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Author: search.filters.author.Li, Guozhu

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    Complex Ionospheric Irregularity Echoes Observed by Low Latitude Long Range Ionospheric Radar
    (2026-01-01)
    Li, Yuxiao
    ;
    Hu, Lianhuan
    ;
    Li, Guozhu
    ;
    Ning, Baiqi
    ;
    Dai, Guofeng
    Using the Low lAtitude long Range Ionospheric raDar (LARID) at Dongfang (19.2°N, 108.8°E), Hainan Island, China, we report a unique case of complex ionospheric irregularities observed on 9 June 2024. The most interesting aspect is the first-time long-range (∼2,000 km) detection of daytime ionospheric irregularities and post-sunset band-like irregularity structures by HF radar at low latitudes. By incorporating VHF radar and global navigation satellite system (GNSS) rate of total electron content index (ROTI) observations, the radio wave propagation modes of the ionospheric irregularity events observed by LARID and evolution of these ionospheric irregularities were analyzed. The daytime ionospheric irregularity echoes observed by LARID over the Indian Ocean exhibited westward drift, evident in both echo patterns and Doppler velocities. These ionospheric echoes were likely backscattered from E region field aligned irregularities by the “downleg” of the 1-hop HF ray path. The post-sunset irregularity echoes observed by LARID over Indian Ocean manifested as a band-like structure. This structure was closely attached to the bottom of ground/sea scatter echoes and showed the same range variation as the ground/sea scatters. GNSS ROTI observation revealed that irregularities primarily appeared south of the magnetic equator and drifted eastward across the eastern longitudes in later hours. Analysis indicates that the displacement of small-scale irregularities within the equatorial plasma bubble event along the magnetic field likely contributed to the band-like irregularity structure observed by LARID and the asymmetric irregularity distribution observed by GNSS.
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    Post-Sunrise Ionospheric Irregularities in Southeast Asia During the Geomagnetic Storm on 19–20 April 2024
    (2025-08-01)
    Abadi, Prayitno
    ;
    Muafiry, Ihsan Naufal
    ;
    Pratama, Teguh Nugraha
    ;
    Putra, Angga Yolanda
    ;
    Faturahman, Agri
    We present new insights into post-sunrise ionospheric irregularities in Southeast Asia during the intense geomagnetic storm of 19–20 April 2024. By utilizing Total Electron Content (TEC) and Rate of TEC Change Index (ROTI) maps, along with ionosondes, we identified the emergence of post-sunset Equatorial Plasma Bubbles (EPBs)—plasma depletion structures and irregularities—in western Southeast Asia on 19 April. These EPBs moved eastward, and the irregularities dissipated before midnight after the EPBs covered approximately 10° of longitude. Interestingly, plasma density depletion structures persisted and turned westward after midnight until post-sunrise the following day. Concurrently, an increase in F-region height from midnight to sunrise, possibly induced by the storm’s electric field, facilitated the regeneration of irregularities in the residual plasma depletions during the post-sunrise period. The significant increase in F-region height was particularly pronounced in western Southeast Asia. As a result, post-sunrise irregularities expanded their latitudinal structure while propagating westward. These findings suggest that areas with decayed plasma depletion structures from post-sunset EPBs that last past midnight could be sites for creating post-sunrise irregularities during geomagnetic storms. The storm-induced electric fields produce EPBs and ionospheric irregularities at longitudes where the surviving plasma depletion structures of post-sunset EPBs are present.
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    Was the Unseasonal Development of Post-Sunset Equatorial Plasma Bubbles in Southeast Asia Driven by Quasi-2-Day Planetary Waves?
    (2025-03-01)
    Dai, Guofeng
    ;
    Li, Guozhu
    ;
    Otsuka, Yuichi
    ;
    Hu, Lianhuan
    ;
    Sun, Wenjie
    Previous studies suggest that the planetary waves in mesosphere and low thermosphere (MLT) could modulate the occurrence of equatorial plasma bubbles (EPBs) via altering post-sunset F layer height. Using simultaneous observations by Global Navigation Satellite System receiver networks, two ionosondes separated by about 10° in longitude, high frequency and very high frequency radars, we investigated the day-to-day variations of post-sunset F layer height and EPB occurrence in southeast Asia during the quasi-2-day planetary wave (QTDW) event in July 2023. The results showed that the post-sunset F layer height over Bac Lieu (9.3°N, 105.7°E) and EPB occurrence had a quasi-2-day (QTD) variation. However, such a 2 day variation of F layer height was confined in a very limited longitude, that is contradictory to the planetary scale characteristics of QTDW. We suggest that the QTD variations of post-sunset F layer height and EPB occurrence over the specific location were not necessarily due to the QTDW in MLT. The local seeding source, as characterized by satellite traces in ionosonde ionograms, could drive the small-scale longitudinal structure of F layer height and play an important role in shaping the QTD variation of EPB. The results implicate that the connection between planetary waves and the EPB occurrence over a specific location should be interpreted carefully, even if the day-to-day variation of post-sunset F layer height shows periodic behavior with planetary wave scale.
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    A Novel Short-Term Prediction Model for Regional Equatorial Plasma Bubble Irregularities in East and Southeast Asia
    (2025-02-01)
    Zhao, Xiukuan
    ;
    Li, Guozhu
    ;
    Xie, Haiyong
    ;
    Hu, Lianhuan
    ;
    Sun, Wenjie
    Equatorial plasma bubble (EPB) irregularities can significantly impact satellite-based communication and navigation systems. Accurate prediction of EPB occurrence is essential for mitigating these impacts. Using the GNSS receiver network and ionosonde data from East and Southeast Asia during 2010–2021, and the rate of TEC change index to characterize the occurrence of EPB irregularities, we developed a novel Spatio-Temporal deep learning model for regional EPB irregularities short-term Prediction (STEP). The model integrates the convolutional neural network and long short-term memory (LSTM) network, together with attention mechanisms, to capture both spatial and temporal features of regional ionospheric irregularities. The results show that for 5-min forecast, the STEP model achieves a root mean square error (RMSE) of 0.062 TECU/min and an R<sup>2</sup> of 0.818, reducing RMSE by 19.48% compared to LSTM and 27.06% compared to gated recurrent unit model. For 60-min prediction, the STEP model can still achieve reasonable accuracy with an RMSE of 0.110 TECU/min and an R<sup>2</sup> of 0.482, showing significant improvement over traditional models. The equatorial F layer height and regional TEC fluctuations were identified as the most critical factors for predicting the generation and duration of EPB irregularities, respectively. The spatial and temporal distributions of EPB irregularities, including their latitudinal variation and delayed onset after sunset, and the occurrence across different days in East and Southeast Asia, were well predicted by the STEP. It is expected that the STEP model would provide a valuable tool for improving the resilience of GNSS against ionospheric scintillations induced by EPB irregularities.