Surface Convergence Research Articles

Constraining Regional Hydrological Sensitivity Over Tropical Oceans

AbstractRegional hydrological sensitivity (i.e., precipitation change per degree local surface warming) contributes substantially to the uncertainty in future precipitation projections over tropical oceans. Here, we investigate the sensitivity of relative precipitation (P*, precipitation divided by the basin average precipitation) to local sea surface temperature (SST) change by dissecting it into three components, namely the sensitivity of P* to relative SST (SSTrel, SST minus the tropical mean SST) changes, the sensitivity of P* to surface convergence changes, and the sensitivity of surface convergence to SST gradient changes. We show that the relationships between P* and SSTrel, and between P*, surface convergence, and SST gradients are largely constant during climate change. This allows us to constrain regional hydrological sensitivity based on present‐day SST‐precipitation relationships. The sensitivity of surface convergence to SST gradient changes is a main source of uncertainty in regional hydrological sensitivity and is likely underestimated in GCMs.

The Calm and Variable Inner Life of the Atlantic Intertropical Convergence Zone: The Relationship Between the Doldrums and Surface Convergence

AbstractThe doldrums are regions of low wind speeds and variable wind directions in the deep tropics that have been known for centuries. Although the doldrums are often associated with the Intertropical Convergence Zone (ITCZ), the exact relationship remains unclear. This study re‐examines the relationship between low‐level convergence and the Atlantic doldrums. By analyzing the frequency distribution of low wind speed events in reanalysis and buoy data, we show that the doldrums are largely confined between the edges of the ITCZ marked by enhanced surface convergence. While the region between the edges is a region of high time‐mean precipitation, low wind speed events occur in the absence of precipitation. Based on these results, we hypothesize that low wind speed events occur in regions of low level divergence rather than convergence.

On the role of small estuaries in retaining buoyant particles

Estuaries, as connectors between land and ocean, have complex interactions of river and tidal flows that affect the transport of buoyant materials like floating plastics, oil spills, organic matter, and larvae. This study investigates surface-trapped buoyant particle transport in estuaries by using idealized and realistic numerical simulations along with a theoretical model. While river discharge and estuarine exchange flow are usually expected to export buoyant particles to the ocean over subtidal timescales, this study reveals a ubiquitous physical transport mechanism that causes retention of buoyant particles in estuaries. Tidally varying surface convergence fronts affect the aggregation of buoyant particles, and the coupling between particle aggregation and oscillatory tidal currents leads to landward transport at subtidal timescales. Landward transport and retention of buoyant particles is greater in small estuaries, while large estuaries tend to export buoyant particles to the ocean. A dimensionless width parameter incorporating the tidal radian frequency and lateral velocity distinguishes small and large estuaries at a transitional value of around 1. Additionally, higher river flow tends to shift estuaries toward seaward transport and export of buoyant particles. These findings provide insights into understanding the distribution of buoyant materials in estuaries and predicting their fate in the land-sea exchange processes.

Surface properties and work function of ZrB2 single crystal

In this study, the surface convergence, surface energy, and work function on various crystal facets of ZrB2 were investigated by using the density functional theory calculations. Zr-terminated surface exhibits is more stable than the B-terminated surface. The electronic structure calculation reveals that ZrB2 exhibits metallic property, and the high density of states near the Fermi level is mainly composed of Zr-d and B-p orbitals. The work function values of the Zr-terminated (0001), (101¯0), (112¯0), and (112¯1) surfaces of ZrB2 are 4.52, 3.83, 4.00, and 2.56 eV, respectively. We found that the surface energy and work function of ZrB2 (112¯1) are the lowest compared to ZrB2 (0001), (101¯0) and (112¯0) surfaces, exhibiting good surface energy stability and providing excellent electron emission performance. This work provides valuable theoretical guidance for the exploration of ZrB2 as a novel cathode material for electron emission.

