Surface Observations Research Articles

Observation of large spin-polarized Fermi surface of a magnetically proximitized semiconductor quantum well

The magnetic proximity effect (MPE) attracts much attention as a promising way for introducing ferromagnetism into a nonmagnetic electron-transport channel. Although the range of MPE is generally limited to the interface, it is extended to several tens of nm in high-quality semiconductor bilayers consisting of a nonmagnetic quantum well (QW) and an underlying ferromagnetic semiconductor (FMS) layer. To elucidate the mechanism of this long-range MPE, it is essential to observe the magnetically proximitized electronic structure of the nonmagnetic semiconductor. Here, by investigating the Shubnikov - de Haas oscillations in nonmagnetic n-type InAs QW / FMS (Ga,Fe)Sb bilayers, we successfully observe the spin-polarized Fermi surface of the InAs QW. The spontaneous spin-splitting energy in the conduction band of the InAs QW reaches 18 meV when applying a negative gate voltage. This large and gate-tunable spin-polarized Fermi surface of a magnetically proximitized InAs QW provides an ideal platform for novel spintronic and topological devices.

Seasonally dependent increases in subweekly temperature variability over Southern Hemisphere landmasses detected in multiple reanalyses

Abstract. The inter-dataset agreement of trends in subweekly near-surface (850 hPa) temperature variability over Southern Hemisphere midlatitude land masses is assessed among 12 global atmospheric reanalysis datasets. A comparison of the climatological temperature variance and dominant sources and sinks of the variance reveals that, except for NCEP-NCAR (R1) and NCEP-DOE (R2), there is a relatively good agreement for their magnitudes and spatial distributions during the satellite era (1980–2022), which indicates that the key features of subweekly variability are sufficiently well represented. A good agreement is noted for the positive trends found in subweekly variability over the satellite era affecting South Africa in September–October–November (SON) and South America in December–January–February (DJF). Although there is agreement in most of the reanalyses concerning the positive trend affecting Australia in SON, this has not yet emerged from the noise associated with interannual variability when considering only the satellite era. It is significant, however, when the period is extended (1954–2022) or limited to the most recent decades (1990–2022). The trends are explained primarily by a more efficient generation of subweekly temperature variance by horizontal temperature advection. This generation is also identified as a source of biases among the datasets. The trends are found to be reproduced even in those reanalyses that do not assimilate satellite data (JRA-55C) or that assimilate surface observations only (ERA-20C, 20CRv2c, and 20CRv3).

Surface—subsurface grain structure relationships

Relationships between surface and subsurface grain structure are studied using a large three-dimensional (3D) microstructural dataset of a nickel-base superalloy Inconel 718. Comparative analyses of microstructural features were performed from both an orthographic, two-dimensional (2D) perspective and a full-3D one to underscore their distinctions on a grain-by-grain basis for a given surface microstructure. A positive correlation between grain size and the number of nearest neighbors of surface grains was observed; however, considerable variability exists per grain. We also present a detailed investigation of 3D surface grain structure and highlight the limitations of 2D surface grain characterizations. Several features of subsurface grain structure, including out-of-plane grain boundary inclination angle, surface-to-subsurface feature proximity, and subsurface grain boundary interface geometry are characterized. The analysis reveals a wide array of highly non-columnar subsurface grain structures with many points at the free surface being closer to grain boundaries and triple junctions beneath the surface than in the surface observation plane. Repeating these analyses for a synthetic dataset without twins reveals that our findings apply to other polycrystalline materials with near-equiaxed grains and limited texture.

