Cloud Region Research Articles

Dual-View 3D Reconstruction via Learning Correspondence and Dependency of Point Cloud Regions.

Multi-view 3D reconstruction generally adopts the feature fusion strategy to guide the generation of 3D shape for objects with different views. Empirically, the correspondence learning of object regions across different views enables better feature fusion. However, such idea has not been fully exploited in existing methods. Furthermore, current methods fail to explore the intrinsic dependency among regions within a 3D shape, leading to a rough reconstruction result. To address the above issues, we propose a Dual-View 3D Point Cloud reconstruction architecture named DVPC, which takes two views images as inputs, and progressively generates a refined 3D point cloud. First, a point cloud generation network is assigned to generate a coarse point cloud for each input view. Second, a dual-view point clouds synthesis network is presented in DVPC. It constructs a regional attention mechanism to learn a high-quality correspondence among regions across two coarse point clouds in different views, so that our DVPC can achieve feature fusion accurately. And then it develops a point cloud deformation module to produce a relatively-precise point cloud via establishing the communication between the coarse point cloud and the fused feature. Lastly, a point-region transformer network is devised to model the dependency among regions within the relatively-precise point cloud. With the dependency, the relatively-precise point cloud is refined into a desirable 3D point cloud with rich details. Qualitative and quantitative experiments on the ShapeNet and Pix3D datasets demonstrate that the proposed DVPC outperforms the state-of-the-art methods in terms of reconstruction quality.

GASKAP-HI Pilot Survey Science III: An unbiased view of cold gas in the Small Magellanic Cloud

AbstractWe present the first unbiased survey of neutral hydrogen absorption in the Small Magellanic Cloud. The survey utilises pilot neutral hydrogen observations with the Australian Square Kilometre Array Pathfinder telescope as part of the Galactic Australian Square Kilometre Array Pathfinder neutral hydrogen project whose dataset has been processed with the Galactic Australian Square Kilometre Array Pathfinder-HI absorption pipeline, also described here. This dataset provides absorption spectra towards 229 continuum sources, a 275% increase in the number of continuum sources previously published in the Small Magellanic Cloud region, as well as an improvement in the quality of absorption spectra over previous surveys of the Small Magellanic Cloud. Our unbiased view, combined with the closely matched beam size between emission and absorption, reveals a lower cold gas faction (11%) than the 2019 ATCA survey of the Small Magellanic Cloud and is more representative of the Small Magellanic Cloud as a whole. We also find that the optical depth varies greatly between the Small Magellanic Cloud’s bar and wing regions. In the bar we find that the optical depth is generally low (correction factor to the optically thin column density assumption of$\mathcal{R}_{\mathrm{HI}} \sim 1.04$) but increases linearly with column density. In the wing however, there is a wide scatter in optical depth despite a tighter range of column densities.

Model emulation to understand the joint effects of ice-nucleating particles and secondary ice production on deep convective anvil cirrus