First principles study on heterogeneous interfaces of TiCu alloys through aluminum addition

This paper investigates the heterogeneous nucleation interface resulting from the addition of Al element to TiCu alloy, focusing on the essential phases Ti2Cu and TiCu. Employing first principles calculations, we explore the refinement mechanism of this interface. Initially, the lattice mismatch between Al/Ti2Cu and Al/TiCu interfaces is calculated to assess the potential for heterogeneous nucleation. Four distinct interfacial types are established following a surface convergence test. The adhesive work (Wad) and Interfacial energy (γ) are computed for each interface to ascertain their crystallization potential. Furthermore, the differential charge density (DCD) and projected density of states (PDOS) for the four interfacial types are determined to analyze bonding characteristics. Results indicate a mismatch degree of 4.09 % for Al (110)/Ti2Cu (110) and 5.29 % for Al (110)/TiCu (110). These values suggest a tendency to form a heterogeneous interface with a coherent lattice, primarily characterized by Cu-Al and Ti-Al metallic bonds. The Al-Ti2Cu interface exhibits a larger nucleation work of 2.23 J/m2 and a smaller interface energy of −53.007 J/m2. This study demonstrates that Al effectively serves as a heterogeneous nucleation center within the Ti2Cu/TiCu system, contributing to substrate phase refinement and strengthening the TiCu alloy. The optimization of these findings provides valuable insights into the alloy's microstructural evolution, facilitating the design and enhancement of advanced materials for diverse applications.

False Alarm Causes and Wind Field Sensitivity Analysis of a Severe Rainfall Event in the Guangdong-Hong Kong-Macao Greater Bay Area Urban Cluster

On May 11, 2022, despite the favorable upper and lower-level circulation patterns of the high-altitude trough, shear line, and southwest jet stream, the urban cluster of the Guangdong-Hong Kong-Macao Greater Bay Area experienced light to moderate rainfall, deviating significantly from the forecasted heavy rain and local heavy rainstorm. This study explores the reasons for false alarms and predictability using ground observation data, radar data, ECMWF-ERA5 reanalysis field data, and ECMWF and CMA-TRAMS forecast data. The results indicate that the warm and moist airflow transported by the low-level jet stream was intercepted by the upstream MCS (mesoscale convective system) along the coastal area of western Guangdong, and inadequate conditions of negative vorticity dynamics led to insufficient moisture, thermodynamic, and dynamic conditions over the urban cluster, preventing the triggering of heavy precipitation. In addition, the 700 hPa westerly flow guiding the airflow and the stable low-level shear line, coupled with surface convergence lines, influenced the northward or southward movement of MCSs along the coastal and inland regions of western Guangdong. The weak and discontinuous intensity of echoes in the upstream Zhaoqing region further hindered the influence of surrounding echoes on the urban cluster. Numerical forecast models ECMWF and CMA-TRAMS overestimated the 850 hPa windspeed and 925 hPa meridional windspeed, resulting in the forecasted urban cluster experiencing heavy rain. Sensitivity tests of wind fields indicate that the 850 hPa wind field information is more sensitive to precipitation in the urban cluster. In this process, weak signal correction can be achieved in strong precipitation forecasts using the distinct signal of lower 850 hPa water vapor flux divergence compared to 925 hPa. Therefore, in the future, when the Guangdong-Hong Kong-Macao Greater Bay Area encounters similar warm-sector heavy rainfall events, adjustments to model forecasts can be made using specific 850 hPa elements such as wind speed, water vapor flux divergence, or specific humidity to enhance predictive accuracy.

Tidal Intrusion Fronts, Surface Convergence, and Mixing in an Estuary with Complex Topography

Abstract Observations from a tidal estuary show that tidal intrusion fronts occur regularly during flood tides near topographic features including constrictions and bends. A realistic model is used to study the generation of these fronts and their influence on stratification and mixing in the estuary. At the constriction, flow separation occurs on both sides of the jet flow downstream of the narrow opening, leading to sharp lateral salinity gradients and baroclinic secondary circulation. A tidal intrusion front, with a V-shaped convergence zone on the surface, is generated by the interaction between secondary circulation and the jet flow. Stratification is created at the front due to the straining of lateral salinity gradients by secondary circulation. Though stratification is expected to suppress turbulence, strong turbulent mixing is found near the surface front. The intense mixing is attributed to enhanced vertical shear due to both frontal baroclinicity and the twisting of lateral shear by secondary circulation. In the bend, flow separation occurs along the inner bank, resulting in lateral salinity gradients, secondary circulation, frontogenesis, and enhanced mixing near the front. In contrast to the V-shaped front at the constriction, an oblique linear surface convergence front occurs in the bend, which resembles a one-sided tidal intrusion front. Moreover, in addition to baroclinicity, channel curvature also affects secondary circulation, frontogenesis, and mixing in the bend. Overall in the estuary, the near-surface mixing associated with tidal intrusion fronts during flood tides is similar in magnitude to bottom boundary layer mixing that occurs primarily during ebbs.

