Concurrent calculation of radiative transfer in the atmospheric simulation in ECHAM-6.3.05p2

​​​​​​​The scalability of the atmospheric model ECHAM6 at low resolution, as used in palaeoclimate simulations, suffers from the limited number of grid points. As a consequence, the potential of current high-performance computing architectures cannot be used at full scale for such experiments, particularly within the available domain decomposition approach. Radiation calculations are a relatively expensive part of the atmospheric simulations, taking up to approximately 50 % or more of the total runtime. This current level of cost is achieved by calculating the radiative transfer only once in every 2 h of simulation. In response, we propose extending the available concurrency within the model further by running the radiation component in parallel with other atmospheric processes to improve scalability and performance. This paper introduces the concurrent radiation scheme in ECHAM6 and presents a thorough analysis of its impact on the performance of the model. It also evaluates the scientific results from such simulations. Our experiments show that ECHAM6 can achieve a speedup of over 1.9× using the concurrent radiation scheme. By performing a suite of stand-alone atmospheric experiments, we evaluate the influence of the concurrent radiation scheme on the scientific results. The simulated mean climate and internal climate variability by the concurrent radiation generally agree well with the classical radiation scheme, with minor improvements in the mean atmospheric circulation in the Southern Hemisphere and the atmospheric teleconnection to the Southern Annular Mode. This empirical study serves as a successful example that can stimulate research on other concurrent components in atmospheric modelling whenever scalability becomes challenging.

RADT-17. FOCUSED ULTRASOUND MEDIATED BLOOD–BRAIN BARRIER OPENING IS SAFE AND FEASIBLE CONCURRENT WITH AND ADJUVANT TO A CLINICAL RADIATION SCHEME FOR BRAINSTEM DMG

Diffuse midline gliomas (DMG) are pediatric tumors with dismal prognosis. When these tumors emerge in the brainstem, there exists no feasible method of surgical resection or systemic intervention, making ionizing radiation the sole therapeutic avenue to date. However, radiotherapy (RT) provides only marginal survival benefit as the topographically diffuse and highly infiltrative tumors spread in areas in which the blood-brain barrier (BBB) is relatively intact. Focused ultrasound (FUS) with intravenous microbubbles provides a compelling solution, transiently and non-invasively opening the BBB to allow drug delivery across the cerebrovasculature. Nonetheless, it remains unclear whether FUS can be safely administered at the brainstem in patients receiving RT. Therefore, the goal of this study was to assess the safety and feasibility of FUS administered concurrent with and adjuvant to a clinical hypofractionated radiation scheme for brainstem DMG. Non-tumor bearing B6 albino mice were randomly assorted into control, RT, FUS, and RT+FUS groups. Mice designated RT+FUS received 39Gy/13fx (hypofractionated RT scheme) to the brainstem with two sessions of FUS approximately 1 week apart. A single-element, spherical-segment FUS transducer driven by a function generator through a power amplifier was used with concomitant microbubble injection to sonicate the brainstem. Magnetic resonance imaging (MRI) was used to confirm BBB opening and cardiopulmonary measures were recorded throughout sonication. Vitals were assessed daily, and all treatment animals underwent Kondziela inverted screen testing and sequential weight lifting to assess brainstem-related strength and motor coordination deficits. In both FUS and RT+FUS mice, MRI confirmed brainstem BBB opening and subsequent closure within 96 hours. Mouse weights were stable, with slight drops (mean=5.5%) following FUS that resolved within three days. No attenuation in cardiorespiratory, strength, and motor coordination measurements was observed from FUS. FUS is a safe and feasible technique for brainstem BBB opening concurrent with and adjuvant to clinical hypofractionated RT.

Concurrent Calculation of Radiative Transfer in the Atmospheric Simulation in ECHAM-6.3.05p2

The scalability of the atmospheric model ECHAM6 at low resolution, as used in palaeoclimate simulations, suffers from the limited number of grid points. As a consequence, the potential of current high performance computing architectures cannot be used at full scale for such experiments, particularly within the available domain-decomposition approach. Radiation calculations are a relatively expensive part of the atmospheric simulations taking approximately up to over 50 % of the total runtime. This current level of cost is achieved by calculating the radiative transfer only once in every two simulation hours. In response, we propose to extend the available concurrency within the model further by running the radiation component in parallel with other atmospheric processes to improve scalability and performance. This paper introduces the concurrent radiation scheme in ECHAM6 and presents a thorough analysis of its impact on the performance of the model. It also evaluates the scientific results from such simulations. Our experiments show that ECHAM6 can achieve a speedup over 1.9x using the concurrent radiation scheme. This empirical study serves as a successful example that can stimulate research on other concurrent components in atmospheric modeing whenever scalability becomes challenging.

