AS1.4

Simulating diurnal cycle of rainfall is a difficult challenge for general circulation models. We developed a global unstructured mesh model, Global-to-Regional Integrated forecast SysTem (GRIST), targeting at unified weather-to-climate forecast. The performance of the model in simulating the summer precipitation over East Asia has been evaluated. Yet the performance from a global perspective remains less understood. In this study, we focus on the simulations of precipitation diurnal cycle during boreal summer, and examine four AMIP simulation results of the GRIST model. These configurations mainly differ in the horizontal resolution. Thus, they reflect the direct changes due to varying resolutions. By refining the resolution over East Asia (VR-EA) and North America (VR-NA) respectively, we analyze the similarities and differences in model behaviors in simulating diurnal cycle of precipitation over these two refinement regions. VR-EA well reproduces the nocturnal rainfall, while VR-NA fails in certain regions respectively. The underlying responses to resolution of these two models are similar. For regions dominated by nocturnal rainfall, the refined resolution significantly increases the composited precipitation intensity at night up to the magnitude of the observation but has little impact on the composite percentage. The percentage of peak rainfall within 00-06h in the model over the Southern Great Plains remains lower than the observation as the resolution refines. Given the much lower occurrence frequency, the contribution of the intense precipitation to the climatological nocturnal rainfall amounts is small in VR-NA. Over East Asia, since the precipitation frequency is comparable to the observation, VR-EA benefits from the increased precipitation intensity due to higher resolution. No apparent artificial features are observed in the transition zone of the variable-resolution mesh. The results suggest that the variable-resolution modeling is cost-effective for simulating the diurnal cycle of climatological summer precipitation.

How to cite: Zhou, Y., Zhang, Y., and Yu, R.: Global variable-resolution model simulation of rainfall diurnal cycle during boreal summer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2617, https://doi.org/10.5194/egusphere-egu22-2617, 2022.

Eleven 40-day long integrations of five different global models with horizontal resolutions of less than 9 km are compared in terms of their global energy spectra. The method of normal-mode function decomposition is used to distinguish between balanced (Rossby wave; RW) and unbalanced (inertia-gravity wave; IGW) circulation. The simulations produce the expected canonical shape of the spectra, but their spectral slopes at mesoscales, and the zonal scale at which RW and IGW spectra intersect differ significantly. The partitioning of total wave energies into RWs an IGWs is most sensitive to the turbulence closure scheme and this partitioning is what determines the spectral crossing scale in the simulations, which differs by a factor of up to two. It implies that care must be taken when using simple spatial filtering to compare gravity wave phenomena in storm-resolving simulations, even when the model horizontal resolutions are similar. In contrast to the energy partitioning between the RWs and IGWs, changes in turbulence closure schemes do not seem to strongly affect spectral slopes, which only exhibit major differences at mesoscales. Despite their minor contribution to the global (horizontal kinetic plus potential available) energy, small scales are important for driving the global mean circulation. Our results support the conclusions of previous studies that the strength of convection is a relevant factor for explaining discrepancies in the energies at small scales. The models studied here produce the major large-scale features of tropical precipitation patterns. However, particularly at large horizontal wavenumbers, the spectra of upper tropospheric vertical velocity, which is a good indicator for the strength of deep convection, differ by factors of three or more in energy. High vertical kinetic energies at small scales are mostly found in those models that do not use any convective parameterisation.

How to cite: Stephan, C., Duras, J., Harris, L., Klocke, D., Putman, W. M., Taylor, M., Wedi, N. P., Žagar, N., and Ziemen, F.: Atmospheric energy spectra in global kilometre-scale models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1924, https://doi.org/10.5194/egusphere-egu22-1924, 2022.

