Wind Feedback Research Articles

Numerical simulations of wind-induced snow redistributions on large-span flat roofs: Development of snow transport along roof span

The existing research on snow drifting on large-span roofs primarily concentrates on snow redistributions on specific roofs, yet it lacks a systematic exploration of snow transport development along the span. This study uses a Eulerian-Lagrangian numerical method incorporating the wind feedback to simulate snow drifting on large-span flat roofs. The method is validated by comparing the numerical simulated sand redistributions on scaled roofs with the experimental data. Based on the numerical simulation, comparisons are made among sand transport on scaled roofs, snow transport on scaled roofs and snow transport on full-scale roofs. The scaled simulations show similar results, while the results of the scaled simulations noticeably differ from those of the full-scale simulation. Characteristics of snow transport on large-span flat roofs are investigated. On the leading and rear edges of the roof, snow transport rate increases significantly, resulting in relatively large erosion. In the middle of the roof, for wind velocities lower than 6 m/s at roof height, snow transport rate decreases along the span, leading to slight deposition; for wind velocities higher than 6 m/s, snow transport rate initially increases along the span, followed by a slight decrease until reaching equilibrium, resulting in large snow erosion followed by deposition.

Disk Wind Feedback from High-mass Protostars. III. Synthetic CO Line Emission

Abstract To test theoretical models of massive star formation it is important to compare their predictions with observed systems. To this end, we conduct CO molecular line radiative transfer post-processing of 3D magnetohydrodynamic simulations of various stages in the evolutionary sequence of a massive protostellar core, including its infall envelope and disk wind outflow. Synthetic position–position–velocity cubes of various transitions of 12CO, 13CO, and C18O emission are generated. We also carry out simulated Atacama Large Millimeter/submillimeter Array (ALMA) observations of this emission. We compare the mass, momentum, and kinetic energy estimates obtained from molecular lines to the true values, finding that the mass and momentum estimates can have uncertainties of up to a factor of 4. However, the kinetic energy estimated from molecular lines is more significantly underestimated. Additionally, we compare the mass outflow rate and momentum outflow rate obtained from the synthetic spectra with the true values. Finally, we compare the synthetic spectra with real examples of ALMA-observed protostars and determine the best-fitting protostellar masses and outflow inclination angles. We then calculate the mass outflow rate and momentum outflow rate for these sources, finding that both rates agree with theoretical protostellar evolutionary tracks.

Evolution and distribution of superbubbles in simulated Milky Way-like galaxies

ABSTRACT Stellar feedback plays a crucial role in regulating baryon cycles of a galactic ecosystem, and may manifest itself in the formation of superbubbles in the interstellar medium. In this work, we used a set of high-resolution simulations to systematically study the properties and evolution of superbubbles in galactic environments. The simulations were based on the SMUGGLE galaxy formation framework using the hydrodynamical moving-mesh code arepo, reaching a spatial resolution of $\sim 4 \, \rm pc$ and mass resolution of $\sim 10^3 \, \rm M_{\odot }$. We identified superbubbles and tracked their time evolution using the parent stellar associations within the bubbles. The X-ray luminosity-size distribution of superbubbles in the fiducial run is largely consistent with the observations of nearby galaxies. The size of superbubbles shows a double-peaked distribution, with the peaks attributed to early feedback (radiative and stellar wind feedback) and supernova feedback. The early feedback tends to suppress the subsequent supernova feedback, and it is strongly influenced by star formation efficiency, which regulates the environmental density. Our results show that the volume filling factor of hot gas (T > 105.5 K) is about $12~{{\ \rm per\ cent}}$ averaged over a region of 4 kpc in height and 20 kpc in radius centred on the disc of the galaxy. Overall, the properties of superbubbles are sensitive to the choice of subgrid galaxy formation models and can, therefore, be used to constrain these models.

