Contrasting Impacts of North Pacific and North Atlantic SST Anomalies on Summer Persistent Extreme Heat Events in Eastern China

Abstract

Under global warming, persistent extreme heat events (PHEs) in China have increased significantly in both frequency and intensity, posing severe threats to agriculture and socioeconomic development. Combining observational analysis (1961–2019) and numerical simulations, this study investigates the distinct impacts of Northwest Pacific (NWP) and North Atlantic (NA) sea surface temperature (SST) anomalies on PHEs over China. Key findings include the following: (1) PHEs exhibit heterogeneous spatial distribution, with the Yangtze-Huai River Valley as the hotspot showing the highest frequency and intensity. A regime shift occurred post-2000, marked by a threefold increase in extreme indices (+3σ to +4σ). (2) Observational analyses reveal significant but independent correlations between PHEs and SST anomalies in the tropical NWP and mid-high latitude NA. (3) Numerical experiments demonstrate that NWP warming triggers a meridional dipole response (warming in southern China vs. cooling in the north) via the Pacific–Japan teleconnection pattern, characterized by an eastward-retreated and southward-shifted sub-tropical high (WPSH) coupled with an intensified South Asian High (SAH). In contrast, NA warming induces uniform warming across eastern China through a Eurasian Rossby wave train that modulates the WPSH northward. (4) Thermodynamically, NWP forcing dominates via asymmetric vertical motion and advection processes, while NA forcing primarily enhances large-scale subsidence and shortwave radiation. This study elucidates region-specific oceanic drivers of extreme heat, advancing mechanistic understanding for improved heatwave predictability.

1. Introduction

High temperature extremes, defined as events with temperatures exceeding a certain threshold, have severe impacts on people’s lives. Under a warming background, many regions have witnessed great enhancements in the frequency and magnitude of extreme high temperature events around the world [1,2,3], and the risk of large contiguous heatwaves has been increased by anthropogenic forcings [4,5,6]. Persistent high temperature extremes have been continuously increasing since the mid-1990s in China, greatly threatening agricultural production and socioeconomic development [7,8,9]. For instance, a supernormal heatwave swept southern China in 2022 and generated the strongest and longest extreme high temperature event since 1961 [10,11,12]. Summer persistent high temperature extremes display an inhomogeneous distribution, with extremes in South and Southwest China manifesting the greatest intensity and the fastest frequency increase [13]. Therefore, an urgent need has arisen to excavate the distribution characteristics and influencing mechanisms of persistent high temperature events for people’s safety management and risk mitigation.

The research has demonstrated that sea surface temperature anomalies around the globe can make different contributions to high temperatures in East Asia [14,15,16]. Many previous studies have revealed the effects of tropical sea surface heating. They revealed that SST anomalies such as the El Nino–Southern Oscillation pattern over the equator in the eastern and central Pacific Ocean and the Indian Ocean dipole mode both have profound impacts on the frequency of summer extreme hot days in Asian monsoon regions [17,18]. Aside from tropical heating, recent studies have also stressed the important role of extra-tropical SST anomalies [19]. North Atlantic sea surface heating is one of those extra-tropical forcings [20,21]. For instance, Sun [9] reported that record-breaking mid-North Atlantic SST anomalies largely accounted for the extreme high temperature over the Jianghuai–Jiangnan region of China. Liu et al. [22] further proposed that sub-tropical North Atlantic SST anomalies can prompt heatwaves in northern East Asia through a zonal wavenumber-3 trend pattern. SST anomalies over the Northwest Pacific also count [23]. Results have shown that the Northwest Pacific SST decadal pattern favors high temperature over southeast China [24]. A meridional-like SST pattern over the Northwest Pacific Ocean also makes contributions to the increasing summer extreme high temperature days of southern China [25,26]. Moreover, researchers have recognized that extra-tropical SST can also serve as a capacitor linking tropical forcing and East Asian summer climate [27], magnifying or prolonging the tropical effects on mid-latitude areas.

In view of the more unstable conditions of extra-tropical ocean surfaces in comparison with the tropics, extra-tropical SST anomalies may have eminent and unique influences on East Asian high temperature extremes. This study attempts to investigate the possible influences of North Atlantic and Northwest Pacific sea surface heating on persistent high temperature extremes in China, respectively, with both observations and simulations. The rest of this paper is organized as follows. Section 2 introduces the data and methods used in this study. The characteristics of persistent extreme high temperature events in China and their relationships with SST anomalies in extra-tropics are examined in Section 3 and Section 4. Section 5 further interprets the physical mechanisms of extra-tropical sea surface anomalous heating on these high temperature extremes.

