Introduced Requirements CF Conventions

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6.1.1 Introduced Requirements

Most of the introduced requirements are taken from the “CF Conformance Requirements and Recommendations” published by the Program for Climate Model Diagnosis Intercomparison PCMDI [10], from the “NetCDF Climate and Forecast CF Metadata Conventions, Version 1.5” [8], and from NetCDF Climate and Forecast CF Metadata Conventions, Version 1.6 -Chapter 9 [16]. For interoperability sake, the following requirement section specifies a CF 1.6 profile by restricting some of the original specifications –i.e. by transforming most of the recommendations into mandatory requirements. Table 1 reports the elements who are considered mandatory for this standard while they are optional for CF 1.6. Table 1. CF elements overruled from optional to mandatory Entity Requirements Condition CF 1.6 condition Exception CF-netCDF Variable standard_name attribute or a long_name attribute. Mandatory Optional Bounday Variable Coordinate Variable axis attribute Manadtory Optional Dimensionless Vertical Coordinate formula_terms attribute Mandatory Optional Spatial‐ temporal CF-netCDF Variable, Dimensions order shall appear in the relative order T , then Z , then Y , then X . In addition, any other Dimension shall be placed to the left of the spatiotemporal Dimensions Mandatory Optional Vertical Coordinate Positive attribute Mandatory Conditional Time Coordinate Calendar attribute Mandatory Optional 8 Copyright © 2013 Open Geospatial Consortium Time Coordinate characterized by a nonstandard calendar month_lengths attribute Mandatory Optional Time Coordinate characterized by a nonstandard calendar for leap years leap_year and leap_month attributes Mandatory Optional Coordinate Variable defined on a horizontal grid not defined on latitude and longitude dimensions coordinates attribute which associates a couple of Coordinate Variables defining the true latitude and longitude coordinates Mandatory Optional Measure Variable Dimensions shall be the same as or a subset of the dimensions of the CF Variable to which they are related Mandatory Optional 9 7 CF-netCDF Data Model

7.1 Extension packages