Delayed X-Ray Brightening Accompanied by Variable Ionized Absorption Following a Tidal Disruption Event

Supermassive black holes can experience super-Eddington peak mass fallback rates following the tidal disruption of a star. The theoretical expectation is that part of the infalling material is expelled by means of an accretion disk wind, whose observational signature includes blueshifted absorption lines of highly ionized species in X-ray spectra. To date, however, only one such ultrafast outflow (UFO) has been reported in the tidal disruption event (TDE) ASASSN–14li. Here we report on the discovery of a transient absorption-like signature in X-ray spectra of the TDE AT2020ksf/Gaia20cjk (at a redshift of z = 0.092), following an X-ray brightening ∼230 days after UV/optical peak. We find that while no statistically significant absorption features are present initially, they appear on a timescale of several days and remain detected up to 770 days after peak. Simple thermal continuum models, combined with a power-law or neutral absorber, do not describe these features well. Adding a partial-covering, low-velocity ionized absorber improves the fit at early times but fails at late times. A high-velocity (v w ∼ 42,000 km s−1), ionized absorber (UFO) provides a good fit to all data. The few-day timescale of variability is consistent with expectations for a clumpy wind. We discuss several scenarios that could explain the X-ray delay, as well as the potential for larger-scale wind feedback. The serendipitous nature of the discovery could suggest a high incidence of UFOs in TDEs, alleviating some of the tension with theoretical expectations.

Intermediate mass black hole feedback in dwarf galaxy simulations with a resolved ISM and accurate nuclear stellar dynamics

AbstractRecent observations have established that dwarf galaxies can host black holes of intermediate mass (IMBH, 100Mȯ < MIMBH ≲ 105 Mȯ). With modern numerical models, we can test the growth of IMBHs as well as their evolutionary impact on the host galaxy. Our novel subsolar-mass (0.8 solar mass) resolution simulations of dwarf galaxies (M* = 2 × 107 Mȯ) have a resolved three-phase interstellar medium and account for non-equilibrium heating, cooling, and chemistry processes. The stellar initial mass function is fully sampled between 0.08–150 Mȯ while massive stars can form HII regions and explode as resolved supernovae. The stellar dynamics around the IMBH is integrated accurately with a regularization scheme. We present a viscous accretion disk model for the IMBH with momentum, energy, and mass conserving wind feedback. We demonstrate how the IMBH can grow from accretion of the cold and warm gas phase and how the presence of the IMBH and its feedback impacts the gas phase structure.

Minimal Mechanisms Responsible for the Dispersive Behavior of the Madden–Julian Oscillation

An attempt has been made to explore the relative contributions of moisture feedback processes on tropical intraseasonal oscillation or Madden–Julian Oscillation (MJO). We focused on moisture feedback processes, including evaporation wind feedback (EWF) and moisture convergence feedback (MCF), which integrate the mechanisms of convective interactions into the tropical atmosphere. The dynamical framework considered here is a moisture-coupled, single-layer linear shallow-water model on an equatorial beta-plane with zonal momentum damping. With this approach, we aimed to recognize the minimal physical mechanisms responsible for the existence of the essential dispersive characteristics of the MJO, including its eastward propagation (k>0), the planetary-scale (small zonal wavenumbers) instability, and the slow phase speed of about ≈5 m/s. Furthermore, we extended our study to determine each feedback mechanism’s influence on the simulated eastward dispersive mode. Our model emphasized that the MJO-like eastward mode is a possible outcome of the combined effect of moisture feedback processes without requiring additional complex mechanisms such as cloud radiative feedback and boundary layer dynamics. The results substantiate the importance of EWF as a primary energy source for developing an eastward moisture mode with a planter-scale instability. The eastward moisture mode exhibits the highest growth rate at the largest wavelengths and is also sensitive to the strength of the EWF, showing a significant increase in the growth rate with the increasing strength of the EWF; however, the eastward moisture mode remains unstable at planetary-scale wavelengths. Moreover, our model endorses that the MCF alone could not produce instability without surface fluxes, although it has a significant role in developing deep convection. It was found that the MCF exhibits a damping mechanism by regulating the frequency and growth rate of the eastward moisture mode at shorter wavelengths.

