Polar Explorer

Web Mercator is infinite at 85.05°. That is a property of the projection, not a limit of the data — ARPEGE's 0.25° grid has a row at 90° in both hemispheres — and it means no Mercator raster can contain a pole at any size. The global Explorer stops at 85° because that is as far as the projection goes.

So the caps get a polar stereographic render instead: true at 70°, oriented on Greenwich, and guaranteed to 45° on every meridian — the corners reach further still, to about 29°. A stereographic raster cannot be draped on a Mercator map surface, which is why this page is a small purpose-built map rather than another layer on the Explorer.

It matters here because the two places Mercator fails hardest are the two where a hemisphere behaves as one system: the polar vortex, the sea-ice margin, and the cross-pole flow between Siberia and Canada are all things a map cut at 85° simply cannot draw. A displaced vortex is the thing upstream of a French cold spell — when it stretches towards Europe, the cold air that reaches the Massif Central a week later is already visible here, and it is visible nowhere else on this site.

Only the global run is here, and that is the data rather than a gap. The other two models on this site are limited-area boxes: ARPEGE-EUROPE stops at 72°N and ICON-EU at 70.5°N, and neither has a southern hemisphere at all, so a stereographic render of either would be a disc of nodata with a crescent of Lapland on one edge. This page did not exist on this site until ARPEGE 0.25° arrived — a polar view needs a model with a pole in it.