WMO Colour Code
Background
Experts have long considered including colour coding for sea-ice charts in the WMO's (World Meteorological Organization) "Sea Ice Nomenclature", but until recently this was considered optional.
However, the widespread use of electronic navigational information systems has brought about a definite need for colour coding on sea-ice charts. As a result, during the 2000-2001 period the International Ice Charting Working Group (IICWG) prepared a draft colour standard consisting of two mutually exclusive colour codes based on:
- total concentration; and
- stage of development.
These proposed codes complement the existing WMO black and white ice symbols and are designed to be flexible.
In 2002, IICWG-participating ice services produced charts according to the proposed standard, to determine whether any difficulties remained. This, as well suggestions from a number of countries, resulted in minor adjustments to the proposed colour codes. The resulting standard was submitted for final adoption and publication by the WMO Secretariat.
Keys to Using and Understanding the WMO Colour Codes
- There are two colour codes for use on sea-ice charts. They are based on:
- total concentration-this code is used when concentration is highly variable but the stage of development is relatively uniform;
- stage of development-this code is used when the stage of development is variable but the concentration is relatively uniform (high).
- The two colour codes are mutually exclusive; only one should be used on a single chart.
- Every chart should include a legend depicting the colour code used.
- "Undefined Ice" is used when it is known that sea ice is in an area, but its characteristics are not known. This is different from "No Information", which indicates that nothing is known about the area.
- No specific colour is assigned to areas of "No Information". Such areas should be clearly indicated on sea-ice charts-text annotation may be used where appropriate; an assigned colour within the code should not be used to indicate "No Information".
- The use of colour codes does not rule out black and white hatching patterns or egg codes; egg codes may be used along with colours.
- Other symbols may be used with the standard colours to depict special ice conditions under national practice.
