Radiative Cooling

We present results from new experiments to study the dynamics of radiative shocks, reverse shocks and radiative precursors. Laser ablation of a solid piston by the Orion high-power laser at AWE Aldermaston UK was used to drive radiative shocks into a gas cell initially pressurised between 0.1 and 1.0 bar with different noble gases. Shocks propagated at 80 ± 10 km/s and experienced strong radiative cooling resulting in post-shock compressions of ×25 ± 2. A combination of X-ray backlighting, optical self-emission streak imaging and interferometry (multi-frame and streak imaging) were used to simultaneously study both the shock front and the radiative precursor. These experiments present a new configuration to produce counter-propagating radiative shocks, allowing for the study of reverse shocks and providing a unique platform for numerical validation. In addition, the radiative shocks were able to expand freely into a large gas volume without being confined by the walls of the gas cell. This allows for 3-D effects of the shocks to be studied which, in principle, could lead to a more direct comparison to astrophysical phenomena. By maintaining a constant mass density between different gas fills the shocks evolved with similar hydrodynamics but the radiative precursor was found to extend significantly further in higher atomic number gases (∼4 times further in xenon than neon). Finally, 1-D and 2-D radiative-hydrodynamic simulations are presented showing good agreement with the experimental data.

Fully coupled simulations of hydrodynamics and radiative transfer are essential to a number of fields ranging from astrophysics to engineering applications. Of particular interest in this work are hypersonic atmospheric entries and associated experimental apparatus, e.g., shock tubes and high enthalpy testing facilities. The radiative transfer calculations must supply to the CFD a heating term in the energy equation in the form of the divergence of the radiative heat flux and the radiative heat fluxes to bounding surfaces. It is most efficient to solve the radiative transfer equation on the same grid as the CFD solution, and this work presents an algorithm with improved accuracy compared to more conventional approaches on both structured and unstructured grids. Results are shown for a number of idealized test problems and for shock radiation during hypersonic entry. Issues of parallelization within a radiation sweep are also discussed.

Fully coupled simulations of hydrodynamics and radiative transfer are essential to a number of fields ranging from astrophysics to engineering applications. Of particular interest in this work are hypersonic atmospheric entries and associated experimental apparatus, e.g., shock tubes and high enthalpy testing facilities. The radiative transfer calculations must supply to the CFD a heating term in the energy equation in the form of the divergence of the radiative heat flux and the radiative heat fluxes to bounding surfaces. It is most efficient to solve the radiative transfer equation on the same grid as the CFD solution, and this work presents an algorithm with improved accuracy compared to more conventional approaches on both structured and unstructured grids. Results are shown for a number of idealized test problems and for shock radiation during hypersonic entry. Issues of parallelization within a radiation sweep are also discussed.

Ecological, natural ways of obtaining energy for building cooling are becoming more and more popular around the world. Reducing energy demand and increasing the renewable energy use can be achieved for example by using radiative cooling. Depending on climatic conditions and the type of cooling system, radiative cooling is able to cover a part of refrigeration needs. The document presents the possible energy yield from using radiative cooling in systems operating at respective parameters in polish climatic conditions.

Ecological, natural ways of obtaining energy for building cooling are becoming more and more popular around the world. Reducing energy demand and increasing the renewable energy use can be achieved for example by using radiative cooling. Depending on climatic conditions and the type of cooling system, radiative cooling is able to cover a part of refrigeration needs. The document presents the possible energy yield from using radiative cooling in systems operating at respective parameters in polish climatic conditions.

The standing slow magneto-acoustic oscillations in cooling coronal loops are investigated. There are two damping mechanisms which are considered to generate the standing acoustic modes in coronal magnetic loops namely thermal conduction and radiation. The background temperature is assumed to change temporally due to optically thin radiation. In particular, the background plasma is assumed to be radiatively cooling. The effects of cooling on longitudinal slow MHD modes is analytically evaluated by choosing a simple form of radiative function that ensures the temperature evolution of the background plasma due to radiation coincides with the observed cooling profile of coronal loops. The assumption of low-beta plasma leads to neglect the magnetic field perturbation and eventually reduces the MHD equations to a 1D system modelling longitudinal MHD oscillations in a cooling coronal loop. The cooling is assumed to occur on a characteristic time scale much larger than the oscillation period that subsequently enables using the WKB theory to study the properties of standing wave. The governing equation describing the time-dependent amplitude of waves is obtained and solved analytically. The analytically derived solutions are numerically evaluated to give further insight into the evolution of the standing acoustic waves. We find that the plasma cooling gives rise to a decrease in the amplitude of oscillations. In spite of the reduction in damping rate caused by rising the cooling, the damping scenario of slow standing MHD waves strongly increases in hot coronal loops.

Tropical ice clouds and their changes in future climate remain challenging issues for global climate modeling and projections. These issues are addressed by examining the interannual variability of ice water path (IWP), an important property of ice cloud, with respect to large-scale vertical velocity in observations, reanalysis and climate model simulations, and by relating the unforced variability to the human-influenced climate change. Here we show that a statistically significant linear relation between interannual anomalies of IWP and 500hPa vertical velocity (ω500) can be identified from all data sets and, moreover, such relationship in each model is closely correlated with its simulated IWP change with respect toω500 change for the future climate. This indicates a robust constraint for the future tropical ice cloud change. Such constraint and observed IWP-ω500relation projectsa 12.8%-16.4% increase of IWP for every -0.01Pa/s change ofω500, equivalent to ~2.96%-3.80% decrease o...

