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Global Climate Models (GCMs) generally exhibit significant biases in the representation of large-scale atmospheric circulation. Even after a sensible bias adjustment these errors remain and are inherited to some extent by the derived downscaling products, impairing the credibility of future regional projections. In this study we perform a process-based evaluation of state-of-the-art GCMs from CMIP5 and CMIP6, with a focus on the simulation of the synoptic climatological patterns having a most prominent effect on the European climate. To this aim, we use the Lamb Weather Type Classification (LWT, Lamb British isles weather types and a register of the daily sequence 736 of circulation patterns 1861-1971. METEOROL OFF, GEOPHYS MEM; 737 GB; DA 1972; NO 116; PP 1-85; BIBL 2P1/2, 1972), a subjective classification of circulation weather types constructed upon historical simulations of daily mean sea level pressure. Observational uncertainty has been taken into account by considering four different reanalysis products of varying characteristics. Our evaluation unveils an overall improvement of salient atmospheric circulation features consistent across observational references, although this is uneven across models and large frequency biases still remain for the main LWTs. Some CMIP6 models attain similar or even worse results than their CMIP5 counterparts, although in most cases consistent improvements have been found, demonstrating the ability of the new models to better capture key synoptic conditions. In light of the large differences found across models, we advocate for a careful selection of driving GCMs in downscaling experiments with a special focus on large-scale atmospheric circulation aspects.

Weather types (WTs) are common atmospheric patterns that shape weather and climate characteristics. While an improved understanding of WTs can provide insights into seasonal predictions, few studies have investigated WT transitions and their impacts on temperature and precipitation across the continental United States (U.S.). This study focuses on 23 WT scenarios, involving five weather type classifications evaluated over the years 1979–2018 derived from 500-hPa geopotential height anomaly. There are five persistent WT scenarios with the same WT on back-to-back days and 18 non-persistent transition scenarios. Two additional non-persistent scenarios had no occurrences during this time. Persistent WT/non-persistent transition scenarios account for ~ 70%/30% of total transition cases, respectively. The weather regime transitions exhibit distinct impacts on temperature and precipitation across the U.S. The impacts of WT transitions on precipitation can be explained by changes in moisture flux and vertical pressure velocity. WT transitions show strong seasonality, with stronger impacts in winter months than summer months, leading to larger temperature and precipitation anomalies. Persistent scenarios of WT transitions account for the vast majority of transition cases and contribute more to individual WT trends. Our results suggest WT transitions play a crucial role in modulating temperature and precipitation anomalies. An improved understanding of WT transitions sets the stage for improving seasonal to sub-seasonal forecasts of the U.S. climate.

Selecting climate model projections is a common practice for regional and local studies. This process often relies on local rather than synoptic variables. Even when synoptic weather types are considered, these are not related to the variable or climate impact driver of interest. Therefore, most selection procedures may not sufficiently account for atmospheric dynamics and climate change impact uncertainties. This study outlines a selection methodology that addresses both these shortcomings. Our methodology first optimizes the Lamb Weather Type classification for the variable and region of interest. In the next step, the representation of the historical synoptic dynamics in Global Climate Models (GCMs) is evaluated and accordingly, low-performing models are excluded. In the last step, indices are introduced that quantify the climate change signals related to the impact of interest. Using these indices, a scoring method results in assessing the suitability of GCMs. To illustrate the applicability of the methodology, a case study of extreme heat in Belgium was carried out. This framework offers a comprehensive method for selecting relevant climate projections, applicable in model ensemble-based research for various climate variables and impact drivers.

Cold- and heat-related mortality poses significant public health concerns worldwide. Although there are numerous studies dealing with the association between extreme ambient temperature and mortality, only a small number adopt a synoptic climatological approach in order to understand the nature of weather systems that precipitate increases in cold- or heat-related mortality. In this paper, the Lamb Weather Type synoptic classification is used to examine the relationship between daily mortality and weather patterns across nine regions of England. Analysis results revealed that the population in England is more susceptible to cold weather. Furthermore, it was found that the Easterly weather types are the most hazardous for public health all-year-long; however, during the cold period, the results are more evident and spatially homogenous. Nevertheless, it is noteworthy that the most dangerous weather conditions are not always associated with extreme (high or low) temperatures, a finding which points to the complexity of weather-related health effects and highlights the importance of a synoptic climatological approach in elucidating the relationship between temperature and mortality.

