Displays

For the first time internationally a model at a resolution on par with operational weather forecast models has been used for national climate scenarios. As part of the UK Climate Projections (UKCP) project, an ensemble of 12 projections at 2.2km resolution have been carried out over the UK. These were launched in September 2019, with the aim of providing an improved simulation of extreme precipitation and also other high-impact events at local scales for the coming decades. At such high (2.2km) resolution, convection can be represented explicitly (‘permitted’) without the need for a parameterisation scheme, leading to a much more realistic representation of hourly precipitation characteristics, including extremes. In this talk initial results from the UKCP local (2.2km) projections will be presented. This includes new understanding of changes in winter mean precipitation, as well as projected changes in hourly precipitation extremes and the frequency of hot spells. I will also discuss remaining outstanding issues and the future outlook for convective-scale climate modelling.

How to cite: Kendon, E., Fosser, G., and Chan, S.: Using a convection permitting model ensemble for projecting future change in high-impact events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2361, https://doi.org/10.5194/egusphere-egu2020-2361, 2020.

While summer rain storms are very intermittent, chaotic and influenced by multiple atmospheric drivers, some statistics of observed short duration precipitation actually display surprisingly simple, regular behaviour. As an example, 10-min rainfall extremes derived from Dutch climate data show a dependency of 13% per degree over an almost 20-degree dew point temperature range. Similar behaviour has also been found in hourly precipitation observations. Each degree of warming reflects 6-7% more moisture in the air,  following from the well-known Clausius-Clapeyron (CC) relation which is the cornerstone to understand and quantify the influence of climate change on precipitation extremes.  According to the above finding, however, precipitation intensities may be increasing with temperature at a rate twice the commonly expected CC rate. In this presentation we will use output from a number of 10-year simulations for present-day and future climate with the convection permitting model HCLIM-AROME to investigate how hourly extremes respond to warming in both a pseudo global warming (PGW) and a GCM driven setup. In particular, we use the scaling diagram -- different percentiles of the rainfall distribution, usually the 90, and 99th conditioned on the occurrence of rain, as a function of dew  point temperature -- as a analysis environment. Focus will be on how the scaling diagram is affected by climate change, and what information can be derived from these changes in scaling. While changes in the scaling diagram between present-day and future climate are in general consistent with a CC prediction, evidence of super CC behaviour, between 10 and 14 % per degree dew point, is also present. The same applies to changes in the most extreme events from the simulations, which show super CC behaviour in both PGW and GCM driven setups when scaled with the appropriate dew point temperature change. 

How to cite: Lenderink, G., van Meijgaard, E., de Vries, H., van Ulft, B., Barbero, R., and Fowler, H.: Using a dew point temperature scaling framework to interpret changes in hourly extremes from convection-permitting model simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8435, https://doi.org/10.5194/egusphere-egu2020-8435, 2020.

Extreme precipitation events have a major impact upon our society. Although many studies have indicated that it is likely that the frequency of such events will increase in a warmer climate, little has been done to assess changes in extreme precipitation at a sub-daily scale. Recently, there is more and more evidence that high-resolution convection-permitting models (CPMs) (grid-mesh typically < 4 km) can represent especially short-duration precipitation extremes more accurately when compared with coarser-resolution regional climate models (RCMs).

This study investigates sub-daily and daily precipitation characteristics based on hourly output data from the HARMONIE-Climate model at 3-km and 12-km grid-mesh resolution over the Nordic region between 1998 and 2018. The RCM modelling chain uses the ERA-Interim reanalysis to drive a 12-km grid-mesh simulation which is further downscaled to 3-km grid-mesh resolution using a non-hydrostatic model set-up.

The statistical properties of the modeled extreme precipitation are compared to several sub-daily and daily observational products, including gridded and in-situ gauge data, from April to September. We investigate the skill of the model to represent different aspects of the frequency and intensity of extreme precipitation as well as intensity–duration–frequency (IDF) curves that are commonly used to investigate short duration extremes from an urban planning perspective. The high grid resolution combined with the 20-year-long simulation period allows for a robust assessment at a climatological time scale and enables us to examine the added value of high-resolution CPM in reproducing precipitation extremes over the Nordic region. Based on the tentative results, the high-resolution CPM can realistically capture the characteristics of precipitation extremes, for instance, in terms of improved diurnal cycle and maximum intensities of sub-daily precipitation.

How to cite: Toivonen, E., Belušić, D., Thomassen, E. D., Berg, P., Christensen, O. B., Dobler, A., Dyrrdal, A. V., Haugen, J. E., Jylhä, K., Kjellström, E., Landgren, O., Lind, P., Lindstedt, D., Matte, D., Mäkelä, A., Olsson, J., Pedersen, R. A., Wang, F., and Yang, W.: Evaluation of extreme precipitation over the Nordic region using a convection-permitting regional climate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10506, https://doi.org/10.5194/egusphere-egu2020-10506, 2020.

We present a multi-model ensemble of regional climate model scenario simulations run at scales allowing for explicit treatment of convective processes (2-3km) over historical and end of century time slices, providing an overview of future precipitation changes over the Alpine domain within the convection-permitting CORDEX-FPS initiative. The 12 simulations of the ensemble have been performed by different research groups around Europe. The simulations are compared with high resolution observations to assess the performance over the historical period and the ensemble of 12 to 25 km resolution driving models is used as a benchmark.

