Radiative Feedback Research Articles

Identifying Three‐Dimensional Radiative Patterns Associated With Early Tropical Cyclone Intensification

AbstractCloud radiative feedback impacts early tropical cyclone (TC) intensification, but limitations in existing diagnostic frameworks make them unsuitable for studying asymmetric or transient radiative heating. We propose a linear Variational Encoder‐Decoder (VED) framework to learn the hidden relationship between radiative anomalies and the surface intensification of realistic simulated TCs. The uncertainty of the VED model identifies periods when radiation has more importance for intensification. A close examination of the radiative pattern extracted by the VED model from a 20‐member ensemble simulation on Typhoon Haiyan shows that longwave forcing from inner core deep convection and shallow clouds downshear contribute to intensification, with deep convection in the downshear‐left quadrant having the most impact overall on the intensification of that TC. Our work demonstrates that machine learning can aid the discovery of thermodynamic‐kinematic relationships without relying on axisymmetric or deterministic assumptions, paving the way for the objective discovery of processes leading to TC intensification in realistic conditions.

The formation of supermassive black holes from Population III.1 seeds. III. Galaxy evolution and black hole growth from semi-analytic modelling

ABSTRACT We present an implementation of Pop III.1 seeding of supermassive black holes (SMBHs) in a theoretical model of galaxy formation and evolution to assess the growth of the SMBH population and the properties of the host galaxies. The model of Pop III.1 seeding involves SMBH formation at redshifts $z\gtrsim 20$ in dark matter minihaloes that are isolated from external radiative feedback, parametrized by isolation distance $d_{\rm iso}$. Within a standard $\Lambda$CDM cosmology, we generate dark matter haloes using the code pinocchio and seed them according to the Pop III.1 scenario, exploring values of $d_{\rm iso}$ from 50 to 100 kpc (proper distance). We consider two alternative cases of SMBH seeding: a halo mass threshold model in which all haloes $\gt 7\times 10^{10}\,\rm M_\odot$ are seeded with $\sim 10^5\,\rm M_\odot$ black holes; an all light seed model in which all haloes are seeded with low, stellar mass black holes. We follow the redshift evolution of the haloes, populating them with galaxies using the GAlaxy Evolution and Assembly theoretical model of galaxy formation, including accretion on SMBHs and related feedback processes. Here we present predictions for the properties of galaxy populations, focusing on stellar masses, star formation rates, and black hole masses. The local, $z\sim 0$ metrics of occupation fraction as a function of the galaxy stellar mass, galaxy stellar mass function, and black hole mass function all suggest a constraint of $d_{\rm iso}\lt 75\:$ kpc. We discuss the implications of this result for the Pop III.1 seeding mechanism.

Investigation of the combustion law of delayed ignition ethanol spill fire in longitudinal ventilation

The environmental conditions under which sustained spill fire accidents occur are complex and variable, and this paper investigates experimentally the effect of longitudinal ventilation in tunnel on the combustion law of delayed ignition spill fires. Experiments on instantaneous ignition and spill fires with delay of 10 s, 20 s, and 30 s were carried out using ethanol at a spill rate of 78 ml/min under a longitudinal wind speed of 0–1.5 m/s in tunnel. The results show that with the increase of longitudinal wind speed the flame inclination of the spill fire increases and the flame length first increases and then decreases. By analysing the force on the fuel layer and the force on the flame, and combining with the previous research, the prediction models of flame length and flame inclination were established. In the case of longitudinal wind speed, the spill fire burning area increases and then decreases with the increase of wind speed, and there is a critical wind speed, which is related to the delayed ignition time. The heat loss of the substrate in the longitudinal wind and the influence of the flame morphology on the thermal radiation feedback of the flame were considered, and it was found that the heat transfer of the fuel layer with the increase of the wind speed was gradually transitioned from the radiation dominated to the convection dominated. It was found that there was a general trend of increasing combustion rate with increasing wind speed and delayed ignition time.