Abstract. Ice crystal formation in the mixed-phase region of deep convective clouds can affect the properties of climatically important convectively generated anvil clouds. Small ice crystals in the mixed-phase cloud region can be formed by heterogeneous ice nucleation by ice-nucleating particles (INPs) and secondary ice production (SIP) by, for example, the Hallett–Mossop process. We quantify the effects of INP number concentration, the temperature dependence of the INP number concentration at mixed-phase temperatures, and the Hallett–Mossop splinter production efficiency on the anvil of an idealised deep convective cloud using a Latin hypercube sampling method, which allows optimal coverage of a multidimensional parameter space, and statistical emulation, which allows us to identify interdependencies between the three uncertain inputs. Our results show that anvil ice crystal number concentration (ICNC) is determined predominately by INP number concentration, with the temperature dependence of ice-nucleating aerosol activity having a secondary role. Conversely, anvil ice crystal size is determined predominately by the temperature dependence of ice-nucleating aerosol activity, with INP number concentration having a secondary role. This is because in our simulations ICNC is predominately controlled by the number concentration of cloud droplets reaching the homogeneous freezing level which is in turn determined by INP number concentrations at low temperatures. Ice crystal size, however, is more strongly affected by the amount of liquid available for riming and the time available for deposition growth which is determined by INP number concentrations at higher temperatures. This work indicates that the amount of ice particle production by the Hallett–Mossop process is determined jointly by the prescribed Hallett–Mossop splinter production efficiency and the temperature dependence of ice-nucleating aerosol activity. In particular, our sampling of the joint parameter space shows that high rates of SIP do not occur unless the INP parameterisation slope (the temperature dependence of the number concentration of particles which nucleate ice) is shallow, regardless of the prescribed Hallett–Mossop splinter production efficiency. A shallow INP parameterisation slope and consequently high ice particle production by the Hallett–Mossop process in our simulations leads to a sharp transition to a cloud with extensive glaciation at warm temperatures, higher cloud updraughts, enhanced vertical mass flux, and condensate divergence at the outflow level, all of which leads to a larger convectively generated anvil comprised of larger ice crystals. This work highlights the importance of quantifying the full spectrum of INP number concentrations across all mixed-phase altitudes and the ways in which INP and SIP interact to control anvil properties.

An Unbiased CO Survey toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. I. Overview: CO Cloud Distributions

Abstract We have analyzed the data from a large-scale CO survey toward the northern region of the Small Magellanic Cloud (SMC) obtained with the Atacama Compact Array (ACA) stand-alone mode of ALMA. The primary aim of this study is to comprehensively understand the behavior of CO as an H2 tracer in a low-metallicity environment (Z ∼ 0.2 Z ⊙). The total number of mosaic fields is ∼8000, which results in a field coverage of 0.26 deg2 (∼2.9 ×105 pc2), corresponding to ∼10% of the area of the galaxy. The sensitive ∼2 pc resolution observations reveal the detailed structure of the molecular clouds previously detected in the single-dish NANTEN survey. We have detected a number of compact CO clouds within lower H2 column density (∼1020 cm−2) regions whose angular scale is similar to the ACA beam size. Most of the clouds in this survey also show peak brightness temperature as low as <1 K, which for optically thick CO emission implies an emission size much smaller than the beam size, leading to beam dilution. The comparison between an available estimation of the total molecular material traced by thermal dust emission and the present CO survey demonstrates that more than ∼90% of H2 gas cannot be traced by the low-J CO emission. Our processed data cubes and 2D images are publicly available.

Gravitational instability in radiative molecular clouds including cosmic ray diffusion and ion Larmor radius corrections

ABSTRACT The effects of cosmic ray (CR) diffusion and finite Larmor radius (FLR) corrections have been studied on the linear gravitational instability of thermally conducting plasmas typically in the H ii regions of molecular clouds. The hydrodynamic fluid–fluid approach is considered for interacting CRs with gravitating, magnetized, and thermally conducting gas in molecular clouds. The magnetohydrodynamic fluid model is formulated considering CR pressure gradients, CR diffusion, and radiative and FLR effects in terms of particle Larmor radius. The dispersion relation of the gravitational instability is analytically derived using the normal mode analysis, and the effects of CRs and FLR corrections have been discussed in longitudinal and transverse modes. It is observed that in the absence of CRs, the FLR effects (magnetic viscosity) reduce the growth rate for wavenumber smaller than a critical value, and above it gets increased. However, the growth rate is strongly suppressed in the presence of combined CRs and FLR effects. The individual behaviour of FLR effects is observed to destabilize the growth rate of the gravitational instability in the presence of CR effects. The CR pressure decreases the growth rates of the gravitational and thermal instabilities, whereas parallel CR diffusion enhances the growth rate of the gravitational instability. The Jeans length of the gravitating gas cloud gets increased due to an increase in the CR-to-gas pressure ratio. It is found that the gravitational collapse of the system is supported by high-energy (above knee) CR particles with the Larmor radii comparable to the cloud size. The present results have been applied to understand the role of CRs and FLR corrections on the gravitational collapse in the H ii regions of molecular clouds.

