Atmospheric Circulation Types Research Articles

Fuzzy time series clustering using autoencoders neural network

<p>This study presents a novel approach that employs autoencoders (AE)—an artificial neural network—for the nonlinear transformation of time series to a compact latent space for efficient fuzzy clustering. The method was tested on atmospheric sea level pressure (SLP) data towards fuzzy clustering of atmospheric circulation types (CTs). CTs are a group of dates with a similar recurrent SLP spatial pattern. The analysis aimed to explore the effectiveness of AE in producing and improving the characterization of known CTs (i.e., recurrent SLP patterns) derived from traditional linear models like principal component analysis (PCA). After applying both PCA and AE for the linear and nonlinear transformation of the SLP time series, respectively, followed by a fuzzy clustering of the daily SLP time series from each technique, the resulting CTs generated by each method were compared to assess consistency. The findings reveal consistency between the SLP spatial patterns from the two methods, with 58% of the patterns showing congruence matches greater than 0.94. However, when examining the correctly classified dates (i.e., the true positives) using a threshold of 0.8 for the congruence coefficient between the spatial composite map representing the CT and the dates grouped under the CT, AE outperformed PCA with an average improvement of 29.2%. Hence, given AE's flexibility and capacity to model complex nonlinear relationships, this study suggests that AE could be a potent tool for enhancing fuzzy time series clustering, given its capability to facilitate the correct identification of dates when a given CT occurred and assigning the dates to the associated CT.</p>

Classification of synoptic processes in the territory of Ukraine using a modified Jenkinson and Collison method

During the year, the territory of Ukraine is under the influence of various synoptic processes, which have a certain evolution in the surface conditions of the region and sometimes lead to the formation of unfavorable and dangerous weather conditions. The classification of synoptic processes makes it possible to create a set of daily synoptic situations taking into account the characteristics of a certain region, both for their use in weather forecasting and for studying the dynamics of regional synoptic processes under climate change. In this study, the modified version of Jenkinson and Collison method is used to classify synoptic processes on the territory of Ukraine, which is based on pressure data at the sea surface level and the geopotential heights at the level 500 hPa. The analysis of the obtained set of daily types of atmospheric circulation for the period 1948-2021 and the composite pressure fields built for each circulation type showed that all synoptic situations are clearly defined according to the classification and have seasonal features of frequency. During the year, advective processes of the western circulation group prevail, eastern advection is also often observed, and this type of circulation dominates in the spring months. The processes of the southern group are most relevant on the cold period of the year. Anticyclones occur more often over the region in winter and autumn, and cyclones are observed in summer and spring. The inclusion of 500 hPa level data in the classification makes it possible to take into account the three-dimensional structure of synoptic objects and distinguish such types of circulation as low cyclones and cold anticyclones, as well as troughs and cut-off lows at heights. It was found that low (thermal) cyclones and anticyclones make up a small proportionof synoptic situations, so the feasibility of their further inclusion in the typification for the territory of Ukraine is being discussed. The processes associated with the cut-off lows at the upper levels turned out to quite rare, but due to the possibility of the formation of dangerous weather conditions, this type of circulation is necessary in the classification of regional synoptic processes.

The Variability of Maximum Daily Precipitation and the Underlying Circulation Conditions in Kraków, Southern Poland

This article studies the intra-annual and long-term variability in the maximum daily precipitation totals and their association with atmospheric circulation in Kraków. It investigates daily precipitation maxima by year and by month. The research is based on daily precipitation totals in the years 1863–2021 and draws on the calendar of atmospheric circulation types by Niedźwiedź. It examines the frequency of precipitation maxima in individual months and their variation from one year to another. No statistically significant trend of change in precipitation over the study period has been found. All annual maximum daily precipitation totals in Kraków fall into the category of heavy precipitation (>10 mm), and almost 99% qualify as very heavy (>20 mm). In the summer months, these are about 3–4 times higher than in winter. The share of the daily precipitation maximum in the monthly total exceeds 30% in all months. The maximum daily precipitation occurring on 5 August 2021 was the highest in the period that extends from the start of instrumental measurements. The study period saw 12 cases of maximum precipitation that belong to ‘flood-inducing’ categories (over 70 mm/day). Such cases of the very heaviest precipitation occurred in cyclonic situations: Cc, Bc, Nc, NEc, Ec and SEc. Most spring and summer maxima were seen on days with a cyclonic circulation. The instances of high daily precipitation in the Kraków area led to the flooding of residential and historic buildings, as well as of municipal infrastructure.