Assessing Radiative Feedbacks and Their Contribution to the Arctic Amplification Measured by Various Metrics

AbstractArctic amplification (AA), characterized by a more rapid surface air temperature (SAT) warming in the Arctic than the global average, is a major feature of global climate warming. Various metrics have been used to quantify AA based on SAT anomalies, trends, or variability, and they can yield quite different conclusions regarding the magnitude and temporal patterns of AA. This study examines and compares various AA metrics for their temporal consistency in the region north of 70°N from the early twentieth to the early 21st century using observational data and reanalysis products. We also quantify contributions of different radiative feedback mechanisms to AA based on short‐term climate variability in reanalysis and model data using the Kernel‐Gregory approach. Albedo and lapse rate feedbacks are positive and comparable, with albedo feedback being the leading contributor for all AA metrics. The net cloud feedback, which has large uncertainties, depends strongly on the data sets and AA metrics used. By quantifying the influence of internal variability on AA and related feedbacks based on global climate model ensemble simulations, we find that water vapor and cloud feedbacks are most heavily affected by internal variability.

A protocol for model intercomparison of impacts of marine cloud brightening climate intervention

Abstract. A modeling protocol (defined by a series of climate model simulations with specified model output) is introduced. Studies using these simulations are designed to improve the understanding of climate impacts using a strategy for climate intervention (CI) known as marine cloud brightening (MCB) in specific regions; therefore, the protocol is called MCB-REG (where REG stands for region). The model simulations are not intended to assess consequences of a realistic MCB deployment intended to achieve specific climate targets but instead to expose responses to interventions in six regions with pervasive cloud systems that are often considered candidates for such a deployment. A calibration step involving simulations with fixed sea surface temperatures (SSTs) is first used to identify a common forcing, and then coupled simulations with forcing in individual regions and combinations of regions are used to examine climate impacts. Synthetic estimates constructed by superposing responses from simulations with forcing in individual regions are considered a means of approximating the climate impacts produced when MCB interventions are introduced in multiple regions. A few results comparing simulations from three modern climate models (CESM2, E3SMv2, and UKESM1) are used to illustrate the similarities and differences between model behavior and the utility of estimates of MCB climate responses that were synthesized by summing responses introduced in individual regions. Cloud responses to aerosol injections differ substantially between models (CESM2 clouds appear much more susceptible to aerosol emissions than the other models), but patterns in precipitation and surface temperature responses were similar when forcing is imposed with similar amplitudes in the same regions. A previously identified La Niña-like response to forcing introduced in the Southeast Pacific is evident in this study, but the amplitude of the response was shown to markedly differ across the three models. Other common response patterns were also found and are discussed. Forcing in the Southeast Atlantic consistently (across all three models) produces weaker global cooling than that in other regions, and the Southeast Pacific and South Pacific show the strongest cooling. This indicates that the efficiency of a given intervention depends on not only the susceptibility of the clouds to aerosol perturbations, but also the strength of the underlying radiative feedbacks and ocean responses operating within each region. These responses were generally robust across models, but more studies and an examination of responses with ensembles would be beneficial.

The origin and evolution of the CII deficit in HII regions and star-forming molecular clouds