We report on experimental investigations into strong, laser-driven, radiative shocks in noble-gas cluster media. Cylindrical shocks launched with several J exhibit strong radiative effects such as increased deceleration and radiative preheat. Using time-resolved propagation data from single-shot streaked Schlieren measurements we observe temporal modulations on shock position and velocity, which we attribute to the thermal cooling instability, an instability which until now has not been observed experimentally.

LEAF-Lite (Laser Enhanced Arc-Jet Facility) is a radiative laser heating facility that has been added to the 60 MW Interaction Heating Facility (IHF) convective plasma arc-jet located at NASA Ames Research Center. Together, these two systems can simulate both convective and radiative heating at heat fluxes reaching 551 W/cm 2 by simultaneously combining a highest measured heat flux of 160 W/cm 2 convective and 391 W/cm 2 radiative heating on a 152-mm x 152-mm wedge model configuration. Adding radiant heating to an existing convective facility better simulates Earth atmospheric entry from hyperbolic lunarreturn speeds. The radiative heat is provided by multiple 50-kW CW IR lasers, which is nearly uniform across the illuminated surface with a total variation less than 6%, while the convective heat is provided by a high enthalpy plasma arc-jet. In a later phase, the facility will expand to test panel test articles of 432-mm x 432-mm and provide 100 W/cm 2 of radiative heating in a plasma convective flow environment. The paper describes this new combined heating capability, its current testing conditions, and the unique application of the laser system with respect to the Orion test flight lunar orbits.

We present a series of 2-dimensional (r, φ) hydrodynamic simulations of marginally self gravitating (M D /M * =0.2, with M * = 0.5M ⊙ and with disk radius R D = 50 and 100 AU) disks around protostars using a Smoothed Particle Hydrodynamic (SPH) code. We implement simple and approximate prescriptions for heating via dynamical processes in the disk. Cooling is implemented with a simple radiative cooling prescription which does not assume that local heat dissipation exactly balances local heat generation. Instead, we compute the local vertical (z) temperature and density structure of the disk and obtain 'photosphere temperature', which is then used to cool that location as a black body. We synthesize spectral energy distributions (SEDs) for our simulations and compare them to fiducial SEDs derived from observed systems, in order to understand the contribution of dynamical evolution to the observable character of a system. We find that these simulations produce less distinct spiral structure than isothermally evolved systems, especially in approximately the inner radial third of the disk. Pattern amplitudes are similar to isothermally evolved systems further from the star but do not collapse into condensed objects. We attribute the differences in morphology to increased efficiency for converting kinetic energy into thermal energy in our current simulations. Our simulations produce temperatures in the outer part of the disk which are very low (∼ 10 K). The radial temperature distribution of the disk photosphere is well fit to a power law with index q ∼ 1.1. Far from the star, corresponding to colder parts of the disk and long wavelength radiation, known internal heating processes (P dV work and shocks) are not responsible for generating a large fraction of the thermal energy contained in the disk matter. Therefore gravitational torques responsible for such shocks cannot transport mass and angular momentum efficiently in the outer disk. Within ∼5-10 AU of the star, rapid break up and reformation of spiral structure causes shocks, which provide sufficient dissipation to power a larger fraction of the near infrared radiated energy output. In this region, the spatial and size distribution of grains can have marked consequences on the observed near infrared SED of a given disk, and can lead to increased emission and variability on ∼ < 10 year time scales. The inner disk heats to the destruction temperature of dust grains. Further temperature increases are prevented by efficient cooling when the hot disk midplane is exposed. When grains are vaporized in the midplane of a hot region of the disk, we show that they do not reform into a size distribution similar to that from which most opacity calculations are based. With rapid grain reformation into the original size distribution, the disk does not emit near infrared photons. With a plausible modification of the opacity, it contributes much more.

Overheating, a general problem both in urban spaces and inside buildings, calls for the deployment of passive cooling techniques to reduce energy consumption, protect the environment and institute satisfactory comfort levels. A key factor in such techniques is the capitalisation on the cooling potential of natural heat sinks. The sky, one such sink, has essentially limitless cooling power. In addition, its temperature on fair nights is lower than that of other environmental sinks (ground and air). The sky's promise in that respect prompted this exploration of the potential of nocturnal radiation cooling. A review of the state of the art revealed that in all the radiative dissipators developed and tested to date the dissipation fluid (water) transferred heat indirectly to the heat sink (the sky) by circulating water inside solar collector pipes. The highest values reported for maximum dissipation power were on the order of 100 W/m 2 . The present study aimed to asses night time dissipation power in a dual system in which water circulated either inside pipes or flowed down the outer surface of the collector. The two modes, one involving in-pipe circulation and the other outer surface downflow, were compared experimentally, for whereas the former has been analysed and assessed by earlier researchers, the latter has not. The empirical findings verified that downflow setups enhanced cooling, delivering up to five-fold the dissipation power obtained with the conventional arrangement.

The Experimental Probe of Inflationary Cosmology (EPIC) is an implementation of the NASA Einstein Inflation Probe mission, to answer questions about the physics of Inflation in the early Universe by measuring the polarization of the Cosmic Microwave Background (CMB). The mission relies on a passive cooling system to cool the enclosure of a telescope to 30 K; a cryocooler then cools this enclosure to 18 K and the telescope to 4 K. Subsequently, an adiabatic demagnetization refrigerator further cools a large focal plane to ~100 mK. For this mission, the telescope has an aperture of 1.4 m, and the spacecraft's symmetry axis is oriented ~45 degrees relative to the direction of the sun. The spacecraft will be spun at ~0.5 rpm around this axis, which then precesses on the sky at 1 rph. The passive system must both supply the necessary cooling power for the cryocooler and meet demanding temperature stability requirements. We describe the thermal design of a passive cooling system consisting of four V-groove radiators for shielding of solar radiation and cooling the telescope to 30 K. The design realizes loads of 20 and 68 mW at the 4 K and 18 K stages on the cooler, respectively. A lower cost option for reaching 40 K with three V-groove radiators is also described. The analysis includes radiation coupling between stages of the radiators and sunshields, and parasitic conduction in the bipod support, harnesses, and ADR leads. Dynamic effects are also estimated, including the very small variations in temperature due to the scan motion of the spacecraft.

