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The Azores High is a persistent atmospheric high-pressure ridge over the North Atlantic surrounded by anticyclonic winds that steer rain-bearing weather systems and modulate the oceanic moisture transport to Europe. The areal extent of the Azores High thereby affects precipitation across western Europe, especially during winter. Here we use observations and ensemble climate model simulations to show that winters with an extremely large Azores High are significantly more common in the industrial era (since ce 1850) than in pre-industrial times, resulting in anomalously dry conditions across the western Mediterranean, including the Iberian Peninsula. Simulations of the past millennium indicate that the industrial-era expansion of the Azores High is unprecedented throughout the past millennium (since ce 850), consistent with precipitation proxy evidence from Portugal. Azores High expansion emerges after ce 1850 and strengthens into the twentieth century, consistent with anthropogenically driven warming. The Azores High over the North Atlantic has expanded due to anthropogenic climate change, disrupting precipitation patterns in western Europe, according to climate modelling and precipitation proxy records spanning the past millennium.

This study comprehensively investigates the impacts on the mean state of the Last Glacial Maximum (LGM) climate, particularly atmospheric circulation over the Northern Hemisphere associated with the different Paleoclimate Modelling Intercomparison Project Phase 4 (PMIP4) ice sheets, ICE-6G_C, GLAC-1D, and PMIP3, using the coupled atmosphere–ocean–vegetation model HadCM3B-M2.1aD. The simulation with PMIP3 ice sheets is colder than either of the two PMIP4 ice sheets mainly because of the larger area of land ice impacting surface albedo. However, changes in the circulation impact sea ice cover resulting in the GLAC-1D simulation being almost as cold. Although the PMIP4 ice sheets also induce different responses in the atmospheric circulation, some common features are identified in all simulations, including strengthening and lateral expansion of the winter upper-level North Atlantic jet with a large southwest-northeast tilt and summertime North Pacific jet, a southward shift of the wintertime Icelandic Low and Azores High and the summertime Pacific High. Compared to terrestrial-ocean reconstructions, all the PMIP4 ice sheet experiments overestimate the LGM cooling and wet conditions. The simulation with the ICE-6G_C ice sheet provides the closest reproduction of LGM climate, while the simulation with the PMIP3 ice sheet shows the coldest LGM climate state. Our study shows that in order to \"benchmark\" the ability of climate models to realistically simulate the LGM climate, we need to have reliable boundary conditions to ensure that any model biases are caused by model limitations rather than uncertainty about the LGM boundary conditions.

The long rains in East Africa are vital for agriculture, water resources, and socio-economic stability, sustaining millions of livelihoods. However, their pronounced interannual variability exacerbates food insecurity, emphasizing the need to understand the region’s rainfall drivers. This study analyzed rainfall variability using Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) data (1981–2023). Empirical Orthogonal Function (EOF) analysis identified a dominant north–south spatial dipole pattern, explaining 27.6% of the variance. Singular Value Decomposition (SVD) highlighted the 600-hPa level as critical for rainfall co-variability with atmospheric variables, guiding composite analyses. Composite analysis of seven dry and eight wet neutral-phase periods revealed that negative sea surface temperature (SST) anomalies over the Indo-Atlantic basin associated with dry periods, while positive anomalies correspond to wet periods. Dry conditions are linked to a strengthened Azores High and weakened Mascarene Highs, whereas wet conditions show the opposite. The Azores High negatively correlates with rainfall, while the Mascarene High shows a positive correlation. Moist air masses from the equatorial Atlantic and Congo basin dominate during wet periods, while weakened dry periods. Negative outgoing longwave radiation (OLR) anomalies enhance wet conditions, while positive anomalies denote dry periods. Warmer temperatures align with wet periods and cooler temperatures with dry periods. In conclusion, the zonal wind at 600-hPa, OLR, and the sea level pressure difference between the Azores and Mascarene Highs were identified as the main contributors to precipitation variability and should be incorporated into modelling efforts. These findings provide crucial insights for improving precipitation modelling and developing robust climate resilience strategies in East Africa. Future research should explore the influence of teleconnection climate modes, such as the Quasi-Biennial Oscillation (QBO), and the mechanisms of the El Niño-Southern Oscillation (ENSO), and assess the impacts of land-use changes on rainfall variability.

