Analysis

The Analysis module provides in-situ computation of diagnostic fields from the ocean model state during a simulation. Analysis fields are computed on the fly at user-specified frequencies and written to output streams, eliminating the need to store large volumes of raw model output for offline post-processing.

In the initial delivery, analysis is configured through pre-defined bundled AnalysisGroups such as GlobalStats. These bundles provide convenient shorthands for commonly-used analysis patterns and are configured entirely through the YAML input file. Future updates will add user-defined composable operator chains for fully customizable analysis, though the capability of using pre-defined bundled groups will persist as convenient defaults.

Background

The Analysis module supports two output modes:

Temporal reduction: Time-averaged output over a specified period (e.g., daily or monthly means). Fields are accumulated each timestep; the reduction is finalized and written at the end of each period. Temporal reduction is configured with the ReductionPeriod parameter. When using temporal reduction, the reduction period must be evenly divisible into the restart interval. This ensures that temporal reduction states can be properly checkpointed and restored. For calendars with variable month lengths, restart intervals based on months can only be divided by reduction periods based on months or periods of 1 day or whole-number fractions of a day, e.g., 6 hours. The Analysis system validates that the reduction period divides evenly into the restart interval during initialization and will abort if this requirement is violated.
Instantaneous output: Snapshots of analysis fields written at specified frequencies (e.g., every 6 hours). Instantaneous output is configured with the SnapshotPeriod parameter.

Configuration Overview

Analysis groups are configured in the YAML input file under Omega: Analysis:. Each group can be independently enabled or disabled. The initial delivery provides the GlobalStats group.

Common Configuration Parameters

All AnalysisGroups support the following parameters:

Enable: Required boolean (true or false). Enables or disables the group.
Filename: Required string. Template for output filenames with optional time-based variables ($Y, $M, $D, $h, $m, $s). The group automatically appends frequency and type information to the filename.
Stream: Optional map of IOStream parameters to customize output behavior. See Stream Parameters below for details.

Analysis Groups

Each AnalysisGroup encapsulates a set of related analysis operations. Groups inherit from the AnalysisGroup base class, which provides common functionality for operator chain construction and stream management.

When initialized, each group:

Parses its configuration to determine which operator chains to build
Registers operator chains with the Analysis orchestrator
Groups chains by output frequency and type (time reduction vs. instantaneous output)
Creates IOStream objects for each unique temporal configuration

All groups automatically handle intermediate operator sharing—if multiple chains require the same intermediate result, it is computed once and reused. Groups also validate that temporal reduction periods divide evenly into the restart interval to ensure proper checkpoint/restart behavior.

Stream Parameters

All AnalysisGroups support the optional Stream sub-node for customizing IOStream output parameters. If omitted, defaults are used.

Default values set by the Analysis module:

UsePointerFile: false
IfExists: append
Precision: double
UseStartEnd: false

All other Stream parameters (FileFreq, FileFreqUnits, PointerFilename, StartTime, EndTime) are empty or disabled by default.

Note: The Filename, Freq, and FreqUnits stream parameters are set automatically by AnalysisGroup configuration. Any user-specified values for these parameters will be overwritten.

For complete IOStream documentation, see the IOStreams section of the User’s Guide.

GlobalStats

Computes global spatial statistics (mean, min, max, standard deviation) for user-specified fields. The mean and standard deviation are weighted so that they do not depend on the mesh resolution: by the area of each cell, edge or vertex for a horizontal field, and by mass (area times pseudo-thickness) for a field with a vertical dimension, with an interface field weighted by half the mass of each adjacent layer. Only active layers take part.

Example:

Omega:
  Analysis:
    GlobalStats:
      Enable: true
      Fields: [Temperature, GeomZInterface, Salinity, NormalVelocity]
      SpatialStats: [Mean, Max, Min, StdDev]
      ReductionPeriod: [1Day, 1Month]
      SnapshotPeriod: [6Hour]
      Filename: global.stats.$Y.nc
      Stream:
        FileFreq: 1
        FileFreqUnits: years
        Precision: single

Group-Specific Parameters:

Fields: Required list of field names to analyze. The simulation will abort if a requested field does not exist.
SpatialStats: Required list of spatial operators.
ReductionPeriod: Optional list of time periods for temporal reduction (e.g., 1Hour, 1Day, 1Month, 1Year). Each period must divide evenly into the restart interval. At least one of ReductionPeriod or SnapshotPeriod must be specified.
SnapshotPeriod: Optional list of intervals for instantaneous output (e.g., 1Hour, 6Hour, 1Day). At least one of ReductionPeriod or SnapshotPeriod must be specified.

Output fields: For each (Field, SpatialStat) combination:

Instantaneous output: FieldName_SpatialStat (e.g., Temperature_SpatialMean)
Temporal reduction: FieldName_SpatialStat_TimeMeanPeriod (e.g., Temperature_SpatialMean_TimeMean1Day)

Output streams: Automatically created and named:

Time reduction: GlobalStats_FreqTimeStats (e.g., GlobalStats_1DayTimeStats)
Instantaneous output: GlobalStats_FreqInstants (e.g., GlobalStats_6HourInstants)

MOC

Computes the Meridional Overturning Circulation (MOC) streamfunction using two methods: latitude-binned regional MOC and transect-based MOC. The MOC represents zonally integrated meridional mass transport as a function of latitude and depth (regional MOC) or depth alone (transect MOC). Output is in Sverdrups (Sv), where 1 Sv = 10⁶ m³/s.