We analyse synthetic emission maps of the CII 158 mu m line and far-infrared (FIR) continuum of simulated molecular clouds (MCs) within the SILCC-Zoom project to study the origin of the observed CII deficit, that is, the drop in the CII /FIR intensity ratio caused by stellar activity. All simulations include stellar radiative feedback and the on-the-fly chemical evolution of hydrogen species, CO, and C$^+$. We also account for further ionisation of C$^+$ into C$^ $ inside HII regions, which is crucial to obtain reliable results. Studying individual HII regions, we show that $I_ FIR $ is initially high in the vicinity of newly born stars, and then moderately decreases over time as the gas is compressed into dense and cool shells. In contrast, there is a large drop in $I_ CII $ over time, to which the second ionisation of C$^+$ into C$^ $ contributes significantly. This leads to a large drop in deficit inside HII regions, with deficit decreasing from 10$^ $ at scales above 10 pc to around 10$^ $ at scales below 2 pc. However, projection effects can significantly affect the radial profile of $I_ CII $, $I_ FIR $, and their ratio, and can create apparent HII regions without any stars. Considering the evolution on MC scales, we show that the luminosity ratio, deficitl , decreases from values of gtrsim 10$^ $ in MCs without star formation to values of around $ $ in MCs with star formation. We attribute this decrease and thus the origin of the CII deficit to two main contributors: (i) the saturation of the CII line and (ii) the conversion of C$^+$ into C$^ $ by stellar radiation. The drop in the deficitl ratio can be divided into two phases: (i) During the early evolution of HII regions, the saturation of CII and the further ionisation of C$^+$ limit the increase in $L_ CII $, while $L_ FIR $ increases rapidly, leading to the initial decline of deficitl . (ii) In more evolved HII regions, $L_ CII $ stagnates and even partially drops over time due to the aforementioned reasons. $L_ FIR $ also stagnates as the gas gets pushed into the cooler shells surrounding the HII region. In combination, this keeps the global deficitl ratio at low values of $

RIGEL: Simulating dwarf galaxies at solar mass resolution with radiative transfer and feedback from individual massive stars

Context. Feedback from stars in the form of radiation, stellar winds, and supernovae is crucial to regulating the star formation activity of galaxies. Dwarf galaxies are especially susceptible to these processes, making them an ideal test bed for studying the effects of stellar feedback in detail. Recent numerical models have aimed to resolve the interstellar medium (ISM) in dwarf galaxies with a very high resolution of several solar masses. However, when it comes to modeling the radiative feedback from stars, many models opt for simplified approaches instead of explicitly solving radiative transfer (RT) because of the computational complexity involved. Aims. We introduce the Realistic ISM modeling in Galaxy Evolution and Lifecycles (RIGEL) model, a novel framework to self-consistently model the effects of stellar feedback in the multiphase ISM of dwarf galaxies with explicit RT on a star-by-star basis. Methods. The RIGEL model integrates detailed implementations of feedback from individual massive stars into the state-of-the-art radiation-hydrodynamics code, AREPO-RT. It forms individual massive stars from the resolved multiphase ISM by sampling the initial mass function and tracks their evolution individually. The lifetimes, photon production rates, mass-loss rates, and wind velocities of these stars are determined by their initial masses and metallicities based on a library that incorporates a variety of stellar models. The RT equations are solved explicitly in seven spectral bins accounting for the infrared to He II ionizing bands, using a moment-base scheme with the M1 closure relation. The thermochemistry model tracks the nonequilibrium H, He chemistry as well as the equilibrium abundance of C I, C II, O I, O II, and CO in the irradiated ISM to capture the thermodynamics of all ISM phases, from cold molecular gas to hot ionized gas. Results. We evaluated the performance of the RIGEL model using 1 M⊙ resolution simulations of isolated dwarf galaxies. We found that the star formation rate (SFR) and interstellar radiation field (ISRF) show strong positive correlations with the metallicity of the galaxy. Photoionization and photoheating can reduce the SFR by an order of magnitude by removing the available cold, dense gas fuel for star formation. The presence of ISRF also significantly changes the thermal structure of the ISM. Radiative feedback occurs immediately after the birth of massive stars and rapidly disperses the molecular clouds within 1 Myr. As a consequence, radiative feedback reduces the age spread of star clusters to less than 2 Myr, prohibits the formation of massive star clusters, and shapes the cluster initial mass function to a steep power-law form with a slope of ∼ − 2. The mass-loading factor (measured at z = 1 kpc) of the fiducial galaxy has a median of ηM ∼ 50, while turning off radiative feedback reduces this factor by an order of magnitude. Conclusions. We demonstrate that RIGEL effectively captures the nonlinear coupling of early radiative feedback and supernova feedback in the multiphase ISM of dwarf galaxies. This novel framework enables the utilization of a comprehensive stellar feedback and ISM model in cosmological simulations of dwarf galaxies and various galactic environments spanning a wide dynamic range in both space and time.

