Diffuse Radiation Research Articles

The influence of stand composition and season on canopy structure and understory light environment in different subtropical montane Pinus massoniana forests.

Canopy structure and understory light have important effects on forest productivity and the growth and distribution of the understory. However, the effects of stand composition and season on canopy structure and understory light environment (ULE) in the subtropical mountain Pinus massoniana forest system are poorly understood. In this study, the natural secondary P. massoniana-Castanopsis eyrei mixed forest (MF) and P. massoniana plantation forest (PF) were investigated. The study utilized Gap Light Analyzer 2.0 software to process photographs, extracting two key canopy parameters, canopy openness (CO) and leaf area index (LAI). Additionally, data on the transmitted direct (Tdir), diffuse (Tdif), and total (Ttot) radiation in the light environment were obtained. Seasonal variations in canopy structure, the ULE, and spatial heterogeneity were analyzed in the two P. massoniana forest stands. The results showed highly significant (P < 0.01) differences in canopy structure and ULE indices among different P. massoniana forest types and seasons. CO and ULE indices (Tdir, Tdif, and Ttot) were significantly lower in the MF than in the PF, while LAI was notably higher in the MF than in the PF. CO was lower in summer than in winter, and both LAI and ULE indices were markedly higher in summer than in winter. In addition, canopy structure and ULE indices varied significantly among different types of P. massoniana stands. The LAI heterogeneity was lower in the MF than in the PF, and Tdir heterogeneity was higher in summer than in winter. Meanwhile, canopy structure and ULE indices were predominantly influenced by structural factors, with spatial correlations at the 10 m scale. Our results revealed that forest type and season were important factors affecting canopy structure, ULE characteristics, and heterogeneity of P. massoniana forests in subtropical mountains.

Lethality of Simulated UV and Solar Diffuse Radiations to Detached Urediniopores of Phakopsora pachyrhizi

Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi, is the most destructive disease on the crop. This work aimed to generate data to understand the detached uredospores survival during the winter fallow in Mato Grosso state, Brazil. Experiment &amp;lsquo;A&amp;rsquo;&amp;mdash;the detached urediniospores maintained and multiplied on Ativa soybean cultivar, were deposited on soybean estract-agar and kept at 25 oC temperature in closed plastic petri dishes and exposed to UV-C (100-280 nm) radiation, distant 30 cm from the plates surface for &amp;lsquo; 0&amp;rsquo;; 60; 120; 180; 240; 300; 360, 420, 480 and 560 minutes. Experiment &amp;lsquo;B&amp;rsquo;&amp;mdash;was similar to previous experiment but spores were exposed to UV-B (280-320 nm) radiation. In Experiment &amp;lsquo;C&amp;rsquo;&amp;mdash;the urediniospores were deposited into empty plastic petri dishes without lids and exposed to direct diffuse sunlight for 0; 60; 120; 180; 240; 300; 360; 420; and 300 minutes. Solar radiation was measured with a pyranometer (Spectrum Technologies, Inc.). After the exposition time, urediniospores were plated on soybean-extract agar, incubated at 25 oC under dark for 8 h and germination assessed under an optical microscope (400&amp;zwj;&amp;times;). Data were submitted to analyses of variance and regression. All experiments were repeated twice. The detached spores exposed to UV-C were killed with 496 minutes, and under UV-B radiation killed with 962.7 minutes and those submitted to direct diffusion solar radiation killed by 15.6 MJ m-2 dose, or 240 minutes exposition to 1,250 w/m2. It can be inferred that the incident solar diffused radiation in Mato Grosso, during the winter fallow, has the daily potential to kill the detached P. pachyrhizi urediniospores.

A novel method for calculating solar radiation on indoor human body under different weather conditions

Indoor occupants may receive large solar heat that affect their health, productivity, and comfort. Most of previous studies focus on indoor occupants with strong direct solar radiation and weak diffuse radiation. Considering the non-uniform solar radiation distribution in the sky, this study proposes the improved HNU Solar Model, a novel method for calculating solar radiation on indoor human body under different weather conditions. The improved HNU Solar Model proposes a new calculation algorithm for calculating non-uniform radiation distributed on indoor human body under different weather conditions, via adding the human body points, windows points, and clearness index to improve the calculation accuracy; then it converts the human-body-received solar radiation into the increase in the mean radiant temperature (Delta MRT). The calculated Delta MRT values by the improved HNU Solar Model were compared with those calculated by Radiance. The results indicate that, for Delta MRT by total solar radiation on typical days with different weather conditions, the absolute error (AE) and the relative error (RE) of the improved HNU Solar Model are usually less than 1.5 °C and 15%, respectively. For the whole-year hourly Delta MRT values, the corresponding AE and RE are usually less than 1 °C and 15%, respectively. Moreover, according to the proposed model, for large-window buildings in medium-latitude regions, indoor occupants are more exposed to direct solar radiation (63%) than diffuse solar radiation (37%); while diffuse radiation can be the dominant solar heat gain of indoor occupants (up to 55%) in buildings in low-latitude regions.