Revisiting a detached stellar structure in the outer north-eastern region of the Small Magellanic Cloud

ABSTRACT The outer north-eastern region of the Small Magellanic Cloud (SMC) is populated by a shell-like overdensity whose nature was recently investigated. We analysed 20 catalogued star clusters projected on to it from Survey of the MAgellanic Stellar History data sets. After carrying out a cleaning of field stars in the star cluster colour–magnitude diagrams (CMDs), and deriving their astrophysical properties from a comparison between the observed and synthetic CMDs, we found that four objects are not genuine star clusters, while the remaining ones are young star clusters (11, age ∼30–200 Myr) and intermediate-age (5, age ∼1.7–2.8 Gyr) star clusters, respectively. The resulting distances show that intermediate-age and some young star clusters belong to the SMC main body, while the remaining young star clusters are nearly 13.0 kpc away from those in the SMC, revealing that the shell-like overdensity is more extended along the line of sight than previously thought. We also found a clear age trend and a blurred metallicity correlation along the line of sight of young clusters, in the sense that the farther a star cluster is from the SMC, the younger, the more metal-rich, and the less massive it is. These young clusters are also affected by a slightly larger interstellar reddening than the older ones in the shell-like overdensity. These outcomes suggest that the shell-like overdensity can possibly be another tidally perturbed/formed SMC stellar structure from gas stripped off its body, caused by the interaction with the Large Magellanic Cloud or the Milky Way.

Validation of satellite estimated convective rainfall products : A case study for the summer cyclone season of 2020

The present work is focused on the performance of convective rainfall products, derived from Meteosat-8 (IODC) at NCMRWF using GFS first guess fields during summer cyclone season 2020. NCMRWF receives Meteosat-8 (IODC) HRIT data in real-time through EUMETCAST terrestrial service. NCMRWF derives the nowcasting products, including Convective Rainfall Rate (CRR), RGB products and cloud imageries in real-time and made available to IMD through the National Knowledge Network (NKN). Here, we focussed on the Amphan and Nisarga cyclones, formed in the Bay of Bengal and the Arabian Sea respectively. The validation of these CRR products is carried against calibrated and merged precipitation product IMERG by GPM missions. Grid to grid comparison of both precipitation products shows a good agreement in convective cloud regions in both the cyclones. Probability of Detection (POD) and Critical success index is very high (~1) in the precipitating clouds region. POD, Success ratios are very high (~1) in the regions of moderate, intense, very intense spells during the two cyclones. The POD is low for light spell (0-10 mm/h) regions. This is expected from CRR a ‘convective cloud’ specific product, which filters out rainfall in stratiform cloud regions. This study shows that CRR can be used in near-real time rainfall monitoring for various applications.

Hygroscopic Seeding Effects of Giant Aerosol Particles Simulated by the Lagrangian‐Particle‐Based Direct Numerical Simulation

AbstractThis study investigated the microphysical responses to seeding giant aerosol particles and supersaturation fluctuations. A Lagrangian‐particle‐based direct numerical simulation is used to resolve the interactions among individual aerosols, droplets, and the fluctuating supersaturation field within a turbulent, adiabatic air parcel. It is shown that the giant seeding particles exert strong solute effects throughout the entire simulation to alter the subsequent collision–coalescence process, implying the importance of including the solute term in droplet growth. Small‐scale supersaturation fluctuations in adiabatic cloud regions have a negligible influence on aerosol activation and droplet condensation. This is because in regions free of entrainment and/or large‐scale mixing, the weak supersaturation fluctuations can be quickly smoothed out via diffusion and remain relatively small in magnitude (with a standard deviation <). In contrast, the activation in our simulations is determined by the seeding modulation of the parcel‐mean supersaturation.

