θ–S Diagram

The θ–S diagram compares potential temperature and absolute salinity for either the current search results or one float’s loaded trajectory.

Open the Diagram

The diagram is available to signed-in users.

1. With Trajectory View off, run a search with no more than 500 profiles. With it on, select a WMO trajectory with no more than 500 cycles.
2. Open Analyze in the map command bar and select Generate θ–S. On narrower layouts, open Map tools first.
3. Select a map marker to highlight that profile, or return to Analyze and select Close θ–S to hide the diagram.

The diagram uses the current search results with Trajectory View off or every cycle in the selected WMO trajectory with it on. If a search exceeds 500 profiles, narrow the date range or geographic bounds. A trajectory over 500 cycles remains disabled; OceanGraph does not sample, split, or page either input.

When OceanGraph needs to generate a new θ–S diagram, Analyze shows progress and provides cancel or retry actions. Cached diagrams open without this generation progress. On narrower layouts, use Map tools. The map and other controls remain usable while the job runs.

With Trajectory View on, θ–S and View section are independent and can remain visible together. When both are visible, selecting a map marker or using the left and right arrow keys changes the selected cycle in the marker, the section’s dashed line, and the highlighted θ–S profile curve together. Starting θ–S and Clustering is mutually exclusive, but an already displayed θ–S diagram can still be closed while Clustering runs.

Read the Display

• The vertical axis is potential temperature and the horizontal axis is absolute salinity.
• Background contours show potential density anomaly referenced to 0 dbar (σ₀). OceanGraph converts potential temperature to Conservative Temperature internally for this TEOS-10 density calculation; the plotted axes do not change.
• The selected profile line uses pressure rows with a finite temperature-salinity pair. Profiles with fewer than two pairs are omitted. Selecting another marker updates the line.

Use the diagram to compare water-mass structure and mixing patterns. For a conceptual explanation, see T-S Diagrams in Oceanography Explained.