On the Examination of the Relationship between Mean and Extreme Precipitation and Circulation Types over Southern Romania

The main goal of the present study is to identify the prevailing atmospheric circulation patterns (circulation types) that are associated with the occurrence of precipitation (both mean and extreme) over southern Romania. A daily circulation type calendar derived from an automatic and objective classification scheme is used in synergy with the daily precipitation time series from five weather stations in the study area for a sixty-year period (1961–2020). Both mean and extreme precipitation do not show statistically significant trends, except for the annual precipitation at Constanța, for the value with daily precipitation totals greater than the 95th percentile at Craiova and the number of days exceeding the 99th percentile at Buzău and Râmnicu -Vâlcea, where significant negative trends were noticed. Moreover, the precipitation trends were analyzed in relation to the atmospheric circulation types. Non-significant positive trends were observed for the precipitation amounts (annually, winter, spring, and autumn) corresponding to very rainy circulation types (C, Cwsw), while for summer, the equivalent trends were negative. Moreover, it became evident that during extreme precipitation events, the predominant circulation types (C, Cwsw) are associated with western or almost western atmospheric circulation and Mediterranean- or Atlantic-originated depressions.

The impact of horizontal resolution on the representation of atmospheric circulation types in Western Europe using the MPI‐ESM model

AbstractIn this study, the added value in using the sea level pressure field from the coupled higher‐resolution version of the Max Planck Institute Earth System Model (MPI‐ESM‐HR), compared to the lower‐resolution version (MPI‐ESM‐LR) for circulation typing, within the regional context of Western Europe was examined. The results show that the MPI‐ESM‐HR and the MPI‐ESM‐LR simulations can produce the classified circulation types (CTs) and their long‐term statistical characteristics as obtained from the ERA5 reanalysis. Overall, there are improvements in the composite maps, probability of occurrence and annual cycle of the simulated CTs in the MPI‐ESM‐HR compared to the MPI‐ESM‐LR. The model bias in simulating the structure of anticyclonic circulations over the Western European landmass was reduced by 14% under MPI‐ESM‐HR. Furthermore, under the shared socio‐economic pathways (SSP2‐4.5 and SSP5‐8.5) future emission scenarios, the historical CTs in the region of assessment were classified, suggesting that in Western Europe, the same historical CTs are present under future climate change scenarios. However, the frequency distribution and geographical structure of some of the CTs in Western Europe are projected to change by the MPI‐ESM model, especially under the higher future emission scenario.

Exceptionally Cold and Warm Spring Months in Kraków Against the Background of Atmospheric Circulation (1874–2022)

In the changing climate, exceptionally warm (EWMs) and dry spring months are increasingly observed. At the same time, exceptionally cold months (ECMs) are less frequent, although their impact on a warming climate becomes significant. Due to the role that such climatic anomalies play in the environment and their effects on human activity, it is very important to explain the causes of their occurrence. For this reason, in this study, the authors have attempted to determine the circulation conditions favourable to the occurrence of extremely cold (ECM) and warm (EWM) spring months in Kraków in the years 1874–2022. The study used the average temperature of individual spring months (March–May), as well as types of atmospheric circulation and air masses from the daily Calendar of Atmospheric Circulation Types for southern Poland. A distinct increase in spring air temperature (0.181 °C/10 years) and its individual months (0.162–0.191 °C/10 years) was confirmed. It was accompanied by a significant increase in the occurrence of EWM and a decrease in ECM. It was also found that the direction of air advection and the related temperature characteristics of air masses have the greatest impact on the occurrence of exceptionally cold or warm months. A slight positive effect of zonal circulation on the temperature increase at the beginning of the spring season and the advection of air from the south in April and east in May was found. In the case of the coldest months (ECMs), low temperatures most often developed in the presence of advection from the NW-N-NE directions.

