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We investigate the sensitivity of simulated cloud properties and surface precipitation to assumptions regarding the size distributions of the precipitating hydrometeors in a one-moment bulk microphysics scheme. Three sensitivity experiments were applied to two composites of 15 convective and 15 frontal stratiform intense precipitation events observed in a coastal midlatitude region (Belgium), which were evaluated against satellite-retrieved cloud properties and radar-rain-gauge derived surface precipitation. It is found that the cloud optical thickness distribution was well captured by all experiments, although a significant underestimation of cloudiness occurred in the convective composite. The cloud-top-pressure distribution was improved most by more realistic snow size distributions (including a temperature-dependent intercept parameter and non-spherical snow for the calculation of the slope parameter), due to increased snow depositional growth at high altitudes. Surface precipitation was far less sensitive to whether graupel or hail was chosen as the rimed ice species, as compared to previous idealized experiments. This smaller difference in sensitivity could be explained by the stronger updraught velocities and higher freezing levels in the idealized experiments compared to typical coastal midlatitude environmental conditions. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the sensitivity of moist processes and surface precipitation during three extreme precipitation events over Belgium to the representation of rain, snow and hail size distributions in a bulk one-moment microphysics parameterisation scheme. Sensitivities included the use of empirically derived relations to calculate the slope parameter and diagnose the intercept parameter of the exponential snow and rain size distributions and sensitivities to the treatment of hail/graupel. A detailed evaluation of the experiments against various high temporal resolution and spatially distributed observational data was performed to understand how moist processes responded to the implemented size distribution modifications. Net vapour consumption by microphysical processes was found to be unaffected by snow or rain size distribution modifications, while it was reduced replacing formulations for hail by those typical for graupel, mainly due to intense sublimation of graupel. Cloud optical thickness was overestimated in all experiments and all cases, likely due to overestimated snow amounts. The overestimation slightly deteriorated by modifying the rain and snow size distributions due to increased snow depositional growth, while it was reduced by including graupel. The latter was mainly due to enhanced cloud water collection by graupel and reduced snow depositional growth. Radar reflectivity and cloud optical thickness could only be realistically represented by inclusion of graupel during a stratiform case, while hail was found indispensable to simulate the vertical reflectivity profile and the surface precipitation structure. Precipitation amount was not much altered by any of the modifications made and the general overestimation was only decreased slightly during a supercell convective case. [ABSTRACT FROM AUTHOR]

Abstract: Using the synoptic-regression based approach developed in Part I of this research, this study estimates future maximum 8 hourly mean O3 levels (m8hO3) using three future SRES (Special Report on Emission) scenarios for a rural background area situated in The Netherlands. The statistical downscaling tool was used to downscale the Atmospheric–Ocean Coupled General Circulation Model (AOGCM) ECHAM5-MPI/OM for the present-day 20 Century (20C) control run (1991–2000) and the future SRES scenarios A2, A1B and B1 for two periods (2051–2060 and 2091–2100). First, the statistical downscaling tool is evaluated in terms of downscaled m8hO3 levels for the present-day climate, using a long record of observed m8hO3 concentrations. It was found that a bias correction is needed and this bias correction is then further used to estimate future m8hO3 concentrations. Under the various SRES scenarios, the overall mean m8hO3 increases with 2.5–6.5 and 6.1–10.9 μg m−3, for the 2051–2060 and 2091–2100 period respectively, which is about 20% of the present-day 10-year average. This effect is enhanced when considering the summer season only, with a range of increase between the different future scenarios of 5.4–12.5 μg m−3 and 13.4–26 μg m−3 (for 2051–2060 and 2091–2100 respectively) against a present-day summer average of 73.5 μg m−3. An increase in maximum temperature and shortwave radiation, associated with a decrease in cloud cover under the various future scenarios are the main drivers of ozone increase. A comparison with August 2003 shows the physical plausibility of our results and reflects that the extreme summer of 2003 might show a close resemblance to future European summers in terms of m8hO3 and meteorological characteristics. [Copyright &y& Elsevier]

Abstract: In order to make projections for future air-quality levels, a robust methodology is needed that succeeds in reconstructing present-day air-quality levels. At present, climate projections for meteorological variables are available from Atmospheric-Ocean Coupled Global Climate Models (AOGCMs) but the temporal and spatial resolution is insufficient for air-quality assessment. Therefore, a variety of methods are tested in this paper in their ability to hindcast maximum 8 hourly levels of O3 and daily mean PM10 from observed meteorological data. The methods are based on a multiple linear regression technique combined with the automated Lamb weather classification. Moreover, we studied whether the above-mentioned multiple regression analysis still holds when driven by operational ECMWF (European Center for Medium-Range Weather Forecast) meteorological data. The main results show that a weather type classification prior to the regression analysis is superior to a simple linear regression approach. In contrast to PM10 downscaling, seasonal characteristics should be taken into account during the downscaling of O3 time series. Apart from a lower explained variance due to intrinsic limitations of the regression approach itself, a lower variability of the meteorological predictors (resolution effect) and model deficiencies, this synoptic-regression-based tool is generally able to reproduce the relevant statistical properties of the observed O3 distributions important in terms of European air quality Directives and air quality mitigation strategies. For PM10, the situation is different as the approach using only meteorology data was found to be insufficient to explain the observed PM10 variability using the meteorological variables considered in this study. [Copyright &y& Elsevier]