An analysis of characteristics of the boreal summer season June-July-August measured daily maximum 2-m air temperatures and associated heat waves (HWs) for 1961–2018 was conducted for three locations on the Croatian Adriatic coast representing its northern (Rijeka), central (Split) and southern (Dubrovnik) extents. Greater values occurred in the second part of the period (1990–2018) than in the first part (1961–1989), including significant (α = 0.01) trends in mean seasonal averages (0.44 to 0.69 °C per decade), extremes, frequencies, duration, and intensity. Exceedances and HWs spanning from 10 June to 24 August were determined in 53 years (out of 58 years) by the 95th and in 9 years by the 99th percentile criteria. Since heat stress often affects health at the beginning of HWs, exceedances of one or more days were all considered regardless of a minimum length or separation. In 30 years, the exceedances occurred at all locations in the same year. There were 122–147 (30–36) HW cases lasting 245–259 (51–54) days for the 95th (99th) thresholds. The maximum event duration was between 9 and 12 (5) days for the 95th (99th) thresholds. During the longest duration event, synoptic conditions were characterized by propagation of a strong and broad ridge of the Azores High extending into southern Europe and by blocking lows from the north. These results show that the Croatian coast, as part of the Mediterranean hot spots , is experiencing a significant increase in warming and associated frequency of HWs, which is likely to continue in the future.

The state of the atmospheric circulation and the associated hydroclimate in the North Atlantic during the last millennium remain the subject of considerable debate in both proxy- and model-based studies. Of particular interest in the Iberian region is the Azores High (AH) system, the southern node of the North Atlantic Oscillation (NAO), an atmospheric dipole closely tied to regional hydroclimate. Hydroclimate-sensitive proxy reconstructions from this region offer some insights into atmospheric dynamics, but large spatiotemporal gaps in these data inhibit a robust evaluation of hydroclimate variability. In this study, we present a continuous, sub-decadally-resolved composite stalagmite carbon isotopic record from three partially overlapping stalagmites from Buraca Gloriosa (BG) cave, western Portugal, situated within the center of the AH, that preserves evidence of regional hydroclimate variability from approximately 800 CE to the present. Chronologies are derived from U/Th dating and annual laminae. Stalagmite carbon isotopic values primarily reflect the amount of effective moisture and reveal generally dry conditions during the Medieval Climate Anomaly (MCA; ~ 850–1250 CE) and Modern Climate/Industrial Era (1850 CE-present), and wetter conditions during the Little Ice Age (LIA; ~ 1400–1850 CE). Multidecadal to centennial variability in the BG record and state-of-the-art last millennium climate model simulations show considerable coherence with precipitation-sensitive records from Spain and Morocco that, like BG, are strongly influenced by the intensity, size, and location of the AH. Model-proxy synthesis suggests that western Portugal was persistently dry during much of the MCA consistent with other NAO reconstructions; however, even considering age uncertainties, the apparent timing in the transition from a relatively dry MCA to a wetter LIA is spatially variable and confirms the non-stationary behavior of the AH system indicated by model output.

This study investigates the dynamical linkage between the meridional mass circulation and cold air outbreaks using the ERA-Interim data covering the period 1979–2011. It is found that the onset date of continental-scale cold air outbreaks coincides well with the peak time of stronger meridional mass circulation events, when the net mass transport across 60°N in the warm or cold air branch exceeds ~88 × 109 kg s−1. During weaker mass circulation events when the net mass transport across 60°N is below ~71.6 × 109 kg s−1, most areas of the midlatitudes are generally in mild conditions except the northern part of western Europe. Composite patterns of circulation anomalies during stronger mass circulation events greatly resemble that of the winter mean, with the two main routes of anomalous cold air outbreaks being along the climatological routes of polar cold air: namely, via East Asia and North America. The Siberian high shifts westward during stronger mass circulation events, opening up a third route of cold air outbreaks through eastern Europe, where lies the poleward warm air route in the winter-mean condition. The strengthening of the Icelandic low and Azores high during stronger mass circulation events acts to close off the climatological-mean cold air route via western Europe; this is responsible for the comparatively normal temperature there. The composite pattern for weaker mass circulation events is generally reversed, where the weakening of the Icelandic low and Azores high, corresponding to the negative phase of the North Atlantic Oscillation (NAO), leads to the reopening and strengthening of the equatorward cold air route through western Europe, which is responsible for the cold anomalies there.

