An idealized model is used to examine the driving influence of localized tropical convection on the wintertime subtropical jet. To avoid preferred convective regions, and instead focus on the response to spontaneously occurring convection, the model is run with fixed, zonally symmetric sea surface temperatures under perpetual solstice conditions. A combination of three complementary analyses is used here: 1) a zonal recentering of the daily data around the longitude of maximum tropical diabatic heating to allow a focus on the strongest convective events, 2) a lag regression onto tropical diabatic heating to examine the time evolution of the circulation response to convection, and 3) an idealized experiment with a switch-on tropical diabatic heating perturbation designed to mimic deep convection. The qualitative picture that emerges suggests that deep convection in the summer hemisphere drives an anomalous localized Hadley cell that crosses into the winter hemisphere and drives a locally strengthened subtropical jet downstream via advection of angular momentum. A key feature associated with this picture is a "pocket" of reduced and homogenized angular momentum through which the local cross-equatorial Hadley cell flows. Momentum fluxes associated with both the divergent overturning circulation and rotational eddies drive this pocket, thus highlighting the complexity in interpreting the angular momentum budget due to the inherent zonally asymmetric and temporally varying nature of tropical convection and associated Hadley cell. Overall, the zonal-mean tropical circulation can be considered a superposition of times and regions with strong convective activity and thus a locally strengthened Hadley cell and subtropical jet, as well as times and regions with weak convective activity. SIGNIFICANCE STATEMENT: This study examines how localized and temporally varying tropical deep convection in the summer hemisphere leads to the formation of a winter hemisphere subtropical jet, given that traditional theories cannot take such space-time inhomogeneities into account. Using targeted idealized experiments and methodologies, we examine the mechanisms at work and find a robust qualitative picture: The longitudinally averaged tropical-subtropical circulation can be considered as an accumulation of times and regions with strong convection and associated circulation, as well as periods with weak convection.

The paper discusses a novel method to diagnose and investigate Rossby wave resonance along a circumglobal midlatitude jet with particular focus on the meridional wave structure. As a framework, the linearized inviscid barotropic vorticity equation is considered on a zonally periodic beta-plane. Zonally symmetric Gaussian-shaped westerly jets of varying amplitude and width are specified as basic states. The system is forced by pseudo-orography with small meridional extent, being located at jet latitude and varying sinusoidally in the zonal direction. Stationary solutions are obtained through straightforward numerical methods. The strength of resonant amplification is diagnosed by systematically varying the zonal wavenumber s, plotting the resulting wave amplitude as a function of s, and quantifying the sharpness of its peak (if existent). The numerical solutions for jet-like basic states are interpreted by reference to analytical solutions obtained for more idealized model configurations. The analysis indicates that a jet with realistic amplitude and width may be subject to a weak form of resonance. Given that the zonal scale of the jet is much larger than its meridional scale, one may expect resonance at no more than one zonal wavenumber sres. The single resonant peak is associated with the first meridional mode, which is established through partial reflection of wave activity at the periphery of the jet flanks. The leakiness of the waveguide implies that the wave amplitude remains finite at the resonant wavenumber even for inviscid wave dynamics. The behavior is very similar as in the classic Charney-Eliassen model, where the channel width must be chosen appropriately and where damping simulates the leakiness of the jet.

The mid-latitude atmospheric circulation is often described as a combination of low-frequency variability, such as weather regimes (WRs) that can persist for weeks, and high-frequency variability, including synoptic systems that shape our daily weather. In the North Atlantic, regimes such as the North Atlantic Oscillation influence the jet stream and affect surface climate. Here we investigate the dynamics governing the interaction between these timescales, and how it is mediated by Rossby Wave Breaking (RWB) events. A simplified equation is derived to explore which processes contribute to RWB through a meridional overturning of high-frequency potential vorticity, providing a dynamical recipe for when and where wave breaking occurs. We show that slowly varying regimes steer the tracks of high-frequency systems, which in turn determine whether the frequency of cyclonic or anticyclonic RWB is enhanced or suppressed. The recurrence of same-type RWB in a similar position can ultimately shape the mean structure of WRs. By linking the structure of WRs to the dynamics of wave breaking, our framework provides a dynamical basis for interpreting variability in midlatitude circulation.