Vision transformer models to measure solar irradiance using sky images in temperate climates

Solar Irradiance measurements are critical for a broad range of energy systems, including evaluating performance ratios of photovoltaic systems, as well as forecasting power generation. Using sky images to evaluate solar irradiance, allows for a low-cost, low-maintenance, and easy integration into Internet-of-things network, with minimal data loss. This work demonstrates that a vision transformer-based machine learning model can produce accurate irradiance estimates based on sky-images without any auxiliary data being used. The training data utilizes 17 years of global horizontal, diffuse and direct data, based on a high precision pyranometer and pyrheliometer sun-tracked system; in-conjunction with sky images from a standard lens and a fish-eye camera. The vision transformer-based model learns to attend to relevant features of the sky-images and to produce highly accurate estimates for both global horizontal irradiance (RMSE =52 W/m2) and diffuse irradiance (RMSE = 31 W/m2). This work compares the model’s performance on wide field of view all-sky images as well as images from a standard camera and shows that the vision transformer model works best for all-sky images. For images from a normal camera both vision transformer and convolutional architectures perform similarly with the convolution-based architecture showing an advantage for direct irradiance with an RMSE of 155 W/m2.

NEW MODELS FOR ESTIMATION OF DIFFUSE SOLAR RADIATION USING METEOROLOGICAL PARAMETERS FOR BENIN, NIGERIA

In this comprehensive study, an extensive 22-year dataset (2001-2022) for Benin (Latitude 6.32 oN, Longitude 5.10 oE and 77.80 m above sea level) were obtained from the National Aeronautic Space Administration (NASA) website. The datasets comprises of the monthly average daily global solar radiation, diffuse solar radiation, relative humidity, atmospheric pressure, wind speed, and mean temperature, was utilized to develop 19 new models for estimating diffuse solar radiation. These models were categorized into five distinct groups: modified Page, Liu and Jordan models; clearness index and one-variable models; two-variable models; three-variable models, and a four-variable model. These models were statistically evaluated using a set of five validation indices—Mean Bias Error (MBE), Root Mean Square Error (RMSE), Mean Percentage Error (MPE), t-test, and the coefficient of determination (R²). The study identified the most effective models in each category. Equation 28b from the modified Page, Liu and Jordan category, Equation 28f from the clearness index and one-variable models, Equation 28j from the two-variable models, and Equation 28o from the three-variable models category were found to be the best-performing models. A comparative assessment of these performed models revealed that the quadratic regression model (Equation 28b) stood out as the most suitable for accurately estimating diffuse solar radiation in Benin. This implies that the developed model equation 28b can be used to estimate the diffuse solar radiation for Benin and locations with similar climatic conditions

Clustering-based assessment of solar irradiation and temperature attributes for PV power generation site selection: A case of Indonesia’s Java-Bali region

This study presents clustering-based assessments of solar attributes for locating potential solar photovoltaic (PV) power plant sites using k-means and density-based spatial clustering of applications with noise (DBSCAN) by examining the yearly average single-attribute and three-attribute clustering on a dataset of long-term hourly-based direct and diffuse irradiation, ambient temperature, and solar PV power output from 2005 to 2022. Three-attribute clustering enables stakeholders to better understand the characteristics of a cluster by collectively identifying three solar attributes and the magnitude of each attribute in an area or cluster. The presence of this information, which constitutes the clusters, suggests that these attributes have different effects on solar PV output power in different clusters. Although k-means is an effective method for investigating potential locations for PV power plant placements, DBSCAN offers users an alternative method for accomplishing a similar goal. In the case of three-attribute clustering of direct irradiation with k-means and DBSCAN, the 18-year mean value of clusters with the highest yearly average value is achieved at very similar values of 0.305 kW/m2 and 0.310 kW/m2, respectively. It turns out that only six years of direct irradiation had an annual mean value of less than 0.305 kW/m2. This finding implies that in the long run, the solar resources in terms of direct irradiation will typically surpass 0.3 kW/m2/MW installed capacity over all areas suitable for PV power plants. While focusing on the Java-Bali region, Indonesia, the findings, and methods appear to be of broader interest to policymakers, particularly in developing countries where solar PV is considered an option for sustainable energy generation.