Cr/CrN coating effect on the fatigue crack nucleation period of Ti-6Al-4V alloy

Ti-6Al-4V alloy is applied in the production of jet engines and other aeronautical components. The Cr/CrN multilayer coating improves the wear, corrosion and oxidation properties of titanium alloys. However, the influence of hard coatings on fatigue properties needs to be investigated to ensure structural integrity. The present work aims to estimate the fatigue crack nucleation and propagation periods of a Cr/CrN coated Ti-6Al-4V alloy at high-stress and low-stress levels. The material used in this work was the Ti-6Al-4V alloy with an equiaxed microstructure and a yield strength of 1000 MPa. The coating was deposited through the DC sputtering method with 8 bilayers of chromium (Cr) and chromium nitride (CrN), achieving 16 layers and a total thickness of about 5 micrometers. Axial fatigue tests were performed at room temperature for the uncoated and coated titanium alloy. Scanning electron microscopy observation of the fracture surfaces showed that the cracks nucleated at the coating and propagated without deflections to the substrate. The Paris law was applied to estimate the fatigue crack propagation period of the Ti-6Al-4V alloy substrate, considering an initial crack with the size of the coating thickness. The results showed that the crack propagation period for the coated samples represented more than 90% of the fatigue life at the high-stress level of 1000 MPa, while it accounts only for about 1% of the fatigue life at the low-stress level of 700 MPa. The fatigue life debit of the Cr/CrN coated material with 8 bilayers and 5 micrometers can be attributed to the significant crack nucleation period reduction due to the brittle layers of CrN compared to the uncoated Ti-6Al-4V alloy. The detrimental coating effect was more substantial at the high-cycle fatigue regime when the crack nucleation period accounts for the majority of the fatigue life.

TemproNet: A transformer-based deep learning model for seawater temperature prediction

Accurate prediction of seawater temperature is crucial for meteorological model understanding and climate change assessment. This study proposes TempreNet, a deep learning model based on a transformer and convolutional neural network, to accurately predict subsurface seawater temperature using satellite observations in the South China Sea. TemproNet uses multivariate sea surface observations such as sea level anomaly (SLA), sea surface temperature (SST), and sea surface wind (SSW) as model inputs, which employs a hierarchical transformer encoder to extract the multi-scale feature, uses a lightweight convolutional decoder to predict seawater temperature. We train and validate the model using the CMEMS temperature dataset and compare its accuracy with Attention-Unet, LightGMB, and ANN. Experimental results show that TemproNet has significantly outperformed other models with RMSE and R2 of 0.52 °C and 0.83 in a 32-layer temperature profile prediction task over 200 m in the South China Sea. In addition, we fully demonstrate the error of our model in space, in time, and at different depths, showing the efficiency and stability of our model. The input sensitivity analysis showed that SST contributed more to predicting shallow water temperature, while SLA significantly impacted the prediction of mid-deep water temperature. The results of this study provide an innovative and reliable solution for seawater temperature prediction and have important implications for meteorological model understanding and climate change assessment.

Study of the wear process in an experimental simulation of a fuselage/runway rubbing contact

In this work, the authors tackle the problem of laboratory simulation of frictional contact in wheels-up emergency landing conditions. To design a novel tribometer simulating the contact between an aircraft structure and a runway, one must carry two complementary main tasks: the understanding of the underlying physical mechanisms and the scaling up of the in-lab results to the scale of interest. The authors propose to progress on the first task by conducting exploratory work using existing resources. Their contribution consists of a multi-scale methodology to reconstruct the wear process in a tribological system within wheels-up emergency landing conditions. This could provide guidance for safer aircraft and runway design. The study falls within the framework of three-body tribology. The proposed multi-scale characterisation methodology is made up of four steps. After describing the whole tribological system, its mechanical response is measured and analysed. This measurement is complemented by surface observations and physicochemical analyses. Finally, all the measurements and observations are discussed to come across a phenomenological wear scenario that revealed friction and wear as system responses with the key role of the third body.

The Characteristics of Tropical Cyclones and Associated High Winds in Shanghai from 2005 to 2020

The characteristics of 21 tropical cyclones (TCs) and associated high winds in Shanghai from 2005 to 2020 are analyzed based on the TC best track data, surface observations, and ERA5 reanalysis dataset. Results indicate that 95% of the TCs causing high winds in Shanghai were generated during July to September, and located to the south of Shanghai for ~80% of the impact time. Divided into four categories according to tracks, the TCs show significant discrepancies in genesis month and location, intensity, size, and duration. The findings of high winds in Shanghai highlight the combination effect of TC intensity, track, and the distance between TCs and Shanghai normalized by TC size (NDSH-TC). The maximum 10‐min sustained (Vmax) and extreme 3‐s wind speeds (Vex) in Shanghai only increase slightly with TC intensity, due to the fact that the stronger TCs are usually farther away from Shanghai. The Vmax and Vex differ in response to different TC tracks and reach the maximum value under TCs moving northward across the land west of Shanghai and the sea east of Shanghai, respectively. The urban and coastal wind speeds are the smallest and the largest respectively, indicating that the largest underlying surface roughness is associated with the most rapid urban construction. The wind speeds under the influence of TCs in four quadrants of Shanghai also present different variations with the NDSH-TC. Additionally, the wind direction in Shanghai is regularly related to the relative position between the TC center and Shanghai. A case study combined with TC In‐Fa (2106) verified the validity of the conclusions, which can provide a reference for TC forecasters to make more accurate wind field predictions.