Studying the Effect of Radiation Pressure on Evolution of a Population III Stellar Cluster

Recent numerical simulations have shown that the unstable disk within the central regime of the primordial gas cloud fragments to form multiple protostars on several scales. Their evolution depends on the mass accretion phenomenon, interaction with the surrounding medium and radiative feedback respectively. In this work, we use a fast semianalytical framework in order to model multiple protostars within a rotating cloud, where the mass accretion is estimated via a Bondi–Hoyle flow and the feedback process is approximated through radiation pressure. We observe that while some of the evolving protostars possibly grow massive (≈1–75 M ⊙) via accretion and mergers, a fraction of them (≈20%) are likely to be ejected from the parent cloud with a mass corresponding to M * ≲ 0.8 M ⊙. These low-mass protostars may be considered as the potential candidates to enter the zero-age-main-sequence phase and possibly survive until the present epoch.

FROT: A Framework to comprehensively describe radiative contributions to temperature responses

Abstract Different human activities and associated emissions of CO2 and non-CO2 radiative forcing agents and feedbacks determine the final state of Earth’s climate. To understand and explain contributions to global temperature changes, many emission-based metrics have been employed, such as CO2-equivalent or -forcing equivalent. None of these metrics, however, include dynamic responses from Earth system feedbacks in terms of carbon and heat redistribution, known to play an increasingly important role in ambitious mitigation scenarios. Here we introduce a framework that allows for an assessment of such feedbacks in addition to CO2, non-CO2 anthropogenic forcing and natural external variability contributions. FROT (Framework for Radiative cOntributions to Temperature response) allows for an assessment of components of direct radiative impact to the system (climate forcing), as well as Earth system feedbacks concerning heat and carbon. The framework is versatile in terms of applications and allows for exploring individual components contributions to, for example, temperature stabilisation simulations, or comparisons in different models and scenarios, as it can reasonably explain their simulated temperature variability. Here, we apply FROT to both an intermediate complexity and a fully coupled Earth system model, as we simulate highly ambitious mitigation scenarios. Comparing temperature stabilisation scenarios, we can show that both net-zero CO2 emissions and small amounts of positive CO2 emissions could lead to a stable global temperature trajectory. Our assessment reveals that the effects of non-CO2 climate forcings, especially the development of sulphate aerosols in the atmosphere, and the dynamics of the carbon cycle, play a pivotal role in the final level of warming and in enabling a temperature stabilisation. Under highly ambitious climate mitigation scenarios it becomes crucial to include Earth system feedbacks, specifically ocean heat uptake, to understand interannual to decadal temperature development, since previously secondary processes now become increasingly dominant. Our framework offers the opportunity to do so.

Radiative Feedback From Dry Environmental Air Accelerates Tropical Cyclogenesis

AbstractA number of recent studies have highlighted how radiative feedback from clouds accelerates tropical cyclone (TC) development by amplifying spatial gradients in radiative heating. This study extends this work by examining how spatial gradients in free tropospheric moisture influence TC development through their impact on environmental radiative heating. We conduct a series of idealized model experiments in which only the longwave radiative heating due to water vapor is modified in the environmental region outside of the TC area. These experiments demonstrate that a vortex in a drier environmental free troposphere experiences faster development. Moreover, weaker vortices actually require a dry environmental free troposphere to develop. The accelerated genesis mainly results from a stronger spatial gradient in moisture‐induced radiative heating, which enhances energy convergence through a stronger transverse circulation. These results highlight a potentially important and overlooked role of dry air in facilitating TC genesis.

