Rapidly reducing carbon dioxide (CO2) levels is essential to meeting the Paris Agreement’s temperature targets. Previous assessments of CO2 removal (CDR) have primarily focused on the hysteresis and invertibility of climate change itself, overlooking quantitative analysis of potential economic impacts of climate change via CDR. In this study, we first develop a powerful neural network model, EconClimNet, trained on decades of economic data from 1,554 sub-national regions worldwide and 111 climate indices derived from the fifth-generation ECMWF atmospheric reanalysis (ERA5). Compared to popular machine learning algorithms used in the Earth science community, EconClimNet achieves superior performance in capturing the intricate relationship between climate indices and economic outcomes. On this basis, we apply EconClimNet to the outputs from idealized CO2 ramp-up and ramp-down experiments from phase 6 of the Coupled Model Intercomparison Project (CMIP6). It is found that altering climate trajectories through idealized CDR can yield significant long-term economic benefits globally, with Oceania overall positioned to experience the greatest gains with an increasing trend of about 1.41 [0.73–8.76] million USD year−1. Unequal economic effects also emerge across income levels. Rich countries see more benefits (an increasing trend of about 1.56 [0.31–6.21] million USD year−1) via CDR, mainly contributed by services (an increasing trend of about 0.03 [0.00–0.23] million USD year−1). Our findings underscore the need for governments to foster the innovation, development, and prudent deployment of CDR technologies, as well as to advance global CDR strategies that prioritize vulnerable nations from a climate justice perspective.

Abstract. Using a single‑column model, we investigate how trigger and closure treatments in ZM, TDK, and UNICON convection schemes affect DCP over China. For late-afternoon rainfall, TDK and ZM schemes with standard CAPE closure simulate precipitation peaks around noon, substantially earlier than observed. The UNICON scheme, with cold‑pool feedback deactivated, also produces a noontime peak. For nocturnal rainfall, all schemes spuriously produce a noontime peak, in stark contrast to the observed nocturnal maximum. These behaviors are closely related to closure assumptions , which is primarily governed by CAPE in ZM and TDK, and responds more directly to surface fluxes in UNICON. By accounting for the imbalance between deep convection and boundary‑layer production through specific modifications: adopting the dCAPE trigger in ZM, activating cold‑pool feedback in UNICON, and applying the non‑equilibrium closure in TDK, the simulated afternoon precipitation is delayed and in better agreement with observations. In addition, allowing elevated convection in ZM and UNICON improves nocturnal rainfall. The improved diurnal cycle is also evident in the diabatic heating fields. All modifications lead to a delayed and more pronounced upward‑tilting heating structure as a result of the suppression of early-afternoon convection, with ZM and TDK extending to higher altitudes, while both intensified and extended in UNICON. These changes alleviate the upper‑level cold bias in TDK and ZM. In UNICON, however, the overly strong convection reverses the upper‑tropospheric bias from cold to warm with stronger magnitude, thereby worsening the bias.

The seasonal evolution of tropical meridional circulation varies across regions and plays a key role in monsoon onset and rainfall migration, with important impacts on agriculture and disaster preparedness. Observations show that these transitions often occur abruptly within days. We develop a new framework to diagnose zonally asymmetric abrupt seasonal changes (ASC) in tropical circulation, using a pseudo-streamfunction (Psi pseudo) and a dual-component vector index (ASCI). Psi pseudo recovers the traditional overturning streamfunction when zonally averaged and is decomposed into rotational and divergent parts via Helmholtz decomposition. Strong ASC is found over land regions containing low-heat-inertia land area and intense deep convection, notably the Maritime Continent and South America. Unlike the zonally symmetric Hadley cell, rotational flow dominates ASC in these regions, with divergent flow contributing in regions with strong convection. These results highlight the essential role of tropical and extratropical eddies in shaping abrupt seasonal transitions in regional tropical circulation.

