Weakening Stage Research Articles

Study on energy damage evolution of multi-flaw sandstone with different flaw lengths

Flaws are common in rock mass engineering. The length and number of flaws have a great influence on the stability of rock mass. In this paper, uniaxial compression tests were carried out on six kinds of multi-flawed sandstone with different flaw lengths. Based on damage mechanics and energy theory, the mechanical variation characteristics, total strain energy, elastic strain energy and dissipation energy evolution law of multi-flawed sandstone with different flaw lengths under uniaxial action were analyzed. Based on the energy dissipation, the damage variable is redefined, and the sandstone damage process is divided into three stages: the initial damage weakening stage I, the damage stability stage II, and the damage accelerated development stage III. Using this conclusion, considering the initial compaction weakening stage of rock samples, Duncan model is introduced to modify the constitutive model of equivalent strain hypothesis. The results show that the theoretical curve is in good agreement with the experimental curve, indicating that the damage constitutive model can accurately reflect the damage and failure process of multi-flaw rock samples with different flaw lengths.

On the Size Discrepancies between Datasets from China Meteorological Administration and Joint Typhoon Warning Center for the Northwestern Pacific Tropical Cyclones

This study analyzes the Northwestern Pacific tropical cyclone (TC) size difference between the China Meteorological Administration (CMA) dataset and the Joint Typhoon Warning Center (JTWC) dataset. The TC size is defined by the near-surface 34-knot wind radius (R34). Although there is a high correlation (correlation coefficient of 0.71) between CMA and JTWC R34 values, significant discrepancies are still found between them. The JTWC tends to report larger R34 values than the CMA for large-sized TCs, while the trend is reversed for compact TCs. Despite spatial distribution discrepancies, both datasets exhibit significant similarity (spatial correlation coefficient of 0.61), particularly in latitudinal distribution; higher R34 values are observed near 25° N. An investigation of key parameters affecting R34 estimations shows that the discrepancies in R34 values between the two agencies’ estimates of TC size are primarily influenced by the size itself and latitude. There is a high correlation between R34 difference and R34 values, with a high correlation of up to 0.58 with the JTWC’s R34 values. There is also a significant correlation between R34 difference and latitude, with a correlation coefficient of 0.26 in both the CMA and JTWC datasets. Case studies of Typhoons “Danas” and “Maysak” confirm distinct characteristics in R34 estimations during different development stages, with the JTWC capturing TC intensification better, while the CMA underestimates TC size during rapid growth phases. During the weakening stage of the TC, both agencies accurately estimate the R34 values. These findings contribute valuable insights into the discrepancies and characteristics of R34 datasets, informing the selection and utilization of data for typhoon research and forecasting.

An Observational Study on the Rapid Intensification of Typhoon Chanthu (2021) near the Complex Terrain of Taiwan

Abstract Intensification of Typhoon Chanthu (2021) along the eastern coast of Taiwan was accompanied by pronounced asymmetry in eyewall convection dominated by wavenumber-1 features, as observed by a dense radar network in Taiwan. The maximum wind speed at 3-km altitude, retrieved from radar observations, exhibited a rapid increase of approximately 18 m s−1 within an 11-h period during the intensification stage, followed by a significant decrease of approximately 19 m s−1 within 8 h during the weakening stage. Namely, Chanthu underwent both rapid intensification (RI) and rapid weakening (RW) within the 24-h analyzed period, posing challenges for intensity forecasts. During the intensifying stages, the region of maximum eyewall convection asymmetry underwent a sudden cyclonic rotation from the eastern to the northern semicircle immediately after the initiation of terrain-induced boundary inflow from the south of the typhoon, as observed by surface station data. This abrupt rotation of eyewall asymmetry exhibited better agreement with radar-derived vertical wind shear (VWS) than that derived from global reanalysis data. This finding suggests that the meso-β-scale VWS is more representative for tropical cyclones than meso-α-scale VWS when the terrain-induced forcing predominates in the environmental conditions. Further examination of the radar-derived VWS indicated that the VWS profile pattern provided a more favorable environment for typhoon intensification. In summary, Chanthu’s RI was influenced by the three factors: 1) terrain-induced boundary inflow from the south of the typhoon, observed by surface station data; 2) low-level flow pointing toward the upshear-left direction; and 3) weak upper-level VWS. Significance Statement Tropical cyclone intensity change has been an important issue for both real-time operation and research, but the influence of terrain on intensity change has not been fully understood. Typhoon Chanthu (2021) underwent a significant intensity change near the complex terrain of Taiwan that was observed by a dense radar network. This study analyzes 24 h of radar and weather station data to investigate Chanthu’s evolution. The analyses indicate that the complex terrain affected the low-level flow near the TC. Such a change in flow pattern provided additional boundary inflow and a relatively favorable vertical wind shear pattern for TC intensification.

Assessment of two grainsize methods for peat sediments and their paleoenvironmental significance: the Yueliangwan Peatland in northeast Asia

Grainsize is an important indicator in paleoenvironmental research. Over the past few decades, different pretreatment methods have been proposed for grainsize determination of peat sediments. Assessing the reliability of the grainsize measurements is critical to ensure the paleoenvironmental significance represented by different grainsize components. In this study, using peat sediments from the Yueliangwan peatland in northeast Asia, the effects of two pretreatment methods on grainsize measurement were compared. It was found that these two pretreatment methods on peat sediments produced grainsize features with totally different parameters and distribution characteristics. Grainsize method 1, which used a hydrogen peroxide water bath treatment, did not reflect accurate results for grainsize in peat sediments. Grainsize method 2, which used muffle furnace combustion, does reflect the true results because the organic matter, such as plant residues, spores and pollen, is totally removed. The presence of this stubborn organic matter in peat samples greatly disturbs the accuracy of grainsize measurements, and the reliability of grainsize measurements can be affected by the presence of stubborn organic matter. Based on the grainsize grade-standard deviation analysis using method 2, the East Asian Winter Monsoon evolutionary history in northeast Asia during the Little Ice Age (1300–1750 CE) was reconstructed and divided into three stages: the strengthening stage (1346–1425 CE), the strongest stage (1425–1525 CE) and the weakening stage (1525–1725 CE).