A Model that Explains the Contrasting SST Trends in the Southern Pacific Ocean

Sea surface temperature (SST) of the southern Pacific Ocean plays an important role in ocean-atmospheric interactions, influencing both regional and global climate and ecosystems. The contrasting SST trends in the southern Pacific Ocean during 1993-2021 are noted by analyzing satellite and in-situ datasets, consisting of SST warming trend (0.05℃·yr−1) in the region of 80°W-180,30°S-50°S and cooling trend (−0.04℃·yr−1) in the area of 60°W-150°W, 55°S-70°S. A detailed trend analysis for the wind and sea ice concentration suggest that Ekman transport and sea ice radiative positive feedback are the two key contributors to the contrasting SST trends. The intensified downwelling (upwelling), induced by the Ekman transport and strengthened westerlies, gives rise to warm (cold) water swarming in (upturning) from lower latitudes (deeper ocean), which causes SST warming (cooling). Moreover, the sea ice increase at higher latitudes, due to both the cold water transport from deeper ocean layers and broken ice transport from polar regions, strengthens the cooling trend through sea ice positive radiative feedback. In conclusion, these findings underscore the complexity of SST trends in the southern Pacific Ocean, highlighting the critical roles of Ekman transport and sea ice radiative feedback in shaping regional climate dynamics.Plain Language Summary: The southern Pacific Ocean is an indispensable part in the climate system while it still remained poorly observed. The SST trend is regarded as a critical indicator of global climate change. Using the satellite and in-situ datasets, we find that the contrasting SST trends from 1993 to 2021, one area in this region is warmed by 0.3℃ per decade, while another area is cooled by -0.1℃ per decade. Considering impacts of various factors such as wind, sea ice and radiation, the primarily explanation is that wind-driven warm (cold) water from the subtropics (deeper ocean) flows in and goes downward (goes upward and flow away) in the warm (cold) area through oceanic circulation and leads to the SST warming (cooling). Additionally, the cooling trend is also related to the cold water that flows to higher latitudes and forms ice there and at the same time, trash ice from polar regions driven by enhanced south wind speed will be transported there. As a result, ice increases, reflects more shortwave radiation to space, and surface downward shortwave radiation decreases which contributes to SST decreases.

Feedback-regulated seed black hole growth in star-forming molecular clouds and galactic nuclei

Context. The detection of supermassive black holes (SMBHs) in high-redshift luminous quasars may require a phase of rapid accretion, and as a precondition, substantial gas influx toward seed black holes (BHs) from kiloparsec or parsec scales. Our previous research demonstrated the plausibility of such gas supply for BH seeds within star-forming giant molecular clouds (GMCs) with high surface density (∼104 M⊙ pc−2), facilitating “hyper-Eddington” accretion via efficient feeding by dense clumps, which are driven by turbulence and stellar feedback. Aims. This article presents an investigation of the impacts of feedback from accreting BHs on this process, including radiation, mechanical jets, and highly relativistic cosmic rays. Methods. We ran a suite of numerical simulations to explore diverse parameter spaces of BH feedback, including the subgrid accretion model, feedback energy efficiency, mass loading factor, and initial metallicity. Results. Using radiative feedback models inferred from the slim disk, we find that hyper-Eddington accretion is still achievable, yielding BH bolometric luminosities of as high as 1041 − 1044 erg/s, depending on the GMC properties and specific feedback model assumed. We find that the maximum possible mass growth of seed BHs (ΔMmax BH) is regulated by the momentum-deposition rate from BH feedback, ṗfeedback/(ṀBHc), which leads to an analytic scaling that agrees well with simulations. This scenario predicts the rapid formation of ∼104 M⊙ intermediate-massive BHs (IMBHs) from stellar-mass BHs within ∼1 Myr. Furthermore, we examine the impacts of subgrid accretion models and how BH feedback may influence star formation within these cloud complexes.