Local scale air quality impacts in the Los Angeles Basin from increased port activity during 2021 supply chain disruptions

Satellite data, surface observations, and a chemical transport model are used to estimate the impacts of increased port activity during 2021 supply chain disruptions on NO2 and PM2.5 in Los Angeles, California.

RaSRNet: An End-to-End Relation-Aware Semantic Reasoning Network for Change Detection in Optical Remote Sensing Images

Optical Remote sensing images (RSIs) are used in surface observation, and one of the most interesting research topics is change detection (CD). The internal problem of RSIs, including multi-scales changed objects and cluttered background, still deserve attention. Existing methods make great efforts to solve this problem but inevitably miss detection, which affects the model performance. To address this dilemma, this article proposes a Relation-aware Semantic Reasoning Network (RaSRNet) in an end-to-end manner to pop-out change objects in RSIs, where the key point is to perceive contextual semantic information. The relation-aware module in RaSRNet combats the lack of contextual information caused by the limited receptive field of the general convolutional layer, which facilitates all-around changed object detection. The multi-level semantic reasoning encoder-decoder backbone in RaSRNet extracts and reconstructs pixel semantic information, alleviates the interference of background noise and improves the integrity recognition of changed objects. In addition, the decoder backend undertakes two semantic segmentation branches, and introduces a semantic reasoning loss between the two branches to infer pixel semantic categories, which provides more accurate semantic features for the CD. Extensive experiments are conducted on the three public RSIs CD datasets, and the results demonstrate that the proposed RaSR-Net can accurately locate changed objects, which consistently outperforms the state-of-the-art CD competitors.

The vortex structure and near‐surface winds of Typhoon Faxai (2019) during landfall. Part I: Observational analysis

AbstractThis two‐part study presents a detailed analysis of (a) the vortex structure, (b) the inner core planetary boundary layer (PBL) wind profile, and (c) the overland surface winds of Typhoon Faxai (2019) during landfall observationally (Part I) and in high‐resolution Weather Research and Forecasting model simulations (Part II). Part I presents a comprehensive observational analysis of (a), (b), and (c) of Typhoon Faxai (2019) based on radar dual‐Doppler analysis and spatially dense surface wind observations over the Kanto region of Japan. An empirical model for the wind reduction factor is proposed and validated with surface observations and radar velocity–azimuth display analyses at Narita and Haneda airports, both of which were affected by the passage of Faxai's inner core. Two distinct PBL jets associated with the inner rain band and the eyewall were observed over Narita Airport, which was located to the right of Faxai's track. Based on the empirical model of , it is found that the maximum surface wind speed observed at Narita Airport was caused by the peak of due to a strong PBL jet associated with the eyewall located as close as 0.3 km from the ground. In addition, the wind swath analysis shows that a large area far inland on the right side of Faxai's track experienced strong surface 10‐min winds due to the combination of the passage of the eyewall PBL jet and the small surface roughness length around agricultural land such as paddy fields and farm fields.

Impact of Adjusted and Nonadjusted Surface Observations on the Cold Season Performance of the Canadian Precipitation Analysis (CaPA) System

Abstract The Canadian Precipitation Analysis System (CaPA) is an operational system that uses a combination of weather gauge and ground-based radar measurements together with short-term forecasts from a numerical weather model to provide near-real-time estimates of 6- and 24-h precipitation amounts. During the winter season, many gauge measurements are rejected by the CaPA quality control process because of the wind-induced undercatch for solid precipitation. The goal of this study is to improve the precipitation estimates over central Canada during the winter seasons from 2019 to 2022. Two approaches were tested. First, the quality control procedure in CaPA has been relaxed to increase the number of surface observations assimilated. Second, the automatic solid precipitation measurements were adjusted using a universal transfer function to compensate for the undercatch problem. Although increasing the wind speed threshold resulted in lower amounts and worse biases in frequency, the overall precipitation estimates are improved as the equitable threat score is improved because of a substantial decrease in the false alarm ratio, which compensates the degradation of the probability of detection. The increase of solid precipitation amounts using a transfer function improves the biases in both frequency and amounts and the probability of detection for all precipitation thresholds. However, the false alarm ratio deteriorates for large thresholds. The statistics vary from year to year, but an overall improvement is demonstrated by increasing the number of stations and adjusting the solid precipitation amounts for wind speed undercatch.