An improvement of the representation of fine scale details of the analyzed fields on a seasonal scale is found, as well as of the onset and peak of the summer diurnal convection. An enhancement of the projected patterns of change and modifications of its sign for the daily precipitation intensity and heavy precipitation over some regions are found with respect to coarse resolution ensemble. A change of the amplitude of the diurnal cycle for precipitation intensity and frequency is also shown, as well also a larger positive change for high to extreme events for daily and hourly precipitation distributions. The results  are challenging and promising for further assessment of the local impacts of climate change.

How to cite: Pichelli, E., Coppola, E., Ban, N., Giorgi, F., Stocchi, P., Alias, A., Belušić, D., Berthou, S., Caillaud, C., Cardoso, R. M., Chan, S., Christensen, O. B., Dobler, A., de Vries, H., Goergen, K., Kendon, E. J., Keuler, K., Lenderink, G., Lorenz, T., Mishra, A. N., Panitz, H.-J., Schär, C., Soares, P. MM., Truhetz, H., and Vergara-Temprado, J.: Precipitation projections of the first multi-model ensemble of regional climate simulations at convection permitting scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2687, https://doi.org/10.5194/egusphere-egu2020-2687, 2020.

Precipitation patterns and climate variability in East Africa and Western South America present high heterogeneity and complexity. This complexity is a result of large-scale and regional controls, such as surrounding oceans, lakes and topography. The combined effect of these controls has implications on precipitation and temperature, and hence, on water availability, biodiversity and ecosystem services. This study focuses on the impact of different physics parameterization in high-resolution experiments performed over equatorial regions with the Weather Research and Forecasting (WRF) model, and how these options affect the representation of precipitation in those regions.

As expected, weather and climate in equatorial regions are driven by physical processes different to those important in the mid-latitudes. Hence, it is necessary to test the parameterizations available in the WRF model. Several sensitivity simulations are performed over Kenya and Peru nesting the WRF model inside the state-of-the-art ERA5 reanalysis. A cascade of increasing grid resolutions is used in these simulations, reaching the spatial resolutions of 3 and 1 km in the innermost domains, and thus, convection permitting scales. Parameterization options of the planetary boundary layer (PBL), lake model, radiation, cumulus and microphysics schemes are changed, and their sensitivity to precipitation is tested. The year 2008 is simulated for each of the sensitivity simulations. This year is chosen as a good representative of precipitation dynamics and temperature, as it is neither abnormally wet or hot, nor dry or cold over Kenya and Peru. The simulated precipitation driven by the ERA5 reanalysis is compared against station data obtained from the WMO, and over Kenya additionally against observations from the Centre for Training and Integrated Research in ASAL Development (CETRAD).

Precipitation is strongly underestimated when adopting a typical parameterization setup for the mid-latitudes. However, results indicate that precipitation amounts and also patterns are substantially improved when changing the cumulus and PBL parameterisations. This strong increase in the simulated precipitation is obtained when using the Grell-Freitas ensemble, RRTM and the Yonsei University schemes for cumulus, long-wave radiation and planetary boundary layer, respectively. During some summer months, the accumulated precipitation is improved by up to 100 mm (80 %) compared to mid-latitudes configuration in several regions of the domains (near the Andes in Peru and over the flatlands in Kenya). Additionally, because the 1- and 2-way nesting options show a similar performance with respect to precipitation, the 1-way nesting option is preferred, as it does not overwrite the solutions in the parent domains. Hence, discontinuous solutions related to switching off the cumulus parameterization can be avoided.

How to cite: Messmer, M., González-Rojí, S. J., Raible, C. C., and Stocker, T. F.: Sensitivity of high-resolution precipitation to physics parameterization options in WRF over equatorial regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1376, https://doi.org/10.5194/egusphere-egu2020-1376, 2020.

Extreme weather is posing constant threat to more than 30 million people living near Lake Victoria or depending on its resources. Thousands of fishermen die every year by severe thunderstorms and associated water currents, while hazardous over-land thunderstorms largely affect people living inland, continuously facing flood risks. These risks call for better understanding of such climate extremes over the region. Climate models are a useful tool to gain insight in the complex behaviour of thunderstorms, especially when simulated at convection-permitting resolution. Such simulations, explicitly resolving deep convection at fine resolutions, have been shown to improve the representation of extreme events in many parts of the world, also in equatorial East-Africa (Finney et al., 2019; Kendon et al., 2019; Van de Walle et al., 2019). As a response, the CORDEX-Flagship Pilot Study “climate extremes in the Lake Victoria basin” (ELVIC) initiative is currently setting up an ensemble of convection-permitting simulations over the region.

At this stage, future climate projections are needed to assess the impact of anthropogenic climate change on extreme weather the region. Therefore, a surrogate global warming approach following Schär et al. (1996), Kröner et al. (2016), Liu et al. (2016) and Rasmussen et al. (2017) has been applied to a convection-permitting COSMO-CLM simulation. In this approach, the lateral boundary conditions from the ERA5 (~31 km resolution) reanalysis are perturbed in accordance with the recent CMIP6 ensemble-mean end-of-century SSP5 8.5 climate change scenario. This approach confers three major advantages over the more conventional methods. First, by perturbing with the ensemble-mean, it excludes uncertainties of GCMs without the need for a time and computational intensive high resolution ensemble approach. Second, it avoids including present-day circulation biases. Third, no intermediate nesting steps are necessary, as the perturbed ERA5 allows a direct downscaling to the convection-permitting climate projection.

Besides the methodology, results for the Lake Victoria basin will be presented. Although the occurrence of extreme over-lake precipitation in the present-day climate is mostly controlled by large- and mesoscale atmospheric dynamics (Van de Walle et al., 2019), its future intensification is mainly attributed to increased humidity (Thiery et al., 2016). Furthermore, the effect of changed large-scale dynamics is assessed, as not only temperature and humidity, but also wind forcing is modified.