Observation and modeling of irradiance near water surface of a photovoltaic pond

Accurate evaluation of near ground solar radiation in photovoltaic (PV) covered areas is essential for controlling adverse environmental effects and comprehensively utilizing the earth’s surface resources. The irradiance near the water surface of a photovoltaic fishpond was measured with eighteen distributed pyranometers. A simplified penetration model is proposed to reveal the shielding effect of PV panels on direct and diffuse irradiance. The model can well capture the spatial–temporal variation of the global irradiance due to the shielding effect of PV arrays. Numerical results show that proper modeling of the shading effect on diffuse irradiance is essential for the calculation accuracy of the cumulative global irradiance loss for various weather types and sky-view restriction levels. The spatial variation range of global radiation penetration ratio under the PV panels is 10%–90%. The spatially-averaged monthly shielding effects show that the maximum (87%) and minimum (46%) relative irradiance loss ratios in the studied PV area occur in December and June, respectively.

Dispersion and damping of magnetohydrodynamic modes in radiative plasmas

The presented work introduces a theoretical model for radiative magnetohydrodynamics (RMHD) in the equilibrium diffusion limit, focusing on the dynamics of radiation energy. For small amplitude waves, the basic set of dynamic equations is perturbed to derive the dispersion relation for three fundamental modes: fast, intermediate, and slow magnetosonic waves in RMHD plasmas. The study reveals that both fast and slow magnetosonic waves exhibit dispersion and damping in RMHD plasma. It is also revealed that mode conversion between fast and slow RMHD waves occurs at specific values of the wavenumber and propagation angle. The investigation extends to exploring the influence of various parameters characterizing radiative plasma, such as radiation pressure, plasma beta, and radiation diffusivity, on the dispersion and damping of magnetosonic modes (both fast and slow) in RMHD plasma. The findings are elucidated through numerical illustrations. The proposed model finds application in scenarios involving optically thick regions within stars, specifically in their inner atmosphere and interior region. In these regions, the transport of radiation adheres to equilibrium diffusion, and radiation pressure and energy density reach magnitudes comparable to thermal energy and pressure.

CLASS Angular Power Spectra and Map-component Analysis for 40 GHz Observations through 2022

Measurement of the largest angular scale (ℓ < 30) features of the cosmic microwave background (CMB) polarization is a powerful way to constrain the optical depth to reionization and search for the signature of inflation through the detection of primordial B-modes. We present an analysis of maps covering 73.6% of the sky made from the 40 GHz channel of the Cosmology Large Angular Scale Surveyor (CLASS) from 2016 August to 2022 May. Taking advantage of the measurement stability enabled by front-end polarization modulation and excellent conditions from the Atacama Desert, we show this channel achieves higher sensitivity than the analogous frequencies from satellite measurements in the range 10 < ℓ < 100. Simulations show the CLASS linear (circular) polarization maps have a white noise level of 125(130)μKarcmin . We measure the Galaxy-masked EE and BB spectra of diffuse synchrotron radiation and compare to space-based measurements at similar frequencies. In combination with external data, we expand measurements of the spatial variations of the synchrotron spectral energy density (SED) to include new sky regions and measure the diffuse SED in the harmonic domain. We place a new upper limit on a background of circular polarization in the range 5 < ℓ < 125 with the first bin showing D ℓ < 0.023 μKCMB2 at 95% confidence. These results establish a new standard for recovery of the largest-scale CMB polarization from the ground and signal exciting possibilities when the higher sensitivity and higher-frequency CLASS channels are included in the analysis.

Expanding microscopic black holes

Two interesting hypotheses about black holes have been proposed. The older one states that microscopic black holes can be accountable for the observed dark matter density. The newer one states that black holes are coupled to the expansion of the universe. Here, we combine those ideas and investigate the behavior of expanding microscopic black holes. We observe two temperatures at which the radiation balances the expansion. While one of the balance points might be important in the analysis of primordial scenarios, the other would lead to a strong diffuse gamma radiation background, which is contradicted by the lack of observations. This establishes another indirect evidence disfavoring the hypothesis of cosmological coupling of black holes.

