Weather Regimes Research Articles

A statewide, weather-regime based stochastic weather generator for process-based bottom-up climate risk assessments in California – Part II: Thermodynamic and dynamic climate change scenarios

This study is the second of a two-part series presenting a novel weather regime-based stochastic weather generator to support bottom-up climate vulnerability assessments of water systems in California. In Part 2 of this series, we present how the model is used to develop an ensemble of climate change scenarios based on both thermodynamic and dynamic signals of climate change. The ensemble includes a suite of 30 climate change scenarios, each consisting of 1000 years of simulated daily climate data (precipitation, maximum temperature, minimum temperature) at a 6 km resolution across the entire state of California. The 30 scenarios represent a range of plausible climate changes to temperature, average precipitation, and precipitation extremes that are reflective of thermodynamic responses of the atmosphere to warming. An additional two scenarios are also created that represent changes in the frequency of weather regimes (e.g., dynamic climate change). Results from these scenarios reveal that when the effects of anthropogenic climate change are combined with plausible realizations of natural climate variability, the severity of extremes in California is amplified significantly. In addition, recent changes in the frequency of large-scale patterns of atmospheric circulation can have impacts of similar magnitude to large (>10%) declines in average precipitation, particularly with respect to drought. The scenarios developed in this work are designed to allow water managers to systematically test the sensitivity of their water system to different combinations of climate change, so that key vulnerabilities can be discovered and then addressed through adaptation planning.

Revisiting the Relationship between Polar Lows and Weather Regimes

Abstract The link between weather regimes (WRs) and polar low (PL) activity is examined over the North Atlantic and North Pacific basins. Compared to earlier studies based on limited, regional PL datasets, our study conducts a more complete evaluation of regional WR–PL relationships using an expanded PL climatology. Our findings show that PL activity is increased over the Norwegian and Barents Seas during the Atlantic ridge regime and decreased over the former region during the Scandinavian blocking regime, with negative impacts also stretching to the Irminger Sea. Over the Labrador and Irminger Seas, PL activity is modulated strongest by the North Atlantic Oscillation (NAO), with positive impacts during the positive phase and vice versa. Over the North Pacific, the Arctic low contributes to increased PL activity over most regions, while the opposite is true for the Pacific wave train regime. The variability of PL activity associated with WRs is strongly related to changes in key environmental conditions. In general, regions of enhanced (reduced) PL activity are coincident with anomalous low-level northerly (southerly) flow and reduced (increased) static stability. Further analysis shows that certain persistent WRs can strongly modulate PL activity over some regions, either due to the amplification or propagation of favorable or unfavorable conditions, which cautions the limitation of regarding WRs as stationary patterns. A previously developed PL genesis potential index is shown to represent the observed impacts well, which serves to confirm the robustness of our findings and suggests the potential applicability of WRs to the subseasonal prediction of PLs. Significance Statement Polar lows are intense small-scale (∼300 km) cyclones that form over high-latitude oceanic regions. The hazardous impacts they pose to coastal communities and maritime and air operations in the Arctic motivate their skillful prediction, which remains a major challenge at lead times beyond a few days. In this study, we relate PLs and the key environmental conditions that favor their development to weather regimes, which are recurrent large-scale circulation patterns that can persist for weeks at a time. We find that weather regimes have strong impacts on polar low activity through the modulation of key environmental conditions. These relationships can potentially be utilized in the extended-range prediction of polar lows.

Identifying wind regimes near Kuwait using self-organizing maps

Optimization of wind energy integration requires knowing the relationship between weather patterns and winds they cause. For a region with less-studied weather such as the Middle East, climatology becomes more vital. The Shagaya Renewable Energy Park in development in Kuwait experiences regional wind regimes that affect wind power production. Weather Research and Forecasting (WRF) model output allowed investigation into the weather regimes most likely to impact Shagaya Park. The self-organizing maps (SOMs) machine-learning method clustered the WRF output into six primary weather regimes experienced by the Middle East. According to the wind regimes mapped by the SOM, two of the six regimes have average wind speeds of approximately 9.9 and 8.6 m s−1 at 80 m near Shagaya Park, as well as wind speed and estimated wind power distributions that are more favorable to wind power production in Kuwait. One regime depicts a strong northwesterly wind called the summer shamal, and the second is associated with strong westerlies. Regimes less favorable for Kuwaiti wind power production are represented by the remaining four SOM nodes: local weak southeasterlies, an African nocturnal low-level jet, a daytime planetary boundary layer, and local northwesterlies from autumn to spring. The remaining four SOM nodes have average wind speeds of 5.7–7.2 m s−1 and wind speed and estimated wind power distributions which indicate regimes less favorable for wind power production in Kuwait.

