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The bow-and-arrow Mesoscale Convective System (MCS) has a unique structure with two convective lines resembling the shape of an archer’s bow and arrow. These MCSs and their arrow convection (located behind the MCS leading line) can produce hazardous winds and flooding extending over hundreds of kilometers, which are often poorly predicted in operational forecasts. This study examines the dynamics of a bow-and-arrow MCS observed over the Yangtze–Huai Plains of China, with a focus on the arrow convection provided. The analysis utilized backward trajectories and Lagrangian vertical momentum budgets to simulations employing the WRF‐ARW and CM1 models. Cells within the arrow in the WRF-ARW simulations of the MCS were elevated, initially forming as convectively unstable air within the low-level jet (LLJ), which gently ascended over the cold pool and converged with the MCS’s mesoscale convective vortex (MCV) at higher altitudes. The subsequent ascent in these cells was enhanced by dynamic pressure forcing due to the updraft being within a layer where the vertical shear changed with height due to the superposition of the LLJ and the MCV. These dynamic forcings initially played a larger role in the ascent than the parcel’s buoyancy. These findings were bolstered by idealized simulations employing the CM1 model. These results illustrate a challenge for accurately forecasting bow-and-arrow MCSs as the updraft magnitude depends on dynamical forcing associated with the interaction between vertical shear associated with the environment and due to convectively generated circulations.

In flood hazard estimation via the analytic hierarchy process (AHP), using the pixel as the basic unit might lead to accuracy relying on the optimal weighting criteria. To this end, considering the sub-watershed as the basic unit is new. In this study, taking the Chaohu Basin in Anhui Province, China, as a study case, the accuracy of the sensitivity of the pixel-based and sub-watershed-based AHP models influenced by weighting criteria was compared. There were 48 judgment ma- trixes defined, following the same order of importance of the involved indicators. Validation ground truthing is constructed by the extracted flooded regions from GF-3 images. As weighting criteria changed, the results indicated that the pixel-based AHP fluctuated significantly, while the correct ratio and fit ratio derived by the sub-watershed-based AHP could improve by >35% and >5%, respectively, over the pixel-based-AHP. It indicated that the sub-watershed-based AHP has an advantage in relying less on in situ weighting criteria than the pixel-based AHP.

The mesoscale vortex (MV) is an important rain-producing system. In this study, the reanalysis data and satellite precipitation products are used to classify MVs into three categories: mesoscale convective vortex (MCV), mesoscale stratiform vortex (MSV), and mesoscale dry vortex (MDV). Then, these three categories of midlevel MVs in China from 2007 to 2016 are investigated. A total of 21 053 MVs are obtained. Most MVs form in the northwest of parent convection, and 45% of MVs generate secondary convection. The Tibetan Plateau is the main MV source region. Steered by the westerlies, MVs mainly move eastward. MCV is active in summer, MDV in winter, and MSV in spring and autumn. MCV diurnal variations are closely related to local topography, and MDVs mainly form around midnight. Composite analyses show that MCVs form near the high-value center of convective available potential energy at the development stage of parent convection. The composite MCV forms near the low pressure trough and the thermal ridge at 500 hPa, and a low-level jet exists to the south of the MCV center. At the initiation and maturity stages of MCV, strong convergence and divergence respectively exist at low levels and 400 hPa. The vortex circulation mainly locates near 500 hPa. Above the vortex is a warm core associated with the latent heat release, and below is a cold anomaly related to the cold pool. In the downshear region, there is strong low-level convergence and ascending motion, higher humidity, and greater latent heat release, which favor the formation of secondary convection.

Motuo and Naqu are two typical regions of the Tibetan Plateau with different geographical locations and climate regimes. These differences may lead to discrepancies in the raindrop size distributions (DSDs) and precipitation microphysical processes between the two regions. This paper investigates discrepancies in the DSDs using disdrometer data obtained during the rainy season in Motuo and Naqu. The DSD characteristics are studied under five different rainfall rate categories and two precipitation types (stratiform and convective). For the total data sets, the number concentrations of drops with diameters D > 0.6 (D < 0.6) mm are higher (lower) in Naqu than in Motuo. The fitted normalized gamma distributions of the averaged DSDs for the five rainfall rate categories show that Naqu has a larger (lower) mass-weighted mean diameter Dm (normalized intercept parameter, log10Nw) than does Motuo. The difference in Dm between Naqu and Motuo increases with the rainfall rate. Convective clusters in Naqu could be identified as continental-like, while convective precipitation in Motuo could be classified as maritime-like. The relationships between the shape factor μ and slope parameter Λ of the gamma distribution model, the radar reflectivity Z and the rainfall rate R are also derived. Furthermore, the possible causative mechanism for the notable DSD variation between the two regions during the rainy season is illustrated using reanalysis data and automated weather station observations. Cold rain processes are mainly responsible for the low concentrations of large drops observed in Naqu, whereas warm rain prevails in Motuo, producing abundant small drops.