How to cite: Van de Walle, J., Brousse, O., Brogli, R., Demuzere, M., Thiery, W., and P.M. van Lipzig, N.: Surrogate climate change projections for the Lake Victoria region with a convection-permitting model., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13559, https://doi.org/10.5194/egusphere-egu2020-13559, 2020.

In recent years convection-permitting models are increasingly often used for retrospective climate studies. Besides the better reproduction of atmospheric processes, the increase in resolution allows for a more accurate representation of land-surface heterogeneities and thus a more realistic depiction of smaller scale characteristics. The work presented here investigates the potential benefits of higher model resolutions on the atmospheric state estimates in possible future regional reanalysis data sets.

Specifically, we employ the ICOsahedral Non-hydrostatic model ICON (the current operational NWP model of the German Meteorological Service DWD) in its Limited Area Mode (ICON-LAM) with a LETKF data assimilation framework.
Simulations are conducted for a free run (dynamical downscaling) and a data assimilation (DA) one for various horizontal resolutions from the operational 2.1 kilometers towards finer resolutions of 1 kilometer and below. In addition, different land surface data sets are used as lower boundary conditions in order to explore their impact under the chosen horizontal resolutions. These experiments are conducted for Central Europe and Germany for the month of June 2019 which includes several extreme events, e.g., heatwave, heavy precipitation.

The presentation evaluates the simulations against non-assimilated observations for the free and DA experiments. The impact of the land-surface heterogeneity and resolution are quantified on both atmospheric and soil variables to account for possible feedback processes. Particular attention is given to the effects on the vertical atmospheric structure and precipitation generation.

How to cite: Valmassoi, A., Keller, J., Friederichs, P., and Hense, A.: Numerical modeling towards the sub-kilometer scale: The potential for regional reanalysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15837, https://doi.org/10.5194/egusphere-egu2020-15837, 2020.

The energy and water cycle of the regional climate is influenced by the phenological development of the vegetation through albedo, sensible and latent heat flux changes. This influences near surface temperature, precipitation and ultimately the boundary layer structure. The phenological stages in turn depend on temperature, day length, water availability and net primary productivity variations. Therefore, vegetation should play an important role in climate simulations. The current implementation of the seasonal vegetation development in the regional climate model COSMO-CLM (CCLM, COSMO 5.0 clm15), represented in the model by the leaf area index (LAI), the root depth or plant coverage, assumes a static, annually recurring cycle. In reality, it varies from year to year depending on the environmental conditions. In particular, the phenology will change with climate change modifying the environment. In this study, we implement the approach of Knorr et al. (2010) to improve the representation of the phenology in CCLM with 3 km horizontal resolution by temperature, day length and water availability. Here, the tuning parameters of the growth rate for grass is adapted from Schulz et al. (2015). Convection-permitting single column simulations are performed over the Lindenberg Meteorological Observatory, the FACE measuring site at Linden close to Gießen, and the TR32 measuring site at Selhausen close to Jülich in Germany. Comparisons of LAI results with observations show significantly improved correlations compared to simulations with the standard phenology over the period from 1999 to 2015. The reaction of the LAI due to years with extreme warm winter and spring or years with extreme dry summer is improved as well. A warmer beginning of the year causes an earlier start of the growing season, whereas a drier summer reduces the LAI due to water limitation. It is also shown, that lower LAI values lead to decreases of latent heat fluxes in the model. The mean amount of strong precipitation events (> 20 mm) is closer to the observations with the new phenology compared to the standard phenology. Further seasonally varying phenology for different plant functional types and its net primary productivity will be implemented in future work.

Ackowledgement:

Computational resources were made available by the German Climate Computing Center (DKRZ) through support from the Federal Ministry of Education and Research in Germany (BMBF). We acknowledge the funding of the German Research Foundation (DFG) through grant nr. 401857120.

Literature:

Knorr, W. et al., 2010. Carbon cycle data assimilation with a generic phenology model. Journal of Geophysical Research: Biogeosciences, 115(G4).

Schulz, J.-P., Vogel, G. & Ahrens, B., 2015. A new leaf phenology for the land surface scheme TERRA of the COSMO atmospheric model. COSMO Newsletter No. 15, p.21-29.

How to cite: Nowatzki, E., Schulz, J.-P., Bettems, J.-M., Luterbacher, J., and Tölle, M.: A Seasonally Varying Phenology for High Resolution Simulations with the COSMO-CLM Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-432, https://doi.org/10.5194/egusphere-egu2020-432, 2020.

Numerical weather prediction (NWP) models generally display comparatively low predictive skill in the Arctic. Particularly, the large impact of sub-grid scale, parameterised processes, such as surface fluxes, radiation or cloud microphysics during high-latitude weather events pose a substantial challenge for numerical modelling. Such processes are most influential during mesoscale weather events, such as polar lows, often embedded in cold air outbreaks (CAO), some of which cause high impact weather. Uncertainty in Arctic weather forecasts is thus critically dependent on parameterised processes. The strong influence from several parameterised processes also makes model forecasts particularly susceptible to compensation of errors from different parameterisations, which potentially limits model improvement.
Here we analyse model output of individual parameterised tendencies of wind, temperature and humidity during Arctic high-impact weather in AROME-Arctic, the operational NWP model used by the Norwegian Meteorological Institute Norway for the European Arctic. Individual tendencies describe the contribution of each applied physical parameterisation to a respective variable per model time step. We study a CAO-event taking place during 24 - 27 December 2015. This intense and widespread CAO event, reaching from the Fram Straight to Norway and affecting a particularly large portion of the Nordic seas at a time, was characterised by strong heat fluxes along the sea ice edge. 
Model intern definitions for boundary layer type become apparent as a decisive factor in tendency contributions. Especially the interplay between the dual mass flux and the turbulence scheme is of essence here. Furthermore, sensitivity experiments, featuring a run without shallow convection and a run with a new statistical cloud scheme, show how a physically similar result is obtained by substantially different tendencies in the model.