Comparative analysis of corneal parameters between DMEK and UT‐DSAEK eyes in 3‐year follow‐up

Aims/Purpose: The aim of the study was to provide a comparative analysis of corneal parameter changes compared to their preoperative values between Descemet membrane endothelial keratoplasty (DMEK) and ultrathin Descemet stripping automated endothelial keratoplasty (UT‐DSAEK) patients.Methods: The study included 27 eyes after UT‐DSAEK and 34 eyes after DMEK. Best corrected visual acuity (BCVA), endothelial cell count (ECC), central corneal thickness (CCT), mean keratometry (MK), mean astigmatism (MA), astigmatism asymmetry (AA) and higher order aberrations (HOAs) were assessed at baseline and 1, 3, 6, 12, 24 and 36 months after the surgery.Results: Patients after DMEK had significantly better BCVA than patients after UT‐DSAEK (mean 0.9 vs. 0.6 at 24th month, respectively, p = 0.002 and 0.9 vs. 0.7 at 36th month of follow‐up, respectively, p = 0.001). From the 3rd month post operation, ECC was higher in the DMEK eyes than in the UT‐DSAEK eyes (p = 0.01). However, the groups did not differ in this parameter at 24th and 36th month of observation. In a bivariate analysis that was adjusted for age, DMEK was associated with a smaller decrease in posterior MK at the 1‐month (β = −0.49, p = 0.002), 3‐month (β = −0.50, p < 0.001), 6‐month (β = −0.58, p < 0.001) and 12‐month (β = −0.49, p < 0.001) follow‐up visits. Significant differences in MK, AA and HOA values of the posterior surface of the cornea at 12th, 24th and 36th month of observation and MA of the posterior surface of the cornea at 24th month of observation were found as well, with no differences in the total values of these parameters. Accordingly, no significant differences in changes in MA, AA or HOAs compared to the baseline values were identified between the eyes after DMEK and UT‐DSAEK at any follow‐up time point.Conclusions: UT‐DSAEK seem to be an easier and safer technique than DMEK while maintaining similar outcomes regarding irregular astigmatism and total keratometry values. Nevertheless, DMEK produces significantly better BCVA outcomes.

The Effect of Varnishing and Soaking on Formability of the AW-5052-H28 Aluminium Alloy Sheets in Erichsen Cupping Test

This article presents the results of experimental tests on the stretch-forming ability of 0.21-mm-thick AW-5052-H28 aluminium alloy sheets used in the production of pull-off cups. Erichsen test under various tribological conditions (dry friction, lubrication with graphite lubricant) was used to assess the sheet formability. Punches with a various diameter of the spherical end (8 and 20 mm) were used in the tests. The effect of soaking conditions and varnishing variants on the value of Erichsen indices IE and IE11 was investigated. The sheets were soaked for 13 minutes at various temperatures: 185°C, 190°C and 200°C. In test conditions without lubrication, the lowest value of the IE index = 3.3 mm was observed for sheets in as-received state and for samples after soaking. However, the highest values of the Erichsen index in tests without lubrication were measured for varnished samples and repeatedly soaked. The tests conducted under lubrication conditions with graphite grease revealed usually higher values of the IE index compared to testing conditions without the use of grease. The values of the IE11 index were approximately twice lower than the IE indices. Observation of the bulge surface revealed a smooth surface, which means that the material is characterised by a fine-grained microstructure.