The detection and the functioning of the mid-summer drought (MSD) represent valuable information due to its socio-economic implications for the Caribbean. Current methods using local-scale rainfall to define the MSD have some limitations. This paper presents a novel approach to detect MSD from regional-scale weather types (WT). Long sequences of a typical summertime anticyclonic WT allow the detection of the onset and demise dates of the MSD for most years in 1950–2021. The MSD defined with WT (MSD-WT) begins rather abruptly on June 13th and concludes on August 21st, on average. While the interannual variations of the MSD-WT onset are relatively weak, long-term trends since 1950 indicate progressive earlier onsets, longer durations, and weakening intensities of the MSD-WT. Our results do not show the anticipated westward shift of the North Atlantic subtropical high pressure typically related to MSD. Instead, they indicate a halt of its eastward shift close to the MSD-WT onset. The absence of significant correlations between MSD-WT onset and either the Tropical North Atlantic or the Eastern Tropical Pacific sea surface temperature (SST) in May–June also suggests a mostly intrinsic atmospheric mechanism locked to the annual cycle, thus limiting the seasonal predictability of the MSD-WT onset. Furthermore, our results indicate a lag between the timing of increased subsidence, acceleration of the Caribbean low-level jet (CLLJ), and intensification of the deep convection over Central America and Mexico. This leads us to develop a novel hypothesis putting forward the monsoon circulation over Meso-America as a potential precursor of the increased subsidence over the Caribbean basin and the synchronous acceleration of CLLJ. The MSD-WT demise is more gradual and corresponds to a decrease in regional-scale mean sea level pressure and a weakening of the CLLJ. MSD-WT demise dates exhibit also relatively larger interannual variations but, unlike its onset, do not show any significant long-term trend. Anomalously warm (cold) Tropical North Atlantic and cold (warm) East Pacific SST from early June are correlated with an earlier (later) MSD-WT demise than usual. MSD-WT demise seems to involve regional-scale air-sea couplings and exhibits thus more seasonal predictability. Finally, despite a consistent response to the CLLJ, distinct processes seem to produce the relatively dry conditions observed over the Pacific coast of Central America and the Caribbean basin during the MSD.

The availability of reliable information on local climatic-tourism conditions is a growing need due to the influence it exerts on the quality of the organizational strategy of tourist destination’s, and travel experience. Evaluations of the tourism potential of the climate have been carried out on a daily or monthly resolution, thus limiting the collection of detailed information that makes it possible to fine-tune tourism management and operational decision-making on an intraday scale. This research is the first case study to analyse the climatic suitability for nature tourism, using the weather types method at hourly resolution. The study applies to arid tourist destinations in Isfahan province (Iran). The detailed resolution has made it possible to identify the time slots favourable to the development of nature tourism in those periods of the year recognized as critical in the daily resolution analyses. In the same way, the hourly resolution has also identified critical bands in those periods indicated as favourable in the evaluations to daily resolution. The hourly resolution provides detailed information that can allow tourists and also tourism managers to establish intraday adaptation strategies that make it possible to develop the activity even in places with extreme climates.