Radiative cooling is an attractive concept for future sustainable energy strategies, as it might enable passive cooling of buildings and photovoltaic systems, hence facilitating energy savings by boosting performance and lifespan. The key idea is the adoption of materials that strongly emit thermal radiation in the atmosphere transparency window (wavelengths between 8 and 13 μm) as cooling layers. Significant progress in the field of metamaterials has enabled the realization of dielectric photonic structures with properties matching radiative cooling requirements and capable of going below ambient temperature. However, these structures are rather expensive and appear unsuitable for today's large-scale manufacturing. In the present work, we have studied radiative cooling applied to Shockley-Queisser solar cells by exploring alternative materials, namely cementitious phases, which exhibit the required properties while being low-cost and scalable. We have determined their emission behavior by electromagnetic simulations and estimated the corresponding solar cell operating temperature by means of a detailed-balance model. The results have been benchmarked against the current state-of-the-art and hint at the possible realization of a new class of radiative coolers based on cheap and scalable cementitious materials.

Abstract. We demonstrate that white coatings consisting of silicone embedded with randomly distributed microbubbles provide highly efficient daytime radiative cooling with inexpensive materials and fabrication processes. In our material system, sunlight is strongly scattered with minimal absorption, and heat is effectively removed through mid-infrared (IR) radiation. In our previous study, solid microsphere-based coatings outperformed commercial solar-rejection white paint in cooling efficiency, but their mechanical robustness needed improvement for practical applications. The material system in our work substantially enhances the mechanical robustness while providing superior cooling performance to commercial solar-rejection paint. For ease of processing, we use nonoptimized structures with reduced optical scattering strength. Strong solar rejection is yet achieved by increasing coating thickness. This strategy is desirable for practical rooftop applications where coating thickness is of minor importance in comparison to cooling performance and materials cost. In addition, silicone is stable in extraterrestrial environments and efficiently radiates heat over broad mid-IR spectrum. These material properties of our silicone coatings promise great potential for radiative cooling in space applications.

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ABSTRACT: Cold-roof finishes and ventilated roofs are widely recognized solutions for mitigating overheating, and their combination offers the potential for enhanced performance. A notable variation of this approach, seen in high-end architectural projects in hot climates, features high-albedo corrugated metal roof canopies positioned above solid flat roofs, creating a wide ventilated space beneath. This configuration merges the simplicity of flat roofs with an extreme form of the attic configuration to effectively dissipate solar heat gain. This study hypothesizes that increasing the number of ventilated thermal barriers beyond one can further improve heat dissipation. To test this hypothesis, the thermal performance of an experimental double- ventilated-cavity roof was evaluated in a school in Mali through monitoring and environmental simulations, complemented by parametric analyses. The results demonstrate that the double- ventilated-cavity roof outperforms conventional single-cavity designs, achieving lower indoor temperatures and greater resilience to the ageing of roof cover materials.

The concept of utilizing directional radiative cooling to correct the problem of thermal lensing in the mirrors of the LIGO/VIRGO gravitational wave detectors has been shown and has prospects for future use. Two different designs utilizing this concept, referred to as the baffled and parabolic mirror solutions, have been proposed with different means of controlling the cooling power. The technique takes advantage of the power naturally radiated by the mirror surfaces at room temperature to prevent their heating by the powerful stored laser beams. The baffled solution has been simulated via COMSOL Multiphysics as a design tool. Finally, the parabolic mirror concept was experimentally validated with the results falling in close agreement with theoretical cooling calculations. The technique of directional radiative thermal correction can be reversed to image heat rings on the mirrors periphery to remotely and dynamically correct their radius of curvature without subjecting the mirror to relevant perturbations.

We present a study of the formation of bow shocks in radiatively cooled plasma flows. This work uses an inverse wire array to provide a quasi-uniform, large scale hydrodynamic flow accelerated by Lorentz forces to supersonic velocities. This flow impacts a stationary object placed in its path, forming a well-defined Mach cone. Interferogram data are used to determine a Mach number of $6, which may increase with radial position suggesting a strongly cooling flow. Self-emission imaging shows the formation of a thin (<60 lm) strongly emitting shock region, where T e $ 40-50 eV, and rapid cooling behind the shock. Emission is observed upstream of the shock position which appears consistent with a radiation driven phenomenon. Data are compared to 2dimensional simulations using the Gorgon MHD code, which show good agreement with the experiments. The simulations are also used to investigate the effect of magnetic field in the target, demonstrating that the bow-shocks have a high plasma b, and the influence of B-field at the shock is small. This consistent with experimental measurement with micro bdot probes.