The Tibetan Plateau (TP) surface heating profoundly regulates the Asian circulation, but its roles in regional clouds and surface radiation budget remain unclear. Here, we investigate the impacts of the TP surface sensible heating on the surrounding Asian cloud fraction and surface radiation budget using numerical climate experiments that vary sensible heat exchange. The TP surface sensible heating, as an elevated heating source, can induce a low-level cyclone surrounding the TP and ascent over the central-eastern TP, pumping air into the middle troposphere. Consequently, spring cloud fractions significantly increase over the east TP and East China (EC) owing to the TP surface heating, enhancing cloud radiative effects and longwave radiation but reducing shortwave and net radiation at the surface, whereas the opposite changes occur over the west TP. The summer TP impacts exhibit more substantial changes in both magnitude and spatial coverage relative to spring states. Due to the coupling between the upper and lower circulations forced by the TP surface heating, increased cloud fractions extend over the whole TP in summer, with enhanced ascent and cloud radiative cooling dominated by the shortwave component. Meanwhile, cloud fractions decrease over Central and North Asia, accompanied by abnormal descent, weakened cloud radiative cooling, and minimal change in net surface radiation due to a weak offset between longwave and shortwave radiations. Our results indicate that the TP surface sensible heating significantly influences the distribution and magnitude of the surrounding Asian cloud fraction and surface radiation budget via circulation responses.

The frequency and severity of summertime synchronous extreme heat waves across the Northern Hemisphere are increasing with global warming, threatening ecosystems, economies, and human health. Understanding the spatiotemporal characteristics of these heat waves is therefore crucial. This study employs the event synchronization climate network method to objectively identify hotspot regions of synchronous extreme heat waves and their dominant synchronization patterns. It further explores the associated large-scale atmospheric circulation patterns and soil moisture feedback processes. Results show that regions including most of Europe, the western Arabian Peninsula, East Asia, Southeast Asia, and the western and southern parts of North America, as well as Greenland, are susceptible to synchronous heat waves. Notably, Southeast Asia and western North America show strong synchronization with the Caspian Sea, while East Asia and southern North America primarily synchronize with northern-central Europe. Southeast Asia-Caspian Sea and East Asia-northern-central Europe synchronization patterns are linked to wave-like anomalies suggestive of northwest-southeastward-propagating Rossby waves, whereas western North America-Caspian Sea and southern North America-central Europe synchronization patterns correspond to zonal wave trains. These circulation patterns feature concurrent anticyclonic anomalies over synchronized heat wave regions, favoring warming through adiabatic subsidence and increased solar radiation. Moreover, concurrent local soil moisture drying increases the likelihood of their co-occurrences by positive land-atmosphere feedback, which likely acts to intensify and prolong heat waves. These findings systematically map synchronous heat wave hotspots and synchronization patterns across the Northern Hemisphere, highlighting novel cross-latitudinal connections and establishing a foundation for future work to disentangle dynamic and thermodynamic influences.

East Asian cold air outbreaks (CAOs) significantly impact agriculture, industry, transportation, and other socioeconomic activities. This study employs a three-dimensional detection technique and self-organizing maps to classify East Asian CAOs into three types: northern type (NT), central type (CT), and southern type (ST). The NT features cold anomalies over northeast Asia with weak warm anomalies in southwest East Asia. The CT shows cold anomalies centered in northern China. The ST features cold anomalies over central and southern China. While the NT and CT are reasonably well simulated, models show greater difficulty in reproducing the ST. It is further found that the NT occurs under the negative Arctic Oscillation (AO) phase, which is associated with the downward propagation of stratospheric disturbances, enhancing positive geopotential height anomalies along northern Russian coast and strengthening negative geopotential height anomalies over East Asia through meridional wave propagation. The ST occurs under a positive AO background, a relationship not robustly captured. The CT occurs under the background of a shifted polar vortex, with anomalous high geopotential signals over the subpolar region propagating downward, accompanied by pronounced meridional wave activity. The ability of models to reproduce the three CAOs may be linked to their representation of meridional wave propagation in key regions and stratosphere-troposphere coupling, especially for the NT. Models with large discrepancies in these circulation features exhibit noticeable biases in East Asian CAOs.

