The present work aims at better understanding regional climate–aerosol interactions by studying the relationships between aerosols and synoptic atmospheric circulation over the Euro-Mediterranean ...region. Two 40-year simulations (1979–2018) have been carried out with version 6.3 of the Centre National de Recherches Météorologiques (National Centre for Meteorological Research) – Aire Limitée Adaptation dynamique Développement InterNational (CNRM-ALADIN) regional climate model, one using interactive aerosols and the other one without any aerosol. The simulation with aerosols has been evaluated in terms of different climate and aerosol parameters. This evaluation shows a good agreement between the model and observations, significant improvements compared to the previous model version and consequently the relevance of using this model for the study of climate–aerosol interactions over this region. A first attempt to explain the climate variability of aerosols is based on the use of the North Atlantic Oscillation (NAO) index. The latter explains a significant part of the interannual variability, notably in winter for the export of dust aerosols over the Atlantic Ocean and the eastern Mediterranean, and in summer for the positive anomalies of anthropogenic aerosols over western Europe. This index is however not sufficient to fully understand the variations of aerosols in this region, notably at daily scale. The use of “weather regimes”, namely persisting meteorological patterns, stable at synoptic scale for a few days, provides a relevant description of atmospheric circulation, which drives the emission, transport and deposition of aerosols. The four weather regimes usually defined in this area in winter and in summer bring significant information to answer this question. The blocking and NAO+ regimes are largely favourable to strong aerosol effects on shortwave surface radiation and near-surface temperature, either because of higher aerosol loads or because of weaker cloud fraction, which reinforces the direct aerosol effect. Inversely, the NAO− and Atlantic Ridge regimes are unfavourable to aerosol radiative effects, because of weaker aerosol concentrations and increased cloud cover. This study thus puts forward the strong dependence of aerosol loads on the synoptic circulation from interannual to daily scales and, as a consequence, the important modulation of the aerosol effects on shortwave surface radiation and near-surface temperature by atmospheric circulation. The role of cloud cover is essential in this modulation as shown by the use of weather regimes.
This study investigates, through regional climate modelling, the surface mass concentration and AOD (aerosol optical depth) evolution of the various (anthropogenic and natural) aerosols over the ...Euro-Mediterranean region between the end of the 20th century and the mid-21st century. The direct aerosol radiative forcing (DRF) as well as the future Euro-Mediterranean climate sensitivity to aerosols have also been analysed. Different regional climate simulations were carried out with the CNRM-ALADIN63 regional climate model, driven by the global CNRM-ESM2-1 Earth system model (used in CMIP6) and coupled to the TACTIC (Tropospheric Aerosols for ClimaTe In CNRM) interactive aerosol scheme. These simulations follow several future scenarios called shared socioeconomic pathways (SSP 1-1.9, SSP 3-7.0 and SSP 5-8.5), which have been chosen to analyse a wide range of possible future scenarios in terms of aerosol or particle precursor emissions. Between the historical and the future period, results show a total AOD decrease between 30 % and 40 % over Europe for the three scenarios, mainly due to the sulfate AOD decrease (between −85 and −93 %), that is partly offset by the nitrate and ammonium particles AOD increase (between +90 and +120 %). According to these three scenarios, nitrate aerosols become the largest contributor to the total AOD during the future period over Europe, with a contribution between 43.5 % and 47.5 %. It is important to note that one of the precursors of nitrate and ammonium aerosols, nitric acid, has been implemented in the model as a constant climatology over time. Concerning natural aerosols, their contribution to the total AOD increases slightly between the two periods. The different evolution of aerosols therefore impacts their DRF, with a significant sulfate DRF decrease between 2.4 and 2.8 W m−2 and a moderate nitrate and ammonium DRF increase between 1.3 and 1.5 W m−2, depending on the three scenarios over Europe. These changes, which are similar under the different scenarios, explain about 65 % of the annual shortwave radiation change but also about 6 % (in annual average) of the warming expected over Europe by the middle of the century. This study shows, with SSP 5-8.5, that the extra warming attributable to the anthropogenic aerosol evolution over Central Europe and the Iberian Peninsula during the summer period is due to “aerosol–radiation” as well as “aerosol–cloud” interaction processes. The extra warming of about 0.2 ∘C over Central Europe is explained by a surface radiation increase of 5.8 W m−2 over this region, due to both a surface aerosol DRF decrease of 4.4 W m−2 associated with a positive effective radiative forcing due to aerosol–radiation interactions (ERFari) of 2.7 W m−2 at the top of the atmosphere (TOA) and a cloud optical depth (COD) decrease of 1.3. In parallel, the simulated extra warming of 0.2∘C observed over the Iberian Peninsula is due to a COD decrease of 1.3, leading to a positive effective radiative forcing due to aerosol–cloud interactions (ERFaci) of 2.6 W m−2 at the TOA but also to an atmospheric dynamics change leading to a cloud cover decrease of about 1.7 % and drier air in the lower layers, which is a signature of the semi-direct forcing. This study thus highlights the necessity of taking into account the evolution of aerosols in future regional climate simulations.