The past few decades of work on stratosphere-troposphere teleconnections have unearthed a variety of different time scales of both upward and downward propagation and their connection to weather at the surface. In an attempt to identify significant patterns of covariance between the surface and the stratosphere without imposing an expected pattern or time scale, we apply maximum covariance analysis (MCA) with a variable time lag between pairs of tropospheric and stratospheric fields. Using over 60 years of ERA5 reanalysis for Northern Hemisphere winters, we use MCA to pick out the time lags and patterns corresponding to the largest covariance between the surface and the stratosphere. By applying new methods to an existing problem, we both verify certain results from previous literature and unearth new insights into the nature of stratosphere-troposphere teleconnections. We find that the greatest covariance occurs when the surface precedes the stratosphere by up to 9 days, corresponding to a sea level pressure anomaly with one pole over the Gulf of Alaska and another over the Ural blocking high that is followed by changes in stratospheric potential vorticity, zonal wind, and Eliassen-Palm (EP) flux. We find evidence for a downward influence of stratospheric potential vorticity and zonal wind on sea level pressure at a time scale of 3-4 days, with a secondary influence from zonal wind alone at 2-3 weeks. The downward influence is characterized by a weaker (stronger) polar vortex followed by anomalously high (low) sea level pressures over the Arctic Ocean, but it does not produce an appreciable anomaly in minimum surface temperatures.

The North Atlantic-Mediterranean region hosts a complex interplay of two storm tracks, linked by multiple weather systems interacting across scales, such as the interplay of low-level cyclones and anticyclones with upper-level Rossby waves. Compared to the well-known inherent cyclogenetic properties of the Mediterranean itself, the role of cross-basin processes, mainly from the North Atlantic, in shaping Mediterranean cyclones remains insufficiently understood. In this study, we use the local wave activity (LWA) framework, applied for the first time to the Mediterranean, for quantifying the relative cyclogenetic contributions of physical processes within and outside the basin, and to assess their impact on cyclone characteristics. Our analysis shows that the waviness of the North Atlantic atmospheric flow enhances the frequency of Mediterranean cyclones and the occurrence of the upper-level streamers that drive them. Eddy momentum flux divergence over the northern Mediterranean coast, combined with local baroclinic LWA sources, plays a central role in cyclone dynamics, affecting storm trajectories and precipitation on subseasonal to monthly time scales. On a broader scale, our analysis demonstrates how wavy flow propagates from the North Atlantic into the Mediterranean basin, transforming throughout the process over the course of 5-10 days. The novel application of the LWA perspective establishes a new dynamically grounded framework for analyzing Mediterranean cyclogenesis and the physical processes that drive it. It also provides new insights into the cross-basin interactions that shape cyclone development, with potential implications for extreme winters and future climate trends in the basin. SIGNIFICANCE STATEMENT: In this work, we study how the waviness of the atmospheric flow and its underlying drivers influence Mediterranean cyclones and their associated rainfall. We use local wave activity, a quantitative framework that has never been applied to the region, to distinguish between local and remote dynamical contributions to storm life cycles. We identify two key processes: highly energetic air from higher latitudes reaching the Mediterranean and local interactions between upper and lower atmospheric levels. Through this novel application, it is shown that specific fluxes of wavy flow contribute to Mediterranean cyclone track variability and rainfall on time scales from 10 days to months, offering new insights into regional storm dynamics and their cross-basin drivers.

Abstract. Resonant amplification of Rossby waves along a circumglobal jetstream was recently hypothesized as the underlying mechanism for the occurrence of extreme weather in observed episodes with large wave amplitudes. An important part of the argument is based on refractive index theory in the framework of the linear barotropic model. The approach makes a number of assumptions and approximations with the goal to diagnose the existence of a zonal waveguide and, hence, the potential for Rossby wave resonance. The current paper compares this approach with a recently developed direct numerical method that makes no further assumptions given the chosen framework and is, hence, considered as more trustworthy. The comparison indicates that the occurrence of waveguides as diagnosed from the refractive index method is both qualitatively and quantitatively inconsistent with the occurrence of resonance in the direct numerical method. It is concluded that the previously-used waveguide diagnostic is not a reliable basis for detecting Rossby wave resonance. The code for the direct numerical method is publicly available to encourage its use in future applications.