Leveraging observational data from the TRMM-KWAJEX field campaign, which captures the evolution of mixed Rossby-gravity (MRG) waves, this study evaluates how parameterization schemes influence convectively coupled MRG waves in the Community Atmospheric Model single-column framework (SCAM). Four configurations are examined: the traditional approach that uses separate deep (ZM) and shallow (UW) convection schemes (CAM_ZMUW), unified shallow-deep convection (CAM_UNICON), unified cloud-turbulence (CAM_CLUBB), and super-parameterization (CAM_SP). While precipitation is relatively insensitive to parameterization choice, diabatic heating fields differ markedly, which shape temperature, moisture and MRG wave characteristics. All simulations capture the general eastward tilt of MRG waves, but with varying fidelity. CAM_ZMUW and CAM_UNICON produce overly strong convection, while CAM_CLUBB underestimates low-level early-phase moistening. Only CAM_CLUBB and CAM_SP reproduce the successive vertical subgrid-scale transport of moist static energy convergence, though the transport is weaker in CAM_CLUBB, whereas mass-flux-based schemes lack coherent vertical organization. Experiments combining Cloud Layers Unified by Binormals (CLUBB) with ZM deep convection behave similarly to CAM_ZMUW, indicating strong sensitivity to deep-convection scheme. Applying stricter convective triggering in ZM convection alleviates the lower-tropospheric dry bias but does not lead to an improved simulation of the convectively coupled MRG wave. The stochastic Subgrid Importance Latin Hypercube Sampler, a Monte Carlo technique designed to integrate over subgrid variability and improve estimates of its effects on microphysical process rates, has a relatively minor impact on MRG modeling in CLUBB. These results underscore the need to improve the representation of shallow-to-deep convective transitions in mass-flux schemes and to enhance the vertical subgrid-scale transport within the CLUBB framework.

Abstract. Extended-range prediction during the transitional seasons remains particularly challenging due to the volatile large-scale circulation background. This study investigates the dynamical linkages, Rossby wave characteristics, and subseasonal predictability of three successive atmospheric blocking events in May–June 2023, which contributed to severe Canadian wildfires, anomalous East Asian precipitation, and European heatwaves. The results indicate that the three blocking episodes are not independent but interconnected through downstream propagation of quasi-stationary Rossby wave energy. Spatiotemporal local diagnostics of phase speed, amplitude, and zonal wavenumber further reveal that all episodes are dominated by slowly propagating, large-amplitude planetary-scale Rossby waves in the troposphere, with zonal wavenumbers typically below the climatological zonal wavenumber. Day-to-day evolution shows abrupt transitions during blocking onset from an eastward-propagating synoptic-scale small-amplitude regime to a quasi-stationary or westward-propagating planetary-scale large-amplitude regime, with the reverse during blocking’s decaying stage. ECMWF ensemble forecasts exhibit high predictability of 500 hPa geopotential height at 15–19-day lead times, with the best performance for the Ural blocking, where skillful members capture both the amplification of wave amplitude and spatial scale. In contrast, forecasts for the Canadian and European blocking show limited growth in wave parameters and associated geopotential height. For all episodes, skillful subseasonal predictions depend on capturing upstream quasi-stationary troughs over the North Pacific or North Atlantic, potentially influenced by exceptionally high sea surface temperatures in these basins during May–June 2023. These findings underscore that the growth in both amplitude and scale contributes to forecast errors in blocking circulation, while upstream wave precursors and external boundary forcing provide key sources of subseasonal predictability for persistent blocking circulation.