Assessment of climate biases in OpenIFS version 43r3 across model horizontal resolutions and time steps

Abstract. We examine the impact of horizontal resolution and model time step on the climate of the OpenIFS version 43r3 atmospheric general circulation model. A series of simulations for the period 1979–2019 are conducted with various horizontal resolutions (i.e. ∼100, ∼50, and ∼25 km) while maintaining the same time step (i.e. 15 min) and using different time steps (i.e. 60, 30, and 15 min) at 100 km horizontal resolution. We find that the surface zonal wind bias is significantly reduced over certain regions such as the Southern Ocean and the Northern Hemisphere mid-latitudes and in tropical and subtropical regions at a high horizontal resolution (i.e. ∼25 km). Similar improvement is evident too when using a coarse-resolution model (∼100 km) with a smaller time step (i.e. 30 and 15 min). We also find improvements in Rossby wave amplitude and phase speed, as well as in weather regime patterns, when a smaller time step or higher horizontal resolution is used. The improvement in the wind bias when using the shorter time step is mostly due to an increase in shallow and mid-level convection that enhances vertical mixing in the lower troposphere. The enhanced mixing allows frictional effects to influence a deeper layer and reduces wind and wind speed throughout the troposphere. However, precipitation biases generally increase with higher horizontal resolutions or smaller time steps, whereas the surface air temperature bias exhibits a small improvement over North America and the eastern Eurasian continent. We argue that the bias improvement in the highest-horizontal-resolution (i.e. ∼25 km) configuration benefits from a combination of both the enhanced horizontal resolution and the shorter time step. In summary, we demonstrate that, by reducing the time step in the coarse-resolution (∼100 km) OpenIFS model, one can alleviate some climate biases at a lower cost than by increasing the horizontal resolution.

Weather regimes associated with summer precipitation over the southeast Tibetan Plateau and the relationship with ENSO

AbstractThe Tibetan Plateau (TP), known as the “Asian water tower,” provides freshwater resources for hundreds of millions of people in Asia. Most of the Asian rivers, such as the Yangtze, the Jinsha, the Salween and the Brahmaputra, are generated from southeastern part of the TP (SETP). In order to explore the influences of atmospheric circulation on the precipitation over the SETP, self‐organizing mapping (SOM) was utilized to identify the weather regimes (WRs) and related precipitation over the SETP and its surrounding areas. The daily scale of large‐scale circulation via ERA5 were classified into nine WRs by the SOM. There are two favourable regimes (rainy WRs) and three adverse ones (rainless WRs) for the SETP precipitation among these WRs, respectively. Furthermore, water vapour transport of the WRs and the relevant effects of ENSO are investigated. The droughts and floods of SETP are determined by the interannual variations of occurred frequency of the WRs. In particular, the SETP is flooded in the years with frequent occurrence of the rainy WRs and vice versa. The occurrence of WRs is closely related to the phase state of ENSO. The 9th WR (SOM9) and the 4th WR (SOM4) are separately occurred more frequently in the El Niño and the La Niña years. Regulation of ENSO on the SETP precipitation are effective through its influences on the state of atmospheric circulation, that is, frequency of various WRs. It implies that the occurred frequency of WRs is modulated by the climate systems and results in the interannual variations of precipitation over the SETP.

