Linda Schlemmer's research while affiliated with Deutscher Wetterdienst and other places

Publications (29)

Article
Full-text available
Six strategies to couple the dynamical core with physical parameterizations in atmospheric models are analyzed from a numerical perspective. Thanks to a suitably designed theoretical framework featuring a high level of abstraction, the truncation error analysis and the linear stability study are carried out under weak assumptions. Indeed, second‐or...
Article
An adequate representation of the interaction between the land surface and the atmosphere is critical for both numerical weather prediction and climate models. The surface energy and mass balances are tightly coupled to the terrestrial water cycle, mainly through the state of soil moisture. An inadequate representation of the terrestrial water cycl...
Preprint
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Over the last decade kilometer-scale weather predictions and climate projections have become established. Thereby both the representation of atmospheric processes, as well as land-surface processes need adaptions to the higher-resolution. Soil moisture is a critical variable for determining the exchange of water and energy between the atmosphere an...
Article
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The single-column mode (SCM) of the ICON (ICOsahedral Nonhydrostatic) modeling framework is presented. The primary purpose of the ICON SCM is to use it as a tool for research, model evaluation and development. Thanks to the simplified geometry of the ICON SCM, various aspects of the ICON model, in particular the model physics, can be studied in a w...
Article
Full-text available
Convection-resolving models (CRMs) can explicitly simulate deep convection and resolve interactions between convective updrafts. They are thus increasingly used in numerous weather and climate applications. However, the truncation of the continuous energy cascade at scales of O(1 km) poses a serious challenge, as in kilometer-scale simulations the...
Article
Currently, major efforts are underway to refine the horizontal resolution of weather and climate models to kilometer-scale grid spacing (Δx). Besides refining the representation of the atmospheric dynamics and enabling the use of explicit convection, this will also provide higher resolution in the representation of orography. This study investigate...
Article
The “grey-zone” of convection is defined as the range of horizontal grid-space resolutions at which convective processes are partially but not fully resolved explicitly by the model dynamics (typically a few kilometers to a few hundred meters). The representation of convection at these scales is challenging as both parameterizing convective process...
Article
Full-text available
Under radiative‐convective equilibrium (RCE), surface moisture fluxes drive convection, while convection‐driven winds regulate surface fluxes. Most simulations of RCE do not resolve the boundary‐layer turbulence that drives near‐surface winds due to too coarse grid spacing and instead parameterize its effects by enforcing a minimum wind speed in th...
Article
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Currently major efforts are underway toward refining the horizontal resolution (or grid spacing) of climate models to about 1 km, using both global and regional climate models (GCMs and RCMs). Several groups have succeeded in conducting kilometer-scale multiweek GCM simulations and decadelong continental-scale RCM simulations. There is the well-fou...
Article
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This review paper explores the field of mesoscale to microscale modeling over complex terrain as it traverses multiple so-called gray zones. In an attempt to bridge the gap between previous large-scale and small-scale modeling efforts, atmospheric simulations are being run at an unprecedented range of resolutions. The gray zone is the range of grid...
Article
Convection-resolving models (CRMs) are established as a solid framework to simulate moist convection in both numerical weather prediction and regional-scale climate projections. However, capturing the different scales of the governing processes is challenging. Previous studies have shown that the size and properties of individual clouds and updraft...
Article
Thermally driven upslope flows in mountainous areas provide favorable conditions for diurnal deep moist convection especially during episodes of weak synoptic forcing. The present study investigates the response of deep convection to axisymmetric orography as a function of orographic width and height by running ensembles of idealized convection-res...
Article
Soil moisture modifies the state of the atmosphere and thus plays a major role in the climate system. Its spatial distribution is strongly modulated by the underlying orography. Yet the vertical transport of soil water and especially the generation of groundwater runoff at the bottom of the soil column are currently treated in a crude way in most a...
Article
The observed increase of convective extreme precipitation intensities with temperature beyond the Clausius-Clapeyron rate has recently directed attention to nonequilibrium processes that might cause the increase. While out-of-equilibrium simulations with perturbed heating conditions show clear increases in convective precipitation intensities, it h...