Example:

Omega:
  Analysis:
    MOC:
      Enable: true
      NumBins: 180
      MinLat: -90.0
      MaxLat: 90.0
      Regions: [Global]
      Transects: []
      ReductionPeriod: [1Month]
      SnapshotPeriod: [1Day]
      Filename: moc.$Y-$M.nc
      Stream:
        FileFreq: 1
        FileFreqUnits: months

Group-Specific Parameters:

NumBins: Optional integer specifying the number of latitude bins for regional MOC (default: 180, approximately 1-degree resolution).
MinLat: Optional minimum latitude in degrees for binning (default: -90.0).
MaxLat: Optional maximum latitude in degrees for binning (default: 90.0).
Regions: Optional list of region names for regional MOC computation (default: [Global]). Regional MOC computes the streamfunction as a function of latitude and depth. Currently only Global is supported; region masks are not yet implemented.
Transects: Optional list of transect names for transect-based MOC computation (default: []). Transect MOC computes the streamfunction as a function of depth only by accumulating transport across specified transect edges. Transect masks are not yet implemented.
ReductionPeriod: Optional list of time periods for temporal reduction. Each period must divide evenly into the restart interval. At least one of ReductionPeriod or SnapshotPeriod must be specified.
SnapshotPeriod: Optional list of intervals for instantaneous output. At least one of ReductionPeriod or SnapshotPeriod must be specified.

Output fields:

Regional MOC: MOC_streamfunction_RegionName (2D: latitude bins × depth)
Transect MOC: MOC_streamfunction_transect_TransectName (1D: depth only)

For temporal reduction, _TimeMeanPeriod is appended (e.g., MOC_streamfunction_Global_TimeMean1Month).

Output streams: Automatically created and named:

Time reduction: MOC_FreqTimeStats (e.g., MOC_1MonthTimeStats)
Instantaneous output: MOC_FreqInstants (e.g., MOC_1DayInstants)

Note

Regional and transect masks are not yet implemented. The Regions parameter currently only supports [Global], and Transects is a placeholder for future functionality. The underlying operator infrastructure is complete and ready for use once the mask fields are implemented in Omega.

MonthlyAverages

Computes monthly time averages of a set of requested global fields. Unlike GlobalStats, no spatial reduction is applied: each requested field is passed directly to a temporal-reduction (TimeMean) operator. The averaging period defaults to one month, but may be overridden with the optional ReductionPeriod parameter. This mirrors the timeSeriesStatsMonthly analysis member in MPAS-Ocean, which delivers monthly means of prognostic and derived fields.

Example:

Omega:
  Analysis:
    MonthlyAverages:
      Enable: true
      Fields: [Temperature, Salinity, NormalVelocity, PseudoThickness]
      ReductionPeriod: [1Month]   # optional; defaults to [1Month]
      Filename: monthly.averages.$Y.nc
      Stream:
        FileFreq: 1
        FileFreqUnits: years

Group-Specific Parameters:

Fields: Required list of field names to average. The simulation will abort if a requested field does not exist.
ReductionPeriod: Optional list of time periods for temporal reduction (e.g., 1Day, 1Month, 1Year). Defaults to [1Month] when not specified. Each period must divide evenly into the restart interval. Any SnapshotPeriod supplied for this group is ignored.

Output fields: For each requested field, a time-averaged field is produced:

FieldName_TimeMeanPeriod (e.g., Temperature_TimeMean1Month)

Output streams: Automatically created and named:

Time reduction: MonthlyAverages_FreqTimeStats (e.g., MonthlyAverages_1MonthTimeStats)

Note

The default field list in Default.yml includes the core prognostic fields (Temperature, Salinity, NormalVelocity, PseudoThickness). Additional registered global fields may be requested by adding them to the Fields list. The averaging period must divide evenly into the restart interval, as described in the Temporal Reduction Period Constraint below.

Usage Notes

Temporal Reduction Period Constraint

When using temporal reduction (ReductionPeriod), the period must divide evenly into the restart interval to ensure proper checkpoint/restart behavior. The Analysis module validates this during initialization. For example, if the restart interval is 6 months, valid periods include 6hours, 1Day, 1Month, 2Months, 3Months, and 6Months, but 5Days or 7Months are invalid.

Field Availability

The Analysis module initializes after the model state and validates that all requested fields exist. If a requested field is not found, the simulation aborts during initialization with an error message.

Intermediate Results

Some analysis operators require intermediate computations. For example, computing the standard deviation requires the mean as input. Currently, when configuring the SpatialStats list, users must include both Mean and StdDev if standard deviation is desired. The mean computation will be automatically shared if multiple statistics require it.

Future Extensions

The Analysis framework is designed for extensibility. Future versions will include:

User-defined composable operator chains: Full control over operator composition specified directly in the configuration file, enabling custom analysis workflows beyond the pre-defined bundles.
Additional pre-defined analysis groups: Bundled groups for common analysis patterns such as AMOC stream function, eddy statistics, regional diagnostics, and more.
Additional operators: Vertical operations, horizontal gradients, spatial filtering, and custom transformations.

The bundled AnalysisGroup types like GlobalStats will persist as convenient shorthands for commonly-used analysis outputs, even as the composable operator capability becomes available.

For detailed information about the Analysis architecture, operator composition, dependency resolution, and extending the module with new operators or groups, see the Analysis section of the Developer’s Guide.