Feedback-driven anisotropy in the circumgalactic medium for quenching galaxies in the simba simulations

ABSTRACT We use the simba galaxy formation simulation suite to explore anisotropies in the properties of circumgalactic gas that result from accretion and feedback processes. We particularly focus on the impact of bipolar active galactic nuclei (AGNs) jet feedback as implemented in simba , which quenches galaxies and has a dramatic effect on large-scale gas properties. We show that jet feedback at low redshifts is most common in the stellar mass range (1–5) × 1010 M⊙, so we focus on galaxies with active jets in this mass range. In comparison to runs without jet feedback, jets cause lower densities and higher temperatures along the galaxy minor axis (simba jet direction) at radii $\gtrsim 0.5r_{200c}-4r_{200c}$ and beyond. This effect is less apparent at higher or lower stellar masses, and is strongest within green valley galaxies. The metallicity also shows strong anisotropy out to large scales, driven by star formation feedback. We find substantially stronger anisotropy at $\lesssim 0.5r_{200c}$, but this also exists in runs with no explicit feedback, suggesting that it is due to anisotropic accretion. Finally, we explore anisotropy in the bulk radial motion of the gas, finding that both star formation and AGN wind feedback contribute to pushing the gas outwards along the minor axis at $\lesssim 1$ Mpc, but AGN jet feedback further causes bulk outflow along the minor axis out to several Mpc, which drives quenching via gas starvation. These results provide observational signatures for the operation of AGN feedback in galaxy quenching.

The energy and dynamics of trapped radiative feedback with stellar winds

ABSTRACT In this paper, we explore the significant, non-linear impact that stellar winds have on H ii regions. We perform a parameter study using three-dimensional radiative magnetohydrodynamic simulations of wind and ultraviolet radiation feedback from a 35 M⊙ star formed self-consistently in a turbulent, self-gravitating cloud, similar to the Orion Nebula (M42) and its main ionizing source θ1 Ori C. Stellar winds suppress early radiative feedback by trapping ionizing radiation in the shell around the wind bubble. Rapid breakouts of warm photoionized gas (‘champagne flows’) still occur if the star forms close to the edge of the cloud. The impact of wind bubbles can be enhanced if we detect and remove numerical overcooling caused by shocks crossing grid cells. However, the majority of the energy in the wind bubble is still lost to turbulent mixing between the wind bubble and the gas around it. These results begin to converge if the spatial resolution at the wind bubble interface is increased by refining the grid on pressure gradients. Wind bubbles form a thin chimney close to the star, which then expands outwards as an extended plume once the wind bubble breaks out of the dense core the star formed in, allowing them to expand faster than a spherical wind bubble. We also find wind bubbles mixing completely with the photoionized gas when the H ii region breaks out of the cloud as a champagne flow, a process we term ‘hot champagne’.

Evolved massive stars at low-metallicity

The mass-loss rate (MLR) is one of the most important parameters in astrophysics, because it impacts many areas of astronomy, such as ionizing radiation, wind feedback, star-formation rates, initial mass functions, stellar remnants, supernovae, and so on. However, the most important modes of mass loss are also the most uncertain, as the dominant physical mechanisms that lead to this phenomenon are stull largely unknown. Here we assemble the most complete and clean red supergiant (RSG) sample (2121 targets) so far in the Small Magellanic Cloud (SMC) with 53 different bands of data to study the MLR of RSGs. In order to match the observed spectral energy distributions (SEDs), we created a theoretical grid of 17 820 oxygen-rich models (“normal” and “dusty” grids are half-and-half) using the radiatively driven wind model of the DUSTY code, covering a wide range of dust parameters. We select the best model for each target by calculating the minimal modified chi-square and visual inspection. The resulting MLRs from DUSTY are converted to real MLRs based on the scaling relation, for which a total MLR of 6.16 × 10−3 M⊙ yr−1 is measured (corresponding to a dust-production rate of ∼6 × 10−6 M⊙ yr−1), with a typical MLR of ∼10−6 M⊙ yr−1 for the general population of the RSGs. The complexity of mass-loss estimations based on the SED is fully discussed for the first time, and our results indicate large uncertainties based on the photometric data (potentially up to one order of magnitude or more). The Hertzsprung-Russell (HR) and luminosity versus median-absolute-deviation (MAD) diagrams of the sample indicate the positive relation between luminosity and MLR. Meanwhile, the luminosity versus MLR diagrams show a “knee-like” shape with enhanced mass loss occurring above log10(L/L⊙)≈4.6, which may be due to the degeneracy of luminosity, pulsation, low surface gravity, convection, and other factors. We derive our MLR relation using a third-order polynomial to fit the sample and compare our results with previous empirical MLR prescriptions. Given that our MLR prescription is based on a much larger sample than previous determinations, it provides a more accurate relation at the cool and luminous region of the HR diagram at low metallicity compared to previous studies. Finally, nine targets in our sample were detected in the UV, which could be an indicator of OB-type companions of binary RSGs.