Observations show that the Asian summer monsoon experienced substantial multi-decadal changes during the early 20th century, including a wetting trend over South Asia and a southward rainfall shift over East Asia. Despite their significance, these variations have received limited attention, and the underlying mechanisms remain poorly understood. This study investigates the role of increased European sulphate aerosol emissions in shaping these monsoon changes using ensemble experiments with the Community Earth System Model. The aerosol-driven rainfall patterns over South and East Asia resemble observations, suggesting that European aerosols played an important role in modulating the monsoon. These changes are linked to large-scale anomalies in surface climate and three-dimensional atmospheric circulation across the Indo-Pacific, which alter moisture transport to the continent, the main driver of the rainfall anomalies. Regional circulation anomalies form part of a hemispheric upper-tropospheric wave train originating over central Europe and extending through the Middle East to the Pacific. The wave train arises as a thermodynamic adjustment to the aerosol-induced surface cooling and related anticyclone over Europe, extends to the upper troposphere, and, while propagating eastward, induces three-dimensional circulation anomalies across Asia that affect the monsoon. These findings provide compelling evidence for the influence of European sulphate aerosols on the early 20th-century monsoon variability, which is relevant for improving current understanding of the regional-scale impacts of anthropogenic aerosols. As European SO2 emissions continue to decline, this study sheds light upon a possible ongoing and future pathway which may significantly modulate the monsoon response to Asian aerosol changes.

The Qiangtang terrane in the central Tibetan Plateau records critical evidence for understanding the early stages of plateau growth. However, the timing, mechanisms, and paleotopographic evolution of the central Qiangtang terrane remain controversial, which limits our understanding of closure of the Tethys Ocean and related uplift of Tibet. This study focuses on the Shuanghu basin of the central Qiangtang terrane, where we integrated new detrital zircon U-Pb geochronology and clumped isotope (Delta 47) thermometry. Our results demonstrate that the detrital zircon age spectra of the Eocene strata in the Shuanghu basin are dominated by populations at 240-190 Ma, 675-500 Ma and 1040-770 Ma, consistent with those from the Cretaceous strata in the same basin. This suggests a persistent sediment source from Late Triassic granitic rocks and pre-Jurassic metamorphic basements within the central Qiangtang, rather than from the northern or southern Qiangtang terranes. Clumped isotope results of ca. 90-120 degrees C indicate that the primary formation temperatures of terrestrial carbonates have been reset, precluding paleoelevation reconstruction, most likely due to recrystallization and vein formation during Neogene east-west extension. Collectively, our new data, together with existing structural, thermochronological, and magmatic evidence, indicate that the Lhasa-Qiangtang collision before the Late Cretaceous triggered widespread crustal shortening, exhumation, and outward-propagating deformation from the central Qiangtang terrane. These processes led to significant surface uplift of the central Qiangtang terrane, establishing a protoplateau prior to the Cenozoic India-Asia collision. These findings highlight the central Qiangtang terrane's role as an initial growth nucleus of the Tibetan Plateau, with its uplift predating Cenozoic continental collision.

The influence of spring surface forcing over the Tibetan Plateau (TP) on the East Asian summer monsoon (EASM) has been extensively studied, but the physical mechanism remains unclear: How could the signal of surface forcing over the TP be maintained to boreal summer? We found that both soil temperature (ST) over the TP and sea surface temperature (SST) over the western Pacific (WP) play key roles for the maintenance of spring TP forcing on the EASM. The key time scales are about 30 days for ST and 40 days for SST. The results show that the triple pattern of precipitation over eastern Asia in summer (especially in July) is highly correlated with spring TP surface forcing, characterized by surface potential vorticity (SPV) forcing as a new metric, which is different from the dipole pattern of other TP metric like the sensible heat (SH) in previous study. Further analysis suggested that TP surface forcing leads to local near-surface heating of air and warm top 0-7-cm surface soil maintaining from early June to early July. Furthermore, the TP surface forcing triggers updrafts and causes increased geopotential height at 200 hPa, stimulating a stationary wave that propagates downstream to the WP and leads to a warm-cored barotropic anticyclone over the WP. Under the high pressure, the top net shortwave radiation (TNSR) increases, heating the near-surface air temperature and leading to warm SST and seawater from 0 to 150 m below the WP, which sustain from mid-June to late July. Our study provides new evidence for the understanding of spring TP forcing on the subseasonal variations of the EASM.