Time-resolved TEM observation of CeO2 surface with electrostatic sub-framing system

Time-resolved TEM observation of CeO2 surface with electrostatic sub-framing system

The study of testosterone and tacrolimus roles on gastrocnemius muscle following experimental sciatic nerve injury in rats

Peripheral nerve damage is a critical disorder causing disability of locomotion. The aim of the study was to clarify the effects of testosterone and tacrolimus on the gastrocnemius muscle following sciatic injury. The study was done on 20 rats (n = 5 in each group) whose left sciatic nerve was crushed for 10 s. The sham group (S) of animals received no medicine; the testosterone group (Tes) received testosterone (5 mg/kg, s.c.); the tacrolimus group (Tac): received tacrolimus (5 mg/kg, p.o.); the testosterone and tacrolimus group (Tes+Tac) received testosterone (5 mg/kg, s.c.) and tacrolimus (5 mg/kg, p.o.) daily for four weeks. The gastrocnemius was assessed by gross observation of the plantar surface of paws; the pelvic limb mass muscle and the muscle diameter ratio of the left pelvic limb to the right one by ultrasonography. The gastrocnemius muscle index (GMI) of the left and right pelvic limb, muscle colour, and pathologic changes were also studied. Pathology study of the gastrocnemius included fatty infiltration, muscle atrophy, presence of inflammatory cells and fibrosis formation. Heel redness and swelling were seen in group Tac. No significant difference was found in the GMI between the Tes and S groups (P > 0.01); its value was higher than in the Tes+Tac and Tac groups (P < 0.01). One rat in group Tes had fatty infiltration grade II. Inflammatory cells were grade I in group Tes but fibrosis formation was grade I in group Tes+Tac. Our results show that tacrolimus and testosterone administration may shorten sciatic nerve regeneration time. Testosterone may diminish gastrocnemius muscle atrophy after sciatic nerve crush.

SA‐RelayGANs: A Novel Framework for the Characterization of Complex Hydrological Structures Based on GANs and Self‐Attention Mechanism

AbstractIncreased availability and quality of surface and subsurface observations provide the chance to improve the perception of hydrological phenomena. An important factor that hinders our understanding of hydrological structures is the characterization of heterogeneous patterns with continuous attributes inside the structures (e.g., porosity, permeability, fluid saturation, etc.). Unlike categorical attributes, continuous attributes convey more realistic characteristics but require more computational resources to characterize such complex earth systems. In this work, we propose a novel deep learning approach for the characterization of complex hydrological realism with continuous attributes based on generative adversarial networks (GANs) and self‐attention mechanism, named SA‐RelayGANs. To address the complexity of heterogeneous hydrological structures, we divide the modeling process into two stages: facies construction stage and property reconstruction stage. In the first stage, we employ an improved GAN with self‐attention mechanism to construct the heterogeneous structures while adhering to hard conditioning constraints. In the second stage, we utilize another GAN with an attribute enhancement term to reconstruct realizations based on the constructed structures and observations. SA‐RelayGANs can successfully predict the statistical distributions of heterogeneous structures with continuous attributes by using limited observations. This study highlights the effectiveness of using GANs to characterize the heterogeneous patterns of hydrological realism and the application over large geoscience fields.

The hydraulic network of the pre-Hispanic city of Tiwanaku (Bolivia): New insights from the integration of canal morphology, hydrogeological and palaeoenvironmental data

Water management enabled the development of ancient societies allowing them to ensure agropastoral production and manufacturing activities. In the Andes, near the shore of Lake Titicaca, the city of Tiwanaku (Bolivia) is one of the largest pre-Hispanic urban centres in South America. Abrupt climate changes in the high-altitude Altiplano during the late Holocene likely forced the population to develop water management strategies. So far, knowledge concerning the existence of a water network around the city of Tiwanaku is limited to hypotheses derived from surface and aerial observations. In this study, geoscience techniques (morphology, geophysics, sedimentology and chronostratigraphy) helped to reconstruct the canals' morphology and their flow dynamics, along with their chronology of operation in a context of hydroclimatic change. Two ca. 30 m large canals bypassing the monumental core and supplied by a shallow water table and multiple tributaries, connected the agricultural and the urban areas. The structure and organization of the network testify to an elaborate knowledge of the local hydrology by the former builders of the city. It ensured water supply and flood management in relation to the extreme intra- and inter-annual variability of precipitations in the central Andes. The palaeogeographical and landscape reconstruction demonstrates that canals were set from natural features during the early Late Formative period (200 BCE to 200 CE) during a wet period likely for water resource management needs. During the Tiwanaku state (before 800 CE), the filling of the canal network with soil and sediment suggests a major change in its use, and possibly its partial abandonment, during a major restructuration of the site, in a period of increased regional precipitation.