Synoptic Weather Patterns and Atmospheric Circulation Types of PM2.5 Pollution Periods in the Beijing-Tianjin-Hebei Region

The variation of PM2.5 concentration in the atmosphere is closely related to the variation in weather patterns. The change in weather pattern is accompanied by the corresponding change in atmospheric circulation characteristics. It is necessary to explore the relationship between PM2.5 concentration changes and atmospheric circulation characteristics during pollution periods. In this paper, Lamb-Jenkinson objective classification method is applied to classify daily atmospheric circulation. The pollution periods are calculated and the atmospheric circulation variation rule is obtained. Combined with the physical parameter field (humidity, potential temperature, and potential height), a typical pollution period is analyzed. Additionally, the influence of atmospheric circulation type variation on PM2.5 concentration and transport channel during the pollution period was obtained. The results show that atmospheric circulation types in the study period are dominated by A-type (anticyclonic), N-type (north), and NE-type (northeast), indicating obvious seasonal differences, and the proportion of C-type (cyclonic) circulation was increased significantly in summer. During the pollution period analysis from 2 to 4 January 2019, atmospheric circulation type changed from N-type to NE-type (northeast), the wind direction changed from southeast wind, and the change of pressure gradient was consistent with the trend of the wind field. Moreover, the physical parameter field assisted in verifying the process of the pollution period from the conducive to the accumulation of PM2.5 to conducive to the deposition of pollutants and external transport. The research results would provide theoretical support for PM2.5 prediction during the pollution period and also supply a theoretical and technical basis for the establishment of ecological compensation standards for air pollution and atmospheric environmental control.

Classification of daily heavy precipitation patterns and associated synoptic types in the Campania Region (southern Italy)

Using a 20-year (2002−2021) dataset of daily precipitation collected by 107 rain gauges in the period from October to May, this study introduces a classification of the main heavy precipitation spatial patterns for the Campania Region (southern Italy). To pursue this aim, we apply a cluster analysis on the most relevant principal modes extracted from a principal component analysis of the between-day correlation matrix. The characteristics of the identified patterns, as well as their interannual and monthly distribution, are presented and discussed. Moreover, using global and regional reanalysis products, we have determined the large-scale and mesoscale atmospheric circulation types associated with heavy precipitation patterns.The heavy precipitation episodes are generally triggered by an upper level trough approaching the southern Italy from west and promoting a very moist southwesterly flow. They have been clustered into six different patterns. The first four exhibit a rainfall amount distribution strongly connected with the orography of the investigated region. In such scenarios, the orographic lifting, the low-level wind convergence induced by the orography and the transport of moisture from local sources (the western and the southern Mediterranean) and from distant regions (the Atlantic and the Africa tropical areas) can be regarded as the primary forcing of heavy rainfall. In the other two patterns, the highest precipitation is generally observed in the coastal areas (Gulfs of Naples and Salerno) and in the northwestern side of the region (Caserta district), respectively. In such circumstances, the abundant precipitation is closely linked to convective activity over the Tyrrhenian Sea, which is sustained by a low-level convergence and, in the sixth pattern, by a moisture plume coming from the tropics.The results of this study provide new insights about the links between torrential precipitation spatial distribution and atmospheric circulation schemes in the southern Italy and promise to add a useful contribution for civil protection activities related to the management of environmental risks.

