BORA IN REGIONAL CLIMATE MODELS: IMPACT OF MODEL RESOLUTION ON SIMULATIONS OF GAP WIND AND WAVE BREAKING

Bora, a mesoscale wind system on the eastern Adriatic coast, profoundly impacts the local weather conditions. During easterly inflow, wave breaking generates heavy downslope winds in the lee of the Dinaric Alps. Additionally, gap winds emerge in canyons like the Vratnik Pass near Senj and enhance the Bora to a jet-like flow. The representation of these processes in numerical models is highly dependent on the surface description and therefore on model grid spacing. This study evaluates two simulations with the regional climate model COSMO-CLM with grid spacing of 0.025° and 0.11° regarding Bora winds. Strong Bora events are discussed in detail using observations between December 1999 and November 2000. The model results show that a 0.025° high-resolution simulation can well reproduce both phenomena gap wind and wave breaking. The 0.11° simulation resolves gap winds surprisingly well but misses wave breaking events

BORA IN REGIONAL CLIMATE MODELS: IMPACT OF MODEL RESOLUTION ON SIMULATIONS OF GAP WIND AND WAVE BREAKING

Bora, a mesoscale wind system on the eastern Adriatic coast, profoundly impacts the local weather conditions. During easterly inflow, wave breaking generates heavy downslope winds in the lee of the Dinaric Alps. Additionally, gap winds emerge in canyons like the Vratnik Pass near Senj and enhance the Bora to a jet-like flow. The representation of these processes in numerical models is highly dependent on the surface description and therefore on model grid spacing. This study evaluates two simulations with the regional climate model COSMO-CLM with grid spacing of 0.025° and 0.11° regarding Bora winds. Strong Bora events are discussed in detail using observations between December 1999 and November 2000. The model results show that a 0.025° high-resolution simulation can well reproduce both phenomena gap wind and wave breaking. The 0.11° simulation resolves gap winds surprisingly well but misses wave breaking events

Mistral and Tramontane wind systems in climate simulations from 1950 to 2100

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Maritime transport and regional climate change impacts in large EU islands and archipelagos

Maritime transport is a vital sector for global trade and the world economy. Particularly for islands, there is also an important social dimension of this sector, since island communities strongly rely on it for a connection with the mainland and the transportation of goods and passengers. Furthermore, islands are exceptionally vulnerable to climate change, as the rising sea level and extreme events are expected to induce severe impacts. Such hazards are anticipated to also affect the operations of the maritime transport sector by affecting either the port infrastructure or ships en route. The present study is an effort to better comprehend and assess the future risk of maritime transport disruption in six European islands and archipelagos, and it aims at supporting regional to local policy and decision-making. We employ state-of-the-art regional climate datasets and the widely used impact chain approach to identify the different components that might drive such risks. Larger islands (e.g., Corsica, Cyprus and Crete) are found to be more resilient to the impacts of climate change on maritime operations. Our findings also highlight the importance of adopting a low-emission pathway, since this will keep the risk of maritime transport disruption similar to present levels or even slightly decreased for some islands because of an enhanced adaptation capacity and advantageous demographic changes.Open Access funding enabled and organized by Projekt DEAL.This work has received funding from the European Union’s H2020 Research and Innovation Programme under grant agreement no. 776661 (SOCLIMPACT project). It was also supported by the EMME-CARE project, which has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 856612, as well as matching co-funding by the Government of the Republic of Cyprus.Peer reviewe