Article
Ensembles of convection-resolving simulations with a simplified land surface are conducted to dissect the isolated and combined impacts of soil moisture and orography on deep-convective precipitation under weak synoptic forcing. In particular, the deep-convective precipitation response to a uniform and a nonuniform soil moisture perturbation is inv...
Article
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Convective momentum transport (CMT) has mostly been studied for deep convection, whereas little is known about its characteristics and importance in shallow convection. In this study CMT by shallow convection is investigated by analyzing both data from large-eddy simulations (LES) and reforecasts performed with the Integrated Forecasting System (IF...
Article
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On summertime fair-weather days, thermally driven wind systems play an important role in determining the initiation of convection and the occurrence of localized precipitation episodes over mountainous terrain. This study compares the mechanisms of convection initiation and precipitation development within a thermally driven flow over an idealized...
Article
The impact of an isolated mesoscale mountain on the diurnal cycle of moist convection and its spatial variation is investigated. Convection-resolving simulations of flow over 3D Gaussian-shaped mountains are performed for a conditionally unstable atmosphere under diurnal radiative forcing. The results show considerable spatial variability in terms...
Article
This study investigates the interplay between atmospheric moisture and deep convective clouds via cold-pool dynamics in the absence of large-scale forcing in a series of cloud-resolving modelling studies. More specifically the contribution of moisture advection, evaporation of rain and surface fluxes to the moisture budget over particular regions o...
Article
Full-text available
A correct representation of the coupling between convection and circulation constitutes a prerequisite for a correct representation of precipitation at all scales. In this study, the coupling between convection and a sea breeze is investigated across three main resolutions: large-eddy resolution where convection is fully explicit, convection-permit...
Article
Current climate models often predict fractional cloud cover on the basis of a diagnostic probability density function (PDF) describing the subgrid-scale variability of the total water specific humidity, qt, favouring schemes with limited complexity. Standard shapes are uniform or triangular PDFs the width of which is assumed to scale with the grid-...
Article
This study investigates how precipitation-driven cold pools aid the formation of wider clouds that are essential for a transition from shallow to deep convection. In connection with a temperature depression and a depletion of moisture inside developing cold pools, an accumulation of moisture in moist patches around the cold pools is observed. Conve...
Article
The importance of soil moisture anomalies on airmass convection over semiarid regions has been recognized in several studies. The underlying mechanisms remain partly unclear. An open question is why wetter soils can result in either an increase or a decrease of precipitation (positive or negative soil moisture–precipitation feedback, respectively)....
Article
Abstractvar REST_ID=21;The influence of soil moisture and atmospheric stability on mid‐latitude diurnal convection and land–atmosphere exchange is investigated in an idealized cloud‐resolving modelling framework using a full set of parametrization schemes. In each member of a series of month‐long experiments, the model attains a state where deep, p...
Article
The influence of topography on the diurnal cycle of mid-latitude, summertime, moist convection is investigated in an idealized framework using cloud-resolving model with a horizontal grid spacing of 2 km. In this framework, the atmosphere is continuously relaxed towards prescribed reference profiles of temperature, specific humidity and wind speed....
Article
This paper introduces an idealized cloud-resolving modeling (CRM) framework for the study of midlatitude diurnal convection over land. The framework is used to study the feedbacks among soil, boundary layer, and diurnal convection. It includes a setup with explicit convection and a full set of parameterizations. Predicted variables are constantly r...
Article
Extreme precipitation events along the Alpine south side (AS) are often forced by upper-level positive potential vorticity (PV) anomalies over western Europe. These so-called PV streamers go along with a dynamical forcing for upward motion, a reduction of the static stability in the troposphere (hence facilitating convection), and are associated wi...
Article
Climate change is expected to moisten the atmosphere and to intensify the hydrological cycle. In the global mean, precipitation is projected to increase, but for Europe climate models suggest that mean summer precipitation will decrease. However, despite this decrease in mean, heavy precipitation events are projected to occur more frequently. The c...