Aerosols play an important role in Europe and the Mediterranean area where different
sources of natural and anthropogenic particles are present. Among them
ammonium and nitrate (A&N) aerosols may ...have a growing impact on regional
climate. In this study, their representation in coarse and fine modes has
been introduced in the prognostic aerosol scheme of the ALADIN-Climate
regional model. This new aerosol scheme is evaluated over Europe and the
Mediterranean Sea, using two twin simulations over the period 1979–2016 with
and without A&N aerosols. This evaluation is performed at local and
regional scales, using surface stations and satellite measurements. Despite
an overestimate of the surface nitrate concentration, the model is able to
reproduce its spatial pattern including local maxima (Benelux, Po Valley).
Concerning the simulated aerosol optical depth (AOD), the inclusion of A&N
aerosols significantly reduces the model bias compared to both AERONET
stations and satellite data. Our results indicate that A&N aerosols can
contribute up to 40 % of the total AOD550 over Europe, with an
average of 0.07 (550 nm) over the period 2001–2016. Sensitivity studies
suggest that biases still present are related to uncertainties associated
with the annual cycle of A&N aerosol precursors (ammonia and nitric acid).
The decrease in sulfate aerosol production over Europe since 1980 produces
more free ammonia in the atmosphere leading to an increase in A&N
concentrations over the studied period. Analyses of the different aerosol
trends have shown for the first time to our knowledge that, since 2005 over
Europe, A&N AOD550 and A&N shortwave (SW) direct radiative forcing
(DRF) are found to be higher than sulfate and organics, making these the
species with the highest AOD and the highest DRF. On average over the period
1979–2016, the A&N DRF is found to be about −1.7 W m−2 at the
surface and −1.4 W m−2 at the top of the atmosphere (TOA) in all sky
conditions over Europe, with regional maxima located at the surface over the
Po Valley (−5 W m−2). Finally, the dimming effect of A&N aerosols
is responsible for a cooling of about −0.2∘ C over Europe
(summer), with a maximum of −0.4 ∘C over the Po Valley. Concerning
precipitation, no significant impact of A&N aerosols has been found.