Mistral and tramontane: Simulation of mesoscale winds in regional climate models

Mistral and Tramontane are wind systems in southern France and the western Mediterranean Sea. Both are caused by similar synoptic situations and channeled in valleys. Their relevance for the climate of the western Mediterranean region motivated this work. The representation of Mistral and Tramontane in regional climate simulations was surveyed with the models ALADIN, WRF, PROMES, COSMO-CLM, RegCM, and LMDZ. ERA-Interim and global CMIP5 simulations (MPI-ESM, CMCC-CM, HadGEM2-ES, and CNRM-CM5) provided the lateral boundary data for the regional simulations regarding the 20th century and two representative concentration pathways for the 21st century (RCP4.5 and RCP8.5). A Mistral and Tramontane time series, a principal component analysis of pressure fields, and a Bayesian network were combined to develop a classification algorithm to identify pressure patterns in favor of Mistral and Tramontane. The regional climate models were able to reproduce the observed climatology of Mistral and Tramontane. Compared to observational data (SAFRAN and QuikSCAT), the simulations underestimate the wind speed over the Mediterranean Sea, mainly at the borders of the main flow. Simulations with smaller grid spacing showed better agreement with the observations. A sensitivity study tested the influence of the Charnock parameter on the Mistral wind field. Its value impacted both wind speed and wind direction. Decreasing the orographic resolution in idealized simulations using COSMO-CLM caused a reduction in wind speed and a broader flow area. Including a parameterization for subgrid scale orography improved the simulation. However, an accurate simulation of Mistral and Tramontane still requires a high-resolution orography. The classification algorithm also was applied to pressure fields from regional climate simulations driven by global simulation data. At the end of the 21st century, only small, non-significant changes in the number of Mistral days per year occur in the projection simulations. The number of Tramontane days per year decreased significantly.Mistral und Tramontane sind die im Westen des Mittelmeeres vorherrschenden Windsysteme. Beide entstehen unter ähnlichen synoptischen Bedingungen und zeichnen sich durch Kanalisierung in Tälern Südfrankreichs aus. Die Relevanz von Mistral und Tramontane für das Klima des westlichen Mittelmeergebiets, unter anderem durch Tiefenwasserbildung, motivierte diese Arbeit. Es wurde die Darstellung von Mistral und Tramontane in regionalen Klimasimulationen mit den Modellen ALADIN, WRF, PROMES, COSMO-CLM, RegCM und LMDZ untersucht. Angetrieben wurden die Simulationen mit Daten aus ERA-Interim und globalen CMIP5 Simulationen (MPI-ESM, CMCC-CM, HadGEM2-ES und CNRM CM5). Zwei repräsentative Konzentrationspfade wurden untersucht (RCP4.5 und RCP8.5). Eine Mistral- und Tramontane-Zeitserie wurde zusammen mit einer Hauptkomponentenanalyse von Druckfeldern und einem Bayesschen Netz zur Entwicklung eines Druckmuster Klassifikationsalgorithmus genutzt. Die regionalen Klimamodelle sind in der Lage die Klimatologie von Mistral und Tramontane zu reproduzieren. Im Vergleich mit Beobachtungsdaten (SAFRAN und QuikSCAT) unterschätzten die Simulationen die Windgeschwindigkeit über dem Mittelmeer, besonders an den Rändern der Hauptströmung. Simulationen mit kleinerer Gitterweite zeigten eine größere Übereinstimmung mit den Beobachtungen. In einer Sensitivitätsstudie wurde der Einfluss des Charnock Parameters auf das Mistral-Windfeld getestet. Es zeigte sich, dass sein Wert sowohl die Windgeschwindigkeit als auch die Windrichtung beeinflusst. Außerdem führte eine Verringerung der Orographiauflösung in idealisierten Simulationen mit COSMO-CLM zu einer geringeren Windgeschwindigkeit und gleichzeitig einem breiteren Mistralstrom. Die Berücksichtigung einer Parametrisierung für subgridskalige Orographie verbesserte die Darstellung. Dies zeigt, dass für eine genaue Simulation von Mistral und Tramontane nicht nur eine hohe Auflösung im numerischen Gitter, sondern auch in der Orographie wünschenswert ist. Der Klassifikationsalgorithmus wurde auch auf Druckmuster aus regionalen Klimasimulationen, die mit globalen Simulationsdaten angetrieben wurden, angewendet. Gegen Ende des 21. Jahrhunderts zeigten sich kleine, statistisch nicht signifikante Änderungen in der Anzahl der Mistraltage pro Jahr für beide repräsentative Konzentrationspfade. Die Anzahl der Tramontanetage pro Jahr nahm jedoch signifikant ab

State of the Simulation of Mesoscale Winds in the Mediterranean and Opportunities for Improvements

The Mediterranean region is a densely populated and economically relevant area with complex orography including mountain ranges, islands, and straits. In combination with pressure gradients, this creates many mesoscale wind systems that cause, e.g., wind gusts and wildfire risk in the Mediterranean. This article reviews the recent state of the science of several mesoscale winds in the Mediterranean and associated processes. Previous work, including case studies on several time ranges and resolutions, as well as studies on these winds under future climate conditions, is discussed. Simulations with grid spacings of 25 to 50 km can reproduce winds driven by large-scale pressure patterns such as Mistral, Tramontane, and Etesians. However, these simulations struggle with the correct representation of winds channeled in straits and mountain gaps and around islands. Grid spacings of 1–3 km are certainly necessary to resolve these small-scale features. The smaller grid spacings are widely used in case studies, but not yet in simulations over large areas and long periods, which also could help to understand the interaction between small-scale phenomena in separate locations. Furthermore, by far not all Mediterranean straits, islands, and mountain gaps were studied in-depth and many interesting Mediterranean small-scale winds still need to be studied