The Structure and Dynamics of an Estuarine Tidal Intrusion Front

AbstractTidal intrusion fronts are surface convergences that occur at constrictions in estuaries during the flood tide, separating incoming higher‐salinity water from lower‐salinity, stratified estuarine water. Previous observations of tidal intrusion fronts describe a V‐shaped planform, with the apex of the V pointing into the estuary, however the significance of this structure has not been previously explained. Observations near the mouth of the James River estuary during the flood tide reveal the development of a quasi‐steady, V‐shaped front. Considering a reference frame oriented normal to the front, the velocity and density structure are consistent with gravity‐current dynamics, but the oblique orientation of the front relative to the impinging flow indicates strong, along‐front shear, which results from vorticity produced by flow separation at the lateral boundaries as well as topographic torque from upstream. The combination of convergence and along‐front shear leads to enhanced mixing, as revealed by acoustic backscatter images of shear instability and persistent subcritical gradient Richardson number in the frontal zone. Oblique fronts such as this tidal intrusion front are common features of estuaries, and they play an important role in vertical exchange due to subduction and mixing of surface water.

Drifter Deployment Strategies to Determine Lagrangian Surface Convergence in Submesoscale Flows

Abstract Surface convergence in the ocean is associated with accumulation of buoyant pollutants as well as with vertical transport that is important to biological activity. Such surface convergence regions are marked by a high dilation rate, i.e., the finite time Lagrangian average divergence. Dilation-rate observations are most easily derived from the change of the area encompassed by a drifter swarm over time. The technological advances that have enabled the deployment of large numbers of drifters in a single experiment have raised new questions about optimal deployment strategies for extracting dilation-rate information with acceptable accuracy and as much spatial coverage as possible. Using a submesoscale-resolving operational model of the Mediterranean Sea, we analyze synthetic trajectories of drifter polygons to evaluate the impact of the number of drifters and their initial separation on the accuracy of the resulting dilation-rate estimates. The results confirm that estimates improve as the circumradius of the polygon decreases and as more drifters are added, but with only a marginal improvement for drifter polygons containing more than four drifters. Moreover, GPS positions obtained from drifters in the ocean are subject to uncertainty on the order of 2–50 m, and when this uncertainty is taken into account, an optimal circumradius can be identified that balances uncertainty from position measurements with that from the area approximations. Significance Statement Locating regions of convergence over a finite time interval on the ocean surface can help in pollution mitigation, locating biological hotspots, and even search-and-rescue operations. Finite time convergence can be quantified using the dilation rate, but it is hard to measure in the ocean. Hence, we present a method to estimate the dilation rate using trajectories of drifters, which are instruments widely used by oceanographers during field experiments to understand the local flow features. We show that even though the drifter-based dilation rates are prone to error as a result of a finite number of drifters and limited GPS accuracy, the estimates locate around 90% of the strongest convergent features in our model.

The inner life of the Atlantic Intertropical Convergence Zone

AbstractThe Intertropical Convergence Zone (ITCZ) is a central component of the atmospheric general circulation, but remarkably little is known about the dynamical and thermodynamical structure of the convergence zone itself. This is true even for the structure of the low‐level convergence that gives the ITCZ its name. Following on from the major international field campaigns in the 1960s and 1970s, we performed extensive atmospheric profiling of the Atlantic ITCZ during a ship‐based measurement campaign aboard the research vessel SONNE in summer 2021. Combining data collected during our north–south crossing of the ITCZ with reanalysis data shows the ITCZ to be a meridionally extended region of intense precipitation, with enhanced surface convergence at its edges rather than in the center. Based on the location of these edges, we construct a composite view of the structure of the Atlantic ITCZ. The ITCZ, far from being simply a region of enhanced deep convection, has a rich inner life, that is, a rich dynamical and thermodynamic structure that changes throughout the course of the year, and has a northern edge that differs systematically from the southern edge.

