Endpoints of the named sections

Exposed so the geometry behind each index can be inspected, plotted, or adjusted, rather than sitting as a constant inside a function body. Neither reproduces a specific published section.

Usage

scotian_shelf_inflow_section()

northeast_channel_section()

Value

a list with from and to, each c(longitude, latitude)

How these were placed

Not by eye. Both were measured against GLORYS monthly surface velocities for January to April 2010 on two diagnostics:

• capture fraction, |mean flow . n| over |mean flow|, which is 1 when the current crosses the section squarely and 0 when it runs along it

• endpoint ratio, the larger endpoint normal velocity over the peak along the section, which is near zero when the section spans the current rather than cutting through it

An earlier pair chosen from a map scored 0.65 and 0.27 on capture. The Northeast Channel one ran nearly along the channel axis, so its transport was the difference between two opposing halves. The current pair score 0.99 and 0.93, with Channel endpoints at about 4% of the peak.

The Northeast Channel line was then cross-checked against ETOPO depth, since bathymetry is what defines that channel: along it, depth runs roughly 120 m, 250 m, 80 m, so it starts on one bank, crosses the deep water, and ends on the other.

Both normals point westerly, into the Gulf, which was verified explicitly rather than inferred from the endpoint order.

docs/methods.md records the full derivation, and docs/section-placement-diagnostics.R re-runs it on any uo/vo extract.

See also

section_transport() for an arbitrary line

Examples

scotian_shelf_inflow_section()
#> $from
#> [1] -66.15  43.54
#> 
#> $to
#> [1] -65.95  42.76
#> 
northeast_channel_section()
#> $from
#> [1] -66.19  42.72
#> 
#> $to
#> [1] -66.61  41.88
#>