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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]

In this paper, we first investigate the effects of a postevening Weddell Sea Anomaly (WSA)‐like plasma patch on a southwestward propagating medium‐scale traveling ionospheric disturbance (MSTID) over Xinglong, China (40.4°N, 117.6°E; Mlat. ~30.4°N). We found that some of this kind of WSA‐like plasma patches moved northward from the equatorial ionization anomaly (EIA) regions to midlatitudes, as they traveled westward into China. During 2012–2016, these plasma patches frequently occurred during the period of May–August with a monthly occurrence rate of over 20%, causing nighttime plasma density enhancements (NPDEs) in midlatitudes of China. Over 50% of these structures were accompanied by concurrent MSTID and Es. We propose that an intense polarization electric field (PEF) associated with an MSTID/Es from the more northern regions of EIA could frequently drive these plasma patches poleward. On the night of 27 June 2014 (Kp < 2−), either an MSTID and an intense Es layer (the maximum foEs >12 MHz) occurred at the onset of the poleward motion of a WSA‐like plasma patch, lending credence to this possibility. The observed plasma patch was pushed poleward to interact with the observed MSTID, causing some poleward extending C‐shaped airglow depletions/enhancements of the MSTID in a transition region where the ionosphere changed from a collapse region to an uplifted one. We attributed those poleward extending airglow depletions to the interaction between the MSTID and the plasma patch because of the secondary gradient drift instability and those of airglow enhancements to the redistribution of plasma. Plain Language Summary: This study found that postevening Weddell Sea Anomaly (WSA)‐like patchy plasma structures frequently occurred during May–August of 2012–2016 in the East Asian regions. Among these plasma patches, a small portion moved northward from the equatorial ionization anomaly (EIA) regions to midlatitudes, as they moved westward into China. On the magnetically quiet night of 27 June 2014 (Kp < 2−), such a plasma patch already moved westward and poleward to the midlatitude region of China, affecting the evolution/propagation of a southwestward propagating medium‐scale traveling ionospheric disturbance (MSTID). This paper, therefore, investigates the interaction between a midlatitude MSTID and a poleward moving WSA‐like plasma patch. We mainly investigate the possible physical mechanisms behind this kind of plasma patches and how they could affect the propagation/evolution of MSTIDs over midlatitudes of China. Key Points: Poleward extending C‐shaped airglow depletions/enhancements of MSTID were caused by interaction between an MSTID and a postevening WSA‐like plasma patchWestward and northward moving WSA‐like plasma patches frequently caused nighttime midlatitude plasma enhancements over Xinglong, ChinaAn intense PEF associated with an MSTID/Es from the more northern regions of EIA could frequently cause poleward motion of the WSA‐like plasma patch [ABSTRACT FROM AUTHOR]

The total electron content (TEC) derived from ground‐based BeiDou geostationary orbit (GEO) satellite receivers lying on both sides of the eclipse path is used to study the ionospheric variations in southern China, particularly targeting eclipse‐induced gravity waves in the ionosphere during the annular solar eclipse on 21 June 2020. Eclipse‐induced gravity waves (GWs) signatures with periods of about 70 min, from wavelet analysis, were identified on both sides of TEC observations, which are most likely to be induced in the thermosphere. However, there were significant differences in the intensity of the gravity waves on both sides of the eclipse path, gravity waves are stronger on the northern side of the eclipse path than on the southern side. Moreover, a postponement of TEC depletion shows on the northern side of the eclipse path which is caused by the convergence effect of the wind field. And at the same obstruction rate, GWs possibly can slightly adjust the postponement of TEC depletion on a small scale. Key Points: The eclipse‐induced thermospheric gravity waves are observed by BeiDou‐geostationary orbit total electron content (TEC) on both sides of the solar eclipse pathGravity waves are stronger on the northern side of the eclipse path than that on the southern side due to convergence effectsThe gravity waves on the northern side may slightly contribute to the postponement of the TEC depletion on a small scale [ABSTRACT FROM AUTHOR]

We acquired measurements of four observable parameters of refracted signals received from the ionosphere (Doppler shift, Doppler spectrum, number of rays, and signal amplitude) with the oblique HF Doppler technique in the city of Harbin during the super typhoon Lekima event of 4–12 August 2019. The ionospheric response was observed by the Harbin Engineering University multifrequency multiple path coherent radio system in the People's Republic of China. The maximum distortion of radio‐wave characteristics and ionospheric disturbances were observed to occur during the day when the super typhoon Lekima energy gained a maximum value and when the super typhoon approached close to the ionospheric part of the radio‐wave propagation paths. The magnitude of the ionospheric disturbances decreased with the distance between the super typhoon and propagation path midpoints. Both aperiodic (chaotic) and quasi‐sinusoidal disturbances were observed to accompany the action of the super typhoon in the ionosphere. The action of the typhoon was often accompanied by up to ±1.5 Hz broadening of the Doppler spectra, 10–30 dBV variations in the signal amplitude, and quasi‐sinusoidal variations in the Doppler shift with 0.10‐ to 0.40‐Hz amplitudes and periods of 20–30 to 70–80 min. The quasi‐sinusoidal variations in the signal amplitude with a ∼24‐min period, T, are due to focusing and defocusing of rays by wavelike disturbances in the electron density. The periods of the quasi‐sinusoidal disturbances were observed to be ∼12–24 min. Such periods pertain to atmospheric gravity waves. The atmospheric gravity waves generated by the super typhoon gave rise to quasi‐sinusoidal variations in the electron density with relative amplitudes of ∼3%–∼19%. Plain Language Summary: Typhoons pertain to high‐energy sources that are capable of giving rise to perturbations in all geospheres. The disturbances produced in the atmosphere and geospace make a significant contribution to the state of space weather, whereas the ionospheric perturbations have a drastic effect on the propagation of HF radio waves. We have used super typhoon Lekima, which took place during the 4–12 August 2019 period, to demonstrate some of the many disturbing influences that typhoons have on the state of space weather and the propagation of HF radio waves. The multifrequency multi path observations have been taken by the coherent radio system located at the city of Harbin (People's Republic of China). Key Points: Atmospheric gravity waves launched by the typhoon Lekima produced ∼3%–∼19% quasi‐sinusoidal electron density variationsSpectrum broadening attained ±1.5 Hz, and Doppler shift varied with 0.10–0.40‐Hz amplitudes and 20–30‐ to 70–80‐min periodsThe action of the super typhoon Lekima was accompanied by 10–30 dBV variations in the signal amplitude [ABSTRACT FROM AUTHOR]