Understanding the Current Definition

Oct 13, 2025 by wbrum.org 90 views

Introduction

In recent discussions, the definition of the standard name sea_ice_area_fraction was found to be ambiguous. This ambiguity arises from the difference in interpretation of the sea-ice concentration and the sea ice area fraction in coastal regions with partial land, open sea, and sea ice. In this article, we propose to improve the text of the definition in the standard name table to more clearly state how the ambiguity must be handled.

Understanding the Current Definition

The present definition of sea_ice_area_fraction is as follows:

"Area fraction" is the fraction of a grid cell's horizontal area that has some characteristic of interest. It is evaluated as the area of interest divided by the grid cell area, or if the cell_methods restricts the evaluation to some portion of that grid cell (e.g. "where sea_ice"), then it is the area of interest divided by the area of the identified portion. It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Sea ice area fraction is area of the sea surface occupied by sea ice. It is also called "sea ice concentration". "Sea ice" means all ice floating in the sea which has formed from freezing sea water, rather than by other processes such as calving of land ice to form icebergs.

The first part of the definition is common to all the _area_fraction standard names and explains that the default interpretation is an area fraction wrt the entire area (of the cell). The second part of the definition is specific to sea_ice_area_fraction and introduces the (widely used variable) sea-ice concentration as the area fraction wrt to the portion of the area that is covered by sea. However, this definition does not clearly address the ambiguity that arises in coastal regions.

Proposed New Definition

To address the ambiguity, we suggest keeping the same structure (the common part, then the specific part) but improving the second part so that it reads:

"Area fraction" is the fraction of a grid cell's horizontal area that has some characteristic of interest. It is evaluated as the area of interest divided by the grid cell area, or if the cell_methods restricts the evaluation to some portion of that grid cell (e.g. "where sea_ice"), then it is the area of interest divided by the area of the identified portion. It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. For a variable to represent the sea-ice concentration (the area fraction of the sea surface that is covered by sea ice) it must have a cell_methods attribute that includes "area:mean over sea". The sea-ice concentration and the sea ice area fraction reported over the entire cell area differ in coastal regions with partial land, open sea, and sea ice. "Sea ice" means all ice floating in the sea which has formed from freezing sea water, rather than by other processes such as calving of land ice to form icebergs.

Key Changes

The proposed new definition includes the following key changes:

Clarification of sea-ice concentration: The new definition clearly states that for a variable to represent the sea-ice concentration, it must have a cell_methods attribute that includes "area:mean over sea".
Addressing ambiguity in coastal regions: The new definition acknowledges that the sea-ice concentration and the sea ice area fraction reported over the entire cell area differ in coastal regions with partial land, open sea, and sea ice.

Benefits of the Proposed Change

The proposed change will provide a clearer definition of sea_ice_area_fraction and address the ambiguity that arises in coastal regions. This will ensure that users of the standard name can accurately interpret the data and make informed decisions.

Conclusion

In conclusion, the proposed new definition of sea_ice_area_fraction will provide a clearer understanding of the standard name and address the ambiguity that arises in coastal regions. We believe that this change will improve the usability and accuracy of the standard name and contribute to the advancement of climate research.

Recommendations

We recommend that the proposed new definition be adopted as the standard definition for sea_ice_area_fraction. This will ensure that users of the standard name can accurately interpret the data and make informed decisions.

Future Work

Future work may include:

Reviewing other standard names: Reviewing other standard names to ensure that they are clear and unambiguous.
Developing guidelines: Developing guidelines for the use of standard names to ensure consistency and accuracy.
Providing training: Providing training for users of standard names to ensure that they understand the definitions and can accurately interpret the data.
Frequently Asked Questions (FAQs) about Standard Names: Clarify the Definition for Sea Ice Area Fraction =============================================================================================

Q: What is the current definition of sea_ice_area_fraction?

A: The current definition of sea_ice_area_fraction is:

"Area fraction" is the fraction of a grid cell's horizontal area that has some characteristic of interest. It is evaluated as the area of interest divided by the grid cell area, or if the cell_methods restricts the evaluation to some portion of that grid cell (e.g. "where sea_ice"), then it is the area of interest divided by the area of the identified portion. It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Sea ice area fraction is area of the sea surface occupied by sea ice. It is also called "sea ice concentration". "Sea ice" means all ice floating in the sea which has formed from freezing sea water, rather than by other processes such as calving of land ice to form icebergs.

Q: What is the proposed new definition of sea_ice_area_fraction?

A: The proposed new definition of sea_ice_area_fraction is:

"Area fraction" is the fraction of a grid cell's horizontal area that has some characteristic of interest. It is evaluated as the area of interest divided by the grid cell area, or if the cell_methods restricts the evaluation to some portion of that grid cell (e.g. "where sea_ice"), then it is the area of interest divided by the area of the identified portion. It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. For a variable to represent the sea-ice concentration (the area fraction of the sea surface that is covered by sea ice) it must have a cell_methods attribute that includes "area:mean over sea". The sea-ice concentration and the sea ice area fraction reported over the entire cell area differ in coastal regions with partial land, open sea, and sea ice. "Sea ice" means all ice floating in the sea which has formed from freezing sea water, rather than by other processes such as calving of land ice to form icebergs.

Q: What is the main change in the proposed new definition?

A: The main change in the proposed new definition is the addition of a requirement for a cell_methods attribute that includes "area:mean over sea" for a variable to represent the sea-ice concentration.

Q: Why is this change necessary?

A: This change is necessary to address the ambiguity that arises in coastal regions with partial land, open sea, and sea ice. The current definition does not clearly state how to handle this ambiguity, and the proposed new definition provides a clear solution.

Q: What are the benefits of the proposed new definition?

A: The benefits of the proposed new definition include:

Improved clarity: The proposed new definition provides a clearer understanding of the standard name and addresses the ambiguity that arises in coastal regions.
Increased accuracy: The proposed new definition ensures that users of the standard name can accurately interpret the data and make informed decisions.
Better consistency: The proposed new definition provides a consistent definition of sea_ice_area_fraction that can be used across different applications and datasets.

Q: What is the next step in the process?

A: The next step in the process is to review and discuss the proposed new definition with the relevant stakeholders and to consider any feedback or suggestions that may be received.

Q: How can I provide feedback on the proposed new definition?

A: You can provide feedback on the proposed new definition by contacting the relevant stakeholders or by submitting a comment or suggestion through the standard name repository.

Q: What is the expected timeline for implementing the proposed new definition?

A: The expected timeline for implementing the proposed new definition will depend on the outcome of the review and discussion process. If the proposed new definition is adopted, it is expected to be implemented as soon as possible.