Kevin I. Hodges’s research while affiliated with University of Reading and other places

Cut-off low (COL) pressure systems significantly influence local weather in regions with high COL frequency, particularly in western North America. Nonetheless, future changes in COL frequency, intensity, and precipitation patterns remain uncertain. This study examines projected COL changes and their drivers in western North America under a high greenhouse gas concentration pathway (SSP585) using a multi-model ensemble from CMIP6 and a feature-tracking algorithm. We compare historical simulations (1980–2009) and future projections (2070–2099), revealing a marked increase in COL track density during summer in the northeast Pacific and western United States, while a strong decrease is projected for winter, associated with shifts in jet streams. Climate models project an increase in COL-related precipitation in future climate, with winter and spring experiencing more intense and localized precipitation, while autumn showing a more widespread precipitation pattern. Additionally, there is an increased frequency of extreme precipitation events, though accompanied by large uncertainties. The projected increase in extreme precipitation highlights the need to understand COL dynamics for effective climate adaptation in affected areas. Further research should aim to refine projections and reduce uncertainties, supporting better-informed policy and decision-making.

The East Asian Summer Monsoon (EASM) plays a pivotal role in redistributing water across East Asia, including contributing a considerable flood risk due to the potential for localized extreme precipitation. To gain insights into future EASM changes, it is crucial to explore the dynamics of a core driver of extreme precipitation during the EASM, the Mei‐yu front (MYF). While prior studies have examined various aspects of EASM in climate models, the comprehensive assessment of the dynamically important, that is, MYF remains largely unexplored. In this study, we evaluate the Mei‐yu front representation in 38 CMIP6 models from May to August using the ECMWF Reanalysis version 5 (ERA5) as reference. Our findings reveal that several CMIP6 models struggle to accurately reproduce the MYF climatology, with performance varying by month. By categorizing models based on the east–west bias of MYF position in May, we identify distinct monthly evolutions in these biases during the EASM season. Our study shows a significant association between the misrepresentation of the MYF climatology in CMIP6 models and the misrepresentation of the Western North Pacific High, particularly its western edge. Other potential sources of biases are based on the misrepresentation of other large‐scale circulation patterns, such as the South Asian High, and are also investigated. Furthermore, the performance evaluation of different aspects of the EASM is compared to previous studies, and the transferability of those principle evaluation findings is discussed.

Global warming is accelerating the decline of Arctic sea ice, with wide‐ranging impacts on the Earth's climate system. Using ERA5 data from 1980 to 2023, we investigated the relationship between winter extratropical storm tracks, atmospheric circulation patterns, and sea ice area (SIA) in three key Arctic regions. We classified the winters into two categories: atmosphere‐driven winters (ADWs), when atmospheric circulation influences sea ice, and ice‐driven winters (IDWs), when sea ice influences atmospheric circulation. This classification was based on the sign of SIA and surface turbulent heat flux anomalies in the Barents‐Kara Sea (BKS), Baffin Bay, Davis Strait, and Labrador Sea (BDL), and Chukchi‐Bering Seas (CBS). Our findings show that in IDWs, reduced SIA has a minor effect on extratropical storm tracks. However, we observed significant midtropospheric cooling over northeastern Asia, aligning with the effects of reduced ice in the BKS during IDWs. This emphasizes the importance of considering the entire tropospheric temperature profile to capture the impact of sea ice loss. In contrast, during ADWs, the BKS and CBS regions experience amplified surface warming and SIA loss due to storm‐induced intrusion of warm and moist air, with sea ice loss in the BKS contributing to strengthening Ural blocking. Although cyclone‐induced heat and moisture intrusion is prevalent, we found no significant trend in track density or mean intensity of positive V extrema in the North Atlantic sector of the Arctic, suggesting that changes in atmospheric circulation are unlikely to be the driver of recent sea ice loss in the BKS.

Cut-off Lows are slow-moving mid-latitude storms that are detached from the main westerly flow and are often harbingers of heavy and persistent rainfall. The assessment of Cut-off Lows in climate models is relatively limited, in fact, there are no studies conducted on the future changes of Cut-off Lows within climate models. Given the importance of Cut-off Lows in leading to severe hazards, here we study them in Coupled Model Intercomparison Project Phase 6’s worst-case future simulations (SSP5-8.5). Most (80%) of the models show that Cut-off Lows with high intensity and longer lifetimes are projected to become more frequent in spring over the land regions of the Northern Hemisphere. Such an increase in Cut-off Low frequency could substantially increase related potential hazards. An increase in Cut-off Low propagation velocity, however, may partly offset this increase in hazard. Lastly, projected changes in the jet stream with possible dynamical linkages to Cut-off Lows corroborate the findings of this study.

The UK Met Office decadal prediction system DePreSys4 shows skill in predicting the number of tropical cyclones (TCs) and TC track density over the eastern Pacific and tropical Atlantic Ocean on the decadal timescale (up to ACC = 0.93 and ACC = 0.83, respectively, as measured by the anomaly correlation coefficient—ACC). The high skill in predicting the number of TCs is related to the simulation of the externally forced response, with internal climate variability also allowing the improvement in prediction skill. The Skill is due to the model’s ability to predict the temporal evolution of surface temperature and vertical wind shear over the eastern Pacific and tropical Atlantic Ocean. We apply a signal-to-noise calibration framework and show that DePreSys4 predicts an increase in the number of TCs over the eastern Pacific and the tropical Atlantic Ocean in the next decade (2023–2030), potentially leading to high economic losses.

