Part of #98.
Why. Rasmus, 2026-09-22: relative geostrophic flow "would be interesting to add to the plotter. For geostrophic flow we do not want to calculate anomalies because right now its relative as we lack a reference point." It shows the California Undercurrent near the coast. He supplied the calculation (gsw, R):
- per station, SA and CT on a 1 dbar grid to 500 dbar;
- dynamic height anomaly
gsw_geo_strf_dyn_height(SA, CT, p, p_ref = 500);
- for each adjacent station pair,
v = (dh2 − dh1) / (f · dx), where f is the Coriolis parameter at the mean latitude and dx the along-line distance. Positive = equatorward;
- average to the plotter's 10 m bins.
What differs from every other product. It lives between stations, not at them. The grain is (cruise, line, station pair, depth bin), and the x-coordinate is the pair's midpoint. There is no climatology and no anomaly. The flow is relative to 500 dbar, so a pair where either cast is shallower than 500 m needs a rule. His script carries the deepest density down (approx(rule = 2)); keep that, and flag the pair.
Done when. calcofi4db::ctd_geostrophic() is tested (a synthetic two-station density front gives the textbook shear) and writes a ctd_geostrophic table in the derived dataset. ctd-transects draws it on the station-pair axis (its own issue).
Ask Rasmus. Keep 500 dbar as the reference, or use the bottom depth of the shallower cast for inshore pairs?
Part of #98.
Why. Rasmus, 2026-09-22: relative geostrophic flow "would be interesting to add to the plotter. For geostrophic flow we do not want to calculate anomalies because right now its relative as we lack a reference point." It shows the California Undercurrent near the coast. He supplied the calculation (
gsw, R):gsw_geo_strf_dyn_height(SA, CT, p, p_ref = 500);v = (dh2 − dh1) / (f · dx), wherefis the Coriolis parameter at the mean latitude anddxthe along-line distance. Positive = equatorward;What differs from every other product. It lives between stations, not at them. The grain is (cruise, line, station pair, depth bin), and the x-coordinate is the pair's midpoint. There is no climatology and no anomaly. The flow is relative to 500 dbar, so a pair where either cast is shallower than 500 m needs a rule. His script carries the deepest density down (
approx(rule = 2)); keep that, and flag the pair.Done when.
calcofi4db::ctd_geostrophic()is tested (a synthetic two-station density front gives the textbook shear) and writes actd_geostrophictable in the derived dataset. ctd-transects draws it on the station-pair axis (its own issue).Ask Rasmus. Keep 500 dbar as the reference, or use the bottom depth of the shallower cast for inshore pairs?