Observed and Simulated Variability of Droplet Spectral Dispersion in Convective Clouds Over the Amazon

AbstractIn this study, the variability of the spectral dispersion of droplet size distributions (DSDs) in convective clouds is investigated. Analyses are based on aircraft measurements of growing cumuli near the Amazon basin, and on numerical simulations of an idealized ice‐free cumulus. In cleaner clouds, the relative dispersion , defined as the ratio of the standard deviation to the mean value of the droplet diameter, is negatively correlated with the ratio of the cloud water content () to the adiabatic liquid water content (), while no strong correlation between and is seen in polluted clouds. Bin microphysics numerical simulations suggest that these contrasting behaviors are associated with the effect of collision‐coalescence in cleaner clouds, and secondary droplet activation in polluted clouds, in addition to the turbulent mixing of parcels that experienced different paths within the cloud. Collision‐coalescence simultaneously broadens the DSDs and decreases , explaining the inverse relationship between and in cleaner clouds. Secondary droplet activation broadens the DSDs but has little direct impact on . The combination of a rather modest DSD broadening due to weak collision‐coalescence with enhanced droplet activation in both diluted and highly undiluted cloud regions may contribute to maintain a relatively uniform within polluted clouds. These findings can be useful for parameterizing the shape parameter () of gamma DSDs in bulk microphysics cloud‐resolving models. It is shown that emulating the observed relationship improves the estimation of the collision‐coalescence rate in bulk microphysics simulations compared to the bin simulations.

Presence of red giant population in the foreground stellar substructure of the Small Magellanic Cloud

ABSTRACT The eastern region of the Small Magellanic Cloud (SMC) is found to have a foreground stellar substructure, which is identified as a distance bimodality (∼12 kpc apart) in the previous studies using red clump (RC) stars. Interestingly, studies of red giant branch (RGB) stars in the eastern SMC indicate a bimodal radial velocity (RV) distribution. In this study, we investigate the connection between these two bimodal distributions to better understand the nature and origin of the foreground stellar substructure in the eastern SMC. We use the Gaia Early Data Release 3 astrometric data and archival RV data of RGB stars for this study. We find a bimodal RV distribution of RGB stars (separated by ∼35–45 km s−1) in the eastern and south-western (SW) outer regions. The observed proper motion values of the lower and higher RV RGB components in the eastern regions are similar to those of the foreground and main-body RC stars, respectively. This suggests that the two RGB populations in the eastern region are separated by a similar distance to those of the RC stars, and the RGB stars in the lower RV component are part of the foreground substructure. Based on the differences in the distance and RV of the two components, we estimate an approximate time of formation of this substructure as 307 ± 65 Myr ago. This is comparable with the values predicted by simulations for the recent epoch of tidal interaction between the Magellanic Clouds. Comparison of the observed properties of RGB stars, in the outer SW region, with N-body simulations shows that the higher RV component in the SW region is at a farther distance than the main body, indicating the presence of a stellar counter-bridge in the SW region of the SMC.

3D point cloud lossy compression using quadric surfaces.

The presence of 3D sensors in hand-held or head-mounted smart devices has motivated many researchers around the globe to devise algorithms to manage 3D point cloud data efficiently and economically. This paper presents a novel lossy compression technique to compress and decompress 3D point cloud data that will save storage space on smart devices as well as minimize the use of bandwidth when transferred over the network. The idea presented in this research exploits geometric information of the scene by using quadric surface representation of the point cloud. A region of a point cloud can be represented by the coefficients of quadric surface when the boundary conditions are known. Thus, a set of quadric surface coefficients and their associated boundary conditions are stored as a compressed point cloud and used to decompress. An added advantage of proposed technique is its flexibility to decompress the cloud as a dense or a course cloud. We compared our technique with state-of-the-art 3D lossless and lossy compression techniques on a number of standard publicly available datasets with varying the structure complexities.