Abstract: A pressing task in numerical weather prediction and climate modelling is the evaluation of modelled cloud fields. Recent progress in spatial and temporal resolution of satellite remote sensing increases the potential of such evaluation efforts. This paper presents new methodologies to compare satellite remote sensing observations of clouds and output of atmospheric models and demonstrates their usefulness for evaluation. The comparison is carried out for two MODerate resolution Imaging Spectrometer (MODIS) scenes from the BALTEX Bridge Campaigns. Both scenes are characterised by low-level clouds with a substantial amount of liquid water. Cloud cover and cloud optical thickness of five different models, LM, Méso-NH, MM5 (non-hydrostatic models), RACMO2, and RCA (regional climate models) as well as corresponding retrievals from high resolution remote sensing observations of MODIS onboard the Terra satellite form the basis of a statistical analysis to compare the data sets. With the newly introduced patchiness parameters it is possible to separate differences between the two scenes on the one hand and between the models and the satellite on the other hand. We further introduce a new approach to spatially aggregate cloud optical thickness. Generally the models overestimate cloud optical thickness which can in part be ascribed to the lack of subgrid-scale variability. However, LM underestimates the frequency of occurrence of cloud optical thickness at values around 25. Furthermore, we compare the standard operational output of the non-hydrostatic models to simulations of the same models including parameterised shallow convection. However, clear improvements in the representation of low-level clouds are not found for these models. A change of the coefficients for autoconversion in RCA shows that LWP and precipitation strongly depend on this parameter. Refined vertical resolution, implemented in RACMO2, leads to a better agreement between model and satellite but still leaves room for further improvements. In general, this study reveals deficiencies of the models in representing low-level clouds, in particular for a stratiform cloud. [Copyright &y& Elsevier]

Abstract: The BALTEX Bridge Campaigns (BBC), which were held in the Netherlands in 2001 and 2003 around the Cabauw Experimental Site for Atmospheric Research (CESAR), have provided detailed information on clouds. This paper is an illustration of how these measurements can be used to investigate whether ‘state-of-the-art’ atmospheric models are capable of adequately representing clouds. Here, we focus on shallow low-level clouds with a substantial amount of liquid water. In situ, ground-based and satellite remote sensing measurements were compared with the output of three non-hydrostatic regional models (Lokal-Modell, LM; Méso-NH; fifth-generation Mesoscale Model, MM5) and two hydrostatic regional climate models (Regional Atmospheric Climate Model version 2, RACMO2; Rossby Centre Atmospheric Model, RCA). For the two selected days, Méso-NH and MM5 reproduce the measured vertical extent of the shallow clouds, but the liquid water content of the clouds is generally overestimated. In LM and the climate models the inversion is too weak and located at a level too close to the surface resulting in an overestimation of the vertical extent of the clouds. A sensitivity integration with RACMO2 shows that the correspondence between model output and measurements can be improved by a doubling of the vertical resolution; this induces an increase in the modelled inversion strength and cloud top pressure. LM and Méso-NH underestimate the lifetime of clouds. A comparison between model output and cloud cover derived from the Moderate Resolution Imaging Spectrometer (MODIS) indicates that this deficiency is not due to advection of too small cloud systems; it is rather due to an overestimation of the variability in the vertical velocity. All models overestimate the specific humidity near the surface and underestimate it at higher atmospheric levels, indicating that the models underestimate the mixing of moisture in the boundary layer. This deficiency is slightly reduced by inclusion of parameterised shallow convection in the non-hydrostatic models, which enhances the mixing of heat and moisture in the boundary layer. Consequently, the explicitly resolved updrafts weaken resulting in reduced condensation rates and lower liquid water path. The temporal variability of cloud occurrence is hardly affected by inclusion of parameterised shallow convection. [Copyright &y& Elsevier]