Diabatic heating due to latent heat release in the storm tracks plays an important but poorly understood role in the maintenance of the zonal-mean midlatitude circulation. To examine how the midlatitude circulation is maintained in the presence of diabatic heating on either side of the jet, a dry model is used to apply mid-tropospheric perturbations to the radiative equilibrium temperature profile to which the model is relaxed, constituting an intermediate step between an externally-imposed diabatic heating and a setup that allows for full diabatic feedbacks. By applying transient switch-on perturbations at various latitudes, the mechanisms by which an equilibrated state is reached are examined. In all cases, the equilibrated circulation exhibits a dynamically-stable structure where the eddies maintain a region of concentrated baroclinicity, latitudinally shifted away from the region of the heating perturbation. However, the initial response is generally very different. When the heating is poleward of the jet, there is an initial thermal-wind adjustment to the heating and weakened eddy heat fluxes, followed later by weakened eddy momentum fluxes aloft that maintain an equilibrated equatorward shift of the jet. Conversely, when the heating is equatorward of the jet, the evolution is more complex with an initial strengthening of the eddy heat fluxes and a weakening of the Hadley cell to balance the heating, in addition to a thermal-wind adjustment that immediately modifies the critical latitudes and thus, the eddy momentum fluxes. These momentum-flux changes encourage a poleward propagation of the anomalies from the subtropics to midlatitudes over 40 days, where they straddle the jet and ultimately yield an equilibrated poleward jet shift. When the heating is at the jet core, the circulation simply weakens rather than exhibiting any latitudinal shift. These mechanisms of self-concentration of the baroclinicity are discussed and compared with previously proposed mechanisms of jet self-maintenance.

Large-amplitude jet stream undulations, central to impactful phenomena such as blocking, sudden stratospheric warmings, and extreme weather, have been suggested to occasionally occur as a result of resonant amplification. A barotropic b-plane model with a constant zonal-mean flow is often used to test this. We examine the effect of the meridional leakage of the wave activity to the subtropics on the quasi-resonant response to a meridionally localized, pure zonal wavenumber forcing. The main novelty of our analysis is the formulation of a leaky boundary condition and the derivation of an analytical solution, which we use to quantitatively examine the effects of a specified amount of waveguide leakage, and compare it to the effects of damping. We further examine the effects of leakage on the resonance of a meridionally concentrated jet, through numerical simulations that include a carefully constructed sponge layer to the south of the jet waveguide. We find that meridional leakage weakens the amplification and zonal-phase change across resonance, similar to what damping does. Leakage also affects the horizontal wave structure equatorward of the forcing, by introducing a westward phase tilt toward the subtropics. Damping, on the other hand, makes the amplitude of the wave decrease away from the forcing on its both sides with only a minor phase tilt. Overall, it is concluded that even quite a large wave leakage toward the equator does not necessarily preclude the possibility of quasi-resonant amplification, but earlier estimates which ignore this leakage by assuming two fully reflecting turning latitudes overestimate the effect by a considerable margin.

Equatorial superrotation is a striking feature in planetary circulations, also found in atmospheric circulation models. Geological evidence shows that Earth was in a state of super-rotation during the Eocene and Pliocene. On Earth, such a time period of super-rotation is sometimes referred to as permanent El Niño. While it is well established that a tropical wave source is needed for superrotation, the mechanism that provides this wave source, and what conditions allow it to be maintained are still not understood, and vary between different models. Specifically, in shallow water models with Earth like parameters, superrotation has only been found when relatively strong thermal damping was added. In this study we examine the spontaneous evolution of super-rotation in fully developed isotropically forced two-dimensional moist shallow-water turbulence, and examine the role of moisture by varying the strength of moisture coupling, and performing large ensembles of simulations. We find that while the dry runs exhibit both superrotation and sub-rotation, with spontaneous transitions between the two states, moisture results in all runs eventually reaching a stable superrotating state. We further find that a stable superrotation develops in the dry runs when we strengthen the thermal damping. We find that a meridional mass flux from the equator to the subtropics, develops in the runs with stable superrotation, and examine the role of this mass flux, which is enabled by the latent heating and the thermal damping, for the maintenance of the stable superrotation.