How to cite: Kähnert, M., Valkonen, T. M., and Sodemann, H.: Diagnosing factors in parameterised and resolved convection with physical tendency output in AROME-Arctic during a Cold-Air Outbreak event, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7610, https://doi.org/10.5194/egusphere-egu2020-7610, 2020.

This study assesses the added-value offered by a regional convection-permitting climate model (CPM) in its representation of sting-jets (SJs); a mesoscale slanted core of strong winds within a Shapiro-Keyser type of cyclone that can lead to extremely damaging surface wind speeds close to southern side of a cyclone’s centre. Low-resolution climate models cannot resolve SJs, and so estimates of risk posed by extreme winds due to SJs are difficult to determine and will likely be underestimated in coarse-resolution climate simulations.

We analyse three 10-year simulations from the UK Met Office, run at a 2.2km resolution over a European domain. The simulations include a hindcast driven by the ERA-Interim reanalysis dataset (ERAI) for the period 2001-2010, as well as a present day (2001-2010) and future simulation (2100-2109) that follows the RCP8.5 scenario. Both climate simulations are driven by a 25km GCM. To diagnose potential SJ storms in each simulation, we firstly identify cyclone tracks with a cyclone tracking algorithm and apply an objective indicator that identifies the warm seclusion of a Shapiro-Keyser cyclone and the slanted core of strong winds of the sting-jet.

Within this presentation, we will present the objective indicator as well as results of the added value seen in the CPM. In order to identify any added value of the CPM, we analyse differences between the CPM and its respective driving data, in terms of storm severity metrics and their future projections.  An example metric used is the Storm Severity Index that quantifies the overall severity of a storm. In all simulations, the conditional PDF of SSI for sting-jet storms is shifted towards higher values compared to PDF of the SSI from all storms within the studied domain. However, we see little difference in the SSI derived from the CPM and its respective driving model/reanalysis when CPM wind speeds are upscaled to the respective driving reanalysis/GCM grid. In further analysis, we will look to explore the added value at a local scale on the native CPM grid.

How to cite: Manning, C., Kendon, E., Fowler, H., Roberts, N., and Berthou, S.: Assessing Sting-Jets in Convection-Permitting Climate Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9158, https://doi.org/10.5194/egusphere-egu2020-9158, 2020.

There is an increased need for more detailed climate information from impact researchers, stakeholders and policy makers for regional-to-local climate change assessments. In order to design relevant and informative planning strategies on these scales it is important to have reliable climate data and information on high spatial O(1km) and temporal (daily to sub-daily) scales. Such high-resolution data is also beneficial for climate impact modellers as input to their models, e.g. hydrological or urban models that operate on regional to local scales. It has been established that regional climate models (RCMs) provide added value compared to coarser global climate models (GCMs) or re-analysis (e.g. ERA-Interim). However, RCMs with standard spatial resolution O(10 − 50km) still suffer from inadequacies in representing important regional-to-local climate phenomena and characteristics, both from the implied ”smoothening” effect within each grid cell which limits the representation of fine scale surface forcings, and the need to parameterize small-scale processes like atmospheric convection. The latter particularly invokes uncertainties in future climate responses of short-duration precipitation extremes such as flash-floods. Here, we compare 20-year simulations with a very high resolution (3 km grid spacing) convection permitting regional climate model (CPRCM) with a standard high-resolution (12 km grid spacing) convection parameterized RCM and their abilities to simulate the climate characteristics of the Nordic region in Europe, with particular focus on precipitation extremes. The study covers both recent past (with boundary data from ERA-Interim and the EC-Earth GCM) and the end of the 21st century (boundary data from EC-Earth using the RCP8.5 radiative forcing scenario). The high model grid resolution combined with the extensive simulated time period which enables assessment on climatological time scales makes this study one of very few for this region.

How to cite: Lind, P., Belušić, D., Kjellström, E., Wang, F., Toivonen, E., Pedersen, R. A., Matte, D., and Dobler, A.: Future response of precipitation extremes over the Nordic region in a convection-permitting regional climate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9167, https://doi.org/10.5194/egusphere-egu2020-9167, 2020.

Hail is a significant convective storm hazard in Croatia, often causing property and crop damage. The existing analysis, based on hailpad network data, shows that western and central regions of Croatia have a significant frequency of high-intensity hail events.

Advances in computational power and recent developments in atmospheric modeling have enabled the use of convection-permitting models (CPM) that can partially resolve deep convective events such as thunderstorms and rain showers. However, hail remains a difficult phenomenon to model or forecast since CPMs are still not able to fully resolve processes involved in producing hail. One way to address this issue is by embedding a physically-based one-dimensional hail model called HAILCAST within a CPM. Here, the HAILCAST model is embedded within the Weather Research and Forecasting (WRF) model.

The selected hail event is analyzed using WRF-HAILCAST model simulations. HAILCAST forecasts the maximum expected hail diameter using a profile of the vertical updraft, temperature, liquid and ice water content from a given WRF timestep and grid columns. Here, a set of numerical convection-permitting experiments are performed to assess the sensitivity of the results to different microphysics and planetary boundary layer (PBL) parameterization schemes and to provide guidance for WRF-HAILCAST tuning. The results are verified by observational (hailpad, hail observations) data as well as with radar, lightning and satellite measurements where available.