Strict energy performance requirements have reduced the building's operational energy use and related environmental impact in the past decades. Consequently, the embodied impacts of buildings gained importance, and hence focussing on the life cycle impacts has become essential to further reduce the environmental impact of buildings. Life cycle assessment (LCA) is an internationally accepted method used for this purpose. Current LCA studies of buildings typically look at their whole life cycle but ignore potential changes in operational energy use due to climate change. However, the latter is expected to influence the operational energy use of buildings to a significant extent. This paper aims to improve the assessment of the operational phase by including variations in the yearly operational energy use caused by climate change and expected changes in the electricity mix as a strategy for climate change mitigation. This adapted dynamic assessment method is used to assess a Belgian office building. The results indicate that a Representative Concentration Pathway (RCP) 8.5 climate change scenario causes a decrease of 18 % for the end use of gas for heating and an increase of 32.4 % for the electricity use for cooling and ventilation. For the case study, the reduction of the environmental impact due to the decrease in gas use compensates the impact increase due to the higher electricity use. An increase in environmental impact in future would however occur if both heating and cooling are provided by electricity. Furthermore, depending on the changes that will occur in the electricity mix, the global warming potential of the office building will change by −13 % for an electricity mix dominated by renewables and by + 10 % for one with mainly production by gas compared to the situation with the current mix. However, the inclusion of a more extended list of environmental indicators shows that the overall environmental impact will only reduce by 4 % or even increase by 7 % compared to the situation with the current mix. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the seasonal variability in freshwater inputs to the Marguerite Bay region (Western Antarctic Peninsula) using a time series of oxygen isotopes in seawater from samples collected in the upper mixed layer of the ocean during 2002 and 2003. We find that meteoric water, mostly in the form of glacial ice melt, is the dominant freshwater source, accounting for up to 5% of the near-surface ocean during the austral summer. Sea-ice melt accounts for a much smaller percentage, even during the summer (maximum around 1%). The seasonality in meteoric water input to the ocean (around 2% of the near-surface ocean) is not dissimilar to that of sea-ice melt (around 2% in 2002 and 1% in 2003), contradicting the assumption that sea-ice processes dominate the seasonal evolution of the physical ocean environment close to the Antarctic continent. Three full-depth profiles of oxygen isotopes collected in successive Decembers (2001–2003) indicate that around 4m of meteoric water is present in the water column at this time of year, and around 1m of sea-ice formed from this same water column. The predominance of glacial melt is significant, since it is known to be an important factor in the operation of the ecosystem, for example by providing a source of nutrients and modifying the physical environment to control the spatial extent and magnitude of phytoplankton blooms. The Western Antarctic Peninsula is undergoing a very rapid change in climate, with increasing ocean and air temperatures, retreating glaciers, and increases in precipitation associated with changes in atmospheric circulation. As climate change continues, we expect meteoric water inputs to the adjacent ocean to rise further. Sea-ice in this sector of the Antarctic has shown a climatic decrease, and we expect a reduction in oceanic sea-ice melt fractions if this change continues. Continued monitoring of the oceanic freshwater budget at the western Peninsula is needed to track these changes as they occur, and to better understand their ecological consequences. [Copyright &y& Elsevier]

The local outdoor climate and building characteristics influence the energy use of a building to an important extent. To design energy efficient and climate robust buildings, it is important to get insights into the energy demand over the building's service life from the early design phase onwards. This paper presents an overview of the different variants of the heating and cooling degree day method. A convection-permitting climate model is furthermore used to obtain heating and cooling degree days (for a baseline temperature of 18 °C) for the RCP 8.5 (high-end) climate change scenario for Belgium on a high-resolution grid of 2.8 km. Area of focus for this paper is Belgium. The results demonstrate a decrease of the HDD with 27% between 1976–2004 (3189 HDD) and 2070–2098 (2337 HDD). In contrast, the CDD were found to increase with a factor 2.4 from 167 CDD to 401 CDD in the same timeline. Smaller reductions in average HDD were moreover found in urban areas compared to rural areas. For the CDD, a higher absolute increase was found for urban areas and the Northeast of Belgium. Image, graphical abstract [ABSTRACT FROM AUTHOR]