ASSESSMENT OF THE DEPENDENCE OF WINTER WHEAT YIELD IN THE CENTRAL BLACK EARTH ECONOMIC REGION ON THE NATURE OF LARGE-SCALE CIRCULATION STRUCTURES OF THE ATMOSPHERE OF THE NORTHERN HEMISPHERE

The relationship between the average values of winter wheat yields in five regions that are part of the Central Black Earth Economic Region and the nature of global atmospheric circulation was analyzed using the typification of elementary circulation mechanisms of the northern hemisphere of the Earth, compiled by B.L. Dzerdzeevsky. The assessment was made for the spring-summer vegetation period of the crop in question, based on data from 1961 to 2020. Also, based on the results obtained, a correlation and regression analysis of the dependence of winter wheat yield on the total repeatability of days with one or another type of global atmospheric circulation for the spring-summer and spring periods of vegetation was carried out. It is noted that the decrease in the yield of winter wheat in relation to the previous year in the regions under consideration is characteristic of the long-term predominance of one type of global atmospheric circulation in the Northern Hemisphere of the Earth. The increase is observed when, in total, during the spring-summer and spring parts of the vegetation period, there is a predominance of two different types of atmospheric circulation.

Spatiotemporal variation of daily precipitation concentration and its potential relationship with climatic factors and land use types in the Haihe River basin, China

AbstractPrecipitation concentration is a key climatic factor in the hydrologic system. The purpose of this study was to explore the spatiotemporal variation in precipitation concentration and its possible relationship with large‐scale atmospheric circulation and land use types. Based on daily precipitation recorded at 254 stations during 1961–2019 throughout the Haihe River basin (HRB), linear slope and Manner–Kendall trend analysis were used to analyse the spatial variations and trends of the annual daily precipitation concentration index (CI). The Pearson correlation coefficient and cross wavelet analysis were used to evaluate potential correlations between CI and eight climatic factors. Meteorological stations were classified into three land use types: urban type (UT), farmland type (FT), and natural type (NT) using hierarchical clustering, and the impacts of land use types on CI variations and trends were investigated. Annual CI in HRB showed a significant downward trend with a linear rate of −0.0058/decade, and about 210 of the 254 stations had a downtrend, in which 42 stations were at the significance level of 0.05 but did not reach the significance level of 0.01, and 52 stations are at the 0.01 significance level. The East Asian monsoon index (EASMI), South Asian monsoon index (SASMI), South China Sea monsoon index (SCSMI), and Southern Oscillation Index (SOI) were positively correlated with CI, whereas the Pacific Decadal Oscillation (PDO), Multivariate ENSO index (MEI), and Western Pacific index (WP) were negatively correlated. The Sunspot index (SS) had a significant resonance period of 9–14‐year with CI. EASMI and ENSO events were the dominant factors driving CI trends. The negative CI trends of UT were more significant than those of FT and NT, with linear slope gaps of −0.0041/decade (UT versus FT) and −0.0064/decade (UT vs. NT), respectively.

Atmospheric circulation types and floods' occurrence; A thorough analysis over Greece

Floods have a direct impact on the society and the environment, causing human losses, affecting individual incomes and national economic activity including infrastructure damages. Atmospheric circulation is strongly related to both mean and extreme climate, with the latter being the driving force of adverse phenomena, such as inundations. The overarching goal of the research is the identification of those atmospheric circulation patterns that are associated with catastrophic flood events over Greece. An updated atmospheric classification scheme consisted of 12 circulation types (5 anticyclonic and 7 cyclonic) is implemented to detect and highlight the flood-dominant circulation types over the domain of interest. It is established that for a 7-year period (from 2012 to 2018), where reliable flood inventories are available as a derivative of the European Union (EU) Flood Directive implementation process, the dominant circulation type is the cyclonic type C with its center to be located over the Cyclades area. The study also reveals that during the most severe floods, the prevailing cyclonic types are substantially deeper than their mean anomaly field. Finally, out of the 14 River Basin Districts of Greece, Thrace (EL14) is the more flood prone area, while Eastern Macedonia (EL11) is far less flood affected. The introduced Floods' Frequency Vulnerability index (FFVI) showed that in the case of significant floods, Western Peloponnese (EL01) and Epirus (EL05) are the most vulnerable River Basin Districts. The proposed methodology of coupling circulation types with flood occurrences can be applied in all EU Member-States and set the base of effective floods' prediction mechanisms at River Basin Districts scales.