Global Solar Radiation and Its Interactions with Atmospheric Substances and Their Effects on Air Temperature Change in Ankara Province

On the analysis of solar radiation and meteorological variables measured in Ankara province in Türkiye from 2017 to 2018, an empirical model of global solar radiation was developed. The global solar radiation at the ground and at the top of the atmosphere (TOA) was calculated and in good agreement with the observations. This model was applied to compute the losses of global solar radiation in the atmosphere and the contributions by atmospheric absorbing and scattering substances. The loss of global solar radiation in the atmosphere was dominated by the absorbing substances. The sensitivity test showed that global solar radiation was more sensitive to changes in scattering (described by a scattering factor S/G, S and G are diffuse and global solar radiation, respectively) than to changes in absorption. This empirical model was applied to calculate the albedos at the TOA and the surface. In 2017, 2018, and 2019, the computed albedos were 28.8%, 27.8%, and 28.2% at the TOA and 21.6%, 22.1%, and 21.9% at the surface, which were in reasonable agreement with satellite retrievals. The empirical model is a useful tool for studying global solar radiation and the multiple interactions between solar energy and atmospheric substances. The comparisons of global solar radiation and its loss in the atmosphere, as well as meteorological parameters, were made at some representative sites on the Earth. Some internal relationships (between G and the absorbing and scattering substances, air temperature and atmospheric substances, air temperature increase and latitude, etc.) were found. Thus, it is suggested to thoroughly study solar radiation, atmospheric substances, and climate change as a whole system and reduce the direct emissions of all atmospheric substances and, subsequently, secondary products (e.g., CO2 and non-CO2) in the atmosphere for the achievement of slowing down climate warming.

Sunlight exposure might account for the relatively low COVID-19 morbidity and mortality in tropical countries.

The present study aimed at exploring whether sunlight exposure might account for the relative difference in COVID-19-related morbidity and mortality between tropical and non-tropical countries. A retrospective observational study was designed and data from the World Health Organization weekly COVID-19 epidemiological update was compiled. We examined the total number of confirmed COVID-19 cases per 100 000 population, as well as the total number of COVID-19-related mortalities per 100 000 population. Solar variables data were obtained from the Global Solar Atlas website (https://globalsolaratlas.info/). These data were analyzed to determine the association of sunlight exposure to COVID-19-related morbidity and mortality in tropical and non-tropical countries. Results revealed a statistically significant decrease in the number of confirmed COVID-19 cases per 100 000 population (P<0.001), as well as the number of COVID-19-related mortalities per 100 000 population (P<0.001) between tropical and non-tropical countries. Analyses of sunlight exposure data found that specific photovoltaic power output, global horizontal irradiation, diffuse horizontal irradiation and global tilted irradiation at optimum angle were significantly inversely correlated to COVID-19-related morbidity and mortality. This suggests that stronger sunlight exposure potentially leads to lower COVID-19-related morbidity and mortality. Findings from this study suggest that the relatively low COVID-19-related morbidity and mortality in tropical countries were possibly due to better sunlight exposure that translates into adequate vitamin D status.

Diffuse Fertilization Effect in Maize and Soybean Is Driven by Improved Light Use Efficiency Rather Than by Light Absorption

AbstractDiffuse radiation can improve the efficiency of terrestrial carbon uptake. Both light absorption and canopy light use efficiency (LUE) are affected by the fraction of diffuse radiation (DF). However, the relative contribution of these two factors to the diffuse fertilization effect (DFE) in the short term is not well understood. To investigate the mechanism of DFE in cropland, we collected gross primary productivity, fraction of absorbed photosynthetically active radiation (FAPAR), and other meteorological parameters from June to August in three crop sites. Our results indicated that the short‐term DFE in soybean and maize was primarily driven by the improvement of LUE rather than light absorption. The LUE increased significantly with DF, while the FAPAR changed a little with DF. The increased DF is typically associated with reduced photosynthetically active radiation (PAR). Our results showed that the potential gain in light absorption and canopy LUE from DF could not fully offset the reduced PAR in soybean and maize. The findings in this study contribute to our understanding of the mechanisms underlying the DFE.