The winter-long merging of the African and Atlantic jets during 2009–2010 was associated with extreme winter weather across the Northern Hemisphere. Past studies have shown that merging of these two jets is linked to weaker Atlantic eddy activity and stronger tropical heating, and is strongly correlated with a negative North Atlantic Oscillation (NAO) state. Here, we examine the relationship between jet merging and extreme weather, taking care to separate out the effects of the NAO and El Niño, in order to be left with the added influence of Atlantic–African jet merging. Our analysis, which examines percentile exceedance and anomaly composites of surface temperature, surface wind, and precipitation, identifies distinct weather signatures of merged-jet winters, notably affecting the Iberian Peninsula, North Africa, the southern Mediterranean, southwest Greenland, and Northern Europe. Additionally, we analyze the relationship between merged jets and shifts in cyclone track orientation contributing to the observed extreme weather patterns over these regions. Furthermore, once we remove the NAO effect from the merged-jet surface temperature anomaly signal, we find that winter-long jet merging coincides with anomalously warm Arctic, cold Eurasian, and strong El Niño conditions. The resulting weaker high-latitude temperature gradient is consistent with a weakening of eddy activity and, alongside stronger tropical heating, is thought to ultimately lead to persistent jet merging. This is consistent with previous theoretical work suggesting that reduced midlatitude baroclinicity and stronger tropical heating result in a transition from coexisting thermally driven subtropical and eddy-driven midlatitude jets to one with a single mixed eddy–thermally driven jet. This provides further evidence that Atlantic–African jet merging constitutes a dynamical regime transition of the Atlantic jet.

Several large scale circulation patterns have been identified in relation to extreme Northern Hemisphere summer heatwaves. Three main ones are a double jet over Eurasia, a positive phase of the summer northern annular mode, and a quasi-wave-3 geopotential height anomaly. While there is some evidence suggesting these patterns are related to each other, the explicit nature of their relation, as well as the explicit mechanisms by which they are related to extreme heatwaves is still not known. The double jet structure has gained attention recently due to evidence that its persistence has been increasing, possibly explaining the rise in the number of extreme heatwaves over Europe. In this paper we study the occurrence and persistence of double jet states in ERA5 and in stationary simulations with the CESM1.2 model, using an index which measures the degree of jet separation. Additionally, we perform simulations with CESM1.2 coupled to a rare event algorithm in order to improve the statistics of rare summer-long double jet states. We find that extreme double jet states are characterised by three centers of extreme high surface temperature and 500hPa geopotential height anomalies, alongside a strong low pressure over the Arctic. The geopotential height anomaly pattern is consistent with both a positive Northern Annular Mode (NAM) and quasi-wave-3 patterns found in the literature. Moreover, we find a large percentage of co-occurrence of heatwaves at these centers, and a double jet state, with the percentage increasing with the duration of the double jet state.