Recent developments in the world of hypersonic flight have brought increased attention to the thermal response of materials exposed to high-enthalpy gases. One promising concept is electron transpiration cooling (ETC) that provides the prospect of a passive heat removal mechanism, rivaling and possibly outperforming that of radiative cooling. In this work, non-equilibrium CFD simulations are performed to evaluate the possible roles of this cooling mode under high-enthalpy conditions obtainable in plasma torch ground-test facilities capable of long flow times. The work focuses on the test case of argon gas being heated to achieve enthalpies equivalent to post-shock conditions experienced by a vehicle flying through the atmosphere at hypersonic speed. Simulations are performed at a range of conditions and are used to calibrate direct comparisons between torch operating conditions and resulting flow properties. These comparisons highlight important modeling considerations for simulating long-duration, hot chamber tests. Simulation results correspond well with the experimental measurements of gas temperature, material surface temperature as well as measured current generated in the test article. Theoretical methods taking into consideration space charge limitations are presented and applied to provide design suggestions to boost the ETC effect in future experiments.

To study the applicability of artificially enhanced impurity radiation for mitigation of the plasma-limiter interaction in reactor regimes, krypton and xenon gases were injected into TFTR supershots and high-l i plasmas. At neutral beam injection (NBI) powers P B ≥ 30 MW, carbon influxes (blooms) were suppressed, leading to improved energy confinement and neutron production in both D and DT plasmas, and the highest DT fusion energy production (7.6 MJ) in a TFTR pulse. Comparisons of the measured radiated power profiles with predictions of the MIST impurity transport code have guided studies of highly-radiative plasmas in ITER. The response of the electron and ion temperatures to greatly increased radiative losses from the electrons was used to study thermal transport mechanisms.

Realistic 3-dimensional (3D), radiative hydrody- namical surface convection simulations of the metal-poor halo stars HD 140283 and HD 84937 have been performed. Due to the dominance of adiabatic cooling over radiative heating very low atmospheric temperatures are encountered. The lack of spectral lines in these metal-poor stars thus causes much steeper temperature gradients than in classical 1D hydrostatic model at- mospheres where the temperature of the optically thin layers is determined by radiative equilibrium. The modified atmospheric structures cause changes in the emergent stellar spectra. In par- ticular, the primordial Li abundances may have been overesti- mated by 0.2-0.35 dex with 1D model atmospheres. However, we caution that our result assumes local thermodynamic equi- librium (LTE), while the steep temperature gradients may be prone to e.g. over-ionization.

Realistic 3-dimensional (3D), radiative hydrodynamical surface convection simulations of the metalpoor halo stars HD 140283 and HD 84937 have been performed. Due to the dominance of adiabatic cooling over radiative heating very low atmospheric temperatures are encountered. The lack of spectral lines in these metalpoor stars thus causes much steeper temperature gradients than in classical 1D hydrostatic model atmospheres where the temperature of the optically thin layers is determined by radiative equilibrium. The modified atmospheric structures cause changes in the emergent stellar spectra. In particular, the primordial Li abundances may have been overestimated by 0.2-0.35 dex with 1D model atmospheres. However, we caution that our result assumes local thermodynamic equilibrium (LTE), while the steep temperature gradients may be prone to e.g. over-ionization.

Impurity seeding experiments during the start-up limiter campaign of Wendelstein 7-X provide first evidence for a localization effect of the three-dimensional magnetic edge structure on the seeded impurities and their radiation distribution and cooling effect. Moreover, species dependencies have been seen. Nitrogen was observed to cool the entire edge plasma, with a stronger electron temperature reduction measured at the downstream position at the limiter. The radiation was limited at the periphery of the confined region. Both the temperature reduction and the radiation enhancement were directly correlated to the injection of the coolant gas. Mitigation of the limiter heat loads was also measured. Neon was observed to affect also the confined plasma with a long-lasting radiation and a cooling of the entire plasma.

Optical Solar Reflectors are devices that combine high reflection for visible wavelengths with a strong emissivity in the infrared. Compared to the conventional rigid quartz tiles used on spacecraft since the 1960s, thin-film solutions can offer a significant advantage in weight, assembly and launch costs. Here, we present a metasurface based approach using an Al-doped * To whom correspondence should be addressed † Electronics ‡ Physics ¶ CREO § NILT 1 ZnO (AZO) transparent conducting oxide as infrared plasmonic material. The AZO is patterned into a metasurface to achieve broad plasmonic resonances with enhanced absorption of electromagnetic radiation in the thermal infrared. In the visible range, the transparent conducting oxide provides low losses for solar radiation, while intrinsic absorption losses in the ultraviolet range are effectively suppressed using a multilayer reflecting coating. The addition of high-emissivity layers to the stack eventually results in comparable emissivity values to the thin plasmonic device, thus defining a window of opportunity for plasmonic absorption as a design strategy for ultrathin devices. The optimized experimental structure achieves solar absorptance (α) of 0.16 and thermal emissivity (ε) of 0.79. Our first prototype demonstrator paves the way for further improvement and large-area fabrication of metasurface solar reflectors, and ultimately their application in space missions.

Pluto&#39;s atmosphere is cold and hazy. Recent observations have shown it to be much colder than predicted theoretically, suggesting an unknown cooling mechanism. Atmospheric gas molecules, particularly water vapour, have been proposed as a coolant; however, because Pluto&#39;s thermal structure is expected to be in radiative-conductive equilibrium, the required water vapour would need to be supersaturated by many orders of magnitude under thermodynamic equilibrium conditions. Here we report that atmospheric hazes, rather than gases, can explain Pluto&#39;s temperature profile. We find that haze particles have substantially larger solar heating and thermal cooling rates than gas molecules, dominating the atmospheric radiative balance from the ground to an altitude of 700 kilometres, above which heat conduction maintains an isothermal atmosphere. We conclude that Pluto&#39;s atmosphere is unique among Solar System planetary atmospheres, as its radiative energy equilibrium is control...