Elucidating the impacts of aerosol radiative effects for mitigating surface O3 and PM2.5 in Delhi, India during crop residue burning period

Atmospheric aerosol radiative effects regulate surface air pollution (O3 and PM2.5) via both the aerosol–photolysis effect (APE) and the aerosol–radiation feedback (ARF) on meteorology. Here, we elucidate the roles of APE and ARF on surface O3 and PM2.5 in the heavily polluted megacity, Delhi, India by using a regional model (WRF-Chem) with constraints from limited surface observations. While APE reduces surface O3 (by 6.1%) and PM2.5 concentrations (by 2.4% via impeding the secondary aerosol formations), ARF contributes to a 2.5% and 17.5% increase in surface O3 and PM2.5, respectively. The ARF from smoke enhances PM2.5 (by 8%), black carbon (by 10%), and primary organic aerosol (by 18%) during late autumn when crop residue burning is significant. The synergistic APE and ARF have a negligible impact on the total concentrations of O3 and PM2.5. Hence, the reduction of PM2.5 may lead to O3 escalation due to weakened APE. Sensitivity experiments indicate the need and effectiveness of reducing VOC emission for the co-benefits of mitigating both O3 and PM2.5 concentrations in Delhi.

Sequential formation of supermassive stars and heavy seed BHs through the interplay of cosmological cold accretion and stellar radiative feedback

ABSTRACT Supermassive stars (SMSs) and heavy seed black holes, as their remnants, are promising candidates for supermassive black hole (SMBH) progenitors, especially for ones observed in the early universe $z\simeq 8.5-10$ by recent JWST observations. Expected cradles of SMSs are the atomic cooling haloes ($M_{\rm halo}\simeq 10^7\ \mathrm{M}_{\odot }$), where ‘cold accretion’ emerges and possibly forms SMSs. We perform a suit of cosmological radiation hydrodynamics simulations and investigate star formation after the emergence of cold accretion, solving radiative feedback from stars inside the halo. We follow the mass growth of the protostars for $\sim 3\ \mathrm{Myr}$, resolving the gas inflow down to $\sim 0.1\ \mathrm{pc}$ scales. We discover that, after cold accretion emerges, multiple SMSs of $m_{\star }\gtrsim 10^5\ \mathrm{M}_{\odot }$ form at the halo centre with the accretion rates maintained at $\dot{m}_{\star }\simeq 0.04\ \mathrm{M}_\odot \mathrm{yr}^{-1}$ for $\lesssim 3\ \mathrm{Myr}$. Cold accretion supplies gas at a rate of $\dot{M}_{\rm gas}\gtrsim 0.01-0.1\ \mathrm{M}_\odot \mathrm{yr}^{-1}$ from outside the halo virial radius to the central gas disc. Gravitational torques from spiral arms transport gas further inwards, which feeds the SMSs. Radiative feedback from stars suppresses $\mathrm{H}_2$ cooling and disc fragmentation, while photoevaporation is prevented by a dense envelope, which attenuates ionizing radiation. Our results suggest that cold accretion can bring efficient BH mass growth after seed formation in the later universe. Moreover, cold accretion and gas migration inside the central disc increase the mass concentration and provide a promising formation site for the extremely compact stellar clusters observed by JWST.

Tropical Intraseasonal Variability as a Leading Moisture Dynamic Mode of the Warm-Pool Background State

Abstract Tropical intraseasonal variability (ISV) is dominated by the Madden–Julian oscillation (MJO), and its spatiotemporal characteristics vary with the Indo-Pacific warm-pool background on seasonal and longer timescales. Previous works have suggested ISV dynamics in various frameworks, whereas a unifying view remains challenging. Motivated by the recent advance in moisture mode theory, we revisit the ISV as a leading moisture mode modulated by varying background states derived from a reanalysis, using a moist linear baroclinic model (mLBM) improved with a simple convective scheme relating convective precipitation to tropospheric and boundary-layer moisture anomalies and simple cloud–radiative feedback representations. Under a boreal winter background state, this mLBM yielded a large-scale but local eastward-propagating mode with a phase speed of 3–5 m/s over the warm-pool region, resembling the MJO. Background lower-tropospheric winds and thermodynamic fields are important in determining the growth rate and periodicity of the leading mode, whose stability depends on cloud–radiative feedback and background state variations. We further demonstrate why the MJO is locally contained in the Indo-Pacific warm-pool region. The local thermal/moisture condition and Walker circulation greatly enhance its instability, but outside this region, this mode is heavily damped. Thus, the expansion/contraction of this warm-pool condition may enhance/reduce its instability and expand/reduce its domain of activity. Prescribing El Niño background causes eastward displacement of the wintertime ISV activity, reminiscent of the observed MJO modulations by El Niño. Under a summer background state, the eastward-propagating leading mode resembles the boreal summer ISV but biased, requiring further model improvements.

