Abstract The 2019 Mw 4.9 Wang Nuea earthquake provides a valuable case study for understanding intraplate faulting and depth-dependent seismotectonics in northern Thailand. This study integrates full-waveform inversion, aftershock relocation, and morphotectonic analysis to investigate the source characteristics of the mainshock and the distribution of associated seismicity. Results indicate that the mainshock occurred as a shallow strike-slip event on an unmapped, steeply dipping fault within the Phayao Fault Zone (PYFZ), at a depth of approximately 7 km. Aftershock focal mechanisms reveal a systematic variation with depth, including reverse faulting at shallow levels, strike-slip faulting at intermediate depths, and normal faulting at greater depth. These findings suggest a vertically stratified deformation regime, controlled by inherited structural fabrics, lithological contrasts, and variations in crustal rheology. The results are consistent with a regional stress field dominated by NNE–SSW compression in the upper crust, transitioning to an extensional regime at depth. Comparative analysis with the 2014 Mw 6.3 Mae Lao earthquake supports this depth-dependent behavior and underscores the role of crustal heterogeneity in shaping intraplate faulting in northern Thailand.
Abstract The temporal evolutions of extreme rainfall (ER) events are highly dynamic. In addition, the destructive potential of ERs is fundamentally governed by multi-dimensional metrics, including rainfall accumulation, event duration, and intra-event rain-rate evolution. However, classical ER clustering methods are based on one-dimensional metrics, therefore suffering from critical limitations and one-sidedness in characterizing ER behaviors. In this work, a novel three-stage multi-dimensional clustering framework based on intra-event rainfall dynamics is proposed to accurately capture the characteristics of regional ER behaviors. This framework identifies three distinct pre-summer ER regimes in South China (SC). Cat-1 ER occurred in mountainous northeastern SC is predominantly contributed by prolonged-duration events with flat intra-event variations and low rainfall intensities. These events are typically associated with strong synoptic forcing. Cat-3 ER concentrated in coastal areas are dominated by short-duration events with a steep intra-event evolution, intense rain rate, and mid-event peaks. These events are likely related to warm-sector rainfall under weak synoptic forcing. Cat-2 ER centered at northwestern SC and coastal areas displays a mixed characteristics of Cat 1 and Cat 3, featuring both synoptic-driven and warm-sector mechanisms. As an extension and complement to traditional ER clustering methods, this framework provides a physically interpretable, objectively categorized spatial map of the pre-summer ER morphology in SC, advancing our understanding of the heterogeneity and synoptic drivers underlying major ER regimes, and offering critical scientific references for targeted flood mitigation and early warnings in the region.
Abstract Tropical maritime regions, such as Indonesia, experience tornadoes. However, the tornado environment in Indonesia remains poorly understood. In this study, we analyzed convective and kinematic parameters associated with 119 tornado cases from 2010 to 2024. Prior to examining tornado environments, the performance of ERA5 reanalysis was evaluated against sounding observations. ERA5 tends to underestimate some parameters in tropical maritime regions, particularly low-level parameters (0–1 km) compared to mid- and deep-level parameters (0–3 km and 0–6 km). Both convective available potential energy (CAPE) and the lapse rate at 0–1 km increase prior to tornadogenesis, highlighting their importance for storm development. CAPE in Indonesia is comparable to that in the U.S. Great Plains, while LR01km is higher than in mid-latitude environments. Shear and storm-relative helicity (SRH) are lower than those observed in mid-latitude regions. Overall, thermodynamic conditions are more conducive to tornado formation in Indonesia than kinematic conditions.
Abstract Low-level jets (LLJs) significantly impact early-summer rainy season over the southeastern coast of mainland China (SECC), yet northerly LLJs over this region remain understudied compared to their southerly counterparts. Utilizing decade-long hourly ERA5 reanalysis, this study establishes a comprehensive climatology and dynamical framework for distinct LLJ types over the SECC. Climatologically, northerly boundary layer jets (NBLJs) peak in April with a shallow core (~ 975 hPa) concentrated over the central Taiwan Strait. Conversely, southerly boundary layer jets (SBLJs) and southerly synoptic-system-related LLJs (SSLLJs) peak in June. SBLJs feature a hotspot north of the strait (~ 950 hPa), while SSLLJs exhibit a dispersed, elevated dual-core structure (700–900 hPa). The driving mechanisms of NBLJs and SBLJs diverge markedly. Despite their shared dependence on low-level pressure gradient forcing, NBLJs and SBLJs develop under fundamentally different synoptic backgrounds. The former are primarily forced by cold high intrusions, while the latter are supported by the northwestern flank of subtropical high. Under the influence of midlatitude cold highs, NBLJs are exceptionally long-lived and exhibit negligible diurnal variations, which can be primarily attributed to modest land–sea thermal gradients and reduced nocturnal radiative cooling. In contrast, SBLJs develop under warm monsoonal southwesterlies and manifest a pronounced bimodal diurnal cycle. Their dominant nocturnal peak is driven by classic inertial oscillations, while a secondary late-afternoon peak is fueled by enhanced cross-shore baroclinicity and thermal winds induced by intense land–sea thermal contrasts. Furthermore, the coastal hills over southeastern mainland China serve as an effective blocking barrier under low Froude-number condition, which redirects northerly low-level flows and contributes to the formation of NBLJs. These findings enrich the conceptual framework for East Asian coastal LLJs, highlighting that NBLJs are primarily associated with synoptic cold highs and terrain blocking, whereas SBLJs are modulated by boundary-layer dynamics and local thermal gradients.
Abstract The QuikSCAT satellite radar scatterometer has observed parallel bands of negative and positive wind stress curls on the inshore and offshore sides of the Kuroshio in the East China Sea, which were not seen in other low-resolution wind products. This study assesses the impact of these small-scale wind variations on ocean simulations by comparing two numerical experiments forced by monthly climatological wind with and without this small-scale component in an eddy-resolving ocean model. By affecting the Ekman upwelling and downwelling, the wind stress curls influence the temperature structure and ocean current. The results show that these small-scale wind variations can reduce the Kuroshio velocity on the onshore side and increase it on the offshore side, accompanied by a systematic cooling of the sea surface temperature (SST) along the Kuroshio path. Although these small-scale winds are prescribed in the East China Sea, they have a significant influence on the downstream surface kinetic energy south of Japan by affecting the state of the Kuroshio. These small-scale wind variations also modulate the seasonal variability of the Kuroshio. The results of this study help to understand various ocean simulations subjected to different wind stress products.