We report the results of the x-ray radiative recombination (RR) experiment at the electron cooler of the ESR storage ring performed, for the first time, for detuned (off-cooling) electron energies. In this experiment the recombination of stored, decelerated bare uranium ions with electrons in the energy range 0-1000 meV was studied by observing K-RR x-ray photons emitted from direct radiative recombination to the lowest n = 1 state. In this way the RR process was studied in a state selective manner for several off-cooling electron energies. The measured dependency of the recombination rate on the relative electron energies for K-shell RR x-ray photons are compared with the predictions of both nonrelativistic and fully relativistic calculations for the radiative recombination. A role of the relativistic effects, which contribute substantially for higher relative electron energies, are discussed. Strong enhancement of the recombination rate is observed for the the zero relative electron energy (cooling condition) for the K-shell.

This paper aims at studying the reliability of a few frequently raised, but not proven, arguments for the modelling of cold gas clouds embedded in or moving through a hot plasma and at sensitizing modellers to a more careful consideration of unavoidable acting physical processes and their relevance. At first, by numerical simulations we demonstrate the growing effect of self-gravity on interstellar clouds and, by this, moreover argue against their initial set-up as homogeneous. We apply the adaptive-mesh refinement code flash with extensions to metal-dependent radiative cooling and external heating of the gas, self-gravity, mass diffusion, and semi-analytic dissociation of molecules, and ionization of atoms. We show that the criterion of Jeans mass or Bonnor–Ebert mass, respectively, provides only a sufficient but not a necessary condition for self-gravity to be effective, because even low-mass clouds are affected on reasonable dynamical time-scales. The second part of this paper is...

This paper aims at studying the reliability of a few frequently raised but not proven arguments for the modeling of cold gas clouds embedded in or moving through a hot plasma and at sensitizing modelers to a more careful consideration of unavoidable acting physical processes and their relevance. At first, by numerical simulations we demonstrate the growing effect of self-gravity on interstellar clouds and, by this, moreover argue against their initial setup as homogeneous. We apply the adaptive-mesh refinement code Flash with extensions to metaldependent radiative cooling and external heating of the gas, self-gravity, mass diffusion, and semi-analytic dissociation of molecules and ionization of atoms. We show that the criterion of Jeans mass or Bonnor-Ebert mass, respectively, provides only a sufficient but not a necessary condition for self-gravity to be effective, because even low-mass clouds are affected on reasonable dynamical timescales. The second part of this paper is dedicated to analytically study the reduction of heat conduction by a magnetic dipole field.We demonstrate that in this configuration, the effective heat flow, i.e. integrated over the cloud surface, is suppressed by only 32 per cent by magnetic fields in energy equipartition and still insignificantly for even higher field strengths.

We numerically investigate the evolution of compact high-velocity clouds (CHVCs) passing through a hot, tenuous gas representing the highly ionized circumgalactic medium (CGM) by applying the adaptive-mesh refinement code flash. The model clouds start from both hydrostatic and thermal equilibrium and are in pressure balance with the CGM. Here, we present 14 models, divided into two mass categories and two metallicities each and different velocities. We allow for self-gravity and thermal conduction or not. All models experience mass diffusion, radiative cooling, and external heating leading to dissociation and ionization. Our main findings are (1) self-gravity stabilizes clouds against Rayleigh–Taylor instability, which is disrupted within 10 sound-crossing times without; (2) clouds can develop Jeans-instable regions internally even though they are initially below Jeans mass; (3) all clouds lose mass by ram pressure and Kelvin–Helmholtz instability; (4) thermal conduction substantial...

Galactic outflows from local starburst galaxies typically exhibit a layered geometry, with cool 104 K flow sheathing a hotter 107 K, cylindrically collimated, X-ray-emitting plasma. Here we argue that winds driven by energy injection in a ring-like geometry can produce this distinctive large-scale multiphase morphology. The ring configuration is motivated by the observation that massive young star clusters are often distributed in a ring at the host galaxy’s inner Lindblad resonance, where larger-scale spiral arm structure terminates. We present parameterized three-dimensional radiative hydrodynamical simulations that follow the emergence and dynamics of energy-driven hot winds from starburst rings. In this letter, we show that the flow shocks on itself within the inner ring hole, maintaining high 107 K temperatures, while flows that emerge from the wind-driving ring unobstructed can undergo rapid bulk cooling down to 104 K, producing a fast hot biconical outflow enclosed by a sheat...

The evolution of anvil clouds detrained from deep convective systems has important implications for the tropical energy balance and is thought to be shaped by radiative heating. We use combined radar-lidar observations and a radiative transfer model to investigate the influence of radiative heating on anvil cloud altitude, thickness, and microphysical structure. We find that high clouds with an optical depth between 1 and 2 are prevalent in tropical convective regions and can persist far from any convective source. These clouds are generally located at higher altitudes than optically thicker clouds, experience strong radiative heating, and contain high concentrations of ice crystals indicative of turbulence. These findings support the hypothesis that anvil clouds are driven towards and maintained at a preferred optical thickness that corresponds to a positive cloud radiative effect. Comparison of daytime and nighttime observations suggests that anvil thinning proceeds more rapidly at night, when net radiative cooling promotes the sinking of cloud top. It is hypothesized that the properties of aged anvil clouds and their susceptibility to radiative destabilization are shaped by the time of day at which the cloud was detrained. These results underscore the importance of small-scale processes in determining the radiative effect of tropical convection.

