Sunday, March 22, 2015

EGG Code (Ice Chart Symbology)

          Ice and iceberg charts serve tactical or strategic planning and operational purposes. They illustrate ice or iceberg conditions at a particular moment in time. The ice information is presented using a standard international code The World Meteorology Organization (WMO) system for sea ice symbology is referred to as the "Egg Code" due to the oval shape of the symbol.
             The basic data concerning concentrations, stages of development (age) and form (floe size) of ice are contained in a simple oval form. A maximum of three ice types is described within the oval. This oval and the coding associated with it are referred to as the "Egg Code". To indicate ice observations interpreted from radar imagery, the oval shall be omitted.

Common Practice 
Canadian Practice

Above figures are shown for thickness, floe sizes or other dimensions, a report coinciding with the end point of a range shall be coded as the higher value.

This code conforms to international convention and shall be used in coding all visual sea ice and lake ice observations without exception.
The symbols Ca CCc and Fa FFc correspond to SSb Sc respectively. In common practice CSe and Fe are no included but in Canada they are using Cd Se and Fe to enable  the reporting of additional classes, especially during freeze-up and break up. 

The specific details and rules for completing each level of information within the egg are given below.


Ct - Total concentration of ice in area, reported in tenths. May be expressed as a single number or as a range, not to exceed two tenths (3-5, 5-7 etc.)

Ca Cb Cc - Partial concentration (Ca, Cb, Cc) are reported in tenths, as a single digit. These are reported in order of decreasing thickness. Ca is the concentration of the thickest ice and Cc is the concentration of the thinnest ice.

Less than 1/10 (i.e. traces) shall not be reported within the oval except to describe open water. When only one ice type is present, the partial concentration shall not be indicated. When one ice type is present with a trace of a thinner type, only total concentration of the major ice type shall be indicated 


Stage of development of thickest (So), second thickest (Sa ), third thickest (Sb ) fourth thickest (Sc ) ice fifth thickest (Sand the thinner ice types Se, of which the concentrations are reported by CCCCrespectively. 

NOTE: If there is a dot (.), all stages of development codes to the left of the dot (.) are assumed to carry the dot (.)) These codes correspond directly with the partial concentrations above. Ca is the concentration of stage Sa, Cb is the concentration of stage Sb, and Cc is the concentration of Sc.

So SSe - Development stage (age) of remaining ice types. So if reported is a trace of ice type thicker/older than SaSe is a thinner ice type which is reported when there are four or more ice thickness types.

Coding for Sea-Ice Stages of Development (SSSSSSe)


Floe Size corresponding to Sa SSc Sd and Se (when Sand Se are greater than a trace).
World Meteorological Organization International procedures also permit reporting of Fand Fas the primary and secondary forms of all the ice without reference to stage of development.

It is Canadian practice to report FFFc as predominant floe sizes of SSSrespectively. This makes it necessary, when only Sa and Sb are present, that Fa and Fb shall be followed by a dash   (-) where Fc would normally appear.

Coding for Forms of Ice (FFFFFe)



9+/10 total ice concentration. 3/10 old ice in small floes, 2/10 thick first-year ice in medium floes, 1/10 thin first-year ice in small floes, 2/10 grey-white ice in small floes, and the remaining 2/10 is new ice with no floe form.

Reference: US / Canada Met Department