Citations

... It is probably difficult to give a generally valid recommendation for timestep size, as many different processes are affected by it. Next to the dynamics, the parameterization 105 of subgrid-scale processes, its call frequency, and the type of coupling to the model dynamics (see for example Ubbiali et al., 2021) also have to be considered. For instance, Barrett et al. (2019) performed idealized simulations using COSMO with 1 km grid spacing and found a 53% reduction in precipitation with a two-moment microphysics scheme when the timestep was increased from 1 s to 15 s. ...
... The grid has 65 vertical levels and the horizontal grid spacing of about 2 km. ICON in the large eddy mode (LEM; Bašták Ďurán et al., 2021;Dipankar et al., 2015;Heinze et al., 2017) was used as a reference. The ICON-LEM was run in a limited-area setup similar to ICON-LAM, but forced by the ICON-D2 operational forecasts and with an LEM physics setup (Dipankar et al., 2015). ...
... Soil moisture-precipitation feedback has been proven consistently in observation and model studies (Findell and Eltahir, 1997;Schär et al., 1999;Pal and Eltahir, 2001). The resolution of orography also proved to impact moist convection (Heim et al., 2020), as orography triggers convection via mechanically and/or thermally induced circulations (Kirshbaum et al., 2018). Chow et al. (2019) mention the strong interplay between the resolution of orography and precipitation in the grey zone. ...
... Climate models without convective parameterizations can successfully better represent some aspects of climate states than those with convective parameterizations by increasing horizontal resolution even if the climate models cannot fully resolve convective clouds (e.g. Senf et al., 2020;Stevens et al., 2020;Vergara-Temprado et al., 2020;Wedi et al., 2020). ...
... A possible cause for the weakness of the surface flux feedback at later stages in the medium-f simulations lies in the model design. Mol et al. (2019) note that many CRMs employ a minimum wind speed threshold to compute latent and sensible heat fluxes. In SAM, this wind speed is 1 m s −1 , such that any grid point with a weaker wind is artificially raised to that threshold when calculating fluxes. ...
... Recent advances in parallel computing have enabled us to achieve global atmospheric simulations with finer horizontal resolution (e.g. Satoh et al., 2017;Schär et al., 2020;Wedi, 2014). Thus, motivation and research infrastructure are now prepared for global cloud resolving simulations that fill the scale gap between climate research and weather forecasting. ...
... Thus, LES usually adopts a computational grid that filters small-scale flow physics, where the subgridscale (SGS) turbulence modeling approach requires that the turbulence kinetic energy (TKE), as well as the effects of the mountain topography are only partially resolved. With this strategy, LES minimizes the effects of unresolved flow physics [9]. These apparent differences of the strategies of LES and NWP suggest that further investigation of the LES methodology for simulating turbulent flow over complex terrain is necessary to better understand atmospheric turbulence [23,24]. ...
... The ensemble of ERA-Interim driven present-day convection-permitting climate simulations have shown superior performance in simulating the precipitation characteristics compared to coarse-resolution climate simulations, although differences between the kilometer-scale simulations and observations still exist (Coppola et al. 2020;Ban et al. 2021). Panosetti et al. (2019) have shown that the kilometer-scale simulations are climatologically more robust in case of strong orographic forcing (domain over the European Alps) and less robust in central German. ...
... Many previous studies show that orographic-induced precipitation is highly related to background flow and mountain geometry (e.g., Imamovic et al., 2019). The primary theoretical mechanism emphasizes the mechanical lifting of moist unstable air masses (Houze, 2012), which could cause precipitation in the windward side of the mountains. ...
... Such methods have also been used to connect land surface model-based groundwater parameterizations into regional atmospheric models to interrogate potential feedbacks, mainly at the continental scale (Anyah et al., 2008;Barlage et al., 2015;Niu et al., 2007;Schlemmer et al., 2018;Seuffert et al., 2002;York et al., 2002). This is an active research area with a myriad of model platforms and coupling strategies. ...