In global storm-resolving models (SRMs), that resolve convection explicitly instead of parameterizing it, microphysical processes are now fundamentally linked to their controlling factors, i.e., the circulation. While in conventional climate models the convective parameterization is one of the main sources of uncertainties (and a popular tuning parameter), this role might be passed on to the microphysical parameterization in global SRMs. In this study, we use a global SRM with two different microphysical schemes. For each scheme we do several sensitivity runs, where in each run we vary one parameter of the applied microphysics scheme in its range of uncertainty. We find that the two microphysics schemes have distinct signatures, e.g., in how condensate is partitioned between ice and snow. In addition, perturbing single parameters of each scheme also affects condensate amounts and hence the heat budget of the tropics. Among the parameters tested, the model is particularly sensitive to the ice fall speed and the width of the raindrop size distribution, which both cause several 10s W/m2 variation in radiative fluxes. Overall, microphysical sensitivities in global SRMs are substantial and resemble inter-model differences such as in the DYAMOND ensemble. 

How to cite: Naumann, A. K. and Esch, M.: Microphysical sensitivities in global storm-resolving simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4433, https://doi.org/10.5194/egusphere-egu22-4433, 2022.

Before an off-shore wind farm is built a thorough resource assessment of all available locations for the farm needs to be performed. Since the power extraction of a wind farm depends on the cube of the wind speed even the mesoscale variability in the wind speed plays an important role in the resource assessment of a wind farm. In order to study mesoscale systems that occur in the vicinity of off-shore wind farms we've set up a convection permitting simulation in COSMO-CLM for the Kattegat sea strait. The Kattegat is particularly interesting since it is an area which features a very irregularly shaped coastline and pronounced coastal effects. Centrally located in the Kattegat lays the 400 MW Anholt wind farm. Operational data of the Anholt wind farm and scatterometer data of the Kattegat are used to validate our simulation. A relatively good agreement between observations and the model output has been found. A variety of mesoscale systems has been identified, both in unstable (e.g. a downburst) as in stable (e.g. gravity waves) conditions. The wind speed variability on temporal scales and on spatial scales over the Kattegat has been investigated. The interactions of the Anholt wind farm with these systems have been investigated using the COSMO-CLM model which incorporates the Fitch wind farm parametrisation. This research is part of a larger project aiming at developing a fast and accurate resource planning and forecasting platform for off-shore wind farms. More information about this project can be found on freewind-project.eu.

How to cite: Neirynck, J., Stoffelen, A., Meyers, J., and van Lipzig, N.: Mesoscale weather systems and their interactions with windfarms: A study for the Kattegat., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5030, https://doi.org/10.5194/egusphere-egu22-5030, 2022.

In global atmospheric modeling the importance of an appropriate ratio of vertical to horizontal model resolution has been emphasized earlier. Theoretical considerations for appropriate ratios have been based, e.g., on quasi-geostrophic considerations for large-scale flows and the dissipation conditions for gravity waves. In limited-area convection-permitting simulations it has been shown that in particular the simulation of shallow cloud layers depends on the vertical model resolution. 
A recent focus in global climate modeling is to increase horizontal resolutions down to a few kilometers grid spacing in order to resolve processes like convection that need to be parameterized at coarser resolutions. In these simulations, often the vertical model resolutions haven’t been changed much in comparison to traditional approaches. Questions like the following may arise: Is this appropriate? How strongly does the climate at storm-resolving horizontal scales depend on vertical resolution? Can convergence of the simulated climate be expected at a certain vertical resolution? Is it useful to invest in further increases of horizontal resolution without a refinement of the vertical grid?
To start answering these questions we have performed simulations with the ICON global atmospheric model at a horizontal resolution of 5 km with three different vertical grids comprising 55, 110, and 190 layers and corresponding vertical resolution in the troposphere of 400, 200, and 100 m, respectively, for a period of 6 weeks.  Here we will show the dependence of selected climate parameters, including the global energy budget, on the vertical resolution. 

How to cite: Schmidt, H. and Rast, S.: The dependence of the climate simulated in a global storm-resolving model on its vertical resolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9110, https://doi.org/10.5194/egusphere-egu22-9110, 2022.