The dates of the transition between winter and summer (W2S) and between summer and winter (S2W) regional-scale atmospheric regimes have been defined using daily weather types above and around the Caribbean basin from 1979 to 2017. The uncertainties due to either the use of two different reanalyses (i.e., NCEP-DOE and ERA-Interim) or the parametrization used for the definition of the transition dates have typically a small impact on the interannual variability of the seasonal transitions. When both reanalyses are considered together, the average W2S transition date occurs, on average, on May 13 (with a standard deviation of 9 days) while the S2W transition date occurs, on average, on October 26 (with a standard deviation of 12 days). The atmospheric characteristics associated with both transitions reveal asymmetries in the annual cycle. The W2S transition is rather abrupt and near-synchronous to a rather sharp increase of rainfall, propagating from Central America to the NE of the Caribbean basin, and a weakening of the Caribbean Low Level Jet. The W2S transition is also not preceded by any significant sea surface temperature (SST) anomalies either in the tropical North Atlantic or the Eastern Pacific. On the other hand, the S2W transition is overall smoother, and anomalously warm (cold) SST over the Caribbean Sea and Gulf of Mexico (Eastern Pacific) during the boreal summer are usually related to a delayed transition (and vice versa). The interannual variations of S2W and W2S transitions are mostly independent to each other. The potential and real-time predictability of the W2S transition is explored using a subseasonal-to-seasonal prediction ensemble (11 runs from 1998 to 2017) from the ECMWF model. Its skill is close to zero with a lead time longer than 15–20 days, confirming the weak impact of the antecedent SST upon the W2S transition. The skill suddenly increases from late April, 2–3 weeks only before the mean W2S transition date. It suggests that some atmospheric forcing, operating from synoptic to intra-seasonal time scale, plays a role, but it seems barely related to any occurrence, or sequence, of specific weather types.

We present an analysis of the impact of circulation weather types (CT) on a factor that might influence biological systems and the human condition, the electric state of the atmosphere. We present results on the influence of CT to the magnitude, the direction (positive or negative), the fluctuation magnitude, and the short-term peaks of the atmospheric electric field (potential gradient, PG), using data from a station in Greece. CTs with high vorticity centers over Greece are associated with high positive and negative excursions of the PG, higher PG variability, and rain events. CTs with thinner 850–500 hPa layer are associated with higher daily mean values of fair-weather PG. We also examine the influence of CT on the frequency and amplitude of the naturally occurring extremely low-frequency electric field fluctuations known as Schumann resonances (SR) using data from a station in Hungary. The first and second mode SR frequencies are increased during CTs associated with higher 500 hPa geopotential heights and higher 850–500 hPa layer thickness. This hints to a lower-upper atmosphere coupling. So, CTs not only influence the general temperature and humidity conditions to which the biosphere is exposed, but they also affect its exposure to atmospheric electric fields.

The Lamb weather type series is a subjective catalogue of daily atmospheric patterns and flow directions over the British Isles, covering the period 1861–1996. Based on synoptic maps, meteorologists have empirically classified surface pressure patterns over this area, which is a key area for the progression of Atlantic storm tracks towards Europe. We apply this classification to a set of daily pressure series from a few stations from western Europe, in order to reconstruct and to extend this daily weather type series back to 1781. We describe a statistical framework which provides, for each day, the weather types consistent enough with the observed pressure pattern, and their respective probability. Overall, this technique can correctly reconstruct almost 75% of the Lamb daily types, when simplified to the seven main weather types. The weather type series are described and compared to the original series for the winter season only. Since the low frequency variability of synoptic conditions is directly related to the North Atlantic Oscillation (NAO), we derive from the weather type series an NAO index for winter. An interesting feature is a larger multidecadal variability during the nineteenth century than during the twentieth century.

This article applies the weather types method to assess the climate suitability for nature-based tourism (NBT) in the arid and hyper-arid climate zones of the province of Isfahan (Iran) based on bioclimatic criteria and the preferences of Iranian domestic tourists identified by means of a survey. To date, there are no climate potential assessments for the practice of nature tourism based on an analysis of climate preferences in the study area. According to the results, the distribution of favorable weather types in the study area between March and November during the period 1998–2017 showed that there is a low season in summer and two high seasons corresponding to autumn and spring. The highest frequencies of weather types conducive to NBT were recorded between the second half of September to the first half of November and between the second half of April until the end of May. The calendars resulting from application of the weather types method will serve as an efficient tool for providing tourists and the region’s main tourist stakeholders with information; in the case of the latter, they will be particularly useful for destination planning and activity scheduling.