Common Error Patterns in the Regional Atmospheric Circulation Simulated by the CMIP Multi‐Model Ensemble

AbstractThe ability of global climate models to reproduce recurrent regional atmospheric circulation types is introduced as an overarching concept to explore potential dependencies between these models. If this approach is applied on a sufficiently large spatial domain, the similarity of the resulting error pattern can be compared from one model to another. By computing a pattern correlation matrix for a large multi‐model ensemble from the Coupled Model Intercomparison Project Phases 5 and 6, groups of comparatively strong correlation coefficients are obtained for those models working with similar atmospheric components. Thereby, frequent shared error patterns are found within the ensemble, which also occur for nominally different atmospheric component models. The error pattern correlation coefficients describing these similarities are nearly unrelated to model performance and can be used as statistical dependency weights.

A Comparative Analysis of Changes in Temperature and Precipitation Extremes since 1960 between China and Greece

The temporal and spatial variations of 26 extreme temperature and precipitation indices for China and Greece were comparatively analysed. Also, their association with atmospheric circulation types was evaluated using multiple linear regression. The calculation of the extreme indices was based on homogenized daily temperature and precipitation time series from 1960 to 2010 for Greece and 2021 for China. Extreme precipitation, intensity, and short-term heavy precipitation increased, while persistent heavy precipitation has decreased since 1960 in China. Short-term heavy precipitation has also shown an increasing trend in Greece, though total precipitation and persistent heavy precipitation decreased there between 1960 and 2010. Extreme cold events have tended to decrease, and extreme warm events have increased in both countries, a fact that can be attributed to global warming. For comparison, climatic warming in China was mainly seen in the half year of winter, while the extreme indices relevant to cold seasons such as FD0 and ID0 presented a small trend in Greece. The observed changes in many climatic indices, including RX5day and WSDI in China and R20MM, RX5day, CDD, PRCPTOT and FD0 in Greece, could be partly explained by those of the main large-scale circulation types in the corresponding regions. The significant multiple correlation coefficients of the main circulation types were up to 0.53 for RX5day and 0.54 for WSDI in China, and 0.74 for PRCPTOT and 0.71 for R20MM in Greece. The relationships between climatic indices and circulation types were closer in Greece than in China, especially for the precipitation indices.

Long-term changes in circulation conditions over southern Poland for the period 1874–2020

Abstract The study presents the long-term and annual trends in atmospheric circulation over southern Poland for the period 1874–2020. The analysis takes into account both the type of atmospheric circulation, and the types of air mass and atmospheric fronts. The study showed that there has been a noticeable decrease in the frequency of anticyclonic types of circulation and of air advection from the west and east, and a slight increase in advection from the south, as well as the presence of anticyclonic centres and cyclonic troughs. The research also found considerable changes in the frequency of the presence of polar air and of stationary and occluded fronts, as well as of days with several fronts moving over the study area.

Climate and ice conditions of East Siberian Sea during Holocene: Reconstructions based on sedimentary geochemical multiproxy

Reconstruction of ice conditions and climate of the East Siberian Sea during the Late Middle Holocene was implemented for the first time using a transfer function method based on marine sedimentation proxies. Transfer functions were developed based on a hydrometeorological time series of changes in mean annual air temperature (ΔT10) and the ice-free period (IF10) for the last 70–90 years and a geochemical time series of bottom sediments accumulated during this time, which were obtained using a submillimeter scanning of the core in the X-ray fluorescence analysis of synchrotron radiation. Geochemical time series of Holocene deposits were obtained from X-ray fluorescence analysis of the core in a step of 1–2 cm. Reconstruction of ice conditions and average annual air temperature revealed a decreasing trend of ΔT10 and IF10, which started from the middle Holocene up to the Little Ice Age due to an orbitally determined decrease in insolation. A synchronous periodicity of changes in ice cover and air temperature was revealed and approximated by periods of 1600 years for IF10 and 1740 years for ΔT10, which are comparable to Bond’s climatic cycles. These results indicates the telecommunication of the Atlantic processes, climate of the East Siberian Sea, and predominance of the cyclonic type of atmospheric circulation during the Holocene.