The high-resolution DYAMOND simulations resolve much of the cloud relevant dynamics and cause a large improvement in the structure and diurnal cycle of clouds and precipitation. Nevertheless, from DYAMOND simulations we know that cloud properties can vary significantly even in high-resolution simulations. We focus on evaluating and if possible constraining ice cloud processes in the tropics, an area that should particularly benefit from the increased resolution because deep convection is resolved and controls the tropical upper tropospheric water budget. We analyse not only the horizontal distribution of IWP but also the cloud phase and cloud vertical structure as they are crucial to Earth’s radiation budget.

When comparing the high-resolution global simulations performed within the DYAMOND project among each other and with passive remote sensing data and ERA5 reanalysis we find that the horizontal distribution of ice water path (IWP) varies significantly. In order to understand better those differences, we analysed the connection between the simulated vertical velocity and the total IWP, and the water path of the individual hydrometeors. While the PDF of tropical vertical velocity simulated by the different models is quite similar, the total ice water path connected with those vertical velocities varies strongly. In most models, high vertical velocities are connected with significantly higher IWP than liquid water path (LWP) except in the ICON simulations which simulates similarly large increases in IWP and LWP. Most models simulate large increases in larger ice hydrometeors for large vertical velocities while FV3 simulates also large increases in ice water connected with deep convection. Differences in cloud phase e.g. when comparing NICAM and ICON simulations are connected with different vertical distributions of the condensate with NICAM IWC reaching higher atmospheric levels than the ICON IWC. We attempt to constrain the vertical distribution using active remote sensing data. 

How to cite: Corko, K. and Burkhardt, U.: Impact of tropical convection on upper tropospheric cirrus in high resolution DYAMOND simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11478, https://doi.org/10.5194/egusphere-egu22-11478, 2022.

AGRIF (Adaptive Grid Refinement In Fortran) is a package for the integration of full adaptive mesh refinement features within a multidimensional finite difference model. This library is used in ocean models like NEMO (Nucleus for European Modelling of the Ocean) to offer the possibility to run multiple levels and 2-way nested embedded zooms. Within the ESiWACE2 project, AGRIF performance have been addressed toward high resolution simulations. 
First, a simple AGRIF configuration within NEMO has been set up to simplify benchmarking, profiling and testing new optimizations ideas. We selected on purpose a configuration with small MPI sudomains to mimic simulations running on high numbers of core. Second, a profiling analysis has let us identify an important overhead. Indeed, on a zoom with a refinement of a factor 3 in both latitude and longitude covering 1/9 of the simulated domain an overhead of 46% has been observed compared with the theoretical performance. The correction of land points used in the interpolation on the zoom has been found to be a major bottlenecks. Third, we implemented an optimization concerning the correction on land point limiting as much as possible the computations and taking advantage of the specificity of each interpolation. This adjustment provided us with a reduction of 25% of the time to solution in the aforementioned configuration. For future work, we identified numerous optimizations including further optimizations of the correction of land points.

How to cite: Irrmann, G., Masson, S., Debreu, L., Guibert, D., and Raffin, E.: Optimizations of Multiscale Simulation with AGRIF, towards Exascale Applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12292, https://doi.org/10.5194/egusphere-egu22-12292, 2022.

On the morning of 10 July 2019, an intrusion of relatively cold and dry air, over the Adriatic Sea, through a "bora jet", gave rise to a frontal structure at the ground, which moved rapidly from the Northern to the Southern Adriatic. The intense thermal gradient (together with a high positive sea surface temperature anomaly), the interaction of the jet with the complex topography of Apennines  and the coastal boundary, generated a storm structure that moved parallel to the central Italy coast. In particular, between 8UTC and 12UTC, a supercell developed along the coast to the north of Pescara city (middle Adriatic), producing rainfall that reached 130 mm in 3 hours, and a violent hailstorm (estimated diameter greater than 10 cm). 

