Air-stagnation episodes based on regional climate models part I: evaluation over Europe

Nieuwenhuyse, Joren Van; Schaeybroeck, Bert Van; Caluwaerts, Steven; Deyn, Jonathan De; Delcloo, Andy; Troch, Rozemien De; Hamdi, Rafiq; Termonia, Piet

doi:10.1007/s00382-023-06665-2

Cited by 5 publications

(2 citation statements)

References 68 publications

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“…Grid-wise bias adjustments on the climate projections are not performed due the danger of altering spatial patterns (Lehner et al, 2023). To ensure that systematic biases are small, all variables are used as differences between two points except the wind speed in 500 hPa, which absolute values were expected to be captured realistically due to conditions close to the free atmosphere (Brands et al, 2011(Brands et al, , 2013Van Nieuwenhuyse et al, 2023). In this study, the names of the individual models are abbreviated.…”

Section: Introductionmentioning

confidence: 99%

Analysing CMIP5 EURO-CORDEX models in their ability to produce south foehn and the resulting climate change impact on frequency and spatial extent over western Austria

Maier,

Lehner,

Klisho

et al. 2024

Preprint

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Abstract. Foehn has an impact on various climatological variables like temperature and humidity in the highly populated valleys of western Austria. With increasing global warming, the question arises as to how well climate projections are able to produce conditions for foehn and how their occurrence changes with climate change. This study uses six XGBoost models to classify south foehn in EURO-CORDEX climate models of CMIP5 generation for two spatial extents (localised and widespread) and three regions Vorarlberg, Tiroler Oberland and Tiroler Unterland in western Austria, located in the Eastern Alps. For each region, a model for distinguishing foehn from no foehn and one to distinguish the foehn event's spatial extent is trained. Several meteorological inputs on pressure levels from ERA5 reanalysis in combination with training data derived from semi-automated weather station data with Objective Foehn Classification are used in the training process. Weights for individual models are derived by analysing the performance of EURO-CORDEX models in their ability to produce south foehn and considering their independence from each other. The performance of individual EURO-CORDEX models is hereby evaluated by analysing their biases for annual occurrence, seasonal accuracy and inter-annual variability in comparison to the training data.The training data confirm other studies by showing that the three selected regions behave differently in their south foehn occurrence and in the portion of widespread events. Bias analysis shows a pronounced negative bias in annual foehn occurrence for models driven by the general circulation model ICHEC-EC-EARTH or MOHC-HadGEM2-ES. EURO-CORDEX models perform similar in capturing south foehn's seasonality, but highly vary in reproducing the inter-annual variability in the historical period. A weighted trend analysis for future behaviour of south foehn in the 21st century shows a slight decrease in south foehn frequency under increasing warming conditions in the Tirol regions but an increase in widespread events in all regions, most pronounced in Vorarlberg at the strongest warming. Further, a shift in foehn seasonality can be observed in all regions with a higher frequency in the spring months and a lower frequency from July to October, also depending on the climate change signal.

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Section: Introductionmentioning

confidence: 99%

Analysing CMIP5 EURO-CORDEX models in their ability to produce south foehn and the resulting climate change impact on frequency and spatial extent over western Austria

Maier,

Lehner,

Klisho

et al. 2024

Preprint

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“…Several relative thresholds have been proposed to define calm or weak wind days: 10 th percentile [33,34], or first tercile [11], for example. Absolute values have also been employed: related to wind measurements limitations (less than 5 knots = 2.57 m/s, [32]), light breezes (below 4 m/s, [35,36]), air stagnation conditions (less than 3.2 m/s, [37,38]), or low wind speeds or calms (less than 1 m/s, [39], being most of them related to days below the cut-in threshold (lowest operational limit of wind turbines [40][41][42][43][44][45]). The WMO [46] observational guidelines (based on the Beaufort wind scale) states that calm wind speed means less than 0.2 m/s (0 m/s is even sometimes used to define calm periods [47]), light air up to 1.5 m/s, or light breeze less than 3.3 m/s.…”

Section: Introductionmentioning

confidence: 99%

Low wind climatology (1979-2018) over Europe from ERA5 reanalysis

Gutiérrez

Molina

Ortega

et al. 2023

Preprint

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Research and wind speed assessment has increased lately among other things, due to its interest as a renewable energy resource. Whereas mean values and trends are commonly studied, less attentions is paid to the evaluation of extremes. In terms of lower winds, it is difficult to find agreement on a definition for those conditions. Here, the long-term characterization of low wind values over oceanic and land regions in Europe is assessed from hourly data of ERA5 reanalysis for the period 1979-2018. An absolute threshold (cut-in) related to a generalized wind power curve is used. The number of hours below cut-in threshold (3 m/s) present a reasonable agreement with the available observations, with annual values around 3000-4000 h for most of the locations over Europe, although severe limitations are found to properly represent wind speed field over mountainous areas. Important differences in the amount of hours below cut-in threshold are obtained between northern and southern regions of the domain, where the overall more complex orography and coast line seems to play a relevant role. Interannual and seasonal low wind variability show differences larger than 20-25\% for both timescales. Atlantic Ocean and Mediterranean regions behave differently, but both with less low wind values than land regions. In terms of persistence, analysis of low wind spells indicate that the largest ones, on annual averages, can reach up to 120 consecutive hours (4-5 days) over many land areas. Overall, mean hourly wind spells range from 10 to 20 h, with more than 200 episodes per year

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Low-wind climatology (1979–2018) over Europe from ERA5 reanalysis

Gutiérrez,

Molina,

Ortega

et al. 2024

Clim Dyn

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Research on wind speed characteristics is of interest for many disciplines from renewable energy to ecology. Whereas mean values and trends are commonly studied, less attentions is paid to the evaluation of other features such as low-wind conditions. However, there is no clear definition of “low-wind” on the literature. Here we propose the Beaufort scale to characterize low-wind values over Europe through a fixed threshold of 3.3 m/s (“light breeze" category). Climatological (1979–2018) assessment is performed using ERA5 reanalysis hourly data. The limited amount of observational stations indicate a 40-year averaged amount of around 3500 low-wind hours/year, comparable to the corresponding ERA5 reanalysis cells, which shows severe limitations over mountainous areas. The European domain features a strong north–south low-wind hours gradient. Remarkable patterns are obtained over coasts and complex orography regions. Seasonal low-wind variability range around 20–25% for most of the regions, and interannual coefficient of variability from 0.05 to 0.17. Oceanic regions present smaller low-wind values than land areas, with Atlantic and Mediterranean regions behaving differently. The largest annual spells (consecutive) hourly low-wind episodes are within the range from 5 to 10 days, (from 120 to 240 h) over many land areas. Annual mean hourly wind spells typically extend from 15 to 25 h, with more than 200 episodes.

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Air-stagnation episodes based on regional climate models part I: evaluation over Europe

Cited by 5 publications

References 68 publications

Analysing CMIP5 EURO-CORDEX models in their ability to produce south foehn and the resulting climate change impact on frequency and spatial extent over western Austria

Analysing CMIP5 EURO-CORDEX models in their ability to produce south foehn and the resulting climate change impact on frequency and spatial extent over western Austria

Low wind climatology (1979-2018) over Europe from ERA5 reanalysis

Low-wind climatology (1979–2018) over Europe from ERA5 reanalysis

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