How to cite: Malečić, B., Jelić, D., Horvath, K., Babić, K., Mikuš Jurković, P., Strelec Mahović, N., and Telišman Prtenjak, M.: Sensitivity of the WRF – HAILCAST model to microphysics and PBL parameterization shemes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9898, https://doi.org/10.5194/egusphere-egu2020-9898, 2020.

Several remarkable hailstorms have occurred on the territory of Switzerland during the month
of May, 2018.
This period has been simulated, using the WRF4.0 model at a convection-permitting
resolution (1.5 km), using different microphysical schemes (Thompson, Morrison, P3).
The surrogate climate change approach has been used for imitating the climate conditions,
corresponding to the end of the 21st century (CMIP5 model data, RCP8.5 scenario).
The HAILCAST-1D model output has been used as a measure of simulated hail size and 5-
minute 3-D radar reflectivity field has been used for cell identification and tracking.
Hailstorms produced in the current climate and in surrogate climate change simulations have
been examined using neighborhood methods and a storm-tracking algorithm. Current-climate
simulated hailstorms were compared with the ground observations and MeteoSwiss radar
data.
The influence of microphysical schemes to the characteristics of simulated hailstorms has
been studied. 

How to cite: Martynov, A., Raupach, T., and Martius, O.: Simulated hailstorms over Switzerland in May 2018 in current and future climate conditions , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15911, https://doi.org/10.5194/egusphere-egu2020-15911, 2020.

We present a case study on extreme rainfall event in Crimea in September 2018. The event was caused by extratropical cyclone forming above the Black Sea. The cyclone approached the Crimean Mountains from the south, producing over 100 mm of rainfall in Yalta on September 6 and causing a flash flood. In the mountains, about 140 mm of rainfall was reported. 

To study this extreme event, we use the WRF model v.4.0.1 forced by the boundary conditions from ECMWF operational analysis with the spatial resolution of approximately 10 × 10 km. The model was run for 8 days of September 1 – 8, and 5 microphysical schemes were tested (WDM6, Morrison, Milbrandt, NSSL, and Thompson). Other model parameters were set identical to CONUS configuration suite. The simulations were done for two one-way nested convective-resolving domains with spatial resolution of 2.7× 2.7 km and 0.9 × 0.9 km. The simulations were verified using the meteorological radar observations in Simferopol airport and GPM measurements.

All of the microphysical schemes substantially underestimate the amount of rainfall reaching the ground compared to observations. However, several schemes (Milbrandt, Morrison, and WDM6) do add value to the forecasts, producing significantly larger amount of rainfall compared to the driving model that almost completely missed it on the local scale. WDM6 performs best to capture the proper location of the squall line and to reproduce the rainfall orographic enhancement in the mountains. The amount of rainfall in the child domain was also slightly larger compared to the parent one. Despite the rainfall underestimation, we also show that the simulated reflectivity patterns are in good agreement with observations, although the convective cores are wider and less intense compared to the observed by the radar.

How to cite: Anisimov, A., Efimov, V., Lvova, M., Popov, V., and Mostamandi, S.: Extreme rainfall event in Crimea: Cloud-resolving modeling and radar observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10550, https://doi.org/10.5194/egusphere-egu2020-10550, 2020.

Climate impact assessments require information about climate change at regional and ideally local scales. Traditionally, this information has been obtained using statistical methods, precluding the linkage of local climate changes to large-scale drivers in a process-based way. As part of recent efforts to investigate the impact of climate change on forest ecosystems in Bavaria, Germany, within the BayTreeNet project, we developed a high-resolution atmospheric modelling dataset, BAYWRF, for the region of Bavaria over the thirty-year period of September 1987 to August 2018. The open-source community-developed atmospheric model employed in this study, WRF, was configured with two nested domains of 7.5- and 1.5-km grid spacing centered over Bavaria and forced at the outer lateral boundaries by ERA5 reanalysis data. Based on a shorter evaluation period of September 2017 to August 2018, we evaluate two aspects of the simulations: (i) we investigate the influence of using grid-analysis nudging; and (ii) we assess model biases compared with an extensive observational data at both two-hourly and daily mean temporal resolutions. Then, we present a brief overview of the full dataset, which will provide a unique and valuable tool for investigating climate change in Bavaria with high interdisciplinary relevance. Minimally subsetted data from the finest resolution WRF domain are available for download at daily temporal resolution from a public repository at the Open Science Foundation.

How to cite: Collier, E. and Mölg, T.: Convection-permitting present-day climatological simulation with WRF over Bavaria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13144, https://doi.org/10.5194/egusphere-egu2020-13144, 2020.

When downscaling to higher resolution, which is common trend in operational weather forecast, air-quality prediction as well as regional climate modeling, capturing the urban effects properly becomes of primary importance to describe the impact of cities and urban structures on weather, climate and air-quality. This is necessary for proper assessment of not only impacts in the cities, but the effectiveness of adaptation and mitigation options applied within cities. It is valid not only for extreme heat waves impact prediction, but as well in air-quality prediction and in long term perspective in connection to climate change impacts. This provides the background for the project within Operational Program Prague - The Pole of Growth “Urbanization of weather forecast, air-quality and climate scenarios for Prague”, shortly URBI PRAGENSI.