Turbulent Cascade and Energy Transfer Rate in a Solar Coronal Mass Ejection

Abstract Turbulence properties are examined before, during, and after a coronal mass ejection (CME) detected by the Wind spacecraft in 2012 July. The power-law scaling of the structure functions, providing information on the power spectral density and flatness of the velocity, magnetic field, and density fluctuations, were examined. The third-order moment scaling law for incompressible, isotropic magnetohydrodynamic turbulence was observed in the preceding and trailing solar wind, as well as in the CME sheath and magnetic cloud. This suggests that the turbulence could develop sufficiently after the shock, or that turbulence in the sheath and cloud regions was robustly preserved even during the mixing with the solar wind plasma. The turbulent energy transfer rate was thus evaluated in each of the regions. The CME sheath shows an increase of energy transfer rate, as expected from the lower level of Alfvénic fluctuations and suggesting the role of the shock-wind interaction as an additional source of energy for the turbulent cascade.

Ice mantles on dust grains: dramatic variation of thickness with grain size

ABSTRACT We compute the desorption rate of icy mantles on dust grains as a function of the size and composition of both the grain and the mantle. We combine existing models of cosmic ray (CR)-related desorption phenomena with a model of CR transport to accurately calculate the desorption rates in dark regions of molecular clouds. We show that different desorption mechanisms dominate for grains of different sizes and in different regions of the cloud. We then use these calculations to investigate a simple model of the growth of mantles, given a distribution of grain sizes. We find that modest variations of the desorption rate with grain size lead to a strong dependence of mantle thickness on grain size. Furthermore, we show that freeze-out is almost complete in the absence of an external ultraviolet (UV) field, even when photodesorption from CR-produced UV is taken into consideration. Even at gas densities of $10^4\, {\rm cm^{-3}}$, less than 30 per cent of the CO remain in the gas phase after 3 × 105 yr for standard values of the CR ionization rate.

A study of the estimation of the photovoltaic potential at the urban level in tropical complex terrain

This work considers photovoltaic solar energy as an alternative to promote the diversification of the energy matrix and contribute to improving energy access to the citizens of Medellin Metropolitan Area, Colombia, a tropical region that is conditioned by the topography and by the different urban morphology. The objective is to direct policies and strategies for more sustainable and resilient energy use in tropical cities on complex terrain through the production of energy from alternative renewable sources. To achieve this, we assess how much of the energy demand can be generated within the city, integrated into the urban morphology at the roofs of existing buildings including the effect of topography. We use meteorological information and power measurements from three experimental solar panels. We analyze the photovoltaic energy potential in Representative Urban Areas (RUA) and provide information relevant to the whole Valley's context to guide sustainable and resilient energy planning. One particular result is about the energy reduction factor due to cloudiness, which quantifies how energy would vary under the region's cloud conditions.

Magnetic Reconnection Within the Boundary Layer of a Magnetic Cloud in the Solar Wind

AbstractThe twisted local magnetic field at the front or rear regions of the magnetic clouds (MCs) associated with interplanetary coronal mass ejections (ICMEs) is often nearly opposite to the direction of the ambient interplanetary magnetic field. There is also observational evidence for magnetic reconnection (MR) outflows occurring within the boundary layers of MCs. In this study, a MR event located at the western flank of the MC occurring on October 3, 2000 is studied in detail. Both the large‐scale geometry of the helical MC and the MR outflow structure are scrutinized in a detailed multipoint study. The ICME sheath is of hybrid propagation‐expansion type. Here, the freshly reconnected open field lines are expected to slip slowly over the MC resulting in plasma mixing at the same time. As for MR, the current sheet geometry and the vertical motion of the outflow channel between ACE‐Geotail‐WIND spacecraft were carefully studied and tested. The main findings on MR include (a) first‐time observation of non‐Petschek‐type slow‐shock‐like discontinuities in the inflow regions; (b) observation of turbulent Hall magnetic field associated with a Lorentz‐force‐deflected electron jet; (c) acceleration of protons by reconnection electric field and their back‐scatter from the slow‐shock‐like discontinuity; (d) observation of relativistic electron near the MC inflow boundary/separatrix; these electron populations can presumably appear as a result of nonadiabatic acceleration, gradient B drift, and via acceleration in the electrostatic potential well associated with the Hall current system; and (e) observation of Doppler‐shifted ion‐acoustic and Langmuir waves in the MC inflow region.

