Cyclonic Velocity Front (Cold-Core Rim)

More detail

What you see. A cold-core eddy is a dip of cold water that turns counter-clockwise. Bright rings and arcs on a dark map. The colors run from dark purple for still water through blue, green and yellow to dark red for the fastest. A dark spot is either slack water or water turning the warm-core way, and the map cannot say which. A color means the same water speed from one day to the next. The color scale runs from still water to about 2.9 knots. On the website the crosshair readout gives the speed in knots when your distance unit is nautical miles.

How to use it. Trust a ring that keeps its shape and its spin across several frames. In Layer Settings you can change the Colormap, the Range and the Opacity.

How it relates to the other eddy layers. The warm-core half is on Anticyclonic Velocity Front (Warm-Core Rim), so switch between the two to see the whole picture. Sea Level Anomaly shows the body of the eddy. This layer's ring sits around a blue patch there. Eddy Probability marks the sharply curved middle of a feature, so its bright patch and this ring sit slightly apart. Currents shows the same forecast speed everywhere. Use Currents for the whole flow, and use the Velocity Front layers to pick out the rims of eddies.

Who makes it. RipIQ makes this layer itself from the forecast sea surface and currents of HYCOM (U.S. Navy model). The layer covers the Gulf of America, the East Coast and Baja.

Its limits. A strong one-way current edge shows up too. A weakly curved patch can swap from one layer to the other between frames. It is surface only, has about 5 nautical miles of real detail, and paints right up to the beach. There are eight frames a day, three hours apart. The newest frame is from a run started between one and four days ago, and the time slider reaches up to 7 days ahead as a forecast.

The numbers

How often it updates	Once a day, as 8 frames three hours apart
How fresh it usually is	The newest frame is from a run started between one and four days ago
How detailed it is	About 5 nautical miles of real detail
Where it covers	Gulf of America, East Coast and Baja, right up to the beach. Outside the regions the map shows the chart alone; the layers stop at the region's edge.
How far back you can look	8 days back
How far forward you can look	Up to 7 days ahead, as a forecast
Goes blank under cloud?	Never
Observed or modeled	Calculated by RipIQ from HYCOM (U.S. Navy model) fields
What you see on screen	Speed, shown only where the water turns the cold-core way. On the website the readout is in knots when your distance unit is nautical miles. The color scale tops out at about 2.9 knots. Surface only

Source: computed by RipIQ from HYCOM model currents and sea surface height.