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In this paper, the interaction between equatorial to low‐latitude postmidnight ionospheric irregularities and large‐scale traveling ionospheric disturbances (LSTIDs) on 14 December 2015 during strong geomagnetic disturbances in China is studied by using multiple ground‐based observations. Postmidnight irregularities initiated near the magnetic equator and extended northward to higher latitudes (∼28°N) until the local early morning period (∼05 LT), which is unusual in the Northern Hemisphere winter. Multibeam observations by the very high frequency coherent scatter radar at Fuke (19.5°N, 109.1°E; dip latitude 14.4°N), Hainan Island, China, showed that the meter‐scale field‐aligned irregularities were still in the evolutionary phase during the postmidnight period (∼04 LT) instead of the fossil structures that must already be in their decay phase. Meanwhile, the emergence of the postmidnight ionospheric irregularities was accompanied by the passage of LSTIDs, as revealed by total electron content measurements. Southward and northward LSTIDs, with velocities of ∼550–570 m/s and periods of ∼80–100 min, that originated from opposite hemispheres met at ∼27°–28°N, and the LSTIDs might produce localized perturbation during their passage to initiate the instability for the postmidnight irregularity development. The height of the ionospheric F‐layer measured by the collocated Digisonde at Fuke was suggested to be modulated by the overshielding penetration electric field and storm‐related atmospheric gravity waves (AGWs). This interesting case gives insight into the important role of storm‐related AGWs in providing seeding sources for plasma bubble development and reveals unique characteristics of coupling between LSTIDs and plasma bubbles during the postmidnight sector. Key Points: Low‐latitude postmidnight ionospheric irregularities and opposite‐propagating large‐scale traveling ionospheric disturbances (LSTIDs) were observed simultaneouslyThe quasiperiodic F‐layer height uplifting might be caused by the storm‐related atmospheric gravity waves and overshielding penetration electric fieldThe LSTIDs produced localized perturbations, initiating the development of instabilities for seeding postmidnight equatorial plasma bubbles [ABSTRACT FROM AUTHOR]

Hainan COherent scatter Phased Array Radar has recorded four patches of daytime F‐region field‐aligned irregularities on 31 May 2021, and it is the first time to investigate the daytime irregularities by the radar imaging technique. In‐beam radar images are plotted on the curved plane transverse to the geomagnetic field lines. The displayed daytime irregularities present the obliquely elongated band‐like structures and the corresponding scatter regions extend to hundreds of kilometers in range and narrow to a few kilometers in the zonal direction. The diffuse and isolated structures were also observed in the radar images. The radar image sequences indicate that the irregularities were continuous in height as they drifted westward. The daytime irregularities maintained the oblique elongated structures that resemble the morphological features of the nighttime equatorial plasma bubbles. Combined with the in situ satellite measurements, these daytime F‐region irregularities are interpreted to be the remnants of the previous night's bubbles and come from the higher altitudes near the magnetic equator. Key Points: Daytime F‐region irregularities in low latitudes were detected by applying in‐beam radar imaging techniqueRadar images of the daytime irregularities exhibit narrow band‐like structures extending hundreds of kilometers verticallyThe band‐like structures are interpreted as remnants of bubbles developed on previous night [ABSTRACT FROM AUTHOR]