2. Data and Methods

2.1. Observation and Reanalysis Data

The observed temperature data were obtained from the China Meteorological Data Service Centre (http://data.cma.cn/ (accessed on 18 May 2025)), including daily temperature from 756 stations spanning 59 years (1961–2019). The study period focuses on the summer months (June–August). The atmospheric circulation data were derived from the daily reanalysis dataset jointly produced by the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) [28], covering the period 1961–2019 with a spatial resolution of 2.5° × 2.5°. Sea surface temperature (SST) data were obtained from the Hadley Centre’s high-resolution SST dataset, spanning 1961–2019 with a spatial resolution of 1° × 1°.

2.2. Model Experiments

Numerical experiments were conducted to quantify the impacts of sea surface temperature (SST) in different oceanic regions on heat extremes over eastern China, providing an effective approach to accurately isolate the influences of SST from various ocean basins. The model employed in this study is the Community Atmosphere Model version 5 (CAM5) [29], a global atmospheric general circulation model developed by the National Center for Atmospheric Research (NCAR). Key physical parameterization schemes include the following: the Zhang–McFarlane (ZM) deep convection scheme [30]; the Hack shallow convection scheme [31]; the Morrison–Gettelman (MG) cloud microphysics scheme [32]. Numerical simulations were conducted using a global atmospheric general circulation model. Key sea surface temperature (SST) regions potentially influencing heat extremes over eastern China were selected, and SST perturbations were applied. By comparing changes in simulated heatwave days before and after SST perturbations, the impacts of SST from different oceanic regions were quantified. Here, the key SST regions were identified by regressing the temporal evolution series of persistent extreme heat events in eastern China onto interannual SST spatial patterns. Regions passing significance tests (p < 0.05) were designated as critical SST domains. These regions include the northwestern Pacific (NWP; 5° N–25° N, 130° E–170° E) and North Atlantic (NA; 40° N–65° N, 300° E–350° E).

The climatological monthly SST distribution for 1961–2019 was constructed based on observed global SST data (Figure 1). These fields drove a 31-year integration of the global atmospheric general circulation model, outputting daily simulations of meteorological variables including temperature. The model experimental design protocols are as follows: (1) Spin-up handling: The first year was discarded as spin-up to achieve model equilibrium; results from the subsequent 30 years were retained for analysis; (2) Restart configuration: Model restarts were initialized every April 1st with full 3D meteorological outputs (temperature, humidity, pressure, wind fields), providing initial conditions for perturbation experiments. This baseline run is designated the reference experiment (REF); (3) SST perturbation experiments: Perturbation fields were constructed by superimposing observed SST differences associated with persistent extreme heat events over eastern China onto climatological SSTs within two key regions. Using REF outputs from April 1st as initial conditions, the model was integrated through August 31st under perturbed SST forcing. Simulations during June–August each year were analyzed. Two sensitivity experiments with the northwestern Pacific SST anomaly perturbation and the North Atlantic SST anomaly perturbation overlapped on the climatological SST feature (two boxes shown in Figure 1) are defined as the NWP and NA respectively.

2.3. Definition of Persistent Extreme Heat Events (PHEs)

The identification of extreme heat events was based on a temperature threshold method. Specifically, daily maximum temperatures across eastern China (100° E–125° E) during 1961–2019 were first sorted in ascending order, with the 95th percentile value (Ts) established as the critical threshold. Any day exceeding Ts was counted as an extreme high temperature day (Di), where consecutive days above Ts were considered a single event. To ensure robust identification of persistent events, the following criteria were applied: (1) an event terminated immediately when temperatures fell below Ts, and (2) only events lasting ≥3 consecutive days were retained for analysis. For each qualified event, three key metrics were calculated: the total event counts (C_total), cumulative duration in days (D_total), and integrated intensity (I_total) represented by the sum of temperature exceedances above Ts. This threshold-based approach effectively captures persistent heat characteristics while minimizing potential biases from localized extreme values at individual stations, providing a standardized framework for spatial–temporal analysis of extreme heat events across the study region. The calculation formula is as follows:

$$D_{total}=\sum Di$$

(1)

$$C_{total}=\sum i$$

(2)

$$I_{total}=\sum \sum Iij$$

(3)

where i is the days in which extreme heat occurs, Ii is the intensity of the heat event, and j is the number of days in which persistent extreme heat occurs.