Variabilities in the jet streams have a significant influence on our weather and climate, and could potentially increase the likelihood of a range of extreme weather events. The winter of 2009/2010 witnessed an unusual equatorward displacement of the Atlantic jet and its subsequent convergence with the African jet, leading to the emergence of a persistent zonally oriented merged jet. At the same time, intense and prolonged negative phase of the North Atlantic Oscillation (NAO) and unusually cold and extreme weather conditions were reported over the Northern Hemisphere. Such a merging was only observed to occur for a whole winter during the winters of 1968-69 and 1969-70. Preliminary results indicate that such persistent winter merged jets could be more frequent in a future global warming scenario and thus it is important to understand this dynamical regime transition of Atlantic jet and its effects on the weather patterns. In this study, we explore the extreme weather distribution over the northern hemisphere during such winter merged jets and its relation to NAO and ENSO. We show that merged jet winter months have a signature weather pattern distribution that is different from the negative NAO phase. We see a decrease in the surface eddy kinetic energy over the midlatitude during such winter leading to an equatorward shift in storm tracks over the Atlantic region and larger stormtrack density over the western Greenland which could potentially lead to the observed distribution of weather patterns. On comparing the surface temperature anomaly composites between the winters of strong negative NAO, EL Nino, and merged jet months we see that the merged jet winters have a significant persistent temperature distribution signature over the tropics and the Arctics. Similar analysis over the north hemisphere for surface wind, precipitation, and snowfall anomalies also shows a preferred persistent distribution over certain regions during the merged jet-state winters.

Rainfall in the Eastern Mediterranean is strongly modulated by complex topography and localized mesoscale processes. General circulation models (GCMs) struggle to capture daily precipitation variability in the region, both in time and in space. Rain in the Eastern Mediterranean occurs within a hierarchy of scales, as synoptic scale structures often drive local rainfall patterns. Daily rain prediction in the region can therefore benefit from analog downscaling-a nonlinear regression of a high-resolution predictand from past synoptic-scale predictors. We present a multiscaled downscaling algorithm of daily rain over Israel. The underlying goal is to create a mechanism-based tool that will improve the analysis and prediction of precipitation on short time scales in models that cannot produce the field explicitly. We train the algorithm using coarse grid ERA5 reanalysis data and measurements from 21 rain gauges. The routine uses a k-nearest neighbours algorithm to find the most similar past instances (i.e., analogs) for every predicted day. Analog selection is performed in two steps, based on scale (synoptic and local), as to not overshadow correlative but local predictors. The algorithm also includes several unique aspects tailored to Mediterranean climate: subdaily predictors of cyclone life cycles; representation of upper level cyclonic drivers; and the inclusion of rainfall potential using the Modified K-Index (MKI). The proposed algorithm has better accuracy (66% correct predictions) compared to non-downscaled reanalysis and climatological predictions. It better captures the spatial rainfall variance, mitigates the "drizzle bias," and improves skill in extreme event prediction. However, it underestimates very rainy events and has trouble fully representing the spatial variance in the region. Nonetheless, our algorithm represents the potential for computationally inexpensive downscaling of daily precipitation in the Mediterranean with various possible applications, for example, characterization of droughts and storms, linking hydrological and synoptic scale processes and introducing uncertainty estimates using large ensembles.

The projected drying of the Mediterranean basin is a robust signal of future climate change. Dynamically, this is manifested as a large anticyclonic anomaly covering the region, alongside a decrease in cyclonic activity. Various processes have been previously proposed as drivers of this trend, both thermodynamical (decreased land-sea temperature gradient) and dynamical (intermediate-scale stationary wave response, poleward shift of the jet stream). Several elements of the North Atlantic large-scale circulation are known to affect Mediterranean cyclonic activity (extratropical storms, jet stream position, weather regimes), individually and through mutual interactions. However, their contribution to the overall drying remains an open question.In this work, we use the framework of Finite Amplitude Local Wave Activity (FALWA; Huang & Nakamura, 2016) to deconstruct the role of the North Atlantic circulation in the projected changes downstream. FALWA is a diagnostic that keeps track of the wave activity ”stored” within circulation undulations, relative to a zonalized flow. It obeys an exact conservation relation; thus, its local rate of change is either due to a flux convergence, or to non conservative source-sink terms. This allows for a closed mechanistic budget analysis of the response, differentiating between horizontal advection by the mean flow, barotropic and baroclinic processes, and diabatic forcing.We analyse this budget in a 10 member CMIP6 ensemble and investigate the multi-model mean circulation response and ensemble spread over the North Atlantic and the Mediterranean basin. Preliminary results show a prominent baroclinic contribution over the eastern North Atlantic combined with enhanced advection of upper tropospheric potential vorticity towards Europe. Both elements imply that the shifting of the North Atlantic storm track plays a role in the projected drying trend of the Mediterranean.

