Yuanlong Li

The coastal oceans off India are vital for the exchange of freshwater between the Bay of Bengal and the Arabian Sea. In this region, ocean salinity, as a proxy for ocean freshwater content, significantly impacts upper‐ocean stratification and air‐sea interaction and serves as a vital indicator of the regional hydrological cycle driven by monsoon circulation. Using data sets from multiple satellite missions, in situ observations, and reanalysis products, this study investigates salinity changes off the West Coast of India (WCI) from 1993 to 2023. Remarkably, we have detected a regime shift around 2013, where the trend reversed from increasing salinity to a notable freshening. A mixed‐layer salinity budget analysis reveals that this freshening is driven jointly by oceanic advection and surface freshwater flux, with advection playing a major role. These changes are linked to the recent positive Indian Ocean Dipole (pIOD) events via oceanic and atmospheric processes. pIOD events induce southerly wind anomalies near the WCI, which enhances the northward intrusion of fresh water. Meanwhile, a pIOD operates synergistically with rapid warming in the western equatorial Indian Ocean, intensifying moisture transport toward the WCI and resulting in increased local precipitation. These findings provide new insights into the mechanisms governing coastal salinity changes and their relationship to the regional hydrological cycle under the combined influence of anthropogenic climate warming and natural variability.

Orbital-scale dynamics of Indo-Pacific Warm Pool (IPWP), Earth’s dominant heat and moisture source, exert far-reaching yet incompletely understood influences on global hydroclimate. Here, by synthesizing sedimentary proxies with transient simulations, we identify a coherent, banded precipitation anomaly across the Asia-Pacific region that cannot be explained by regional dynamics alone. We show that seasonal deep convection over the IPWP excites planetary Rossby waves. On orbital timescales, their integrated effects are consistent with precessional forcing, while precession simultaneously modulates the large-scale atmospheric background state that influences their spatial organization. Guided by summer circulation, the Rossby-wave-related responses extend poleward and reorganize large-scale moisture transport and precipitation across the mid- and high-latitudes. The cumulative wave response and background-state modulation provide a robust dynamical linkage between tropical convection and extratropical hydroclimate on orbital timescales. This mechanism offers a physically consistent interpretation for how low-latitude orbital forcing imprints hydroclimate variability across Pan-Asia via planetary-wave dynamics.

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In 2024, a record-breaking marine heatwave (MHW) occurred in the East China Seas (ECSs), lasting four months and featuring consecutive 21 d periods exceeding the extreme heatwave threshold. Based on a mixed–layer heat budget analysis, this study identifies the dominant contribution of increased shortwave radiation, which is closely linked to atmospheric high–pressure anomalies. These high-pressure anomalies were established via a teleconnection pathway triggered by a series of cross-basin extremes. Specifically, extreme warming in the North Atlantic (NA), together with slightly cooler conditions in the eastern equatorial Pacific, produced a pronounced cross-basin sea surface temperature contrast. This contrast subsequently contributed to unprecedented precipitation over North Africa. These remote extremes further excited a strong wave train, ultimately leading to the record-breaking MHW. Under the background of sustained NA warming, this teleconnection pathway becomes more pronounced and continues to facilitate MHW development. This study advances our understanding of the mechanisms by which remote signals trigger MHWs and highlights the potential for increased MHW risk in a warming climate.

Employing the spaceborne observations from scatterometers (QuikSCAT and ASCAT), we quantify the contributions of different mechanisms to the Arctic MYI area changes over two decades (1999/2000–2017/2018). Specifically, the loss mechanisms (export, melt, deformation) and gain mechanism (replenishment) associated with MYI area variations are examined. On average, there was an annual (October‐September) MYI area loss of 1,080.3 × 10 ³ km ² due to export, melt, and deformation of 749.2 × 10 ³ km ² , 222.5 × 10 ³ km ² , and 108.6 × 10 ³ km ² , respectively. The substantial MYI depletion was largely offset by replenishment from the aging of first‐year ice (FYI) at the end of the melt season, which on average amounted to 993.8 × 10 ³ km ² in the Arctic Ocean. Therefore, a net annual MYI area loss of −86.5 × 10 ³ km ² emerged in the Arctic. The consecutive occurrence of the anomalously low MYI replenishment from 2005 to 2007 was responsible for the dramatic decadal decline of MYI area between the QuikSCAT (P1:2000‐2008) and ASCAT (P2: 2009–2018) periods from 3.29 × 10 ⁶ km ² during P1 dropping a half to 1.61 × 10 ⁶ km ² during P2. Moreover, the recently enhanced melt and deformation processes were favorable in maintaining the Arctic MYI at the low‐level coverage during P2 relative to P1. The thermodynamic (melt and replenishment) and dynamic mechanisms (export) related to MYI variations are linked to Dipole Anomaly (DA), whereas North Atlantic Oscillation (NAO) acts to influence the thermodynamic mechanism (melt and replenishment). On the other hand, no significant connection is identified for Arctic Oscillation (AO) or Barents‐Beaufort Oscillation (BBO).