Formation of star clusters and enrichment by massive stars in simulations of low-metallicity galaxies with a fully sampled initial stellar mass function

ABSTRACT We present new griffin project hydrodynamical simulations that model the formation of galactic star cluster populations in low-metallicity (Z = 0.00021) dwarf galaxies, including radiation, supernova, and stellar wind feedback of individual massive stars. In the simulations, stars are sampled from the stellar initial mass function (IMF) down to the hydrogen-burning limit of 0.08 M⊙. Mass conservation is enforced within a radius of 1 pc for the formation of massive stars. We find that massive stars are preferentially found in star clusters and follow a correlation set at birth between the highest initial stellar mass and the star cluster mass that differs from pure stochastic IMF sampling. With a fully sampled IMF, star clusters lose mass in the galactic tidal field according to mass-loss rates observed in nearby galaxies. Of the released stellar feedback, 60 per cent of the supernova material and up to 35 per cent of the wind material reside either in the hot interstellar medium (ISM) or in gaseous, metal-enriched outflows. While stellar winds (instantaneously) and supernovae (delayed) start enriching the ISM right after the first massive stars form, the formation of supernova-enriched stars and star clusters is significantly delayed (by >50 Myr) compared to the formation of stars and star clusters enriched by stellar winds. Overall, supernova ejecta dominate the enrichment by mass, while the number of enriched stars is determined by continuous stellar winds. These results present a concept for the formation of chemically distinct populations of stars in bound star clusters, reminiscent of multiple populations in globular clusters.

Impact of Cyclonic Wind Anomalies Caused by Massive Winter Sea Ice Retreat in the Barents Sea on Atlantic Water Transport Toward the Arctic: A Model Study

AbstractThe Arctic is warming much faster than the global average. This is known as Arctic Amplification and is caused by feedbacks in the local climate system. In this study, we explore a previously proposed hypothesis that an associated wind feedback in the Barents Sea could play an important role by increasing the warm water inflow into the Barents Sea. We find that the strong recent decrease in Barents Sea winter sea ice cover causes enhanced ocean‐atmosphere heat flux and a local air temperature increase, thus a reduction in sea level pressure and a local cyclonic wind anomaly with eastward winds in the Barents Sea Opening. By investigating various reanalysis products and performing high‐resolution perturbation experiments with the ocean and sea ice model FESOM2.1, we studied the impact of cyclonic atmospheric circulation changes on the warm Atlantic Water import into the Arctic via the Barents Sea and Fram Strait. We found that the observed wind changes do not significantly affect the warm water transport into the Barents Sea, which rejects the wind‐feedback hypothesis. At the same time, the cyclonic wind anomalies in the Barents Sea increase the amount of Atlantic Water recirculating westwards in Fram Strait by a downslope shift of the West Spitsbergen Current, and thus reduce Atlantic Water reaching the Arctic basin via Fram Strait. The resulting warm‐water anomaly in the Greenland Sea Gyre drives a local anticyclonic circulation anomaly.