The tropical overturning circulation is examined in a moist aquaplanet general circulation model forced using a non‐interactive sea‐surface temperature (SST) distribution that varies between a present‐day Earth‐like profile and one that is globally uniform. A Hadley cell (HC)‐like flow is observed in all experiments along with the poleward transport of heat and angular momentum. In simulations with non‐zero SST gradients, deep convection near the Equator sets up a deep tropical cell; midlatitude baroclinic Rossby waves flux heat and angular momentum poleward, reinforcing the thermally direct circulation. As the imposed SST gradient is weakened, the HC transitions from a thermally and eddy‐driven regime to one that is completely eddy‐driven. When the SST is globally uniform, equatorial waves concentrate precipitation in the Tropics and facilitate the lower‐level convergence necessary for the ascending branch of the HC. Midlatitude Rossby waves generated near the surface become very weak, but upper‐level baroclinicity generates waves that cause equatorward transport of heat and poleward transport of momentum. Moreover, these upper‐level waves induce a circulation that opposes the time‐mean HC, thus highlighting the role of tropical waves in driving an overturning circulation that looks similar to the present‐day Earth‐like case, even for the case with globally uniform SSTs. In all cases, anomalies associated with the tropical waves closely resemble those that sum to give the upper‐level zonal mean divergent outflow. Through their ability to modulate tropical rainfall and the related latent heating, equatorial waves cause considerable hemispheric asymmetry in the HC and impart synoptic and intraseasonal variability to the tropical overturning circulation.

The atmospheric circulation response to global warming is an important problem that is theoretically still not well understood. This is a particular issue since climate model simulations provide uncertain, and at times contradic- tory, projections of future climate. In particular, it is still unclear how a warmer and moister atmosphere will affect midlati- tude eddies and their associated poleward transport of heat and moisture. Here we perform a trend analysis of three main components of the global circulation}the zonal-mean state, eddies, and the net energy input into the atmosphere}and examine how they relate in terms of a moist static energy budget for the JRA-55 reanalysis data. A particular emphasis is made on understanding the contribution of moisture to circulation trends. The observed trends are very different between the hemispheres. In the Southern Hemisphere there is an overall strengthening and during boreal summer, also a poleward shifting, of the jet stream, the eddies, and the meridional diabatic heating gradients. Correspondingly, we find an overall strengthening of the meridional gradients of the net atmospheric energy input. In the Northern Hemisphere, the trend pat- terns are more complex, with the dominant signal being a clear boreal winter Arctic amplification of positive trends in lower-tropospheric temperature and moisture, as well as a significant weakening of both bandpass and low-pass eddy heat and moisture fluxes. Consistently, surface latent and sensible heat fluxes, upward and downward longwave radiation, and longwave cloud radiative fluxes at high latitudes show significant trends. However, radiative fluxes and eddy fluxes are in- consistent, suggesting data assimilation procedures need to be improved.

Variability in the jet stream can have a significant influence on the distribution of extreme weather, with winter-long anomalies leading to extreme seasons. During winter of 2009/2010, the Atlantic and African jets were anomalously merged for most of the winter, resulting in a persistent zonally oriented single jet. At the same time, intense and prolonged negative phase of the North Atlantic Oscillation (NAO) and unusually cold and extreme weather conditions were reported over the Northern Hemisphere. Such a merging was only observed to occur for a whole winter during the winters of 1968-69 and 1969-70. Preliminary results indicate that such persistent winter merged jets could be more frequent in a future global warming scenario and thus it is important to understand this rare dynamical jet state and its effects on the weather patterns. In this study, we explore the associated distributions of extreme weather during merged-jet winter months, in comparison to the distribution of extremes during negative NAO months. We show that merged jet winter months have a signature weather pattern distribution that is different from the negative NAO phase, affecting Northern Africa, Europe and south-west Greenland, which is associated with synoptic storms tending to either propagate zonally towards the Mediterranean, with a secondary northward then westward branch propagating to Greenland. We further find a complex relation to Arctic-Eurasian temperature anomalies. Once we remove the NAO-related high-latitude cold surface temperature anomalies, we find that Atlantic-African jet merging, especially the winter-long persistent ones, occur during winters with unusually warm Arctic and cold Eurasia. This is consistent with the theory that winter-long jet merging represents a dynamical regime transition to a merged jet, which is more likely to occur when mid-latitude baroclinicity is weaker.

