Calculating salinity variance fluxes using isohaline coordinates

Vertical salinity variance (SV) budgets are derived using the isohaline Total Exchange Flow (TEF) framework, with the advection of vertical SV quantified by the dispersion of salinity classes across sections. A numerical model of the Changjiang Estuary is used to demonstrate the application of this method. The analysis is focused on the North Channel (NC) segment where strong stratification is produced during neap tides. We find that the advection of vertical SV is stronger than that of horizontal SV during early neap due to the landward excursion of stratified water. However, strong northerly winds can significantly decrease the contribution of advection of vertical SV but increase the advection of horizontal SV into the NC due to the landward transport of relatively well-mixed saline water. This process increases the seaward advection of vertical SV in the southern channels. In addition, we highlight that the vertical SV dissipation (mixing) term balances the straining term and peaks at late neap in the NC, coinciding with the maximum volume-integrated vertical SV.