The relation between Rossby wave-breaking events and low-level weather systems

Abstract. Rossby wave-breaking events describe the last stage in the life cycle of baroclinic atmospheric disturbances. These breaking events can strongly influence large-scale circulation and are also related to weather extremes such as heat waves, blocking, and extreme precipitation events. Nonetheless, a complete understanding of the synoptic-scale dynamics involved with the breaking events is still absent. For example, it is not clear how well the theoretical life cycle experiments, which use a specified initial perturbation with a single zonal wavenumber and a prescribed simplified initial zonal jet, capture the life cycle of real-atmosphere weather systems. Here we combine a storm-tracking technique together with a wave-breaking detection algorithm to examine how upper-level wave breaking and surface weather systems are related in the North Atlantic during winter. These datasets allow us to examine whether upper-level wave breaking and low-level weather systems always occur simultaneously and if we can identify preferred relations between the surface weather system type (cyclone or anticyclone) and the type of the upper-level breaking event (cyclonic or anticyclonic wave breaking denoted CWB or AWB, respectively). We find that in the North Atlantic, most weather systems are associated with AWB and/or CWB at some point during their lifetime, while only few cyclones and anticyclones do not involve any upper-level wave breaking (roughly 11 % and 15 %, respectively). Our results imply that composites of cyclones and anticyclones involve a mixture of different types of life cycles, depending on whether they involve CWB or AWB, as well as their position relative to the Rossby wave-breaking (RWB) center. Moreover, the system characteristics (including actual and relative positions, intensities, and displacements) differ depending on the associated breaking type. We distinguish between “same-pairing” cases (i.e., cyclone with CWB and anticyclones with AWB) and “opposite-pairing” cases (i.e., cyclones with AWB and anticyclones with CWB). Compositing the cyclones and anticyclones based on this criterion, we find that in similar pairings 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), but, for opposite pairings, 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. A better understanding of the different life cycles of real-atmosphere cyclones and anticyclones and the upper-level breaking they involve is important for exploring the relation between storm tracks and slowly varying weather regimes and how they are mediated by RWB events.

The Dynamical Footprint of Year‐Round North American Weather Regimes

AbstractWeather regimes have been defined over multiple regions and used in a range of practical applications, including subseasonal‐to‐seasonal forecasting and climate model evaluation. Despite their widespread use, the extent to which regimes reflect physical modes of the atmosphere is seldom investigated. Here, we adopt a year‐round classification of four North American weather regimes, with a fifth “no regime” class, and leverage dynamical systems theory to investigate their dynamical properties. We find that when the atmospheric flow is assigned to a regime, it displays persistent characteristics and a lifecycle‐like temporal evolution. We further find that, regardless of season, these characteristics are enhanced when the atmospheric flow displays a comparatively strong projection onto the cluster‐mean of the regime to which it is assigned (while the reverse is true for a weaker projection). We interpret these results as evidence that the four North American weather regimes are physically‐meaningful, with a clear dynamical footprint.

Экспедиции клуба Портулан в район г. Мунку-Сардык в 2022 году

We summarize the results of the 2022 expeditions of the student-teaching club "Portulan" to the Munku-Sardyk mountain area, which included field scientific research of nival-glacial formations, river and near-slope aufeis, slope forms of relief and processes forming them in the valleys of the Bely Irkut, Muguvek, Bugovek rivers: regime surveys of high-mountainous aufeis, as well as traditionally conducted monitoring of weather and temperature regime over the entire vertical extent of the relief, study of the stone stream "Active" and summer condition of glaciers, aufeis and snowfields.

Transpiration Dynamics in Co-Located Maize, Sorghum, and Soybean Closed Canopies and Their Environmental Controls

Highlights Hourly sap flow measured in co-located and identically managed maize, sorghum, and soybean closed canopies. PAR, VPD, and ETr were strongly correlated to transpiration (T) normalized by LAI. Negative response of T to high VPD (3-4 kPa) was observed for maize and sorghum. Counterclockwise hysteresis observed for diurnal T-VPD and T-PAR. MLR models were developed to estimate T using VPD and PAR. Abstract. Transpiration (T) dominates terrestrial hydrological fluxes and is strongly coupled with vegetation productivity and water use efficiency across different biomes, including agricultural systems. Studying how T in field crops responds to environmental variability has important implications to inform and predict agroecosystems’ response to a changing environment. However, comparative T rates among major field crops remain unknown in many regions where drought severity and limited freshwater availability are projected, such as the Central U.S. Plains. We address this knowledge gap by monitoring and characterizing hourly T for field-grown maize, grain sorghum, and soybean crops under the same weather, soil, and management regimes using sap flow sensors. The relationships among crop-specific T and air temperature (Tair), relative humidity (RH), wind speed (u2), vapor pressure deficit (VPD), incoming shortwave radiation (Rs), photosynthetically active radiation (PAR), net radiation (Rn), and grass- and alfalfa-reference evapotranspiration (ETo, ETr) were investigated. T normalized by leaf area index (T LAI-1) was most correlated with PAR (r=0.88), ETr (r=0.84), and VPD (r=0.81). Mean sensitivity of T LAI-1 to unit change in Tair, Rs, PAR, Rn, u2, RH, VPD, and ETr for maize and sorghum was 88% and 59% greater than that of soybean, respectively. All crops showed non-linear T LAI-1 response to increasing VPD, and a negative response of T LAI-1 to VPD was observed in the 3.0-4.0 kPa VPD range for maize and sorghum. Each crop demonstrated a counterclockwise hysteresis effect to diurnal T-VPD and T-PAR, which was 177% and 87% greater (for T-VPD) and 44% and 17% greater (for T-PAR) in maize and sorghum, respectively, than soybean. Transpiration has rarely been measured in row crops, especially in a comparative fashion, and thus, the concurrent T dynamics and their environmental controls characterized in this research are of critical importance. These data can be instrumental for quantitatively assessing change in true crop water use (transpiration) and thus crop suitability under projected environmental change. Keywords: Hysteresis, Photosynthetically active radiation, Reference evapotranspiration, Sapflow, Vapor pressure deficit.