Solar and Wind Data Recognition: Fourier Regression for Robust Recovery

Accurate prediction of renewable energy output is essential for integrating sustainable energy sources into the grid, facilitating a transition towards a more resilient energy infrastructure. Novel applications of machine learning and artificial intelligence are being leveraged to enhance forecasting methodologies, enabling more accurate predictions and optimized decision-making capabilities. Integrating these novel paradigms improves forecasting accuracy, fostering a more efficient and reliable energy grid. These advancements allow better demand management, optimize resource allocation, and improve robustness to potential disruptions. The data collected from solar intensity and wind speed is often recorded through sensor-equipped instruments, which may encounter intermittent or permanent faults. Hence, this paper proposes a novel Fourier network regression model to process solar irradiance and wind speed data. The proposed approach enables accurate prediction of the underlying smooth components, facilitating effective reconstruction of missing data and enhancing the overall forecasting performance. The present study focuses on Midland, Texas, as a case study to assess direct normal irradiance (DNI), diffuse horizontal irradiance (DHI), and wind speed. Remarkably, the model exhibits a correlation of 1 with a minimal RMSE (root mean square error) of 0.0007555. This study leverages Fourier analysis for renewable energy applications, with the aim of establishing a methodology that can be applied to a novel geographic context.

The Inner Disk Rim of HD 163296: Linking Radiative Hydrostatic Models with Infrared Interferometry

Previous studies of the protoplanetary disk HD 163296 revealed that the morphology of its sub-au infrared emission encompasses the terminal sublimation front of dust grains, referred to as the inner rim, but also extends into the (supposedly) dust-free region within it. Here, we present a set of radiative hydrostatic simulations of the inner rim in order to assess how much the rim alone can contribute to the observed interferometric visibilities V, half-light radii R hl, and fractional disk fluxes F in the wavelength range 1.5–13 μm. In our set of models, we regulate the cooling efficiency of the disk via the boundary condition for radiation diffusion and we also modify the shape of the sublimation front. We find that when the cooling efficiency is reduced, the infrared photosphere at the rim becomes hotter, leading to an increase in R hl sufficient to match the observations. However, the near-infrared disk flux is typically too low ( F≃0.25 at 1.5 μm), resulting in H-band visibility curves located above the observed data. We show that the match to the H-band observations up to moderate baselines can be improved when a wall-shaped rather than curved sublimation front is considered. Nevertheless, our model visibilities always exhibit a bounce at long baselines, which is not observed, confirming the need for additional emission interior to the rim. In summary, our study illustrates how the temperature structure and geometry of the inner rim need to change in order to boost the rim’s infrared emission.

CFD Analysis for a New Trombe Wall Concept

The envelope (façade) of a building is the first barrier between the exterior and the interior of the building and withstands the highest variation in temperature and solar radiation. Trombe walls are used to take advantage of that and contribute to the heating of interior air, helping the heating system. In this study, a new Trombe wall design is presented to contribute significantly to the indoor ventilation of residential buildings. For this, an exterior wall equipped with a proposed Trombe system was studied in a numerical simulation analysis. The proposed systems consist of two important sections, an exterior one and an interior one. The air cavities on the exterior of the wall, covered with silica glass, are the first heat-transfer layer. The secondary layer used for heat transfer, on the interior, is comprised of a MPCLB wall of 115 mm. The air circulation from the exterior to the interior was established as forced convection with a ventilator. The air circulates through the first heating layer on the exterior air cavities and then passes through the second heating layer on the interior MPCLBs. Two cities in Romania were considered to represent the coldest and hottest climates in Romania. Brașov represents the cold climate and Constanța represents the hot climate. In the investigation, both the presence and absence of solar radiation were taken into account. In total, four cases were established. For all four cases, monthly research was made using monthly mean temperatures, and direct and diffuse solar radiation. The results are promising and illustrate that the system works best during the transitional seasons of spring and autumn. The lower the outdoor temperature, the higher the temperature can be increased. Overall, solar radiation accounted for an average 2 °C increase. The temperature increase varied between 3.4 °C and 15.99 °C for Brașov and between 6.42 °C and 12.07 °C in Constanța. This study presents an alternative way to use the Trombe wall for indoor ventilation purposes throughout the year, compared to traditional uses for the Trombe wall for indoor heating.

Study on the impact of valley orientation on solar radiation shading of roofs in western Sichuan

Solar energy is a commonly used renewable energy source in buildings. In the high-altitude mountainous regions of western Sichuan, solar energy resources are abundant, but the complex and variable terrain significantly affects the shading of solar radiation on building roofs. In the mountainous regions of western Sichuan, towns located in valley terrain are the most prevalent, accounting for as much as 42.14%. Therefore, based on the mountainous solar radiation estimation method, this study estimates the direct radiation shading rate and diffuse radiation shading rate for building roofs in the valley towns of western Sichuan. The research delves into the analysis of the impact of valley terrain characteristics on the shading of solar radiation on building roofs. The study reveals that, for a specific valley town, the orientation of the valley has a more significant impact on the shading of direct radiation compared to its impact on diffuse radiation. When the town's orientation approaches an east-west direction, both direct and diffuse radiations are less affected by terrain shading.

