Dataset: Relative Particle Density (RPD) calculations using High Frequency Radar (HFR) observed surface currents around Palmer Deep Canyon from January to March of 2020

Methods for these LCS results can be found in Veatch, et al. (2024, in revision).

Relative Particle Density provides the normalized density of drifters within each gridded bin of the study system. Relative Particle Density calculations begin with tracking virtual particles through a velocity field that are released over a regular grid. RPD is calculated by summing the number of drifters in each grid box, and normalizing by the median number of drifters in all grid boxes. In the following analysis, new particles were released in a regular grid across the 80 % coverage of the HFR footprint every three hours. Particles were not counted until they had been advected in the velocity field for 6 hours (when the autocorrelation of the HFR velocities cross the e-fold), and were no longer counted when they were advected out of the HFR domain, or after they became three days old. Given the average residence time of 2 days (Kohut et al., 2018), the three-day threshold was chosen to coordinate with the time phytoplankton will spend in the surface layer of our study domain. This methodology follows that used by (Oliver et al. 2019). RPD reports the normalized number of drifters present in each gridded bin at each timestamp. Two dimensional RPD assumes that no particles are lost from the surface layer due to vertical velocity, meaning that the integrated surface divergence in the x-y plane is assumed to be zero. Therefore, RPD will map the instantaneous concentration of surface associated particles across the entire domain given the evolving surface current fields provided by the HFR.