In the comparison of different urban parameterizations in WRF and RegCM we demonstrate the importance of urban models in the high resolution simulations, especially under conditions of heat waves. There are differences in the impacts of such parameterizations in different models, but basically all are able to capture the effects of urban heat island in these simulations, which can be quite significant and achieve up to about 8-10 °C difference between the city and its vicinity for large cities during night time, but even in smaller cities like the City of Prague (about 1.5M), it can be more than 5°C. More detailed analysis of the effects in terms of energy balance in the city and remote areas in high resolution simulations will be presented, as well as the impacts on other parameters, especially those connected to air-quality like mixing layer height, stability, etc., where the proper choice of the parameterization really matters and simplistic option like bulk in WRF rather fails.

CORDE FPS on urbanization, which is under preparation, will be introduced with its aims and potential tasks.

How to cite: Halenka, T., Belda, M., Huszar, P., Karlicky, J., and Novakova, T.: On the urban effects in high resolution weather forecast and regional climate simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21747, https://doi.org/10.5194/egusphere-egu2020-21747, 2020.

There is actually no limitation of current high-resolution weather model for producing simulation and forecast of convection at kilometer and infra-kilometer horizontal resolutions. However, the disappointing results as well as the associated huge amount of computer resources required may lead to focus on Large Eddy Simulation model instead. However, the use of LES is not trivial and required a long and non-portable adjustment over the region of interest. Also, it is difficult to use in operational mode for daily forecast since they require specific inputs.

In the other side, pushing the current regional or Limited Area Model towards very high resolution is a convenient way to reach explicit resolution of convective process for instance. However, an explicit simulation is not a guarantee of a realistic result mainly due to the fact that initial condition is crucial as well as all other descriptions of the environment (soil, vegetation, sst, etc) and use of correct parameterization schemes.

For instance, within the WRF model framework, one can identify more than 4000 set of parameterizations plus all the scheme adjustments and threshold associated to.

However, a physically based analyze of what it is necessary for a realistic and explicit convection simulation may conduct a physicist user to define its “ideal” physics with what it already exists in the model. It may conduct to so-called unrealistic model requests in term of computation requirement regarding the radiative, the turbulence and the microphysics schemes but it does works with HPC systems. This kind of parameterization will be presented here and used with a very realistic vertical circulation into convective systems with convective updraft and downdraft modelling, from few meters up to several kilometers height.

How to cite: messager, C. and honnorat, M.: Non-reasonable but efficient use of schemes in current model to improve realistic explicit convection modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13855, https://doi.org/10.5194/egusphere-egu2020-13855, 2020.

Moving towards convection permitting simulations up to few kilometers scale are emerging solutions to the challenge and complexities in simulating different convective phenomena especially over mountainous regions. In this study we execute sensitivity experiments with the non-hydrostatic regional climate model REMO-NH at convection permitting resolution (~3km). We use this model in three setups where different parameterization schemes for horizontal diffusion are tested. In the first setup “DIFF2” we utilize the standard 2^nd order diffusion while the second setup “DIFF4” applies 4^th order diffusion. The higher order has a smaller impact on larger scales so that the atmospheric fields exhibit more details, especially in regions with high convective activity. In the third setup “TURB3D”, REMO-NH runs with a new 3D Smagorinsky-type turbulence scheme instead of the artificial diffusion schemes. Though turbulent horizontal diffusion is of second order in this setup, it incorporates a spatially and temporally varying exchange coefficient so that flows with little deformation remain unaffected. The domain of the simulations driven with EURO-CORDEX boundary data covers Germany and the time integration spans the year 2006.

Selected cases reveal a better representation of convective elements in DIFF4 and TURB3D when compared with DIFF2. We cannot compare these individual cases directly to observations since REMO-NH is not a reanalysis but a climate model. However, the spatial precipitation fields deduced from DWD radar data have characteristics which are more similar to DIFF4 and TURB3D than to DIFF2. More details are resolved in DIFF4 and TURB3D since the diffusion mainly act at the smallest spatial scales resolved by the model. DIFF2 smoothes convective activity drastically so that it appears in the form of unrealistically wide convective cells. On the other hand, the statistics of precipitation (seasonal average, standard deviation and 95th percentile) show a better agreement with observations in the simulation DIFF2 and TURB3D. TURB3D appears to be the best compromise regarding the simulation of precipitations fields. However, TURB3D exhibits a warm bias in the 2m temperature field in autumn and winter. Further model development may help to overcome this issue.

How to cite: Frisius, T., Jacob, D., Reca Remedio, A., Sieck, K., and Teichmann, C.: The effect of horizontal diffusion parameterization in convection-permitting REMO-NH simulations over Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17888, https://doi.org/10.5194/egusphere-egu2020-17888, 2020.

Convection-permitting models (CPMs) provide a better representation of sub-daily precipitation statistics and convective processes, both on climate and NWP time scales, mainly thanks to the possibility to switch off the parameterisation of convection. The improved realism of these models gives us greater confidence in their ability to project future changes in short-duration precipitation extremes.

The first 12-member ensemble of convection-permitting climate simulations over the UK was completed within the latest updates to the UK Climate Projections (UKCP). The 20-year long CPM simulations for present-day and end of century periods are nested in an ensemble of regional climate model (RCM) simulations over Europe driven by a global climate model ensemble. In the driving ensembles, uncertain parameters in the model physics are varied within plausible bounds to sample uncertainty. Although no perturbations are applied directly to the CPMs, this project allow us to provide a first-ever estimate of uncertainty at convection-permitting scale and thus provide UK risk assessment studies with more reliable climate change projections at local and hourly scales.

Here we will present results looking at the uncertainty in future changes in hourly precipitation extremes across the CPM ensemble, and how this differs from the driving RCM ensemble.