Ubiquitous Sea Surface Temperature Anomalies Increase Spatial Heterogeneity of Trade Wind Cloudiness on Daily Time Scale

Abstract The impact of weak submeso- to mesoscale SST anomalies on daily averaged trade cumulus cloudiness is investigated using satellite observations that have been validated against shipboard measurements from the Atlantic Tradewind Ocean–Atmosphere Mesoscale Interaction Campaign (ATOMIC). Daily spatial SST anomalies are identified from GOES–POES Blended SST analysis within a 10° × 10° region during January and February 2020. Daily averaged cloud fraction and 10-m neutral wind from satellite observations and reanalysis are composited over the identified SST features, using a common coordinate system based on the near-surface background wind directions. Composites of satellite cloud fraction show a statistically significant increase of cloudiness over the SST warm core with a reduction of cloudiness away from it. These responses are largely the same but with opposite signs over SST cold anomalies, suggesting that spatial heterogeneity in SST can locally imprint on daily cloud fraction. Composites of daily 10-m wind speed and wind convergence anomalies from both satellite and reanalysis show that surface wind speed is increased over SST warm anomalies, implying enhanced turbulence over warmer SSTs. Correspondingly, the surface convergence anomalies in these composites are located around the maximum downwind SST gradient, offset downwind from the cloudiness anomalies. These results indicate that the response of daily cloudiness to these SST anomalies is more likely generated by spatial variability of surface-driven turbulence and surface fluxes rather than that of surface or boundary layer convergence.

The Impact of Surface Drag on the Structure and Evolution of Surface Boundaries Associated with Tornadogenesis in Simulated Supercells

Abstract Surface boundaries in supercells have been suspected of being important in the arrangement and concentration of vorticity for the development and intensification of tornadoes, but there has been little attention given to the effects of the underlying surface roughness on their behavior. This study investigates the impact of surface drag on the structure and evolution of these boundaries, their associated distribution of near-surface vorticity, and tornadogenesis and maintenance. Comparisons between idealized simulations without and with drag introduced in the mature stage of the storm prior to tornadogenesis reveal that the inclusion of surface drag substantially alters the low-level structure, particularly with respect to the number, location, and intensity of surface convergence boundaries. Substantial drag-generated horizontal vorticity induces rotor structures near the surface associated with the convergence boundaries in both the forward and rear flanks of the storm. Stretching of horizontal vorticity and subsequent tilting into the vertical along the convergence boundaries lead to elongated positive vertical vorticity sheets on the ascending branch of the rotors and the opposite on the descending branch. The larger near-surface pressure deficit associated with the faster development of the near-surface cyclone when drag is active creates a downward dynamic vertical pressure gradient force that suppresses vertical growth, leading to a weaker and wider tornado detached from the surrounding convergence boundaries. A conceptual model of the low-level structure of the tornadic supercell is presented that focuses on the contribution of surface drag, with the aim of adding more insight and complexity to previous conceptual models. Significance Statement Tornado development is sensitive to near-surface processes, including those associated with front-like boundaries between regions of airflow within the parent storm. However, observations and theory are insufficient to understand these phenomena, and numerical simulation remains vital. In our simulations, we find that a change in a parameter that controls how much the near-surface winds are reduced by friction (or drag) can substantially alter the storm behavior and tornado potential. We investigate how surface drag affects the low-level storm structure, the distribution of regions of near-surface rotation, and the development of tornadoes within the simulation. Our results provide insight into the role of surface drag and lead to an improved conceptual model of the near-surface structure of a tornadic storm.