Двадцать третья летняя научно-исследовательская экспедиция клуба Портулан в район г. Мунку-Сардык

Summarizes the results of the summer expeditions 2024 of the student-teaching club "Portulan" and the Institute of Geography named after V.B. Gubkin. V.B.Sochava SB RAS to the Munku-Sardyk mountain area, which included field research of nival and glacial formations, river ice, slope relief forms and hazardous processes in the valleys of the Bely Irkut and Muguvek rivers: weather and temperature regime were traditionally monitored over the entire vertical relief span, thermochron readings were taken, the stone stream "Active" was surveyed, summer condition of Peretolchina and Radde glaciers and snowfields was assessed, water samples were taken to assess the share of glacier, ground and surface water inputs.

REASONS FOR CHANGES IN THE SOIL-AIR REGIME AS A RESULT OF IRRIGATION OF CROPS WITH MINERALIZED WATER

This article describes the weather regime of the soil, the methods of its management, the changes that occur as a result of the use of mineralized water in crop irrigation.

Classification of Warm-Season Precipitation in High-Resolution Rapid Refresh (HRRR) Model Forecasts over the Contiguous United States

Abstract This study uses the convective adjustment time scale to identify the climatological frequency of equilibrium and nonequilibrium convection in different parts of the contiguous United States (CONUS) as modeled by the operational convection-allowing High-Resolution Rapid Refresh (HRRR) forecast system. We find a qualitatively different climatology in the northern and southern domains separated by the 40°N parallel. The convective adjustment time scale picks up the fact that convection over the northern domains is governed by synoptic flow (leading to equilibrium), while locally forced, nonequilibrium convection dominates over the southern domains. Using a machine learning algorithm, we demonstrate that the convective adjustment time-scale diagnostic provides a sensible classification that agrees with the underlying dynamics of equilibrium and nonequilibrium convection. Furthermore, the convective adjustment time scale can indicate the model quantitative precipitation forecast (QPF) quality, as it correctly reflects the higher QPF skill for precipitation under strong synoptic forcing. This diagnostic based on the strength of forcing for convection will be employed in future studies across different parts of CONUS to objectively distinguish different weather situations and explore the potential connection to warm-season precipitation predictability. Significance Statement An objective classification metric that can delineate a wide range of forecasts into distinct scenarios can serve as a valuable tool. This study represents a pioneering effort in utilizing the convective adjustment time scale to identify the climatological frequency of warm-season precipitation under varying levels of synoptic forcing in different parts of the contiguous United States (CONUS). The results demonstrate that the convective adjustment time scale is a robust metric for categorizing precipitation events and establishing a direct link to their predictability. Overall, this study provides a valuable framework for future studies focused on the CONUS domain, offering guidance on how to employ the convective adjustment time scale to classify weather regimes and explore the influence of environmental conditions on predictability of convection.

Weather whiplash events in Europe and North Atlantic assessed as continental-scale atmospheric regime shifts

The term “weather whiplash” describes abrupt transitions from one persistent weather regime to another substantially different one, such as from a frigid cold spell to anomalous warmth. Weather whiplash events (WWEs) are often highly disruptive to agriculture, ecosystems, infrastructure, and human activities. While no consistent definition exists, we identify WWEs based on substantial shifts in the continental-scale, upper-atmosphere circulation. As first demonstrated in our earlier study focused on the NE Pacific/North American region, a WWE is detected when one persistent, large-scale pattern in 500 hPa height anomalies shifts to another distinctly different one. Patterns are identified using self-organizing maps (SOMs), which create a matrix of representative patterns in the data. In the present study, we apply this approach to identify WWEs in the North Atlantic/European sector. We analyze the occurrence of WWEs originating with long-duration events (four or more days) in each pattern. A WWE is detected when the pattern two days following a long-duration event is substantially different, measured with distance thresholds internal to the matrix. Changes in WWE frequency, past and future, are assessed objectively based on reanalysis output and climate model simulations. We find that future changes under RCP 8.5 forcing exhibit distinct trends, especially in summer months, while those based on reanalysis are less clear. Patterns featuring positive height anomalies in high latitudes are projected to produce more WWEs in the future, while patterns exhibiting negative anomalies produce fewer. Shifts in temperature and precipitation extremes associated with these WWEs are diagnosed.