Previous studies have explored the possible impact of joint El Ni & ntilde;o-Southern Oscillation (ENSO)-Quasi-Biennial Oscillation (QBO) forcings on the northern winter stratospheric circulation. This study continues to investigate the relative contributions of the nonlinearity and linearity of joint ENSO-QBO forcings in the total circulation anomaly. The possible interference of ENSO (QBO) signals within QBO (ENSO) is removed before the pure QBO (ENSO) signals in the circulation are calculated. A linear superposition of the pure QBO + ENSO signals is compared with the joint ENSO-QBO composite patterns. It is revealed that the combined ENSO-QBO effect is nearly a linear summation of the pure ENSO + QBO signals in the stratosphere, displaying strong linearity. This linearity decreases slightly from the stratosphere to the troposphere, and the nonlinearity of the joint ENSO-QBO impact increases in regional tropospheric circulation. The linearity and nonlinearity of the joint ENSO-QBO impact in the troposphere are nonuniformly distributed: Lower-to-mid latitude circulation changes associated with configured ENSO-QBO forcings are nearly a linear combination of pure ENSO and QBO signals, while nonlinearity soon dominates the total circulation anomaly pattern at high latitudes, with the ENSO signals overwhelming the QBO signals, especially for the El Ni & ntilde;o-EQBO (QBO easterly phase) configurations. This study provides evidence that linearity of the joint ENSO-QBO impact prevails in the stratosphere and tropical troposphere, while nonlinearity exists in the Arctic troposphere.

Abstract Improving the simulation of the Asian summer monsoon (ASM) precipitation pattern remains a critical challenge in global climate models, which often exhibit persistent regional biases. In this study, a targeted parameter tuning strategy is introduced to identify and optimize key physical parameters in the FGOALS‐f2 model, with the specific goal of enhancing its ASM representation quickly and economically. We employed a series of experiments that included two types of perturbed parameter ensemble (PPE) from a total of 65 parameters under a seasonal forecasting framework; more than 500 seasonal forecasting experiments were carried out, and the experiments were ultimately tested in long‐term Atmosphere Model Intercomparison Project (AMIP)‐type and Coupled Model Intercomparison Project (CMIP)‐type simulations. Our results indicate the importance of parameters in deep convection and cloud microphysics schemes, specifically governing entrainment and subgrid hydrometeor fall speeds, as the most sensitive parameters for ASM simulation. Optimizing these parameters could substantially reduce long‐standing precipitation biases over East Asia, the South Indian Ocean, and the Maritime Continent. However, our experiments also reveal a quantifiable skill limit for parameter tuning alone. The precipitation simulations for the Bay of Bengal and western Pacific exhibited persistently low skill and uncertainty. This work demonstrates that PPE experiments based on seasonal hindcasting can be used to quickly test model sensitivity to different atmospheric parameters, while the influences of different parameters are similar in most of the monsoon regions in both the seasonal hindcasting and AMIP‐type simulations.

North China frequently experiences devastating extreme precipitation events (EPEs). Upstream spatiotemporal propagation characteristics of EPEs can provide useful precursors for forecasting North China EPEs but remains poorly understood. Using climate network analysis, two dominant EPEs propagation pathways, that is, a northwestern pathway from West Siberian Plain (6-day lead) and a southwestern pathway from Tibetan Plateau (TP) (3-day lead), are identified during the warm season. The northwestern pathway is driven by an eastward-propagating mid-latitude wave train coupled with Arctic cyclone. The cyclone in the wave train drives the southeastward-propagating EPEs, and when it merges with the Arctic cyclone, its downstream anticyclone is enhanced, ultimately inducing North China EPEs. The southwestern pathway stems from quasi-stationary waves coupled with Arctic anticyclone. Interactions between anticyclone in the wave train and Arctic anticyclone generate a TP cyclone, whose intensification and eastward expansion propel EPEs northeastward and strengthen the Northeast Asian anticyclone, ultimately causing North China EPEs.