Calibrating Cosmological Simulations with Implicit Likelihood Inference Using Galaxy Growth Observables

In a novel approach employing implicit likelihood inference (ILI), also known as likelihood-free inference, we calibrate the parameters of cosmological hydrodynamic simulations against observations, which has previously been unfeasible due to the high computational cost of these simulations. For computational efficiency, we train neural networks as emulators on ∼1000 cosmological simulations from the CAMELS project to estimate simulated observables, taking as input the cosmological and astrophysical parameters, and use these emulators as surrogates for the cosmological simulations. Using the cosmic star formation rate density (SFRD) and, separately, the stellar mass functions (SMFs) at different redshifts, we perform ILI on selected cosmological and astrophysical parameters (Ω m , σ 8, stellar wind feedback, and kinetic black hole feedback) and obtain full six-dimensional posterior distributions. In the performance test, the ILI from the emulated SFRD (SMFs) can recover the target observables with a relative error of 0.17% (0.4%). We find that degeneracies exist between the parameters inferred from the emulated SFRD, confirmed with new full cosmological simulations. We also find that the SMFs can break the degeneracy in the SFRD, which indicates that the SMFs provide complementary constraints for the parameters. Further, we find that a parameter combination inferred from an observationally inferred SFRD reproduces the target observed SFRD very well, whereas, in the case of the SMFs, the inferred and observed SMFs show significant discrepancies that indicate potential limitations of the current galaxy formation modeling and calibration framework, and/or systematic differences and inconsistencies between observations of the SMFs.

Critical Metallicity of Cool Supergiant Formation. I. Effects on Stellar-mass Loss and Feedback

This paper systematically studies the relation between metallicity and mass loss of massive stars. We perform one-dimensional stellar evolution simulations and build a grid of ∼2000 models with initial masses ranging between 11 and 60 M ⊙ and absolute metallicities Z between 0.00001 and 0.02. Steady-state winds, comprising hot main-sequence winds and cool supergiant winds, are the main drivers of the mass loss of massive stars in our models. We calculate the total mass loss over the stellar lifetime for each model. Our results reveal the existence of a critical metallicity Z c at Z ∼ 10−3, where the mass loss exhibits a dramatic jump. If Z > Z c, massive stars tend to evolve into cool supergiants, and a robust cool wind is operational. In contrast, if Z < Z c, massive stars usually remain as blue supergiants, wherein the cool wind is not activated and the mass loss is generally weak. Moreover, we calculate the wind feedback in a 105 M ⊙ star cluster with the Salpeter initial mass function. The kinetic energy released by winds does not exhibit any significant transition at Z c because the wind velocity of a cool supergiant wind is low and contributes little to the kinetic energy. The effects of critical metallicity provide implications for the fates of metal-poor stars in the early universe.

A Massive Star Is Born: How Feedback from Stellar Winds, Radiation Pressure, and Collimated Outflows Limits Accretion onto Massive Stars

Massive protostars attain high luminosities as they are actively accreting and the radiation pressure exerted on the gas in the star’s atmosphere may launch isotropic high-velocity winds. These winds will collide with the surrounding gas producing shock-heated (T ∼ 107 K) tenuous gas that adiabatically expands and pushes on the dense gas that may otherwise be accreted. We present a suite of 3D radiation-magnetohydrodynamic simulations of the collapse of massive prestellar cores and include radiative feedback from the stellar and dust-reprocessed radiation fields, collimated outflows, and, for the first time, isotropic stellar winds to model how these processes affect the formation of massive stars. We find that winds are initially launched when the massive protostar is still accreting and its wind properties evolve as the protostar contracts to the main sequence. Wind feedback drives asymmetric adiabatic wind bubbles that have a bipolar morphology because the dense circumstellar material pinches the expansion of the hot shock-heated gas. We term this the “wind tunnel effect.” If the core is magnetized, wind feedback is less efficient at driving adiabatic wind bubbles initially because magnetic tension delays their growth. We find that wind feedback eventually quenches accretion onto ∼30 M ⊙ protostars that form from the collapse of the isolated cores simulated here. Hence, our results suggest that ≳30 M ⊙ stars likely require larger-scale dynamical inflows from their host cloud to overcome wind feedback. Additionally, we discuss the implications of observing adiabatic wind bubbles with Chandra while the massive protostars are still highly embedded.