Multimode Masers of Thermally Polarized Nuclear Spins in Solution NMR.

We present experimental single and multimode sustained ^{1}H NMR masers in solution on thermally polarized spins at room temperature and 9.4T achieved through the electronic control of radiation feedback (radiation damping). Our observations illustrate the breakdown of the usual three-dimensional Maxwell-Bloch equations for radiation feedback and a simple toy model of few coupled classical moments is used to interpret these experiments. This Letter represents a significant step to bring the spontaneous radiation damping based NMR masers in various contexts to the next stage of feedback-controlled and reproducible experiments.

Fire and smoke transport dynamics in a dead-end tunnel under heavy rainfall

Fire is one of the most common major accidents during tunnel construction and operation. This work conducted scale-model experiments to investigate the pool burning progress and flame characteristics in a dead-end tunnel with one end closed and the other open under heavy rainfall. The results show that, compared to opening both ends, the global burning time of fires is significantly decreased, and the quasi-stable burning phase is advanced under the combined effects of the closed end and heavy rainfall. The reason is that the increase in ceiling temperature, resulting from the accumulation of hot smoke, leads to an increase in radiative feedback of the fuel from the environment and an acceleration in the pool's burning rate. A coefficient (denoted by γ) is defined to evaluate the increase in the burning rate resulting from the dead-end. The enhancement ratio is found to be related to rainfall intensity, raindrop size, and pool size, and a correlation has been established based on the experimental results. The fire has an increased flame height and a reduced tilt angle under the impact of the dead-end. The changes in flame geometry parameters are mainly influenced by thermal buoyancy and the restriction of the dead-end. Prediction formulas for flame height and tilt angle under the combined effects of the dead-end and heavy rainfall have been proposed based on theoretical analysis. Under these combined effects, the tunnel space becomes eroded by dirty air.

Exploring the connection between AGN radiative feedback and massive black hole spin

We present a novel implementation for active galactic nucleus (AGN) feedback through ultrafast winds in the code GIZMO. Our feedback recipe accounts for the angular dependence of radiative feedback on black hole spin. We self-consistently evolve in time (i) the gas-accretion process from resolved scales to a smaller scale unresolved (subgrid) AGN disk, (ii) the evolution of the spin of the massive black hole (MBH), (iii) the injection of AGN-driven winds into the resolved scales, and (iv) the spin-induced anisotropy of the overall feedback process. We tested our implementation by following the propagation of the wind-driven outflow into an homogeneous medium, and here we present a comparison of the results against simple analytical models. We also considered an isolated galaxy setup, where the galaxy is thought to be formed from the collapse of a spinning gaseous halo, and there we studied the impact of the AGN feedback on the evolution of the MBH and of the host galaxy. We find that: (i) AGN feedback limits the gas inflow that powers the MBH, with a consequent weak impact on the host galaxy characterized by a suppression of star formation by about a factor of two in the nuclear (≲kpc) region; (ii) the impact of AGN feedback on the host galaxy and on MBH growth is primarily determined by the AGN luminosity rather than by its angular pattern set by the MBH spin (i.e., more luminous AGNs more efficiently suppress central star formation (SF), clearing wider central cavities and driving outflows with larger semiopening angles); (iii) the imprint of the angular pattern of AGN radiation emission is detected more clearly at high (i.e., Eddington) accretion rates. At such high rates, the more isotropic angular patterns, as occur for high spin values, sweep away gas in the nuclear region more easily, therefore causing a slower MBH mass and spin growths and a higher quenching of SF. We argue that the influence of spin-dependent anisotropy of AGN feedback on MBH and galaxy evolution is likely to be relevant in those scenarios characterized by high and prolonged MBH accretion episodes and by high AGN wind–galaxy coupling. Such conditions are more frequently met in galaxy mergers and/or high-redshift galaxies.