With more than 1.5 million inhabitants, the capital city of Kampala, Uganda, is one of the most populated areas in Sub-Saharan Africa. Moreover, with a growth rate of more than 4 percent, it is considered as one of the fastest growing cities on the planet. As current and future impacts of this urbanization on the regional climate is still unknown, some recent studies developed frameworks in order to apply urban climate models over this city. Brousse et al. (2019) uses the simple urban canopy scheme TERRA URB embedded in the COSMO-CLM model. Although this scheme has already proven its validity in several cases (Wouters et al., 2016; Demuzere et al., 2017), obtaining input parameters for the urban canopy model valid for Kampala is difficult. In fact, as urban climate models requires thermal and geometrical canopy input variables, Local Climate Zones are often considered as powerful tools for parameterization of the model following the WUDAPT framework (Ching et al., 2018). Yet the values extracted out of the ranges proposed by Stewart and Oke that were applied until now, are mostly derived out of Western cities. Therefore in order to improve the parametrization of the urban climate model and to validate the applicability of the LCZ scheme over East African cities, this study sets up a methodology for obtaining a novel range of parameters per LCZ class within the city of Kampala.In situ data were obtained during a field exercise in the summer months of 2018. A representative sample of measuring points was selected along transects throughout the city of Kampala. This selection required a point coverage that is proportional to the spatial occurrence of each LCZ class. This sampling procedure permitted the acquisition of about 1300 measurement points. Measured variables consist of quantitative (road width, distance between houses, heights of buildings) and qualitatively estimated (vegetation fraction, road-wall-roof material) variables needed (in)directly by the urban parametrization scheme. Combining these measurements with the LCZ map created by Brousse et al. (2018) allow for the definition of a more trustworthy representation of the city of Kampala. The new ranges obtained from the field campaign are thoroughly examined for each of the abovementioned parameters and compared with the defaults, focusing on physical explanations for statistically significant differences between LCZ classes. First, based on deviations from default settings, the potential effect of the tropical urban structure on the local climate is estimated. In a next step, the results of this study will serve as input for the urban parametrization scheme. Online coupled with a high resolution climate model, the effects of the newly defined urban presence on the regional climate in larger Kampala will be explored. [ABSTRACT FROM AUTHOR]

Recent findings point out the importance of ice shelf dynamics to control the mass balance of the Antarctic Ice Sheet. Wind-induced processes play a key role in the health of the ice shelves: the surface energy balance and surface melt of the ice shelves is affected by processes such as drifting snow, frequently observed at the surface of the Antarctic continent. The relocation of drifting snow particles and sublimation locally lead to the emergence of blue ice areas (BIAs), that have a lower albedo than snow, and thereby invokes a positive feedback enhancing local surface melting, common in the vicinity of ice shelves grounding line. An understanding of these processes can be achieved by using a regional climate model. However, for this purpose a blowing snow routine needs to be implemented.We implement the simple bulk model for blowing snow from Déry and Yau (2001) in the regional atmospheric COSMO-CLM model coupled to the land component of CESM, the Community Land Model. The coupled COSMO-CLM² model was adapted to accurately represent the Antarctic conditions, contributing to the CORDEX-ANT effort and includes snowpack adaptations for a better perennial snow surface and mass balance representation over the ice sheets and glaciers. A simulation over the Roi Baudouin Ice Shelf, East Antarctica includes the blowing snow routine and allows us to analyze the effect of the displacement and sublimation of the drifting snow particles on the surface mass balance and dynamics of East Antarctic ice shelves. More precisely, by initiating two simulations with either a uniform snowpack, or the existing BIAs (and their characteristics) we can evaluate the ability of the routine to create or maintain the existence of the BIAs. Expected results of the two simulations will give insights on processes leading to ablation induced by the wind over the ice shelf, and the comparison between the two scenarios will enable to quantify wind-albedo and melt-albedo feedbacks on theRoi Baudouin Ice Shelf. [ABSTRACT FROM AUTHOR]

As one of the stormiest places in the world, the Lake Victoria region (East-Africa) is prone to hazardous climate extremes. More than 5000 fishermen die every year due to heavy and hardly predictable thunderstorms happening over the lake (Semazzi et al., 2011), emphasizing the need to thoroughly study the area. Thiery et al. (2015) were first to model the climate of this region at high resolution (~7 km) and gain insights on the regional climatology of the African Great Lakes. As a follow-up, this study therefore aims at unraveling the interaction of Lake Victoria on the initiation, development and behavior of mesoscale convective systems.To assess the influences of Lake Victoria on the mesoscale convective systems, two regional climate simulations are performed with COSMO-CLM and compared over a time period of 8 years (2010-2017). One reference simulation is run with the presence of Lake Victoria while the second excludes the lake. The simulation techniques are identical and consist of a direct dynamical downscaling procedure from ERA-5 reanalysis to a domain at a convection permitting resolution of 2.8 km. The model set-up follows the CORDEX-Africa tropical set-up proposed by Panitz et al. (2014), and supplements the original microphysics scheme by the two-moment scheme. To accurately represent the lake structure in the first simulation, the model is coupled to the Freshwater Lake model (FLake).Analysis of the model output will improve our understanding of the impact of unstable boundary layer air over Lake Victoria on the development and progress of lake-land interaction induced convective systems. The accurate model output will also serve as boundary conditions for a 1 km resolution domain centered over Kampala (the capital city of Uganda) to study the urbanization impact on the regional climate as proposed by Brousse et al. (2018, 2019). [ABSTRACT FROM AUTHOR]