Organic aerosols are predominantly emitted from biomass burning and biofuel use. The fraction of these aerosols that strongly absorbs ultraviolet and short visible light is referred to as brown ...carbon (BrC). The life cycle and the optical properties of BrC are still highly uncertain, thus contributing to the uncertainty of the total aerosol radiative effect. This study presents the implementation of BrC aerosols in the Tropospheric Aerosols for ClimaTe In CNRM (TACTIC) aerosol scheme of the atmospheric component of the Centre National de Recherches Météorologiques (CNRM) climate model. This implementation has been achieved using a BrC parameterization based on the optical properties of Saleh et al. (2014). Several simulations have been carried out with the CNRM global climate model, over the period of 2000–2014, to analyze the BrC radiative and climatic effects. Model evaluation has been carried out by comparing numerical results of single-scattering albedo (SSA), aerosol optical depth (AOD), and absorption aerosol optical depth (AAOD) to data provided by Aerosol Robotic Network (AERONET) stations, at the local scale, and by different satellite products, at the global scale. The implementation of BrC and its bleaching parameterization has resulted in an improvement of the estimation of the total SSA and AAOD at 350 and 440 nm. This improvement is observed at both the local scale, for several locations of AERONET stations, and the regional scale, over regions of Africa (AFR) and South America (AME), where large quantities of biomass burning aerosols are emitted. The annual global BrC effective radiative forcing (all-sky conditions) has been calculated in terms of both aerosol–radiation interactions (ERFari, 0.029 ± 0.006 W m−2) and aerosol–cloud interactions (ERFaci, −0.024 ± 0.066 W m−2). This study shows, on an annual average, positive values of ERFari of 0.292 ± 0.034 and 0.085 ± 0.032 W m−2 over the AFR and AME regions, respectively, which is in accordance with the BrC radiative effect calculated in previous studies. This work also reveals that the inclusion of BrC in the TACTIC aerosol scheme causes a statistically significant low-level cloud fraction increase over the southeastern Atlantic Ocean during the burning season partially caused by a vertical velocity decrease at 700 hPa (semi-direct aerosol effect). Lastly, this study also highlights that the low-level cloud fraction changes, associated with more absorbing biomass burning aerosols, contribute to an increase in both solar heating rate and air temperature at 700 hPa over this region.
IMPORTANCE: Optimal transfusion strategies in traumatic hemorrhage are unknown. Reports suggest a beneficial effect of 4-factor prothrombin complex concentrate (4F-PCC) on blood product consumption. ...OBJECTIVE: To investigate the efficacy and safety of 4F-PCC administration in patients at risk of massive transfusion. DESIGN, SETTING, AND PARTICIPANTS: Double-blind, randomized, placebo-controlled superiority trial in 12 French designated level I trauma centers from December 29, 2017, to August 31, 2021, involving consecutive patients with trauma at risk of massive transfusion. Follow-up was completed on August 31, 2021. INTERVENTIONS: Intravenous administration of 1 mL/kg of 4F-PCC (25 IU of factor IX/kg) vs 1 mL/kg of saline solution (placebo). Patients, investigators, and data analysts were blinded to treatment assignment. All patients received early ratio-based transfusion (packed red blood cells:fresh frozen plasma ratio of 1:1 to 2:1) and were treated according to European traumatic hemorrhage guidelines. MAIN OUTCOMES AND MEASURES: The primary outcome was 24-hour all blood product consumption (efficacy); arterial or venous thromboembolic events were a secondary outcome (safety). RESULTS: Of 4313 patients with the highest trauma level activation, 350 were eligible for emergency inclusion, 327 were randomized, and 324 were analyzed (164 in the 4F-PCC group and 160 in the placebo group). The median (IQR) age of participants was 39 (27-56) years, Injury Severity Score was 36 (26-50 major trauma), and admission blood lactate level was 4.6 (2.8-7.4) mmol/L; prehospital arterial systolic blood pressure was less than 90 mm Hg in 179 of 324 patients (59%), 233 patients (73%) were men, and 226 (69%) required expedient hemorrhage control. There was no statistically or clinically significant between-group difference in median (IQR) total 24-hour blood product consumption (12 5-19 U in the 4F-PCC group vs 11 6-19 U in the placebo group; absolute difference, 0.2 U 95% CI, −2.99 to 3.33; P = .72). In the 4F-PCC group, 56 patients (35%) presented with at least 1 thromboembolic event vs 37 patients (24%) in the placebo group (absolute difference, 11% 95% CI, 1%-21%; relative risk, 1.48 95% CI, 1.04-2.10; P = .03). CONCLUSIONS AND RELEVANCE: Among patients with trauma at risk of massive transfusion, there was no significant reduction of 24-hour blood product consumption after administration of 4F-PCC, but thromboembolic events were more common. These findings do not support systematic use of 4F-PCC in patients at risk of massive transfusion. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03218722
PDF