Mapping and characterizing magnetic fields in the Rho Ophiuchus-A molecular cloud with SOFIA/HAWC+

Context. Together with gravity, turbulence, and stellar feedback, magnetic fields (B-fields) are thought to play a critical role in the evolution of molecular clouds and star formation processes. The polarization of thermal dust emission is a popular tracer of B-fields in star-forming regions. Aims. We aim to map the morphology and measure the strength of B-fields of the nearby molecular cloud, rho Ophiuchus-A (ρ Oph-A), to understand the role of B-fields in regulating star formation and in shaping the cloud. Methods. We analyzed the far-infrared (FIR) polarization of thermal dust emission observed by SOFIA/HAWC+ at 89 and 154 μm toward the densest part of ρ Oph-A, which is irradiated by the nearby B3/4 star, Oph-S1. These FIR polarimetric maps cover an area of ~4.5′ × 4.5′ (corresponding to 0″.18 × 0″.18 pc2) with an angular resolution of 7.8″ and 13.6″ respectively. Results. The ρ Oph-A cloud exhibits well-ordered B-fields with magnetic orientations that are mainly perpendicular to the ridge of the cloud toward the densest region. We obtained a map of B-field strengths in the range of 0.2–2.5 mG, using the Davis-Chandrasekhar-Fermi (DCF) method. The B-fields are strongest at the densest part of the cloud, which is associated with the starless core SM1, and then decrease toward the outskirts of the cloud. By calculating the map of the mass-to-flux ratio, Alfvén Mach number, and plasma β parameter in ρ Oph-A, we find that the cloud is predominantly magnetically sub-critical, sub-Alfvénic, which implies that the cloud is supported by strong B-fields that dominate over gravity, turbulence, and thermal gas energy. The measured B-field strengths at the two densest subsregions using other methods that account for the compressible mode are relatively lower than that measured with the DCF method. However, these results do not significantly change our conclusions on the roles of B-fields relative to gravity and turbulence on star formation. Our virial analysis suggests that the cloud is gravitationally unbound, which is consistent with the previous detection of numerous starless cores in the cloud. By comparing the magnetic pressure with the radiation pressure from the Oph-S1 star, we find that B-fields are sufficiently strong to support the cloud against radiative feedback and to regulate the shape of the cloud.

Decadal Relationship Between Arctic SAT and AMOC Changes Modulated by the North Pacific Oscillation

AbstractThe faster warming for Arctic Ocean surface air temperature (SAT) relative to that at lower latitude is connected with various processes, including local radiation feedback, poleward oceanic and atmospheric heat transport. It is unclear how combinations of different low‐frequency internal climate modes influence Arctic amplification on the decadal timescale. Here, the decadal Arctic SAT variation, its connection with the Atlantic meridional overturning circulation (AMOC) and possible underlying mechanisms, are investigated based on several independent observational proxies, pre‐industrial experiments, and historical large ensembles of two CMIP6 models. Our study suggests that AMOC and Arctic SAT vary in phase on the decadal timescale, whereas this relationship is insignificant at the interannual timescale. Further analysis shows that the AMOC accompanied with cross‐basin oceanic water/heat transport between Atlantic and Arctic would alter air–sea interface exchange over the melting ice regions, and then amplified poleward atmospheric heat and moisture transports. The resulting enhanced downward longwave radiation ultimately warms the Arctic SAT. Additionally, the decadal‐scale North Pacific Oscillation (NPO) can modulate the relationship between AMOC and Arctic SAT by influencing poleward moisture transport and cross‐basin circulation. Specifically, the phase shift of combined NPO and AMOC can contribute 14%–41% covariance relationship between AMOC and Arctic SAT. Our study provides potential sources for predicting the Arctic climate and constraining its uncertainty in future projections.