Theory 23/Earth, Climate & Energy /Tropical meteorology
Rapid Intensification Needs an Eddy
Intensification is forecast from warm water. The warm water has to be in the right shape.
Rapid intensification of a tropical cyclone requires an ocean eddy of a critical size relative to the storm, so the event should be predicted from eddy diameter rather than from sea surface temperature.
01The evidence
Rapid intensification occurs over warm eddies and not over equally warm uneddyed water, which points to structure rather than temperature.
02The tension
Forecast models use sea surface temperature and ocean heat content, which predict intensification from how warm the water is and miss whether the storm can draw on it.
03The mechanism
A storm mixes the ocean as it passes, cooling the surface. An eddy deep enough and wide enough relative to the storm's mixing footprint resupplies heat during the passage; a thin warm layer is exhausted.
That makes the eddy-to-storm size ratio the determinant, and predicts a threshold below which the warm water does not help.
04What this is not
Those models use how much heat is available. This uses its geometry, which explains failures over thin warm layers.
05Predictions
- P1Intensification should track eddy-to-storm size ratio.
- P2Thin warm layers should not support it.
- P3Eddy diameter should predict better than heat content.
06Refutation
Rapid intensification tracking heat content at controlled eddy size would restore the thermal model.
07What it changes
It would change intensity forecasting.