Concentration and condition of American lobster postlarvae in small‐scale convergences

AbstractInvertebrate larvae are often abundant in the surface ocean, which plays a key role in their dispersal and connectivity. Pelagic microhabitats characterized by small‐scale hydrographic variability are complex and ubiquitous in the coastal ocean, but their study is challenging, and they have been largely neglected in meroplankton ecology. Surface convergences, i.e., surface microhabitats featuring convergent horizontal currents, may aggregate the last larval stage of the American lobster and could provide shelter and food for Stage IV postlarvae and thus enhance their condition. We tested these hypotheses by conducting a series of cruises in the southwestern Gulf of Maine in summer 2021, sampling 15 paired sets of potential convergences and off‐convergence unstructured habitat. We measured postlarval abundance, surface hydrography, acoustic backscatter, and circulation. Experiments and image analysis compared condition, color, and morphology of postlarvae sampled inside and outside potential convergences. Potential convergences varied in near‐surface hydrographic patterns, with most displaying consistency among two transects and diverse patterns in salinity and temperature (e.g., across‐convergence gradients with equal or different signs). While the highest postlarval abundances were found in convergences, abundance patterns on and off convergences were not consistent, and another analysis indicated higher abundance in convergences than in a 7‐year untargeted surface ocean data set. Experiments indicated no survivorship differences among convergence and non‐convergence individuals at two temperatures, while image analyses revealed differences in color and size. Physical measurements and qualitative neuston community analyses indicated substantial heterogeneity among potential convergences. Our results reinforce that small‐scale heterogeneities are highly variable but important to the ecology of meroplankton, including the pelagic and neustonic habitats where lobster postlarvae are abundant.

Application of multi-source data in a tornado process in Jiangsu province

This paper analyzes the weather background and triggering mechanism before the occurrence of an EF3 tornado on 14 May 2021, in southern Jiangsu, using multi-source data. Results show that 1) the tornado occurred in the warm and humid area inside the low-level shear line and the inverted trough at the surface, the southeast wind field to the east of the surface convergence line and high value area of water vapor flux on the left side of low altitude jet axis exit zone. 2) The intensity of the heavy rainfall supercell storm was strengthened after entering the Taihu Lake, and mesocyclones were detected with decreasing heights and increasing shear strengths which leading to the formation of the tornado parent storm. Tornado vortex storm bottom height dropped to 0.3km, the shear value increased to 169.1 × 10−3 s-1, strong echoes above 60 dBZ reached to the ground, the difference between the lowest elevation Radial velocity (LLDV) and the maximum Radial velocity (MXDV) reached up to the largest value when tornado occurred. 3) The strong convergence of the ground and the enhancement of mesoscale frontal zone resulted in the strong development of thunderstorm cells. The deep rear inflow behind the heavy precipitation supercell storm passed through the stratiform cloud area and produced strong updraft due to the convergence of wind direction and wind speed. The updrafts generated vertical vorticity under the influence of wind shear, which was further stretched in the middle layer of the troposphere to form the core of the tornado. 4) The flat underlying surface, abundant water vapor, lake surface thermal boundary, and strong wind convergence on the east bank of Taihu Lake provided favorable conditions for the occurrence of the tornado. The centers of the mesocyclones in the lower and middle layers were close to each other in the horizontal direction, which provided stable and vertical updrafts for the mesocyclones and strengthened the suction effect of the mesocyclones on the low-level vortices, facilitating the formation of the tornado.

A Quantification of Heat Storage Change-Based Evaporation Behavior in Middle–Large-Sized Lakes in the Inland of the Tibetan Plateau and Their Temporal and Spatial Variations

