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In the autumn, the French Mediterranean area is frequently exposed to heavy precipitation events whose daily accumulation can exceed 300 mm. One of the key processes contributing to these precipitation amounts is deep convection, which can be explicitly resolved by state-of-the-art convection-permitting models to reproduce heavy rainfall events that are comparable to observations. This approach has been tested and performed at climate scale in several studies in recent decades for different areas. In this research, we investigate the added value of using an ensemble of three climate simulations at convection-permitting resolution (approx. 3 km) to replicate extreme precipitation events at both daily and shorter timescales over the south of France. These three convection-permitting simulations are performed with the Weather Research and Forecasting (WRF) Model. They are forced by three EURO-CORDEX simulations, which are also run with WRF at the resolution of 0.11 ∘ (approx. 12 km). We found that a convection-permitting approach provides a more realistic representation of extreme daily and 3-hourly rainfall in comparison with EURO-CORDEX simulations. Their similarity to observations allows use for climate change studies and its impacts. [ABSTRACT FROM AUTHOR]

In the autumn, the French Mediterranean area is frequently exposed to heavy precipitation events whose daily accumulation can exceed 300 mm. One of the key processes contributing to these precipitation amounts is the deep convection, which can be resolved explicitly by state-or-the-art convection-permitting model to reproduce heavy rainfall events that are comparable to observations. However, this approach has never been used in climate simulation for the Mediterranean coastal region. In this research, we investigate the added values of using three ensembles of climate simulations at convection-permitting resolution (approx. 3 km) in replicating extreme precipitation events in both daily and shorter time scale over the South of France. These three convection-permitting simulations are performed with the Weather Research and Forecasting Model (WRF). They are forced by three EURO-CORDEX simulations, which are also downscaled with WRF at the resolution of 0.11° (approx. 12 km). We found that a convection-permitting approach provides a more realistic representation of extreme daily and 3-hourly rainfall simulations in comparison with EURO-CORDEX simulations. Their similarity with observations allows a use for climate change studies and its impacts. [ABSTRACT FROM AUTHOR]

Compares two different definitions of midlatitude weather regimes. Emergence of weather regimes in dynamical meteorology as a particular representation of atmospheric dynamics; Recurrent atmospheric patterns; Quasi-stationary patterns; Use of cluster analysis; Performance of analysis over Atlantic and Pacific sectors; Description of methodology used to identify quasi-stationary regimes.

Presents a study of low-frequency oscillations and weather regimes in the midlatitudes of the Northern Hemisphere. The multichannel singular spectrum analysis; The low-frequency oscillations and weather regimes; Results and conclusions.

Climate simulations at convection-permitting resolution have been used more frequently thanks to the development of computational power. Those simulations can produce realistic surface fields in regions of complex orography that play a vital role in initializing convective processes. They also resolve physically deep convection system in sub-grid scale. Consequently, the simulation of downpour events, especially in sub-daily time scale, is expected to be enhanced and better represented in a changing climate, which is necessary for climate impact studies. In this research, we investigate the advantages of using two ensembles of high resolution (approx. 3 km) simulations in replicating extreme precipitation in both daily and shorter time scale over the South of France during a historical period (1951-1980). These two convection-permitting simulations (CPS) are performed with the Weather Research and Forecasting Model (WRF). They are forced by EURO-CORDEX simulations, which are also downscaled with WRF at the resolution of 12-km and driven by HADGEM and IPSL models (i.e. the 3-km is not nested simultaneously within 12-km downscaling from GCMs). All simulations are evaluated using a metric of extreme indices against in-situ and gridded observations to quantify the added value of CPSs compared to convection-parameterized simulations. In addition, the analysis of the dependence of water holding capacity on temperature is also considered. These assessments would facilitate a more reliable attribution of extreme hourly precipitation to climate change, which has been a big challenge to scientific community so far. [ABSTRACT FROM AUTHOR]

The impact of meteorological forcings on gas phase air pollutants (ozone and nitrogen dioxide) over Europe was studied using four offline chemistry transport models (CTMs) as part of the IMPACT2C project. This study uses long (20- and 30-year) simulations to evaluate the present-day performance of the CTMs, which is a necessary first step before undertaking any analysis of future air quality impacts. Two sets of meteorological forcings were used for each model: reanalysis of past observation data (ERA-Interim) and Global Climate Model (GCM) output. The results for the simulations forced by reanalysis data were assessed in relation to AirBase v7 measurement data, and it was determined that all four models slightly overpredict annual O 3 values (mean biases range between 0.7 and 6.6 ppb) and three out of the four models underpredict observed annual NO 2 (mean biases range between −3.1 and −5.2 ppb). The simulations forced by climate models result in spatially averaged monthly concentrations of O 3 that are generally between 0 and 5 ppb higher than the values obtained from simulations forced by reanalysis data; therefore it was concluded that the use of climate models introduces an additional bias to the results, but this bias tends not to be significant in the majority of cases. The bias in O 3 results appears to be correlated mainly to differences in temperature and boundary layer height between the two types of simulations, whereas the less significant bias in NO 2 is negatively correlated to temperature and boundary layer height. It is also clear that the selection of chemical boundary conditions is an important factor in determining the variability of O 3 model results. These results will be used as a baseline for the interpretation of future work, which will include an analysis of future climate scenarios upon European air quality. [ABSTRACT FROM AUTHOR]

Monitoring aerosols over wide areas is a scientific challenge with important applications for human health and the understanding of climate. Aerosol optical depth (AOD) measurements from satellites can improve the highly needed analyzed and forecasted distributions of ground-level aerosols in combination with models and ground-based measurements. To assess the benefit of future satellite AOD measurements, an observing system simulation experiment (OSSE) is developed. In this pilot study, the OSSE is applied to total AOD measurements from a flexible combined imager (FCI) proposed to fly on a geostationary satellite. OSSEs are widely used in the meteorological research community, but their use for air quality applications and specifically for aerosols is new. In this paper, the functionality and potential of the developed OSSE for evaluation of aerosol data from future satellite missions are demonstrated. The results show a positive impact of adding AOD observations next to in situ observations for the analysis of PM2.5 (particles smaller than 2.5 μm in median diameter) distributions. However, the development of an OSSE for aerosols presents a number of further challenges, as discussed in this paper, which prohibits a detailed quantitative analysis of the results of this pilot study. [ABSTRACT FROM AUTHOR]