Addressing radiation and cloud uncertainties with the new radiation scheme ecRad in ICON

<p>Radiation in the atmosphere provides the energy that drives atmospheric dynamics and physics on all scales, so determining radiative balance correctly is crucial for understanding processes ranging from cloud particle growth to climate. Radiation schemes in global weather and climate models make assumptions to simplify the complex interaction of radiation with the Earth system, such as treating radiative transfer in only the vertical dimension. Capturing cloud-radiation interactions is particularly challenging since clouds vary strongly on small spatial and temporal scales not resolved in the models, and also interact strongly with radiation. In models, sub-grid atmospheric variables are simplified, describing three-dimensional cloud geometry, cloud particle size and shape and complex scattering functions with a few parameters. Uncertainties in these assumptions contribute to the large lingering uncertainty in the climatic role of clouds.</p><p>The new modular radiation scheme ecRad provides the opportunity to vary these parametrisations and assumptions individually to determine their impact. Several options are available for the radiation solver, cloud vertical overlap and horizontal inhomogeneity treatment and cloud ice and water optical property parametrisations. The solver SPARTACUS is the only radiation solver in a global model that can treat 3D radiative effects.</p><p>We use ecRad as the new operational radiation scheme in the DWD global model ICON to investigate the sensitivity of radiation results to radiation model assumptions and input variables such as cloud particle size and cloud geometry, as well as the varying role of cloud-radiation interactions in regional cloud regimes. We find that ecRad with an up-to date solar spectrum agrees much better with exact line-by-line radiation calculations than previous radiation models. In ICON, ecRad improves the global radiation balance, model physics and forecast performance.</p><p> </p>

Machine Learning Emulation of 3D Cloud Radiative Effects

<p>The treatment of cloud structure in radiation schemes used in operational numerical weather prediction and climate models is often greatly simplified to make them computationally affordable. Here, we propose to correct the current operational scheme ecRad – as used for operational predictions at the European Centre for Medium-Range Weather Forecasts – for 3D cloud radiative effects using computationally cheap neural networks. The 3D cloud radiative effects are learned as the difference between ecRad’s fast Tripleclouds solver that neglects 3D cloud radiative effects, and its SPeedy Algorithm for Radiative TrAnsfer through CloUd Sides (SPARTACUS) solver that includes them but increases the cost of the entire radiation scheme. We find that the emulator increases the overall accuracy for both longwave and shortwave with a negligible impact on the model’s runtime performance.</p>

Les travaux de Jean-François Geleyn sur la paramétrisation du rayonnement atmosphérique

Cet article résume les activités de Jean-François Geleyn qui ont abouti à un schéma de rayonnement de pointe adapté à la prévision numérique du temps. L'objectif principal - traiter les interactions nuage-rayonnement - a été atteint grâce à une amélioration considérable de l'approche à bandes larges (la vision avec deux seuls intervalles spectraux, l'un pour les courtes longueurs d'onde pour le rayonnement solaire, l'autre pour les grandes longueurs d'onde pour le rayonnement thermique), en ouvrant la voie à un appel intermittent du schéma dans le temps. Le schéma qui en résulte offre une alternative compétitive par rapport aux approches traditionnelles en « k-distribution corrélée » utilisant des méthodes plus précises mais plus coûteuses, méthodes qui ne permettent pas la mise à jour en temps réel des effets radiatifs des nuages. The paper summarizes the activities of Jean-François Geleyn leading to a state-of-the-art radiation scheme tailored for numerical weather prediction. The main goal - dealing with cloud-radiation interactions - was reached thanks to significant improvements to the broadband approach allowing for single shortwave and single longwave intervals, opening a way to selective intermittency. The resulting scheme offers an alternative competitive to the mainstream approach that uses very accurate but expensive correlated k-distribution method, not allowing for timely update of cloud radiative effects.