The net radiative effects of tropical clouds are determined by the evolution of thick, freshly detrained anvil clouds into thin anvil clouds. Thick anvil clouds reduce Earth's energy balance and cool the climate, while thin anvil clouds warm the climate. To determine role of these clouds in climate change we need to understand how interactions of their microphysical and macrophysical properties control their radiative properties. We explore anvil cloud evolution using a cloud-resolving model in three-simulation setups of increasing complexity to disentangle the impacts of the various components of diabatic heating and their interaction with cloud-scale motions. The first phase of evolution and rapid cloud spreading is dominated by latent heating within convective updrafts. After the convective detrainment stops, most of the spreading and thinning of the anvil cloud is driven by cloud radiative processes and latent heating. The combination of radiative cooling at cloud top, latent cooling due to sublimation at cloud base, latent heating due to deposition and radiative heating in between leads to a sandwich-like, cooling-heating-cooling structure. The heating sandwich promotes the development of two within-anvil convective layers and a double cell circulation, dominated by strong outflow at 12-km altitude with inflow above and below. Our study reveals how small-scale processes including convective, microphysical processes, latent and radiative heating interact within the anvil cloud system. The absence or a different representation of only one component results in a significantly different cloud evolution with large impacts on cloud radiative effects. Clouds have a large influence on climate. Thick clouds reflect part of the solar (or shortwave) radiation back to space and therefore cool the climate. On the other hand, wispy and thin high clouds do not reflect much of solar radiation. They form high in the atmosphere at cold temperatures and therefore keep part of the terrestrial (or longwave) radiation within the atmosphere. They warm the climate, similarly to greenhouse gasses. The evolution of thunderstorm clouds is of particular interest as it involves a transition from the thick clouds that cool the climate to the thin high clouds that warm the climate. We study small-scale processes that drive this transition and their delicate balance and interactions. Tiny differences in how ice crystals form, grow, shrink, or interact with solar or terrestrial radiation can lead to large differences in the climatic role of thunderstorm clouds. Such processes are currently not represented in models we use for climate projections. Our findings may ultimately lead to improvements in the representation of thunderstorm cloud life cycles in climate models and therefore increase the trust in projections of future climate.

The radiative cooling rate in the tropical upper troposphere is expected to increase as climate warms. Since the tropics are approximately in radiative-convective equilibrium (RCE), this implies an increase in the convective heating rate, which is the sum of the latent heating rate and the eddy heat flux convergence. We examine the impact of these changes on the vertical profile of cloud ice amount in cloud-resolving simulations of RCE. Three simulations are conducted: a control run, a warming run, and an experimental run in which there is no warming but a temperature forcing is imposed to mimic the warming-induced increase in radiative cooling. Surface warming causes a reduction in cloud fraction at all upper-tropospheric temperature levels but an increase in the ice mixing ratio within deep convective cores. The experimental run has more cloud ice than the warming run at fixed temperature despite the fact that their latent heating rates are equal, which suggests that the efficiency of latent heating by cloud ice increases with warming. An analytic expression relating the ice-related latent heating rate to a number of other factors is derived and used to understand the model results. This reveals that the increase in latent heating efficiency is driven mostly by 1) the migration of isotherms to lower pressure and 2) a slight warming of the top of the convective layer. These physically robust changes act to reduce the residence time of ice at any particular temperature level, which tempers the response of the mean cloud ice profile to warming. SIGNIFICANCE STATEMENT: Here we examine how the amount of condensed ice in part of the atmosphere}the tropical upper troposphere (UT)}responds to global warming. In the UT, the energy released during ice formation is balanced by the emission of radiation to space. This emission will strengthen with warming, suggesting that there will also be more ice. Using a model of the tropical atmosphere, we find that the increase in ice amount is mitigated by a reduction in the amount of time ice spends in the UT. This could have important implications for the cloud response to global warming, and future work should focus on how these changes are manifested across the distribution of convective cloud types.

Summer frosts occur frequently on the Bolivian Altiplano (4000 m) and cause severe damage to potato and quinua crops. A regional statistical study of frost risks must combine meteorological data with satellite data. In this work, a new method is developed to use NOAA satellite temperatures together with local minimum air temperature data. This method enables point meteorological data (with important historical records) to be combined with satellite data (spatially extended but with poor temporal coverage). The method involves several stages including a classi®cation of the Altiplano based on the meteorological stations, a calculation of minimum temperatures over the whole Altiplano for several years of data, and ®nally the computation of minimum temperatures and frost risk percentage maps. The precision obtained in the resulting synthesis images is 0.88C for the average minimum temperatures and 9% for frost risk maps.

In order to address the interactive and evolutionary nature of the cloud-radiation interaction, we have coupled to a Large Eddy Simulation (LES) model the sophisticated multi-dimensional radiative transfer (MDRT) scheme of Evans (Spherical Harmonics Discrete Ordinate Method; 1998). Because of computational expense, we are at this time only able to run 2D experiments. Preliminary runs consider only the broadband longwave

Recent X-ray observations of galaxy clusters show that the distribution of intra-cluster medium (ICM) metallicity is remarkably uniform in space and time. In this paper, we analyse a large sample of simulated objects, from poor groups to rich clusters, to study the dependence of the metallicity and related quantities on the mass of the systems. The simulations are performed with an improved version of the smoothed-particle-hydrodynamic GADGET-3 code and consider various astrophysical processes including radiative cooling, metal enrichment and feedback from stars and active galactic nuclei (AGNs). The scaling between the metallicity and the temperature obtained in the simulations agrees well in trend and evolution with the observational results obtained from two data samples characterized by a wide range of masses and a large redshift coverage. We find that the iron abundance in the cluster core (r < 0.1R 500 ) does not correlate with the temperature nor presents a significant evolution. The scale invariance is confirmed when the metallicity is related directly to the total mass. The slope of the best-fitting relations is shallow (β ∼ -0.1) in the innermost regions (r < 0.5R 500 ) and consistent with zero outside. We investigate the impact of the AGN feedback and find that it plays a key role in producing a constant value of the outskirts metallicity from groups to clusters. This finding additionally supports the picture of early enrichment.