A large number of different-sized lakes exist in the inland area of the Tibetan Plateau (TP), which are examples of the important connection between the atmosphere and hydrosphere through the analysis of lake surface convergence and evaporation processes. The evaporation level changes that occur in middle–large-sized lakes (surface area > 50 km2) in the area directly influence the regional mass and energy balance values, atmospheric boundary layer heat and humidity structures, and weather processes occurring in the lower-reach areas. The studies conducted in the literature at present, concerning lake evaporation processes, generally overlook the differences in lake heat storage behavior due to the reduced amount of data in the literature concerning lake bathymetry. According to the in situ bathymetric data obtained for 68 middle–large-sized lakes in the inner basin of the TP, in this study, we calculated their heat storage (G) change values by using the different vertical-depth water-temperature-change integral method, and we established a regression equation for the heat storage and lake surface net radiation values for 68 lakes. The evaporation rates of 134 middle–large-sized lakes larger than 50 km2 in the inland are of the TP were calculated by obtaining the G regression result and adopting it into the Penman model, as well as estimating the evaporation losses of theses 134 lakes from 2002 to 2018. The result shows that the annual average evaporation rate for these lakes is 927.39 mm/year, with an insignificant upward trend (0.10 mm/year). This method achieved good accuracy compared with the Bowen ratio method, which estimates the evaporation rate during the ice-free season, with a high correlation coefficient (R) value of 0.95 and least root mean square error (RMSE) value of 61 mm. The annual mean evaporation rate can be divided into the southern and northern lake groups along a 34°N line with a difference of 314.41 mm/year. The annual average evaporation volume of these lakes was 25.02 km3 and showed an upward trend of 0.35 km3/year. Among them, the annual average evaporation volume contribution ratio of level-1 lakes (50 km2 ≤ lake’s area < 100 km2, 61 lakes) was 14.04%, showing an upward trend, and the contribution of level-3 lakes (lake’s area ≥ 500 km2, 10 lakes) was 41.50%, showing a downward trend. There were no obvious changes in the level-2 lakes (100 km2 ≤ lake’s area < 500 km2, 63 lakes), which maintained at the same level in approximately 44.46%. Air temperature is the most important factor affecting the evaporation rate of lakes, while the lake surface area is the main factor affecting lake evaporation volume. Our study, considering the actual lake heat storage value, provides a useful reference for further improving lake water budget balance values and watershed hydrologic features in the inland closed lakes located in the TP.

Modulation effects of submarine internal wake waves on free surface divergence field

Disturbances of a submarine in a stratified flow stimulate an infinite mode of internal waves with multiple dispersion relationships. The surface convergence and divergence field are then modulated by such trailing waves, affecting the spatial distribution of microscale waves and leaving traces that are easily detected by Synthetic Aperture Radar. The present modified model combines the source-caused internal waves theory with the wind-waves spectrum model and coupling wave components of the full wave systems decomposed by the Fourier series method based on the second-order multi-directional irregular waves interactions theory. The effects of maximum Brunt–Vaisala frequency amplitude and depth, internal wave modes, submarine dive depth and velocity, wind speed, and wind direction are discussed in this study. It is shown that after the appearance of mode 0, the wake waves have an appreciable effect on the modulation of the free surface wind-wave field. However, this effect is not fixed to manifest as an enhancement of the free surface convergence or divergence field intensity. The free surface field has the maximum divergence intensity amplitude under the downwind sailing condition when the submarine is sailing at low speed. At high speed, the maximum divergence intensity amplitude is at an angle of 30° between the sailing direction and the wind direction, while the minimum divergence intensity is downwind.

Formation Mechanisms of the “5·31” Record-Breaking Extreme Heavy Rainfall Process in South China in 2021

Based on the fifth-generation European Center for Medium-Range Weather Forecasts reanalysis data (ERA5), the real-time observation data from weather stations, and the radar products in Guangdong Province, we analyze the precipitation properties and formation mechanisms of the “5·31” extreme heavy rainfall process with record-breaking 3-h accumulated rainfall in South China during 2021. The results show that the extreme heavy rainfall process is caused by the joint actions of weather systems such as a weak upper-level short-wave trough, a surface stationary front, and a low-level southwesterly jet. Before the heavy precipitation process, there is large precipitable water content and deep warm clouds, which provides a potential for the occurrence and development of the heavy rainfall process in Longhua Town of Longmen County and its surrounding areas. Simultaneously, the low-level southwesterly jet provides abundant warm-wet water vapor for the heavy rainfall area. The vertical atmospheric environmental conditions, such as strong horizontal temperature gradient, high convective available potential energy, high-temperature difference between 850 hPa and 500 hPa, and low convective inhibition, maintain for a long duration in the heavy rainfall area, which are favorable for the occurrence and development of high-efficiency convective precipitation caused by water vapor condensation due to the uplift of low-level warm-wet airflows. The combined effects of the enhanced low-level southwesterly airflow, the stationary front, the mesoscale surface convergence line generated by cold pool outflows, the terrain influence, and the train effect of the precipitation echoes make heavy precipitation near Longhua last longer and stronger than other areas, leading to the extreme heavy rainfall with the record-breaking 3-h accumulated rainfall in Longhua.

