Data for 'Surface heat fluxes drive a two-phase response in Southern Ocean mode water stratification'

The files contained here are the output/sensitivity files of four adjoint sensitivity experiments in ECCOv4r2 that are combined to create the sensitivity of large-scale stratification to surface heat flux. (-f/Delta z) * (-alpha * (ADJqnet_t1 - ADJqnet_t2) + beta * (ADJqnet_s1 - ADJqnet_s2)) (Equation 7 in paper, where C = net heat flux).  The files contained here are the output/sensitivity files for 6 years at 14 day time steps.

ADJqnet_t1: (d J_1(theta_u)/ d qnet), Sensitivity of potential temperature over the upper depths to net heat flux.

ADJqnet_t2: (d J_2(theta_l)/ d qnet), Sensitivity of potential temperature over the lower depths to net heat flux.

ADJqnet_s1: (d J_3(salt_u)/ d qnet), Sensitivity of salinity over the upper depths to net heat flux.

ADJqnet_s2: (d J_4(salt_l)/ d qnet), Sensitivity of salinity over the lower depths to net heat flux.

Paper Abstract: Subantarctic mode waters (SAMW) have low stratification and are formed through subduction from thick winter mixed layers in the Southern Ocean. To investigate how external forcing affects the stratification in mode water formation regions in the Southern Ocean, we conduct a set of adjoint sensitivity experiments. The objective function is the annual-average stratification over the mode water formation region, which is evaluated from potential temperature and salinity adjoint sensitivity experiments. The analysis of impacts, from the product of sensitivities and forcing variability, identifies the separate effects of the wind stress, heat flux, and freshwater flux, revealing that the dominant control on stratification is from surface heat fluxes, as well as a smaller effect from zonal wind stress. The adjoint sensitivities of stratification to surface heat flux reveal a surprising change in sign over 2 years lead time. Surface cooling leads to the expected initial local decrease in stratification. However, there is a delayed response to surface cooling leading to an increase in stratification. This delayed response in stratification involves atmospheric damping of the surface thermal contribution, so that eventually the oppositely-signed advective haline contribution dominates. This two-phase response of stratification is found to hold over mode water formation regions in the South Indian and Southeast Pacific sectors of the Southern Ocean, where there are strong advective flows linked to the Antarctic Circumpolar Current.