovidio et al, 2013;Condie & Condie, 2016;Limer et al, 2020;Bello-Fuentes et al, 2021), this loss of energy could imply a loss of the coherence of their structure and thus of their capacity to accumulate/trap material. One of the main mechanisms that generate coherent eddy structures, are baroclinic instabilities (Stammer, 1997), and these can be modified by tidal forcing (Lin et al, 2023). While no specific research has been done on the impact of internal waves on the retention capacity of eddies, some studies have been done with surface waves.…”

Comment on egusphere-2024-1332

“…The model-simulated elevation, temperature, salinity, and circulation patterns were validated by Huang et al (2019) and Lin et al (2022Lin et al ( , 2023. In this study, we focus directly on the analysis and discussion of the Qingdao cold water mass.…”

“…The model domain includes the Bohai and Yellow Sea, ranging from 31.885°N to 40.942°N and from 117.572°E to 126.915°E, respectively (Fig. 1 in Lin et al (2023)). The open boundary across the Yellow Sea extends from Qidong in China eastward to the southern tip of the Korean Peninsula, and radiation boundary conditions are used.…”

“…Previous work (Lin et al 2022(Lin et al , 2023 indicated that deviations exist within the ensemble members if the ensemble simulations are conducted with almost the same model configuration except for slight perturbations in the initial conditions.…”