Numerical Study on the Genesis of Incipient Vortex of a Tropical Storm over the South China Sea. Part II Sensitivity of Sea Surface Sensible Heating

The experiments are conducted to determine the impact of the anomalous surface sensible heating (SH) from the South China Sea (SCS) on the incipient vortex of the storm Mindulle (2010) formation by using the Weather Research and Forecasting (WRF) model, including the control-run with and the sensitivity-run without such heating. Significant impact is seen, with the incipient vortex failing to generate without the related SH. Based on the atmospheric thermal adaption theory, the outputs reveal that the genesis of the incipient vortex can be divided into the formation stage and the strengthen stage. At the formation stage, the surface SH favoured the enhancement of the surface convergence. Thus strong westerlies and southerlies along with the topography forcing constrain updrafts over the Luzon Island. The non-uniform condensation latent heating (LH) released by the vertical motion creates the cyclonic vorticity in the lower atmosphere, which was conducive to the incipient vortex formation. At the strengthen stage, the more intense LH due to the enhanced ascending motions mainly contributed to cyclonic vorticity generation. Therefore, the incipient vortex continuously strengthened and attained to the intensity of tropical storm. The simulation results illustrate that the development of the Mindulle (2010) is a “bottom-up” process.

Comparative analysis of two impact systems in a snowstorm in Dalian

In this study, the two influence systems in a snowstorm that occurred in January 2021 are analyzed using conventional observation, intensive snowfall observation data and NCEP-FNL 0.25°×0.25° analysis data. The results show that, first, the westerly trough combined with the surface convergence line and the sub cold front produces strong snowfall in the southern part of the Liaodong Peninsula, then the strong cold air moves southward into the cold flow snowfall. When the westerly trough system has a large water vapor flux, deep wet layer and strong ascending motion, the surface is accompanied by the obvious warm tongue in southwest Dalian and cold pad in the inland, and there is obvious frontogenesis process, with heavy snowfall. The intensity of cold advection is closely related to the amount of snowfall: the stronger the cold advections, the greater the snowfall will be. The combination of mid-upper-level divergence with negative vorticity and convergence with positive vorticity near the ground is also an advantage for heavy snowfall. Cold flow snowfall exhibits strong local characteristics. Compared with the westerly trough system, the cold flow snowfall has a smaller influence area and intensity. The combination of strong ascending motion and wet area is also one of the focuses of cold flow snowfall forecast in Dalian.

First principles analysis on the nucleation interface of La2O3[formula omitted]/NbC[formula omitted

Niobium carbide (NbC), as a reinforcement phase, has been applied in the alloy to enhance its service life. It is important to refine the NbC in the alloy. In this paper, the nucleation interface of La2O3(11̅0)/NbC(11̅0) was analyzed and the mechanism of NbC refined by La2O3 was investigated by first principles. Firstly, the mismatch degree of La2O3/NbC interface was calculated. According to the surface convergence, the interface models of La2O3/NbC were established. Then, the combined work and energy of the La2O3/NbC interfaces were calculated. Finally, the interface bonding properties were analyzed by the charge density, differential charge density and projected density of states. The results show that the mismatch degree of La2O3(11̅0)/NbC(11̅0) interface is smallest, which is 7.1%. La2O3(11̅0) and NbC(11̅0) lattice planes were selected to establish four kinds of interface models, which are named as O-Hollow, O-Interface, OLa-Hollow and OLa-Interface in turn. The adhesive work of O-Hollow interface is the largest, which is 0.995J/m2. And its interface energy is the smallest, which is 3.055J/m2. Meanwhile, the bonding types of O-Hollow interface are mainly a combination of La-C and Nb-O bonds. In summary, La2O3 can be as a moderate effective heterogeneous nucleus of NbC, then NbC be refined by La2O3.