DOI: 10.5061/dryad.x3ffbg7tk
title: Data from: Semidiurnal inner shelf flow in the Southern California Bight

description: Semidiurnal variability of alongshore currents on the inner shelf of the
 Southern California Bight is investigated using a 7 year velocity and
 pressure time series. Analysis reveals that the M2-frequency alongshore
 current varies significantly over spatial scales of O(10km),
 inconsistent with the expected progressive surface tide. Instead, the
 observed variability is attributed to the influence of a
 northward-propagating, superinertial coastal trapped wave (CTW)
 that generates a quasi-barotropic (QBT) flow, defined as the portion of
 the depth-averaged alongshore current that is out of phase with the
 surface tide. A superinertial CTW model, forced by realistic
 bathymetry and stratification conditions, suggests that the
 dominant mode of variability is likely a mode-1 CTW with a
 wavelength of approximately 50km. The observations and model also
 reveal that seasonal changes in stratification modulate the
 wavelength and phase speed of the CTW, leading to a seasonal pattern in
 the phasing of the quasi-barotropic alongshore flow. These findings
 provide a new perspective on the complex dynamics governing semidiurnal
 variability of alongshore currents on the inner shelf of the Southern
 California Bight and highlight the importance of considering the effects
 of superinertial CTWs when examining coastal dynamics.
description: # Data from: Semidiurnal inner shelf flow in the Southern California Bight
 [https://doi.org/10.5061/dryad.x3ffbg7tk](https://doi.org/10.5061/dryad.x3ffbg7tk) This dataset accompanies research investigating semidiurnal current variability on the inner shelf of the Southern California Bight. The observational data spans seven years (August 2011 to September 2018), collected at three monitoring sites along the 33m isobath off Southern California. The dataset integrates field measurements with numerical modeling results to examine coastal trapped wave dynamics and their influence on inner shelf circulation. ## Dataset Organization and Specifications ### Observational Data (SD\_IT\_Current\_Data.mat) This MATLAB file contains the primary acoustic Doppler current profiler (ADCP) measurements, with variables stored in a structured array format. The data encompasses: Velocity measurements (m/s): * Depth-averaged alongshore and cross-shore components * Filtered within the semidiurnal band (11-14.5 hours) * Positive values indicate northward/eastward flow * Sampling interval: 5 minutes, derived from 50-point ensemble averages of 6-second measurements Bottom measurements at 33m depth: * Pressure (decibars), referenced to surface * Temperature (°C) * Time series in UTC (MATLAB datenum format) Quality control parameters: * Top 15% and bottom 3.1m of water column excluded from depth-averaging * Periodic NaNs result from regular maintenance of the equipment ### Phase Analysis Data (Quasi-Barotropic.mat) Contains processed data for quasi-barotropic current analysis: * Time-averaged phase calculations for depth-averaged alongshore current * Time-averaged phase of bottom pressure ### Environmental Data Bathymetry_Profiles.mat: * Cross-shore bathymetric profiles between monitoring sites * Referenced to 100m depth datum * Average spacing approximately 140m N-S * Derived from NOAA's San Diego 1/3 arc-second MHW Coastal Digital Elevation Model * Profiles span Point Loma to La Jolla, La Jolla to Cardiff, and Point Loma to Cardiff sections * **Update: 04/23/25** * Bathymetry has been corrected for an erroneous scale factor. Seasonal_N_2.mat: * Seasonal buoyancy frequency (N²) profiles (rad²/s²) * Temporal coverage: 2008-2018 * Vertical profiles to 609m depth * Data from CalCOFI CTD casts (Line 93.3 Station 28) * Seasonal groupings: December-February, March-May, June-August, September-November * Processing: 10m median filter applied to raw profiles ### Model Results scatter_invisc Files: * Coastal trapped wave (CTW) model output * Solutions for each bathymetry-stratification combination * Includes resonant mode characteristics * Wave properties: wavelength, phase speed * Vertical and cross-shore structure of pressure and velocity fields * **Update: 04/23/25** * Added scatter_invisc_SoCal_February2025_Xsection_ih2_is1.mat, which shows the above for the updated bathymetry. RunsForPub_bathy2_strat1.mat: * Specific model results featured in manuscript Figure 9 * Demonstrates wavelength sensitivity to environmental parameters * Cross-shore pressure field structure ## Code Availability The CTW model implementation builds upon code available at: [https://github.com/bzemskova/coastal_internal_tides](https://github.com/bzemskova/coastal_internal_tides) Modifications include integration of measured bathymetry profiles and seasonal stratification variation handling. The repository contains complete documentation and usage instructions for reproducing the model results. This dataset supports comprehensive analysis of inner shelf dynamics in the Southern California Bight, particularly focusing on the role of coastal trapped waves in determining semidiurnal current variability. Users are encouraged to contact the authors for additional guidance on data interpretation or model implementation.