Effect of Sowing Time Induced Weather Regimes on Growth and Yield of Chickpea under Irrigated Condition

A field experiment conducted to study the effect to find out optimum time of sowing and suitable cultivar for sustainable chickpea production in the region. The study was undertaken to find yield variation with extended sowing date. Five different sowing dates viz., 30th October (44 MW), 15th November (46 MW), 30th November (48 MW), 15th December (50 MW) and 30th December (52 MW) with two chickpea cultivars viz., JAKI 9218 and Vijay were studied. The varieties selected dominated chickpea cultivation in the region. The results revealed that crop sown on 30th October produced higher but statistically equivalent number of pods/plant, number of seeds/plant and grain yield as compared to 15th November sowing. Crop sown on 30th October accumulated higher Growing Degree Days (GDD: 2012 day0C) and Heliothermal Units (HTU: 13515 0C day hr) closely followed by 15th November sown crop (GDD; 1975-day 0C, HTU: 13130 0C day hr) during cropping period from vegetative to pod-seed development phase. The number of pods/plant, weight of seed/plant and test weight was higher in cultivar JAKI 9218 than Vijay. Maximum GDD (1888 0C day) and HTU (12706 0C day hr) were accumulated by cultivar JAKI 9218 closely followed by Vijay (GDD: 1856 0C day; HTU: 12449 0C day hr).

Climate variability on Fit for 55 European power systems.

The use of variable renewable energy sources to generate electricity introduces a dependency on meteorological factors into power systems. With the renewables share growing globally, often driven by political pressures, the reliability and efficiency of power systems are increasingly affected by this dependency. In this paper, we investigate the impact of the natural variability of meteorological parameters on the European power system in 2030. We specifically focus on (1) analysing the main European weather patterns affecting renewable energy production and (2) understanding the co-variability of this production among European countries. The identification of a set of patterns in the behaviour of key power system operation indicators allows us to analyse the relationship between large-scale weather regimes and daily power system operations in a 2030 European energy context. Regarding renewable generation, analysis of the co-variability shows that European power systems tend to form two clusters, in each of which all the regions tend to show a positive correlation among themselves and a negative correlation with the other cluster. Our analysis of the most important large-scale weather regimes shows that during cyclonic patterns, the carbon intensity of all the European power systems is lower than normal, while the opposite happens during blocking regimes.

How Have Hydrological Extremes Changed over the Past 20 Years?

Abstract Severe floods and droughts, including their back-to-back occurrences (weather whiplash), have been increasing in frequency and severity around the world. Improved understanding of systematic changes in hydrological extremes is essential for preparation and adaptation. In this study, we identified and quantified extreme wet and dry events globally by applying a clustering algorithm to terrestrial water storage (TWS) data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (FO). The most intense events, ranked using an intensity metric, often reflect impacts of large-scale oceanic oscillations such as El Niño–Southern Oscillation and consequences of climate change. The severity of both wet and dry events, represented by standardized TWS anomalies, increased significantly in most cases, likely associated with intensification of wet and dry weather regimes in a warmer world, and consequently, exhibited strongest correlation with global temperature. In the Dry climate, the number of wet events decreased while the number of dry events increased significantly, suggesting a drying trend that may be attributed to climate variability and possible increases in irrigation and reliance on groundwater. In the Continental climate where temperature has risen faster than global average, dry events increased significantly. Characteristics of extreme events often showed strong correlations with global temperature, especially when averaged over all climates. These results suggest changes in hydrological extremes and underscore the importance of quantifying total water storage changes when studying hydrological extremes. Extending the GRACE/FO record, which spans 2002 to the present, is essential to continuously tracking changes in TWS and hydrological extremes.