We conduct a process-oriented analysis of the summertime diurnal cycle of precipitation (DCP) over China by comparing three widely used reanalyses (ERA5, JRA-55, and MERRA-2) with satellite observations. While all reanalyses capture the observed nocturnal precipitation peak related to elevated convection, they differ substantially in simulating the daytime rainfall timing. JRA-55 and MERRA-2 better capture the observed timing, whereas ERA5 exhibits a systematic 3 h phase advance. The superior performance of JRA-55 is attributed to its gradual development of deep convection, supported by sustained heating and convective eddy transport. In contrast, ERA5 develops deep convection too rapidly, resulting in premature peaks in heating and precipitation. MERRA-2 also produces early-peaking convective rainfall, but with notably weaker intensity, suggesting that its better diurnal cycle is achieved largely through the suppression of convective precipitation. Diurnal cloud structures further corroborate these differences. Whereas JRA-55 exhibits a slowly developing, upward-tilting cloud structure from morning to afternoon, ERA5 and MERRA-2 peak earlier and have a shorter duration. The role of large-scale forcing, quantified by CAPE and dynamic CAPE (dCAPE), is further tied to the performance of the convection schemes. Results show the peak timing of dCAPE lags that of CAPE and aligns more closely with the observed precipitation. While convective precipitation in ERA5 and MERRA-2 tracks CAPE more closely, in JRA-55 it aligns better with dCAPE, thereby yielding a more realistic DCP. This contrast highlights the critical influence of triggering choice on cumulus convection.

The timing and mechanisms of surface uplift in western central Tibet remain debated due to inconsistent Eocene paleoelevation estimates. To address this issue, we integrate zircon U-Pb geochronology, stable and clumped isotope analyses, and compound-specific carbon isotope analyses from the Eocene Kangtuo Formation in the Gerze basin. Zircon U-Pb dating of interbedded andesite constrains the depositional age of the Kangtuo Formation between 48 and 37 Ma. Leaf wax n-alkane carbon isotopes indicate a relatively humid environment, comparable to other contemporaneous basins in central Tibet. The absence of a Gangdese-induced rain shadow implies that the central valley maintained an independent westerly-derived moisture supply. Furthermore, clumped isotope thermometry yields carbonate formation temperatures of 36-43 degrees C, which we interpret as reflecting a mean annual air temperature of similar to 25 degrees C after accounting for reasonable seasonal biases. Comparison with coeval low-elevation sea surface temperature records, applying a lapse rate of -4.0 to -6.0 degrees C/km, yields a paleoelevation of 1.2 +/- 0.4 km. This is independently supported by delta O-18-based paleoaltimetry, which suggests an elevation of 1.3 (+0.2/-0.1) km. Collectively, these multi-proxy results indicate that the Gerze basin stood at a modest elevation of 1.3 +/- 0.1 km during the middle-late Eocene. These findings imply that the >3 km of subsequent surface uplift after 37 Ma was primarily driven by lithospheric mantle delamination or convective removal rather than by additional crustal thickening. This study provides new constraints on the paleotopography and hydrological regime of central Tibet and offers insights into the geodynamic mechanisms of plateau uplift.