How to cite: Fosser, G., Kendon, E., Chan, S., and Stephenson, D.: UKCP: Understanding uncertainty in future changes in precipitation extremes at convection-permitting scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14870, https://doi.org/10.5194/egusphere-egu2020-14870, 2020.

Atmospheric fronts play a major role in day-to-day life and are well known for sharp changes in local weather conditions. In mountainous regions, the interaction between fronts and the orography supports the development of characteristic precipitation patterns and may even cause specific weather phenomena, like thunderstorms, föhn events, and others. It is therefore an interesting question, how such fronts evolve in the next few days or how they will behave under changing climate conditions.

However, due to the complexity of fronts and limitations in numerical weather prediction or climate models, state-of-the-art automated front detection algorithms are largely restricted to the model they are applied onto. In particular, the outcome of these algorithms depends the discretization scheme of the underlying model (e.g. the grid spacing) and hence they may fail in model intercomparison or evaluation studies when data is given in various different grids.

In the present work, a diagnostic front detection algorithm, that is designed to overcome such model dependencies, is introduced and its applicability for model intercomparison is demonstrated by means of simple analytic test functions and idealized simulations of a baroclinic wave (i.e. the Jablonowksi and Williamson test) conducted with MPAS (60 km and 15 km grid spacing). Finally, the algorithm is exemplarily applied onto latest WRF evaluation simulations (15 km and 3 km grid spacing) from the CORDEX-FPS Convection initiative and the Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF) (~25 km grid spacing) to investigate differences in front statistics in the greater Alpine region of the period 2006 to 2009.

The study is funded by the Austrian Klima- und Energiefonds through the Austrian Climate Research Programme (ACRP) by means of the project "Research for Climate Protection: Value-adding Convection-Permitting Climate Simulations Austria" (reclip:convex, project id: B769999).

How to cite: Truhetz, H., Heinzeller, D., Ritter, R., and Herbsthofer, L.: Front related model evaluation of multi-year simulations from hydrostatic to convection-permitting scales in the greater Alpine region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17810, https://doi.org/10.5194/egusphere-egu2020-17810, 2020.

Changes in precipitation at local to regional scales in a warmer world remain highly uncertain. This is especially true of both moderate and high extremes (e.g. > 90%-iles and > 99.9%-iles, respectively). While a relationship between increasing model resolution and increasing precipitation (both means and extremes) appears to be present for both GCMs and RCMs there are conflicting results when convection-permitting scales are reached. These differences can be region as well as model dependent. A project under the auspices of the World Climate Research Program’s (WCRP) Coordinated Regional Downscaling Experiments Flagship Pilot Studies program (CORDEX-FPS) was established to investigate these, and other issues. This initiative aims to build first-of-their-kind ensemble climate experiments using convection permitting models to investigate present and future convective processes and related extremes over Europe and the Mediterranean. In this presentation we offer a first look at the scenario simulations (Historical 2000-2009 and RCP8.5 2090-99 timeslices) and an analysis of precipitation changes and their drivers over various sub-regions of a large domain, which cover the Alps, parts of central Europe and the Mediterranean and Adriatic coasts (0-17E x 40-50N). This study employs an innovative precipitation separation algorithm specifically designed for use with km-scale models. The algorithm separates convective, stratiform and orographic precipitation, which allows for a more nuanced understanding of projected change. The method is based on physical processes such as vorticity and vertical velocity. This new approach focuses on the physical processes leading to precipitation of a certain types rather than use the circular reasoning of employing the result to determine the cause. As a result we are able to see that despite overall drying in some seasons increasing intensity of convective precipitation contributes toward the shift to more intense extremes. We conclude with a discussion of the changes to the underlying physical processes driving convective and other types of precipitation at highly localized scales.

How to cite: Sobolowski, S. and the CORDEX Flagship Pilot Study on Convection over Europe and the Mediterranean: Changes in future precipitation characteristics over the Alpine region in a multi-model convection-permitting ensemble: the role of shifting intensities , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19716, https://doi.org/10.5194/egusphere-egu2020-19716, 2020.

Convection permitting climate models (CPMs) agree on an increase in short-term, extreme precipitation in the future. However, different studies using CPM simulations found regionally varying temperature scaling rates of hourly extreme precipitation either close to or above the Clausius-Clapeyron-rate (CC-rate) of 7%/K. These variations suggest that the dynamics of convective events strongly regulate the local scaling rates. In order to understand how the characteristics of convective events change in the future, we apply a tracking algorithm to precipitation data with 5-min temporal resolution from a regional climate model (COSMO-CLM) simulation. The model is run over central Europe at a grid size of 0.025° for an evaluation period (1981-2015) driven by ERA-Interim reanalysis data, as well as a present-day (1976-2005) and a future (2071-2100) period driven by the EC-Earth global model. We investigate the temperature scaling of convective cell characteristics like total precipitation per cell, mean area, lifetime and maximum intensity, as well as changes in the diurnal cycle of convective cells which might explain the overall scaling rates. The cell characteristics precipitation sum, mean area and maximum intensity show an exponential increase with temperature across most of the temperature range with a drop-off at high temperatures very similar to fixed location scaling curves. While the maximum intensity and area scale at rates close to the CC-rate, the precipitation sum scales at a rate close to twice the CC-rate. In contrast to this, the lifetime of convective cells does not increase with temperature but stays constant with a drop-off at high temperatures. The future simulation shows a shift of the scaling curves towards higher peak values at higher temperatures. Convective activity is projected to decrease during daytime and increase during nighttime. While the mean intensity of convective cells increases throughout the whole day, the number of cells is reduced during the afternoon peak and increased during nighttime. This leads to a slight reduction of convective precipitation during daytime and almost a doubling of convective precipitation during nighttime.