East Siberian Sea: Interannual heterogeneity of the suspended particulate matter and its biogeochemical signature

The East Siberian Sea (ESS) is the largest, shallowest and most icebound Arctic marginal sea. It receives substantial input of terrigenous material and climate-vulnerable old organic carbon from both coastal erosion and rivers draining the extensive permafrost-covered watersheds. This study focuses on the interannual variability and spatial distribution of suspended particulate matter (SPM) in the surface and bottom waters of the ESS during the ice-free period in 2000, 2003, 2004, 2005 and 2008. We report on the composition and variability of particulate organic carbon (POC), total nitrogen (TN), POC/TN ratios, carbon and nitrogen isotopes (δ13C, δ15N) and provide estimates of the contribution of terrestrial organic carbon (terrOC) based on the δ13C isotopic values.The results show that interannual SPM distribution and elemental-isotopic characteristics of POC differ significantly between the western biogeochemical province (WBP; West of 165oE) and the eastern biogeochemical province (EBP; East of 165oE) of the ESS. The SPM mean concentration in the WBP is almost an order of magnitude higher than in the EBP. From west-to-east of the ESS, SPM tends to become more depleted in δ15N, while the δ13C becomes isotopically heavier. This trend can be explained by a shift in organic matter sources from terrigenous origin (erosion of the coastal ice complex and riverine POC) to becoming dominantly from marine plankton.The maximum contribution of terrOC to POC reached 99% in parts of the WBP, but accounts for as low as 1% in parts of the EBP. At the same time, the type of atmospheric circulation and its associated regime of both water circulation and ice transport control a displacement of the semi-stable biogeochemical border between WBP and EBP to the east or to the west if compared to its long-term average position near 165oE. Our multi-year investigation provides a robust observational basis for better understanding of the transport and fate of terrigenous material upon entering the ESS shelf waters. Our results also provide deeper insights into the interaction in the land-shelf sea system of the largest shelf sea system of the World Ocean, the East Siberian Arctic Shelf system.

A deep learning based classification of atmospheric circulation types over Europe: projection of future changes in a CMIP6 large ensemble

High- and low pressure systems of the large-scale atmospheric circulation in the mid-latitudes drive European weather and climate. Potential future changes in the occurrence of circulation types are highly relevant for society. Classifying the highly dynamic atmospheric circulation into discrete classes of circulation types helps to categorize the linkages between atmospheric forcing and surface conditions (e.g. extreme events). Previous studies have revealed a high internal variability of projected changes of circulation types. Dealing with this high internal variability requires the employment of a single-model initial-condition large ensemble (SMILE) and an automated classification method, which can be applied to large climate data sets. One of the most established classifications in Europe are the 29 subjective circulation types called Grosswetterlagen by Hess & Brezowsky (HB circulation types). We developed, in the first analysis of its kind, an automated version of this subjective classification using deep learning. Our classifier reaches an overall accuracy of 41.1% on the test sets of nested cross-validation. It outperforms the state-of-the-art automatization of the HB circulation types in 20 of the 29 classes. We apply the deep learning classifier to the SMHI-LENS, a SMILE of the Coupled Model Intercomparison Project phase 6, composed of 50 members of the EC-Earth3 model under the SSP37.0 scenario. For the analysis of future frequency changes of the 29 circulation types, we use the signal-to-noise ratio to discriminate the climate change signal from the noise of internal variability. Using a 5%-significance level, we find significant frequency changes in 69% of the circulation types when comparing the future (2071–2100) to a reference period (1991–2020).