The onset of the summer monsoon marks an abrupt transition in the local annual hydrological cycle. As the earliest-established monsoon subsystem, the monsoon onset over the Bay of Bengal (BOB) not only influences early summer precipitation in the region but also plays a pivotal role in the subsequent progression of the Asian summer monsoon. Composite analysis in this study reveals that both the timing and northward propagation speed of monsoon-triggering intraseasonal oscillations (MTISOs) affect the reversal date of the upper-tropospheric meridional temperature gradient. Our results indicate that the occurrence of tropical deep convection is closely linked to Ocean–Land–Atmosphere interactions over the Indian Ocean, particularly modulated by the cross-equatorial flows (CEFs) over the BOB and the Somali region. Prior to monsoon onset, the springtime land-sea thermal contrast (LSTC) acts as a key driver, influencing the strength of the BOB-CEF and consequently the initiation of MTISO. When LSTC is anomalously stronger, the BOB-CEF can establish earlier and then promote the development of tropical convection. In Contrast, when LSTC is weaker, initiation of the MTISO is dominated by the Somali CEF. On a larger scale, diabatic-heating anomalies associated with Maritime Continent convection induce upper-tropospheric anticyclonic anomalies and further modify the vertical easterly shear over Southeast Asia, which can either promote or hinder the propagation of MTISO. In summary, anomalous monsoon onsets over the BOB are governed by a coupling process between lower-level Ocean–Land–Atmosphere interactions and upper-level circulation anomalies linked to Maritime Continent convection. This highlights the critical role of multi-scale interactions during the transitional season of the Asian summer monsoon.

Synchronous extreme heatwaves across Eurasia have become more frequent in recent decades, posing severe risks to ecosystems, society, and human health. Meanwhile, rapid Arctic Sea ice loss due to Arctic amplification has emerged as a crucial driver of extreme weather and climate events. However, its specific contribution to Eurasian synchronous heatwaves remains poorly understood. Using climate networks, atmospheric dynamic diagnostics, and numerical experiments, we revealed an interdecadal increase in the interannual relationship between Barents Sea ice and Europe-East Asian synchronous heatwaves after 2000. During 2000-2022, the persistent sea ice loss in the northern Barents Sea from late spring to summer, combined with strong land-atmosphere feedback over northwestern Europe, triggers and sustains a northwestern European anticyclone. This anticyclone disturbance, positioned north of the Eurasian subtropical jet, excites a northwest-southeastward propagating Rossby wave train in summer. Thus, another anticyclone is induced in the north of Tibetan Plateau. Together, these two anticyclones provide favorable atmospheric conditions for the occurrence of Europe-East Asian synchronous heatwaves. During 1979-1999, however, sea ice anomalies were primarily confined to the southern Barents Sea. The associated feedback processes and atmospheric circulation anomalies are too weak to excite and sustain a northwestern European anticyclone, thereby limiting the occurrence of such synchronous heatwaves in summer. These findings highlight the growing influence of Arctic Sea ice loss on midlatitude summer extremes and offer new insights into the mechanisms behind Europe-East Asian synchronous heatwaves in a warming climate.

The surface potential vorticity (PV) over the Tibetan Plateau (TP) plays a crucial role in weather and climate anomalies across eastern China. However, the drivers behind the surface PV variation have rarely been explored. Using observational, reanalysis, and model simulation data, this study examines the basic characteristics of the surface PV over the TP, then focuses on identifying the driver responsible for its interdecadal variation over the western TP during boreal winter. Results indicate that both the intensity and variability of surface PV exhibit a distinct seasonal cycle, with a minimum in the warm season and a maximum in the cold season. During boreal winter, the interdecadal variation of surface PV is thermally driven by the surface static stability, which is closely linked to the surface diabatic heating rate. Further results reveal a significant interdecadal relationship between the surface PV over the western TP and the amount of local snow. Analyses of radiation and heat fluxes demonstrate that increased snow depth enhances the upward reflection of incoming shortwave radiation, suppresses upward longwave radiation and sensible heat flux, and thereby intensifies surface diabatic cooling. This diabatic cooling strengthens the atmospheric static stability, leading to enhanced surface PV. Conversely, decreased snow depth results in the opposite situation. The validity of the proposed mechanism—encompassing snow depth, diabatic heating anomalies, static stability, and surface PV—is corroborated by numerical simulations. Beyond the albedo and hydrological effects of snow, the relationship between snow and surface PV revealed in this study introduces a new perspective: a distinct PV effect of snow.