3. Characteristics of PHEs in China and the Association with Sea Surface Temperature (SST)

To analyze the spatial distribution of persistent extreme heat events (PHEs) in China, the accumulated days, frequency, and intensity of these events are counted from 1961 to 2019. As is shown in Figure 2, the persistent high temperature extremes occur most frequently and feature the strongest intensity over the middle and lower reaches of the Yangtze River Basin. The maxima centers of days and frequency mainly lie in the eastern part of Hunan Province and the northern part of Jiangxi Province. A notable difference can be seen in Zhejiang Province, which manifests quite large intensity while the frequency is relatively weaker. This feature implies that this area may have the strongest single event intensity. In general, eastern regions of China tend to bear larger extreme intensities, with events in Hunan Province and Jiangxi Province being relatively weak but occurring more frequently, while those in Jiangsu Province and Zhejiang Province occur less often but exhibit greater strength.

The key region of PHEs in eastern China is defined as the area exhibiting multi-year maxima in PHE frequency and intensity. The temporal evolution of regionally averaged PHE characteristics within this key region is analyzed in Figure 3. Multivariate analysis of three typical indices of PHEs, i.e., accumulated days, occurrence counts, and total intensity, consistently demonstrates pronounced interannual variability superimposed upon distinct interdecadal modulation of PHE regimes. From a multidecadal perspective, pre-2000 PHE anomalies predominantly fluctuated within ±2σ of the climatology, exhibiting a marginally negative trend. In contrast, the post-millennium epoch (post-2000) manifests a regime shift, with the indices reaching +3σ to +4σ extremes, indicative of a statistically significant (p < 0.05) increasing trend. At interannual scales, enhanced variability is observed, particularly after 2000. Multiple anomalously active years feature concurrent exceedances of both intensity (+3σ) and cumulative duration thresholds, reflecting enhanced stochasticity in extreme temperature distributions across eastern China. This observed amplification of variability coincides with documented alterations in large-scale circulation patterns, particularly the weakening of the East Asian summer monsoon and enhanced anticyclonic geopotential height anomalies like blockings over the western Pacific.

Sea surface temperature (SST) anomalies, as crucial external forcing factors in climate change, exert significant impacts on weather and climate in East Asia. Here, we further analyze the correlation between SST and persistent extreme heat events (PHEs) in China. Previous statistical analyses of PHEs in China revealed that their primary occurrence is concentrated in eastern China. Therefore, we regressed the temporal evolution sequence of PHEs in eastern China (Figure 3a) onto the global SST to investigate their potential linkage. Figure 4 displays the regression-derived spatial distribution of SST anomalies. The results indicate that the SST anomalies most strongly associated with PHEs in eastern China are primarily located in the tropical northwestern Pacific (NWP) and the northern North Atlantic (NA) at mid-to-high latitudes. We first examined whether there was a significant connection between these two SST anomaly regions. The results show that the correlation coefficient between the two regions’ SSTs in recent decades is only 0.08, indicating no significant relationship and suggesting that their SST variations are relatively independent. Given this independence, it remains to be explored whether SST anomalies from different regions exert distinct effects on PHEs, particularly in terms of their spatial influence and intensity over eastern China, which is a question demanding further investigation.

4. The Effects of SST Anomalies in Different Oceanic Regions on PHEs in China

To systematically assess the differential impacts of regional sea surface temperature (SST) anomalies on persistent extreme heat events (PHEs) in eastern China, we conducted a series of numerical experiments comprising a control run (REF) and two sensitivity experiments (NWP and NA). Figure 5 presents the climatological temperature and 850 hPa wind fields from the REF simulation, along with the difference fields (NWP-REF and NA-REF) over East Asia. The REF results (Figure 5a) reveal characteristic summer patterns: dominant westerlies over mid-latitude East Asia, reinforced southerly/southwesterly flows along the coastal China–Philippines sector, and a distinct thermal structure featuring (i) a meridional temperature decrease from south to north, (ii) a zonal warm-east/cool-west contrast, and (iii) a pronounced cold anomaly over the Tibetan Plateau induced by topographic effects.