How to cite: Purr, C., Brisson, E., and Ahrens, B.: Temperature scaling of convective cells in present and future conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20581, https://doi.org/10.5194/egusphere-egu2020-20581, 2020.

The DYAMOND (DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains) project is an intercomparison project for global storm resolving models with horizontal resolutions < 5km. In Phase 0, nine models participated in simulating a 40 day period from August 2016 on. Now, Phase 0 of DYAMOND will be complemented by a boreal winter period and atmospher-ocean coupled models with the goal to: (i) compare the representation of the Madden-Julian-Oscillation in this class of models; (ii) investigate the effect of the atmosphere-ocean coupling at storm and ocean-eddy resolving scales on convection and the general circulation; and (III) link to the EUREC4A campaign, which targets meso-scale convection patterns and the coupling to the upper ocean processes. First results from the intercomparison of this new class of climate models will be presented, giving an outlook to the future of climate modelling.

How to cite: Klocke, D. and the DYAMOND Team: Intercomparison of global storm resolving (coupled) climate models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18958, https://doi.org/10.5194/egusphere-egu2020-18958, 2020.

Tropical Africa is subject to weather extremes at a variety of space- and time-scales, leading to droughts, floods and severe storms. The weather has a huge impact on the local population: droughts and floods impact on weather dependent industries such as agriculture or fishing, which much of the population rely on for their livelihoods, while severe storms can lead to destruction of property and even loss of life. Despite this, global numerical weather prediction performance remains notoriously poor in tropical Africa, particularly at smaller scales.

The UK Met Office has recently begun running an ensemble weather forecasting system for tropical Africa at convection permitting scale (4.4 km). This forecasting system clearly has enormous potential to enable improved weather forecasts in  tropical Africa. Previous studies indicate that convection permitting models can provide greater skill than lower resolution global models for sub-regions within tropical Africa. However, skill remains fairly poor and further evaluation work is necessary to identify potential model improvements.

This presentation describes an evaluation of the lifecycles of convective systems in the UK Met Office tropical Africa model. 10.8 micron brightness temperatures are used to identify and follow convective systems both in the model and in geostationary satellite observations, which provide both high temporal (15 minute) and spatial (~3 km) resolution. We evaluate the size, diurnal cycle, propagation, initiation and lifecycle of convective systems in the model and the link between these properties and the magnitude of surface precipitation produced. Finally we analyse and evaluate the response of storm systems and hence precipitation in the model to large scale atmospheric drivers such as the Madden-Julian Oscillation and African easterly waves. This process oriented evaluation helps identify of the causes of model errors, facilitating future improvements in the model.

How to cite: Hill, P., Stein, T., Cafaro, C., Woodhams, B., and Webster, S.: Evaluation of convective lifecycles in convection permitting weather forecasts for tropical Africa., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18097, https://doi.org/10.5194/egusphere-egu2020-18097, 2020.

The Lake Victoria Basin is home to largest freshwater lake (Lake Victoria; LV) in Africa and second largest in the world. Each year on the order of 1,000 fisherman are lost on LV during intense night-time thunderstorms. Despite this, until recently, understanding of the processes contributing to heavy rainfall events was very limited. In this study we present a 10-year (2006-2015) convection permitting (3km grid-spacing) simulation (CPS) of the Lake Victoria Basin using the RegCM version 4.7.0. A lake model is utilized in order to couple the lake regions with RegCM, which has been shown to be of great importance for simulating a realistic lake surface temperature (LST) over LV. The simulated LST from the CPS shows a general warm bias when comparing to ARC Lake observations, however the annual cycle of LST is well represented by the CPS. In the coarser simulation the LST has a large cool bias because of the absence of any lake coupling and this contributes to a large dry bias over LV. The CPS shows a much-improved seasonal rainfall pattern over LV, however there is a general overestimation of the rainfall by the CPS during the peaks in the rainy seasons (March-May; October-December). The CPS shows an improved ability to produce extreme rainfall (>100mm/day) over the western portion of the lake which is consistently found in satellite and in-situ observations. The distribution of rainrates over LV in the CPS is much closer to satellite derived rainfall observations compared to the coarse simulation, demonstrating the improvements made to the simulation of cloud microphysics processes when moving to convection permitting grid-spacing. Mesoscale circulations associated with the diurnal cycle over LV are an important driver of intense night-time thunderstorms. An analysis of the diurnal rainfall cycle over LV shows that the CPS well represents the timing of nocturnal rainfall over the lake which is associated with a strong landbreeze, however the daytime peak in rainfall over the land surrounding the lake is too early. Extreme nocturnal rainfall events over the lake in satellite observations show a clear migration from the previous daytime peak in rainfall westward onto the lake during the night. This suggests a connection between extreme rainfall events at night and the preceding daytime peak in rainfall over land. In the CPS these daytime peaks over the land occur too early and the lakebreeze circulation appears weak compared to the nocturnal landbreeze which is very prominent. The coarse resolution lake coupled simulation shows a surprisingly robust ability to simulate seasonal and annual rainfall associated with mesoscale lake circulations compared to the CPS. The improvement over the coarser simulation seems to be in the CPS’s ability to capture convection scale interactions which may be important for extreme rainfall events.

How to cite: Müller, S. K., Glazer, R., and Coppola, E.: Lake coupled convection permitting simulations over the Lake Victoria basin with RegCM4.7: What is the benefit of permitting convection? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19343, https://doi.org/10.5194/egusphere-egu2020-19343, 2020.