What is the Fujiwara effect? Explain its impact on the movement and intensity of tropical cyclones.

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Ghissu Editorial · Accepted Answer

The Fujiwara effect is the mutual rotation of two cyclones within roughly 1,400 km of each other, which bends, stalls or loops their tracks and can weaken, absorb or merge them. Typhoon Parma looped over Luzon in 2009 under Melor's influence, and Hinnamnor absorbed Gardo in 2022.

**Introduction**

The Fujiwara (Fujiwhara) effect is the interaction of two cyclones that come within roughly 1,400 km of each other and rotate around a common centre. Sakuhei Fujiwhara described it in 1921 from experiments with water vortices.

**Impact on the Movement of Tropical Cyclones**

SKETCH: flow | Stages of binary cyclone interaction
- Approach within ~1,400 km
- Capture
- Mutual orbit
- Merger or escape

1. **Mutual orbit**: The pair rotates around a common centroid, anticlockwise in the Northern Hemisphere, pulling each storm off the track its steering winds would give.
2. **Larger storm dominates**: The centroid lies near the bigger storm, so the smaller one swings around it like a satellite.
3. **Stalled and looping tracks**: Typhoon Parma (2009), held back by Typhoon Melor, lingered over northern Luzon and caused prolonged flooding.
4. **Forecast uncertainty**: Small changes in separation decide whether the pair merges or escapes, so binary storms widen track errors.

**Impact on the Intensity of Tropical Cyclones**

1. **Absorption and merger**: The dominant cyclone can draw in the weaker one's circulation, as Typhoon Hinnamnor absorbed Tropical Storm Gardo in 2022.
2. **Shear and weakening**: Outflow from the larger storm imposes vertical wind shear that disrupts the smaller one's warm core.
3. **Competition for energy**: Two storms over the same warm sea compete for heat and moisture.
4. **Occasional strengthening**: A merger can sometimes produce a larger, longer-lived system that raises the stakes for coastal warning.

**Conclusion**

The Fujiwara effect turns two cyclones into a coupled system whose tracks bend or loop and whose strength can fall or rise. Recognising it early in forecasts gives coastal populations sharper warnings and more time to prepare.

What is the Fujiwara effect? Explain its impact on the movement and intensity of tropical cyclones.

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