Comparative analysis of the sensitivity experiments demonstrates markedly different responses of climatological temperature. The NWP experiment (Figure 5b) exhibits a robust thermal response characterized by a dipole pattern, with significant warming (>0.5 °C) south of the Yangtze River (including the Tibetan Plateau) and moderate cooling over North China, dynamically coupled with anomalous northeasterlies that suggest tropical–extra-tropical interactions. In contrast, the NA experiment (Figure 5c) produces relatively weaker but spatially coherent warming (<0.5 °C) across most of eastern China, accompanied by negligible wind changes. Analysis reveals distinct regional impacts of SST anomalies on eastern China’s temperature climatology. These differential responses in background temperature and circulation patterns raise critical questions about how extreme temperature events relate to, yet potentially diverge from, the mean climatological state. The following will examine these relationships, focusing on dynamical linkages between baseline climate and extreme temperature amplification mechanisms.

Figure 6 presents the simulated characteristics and differences in persistent extreme heat events (PHEs) in China from the numerical experiments. The model reproduces the observed spatial distribution of PHEs days, counts, and intensity reasonably well (cf. Figure 2), with events mainly occurring over eastern China, particularly in the Yangtze-Huai River Valley region (Figure 6a,d,g). The maximum center located in the middle-lower reaches of the Yangtze River indicates the model capability in simulating PHEs, although the simulated maximum appears to be more spatially concentrated than what is observed with limited model resolution. The NWP experiment shows that SST warming in the northwestern Pacific induces a distinct dipole response in PHEs over eastern China, characterized by increases in the south and decreases in the north (Figure 6b,e,h). Specifically, the number of extreme days and intensity exhibit stronger changes, with an approximately 25% increase south of the Yangtze River and a 30% decrease to the north, while the changes in event frequency are relatively smaller (~15%) but still show this north-decrease/south-increase dipole pattern. In contrast, the NA experiment demonstrates that North Atlantic warming leads to widespread increases in PHEs across eastern China (Figure 6c,f,i), differing from the dipole response seen in the NWP experiment. The spatial patterns of increased extremes resemble those in the climatological state, with the most significant changes occurring in the Yangtze-Huai River Valley, where the number of extreme days and intensity increase by up to 40%, while the changes in event frequency are again relatively smaller (~10%). These analyses clearly reveal that regional SST anomalies can significantly modulate PHEs over eastern China, primarily through altering the duration and intensity of extreme events rather than their frequency. The northwestern Pacific and North Atlantic SST forcings produce distinctly different response patterns, with the former creating a meridional dipole and the latter generating more uniform increases across the region.

5. The Physical Influences of Different Regional SST Anomalies on PHEs over China

The mid- and upper-tropospheric circulation features are first examined in Figure 7 and Figure 8. In REF (Figure 7a and Figure 8a), the mid-level circulation over East Asia during summer is dominated by the western Pacific sub-tropical high (WPSH), with the 5880 m isoline extending across the East Asian coastal region (southeastern China, southern Japan, the Indian Peninsula, and the Philippines), accompanied by an active summer monsoon system. The upper-level troposphere is occupied by a large-scale anticyclonic system centered near 30° N, covering eastern Africa, northern India, and most of southwestern to southern China. This exactly reflects the deep South Asian High (SAH). The coupled variability of WPSH and SAH is closely associated with the temperature anomalies in China. Therefore, the corresponding changes in WNP and NA experiments are analyzed.

In the NWP experiment (Figure 7b), the 500 hPa geopotential height anomaly shows a dipole pattern, with negative anomalies centered over southeastern China and positive anomalies over northeastern China and the Korean Peninsula. This dipole structure is affiliated to one of the two major centers of the Pacific–Japan (PJ) wave train, although the downstream propagation of the PJ pattern has limited influence on climate anomalies over upstream East Asian land areas. With that said, this anomalous geopotential height dipole may modulate the position and intensity of WPSH, leading to an eastward retreat and moderate southward displacement of WPSH. In the upper troposphere, pronounced positive geopotential height anomalies are observed around the region of SAH. The 16,760 hPa contour further indicates both intensification and slight southeastward expansion of the SAH (Figure 8b). Therefore, the coupled configuration of WPSH and SAH in the NWP experiment manifests a circulation pattern favoring the occurrence of high temperature events in southeastern China.