Enhanced net CO2 exchange of a semideciduous forest in the southern Amazon due to diffuse radiation from biomass burning

Abstract. Carbon cycling in the Amazon fundamentally depends on the functioning of ecosystems and atmospheric dynamics, which are highly intricate. Few studies have hitherto investigated or measured the radiative effects of aerosols on the Amazon and Cerrado. This study examines the effects of atmospheric aerosols on solar radiation and their effects on net ecosystem exchange (NEE) in an area of semideciduous tropical forest in the north of Mato Grosso. Our results show that for a relative irradiance (f) 1.10–0.67, a decrease in incident solar radiation is associated with a reduction in the NEE. However, an average increase of 25 %–110 % in NEE was observed when pollution levels and aerosol optical depth (AOD) were above ≈ 1.25 and f &lt; 0.5. The increase NEE was attributed to the increase of up to 60 % in the diffuse fraction of photosynthetically active radiation. The change in AOD and f was mainly attributable to biomass burning organic aerosols from fires. Important influences on vapor pressure deficit (VPD) as well as air temperature (Tair) and canopy (LCT), induced by the interaction between solar radiation and high aerosol load in the observation area, were also noticed. On average, a cooling of about 3–4 ∘C was observed for Tair and LCT, and a decrease of up to 2–3 hPa was observed for VPD. Given the long-distance transport of aerosols emitted by burning biomass, significant changes in atmospheric optical properties and irradiance will impact the CO2 flux of semideciduous forests distributed in the region.

High order conservative Lagrangian schemes for two-dimensional radiation hydrodynamics equations in the equilibrium-diffusion limit

Radiation hydrodynamics equations (RHE) refer to the study of how interactions between radiation and matter influence thermodynamic states and dynamic flow, which has been widely applied to high temperature hydrodynamics, such as inertial confinement fusion (ICF) and astrophysical gaseous stars. Solving RHE accurately and robustly even under the equilibrium diffusion approximation is a challenging task. To address this, we develop two types of high order conservative Lagrangian schemes for RHE in the equilibrium-diffusion limit for the two dimensional case on the Lagrangian moving mesh. Based on the multi-resolution WENO reconstruction for the spatial discretization and strong stability preserving Runge-Kutta (SSP-RK) time discretization, we first develop an explicit Lagrangian scheme with the HLLC numerical flux to achieve high order accuracy in space and time. We also discuss the positivity-preserving property of the high order explicit Lagrangian scheme. To overcome the severe time step restriction arising from the nonlinear radiation diffusion term in the explicit scheme, we further present a high order explicit-implicit-null (EIN) Lagrangian scheme. By adding a sufficiently large linear diffusion term on both sides of the scheme, we treat the complicated nonlinear parts explicitly and efficiently, and treat the added linear diffusion term on the right-hand side implicitly with a relaxed time step restriction. According to our numerical experiments, these two types of Lagrangian schemes are high order accurate, conservative and can capture the interfaces automatically. Additionally, the explicit scheme is found to be non-oscillatory and can preserve positivity while maintaining the original high order accuracy.

Migration of low-mass planets in inviscid discs: the effect of radiation transport on the dynamical corotation torque

ABSTRACT Low-mass planets migrate in the type-I regime. In the inviscid limit, the contrast between the vortensity trapped inside the planet’s corotating region and the background disc vortensity leads to a dynamical corotation torque, which is thought to slow down inward migration. We investigate the effect of radiative cooling on low-mass planet migration using inviscid 2D hydrodynamical simulations. We find that cooling induces a baroclinic forcing on material U-turning near the planet, resulting in vortensity growth in the corotating region, which in turn weakens the dynamical corotation torque and leads to 2–3× faster inward migration. This mechanism is most efficient when cooling acts on a time-scale similar to the U-turn time of material inside the corotating region, but is none the less relevant for a substantial radial range in a typical disc (R ∼ 5–50 au). As the planet migrates inwards, the contrast between the vortensity inside and outside the corotating region increases and partially regulates the effect of baroclinic forcing. As a secondary effect, we show that radiative damping can further weaken the vortensity barrier created by the planet’s spiral shocks, supporting inward migration. Finally, we highlight that a self-consistent treatment of radiative diffusion as opposed to local cooling is critical in order to avoid overestimating the vortensity growth and the resulting migration rate.