We perform a set of general relativistic, radiative, magneto-hydrodynamical simulations (GR-RMHD) to study the transition from radiatively inefficient to efficient state of accretion on a non-rotating black hole. We study ion to electron temperature ratios ranging from T i /T e = 10 to 100, and simulate flows corresponding to accretion rates as low as 10 -6 ṀEdd , and as high as 10 -2 ṀEdd . We have found that the radiative output of accretion flows increases with accretion rate, and that the transition occurs earlier for hotter electrons (lower T i /T e ratio). At the same time, the mechanical efficiency hardly changes and accounts to ≈3 per cent of the accreted rest mass energy flux, even at the highest simulated accretion rates. This is particularly important for the mechanical active galactic nuclei (AGN) feedback regulating massive galaxies, groups and clusters. Comparison with recent observations of radiative and mechanical AGN luminosities suggests that the ion to electron temperature ratio in the inner, collisionless accretion flow should fall within 10 < T i /T e < 30, i.e. the electron temperature should be several percent of the ion temperature.

We analyse the radial pressure profiles, the intracluster medium (ICM) clumping factor and the Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy clusters and groups identified in a set of hydrodynamical simulations based on an updated version of the TREEPM-SPH GADGET-3 code. Three different sets of simulations are performed: the first assumes non-radiative physics, the others include, among other processes, active galactic nucleus (AGN) and/or stellar feedback. Our results are analysed as a function of redshift, ICM physics, cluster mass and cluster cool-coreness or dynamical state. In general, the mean pressure profiles obtained for our sample of groups and clusters show a good agreement with X-ray and SZ observations. Simulated cool-core (CC) and non-cool-core (NCC) clusters also show a good match with real data. We obtain in all cases a small (if any) redshift evolution of the pressure profiles of massive clusters, at least back to z = 1. We find that the clumpiness of gas density and pressure increases with the distance from the cluster centre and with the dynamical activity. The inclusion of AGN feedback in our simulations generates values for the gas clumping ( √ C ρ ∼ 1.2 at R 200 ) in good agreement with recent observational estimates. The simulated Y SZ -M scaling relations are in good accordance with several observed samples, especially for massive clusters. As for the scatter of these relations, we obtain a clear dependence on the cluster dynamical state, whereas this distinction is not so evident when looking at the subsamples of CC and NCC clusters.

In a thermally bistable medium, cold, dense gas is separated from warm, rarified gas by thin phase transition layers, or fronts, in which radiative heating/cooling, thermal conduction, and convection of material are balanced. While these fronts have received only scant attention in the literature, and are not resolved by most current numerical simulations, they have been shown to have important ramifications for transport processes and structure formation in the diffuse interstellar medium. Here, we discuss calculations of their hydrodynamic and magnetohydrodynamic stability properties.

The effects of wind shear and radiative cooling on the stratocumulus‐topped boundary layer (STBL) were investigated via a set of large‐eddy simulations. The set‐up of the numerical experiments was based on Flight TO13 from the Physics of Stratocumulus Top (POST) field campaign, in which sensible and latent heat fluxes at the surface were small and thermodynamic conditions prevented cloud‐top entrainment instability.The results demonstrate that the presence of radiative cooling invigorated convective circulations across the STBL and sharpened the inversion above the cloud, while wind shear at the top of the STBL was a source of turbulence in the capping inversion and caused dilution of the cloud top. The flux and gradient Richardson numbers in the capping inversion and in the topmost layer of the cloud were nearly critical.Analysis of the turbulent kinetic energy (TKE) budget and its transport indicated that turbulence in the inversion capping the cloud was produced locally by wind s...

Recent work suggests that the mass-loss rate of the primary star η A in the massive colliding wind binary η Carinae dropped by a factor of 2-3 between 1999 and 2010. We present results from large-(±1545 au) and small-(±155 au) domain, 3D smoothed particle hydrodynamics (SPH) simulations of η Car's colliding winds for three η A mass-loss rates ( ṀηA = 2.4, 4.8, and 8.5 × 10 -4 M ⊙ yr -1 ), investigating the effects on the dynamics of the binary wind-wind collision (WWC). These simulations include orbital motion, optically thin radiative cooling, and radiative forces. We find that ṀηA greatly affects the time-dependent hydrodynamics at all spatial scales investigated. The simulations also show that the post-shock wind of the companion star η B switches from the adiabatic to the radiative-cooling regime during periastron passage (φ ≈ 0.985 -1.02). This switchover starts later and ends earlier the lower the value of ṀηA and is caused by the encroachment of the wind of η A into the acceleration zone of η B 's wind, plus radiative inhibition of η B 's wind by η A . The SPH simulations together with 1D radiative transfer models of η A 's spectra reveal that a factor of two or more drop in ṀηA should lead to substantial changes in numerous multiwavelength observables. Recent observations are not fully consistent with the model predictions, indicating that any drop in ṀηA was likely by a factor 2 and occurred after 2004. We speculate that most of the recent observed changes in η Car are due to a small increase in the WWC opening angle that produces significant effects because our line-of-sight to the system lies close to the dense walls of the WWC zone. A modest decrease in ṀηA may be responsible, but changes in the wind/stellar parameters of η B , while less likely, cannot yet be fully ruled out. We suggest observations during η Car's next periastron in 2014 to further test for decreases in ṀηA . If ṀηA is declining and continues to do so, the 2014 X-ray minimum should be even shorter than that of 2009.