ENSO atmospheric feedbacks under global warming and their relation to mean-state changes

Two atmospheric feedbacks play an important role in the dynamics of the El Niño/Southern Oscillation (ENSO), namely the amplifying zonal wind feedback and the damping heat flux feedback. Here we investigate how and why both feedbacks change under global warming in climate models participating in the 5th and 6th phase of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) under the business-as-usual scenario (RCP8.5 and SSP5-8.5, respectively). The amplifying zonal wind feedback over the western equatorial Pacific (WEP) becomes significantly stronger in two third of the models, on average by 12 ± 7% in these models. The heat flux damping feedback over the eastern and central equatorial Pacific (EEP and CEP, respectively) increases as well in nearly all models, with the damping effect increasing on average by 18 ± 11%. The simultaneous strengthening of the two feedbacks can be explained by the stronger warming in the EEP relative to the WEP and the off-equatorial regions, which shifts the rising branch of the Pacific Walker Circulation to the east and increases the mean convection over the CEP. This in turn leads to a stronger vertical wind response during ENSO events over the CEP that strengthens both atmospheric feedbacks. We separate the climate models into sub-ensembles with STRONG and WEAK ENSO atmospheric feedbacks, as 2/3 of the models underestimate both feedbacks under present-day conditions by more than 40%, causing an error compensation in the ENSO dynamics. The biased mean state in WEAK in 20C constrains the ENSO atmospheric feedback projection in 21C, as the models of the WEAK sub-ensemble also have weaker ENSO atmospheric feedbacks in 21C. Further, due to the more realistic dynamics and teleconnections, we postulate that one should have more confidence in the ENSO predictions with models belonging to the STRONG sub-ensemble. Finally, we analyze the relation between ENSO amplitude change and ENSO atmospheric feedback change. We find that models simulating an eastward shift of the zonal wind feedback and increasing precipitation over the EEP during Eastern Pacific El Niño events tend to predict a larger ENSO amplitude in response to global warming.

Modeling Evolution of Galactic Bars at Cosmic Dawn

We study the evolution of galactic bars using a suite of very high-resolution zoom-in cosmological simulations of galaxies at z ∼ 9–2. Our models were chosen to lie within similar-mass dark matter (DM) halos, log(M vir/M ⊙) ∼ 11.65 ± 0.05, at z = 6, 4, and 2, in high- and low-overdensity environments. We apply two galactic wind feedback mechanisms for each model. All galaxies develop subkiloparsec stellar bars differing in their properties. We find that (1) the high-z bars form in response to various perturbations: mergers, close flybys, cold accretion inflows along the cosmological filaments, etc.; (2) these bars account for the large mass fraction of galaxies; (3) bars display large corotation-to-bar size ratios, are weaker compared to their low-redshift counterparts by measuring their Fourier amplitudes, and are very gas-rich; (4) their pattern speed does not exhibit monotonic decline with time owing to braking against DM, as at low z; (5) bar properties, including their stellar population (star formation rates and metal enrichment), depend sensitively on prevailing feedback; and (6) bars can weaken substantially during cosmological evolution, becoming weak oval distortions—hence bars are destroyed and reformed multiple times, unlike their low-z counterparts. In all cases, bars in our simulations have been triggered by interactions. In summary, not only do stellar bars appear to be a contemporary phenomenon, but based on increased frequency of mergers, flybys, and the strength of cold accretion flows at high z, we also expect them to be ubiquitous at redshifts ≳2—the epoch of rapid galaxy growth and larger stellar dispersion velocities.

Emergence of galactic morphologies at cosmic dawn: input from numerical modelling

ABSTRACTWe employ a series of high-resolution zoom-in cosmological simulations to analyse the emerging morphology of main galaxies in dark matter haloes at z ≳ 2. We choose haloes of similar masses, ${\rm log}\, M_{\rm vir}/{\rm M_\odot }\sim 11.65\pm 0.05$, at the target zf = 6, 4, and 2. The rationale for this choice allows us to analyse how the different growth rate in these haloes propagates down to galaxy scales, affecting their basic parameters. Halos were embedded in high/low overdensity regions, and two versions of a galactic wind feedback were employed. Our main results are: (1) Although our galaxies evolve in different epochs, their global parameters remain within narrow range. Their morphology, kinematics, and stellar populations differ substantially, yet all host sub-kpc stellar bars; (2) The star formation rates appear higher for larger zf; (3) Bulges and stellar spheroids were separated by stellar kinematics, discy bulges were revealed using the Sersic method and photometry.The bulge-to-total mass ratios appear independent of the last merger time for all zf. The spheroid-to-total mas ratios lie within ∼0.5–0.8; (4) The synthetic redshifted, pixelized, and PSF-degraded JWST images allow detection of stellar discs at all zf. (5) Based on the kinematic decomposition, rotational support in discs depends on the feedback type, but increases with decreasing zf; (6) Finally, the ALMA images detect discs at all zf, but spiral structure is detectable in zf = 2 galaxies. Moreover, galaxies follow the Tully–Fisher relation, being separated only by the galactic wind feedback.