A sustained heavy rainfall event occurred over the Sichuan basin in southwest China during 10–18 August 2020, showing pronounced diurnal rainfall variations with nighttime peak and afternoon minimum values, except on the first day. Results show that the westward extension of the anomalously strong western Pacific subtropical high was conducive to the maintenance of a southerly low-level jet (LLJ) in and to the southeast of the basin, which favored continuous water vapor transport and abnormally high precipitable water in the basin. The diurnal cycle of rainfall over the basin was closely related to the periodic oscillation of the LLJ in both wind speed and direction that was caused by the combination of inertial oscillation and terrain thermal forcing. The nocturnally enhanced rainfall was produced by moist convection mostly initiated during the evening hours over the southwest part of the basin where high convective available potential energy with moister near-surface moist air was present. The convective initiation took place as cold air from either previous precipitating clouds from the western Sichuan Plateau or a larger-scale northerly flow met a warm and humid current from the south. It was the slantwise lifting of the warm, moist airflow above the cold air, often facilitated by southwest vortices and quasi-geostrophic ascent, that released the convective instability and produced heavy rainfall.

A multiscale observational analysis of a nocturnal extreme rainfall event that occurred at Changtu in Northeast China on 14 July 2017 is performed using global analysis, automated surface observations, Doppler radar, rawinsonde, and disdrometer data. Results show that the large-scale environment was characterized by high convective available potential energy and precipitable water, moderate convective inhibition, and a southwesterly low-level jet (LLJ) capped by an inversion layer. The first and subsequent convective cells developed along a quasi-stationary surface convergence zone in a convection-void region of a previously dissipated meso-α-scale convective line. Continuous convective initiation through backbuilding at the western end and the subsequent merging of eastward-moving convective cells led to the formation of a near-zonally oriented meso-β-scale rainband, with reflectivity exceeding 45 dBZ (i.e., convective core intensity). This quasi-stationary rainband was maintained along the convergence zone by the LLJ of warm moist air, aided by local topographical lifting and convectively generated outflows. A maximum hourly rainfall amount of 96 mm occurred during 0200–0300 Beijing standard time as individual convective cores with a melting layer of >55 dBZ reflectivity moved across Changtu with little intermittency. The extreme-rain-producing stage was characterized with near-saturated vertical columns, and rapid number concentration increases of all raindrop sizes. It is concluded that the formation of the meso-β-scale rainband with continuous convective backbuilding, and the subsequent echo-training of convective cores with growing intensity and width as well as significant fallouts of frozen particles accounted for the generation of this extreme rainfall event. This extreme event was enhanced by local topography and the formation of a mesovortex of 20–30 km in diameter.

This paper reviews the major progress on development of the science and prediction of heavy rainfall over China since the beginning of the reform and opening-up of new China (roughly between 1980 and 2019). The progress of research on the physical mechanisms of heavy rainfall over China is summarized from three perspectives: 1) the relevant synoptic weather systems, 2) heavy rainfall in major sub-regions of China, and 3) heavy rainfall induced by typhoons. The development and application of forecasting techniques for heavy rainfall are summarized in terms of numerical weather prediction techniques and objective forecasting methods. Greatly aided by the rapid progress in meteorological observing technology and substantial improvement in electronic computing, studies of heavy rainfall in China have advanced to investigating the evolution of heavy-rain-producing storms and observational analysis of the cloud microphysical features. A deeper and more systematic understanding of the synoptic systems of importance to the production of heavy rainfall has also been developed. Operational forecast of heavy rainfall in China has changed from subjective weather event forecasts to a combination of both subjective and objective quantitative precipitation forecasts, and is now advancing toward probabilistic quantitative precipitation forecasts with the provision of forecast uncertainty information.

This paper presented a high-temperature furnace with double electric stove wires for the test of high-temperature creep rupture, adopted the 5 mm electric stove wire in diameter, and the wires are made up of the working stove wire and the alternate stove wire. When the tester system detects the working stove wire is fractured, it will automatically and quickly switch the power supply circuit from the working stove wire to the alternate stove wire. Then the alternate stove wire starts to heat to keep the high-temperature furnace working, reducing the loss caused by the interruption of the test on account of the fractured stove wire. Experimental result indicates that the high-temperature furnace with double electric stove wires can solve the problem that when the stove wire is fractured, the test is difficult to proceed for a long time and high-temperature creep rupture test with the classical high-temperature furnace. Besides, the 5 mm in diameter electric stove wire can also meet the temperature control on the ultra-high-temperature (such as 1200 °C) Creep test.