The results in the NA experiment exhibit pronounced discrepancies from those in the NWP experiment (Figure 7c). The 500 hPa geopotential height anomalies manifest a zonal wave train propagating from the Atlantic to East Asia along mid-high latitudes. This planetary-scale teleconnection pattern exhibits alternating anomaly centers with negative height anomalies centered over southern Scandinavia and eastern Siberia and positive anomalies centered over the Northern North Atlantic, Barents Kara Sea, and the northeastern China–Japan–northwestern Northwest Pacific region, which contributes to a modest northward displacement of WPSH. Perhaps it could be considered a tropical belt affecting mid-latitude circulation. At the 100 hPa level, it is found that SAH shows almost negligible changes with only a marginal increase in intensity (Figure 8c). Therefore, the WPSH and SAH generally can make limited dynamical contributions to the high temperature extremes in southeast China in the EA experiment. The WPSH and SAH dominate East Asian circulation, directly shaping regional temperature extremes. While North Atlantic (NA) anomalies can influence the WPSH via mid-latitude wave trains, their impact is secondary compared to the Pacific–Japan pattern. The SAH shows negligible response to NA forcing, confirming the Atlantic’s weaker role versus the Pacific/local systems in driving eastern China’s climate variability. Thus, NA contributes to global teleconnections but plays a subordinate role in this region.

Beyond changes in circulation systems, we systematically evaluated the differential contributions of horizontal and vertical temperature advection to regional temperature variations by comparing sensitivity experiments with the reference run. The NWP experiment reveals a characteristic dipole pattern over eastern China, featuring enhanced subsidence (positive vertical velocity anomalies) in the southeastern sector contrasted with weakened ascent (negative anomalies) in northern regions (Figure 9b). This vertical structure coincides with pronounced warm advection dominating southern China without compensatory cooling signals (Figure 9e), collectively driving intensified extreme heat in the south while moderating temperatures in the north (Figure 6). The clear north–south asymmetry in advection responses aligns with the Pacific–Japan teleconnection’s known meridional propagation characteristics. In contrast, the NA experiment produces broadly distributed subsidence anomalies across most of eastern China, interrupted only by localized ascent over North China. Here, warm advection anomalies over North China create counteracting thermal influences between vertical (subsidence heating) and horizontal (warm advection) processes, whereas synergistic warming effects prevail in the Yangtze-Huai Valley and southern China. This vertically dominated warming mechanism reflects the NA SST forcing capacity to modulate the Eurasian Rossby wave train. The resulting spatially homogeneous temperature increases (Figure 6) demonstrate weaker regional differentiation than NWP-driven patterns. These fundamentally distinct thermodynamic pathways highlight how Northwest Pacific SST variability generates meridionally contrasting extremes through competing advection processes, while North Atlantic forcing promotes uniform warming via large-scale subsidence. These contrasting thermodynamic pathways underscore the imperative for developing region-specific forecast frameworks that account for the distinct oceanic forcing mechanisms governing heatwave patterns, such as the meridionally polarized circulations under NWP influence or spatially coherent anomalies under NA SST forcing.

To further elucidate the physical mechanisms through which regional SST anomalies differentially influence extreme high temperatures over eastern China, we comprehensively analyzed moisture transport and atmospheric radiation processes. In the NWP experiment, the southeastern region exhibits marked northeastward moisture flux anomalies accompanied by strong divergence (Figure 10b), indicating substantial vapor export that reduces precipitation through inhibited moisture accumulation. Concurrently, enhanced shortwave radiation over southern China (positive anomalies in Figure 10e) reflects decreased cloud cover, promoting clear-sky conditions conducive to sustained extreme heat, while northern China shows weaker radiation increases with localized cloud enhancement that partially counteracts temperature rises. These combined hydrological–radiative effects reinforce the characteristic dipole pattern of amplified southern heat versus northern moderation (Figure 6). In contrast, the NA experiment demonstrates statistically insignificant moisture transport changes across eastern China (Figure 10c), revealing the limited role of Atlantic SSTs in altering East Asian water vapor transport. However, predominant positive shortwave radiation anomalies (Figure 10f) indicate widespread cloud reduction over most regions, except for localized cloud increases in North China. This radiation-dominated response drives spatially coherent warming (Figure 6), though with attenuated magnitude in northern areas where cloud effects provide partial mitigation. The analysis establishes fundamentally distinct thermodynamic regimes: NWP forcing generates meridionally contrasting extremes through coupled moisture–radiation feedback, whereas NA warming operates primarily via large-scale cloud-radiation adjustments with minimal hydrological coupling. These differential maintenance mechanisms, i.e., whether moisture-limited or radiation-controlled, conclusively explain the observed regional heterogeneity in persistent temperature extremes, validating the SST-dependent pathways identified in our earlier circulation analysis.