Differences in the Ice Particle Shattering Impact on the CIP Measurements in the Stratiform Cloud Region and the Embedded Convection Region

Stratiform clouds with embedded convective cells is an important precipitation system. Precise knowledge of the cloud’s microphysical structure can be useful for the development of a numerical weather prediction model and precipitation enhancement. Airborne measurement is one of the important ways for determining the microphysical structure of clouds. However, cloud particle shattering during measurement poses a serious problem to the measured microphysical characterization of clouds. In order to study the different influences of the shattered ice particles on the standard cloud imaging probe (CIP) measurement in the stratiform cloud region and the convective cloud region, a time-variant threshold method to identify the shattered fragments is presented. After application of this algorithm, the shattered fragments were recognized and their impacts on the particle size distribution (PSD), particle number concentration and ice water content measurement were analyzed. It was found that the shattering effect on the PSD decreases with the increasing size of less than 400 μm, fluctuates between 400 μm and 1000 μm and slightly increases with the increasing size of larger than 1000 μm on average in a stratiform region and a convective region. However, the average ratio of PSD uncorrected to that corrected for shattering events using the presented algorithm in convective clouds is larger than that in the stratiform regions in the whole size, and nearly twice that in the size of less than 1000 μm. The measured number concentration can be overestimated by up to a factor of 3.9 on average in a stratiform region, while in a convective region, it is 7.7, nearly twice that of a stratiform region. The ice water content in a stratiform region can be overestimated by 29.5% on average, but by 60.7% in a convective region. These findings can be helpful for the cloud physics community to use the airborne CIP measurement data for numerical weather and climate models.

Chemical Complexity of Phosphorous-bearing Species in Various Regions of the Interstellar Medium

Abstract Phosphorus-related species are not known to be as omnipresent in space as hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers spotted very few P-bearing molecules in the interstellar medium and circumstellar envelopes. Limited discovery of the P-bearing species imposes severe constraints in modeling the P-chemistry. In this paper, we carry out extensive chemical models to follow the fate of P-bearing species in diffuse clouds, photon-dominated or photodissociation regions (PDRs), and hot cores/corinos. We notice a curious correlation between the abundances of PO and PN and atomic nitrogen. Since N atoms are more abundant in diffuse clouds and PDRs than in the hot core/corino region, PO/PN reflects <1 in diffuse clouds, ≪1 in PDRs, and >1 in the late warm-up evolutionary stage of the hot core/corino regions. During the end of the post-warm-up stage, we obtain PO/PN > 1 for hot core and <1 for its low-mass analog. We employ a radiative transfer model to investigate the transitions of some of the P-bearing species in diffuse cloud and hot core regions and estimate the line profiles. Our study estimates the required integration time to observe these transitions with ground-based and space-based telescopes. We also carry out quantum chemical computation of the infrared features of PH3, along with various impurities. We notice that SO2 overlaps with the PH3 bending-scissoring modes around ∼1000–1100 cm−1. We also find that the presence of CO2 can strongly influence the intensity of the stretching modes around ∼2400 cm−1 of PH3.