An 8-yr (i.e., 2008–15) climatology of the spatiotemporal characteristics of hail events in China and their associated environmental conditions are examined using hail observations, L-band rawinsondes, and global reanalysis data. A total of 1003 hail events with maximum hail diameter (MHD) of greater than 5 mm are selected and then sorted into three hail-size bins. Hail events with the largest MHD bin correspond to the median vertical wind shear in the lowest 6-km layer (SHR6) of 21.6 m s−1, precipitable water (PW) of 34.8 mm, and convective available potential energy (CAPE) of 2192 J kg−1. Hail with different MHD bins share similar freezing-level heights (FLHs) of about 4000 m. The thickness of the hail growth zone is thinner for hail events with the largest MHD bin. Hail events with different MHD bins display seasonal variations associated with the summer monsoon; that is, the hail season starts in South China in spring and then shifts to North China in summer. Larger hail is mainly observed during the spring in South China before monsoon onset in the presence of an upper-level jet and a low-level southwesterly flow accounting for large SHR6 and PW. In contrast, smaller-MHD hailstorms occur mainly during the summer in North China when surface heating is high and the low-level southerly flow shifts northward with pronounced baroclinicity providing large CAPE and PW, moderate SHR6, and low FLH. Environmental CAPE and SHR6 for large hailstones in China are comparable in magnitude to those in the United States but larger than those in some European countries.

Devastating tornadoes in China have received growing attention in recent years, but little is known about their formation, structure, and evolution on the tornadic scale. Most of these tornadoes develop within the East Asian monsoon regime, in an environment quite different from tornadoes in the U.S. In this study, we used an idealized, high-resolution (25-m grid spacing) numerical simulation to investigate the deadly EF4 (Enhanced Fujita scale category 4) tornado that occurred on 23 June 2016 and claimed 99 lives in Yancheng, Jiangsu Province. A tornadic supercell developed in the simulation that had striking similarities to radar observations. The violent tornado in Funing County was reproduced, exceeding EF4 (74 m s–1), consistent with the on-site damage survey. It was accompanied by a funnel cloud that extended to the surface, and exhibited a double-helix vorticity structure. The signal of tornado genesis was found first at the cloud base in the pressure perturbation field, and then developed both upward and downward in terms of maximum vertical velocity overlapping with the intense vertical vorticity centers. The tornado’s demise was found to accompany strong downdrafts overlapping with the intense vorticity centers. One of the interesting findings of this work is that a violent surface vortex was able to be generated and maintained, even though the simulation employed a free-slip lower boundary condition. The success of this simulation, despite using an idealized numerical approach, provides a means to investigate more historical tornadoes in China.

Mesoscale vortices, which appear at middle and lower levels of rainstorms, are cyclonic circulations with a size ranging from tens of kilometers to several hundred kilometers. Mesoscale vortices often have close relationships with convective activities. The ERA-Interim dataset and an automatic vortex-searching method were used to identify the mesoscale vortices occurring over China in 2015 and their basic characteristics were analyzed. The mesoscale vortices are divided into three categories: mesoscale convective vortices, mesoscale stratiform vortices, and mesoscale dry vortices. The mesoscale convective vortices have the largest intensity, size, and duration, whereas the mesoscale dry vortices have the smallest. Mesoscale convective vortices are able to form in any direction of the parent mesoscale convective system, although the secondary convection tends to appear to the southeast of the parent vortices. The mesoscale vortices tend to generate in the transition area between high and low altitudes. The leeward side of the Tibetan Plateau is the main source region of mesoscale vortices in China. Most of vortices are generated at midday and midnight. The activities of mesoscale convective vortices and mesoscale stratiform vortices peak in summer, whereas those of the mesoscale dry vortices peak in winter.

Lightning mapping with radio frequency location systems plays a more and more important role in understanding the mechanism of lightning discharges during thunderstorms. Here we present a comprehensive analysis of the electromagnetic field measurements and 3-dimensional (3D) mapping of two coincident lightning flashes: an upward positive flash (+CG) with long preceding upward negative leader (UNL), which was triggered by the in-cloud (IC) activity of a nearby downward negative flash (−CG). The flashes were mapped with a low frequency (LF) mapping array deployed near Duke University and during a late-spring thunderstorm passing a plain area. The 3D LF maps show that the IC activity related to the −CG moved negative charge away from the location overhead the UNL. The UNL developed firstly upward for about 2 km and then extended horizontally for about 8 km at that height with a mean speed of 6.2 × 105 m/s. The channel line charge density of the UNL was estimated to range from −542 μC/m to −9.21 mC/m with a mean value of −3.46 mC/m. The total positive charge transferred from the cloud to ground by the +CG flash was estimated to be about 5.8C. From the 3D maps, we inferred that the IC activity relating to the −CG flash which moved negative charge away from overhead region of the UNL could be responsible for the UNL initiation. And the existence of extensive lower positive charges further favored the long horizontal propagation of the UNL inside the cloud.