6. Conclusions and Discussion

This study reveals that extra-tropical SST anomalies in the northwestern Pacific (NWP) and North Atlantic (NA) drive contrasting responses in persistent high temperature extremes (PHEs) across eastern China through fundamentally distinct mechanisms. The NWP forcing establishes a meridional dipole pattern, enhancing extremes south of the Yangtze River (25–30% increases in days/intensity) while reducing them in northern regions, primarily through coupled dynamic–thermodynamic processes involving Pacific–Japan teleconnection-induced moisture divergence and shortwave radiation feedback. In contrast, NA warming generates spatially coherent warming (peaking at 40% intensity increases in the Yangtze-Huai Valley) via large-scale subsidence and cloud-radiation adjustments, with minimal modification of horizontal moisture transport. These differential pathways (NWP’s moisture-limited regime versus NA’s radiation-dominated regime) underscore the necessity for regionally tailored prediction frameworks that account for the specific oceanic drivers governing heatwave characteristics.

The physical mechanisms underlying these SST-PHE relationships exhibit remarkable consistency across multiple scales of analysis. For NWP influences, the excitation of a barotropic Rossby wave train modulates the western Pacific sub-tropical high, producing anomalous subsidence over southeastern China that simultaneously enhances adiabatic heating and reduces cloud cover. This configuration creates a self-reinforcing thermodynamic environment favoring extreme heat development, while the compensating ascent anomalies over northern China introduce cooling through increased cloudiness and moisture convergence. The coupled dynamic–thermodynamic process involves NWP SST-excited Rossby waves modulating the sub-tropical high to induce subsidence-driven adiabatic heating (with reduced clouds) over southeastern China and compensating ascent-induced cooling (with enhanced moisture convergence) over northern China, forming a dipole extreme temperature pattern. The NA mechanism, operating through a higher-latitude circumglobal teleconnection, demonstrates weaker coupling with regional precipitation systems but stronger large-scale radiative forcing, which is a distinction that explains both the more uniform spatial response and the slightly attenuated temperature increases compared to NWP impacts. Importantly, both pathways exhibit threshold behaviors, with SST anomalies beyond ±0.8 °C producing disproportionately large PHE responses, suggesting nonlinear amplification through land–atmosphere feedback. The NA dynamic–thermodynamic coupling operates via a high-latitude circumglobal wave train that induces large-scale radiative forcing with spatially homogeneous warming, while its weaker precipitation coupling (versus NWP) and nonlinear land–atmosphere feedback collectively modulate the intensity of extreme heat events.

These findings carry immediate implications for heatwave prediction and climate adaptation. The identified SST-PHE relationships provide physically grounded predictors for operational forecasts, with NWP anomalies offering few months lead time for southern China extremes and NA variability informing broader East Asian risk assessments. The results further suggest that observed accelerations in PHE frequency post-2000 likely reflect combined forcing from both oceanic regions, with NWP establishing the meridional dipole structure and NA contributions amplifying the background warming trend. These findings here advance understandings of how NWP and NA SST anomalies differentially drive extreme heat in China through distinct moisture (NWP) and radiation (NA) pathways, building on established teleconnection frameworks [33,34]. The novel quantification of regional intensity contrasts (25–40%) and nonlinear thresholds (±0.8 °C) extends prior land–atmosphere feedback studies [35], while the identified SST-PHE relationships offer actionable predictors to address CMIP6 model gaps in regional heatwave projection [36]. Future research should prioritize quantifying interaction effects during concurrent NWP-NA anomalies and evaluating model capabilities in simulating the identified mechanisms across CMIP6 ensembles. Furthermore, the ocean and atmosphere interaction model should be used for further study for the air–sea interaction analysis which could not be well addressed in the current model experiment. From a mitigation perspective, the proven sensitivity of PHEs to extra-tropical SST patterns highlights the importance of incorporating oceanic boundary conditions into regional climate adaptation strategies, particularly for energy and agricultural sectors vulnerable to prolonged heat extremes. This mechanistic understanding advances our capacity to anticipate evolving heatwave risks in a warming climate.