Abstract We present an investigation of a prominent 4.8‐hr tidal wave observed at altitudes between 260 and 500 km, using data collected by the Arecibo incoherent scatter radar during March 17–20, 2015. Within this altitude range, the 4.8‐hr tide exhibits amplitudes of approximately 25 m/s, surpassing the semidiurnal tide and being twice as large as the diurnal tide. To our knowledge, this is the first report of such a strong 4.8‐hr tide. Notably, two consecutive midnight ionospheric collapses occurred on the night of March 17–18. Our analysis reveals that both the 4.8‐hr tide in the meridional wind and the zonal electric field are crucial to the generation the first collapse, while the former playing a more important role in the formation of the second collapse. The generation of the 4.8‐hr tide and the variability of the zonal electric field are likely associated with the effects of a major geomagnetic storm.

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