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The eastward‐moving large‐scale convective system associated with the Madden‐Julian Oscillation (MJO) significantly impact global weather and climate. Recent decades have seen notable changes in the MJO's lifecycle due to non‐uniform tropical ocean warming, with the roles of natural climate variability and anthropogenic influence still requiring quantification. This study examines observed and projected long‐term changes in the MJO phase speed using four twentieth‐century reanalyses and CMIP6 simulations. We find a substantial increase in MJO phase speed in three reanalyses during the twentieth century (0.6–1.2 m s⁻1 century⁻1) and further increase in MJO phase speed during the twenty‐first century (0.3–1.5 m s⁻1 century⁻1), with notable multidecadal fluctuations. We attribute the overall acceleration of the MJO to the global warming‐driven increase in the meridional moisture gradient around the warm pool while attributing the multidecadal variability in the MJO phase speed to changes in the zonal moisture gradient associated with the Pacific Decadal Oscillation. Plain Language Summary: The Madden‐Julian Oscillation (MJO) is a crucial phenomenon in the tropics that impacts weather and climate globally. Although earlier research has discussed the observed changes in the MJO lifecycle due to tropical ocean warming, we still need to understand the role of natural climate variability associated with the MJO lifecycle. This study uses twentieth century reanalyses and future climate model projections to investigate how the speed of the MJO propagation has changed over time. We find that the speed of the MJO's eastward propagation has increased significantly in three of the reanalyses during the twentieth century and continues rising in the twenty‐first century. We believe that the overall increase in MJO speed is due to global warming, which enhances the meridional moisture difference around the warm pool area. We also noted significant multidecadal variation in the MJO propagation speed. The multidecadal changes in MJO speed are linked to variations in the zonal moisture difference influenced by the Pacific Decadal Oscillation. Key Points: Increasing MJO phase speed is identified in three twentieth‐century reanalysesWe attribute the MJO's eastward acceleration to the long‐term changes in the meridional moisture gradientPacific Decadal Oscillation influences multidecadal variation in the MJO phase speed [ABSTRACT FROM AUTHOR]

This study investigates the interannual variations in regional mean sea levels (MSLs) of the northeast Asian marginal seas (NEAMS) during August, focusing on the role of typhoon activity from 1993 to 2019. The NEAMS are connected to the Pacific through the East China Sea (ECS) and narrow, shallow straits in the east, where inflow from the southern boundary (ECS), unless balanced by eastern outflow, leads to significant convergence or divergence, as well as subsequent changes in regional MSLs. Satellite altimetry and tide-gauge data reveal that typhoon-induced Ekman transport plays a key role in MSL variability, with increased inflow raising MSLs during active typhoon seasons. In contrast, weak typhoon activity reduces inflow, resulting in lower MSLs. This study's findings have significant implications for coastal management, as the projected changes in tropical cyclone frequency and intensity due to climate change could exacerbate sea level rise and flooding risks. Coastal communities in the NEAMS region will need to prioritize enhanced flood defenses, early warning systems, and adaptive land use strategies to mitigate these risks. This is the first study to link typhoon frequency directly to NEAMS MSL variability, highlighting the critical role of wind-driven processes in regional sea level changes. [ABSTRACT FROM AUTHOR]

Typhoons, fueled by warm sea surface waters, heighten concern as they increasingly interact with frequent Marine Heatwaves (MHWs) in a changing climate. Typhoon Hinnamnor (2022) weakened and re‐intensified as it approached the Korean Strait, interacting with an underlying MHW in the northern East China Sea (nECS). In‐situ observations and reanalysis products revealed a significant increase in latent heat loss from the nECS during the MHW period, contributing to the typhoon re‐intensification. Strong sea surface wind forcing with the typhoon enhanced vertical mixing and upwelling, resulting in a pronounced (0.90°C) sea surface cooling after the typhoon passage, facilitating MHW disappearance with reduced thermal stratification. During MHWs, increased background stratification increases temperature oscillations associated with semidiurnal internal tides. Furthermore, post‐typhoon changes in stratification weakened semidiurnal internal tides due to unfavorable conditions for generation from a nearby source. These findings highlight the importance of continuous time‐series observations to monitor interactions among climatic extremes. Plain Language Summary: Typhoons, powered by warm ocean waters, are causing more concern as they increasingly interact with frequent episodes of extremely warm sea conditions known as Marine Heatwaves (MHWs) in a changing climate. This study focuses on Typhoon Hinnamnor in 2022, which went through a weakening and then strengthened as it moved to the Korean Strait and encountered an MHW in the northern East China Sea (nECS). By using in‐situ data collected in the nECS and additional data analysis, we discovered a significant increase in heat loss from the nECS during the MHW, contributing to the intensification of typhoon. The powerful winds from the typhoon caused enhanced mixing and cooling of the sea surface after it passed, helping to cause the disappearance of the MHW and reduce the layering of temperatures in the ocean. During MHW, strong layering strengthens the temperature oscillation linked with the semidiurnal internal tides in the ocean. After typhoon passage there is a decrease in the layering in the ocean, thus weakening the internal tide. The study emphasizes the importance of continuous observations to understand and monitor these interactions in our changing climate. Key Points: Typhoon Hinnamnor (2022) re‐intensified after interacting with the underlying Marine Heatwave (MHW) in the East China SeaTyphoon wind‐driven mixing caused the disappearance of the underlying MHWStratification change accompanied by MHW, and typhoon reduced the local activities of semidiurnal internal tides [ABSTRACT FROM AUTHOR]

We use autonomous nitrate (NO3-), oxygen (O 2), and dissolved inorganic carbon (DIC) observations to examine the relationship between ratios of C:N:O at an upwelling site in the Southern California Current System. Mean ratios and 95% confidence intervals observed by sensors over 8 months were NO3-:O2-=0.11- ±-0.002, NO3-:DIC-=-0.14-±-0.001, and DIC:O2-=0.83-±-0.01, in good agreement with Redfield ratios. Variability in the ratios on the weekly time scale is attributable to shifts in biological demand and nutrient availability and shown to exhibit a spectrum of values ranging from near 100% New Production to 100% Regenerated Production. Key Points Chemical sensors provide a means to observe the Redfield ratios Redfield ratios vary on the weekly timescale The f ratio ranges from 100% New to 100% Regenerated Production © 2014. American Geophysical Union. All Rights Reserved.