In this work, the frontal dynamics and the genesis of the thunderstorm are studied using the numerical system COAWST. Local polarimetric radar observations are also used to check the consistency of the simulations in the mature phase of the supercell. Numerical experiments are performed using a 1 km grid over central Italy, initialized using the ECMWF IFS analysis/forecasts. The sensitivity study investigates the role of the orography, the sea surface temperature (SST) and the coupling between ocean and atmosphere. Orography tests include simulations where the relevant peaks of the Apennine range  (such as Gran Sasso and Picentini) are removed as well as cases where their peaks are modified compared to their real values. In terms of SST, we employ, using an uncoupled approach, the ECMWF SST dataset, the MFS-CMEMS Copernicus dataset at 4 km, 0.01°C Satellite SST, and we investigate the role of the SST anomaly (adding +1°C and +2°C to the real field). The role of the ocean-atmosphere interaction is tested using the COAWST numerical model using an ocean model numerical grid at 1 km resolution over the whole Adriatic Sea. 

The preliminary results show that the topography and in particular  the interaction with the peaks of the Apennine range plays a fundamental role in the dynamics of the cold pool that trigger the convective system. Also, the SST anomaly is found to play an important role in the development of the supercell. In particular, we observed that the simulations forced with MFS-CMEMS SST and the COAWST model runs produce a very realistic SST, in terms of spatial and temporal distribution, but colder by about 1.5 °C in absolute value if compared to observed satellite data. This difference generates lower heat fluxes, less evaporation, weaker precipitations and smaller hail than using warmer SSTs. 

How to cite: Ferretti, R., Mazzarella, V., Marzano, F., Miglietta, M. M., Picciotti, E., Montopoli, M., Baldini, L., Vulpiani, G., Tiesi, A., Mazzà, S., and Ricchi, A.: Analysis of the development mechanisms of a large-hail storm event, on the Adriatic Sea using an atmosphere-ocean coupled model (COAWST), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12876, https://doi.org/10.5194/egusphere-egu22-12876, 2022.

Numerical simulations at cloud-resolving scales have becoming practical for both research and operational applications due to advances in computing technology.  However, deploying such capabilities beyond a limited scale (e.g., extended metropolitan region, large watershed) typically remains out of reach due to the computational cost and the complexity of the systems to support such work.  Yet such capabilities are needed to address the local impacts of precipitation events that can impact much broader areas.  In particular, convective storms driven by monsoons remain unresolved by current numerical weather prediction systems applied to sub-Saharan Africa.  To address this problem, the African Rainfall Project (ARP) was initiated to deploy the community Weather Research Forecast (WRF) model across this region at 1x1 km horizontal resolution on the World Community Grid (WCG).  WRF is configured to capture a diversity of geographic conditions in the region with appropriate boundary layer, land surface and cloud microphysics and parameterizations in addition to high vertical and temporal resolution.  WCG provides a fully distributed computational environment that crowd-sources unused computing power from volunteers’ devices and donates it to scientific projects.  As such, all computations must be embarrassingly parallel, which creates a challenge for models like WRF.  Hence, each instance of WRF must operate serially on a volunteer’s device.  To address the regional-scale simulations, sub-Saharan Africa is decomposed into individual 52 by 52 km domains at 1x1km as the third nest in two-way telescoping grids with common centroids.  The outer domains are at 3 and 9 km resolution, respectively with the same vertical resolution.  Each 48-hour simulation is done as a cold-start forced by reanalysis with output saved every 15 minutes.  The collection of these simulations will cover at least one year to capture seasonal variations.  Since there is no operational imperative, the ability of typical volunteer’s system to compute each simulation in several hours is practical.  Scaling is achieved with many thousands of systems being deployed simultaneously.  With this decomposition, over 35000 overlapping domains cover the region.  During post-processing, the individual simulations are stitched together to create a consistent, single output for over for the period of study.  Although the focus is precipitation, the simulations provide additional standard output for 2m temperature and 10m horizontal wind velocity, for example.  We will report on the results to date and validation in comparison to in situ (e.g., from TAHMO, www.tahmo.org) and remotely sensed observations as well as conventional WRF deployments for a large computational domain covering a small subset of the region.

How to cite: Treinish, L., van de Giesen, N., and Le Coz, C.: Meso-gamma-scale numerical weather simulations for sub-Saharan Africa via grid-based, distributed computing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12956, https://doi.org/10.5194/egusphere-egu22-12956, 2022.