Evaluation of ECMWF Radiation Scheme Using Aircraft Observations of Spectral Irradiance above Clouds

A novel approach to compare airborne observations of solar spectral irradiances measured above clouds with along-track radiative transfer simulations (RTS) is presented. The irradiance measurements were obtained with the Spectral Modular Airborne Radiation Measurement System (SMART) installed on the High Altitude and Long Range Research Aircraft (HALO). The RTS were conducted using the operational ecRad radiation scheme of the Integrated Forecast System (IFS), operated by the European Centre for Medium-Range Weather Forecasts (ECMWF), and a stand-alone radiative transfer solver, the library for Radiative transfer (libRadtran). Profiles of observed and simulated radar reflectivity were provided by the HALO Microwave Package (HAMP) and the Passive and Active Microwave Transfer Model (PAMTRA), respectively. The comparison aims to investigate the capability of the two models to reproduce the observed radiation field. By analyzing spectral irradiances above clouds, different ice cloud optical parameterizations in the models were evaluated. Simulated and observed radar reflectivity fields allowed the vertical representation of the clouds modeled by the IFS to be evaluated, and enabled errors in the IFS analysis data (IFS AD) and the observations to be separated. The investigation of a North Atlantic low pressure system showed that the RTS, in combination with the IFS AD, generally reproduced the observed radiation field. For heterogeneously distributed liquid water clouds, an underestimation of upward irradiance by up to 27% was found. Simulations of ice-topped clouds, using a specific ice optics parameterization, indicated a systematic underestimation of broadband cloud-top albedo, suggesting major deficiencies in the ice optics parameterization between 1242 and 1941 nm wavelength.

Mars' Annular Polar Vortex

<p><span>The Martian winter polar vortex </span><span>has recently been shown to be</span><span> annular in nature, with a local minimum in potential vorticity near the pole. This suggests barotropic instability, yet the vortex is remarkably persistent. It has been shown that its annular nature may be due to the release of latent heat from CO</span><span>2</span><span> condensation, CO<sub>2</sub> clouds, changes in dust distributions, and the strength of the Hadley circulation circulation, with many of these being interlinked</span><span>.</span><span> In this poster, we present </span><span>results </span><span>using the the Mars Analysis Correction Data Assimilation (MACDA) reanalysis dataset, which demonstrates clearly the annular vortex. Additionally</span><span>, we perform simulations of the Martian atmosphere and its response to varying topography and radiation scheme in the flexible Isca framework, a climate model capable of simulating the Martian basic state at varying levels of complexity. It is noted that the strength of the Martian polar vortex is significantly lower in Isca simulations than in the MACDA dataset. Through further simulations with Isca, we aim to investigate the effect of CO</span><span>2</span><span> condensation on the strength and shape of the Martian polar vortex.</span></p>

Impacts of Ice Cloud Particle Size Uncertainty on Radiation, and Precipitation and Climate Sensitivity and the Significance of Future Satellite-Based Constraints

<p>Ice cloud particle size is important to determining ice cloud radiative effect and precipitating rate. However, there is a lack of accurate ice particle effective radius (R<sub>ei</sub>) observation on the global scale and the parameterization of R<sub>ei</sub> in climate models is poorly constrained. We conduct a modeling study to assess the sensitivity of climate simulations to R<sub>ei</sub>. Perturbations to R<sub>ei</sub> are represented in ice fall speed parameterization and radiation scheme, respectively, in NCAR CESM1 model with a slab ocean configuration. We show that an increase in ice fall speed due to a larger R<sub>ei</sub> results in a longwave cooling dominating over a shortwave warming, a global mean surface temperature decrease, and precipitation suppression. Similar longwave and shortwave cloud radiative effect changes occur when R<sub>ei</sub> is perturbed in the radiation scheme. Perturbing falling snow particle size (R<sub>es</sub>) results in much smaller changes in the climate responses. We further show that varying R<sub>ei</sub> and R<sub>es</sub> by 50% to 200% relative to the control experiment can cause climate sensitivity to differ by +12.3% to −6.2%. A future mission under design with combined multi-frequency microwave radiometers and cloud radar can reduce the uncertainty ranges of R<sub>ei</sub> and R<sub>es</sub> from a factor of 2 to ±25%, which would help reducing the climate sensitivity uncertainty pertaining to ice cloud particle size by approximately 60%.</p><p> </p>