Plain Language Summary In this study, we use a cutting‐edge global storm‐resolving model called Geophysical Fluid Dynamics Laboratory eXperimental System for High‐resolution prediction on Earth‐to‐Local Domains (X‐SHiELD) to understand how intense storms, known as midlatitude cyclones, might change as the climate warms. Specifically, we examine how a 4° $4{}^{\circ}$C increase in sea surface temperatures affects these storms in the Northern Hemisphere over a 2‐year period. Our simulations show that the tracks of midlatitude cyclones tend to shift toward the poles as temperatures rise, which is consistent with previous climate model projections. What makes this study unique is the use of X‐SHiELD, a high‐resolution storm‐resolving model that can simulate both the warm and cold parts of these cyclones in far greater detail than traditional models. This allows us to observe changes that other models miss. For example, we find that the warm parts of the cyclones experience much stronger winds and heavier rainfall, with increases by up to 15% locally in wind speeds and in rainfall for every degree of warming. These findings suggest that as the climate warms, midlatitude cyclones will pose greater risks, especially from their warm sectors, and highlighting the importance of storm‐resolving models like X‐SHiELD.

Plain Language Summary The Arctic Oscillation (AO) plays an important role in the variability of weather and climate across the entire Northern Hemisphere. This study investigates the correlation between the numbers of extratropical cyclones entering and leaving the Arctic and the AO synoptic variability. The value of the NCF in the North Atlantic region minus that in the North America region is defined as the Joint Net Cyclone Flux (JNCF) which is significantly correlated with the AO synoptic variability with a correlation coefficient of 0.32. The composites of SLP relative to the JNCF index manifest as AO‐like anomalies. Piecewise potential vorticity (PV) inversion results further reveal the quantitative forcing of extra‐tropical cyclones on the synoptic‐scale AO‐like geopotential height anomalies at different altitudes. The effects of extratropical cyclones are more important than Arctic stratospheric PV intrusions. Furthermore, the upper‐level dynamic processes among all extratropical cyclone effects dominate the evolution of synoptic‐scale AO‐like geopotential height anomalies, whereas the mid‐troposphere latent heat release contributes little. Interestingly, the effects of the lower‐troposphere static stability and baroclinicity on the AO‐like synoptic anomalies are completely opposite between the western and eastern parts of the North Atlantic‐Arctic sector.

In this work, we present and preliminarily evaluate a novel dataset of European windstorms associated with extratropical cyclones (ETCs) based on the whole ERA5 reanalysis period (1940–present). This dataset is produced within the Copernicus Climate Change Service (C3S) Enhanced Operational Windstorm Service (EWS), to promote a knowledge-based assessment of the nature and temporal evolution of European windstorms associated with ETC. Such a dataset is primarily thought to provide high-quality, standardized data on windstorms that support various industries, particularly insurance and risk management, by offering insights into the intensity, density spatial patterns, and, if coupled downstream, with vulnerability and exposure information, the impact of windstorms. EWS includes two datasets: windstorm tracks, based on two tracking algorithms (TRACK and TempestExtremes), and windstorm footprints, produced considering both original-resolution ERA5 variables and statistically downscaled ERA5 variables, with a target grid at 1 km resolution. A preliminary analysis of the datasets shows increasing number of cold-semester windstorms and the associated footprint wind gusts magnitude over a portion of the European territory. The choice of the tracking algorithm is shown to be an important factor in the decision-making process, as it results in non-negligible uncertainties in main windstorm statistics.

This study assesses the performance of the latest phase of Coupled Model Intercomparison Project (CMIP6) models in simulating easterly wave disturbances (EWD) over the tropical South Atlantic (TSA) impacting northeast Brazil (NEB). Initially, we evaluate simulated precipitation from 17 historical CMIP, 16 AMIP, 7 hist-1950, and 10 highresSST-present models against the Global Precipitation Climatology Project (GPCP) dataset to identify models that accurately reproduce the spatial and temporal precipitation patterns in the study region. The ensemble's spatial analysis demonstrates their capability in reproducing annual and seasonal precipitation climatology. However, models underestimate precipitation intensity along NEB's coast while overestimating it in TSA and NEB's north. Model uncertainties tend to be greater with higher latitudes. The models represented the annual cycle in all subareas within the study region, particularly from July to October, albeit with a greater spread in the first half of the year, especially over the Intertropical Convergence Zone (ITCZ). Based on it, three top-performing models from each ensemble were selected for EWD evaluation. The automatic tracking algorithm for EWDs showed the model's ability to represent mean values of EWD lifetime (~ 6 days) and phase speed (~ 7 m s⁻¹) as found in ERA5 reanalysis. However, they failed to capture EWD's interannual variability or climatological mean frequency. Despite CMIP6 model weaknesses, they accurately identified two primary EWD genesis regions: one over the TSA and another near the West African coast. Overall, CMIP6 models, particularly atmospheric and high-resolution models (HighResMIP), effectively captured precipitation climatology and EWD characteristics over NEB and the adjacent TSA.