Uncovering Ocean Mixed Layer Dynamics from the Sea Surface State

Data and Code Description Manuscript_Data All data used to generate the figures in the manuscript and Supporting Information. Manuscript_Figures MATLAB scripts for generating all figures in the manuscript and Supporting Information. analysis_llc 1_basics: script1_find_indices.py Find the i, j, and face indices for selected region. set_constant.py, set_colormaps.pySet domain name, horizontal indices, the start and end time indices, and colormaps. py01_24h_avg_TSW.py, py02_24h_avg_surface.pyCompute daily mean 3D output: temperature, salinity, and vertical velocity. Compute daily mean 2D output: surface velocities, wind stress, SSH, KPP boundary layer depth, etc. py03_rho_daily.py, py03_Hml_daily.pyCompute daily mean potential density and 10-m referenced mixed layer depth. Compute surface (0.5-m) referenced mixed layer depth. py08_vorticity_strain_calc.py, py08_vorticity_strain_plot.py Compute and plot surface strain rate, surface vorticity, and surface divergence py19_Lambda_MLI.py, py20_Lambda_MLI_timeseries_excludeShallowHml,py, py20_Lambda_MLI_timeseries.py Compute mixed layer horizontal buoyancy gradient M2, vertical buoyancy gradient N2, and the wavelength of the most unstable mixed layer instability waves. save_data_manuscript_Fig2.py, save_data_manuscript_surface.py, save_data_timeseries_Fig1.py Save timeseries and spatial fields needed for creating figures for the manuscript. 2_surface_forcing: py28_Ekman_buoyancy_flux_hourly.py, py28_Ekman_buoyancy_flux_daily.pyCompute Ekman buoyancy flux using hourly or daily model output. py07_Qnet_mean.pyCompute surface buoyancy flux (contributed by net heat flux/freshwater flux) py27_wind_stress_daily.pyCalculate daily and domain-averaged wind stress magnitude. py29_KPPhbl_vs_MLD.pyPlot the KPP boundary layer height and compare it to the mixed layer depth. 3_eddy_buoyancy_flux: py31_hourly_rho.pyCompute hourly potential density, surface referenced mixed layer depth, and 10-m referenced mixed layer depth. hourly_wb_Gaussian_calc.py (parallel), hourly_wb_Gaussian_calc_sequential.py, py31_hourly_wb_timeseries.py (parallel), py31_hourly_wb_timeseries_sequential.py Compute total, mean, and eddy vertical buoyancy fluxes using hourly model output and a Gaussian filter, exclude regions where the mixed layer depth is shallower than 10m. The filter size is a constant (e.g., 30 km), or determined from the 60-day average wavelength of the most unstable mode of mixed-layer instability. py31_hourly_wb_timeseries.py Compute the domain averaged eddy vertical buoyancy fluxes, and plot the time series. py31_hourly_wb_calc.py (parallel), py31_hourly_wb_calc_sequential.py Compute total, mean, and eddy vertical buoyancy fluxes using hourly model output and coarse-graining ("box filter"), exclude regions where the mixed layer depth is shallower than 10m. py31_wb_CoarseGraining_MixedlayerAvg_calc.py, py31_wb_CoarseGraining_MixedlayerAvg_plot.py, py31_wb_CoarseGraining_MixedlayerAvg_timeseries.pyCompute total, mean, and eddy vertical buoyancy fluxes using daily averaged data, using a box filter. Compute their domain averages, and plot the time series. 4_steric_height: py23_rho_insitu_hydrostatic_pressure.pyCompute in-situ density and estimate hydrostatic pressure. py24_steric_height_Wang25_timeseries.py, py24_steric_height_Wang25_timeseries2.py Compute and save the domain-averaged time series of steric height anomaly following Jinbo Wang et al. (2025). save_steric_gradient_maps.py Save maps of the gradient magnitude of the steric height for the manuscript. 5_SSH: py25_SSH_submesoscale_GaussianFilter_time_varying.pyCompute submesoscale sea surface height (SSH) gradient by applying a time-varying Gaussian filter to SSH. The filter scale is set by the wavelength of the most unstable mixed layer instability waves. py25_SSH_submesoscale_GaussianFilter.pyCompute submesoscale sea surface height (SSH) gradient by applying a constant Gaussian filter to SSH. py25_timeseries_SSH_submeso_grad_laplace.pyCompute the time series of domain-averaged submesoscale SSH gradient magnitude. save_SSH_submeso_gradient_maps.py Save the data required to calculate the vertical heat flux. 6_Turner_angle: TurnerAngle_BuoyancyRatio_daily_calc.py, TurnerAngle_BuoyancyRatio_timeseries.pyCompute the horizontal and vertical Turner angles and the density ratio. Save the data and plots, and compute domain-averaged time series. 7_mixed_layer_depth: py30_Hml_tendency_ver3.py Plot the daily-averaged budget terms driving the change of the mixed layer depth; plot a 7-day rolling mean. Reconstruct mixed layer depth from these terms, and compare it against the true mixed layer depth. 8_vertical_heat_flux: hourly_VHF_diagnosed_calc.py (parallel), hourly_VHF_diagnosed_calc_sequential.py, hourly_VHF_timeseries.py Compute total, mean, and eddy vertical heat fluxes using hourly model output and a Gaussian filter, exclude regions where the mixed layer depth is shallower than 10m. The filter size is a constant (e.g., 30 km), or determined from the 60-day average wavelength of the most unstable mode of mixed-layer instability. VHT_theory_BuoyancyRatio.py The vertical heat flux is reconstructed from the surface buoyancy ratio and mixed-layer steric height or submesoscale SSH, and then compared with the diagnosed VHF. VHF_theory_calc.py The vertical heat flux is reconstructed from the surface horizontal Turner angle and mixed-layer steric height or submesoscale SSH, then compared with the diagnosed VHF. analysis_swot llc2swot_sbatch.pyExtracts sea surface height anomaly data from LLC4320 for the same day of the year, but a different year than the SWOT observations. This script was adapted from model2SWOT.py in the SynthOcean package and includes parallel computing. llc2swot_combine_nc.pyCombines all individual swaths from LLC4320 into a single NetCDF file. llc2swot_plot.pyGenerates plots of the LLC4320 swaths.