The Influence of Atmospheric Circulation on Mean and Extreme Weather Conditions on Kaffiøyra (NW Spitsbergen, Svalbard Archipelago) in the Summer Seasons 1975–2015

The paper presents results describing the influence of Atmospheric Circulation (AC) on meteorological conditions on Kaffiøyra (NW Spitsbergen, Svalbard Archipelago) in 23 summer seasons (July 21–August 31) in the years 1975, 1977–80, 1982, 1985, 1989, 1997–2000, 2005–15. The analysis covered the diurnal sums or means of major meteorological parameters: total cloudiness, sunshine duration, air temperature, wind speed, relative air humidity, water vapour pressure, and precipitation. Extreme weather events in terms of any given parameter were defined as days whose diurnal values (mean/sum) were in the ≤5th or ≥95th percentiles. The influence of AC on meteorological conditions on Kaffiøyra was analysed using the calendar of circulation types (CT) by T. Niedźwiedź et al. (Calendar of atmospheric circulation types for Spitsbergen–a digital dataset, 2018). In the study area, the variability of individual meteorological parameters depends primarily on air-mass advection direction, while type of baric regime is less important. Our study highlights that the greatest positive anomalies and a significant frequency of extreme values of cloudiness, wind speed, air temperature, humidity and precipitation occurred during air mass advection mainly from the SW and S. It was also demonstrated that sunshine duration correlated statistically significantly with the frequency of the anticyclonic macrotype, and precipitation with the cyclonic macrotype. The results confirmed that atmospheric circulation plays the most important role in shaping weather conditions in Spitsbergen.

Atmospheric circulation types controlling rainfall in the Central American Isthmus

AbstractRainfall mechanisms in the Central American Isthmus are controlled by complex physical interactions across spatial and temporal scales, which are reflected on the dynamics of atmospheric circulation patterns affecting the region. However, physical mechanisms and their relationships with thermodynamic distributions connected to overturning circulations remain elusive. Here, a set of six recurrent daily atmospheric patterns, or weather types (WT), is defined using a k‐means++ clustering algorithm on standardized fields of Convective Available Potential Energy (CAPE) and winds at 925, 850, and 200 hPa. The relationships between these weather types, their temporal characteristics, and anomalous distributions of moisture flux divergence, equivalent potential temperature (saturated and unsaturated), and observed rainfall are used to describe physical processes controlling the latter, for all seasons. Regional observed rainfall is analysed from a set of 174 automatic stations from all countries from Mexico to Panama. By modulating vertically integrated moisture fluxes, these weather types, and the different climate drivers linked to them, control the temporal and spatial rainfall characteristics in the region, especially over the Pacific side of the isthmus. During some stages of the regional rainy season, described by two weather types, thermal anomalies in convective quasi‐equilibrium characteristic of the upward branch of the Hadley cell force westerly flow over Central America, enhancing rainfall. While during other stages, the enhancement of the trades and the displacement of convection to the ITCZ area over the eastern tropical Pacific, characteristic of the midsummer drought, diminishes rainfall. This study sets the stage for a better understanding of the mechanistic relationship between these weather types and rainfall characteristics in general, like onset, demise, and duration of rainy seasons. Hence, these results can inform process‐based model diagnostics aiming at bias‐correcting climate predictions at multiple timescales.

Increasing atmospheric dust transport towards the western Mediterranean over 1948\u20132020

In this study, global reanalysis dataset fields of meteorological parameters (temperature and geopotential height at different atmospheric levels) in the period 1948–2020, were used to characterize the main dynamic and thermodynamic features of African dust outbreaks (ADO) produced over regions of the Iberian Peninsula and the Balearic Islands. The record of ADO previously identified with a tried-and-true procedure in 8 different areas of this domain in the period 2001–2020 and the data sets of dust load contributions estimated for all ADO days in each region, were used to check our results. Thus, we demonstrated that air masses of African origin produced a significant increase in the levels of certain thermodynamic variables (geopotential thickness in the 1000–500 hPa layer (GT), mean potential temperature between 925 and 700 hPa (TPOT), and temperature anomalies at 850 hPa (TANOM)) over the regions of study, especially when particular synoptic-scale atmospheric circulation types (CT) occurred. Moreover, higher levels of the three thermodynamic parameters resulted in events with higher contributions of dust load to the regional background levels of PM10 in all regions. Finally, we obtained a statistically significant upward trend for days under ADO CT and their associated daily mean values of GT, TPOT and TANOM from 1948 to 2020. These results point to an increase in the frequency of air mass transport from North Africa to the western Mediterranean basin and on the intensity of the ADO produced as a consequence of this transport, over 1948–2020.