Refined UNet v3: Efficient end-to-end patch-wise network for cloud and shadow segmentation with multi-channel spectral features

Semantic segmentation is one of the essential prerequisites for computer vision tasks, but edge-precise segmentation stays challenging due to the potential lack of a proper model indicating the low-level relation between pixels. We have presented Refined UNet v2, a concatenation of a network backbone and a subsequent embedded conditional random field (CRF) layer, which coarsely performs pixel-wise classification and refines edges of segmentation regions in a one-stage way. However, the CRF layer of v2 employs a gray-scale global observation (image) to construct contrast-sensitive bilateral features, which is not able to achieve the desired performance on ambiguous edges. In addition, the naïve depth-wise Gaussian filter cannot always compute efficiently, especially for a longer-range message-passing step. To address the aforementioned issues, we upgrade the bilateral message-passing kernel and the efficient implementation of Gaussian filtering in the CRF layer in this paper, referred to as Refined UNet v3, which is able to effectively capture ambiguous edges and accelerate the message-passing procedure. Specifically, the inherited UNet is employed to coarsely locate cloud and shadow regions and the embedded CRF layer refines the edges of the forthcoming segmentation proposals. The multi-channel guided Gaussian filter is applied to the bilateral message-passing step, which improves detecting ambiguous edges that are hard for the gray-scale counterpart to identify, and fast Fourier transform-based (FFT-based) Gaussian filtering facilitates an efficient and potentially range-agnostic implementation. Furthermore, Refined UNet v3 is able to be extended to segmentation on multi-spectral datasets, and the corresponding refinement examination confirms the development of shadow retrieval. Experiments and corresponding results demonstrate that the proposed update can outperform its counterpart in terms of the detection of vague edges, shadow retrieval, and isolated redundant regions, and it is practically efficient in our TensorFlow implementation. The demo source code is available at https://github.com/92xianshen/refined-unet-v3.

Impact of high- and low-vorticity turbulence on cloud–environment mixing and cloud microphysics processes

Abstract. Turbulent mixing of dry air affects the evolution of the cloud droplet size spectrum via various mechanisms. In a turbulent cloud, high- and low-vorticity regions coexist, and inertial clustering of cloud droplets can occur in low-vorticity regions. The nonuniformity in the spatial distribution of the size and in the number of droplets, variable vertical velocity in vortical turbulent structures, and dilution by entrainment/mixing may result in spatial supersaturation variability, which affects the evolution of the cloud droplet size spectrum via condensation and evaporation processes. To untangle the processes involved in mixing phenomena, a 3D direct numerical simulation of turbulent mixing followed by droplet evaporation/condensation in a submeter-sized cubed domain consisting of a large number of droplets was performed in this study. The analysis focused on the thermodynamic and microphysical characteristics of the droplets and the flow in high- and low-vorticity regions. The impact of vorticity generation in turbulent flows on mixing and cloud microphysics is illustrated.

Photovoltaic power forecast based on satellite images considering effects of solar position

The rapid variation of clouds is the main factor that causes the fluctuation of photovoltaic power.11This work was supported by the National Key Research and Development Program of China under Grant 2019YFE0118400.The satellite images contain plenty of information about clouds, applicable for photovoltaic power forecast. However, in practice, two main factors obstruct the application of the satellite images: 1) the relatively low update frequency of the satellite images mismatches the photovoltaic power forecasting frequency, and 2) the cloud region that blocks the sunlight changes significantly with time. In this paper, a novel satellite image-based approach for photovoltaic power forecast is proposed to overcome these obstacles and achieve accurate forecasting results. Firstly, concerning the hourly updated satellite images, a nonlinear cloud movement forecasting model, considering the thickness and shape changes of the cloud, is presented to forecast the hourly variation of the images. Secondly, an active cloud region selection rule is derived based on the changing solar position to dynamically select the cloud region that blocks the concerned photovoltaic power station in a satellite image. Thirdly, a sequential cloud region selection algorithm is provided to estimate the intra-hour variation of the cloud to match the photovoltaic power forecasting frequency. Finally, the photovoltaic power is predicted using the XGBoost algorithm concerning the effects of the cloud and other influencing factors. Testing results show that the proposed method can achieve more accurate photovoltaic power forecasts using the low update frequency satellite images. Meanwhile, the superior performance compared with other benchmarks also verifies the effectiveness of considering cloud information obtained by the proposed method for photovoltaic power forecast.