Interpreting ice charts: chapter 1

The Egg Code

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.

In the following figures and tables where ranges 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.

The following is a summary diagram of the Egg Code. This code conforms to international convention and shall be used in coding all visual sea ice and lake ice observations without exception.

The symbols C_a C_bC_c and F_a F_bF_c correspond to S_aS_b S_c respectively.

There are some minor additions to the egg code symbology that are Canadian practice. In Canada, to enable the reporting of additional ice classes, especially during freeze-up and break-up, C_d S_e and F_e can be used. This should not be a common occurrence.

The following pages describe the specific details and rules for completing each level of information within the egg.

Concentration (C)

Total concentration (C_t ) of ice in the area reported in tenths and partial concentrations of thickest (C_a ), second thickest (C_b ), third thickest (C_c ) and fourth thickest (C_d ) ice in tenths.

Notes:

1. Less than 1/10 (i.e. traces) shall not be reported within the oval except to describe open water (see Example 1, section 3.8).
2. C_d shall only be included when S_d and S_e are reported (see Example 2, section 3.8).
3. When S_d is used and C_d is omitted, C_d equals C_t-(C_a+C_b+C_c) (see Example 3, section 3.8).
4. When only one ice type is present, the partial concentration shall not be indicated (see Example 4, and Example 5, section 3.8).
5. When one ice type is present with a trace of a thinner type, only total concentration of the major ice type shall be indicated (see Example 5, section 3.8 ).

Stage of Development (S)

Stage of development of thickest (S_o), second thickest (S_a), third thickest (S_b) and fourth thickest (S_c) ice and the thinner ice types S_d and S_e, of which the concentrations are reported by C_a C_b C_c C_d respectively.

Notes:

1. Reference to thicker ice should be understood to mean older ice and conversely, thinner ice to mean younger ice types.
2. Ice is designated as Sea, Lake or River Ice depending on where it forms. In Canada, the practice is to use lake-ice coding to report ice in the Great Lakes and the St. Lawrence Seaway. Elsewhere, including the St. Lawrence River east of Montreal, sea-ice coding is used for stages of development.
3. S_a, S_b and S_c shall have concentrations of at least 1/10, except when C_t is zero (see Example 1, section 3.8).
4. Reporting of S_a, S_b and S_c should generally be restricted to a maximum of three significant classes. In exceptional cases further classes may be reported as follows:
   • S_o- Stage of ice development thicker than S_a, but having a concentration less than 1/10 (see Example 6, section 3.8).
   • S_d- Stage of development of the thickest remaining ice types (if more than one type remains). It is the fourth stage present after S_a, S_b and S_c.
   • S_e- Shall only be reported when a thinner ice type remains after S_d. Partial concentration of S_e is obtained by subtracting partial concentrations (C_a C_b C_c C_d) from total concentration (C_t) (see Example 2, section 3.8).
5. When S_e is not present, S_d may be a trace of ice (see Example 6, section 3.8).
6. Concentration shall not be indicated for S_o and S_e(see Example 2, section 3.8, and Example 6, section 3.8).
7. Concentration shall not be indicated for S_d when S_e is not present (see Example 3, section 3.8, and Example 5, section 3.8).

Coding for Sea-Ice Stages of Development (S_o S_a S_b S_c S_d S_e)

Coding for Lake-Ice Stages of Development (S_o S_a S_b S_c S_d S_e)

Notes:

Form of Ice (F)

Floe Size corresponding to S_a S_b S_c S_d and S_e (when S_d and S_e are greater than a trace).

Notes:

1. World Meteorological Organization International procedures also permit reporting of F_pand F_s as the primary and secondary forms of all the ice without reference to stage of development.
2. It is Canadian practice to report F_aF_bF_c as predominant floe sizes of S_aS_bS_crespectively. This makes it necessary, when only S_a and S_b are present, that F_a and F_b shall be followed by a dash (-) where F_c would normally appear (see Example 7, section 3.8)

Coding for Forms of Ice (F_a F_b F_c F_d F_e)

Notes:

1. Width refers to the maximum horizontal extent.
2. At least one code 8 must be used for fast or consolidated ice. Other ice types embedded may retain their floe size (see Example 9, section 3.8).
3. Occasionally the stage of development of fast ice cannot be determined. The area shall be blackened-in to denote fast ice (see Table 3.9).
4. New sea ice does not have a definite form; therefore, when this stage of development occurs as S_a, S_b or S_c, the symbol X shall be used to designate floe size (see Example 4, section 3.8).
5. Floe size is not included for S_o, S_d and S_e if the concentration of these ice types is less than 1/10. Otherwise floe sizes for S_d and S_e are optional.
6. If there is a significant variation in floe sizes in an area containing only one particular ice type, the Ice Service Specialist may enter the applicable floe-size Categories in the lowest part of the oval reserved for floe size. The largest floe-size category shall be put on the left side within the oval, followed by the other applicable floe sizes. In this case, the partial concentrations listed (C_a C_b C_c C_d) would match the partial concentration of floe sizes, instead of different ice types.

Coding and Symbology for Strips and Patches

The symbol, placed at the bottom of the oval in the section reserved for Form of Ice, indicates that the ice is in strips and patches; the concentration within the strips and patches is represented by C.(see Example 11, section 3.8).

When strips and patches are observed in open-water areas, the symbol shall be placed to denote the position of the strips and patches. If the ice in the strips and patches is of the same composition as that inside an adjacent ice edge, no oval is required. If the ice in the strips and patches is of a different composition, an oval shall be used with an arrow or arrow(s) to the strips-and-patches symbol(s). To avoid confusion, the strip symbol must be included with the total concentration (see Example 10, section 3.8).

In an area where the ice is arranged in strips and patches and the ice floes are medium or greater, the floe size shall be indicated by using two ovals. The floe sizes are indicated as normal in the first oval, with the symbol placed between the first and second ovals. Thesymbol is repeated in the second oval beside the total concentration of the strips and patches (see Example 12a, section 3.8).

An alternate way of reporting the same situation as above:

In an area where the ice is arranged in strips and patches and the ice floes are medium or greater, the floe sizes shall be indicated as normal. Both the total concentration and the concentration within the strips will be placed in the space reserved for C_t, with the symbol between them. When this option is used, C_a C_b C_c and possibly C_d refer to the total concentration and not the concentration within the strips. For example, C_t can be reported as 29 meaning the total concentration is 2 tenths with strips of 9 tenths and the partial concentration(s) shall equal 2 tenths (see Example 12b, section 3.8).

In an area of ice where some thicker ice type(s) is (are) embedded as strips and patches, these shall be indicated by the use of two ovals. The overall partial concentrations of the ice types are indicated in the first oval and the concentrations within the strips and patches are indicated in the second oval. The symbol shall be placed between the two ovals and along with the total concentration in the second oval (see Example 13, section 3.8).

Coding for Brash

If 1 tenth or more of brash is present, it will always be C_a.

If brash is present, S_a will always be a dash (-), otherwise the normal table is to be used.

Brash is already indicated in the table as 1, therefore F_a= 1 confirms the dash (-) for S_a.

Four digits (VKMT) shall be added below the oval to indicate the thickness concentration breakdown of the brash that is present. Table 3.4 (below) shows the thickness Categories for agglomerated brash. The breakdown shall be entered going from right (T) to left (V). In the case where there is no thickness for thin but there are entries for medium, thick and very thick a zero (0) shall be placed in the thin column. This also holds true for medium (M) and thick (K) regardless of the combination (see Example 14, to Example 17, section 3.8).

Thickness Categories for Brash (VKMT)