Overview (Draft)

Note

This specification defines the AMOCatlas Format v0.1 (AC-0.1), a standardized data format for Atlantic Meridional Overturning Circulation (AMOC) observational datasets. AC-0.1 is based on OceanSITES-1.5 with specific extensions and modifications for AMOC monitoring requirements.

The AMOCatlas Format v0.1 (AC-0.1) provides a standardized framework for organizing, documenting, and distributing AMOC observational data. It builds upon established oceanographic data standards while addressing the specific needs of AMOC research and monitoring.

Base Standards:

  • CF-1.8: Climate and Forecast Metadata Conventions

  • OceanSITES-1.5: Ocean sustained interdisciplinary time series

  • ACDD-1.3: Attribute Convention for Data Discovery

Documentation Structure:

This format specification is supported by detailed reference documentation:

  • Variables: Comprehensive variable naming conventions and metadata standards

  • Units: UDUNITS-2 compliant unit definitions with AMOC-specific extensions

  • Variable Summary (auto-generated): Auto-generated variable mapping tables from standardized datasets

Format Identification

Datasets following AC-0.1 format are identified by the following global attributes:

Conventions = "CF-1.8, ACDD-1.3, OceanSITES-1.5"
format_version = "AC-0.1"
standard_name_vocabulary = "CF Standard Name Table v84"

Key Features

Coordinate System Standards

Coordinate Names (UPPERCASE):

  • TIME: Temporal coordinate (datetime64[ns] in xarray)

  • DEPTH: Depth below sea surface (positive downward, units: m)

  • LATITUDE: Geographic latitude (units: degree_north)

  • LONGITUDE: Geographic longitude (units: degree_east)

  • PRESSURE: Pressure coordinate (units: dbar)

  • SIGMA0: Potential density anomaly coordinate (σ₀, reference_pressure: 0 dbar)

  • SIGMA2: Potential density anomaly coordinate (σ₂, reference_pressure: 2000 dbar)

Rationale: Ensures consistent coordinate identification across all AMOC datasets regardless of source format variations.

Variable Naming Framework

Variables use UPPERCASE naming with underscores for readability, following CF-1.8 standard names where available. Key patterns include:

Transport Variables (TRANS_ prefix):

  • Pattern: TRANS_{component} or TRANS_{depth1}_{depth2}

  • Examples: TRANS_EKMAN, TRANS_FC, TRANS_0_800

  • Units: Sverdrup (full spelling to avoid confusion with sievert)

Overturning Variables (MOC_ with coordinate specification):

  • MOC or MOC_Z: Overturning in depth coordinates

  • MOC_SIGMA0: Overturning in σ₀ density coordinates

  • MOC_SIGMA2: Overturning in σ₂ density coordinates

Heat/Freshwater Transport:

  • MHT_*: Meridional heat transport (units: PW)

  • MFT_*: Meridional freshwater transport (units: Sverdrup)

  • Regional qualifiers: _EAST, _WEST, _GYRE, _OT

Uncertainty Variables (_ERR suffix):

  • Pattern: {VARIABLE}_ERR

  • Examples: MOC_SIGMA0_ERR, MHT_ERR, TRANS_EKMAN_ERR

  • Units: Always identical to parent variable

For complete variable specifications, see Variables.

Unit Standardization

Preferred Units:

  • Transport: Sverdrup (1×10⁶ m³/s)

  • Heat transport: PW (1×10¹⁵ W)

  • Temperature: degree_C

  • Salinity: 1 (practical salinity, dimensionless)

  • Pressure: dbar

  • Coordinates: degree_north, degree_east

Rationale:

  • Sverdrup reflects appropriate scales for AMOC and avoids Sv/sievert confusion

  • PW makes heat transport values more readable than base SI watts

  • CF-compliant coordinate units enable automatic identification

For complete unit specifications, see Units.

Metadata Requirements

Required Variable Attributes:

  • standard_name: From CF-1.8 vocabulary where available

  • long_name: Human-readable description

  • units: UDUNITS-2 compliant units following AC-0.1 preferences

  • description: Extended description (optional but recommended)

Required Global Attributes:

  • title, summary, source

  • array, id

  • contributor_name, contributor_email, contributor_role

  • format_version, date_created

Deviations from Standards

AC-0.1 intentionally modifies CF-1.8/OceanSITES-1.5 conventions in specific cases:

Key Deviations from CF-1.8/OceanSITES-1.5

Aspect

Standard Convention

AC-0.1 Modification

Transport Units

m3 s-1 (CF standard)

Sverdrup (readability, scale appropriateness)

Heat Transport Units

Variable (W, TW, etc.)

PW (consistent scale)

Variable Prefixes

Variable naming

TRANS_ for transport, MOC_ for overturning

Coordinate Names

Variable (lat, latitude, etc.)

Standardized UPPERCASE (TIME, DEPTH, etc.)

These deviations are scientifically justified and documented for community review.

Standards Compliance

Format Identification:

  • Global attribute: format_version = "AC-0.1"

  • Conventions: "CF-1.8, ACDD-1.3, OceanSITES-1.5"

  • Standard name vocabulary: "CF Standard Name Table v84"

Variable Compliance:

Every AC-0.1 variable includes: - CF-1.8 compliant standard_name where available - Human-readable long_name - UDUNITS-2 compliant units - Extended description with methodology details

Format Validation

AC-0.1 compliance can be validated using the AMOCatlas compliance checker:

from amocatlas.compliance_checker import validate_ac1_format

# Validate a dataset
results = validate_ac1_format(dataset)

# Check for AC-0.1 compliance
if results.is_compliant:
    print("Dataset is AC-0.1 compliant")
else:
    print("Compliance issues found:")
    for issue in results.issues:
        print(f"  - {issue}")

Version History

AC-0.1 (2026-02-08):

  • Initial format specification

  • Based on OceanSITES-1.5 with AMOC-specific extensions

  • Establishes variable naming conventions and unit standards

  • Defines coordinate system requirements

  • Implements uncertainty variable convention

  • CF-1.8 compliance with documented deviations

References