The effects of thin to moderately thick cirrus clouds on daytime air temperature rise or nighttime air temperature fall near the ground can be approximated as linearly proportional to the change in solar heating, or nocturnal radiative cooling, of the surface, produced by the clouds. It is estimated that a uniform overcast of cirrus with a thickness comparable to an average aircraft contrail will reduce daytime heating by I0 to 20% and nighttime cooling by up to 50% compared to the heating and cooling that would have occurred in cloudless conditions.

A field assessment of thermal comfort was conducted at Mehran University of Engineering and Technology, situated in the subtropical region of Pakistan. The results show that people of the area were feeling thermally comfortable at effective temperature of 29.85 1C (operative temperature 29.3 1C). A comparison of this neutral effective temperature was made with the neutral effective temperature determined from adaptive models. It is found that the neutral effective temperature determined during this study closely match that of the adaptive model based on either indoor temperature or both indoor and outdoor temperatures. The results of thermal acceptability assessment show that more than 80% of occupants were satisfied at an effective temperature of 32.5 1C, which is 6.5 1C above the upper boundary of ASHRAE thermal comfort zone. Naturally ventilated classrooms and air-conditioned offices of the University were simulated using TRNSYS system simulation program for two cases, once when conventional air-conditioning is used for providing thermal comfort, and when comfort is achieved through radiant cooling. In the simulation, cooling tower was used to regenerate cooling water for the radiant cooling system. Energy consumption was estimated from simulation of both cases. The results show that it is possible to achieve thermal comfort for most of the time of the year through the use of radiant cooling without a risk of condensation of moisture from air on the radiant cooling surfaces. A comparison of the energy consumption estimates show that savings of 80% is possible in case thermal comfort is achieved through radiant cooling instead of conventional air-conditioning.

Desert dust interacts with shortwave (SW) and longwave (LW) radiation, influencing the Earth radiation budget and the atmospheric vertical structure. Uncertainties on the dust role are large in the LW spectral range, where few measurements are available and the dust optical properties are not well constrained. The first airborne measurements of LW irradiance vertical profiles over the Mediterranean were carried out during the Ground‐based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign, which took place in spring 2008 at the island of Lampedusa. The experiment was aimed at estimating the vertical profiles of the SW and LW aerosol direct radiative forcing (ADRF) and heating rates (AHR), taking advantage of vertically resolved measurements of irradiances, meteorological parameters, and aerosol microphysical and optical properties. Two cases, characterized respectively by the presence of a homogeneous dust layer (3 May, with aerosol optical depth, AOD, at 500 n...

A Green Economy can be referred to as that type of economy which basically goes on to target to reduce the surrounding environmental hazards along with taking care of the ecological scarcities which in the process goes on to help in having better sustainable development without further degrading the surrounding environment. A Green Economy can also be referred to that type of economy which aims to have the needed economic growth along with reduction in adverse impacts of various modern day's economic processes , procedures and activities on the surrounding environment. As observed the concept of Green Economy is getting accepted all over the world as a method to promote better day to day living for the normal human beings of the modern world by adopting those types of measures , practices and procedures which will go on to reduce various types of environmental hazards to make the world a better place to live in for not only the current generation but also for the future generations to come in our planet earth. The process of moving towards a green economy model from the existing economic model of a country , needs to take care of a number of other separate issues like increasing the process and procedures of utilisation of more and more renewable energy sources , take specific measures to develop more advanced types of clean technologies , think and implement specific steps to increase efficient utilisation of energy sources and reduce unnecessary wastages of various types of energy , etc , In this paper our main aim has been to study the advantages and disadvantages of introducing and implementing the Green Economy model in various modern world countries and the data needed to carry on the study has been collected by applying various methods of primary and secondary methods of data collection .

We study the behaviour of multiple radiative-cooling algorithms implemented in seven semianalytic models (SAMs) of galaxy formation, including a new model we propose in this paper. We use versions of the models without feedback and apply them to dark matter haloes growing in a cosmological context, which have final virial masses that range from 10 11 to 10 14 M. First, using simplified smoothly growing halo models, we demonstrate that the different algorithms predict cooling rates and final cold gas masses that differ by a factor of ∼5 for massive haloes (≥10 12 M). The algorithms are in better agreement for less massive haloes because they cool efficiently and, therefore, their cooling rates are largely limited by the halo accretion rate. However, for less massive haloes, all the SAMs predict less cooling than corresponding 1D hydrodynamic models. Secondly, we study the gas-accretion history of the central galaxies of dark matter haloes using merger trees. The inclusion of mergers alters the cooling history of haloes by locking up gas in galaxies within small haloes at early times. For realistic halo models, the dispersion in the cold gas mass predicted by the algorithms is 0.5 dex for high-mass haloes and 0.1 dex for low-mass haloes, while the dispersion in the accretion rate is about two times larger. Comparing to cosmological smoothed particle hydrodynamic simulations, we find that most SAMs systematically underpredict the gas-accretion rates for low-mass haloes but overpredict the gas-accretion rates for massive haloes. Although the models all include both 'rapid'-and 'slow'-mode accretion, the transition between the two accretion modes varies between models and also differs from the simulations. Finally, we construct a new phenomenological model that explicitly incorporates cold halo gas and a gradual transition between the cold and hot modes of gas accretion to illustrate that such a class of models can better match the results from cosmological hydrodynamic simulations. The large dispersion in cooling rates between different SAMs influences parameter choices for other galaxy physics, including star formation and feedback. Therefore, careful parametrizations of the multimode gas cooling and accretion mechanisms in simulations are necessary to ensure that the predictions from SAMs are reliable.