Research on variable pitch control strategy of direct-driven offshore wind turbine using KELM wind speed soft sensor

This study proposes a modeling method of soft measurement of offshore wind speed using Kernal Extreme Learning Machine (KELM). The soft measurement model of offshore wind speed is presented based on the data-driven method and kernel function extreme learning machine. An improved gray Wolf optimization algorithm is applied to optimize its parameters to enhance the measurement accuracy. Finally, based on the established offshore wind speed measurement model, a feedforward and feedback variable rotor controller is designed and verified by simulation, which proves the effectiveness of the research in this study.

Star Formation Regulation and Self-pollution by Stellar Wind Feedback

Abstract Stellar winds contain enough energy to easily disrupt the parent cloud surrounding a nascent star cluster, and for this reason they have long been considered candidates for regulating star formation. However, direct observations suggest most wind power is lost, and Lancaster et al. recently proposed that this is due to efficient mixing and cooling processes. Here we simulate star formation with wind feedback in turbulent, self-gravitating clouds, extending our previous work. Our simulations cover clouds with an initial surface density of 102–104 M ⊙ pc−2 and show that star formation and residual gas dispersal are complete within two to eight initial cloud freefall times. The “efficiently cooled” model for stellar wind bubble evolution predicts that enough energy is lost for the bubbles to become momentum-driven; we find that this is satisfied in our simulations. We also find that wind energy losses from turbulent, radiative mixing layers dominate losses by “cloud leakage” over the timescales relevant for star formation. We show that the net star formation efficiency (SFE) in our simulations can be explained by theories that apply wind momentum to disperse cloud gas, allowing for highly inhomogeneous internal cloud structure. For very dense clouds, the SFE is similar to those observed in extreme star-forming environments. Finally, we find that, while self-pollution by wind material is insignificant in cloud conditions with moderate density (only ≲10−4 of the stellar mass originated in winds), our simulations with conditions more typical of a super star cluster have star particles that form with as much as 1% of their mass in wind material.

Absence of Tropical Cyclone Genesis Over the Western North Pacific in July 2020 and Its Prediction by CFSv2

There were no TCs generated in July 2020 over the western North Pacific (WNP), which was the first time this had happened during since 1980. This study attempts to understand the cause of there having been no TCs generated in July 2020, and evaluates the prediction skill for the large-scale environmental conditions associated with the TC genesis number (TCGN). Results show that the main causes were the abnormal warming of sea surface temperature (SST) in the North Indian Ocean (NIO) and North Atlantic in July and the abnormal decrease in SST from April and May in the Niño4 region. The NIO SST can affect the large-scale environmental conditions via the SST–precipitation–wind feedback mechanism. Through the interaction between the tropical North Atlantic and the NIO, the abnormally warm North Atlantic SST further strengthened the impact of the NIO SST on the environmental conditions. The monthly difference (MD) of the Niño4 index from April to May is significantly correlated with the TCGN in July. Not only can the Niño4 MD in May affect the environmental conditions by affecting the WNP anticyclone, but it can also affect the NIO SST and precipitation anomalies through a shift in the position of the Walker circulation. Besides, the activity of the MJO also had a certain impact on the absence of TC genesis in July 2020. Although CFSv2 can successfully predict the local feedback affecting the July TCGN, it fails to forecast the large-scale environmental conditions associated with the absence of TC genesis over the WNP in July 2020.