The decision-making procedures of the meteorological service concerning the extreme thunderstorm in Beijing on July 21, 2012, were simulated and analyzed in a scenario using a Bayesian decision-support model. A thorough analysis of the decision-making process during that terrible thunderstorm demonstrated that a decision-support model can be used to make optimal decisions regarding uncertainty problems in the meteorological service supported by current meteorological technology and data resources, e.g., the mesoscale numeric weather prediction (NWP) system and observational data. Using NWP grid data, we assessed the flooding and debris flow risks on that day, and the high risks were clearly apparent. Consulting the historical flooding records, we also recognized the high thunderstorm risk that day even though the predicted precipitation was reported as 100–200 mm in most areas. Because of the low probability of extreme precipitation indicated by climate data, the posteriori probability estimated by the Bayesian model was only 23.1 %. For the differences between expected losses in a disaster and a non-disaster state, issuing a prediction for a non-disaster state could obviously lead to greater expected losses than predicting a disaster state. Therefore, it would be advisable to provide a disaster state prediction and take a correspondingly worst case scenario outlook in the meteorological service, which was the optimal decision-making strategy at that time. This study reveals that (1) the objective promotion of an emergency response level corresponding to a severe weather warning is recommended to realize the advantages of a worst case scenario prediction, even if the forecasters underestimate the devastating impact of the weather, and thus, it can obviously relieve unnecessary pressure on forecasters, and (2) the public should be provided with uncertainty information along with severe weather forecasts and warnings so, as the end users of meteorological services, they can make better informed decisions.

This study aims to investigate the influence of friction in an automatic ball balancing system. A precise kinetic model is presented for a commercial optical disk drive with an automatic ball balancer. The equations of motion, with the effects of frictional and driving forces taken into account, are derived based on this model. To investigate the influence of friction on the dynamic behavior of the system, different friction coefficients and initial ball positions were considered and the equations were solved numerically with a commercial software package, Matlab. The results do not only indicate that friction prevents the ball from reaching the desired positions to automatically balance the system but also reveal that the balls can be set into oscillation in steady state. Finally, experiments are designed and carried out to verify the theoretical analysis.

We perform a theoretical evaluation of the strain field in a p-channel transistor with silicongermanium (Si1−yGey) stressors in the source and drain regions. The strain field comprises a lateral compressive strain component and a vertical tensile strain component. The lateral strain component is larger in magnitude and more uniformly distributed as compared to the vertical strain component. The impact of transistor design parameters, such as the Ge mole fraction y in the stressors, the spacing L between stressors, the stressor depth, and the raised stressor height, on the strain field are investigated. Hole mobility enhancement larger than 30% is achievable wth L = 50 nm and y = 0.15. More aggressive mobility enhancement targets may be achievable by reducing the stressor spacing and employing a stressor with a larger lattice mismatch with the Si channel.

Size-resolved aerosol number and mass concentrations and the mixing ratios of O 3 and various trace gases were continuously measured at an urban station before and during the Beijing Olympic and Paralympic Games (5 June to 22 September, 2008). 23 new particle formation (NPF) events were identified; these usually were associated with changes in wind direction and/or rising concentrations of gas-phase precursors or after precipitation events. Most of the NPF events started in the morning and continued to noon as particles in the nucleation mode grew into the Aitken mode. From noon to midnight, the aerosols grew into the accumulation mode through condensation and coagulation. Ozone showed a gradual rise starting around 10:00 local time, reached its peak around 15:00 and then declined as the organics increased. The dominant new particle species were organics (40–75% of PM 1 ) and sulphate; nitrate and ammonium were more minor contributors. DOI: 10.1111/j.1600-0889.2011.00533.x

The strain field in the silicon channel of a metal–oxide–semiconductor transistor with silicon–germanium (Si1−yGey) source and drain regions was evaluated using a finite-element method. The physical origin of the vertical and lateral strain components in the transistor channel region was explained. The magnitude and distribution of the strain components, and their dependence on device design parameters such as the spacing L between the Si1−yGey stressors and the Ge mole fraction y in the stressors were investigated. Reducing the interstressor spacing L or increasing the Ge mole fraction y in the stressors increases the magnitude of the vertical tensile strain and the lateral compressive strain in the portion of the channel region where the inversion charge resides. This is beneficial for improving the hole mobility in p-channel metal–oxide–semiconductor transistors.