Surface anticyclones connected to the ridge of an upper-tropospheric Rossby wave are the dynamical drivers of mid-latitude summer heatwaves. It is, however, unclear to which extent an anomalously low zonal phase speed of the wave in the upper troposphere is necessary for persistent temperature extremes at the surface. Here, we use spectral analysis to estimate a categorical phase speed for synoptic-scale waves. A composite analysis of ERA5 reanalysis data reveals how a meridional shift in the Rossby wave packet envelope associated with a change in phase speed alters the geographically phase-locked stationary wave pattern. In both composites for amplified low or high phase speed waves, respectively, the ridges and troughs of these temporal-mean wave trains show enhanced and reduced heatwave frequency. The phase speed of synoptic-scale waves is, hence, crucial for where, but less important for whether heatwaves occur.

Rossby Wave Breaking (RWB) events describe the last stage in the life cycle of baroclinic atmospheric disturbances. These breaking events can strongly influence the large-scale circulation and are tightly related to low-frequency weather regimes. In addition, RWBs are often associated with weather extremes such as heat waves, blockings, and extreme precipitation events. Here we examine the three-way interaction between RWB, weather regimes, and surface weather in the North Atlantic. This is done by combining a RWB detection algorithm, a storm-tracking routine, and a clustering technique to identify low-frequency circulation regimes in the North-Atlantic. We find that regardless of weather regime, most cyclones and anticyclones are associated with an Anticyclonic Wave Breaking (AWB) and/or a Cyclonic Wave Breaking (CWB) at some point during their lifetime, while very few storms do not involve any upper-level wave breaking (~11%). Moreover, storm characteristics (e.g., actual and relative positions, intensities, and displacements) differ depending on the associated breaking type. In “same-pairing” cases (i.e., cyclones with CWB and anticyclones with AWB) the surface system is positioned so that its associated upper-level winds would enhance the breaking (the anomalous circulation is in the same direction as the background shear). In “opposite-pairing” cases (i.e., cyclones with AWB and anticyclones with CWB), the upper-level winds associated with the surface system do not act to enhance the breaking which occurs in the direction of the background shear. In addition, we find that the surface storm characteristics are significantly altered with the weather regime, with distinct and clearly preferred storm paths in each cluster. We suggest a picture in which the resulting RWB frequencies and positions in each cluster are modified by the corresponding tracks of cyclones and anticyclones, with the maximum breaking found where there is a constructive interaction with the low-frequency flow. The positions of RWBs, in turn, shape the overall cluster structure and contributes to the persistence of the weather regime. An improved understanding of the relation between weather systems, RWB events, and weather regimes can also help us improve our understanding of and confidence in projected future circulation changes (e.g., by relating changes in the frequency and positions of RWB events, storm-tracks, and the North-Atlantic jet).

Abstract Surface anticyclones connected to the ridge of an upper‐tropospheric Rossby wave are the main dynamical drivers of mid‐latitude summer heatwaves. It is, however, unclear to what extent an anomalously low zonal phase speed of the wave in the upper troposphere is necessary for persistent temperature extremes at the surface. Here, we use spectral decomposition to separate fast and slow synoptic‐scale waves. A composite analysis of ERA5 reanalysis data reveals that, while in some regions heatwaves become more frequent during episodes of weak or no phase propagation, temperature extremes in other regions are commonly associated with more rapidly eastward propagating Rossby waves. Reflected in the mean heatwave duration as well, this relationship is possibly linked to a longitudinal phase preference of slow and fast waves or a meridional storm track shift. These findings open up new questions about the influence of mid‐latitude dynamics on temperature extremes.