The presence of warm boundary layer stratiform clouds over the eastern North Atlantic (ENA) region is commonly influenced by the Azores High, especially during the summer season. To investigate comprehensive aerosol–cloud interactions, this study employs the Weather Research and Forecasting model coupled with a chemistry component (WRF-Chem), incorporating aerosol chemical components that are relevant to the formation of cloud condensation nuclei (CCN) and accounting for aerosol spatiotemporal variation. This study focuses on aerosol indirect effects, particularly the long-range transport of aerosols, in the ENA region under three different weather regimes: a ridge with a surface high-pressure system, a post-trough with a surface high-pressure system, and a weak trough. The WRF-Chem simulations conducted at a near-large-eddy scale offer valuable insights into the model's performance, especially in terms of its ability to use high spatial resolution to capture mesoscale cloud features across various weather regimes. Our result shows that introducing 5 times more aerosols to either non-precipitating or precipitating clouds significantly increases ambient CCN numbers, resulting in, to varying degrees, higher liquid water path (LWP) values. The substantial aerosol–cloud interaction especially occurs in the precipitating clouds and demonstrates the susceptibility of the LWP to changes in CCN under different regimes. Conversely, thin, non-rain clouds at the edges of a cloud system are prone to evaporation, exhibiting an aerosol drying effect. The aerosols released during this process transition back to the accumulation mode, facilitating future activation. This dynamic behavior is not adequately represented in prescribed-aerosol simulations.

The influence of the stratospheric Quasi-biennial oscillation (QBO) on global monsoon systems and their extratropical teleconnections is investigated using 42 years (1979–2020) of monthly mean ERA-5 reanalyses data, excluding the ∼ 22 % of months with Niño 3.4 index above ±1.0 K. This study provides a unified perspective on how the QBO modulates the global monsoon system for neutral to moderate ENSO conditions, with applications to northern summer and winter. During JJA, QBO westerly (W) at 50 hPa coincides with enhanced rainfall over the Maritime Continent and less over the Western Pacific. For the same JJA and QBO W, the zonal mean cold anomaly in the subtropical UTLS associated with the QBO mean meridional circulation (MMC) acts to reduce static stability in the Northwest Pacific. This coincides with a weaker anticyclonic lower tropospheric circulation and eastward shift in convective rainfall from south of Japan. During DJF, QBO modulation of tropical deep convection alters the planetary wave train pattern emanating from the tropics along the UTLS. QBO W at 50 hPa promotes a positive North Atlantic Oscillation (NAO) phase, with an enhanced Azores High, stronger North Atlantic jet stream, and westward shift in precipitation toward North America. QBO W at 70 hPa promotes a positive Pacific North America (PNA) phase, with anomalous northeastward flow into Alaska and above average precipitation, accompanied by reduced precipitation along the west coast of the United States. In each case, the opposite effect is observed during QBO easterly (E).

The Canary/Iberia region (CIR), part of the Canary Current Upwelling System, is well-known for its coastal productivity and crucial role in enriching the oligotrophic open ocean through the offshore transport of the upwelled coastal waters. Given its significant ecological and socio-economic importance, it is essential to assess the impact of climate change on this area. Therefore, the goal of this study is to analyze the climate change signal over the CIR using a high-resolution regional climate system model driven by the Earth system model MPI-ESM-LR under RCP8.5 scenario. This modelling system presents a regional atmosphere model coupled to a global ocean model with enough horizontal resolution at CIR to examine the role of the upwelling favourable winds and the ocean stratification as key factors in the future changes. CIR exhibits significant latitudinal and seasonal variability in response to climate change under RCP8.5 scenario, where ocean stratification and wind patterns will play both complementary and competitive roles. Ocean stratification will increase from the Strait of Gibraltar to Cape Juby by the end of the century, weakening the coastal upwelling all year long. This increase in stratification is associated with a freshening of the surface layers of the North Atlantic. However, modifications in the wind pattern will play a primary role in upwelling source water depth changes in the southernmost region of the CIR in winter and in the north of the Iberian Peninsula in summer. Wind pattern changes are related to the intensification of the Azores High in winter and to a deepening of the Iberian thermal low in summer months.

The aim of this study is to elucidate the primary factors influencing the development, strength, and longevity of mesoscale convective systems (MCSs) in southwest Iran. Focusing on dynamic and thermodynamic factors, this research investigates their impact on MCSs’ maximum area, longevity, and precipitation characteristics. The study reveals that MCS characteristics are intricately linked to environmental factors such as humidity, convective available potential energy (CAPE), and low-level wind shear, predominantly within the Red Sea convergence zone. These factors are, in turn, influenced by larger atmospheric phenomena like Sudan’s low, Saudi Arabia’s high, and the Azores high. Multiple linear regression analysis identifies low-level wind shear along the Red Sea convergence zone and the 300 hPa wind speed along the subtropical jet stream as significant predictors for both the maximum and mean precipitation of MCSs. Notably, CAPE over the west of the Red Sea emerges as crucial for maximum precipitation, while sensible heat flux over Eastern Europe is key for mean precipitation estimation. The findings also underscore that humidity variables and 850 hPa wind speed are vital in determining the longevity and area of MCSs. This study contributes to a better understanding of the environmental conditions influencing MCS occurrence, aiding in the prediction of heavy precipitation events in subtropical regions like southwest Iran.