16-channel snapshot multispectral imaging based on integrated Fabry Perot microcavity array

<sec>By designing and fabricating a narrow-band Fabry-Perot multi-beam interference spectroscopic microcavity array, and integrating it with a visible light detector focal plane array, we demonstrate a small compact multispectral imaging detector. The micro-cavity filter array with 4×4 basic repeating units and a total of 2048×2048 pixels is obtained on a quartz substrate by the four-fractal combination lithograph-etching process. Then the micro miniatured multispectral imaging detector is formed by fitting with the detector chip. The depth and precision of the etching will determine the distribution and offset of the central wavelength of the narrowband spectral channel respectively. The results show that the etching rate of reactive ion is (3.6 ± 0.2) Å/s, and the process is stable and controllable. Due to the different etching depths, the basic repeating unit forms 16 different levels of steps, and the process achieves the design expectation well.</sec><sec>The results are obtained as follows: the response spectrum peak of the microcavity array sample varies from 520 to 680 nm, the free spectrum range is 160 nm, the full width at the half-peak is less than 10 nm, the transmittance is about 70%, the relative half-width of the transmittance peak at 590 nm is 1.19%, and the waveform coefficient is 2.78. A 16-channel multispectral camera is constructed by using the optical micro-precision assembly device to realize the precise alignment and the fitting of the micro-cavity filter array and the image sensor. Xenon lamp and monochromator are used as tunable wavelength monochromatic cooperative light source to detect the effect of 16-channel snapshot multispectral imaging on a pixel scale. The results show that the multispectral imaging detector has 16 different narrow-band response spectra. The characteristic spectrum of the target can be clearly distinguished by spectral channel.</sec><sec>When imaging the target with known spectral characteristics, for a certain frame of multi-spectral image, selecting a suitable spectral channel can eliminate the background in the field of view through image subtraction and improve the contrast of the target. In the dark room condition, we take the LED light source with center wavelength varying in a range between 528 and 589 nm as the target (the wavelength coincides with the working wavelength of the spectral channel), and effectively suppress the background through the spectral differential intensity subtraction, which can improve the accuracy and sensitivity of the target capture. The 16-channel snapshot multi-spectral imaging detector based on integrated Fabry-Perot microcavity array has the advantages of small size, high integration and strong environmental adaptability, and is expected to play a role in realizing the real-time detection of weak moving targets, auxiliary diagnosis of skin surface observation, and high dynamic range imaging of target observation under backlight conditions.</sec>

Energy Consumption Characteristics Study of Surface Meteorological Observation Station in North and South China

Surface meteorological observation is one of the most important sources of primary data for the meteorological sector and are crucial to the accuracy of weather forecasting. China’s meteorological authorities have built a dense network of surface observation stations, which require a considerable amount of electrical energy to keep the network running normally. There has been a lack of analytical studies dedicated to the energy consumption of surface meteorological observation stations domestically and internationally. This paper selects measured energy consumption data of 4 surface meteorological observation stations in two typical provinces (autonomous regions) in the north and south China over the past two years, and proposes, for the first time, to use the average power of the surface meteorological observation station, adopts the electrical energy consumption calculation method, carries out energy consumption calculation and analysis by month, sub-region and season, derives the characteristics of energy consumption changes of the surface meteorological observation station, and proposes energy saving and consumption reduction measures.

Numerical investigation of impinging plume under vacuum and realistic nozzle outlet condition

During a lunar module landing, the gas extended from the engine nozzle impinges on the lunar surface. A recirculation bubble could form beneath the surface shock wave, which alters the flow pattern close to the surface, thus affecting the surface soil transportation process. This study conducted numerical simulations to investigate the flow characteristics, formation mechanism, and effects of this recirculation bubble on surface soil erosion using direct simulation Monte Carlo method or solving the Navier–Stokes equations. It is found that during the descent, the recirculation zone under the surface shock wave first disappears and then reappears. The shock wave systems in the plume at different lander heights is analyzed, revealing that the formation of the recirculation bubble can be attributed to the total pressure loss due to gas crossing different wave structures. When the lander descends to a close proximity to the lunar surface, the recirculation bubble can even expand into the nozzle. Furthermore, this study investigated the effects of the recirculation bubble on lunar soil transportation by a gas–solid two-phase solver. It is shown that the recirculation bubble at low landing altitude will entrain the lunar dusts and result in a high ejection angle of the latter, thus aggravating the obstruction of surface observation for the safe landing.