Evaluation of the vulnerability of wild bird populations during heatwave events: implications for biodiversity conservation

Heatwaves, defined as prolonged periods of excessive heat, are becoming more frequent and severe due to global climate change. These extreme heat events can have significant impacts on ecosystems and wildlife, particularly on avian fauna. Birds, as vital components of ecosystems, are highly susceptible to the adverse effects of heatwaves. Impacts directly attributable to adverse weather and changing climate regimes include a higher risk of mortality, reduced breeding success, compromised body condition and immunocompetence, declining populations, range changes, and potentially maladaptive behavioral adjustments in foraging, parental care, and migration. This vulnerability is exacerbated by the loss and degradation of their natural habitats, which hinders their ability to adapt to constantly changing climatic conditions. Understanding the vulnerability of bird populations during heatwaves is essential for devising effective conservation strategies. Conservation efforts should focus on preserving and restoring critical bird habitats, providing access to freshwater sources, and creating artificial shelters. Additionally, public education plays a significant role in raising awareness about the importance of bird conservation during heatwave events and in the broader context of climate change. In analyzing the subject, the study aims to provide more precise information to support the public decisions to be made, as well as to guide awareness for the implementation of conservation actions.

Comparison of Cluster Analysis Methods for Identifying Weather Regimes in the Euro-Atlantic Region for Winter and Summer Seasons

Comparison of Cluster Analysis Methods for Identifying Weather Regimes in the Euro-Atlantic Region for Winter and Summer Seasons

Understanding the Contributions of Paleo‐Informed Natural Variability and Climate Changes to Hydroclimate Extremes in the San Joaquin Valley of California

AbstractTo aid California's water sector to better understand and manage future climate extremes, we present a method for creating a regionally consistent ensemble of plausible daily future climate and streamflow scenarios that represent natural climate variability captured in a network of tree‐ring chronologies, and then embed anthropogenic climate change trends within those scenarios. We use 600 years of paleo‐reconstructed weather regimes to force a stochastic weather generator, which we develop for five subbasins in the San Joaquin Valley of California. To assess the compound effects of climate change, we create temperature series that reflect projected scenarios of warming and precipitation series that have been scaled to reflect thermodynamically driven shifts in the distribution of daily precipitation. We then use these weather scenarios to force hydrologic models for each of the five subbasins. The paleo‐forced streamflow scenarios highlight periods in the region's past that produce flood and drought extremes that surpass those in the modern record and exhibit large non‐stationarity through the reconstruction. Variance decomposition is employed to characterize the contribution of natural variability and climate change to variability in decision‐relevant metrics related to floods and drought. Our results show that a large portion of variability in individual subbasin and spatially compounding extreme events can be attributed to natural variability, but that anthropogenic climate changes become more influential at longer planning horizons. The joint importance of climate change and natural variability in shaping extreme floods and droughts is critical to resilient water systems planning and management in the San Joaquin.

Comparison of Cluster Analysis Methods for Identification of Weather Regimes in Euro-Atlantic Region for Winter and Summer Seasons

Various methods of cluster analysis are used for identification of large-scale atmospheric circulation regimes or weather regimes (WRs). In this paper we compare four most commonly used clustering methods – k-means (KM), Ward’s hierarchical clustering (HW), Gaussian mixture model (GM) and self-organizing maps (SOM) to analyze WRs in Euro-Atlantic region. The data used for WRs identification are 500 hPa geopotential height fields (z500) from the ERA5 reanalysis for the 1940–2022 period. Four classical wintertime weather regimes are identified by the KM method – two regimes associated with positive and negative phases of the North Atlantic Oscillation (NAO+ and NAO–), a regime associated with the Scandinavian blocking (SB) and a regime characterized by elevated pressure over the Northern Atlantics. For summer months KM method gets WRs that are similar by their spatial structure to the classical winter ones. The SOM method yields results that are almost identical to the results of KM method. Unlike KM and SOM methods, HW and GM do not catch the spatial structure of all four classical winter Euro-Atlantic weather regimes and their summer analogues. Compared to WRs of the KM and SOM methods, WRs obtained by HW and GM methods explain less z500 variance, they have different occurrences, persistence and transition features. Summer and winter WRs obtained by HW and GM methods are less similar to each other compared to WRs provided by KM method. Average spatial correlation coefficients between mean z500 fields of WRs obtained by KM and HW methods are 0.76 in winter and 0.83 in summer, 0.70 in winter and 0.72 in summer for KM and GM methods and 0.41 in winter and 0.44 in summer for the regimes between HW and GM methods, respectively. There are statistically significant trends of seasonal occurrence of WRs found by some of the studied clustering methods – a positive trend for the occurrence of the NAO+ regime and a negative trend for the occurrence of the NAO– regime.