Effect of compressive stress on corrosion protection performance of phytic acid conversion coating on carbon steel

As an environmentally friendly organic coating, phytic acid conversion coating (PACC) has been widely used for the protection of metals. In this study, the evolution of PACC on carbon steel under compressive stress is studied via multiple electrochemical and morphological approaches. Interestingly, electrochemical results show that a strengthening effect on PACC can be found when proper stress is applied, which is much distinct from the rule for oxide passive films. The proper compressive stress can effectively improve the corrosion protection performance of PACC, thus enhancing the corrosion resistance of carbon steel to chloride attack. As the applied stress increases, a detrimental effect is confirmed for compressive stress on the PACC layer. The protective PACC layer with the highest protection efficiency and coating adhesion is obtained at 100 MPa. In combination with the observations of SEM/XPS, a three-stage model is proposed to illustrate the evolution of PACC under compressive stress. In the natural stage, numerous cracks form in the PACC layer. In the strengthening stage, the PACC layer is compacted and the cracks in it are greatly healed. In the weakening stage, buckles and partial shedding emerge due to the overlarge stress.

Tree Storey Structure and Condition Dynamics in Middle-Taiga Native Spruce Forests of the Northern Ural Foothills

The paper focuses on the dynamic processes occurring in indigenous spruce phytocenoses developing on the territory of one of the large reserves of spontaneous dark coniferous taiga in the European North – the Pechoro-Ilychsky Reserve. The aim of the study was to assess the size structure dynamics of the forest stands and the undergrowth, as well as changes in their vital status in naturally developing spruce stands of the green moss and long-stem moss groups of forest types in the foothills of the Northern Urals (the basin of the upper reaches of the Pechora River). The spruce stands, mixed in composition and complex in structure, form a cyclic uneven-aged type of structure. For the middle taiga indigenous spruce forests, based on the assessment of inequality in the woody plants’ sizes distribution, the results of the long-term structure monitoring of the forest stands and the undergrowth on four permanent sample plots were analysed. In forest stands of different types, a similar dynamics of tree differentiation by trunk volume and undergrowth by trunk height was observed. There is a significant accumulation of small woody plants individuals, with a smooth, evenly fading distribution of their numbers in the direction of size increase. Under the canopy of forest stands there is a continuous regrowth process. According to the data of stationary observations of the vitality and damage degree of trees and undergrowth of spruce forests, based on a visual assessment of a woody plant state according to the characteristics of the crown, a slightly weakened condition of both the upper tree layers of the phytocenosis and the lower – undergrowth was revealed. Spruce stands are at the stage of initial weakening or are already weakened, the undergrowth is predominantly healthy.

Семиотическое ослабление сильного иероглифического знака «солнце» в китайском языке

The aim of the study is to identify the features of strong character signs from the perspective of the semiotic weakening law (using the Chinese character “sun” as an example). The Chinese character system is a heterogeneous system with different types of signs (strong, weakened and weak signs). To figure out the place and role of a strong sign in this system and to describe its basic features, the paper provides the description of different character categories in compliance with their stages of semiotic weakening. The analysis showed that pictograms and simple indicatives belong to the strong signs, idiographic, transfer and loan characters belong to the weakened signs, while phonosemantic compound characters belong to the weak signs. The work is novel in that it describes both the basic features of strong character signs and the process of semiotic weakening from the perspective of evolutionary and hierarchic relations. As a result, the study revealed that strong characters lose grammatical independence and retain their semantic meaning. It was also concluded that the more strong signs become a part of the writing system, the more they weaken and become conventional.

The abnormal track of super typhoon Hinnamnor (2022) and its interaction with the upper ocean

The upper ocean response and feedback to super typhoon Hinnamnor (2022) were systematically investigated considering multi-satellite, Array for Real-time Geostrophic Oceanography (Argo) float and reanalysis data. Hinnamnor experienced three main stages: a rapid intensification (RI) stage with a high moving speed along a westward track, a rapid weakening (RW) stage with a low moving speed along a northward sudden-turning track and a re-intensification (Re-I) stage with a moderate speed along a northward track. At the westward straight-line stage, despite the thin warm water layer (D26 < 40 m) and shallow mixed layer depth (MLD) (<20 m), its fast movement (∼8.1 m/s) tended to generate weaker sea surface temperature (SST) cooling (approximately 1 °C) and shorter cooling exposure. Consequently, the negative feedback decreased (negative feedback factor FSST:approximately−0.47to−0.20), causing Hinnamnor's rapid intensification (25 knots/6 h). Although the MLD was deeper (approximately 30 m) and the warm water layer was thicker (approximately 60 m) at the sudden-turning stage, the low translation speed (<2 m/s) tended to generate stronger SST cooling (approximately 5.6 °C) and longer cooling exposure, both of which intensified the negative feedback (FSST:approximately−0.8to−0.4), causing Hinnamnor's rapid weakening (−22 knots/6 h). At the northward stage, Hinnamnor re-intensified under a weak warm eddy with a moderate moving speed (3.6–5.4 m/s). An intriguing leftward bias in SST cooling occurred due to the preexisting cold eddy (CE) on the left side of the track. Analysis of the Argo floats in the RI and RW regions showed that the enhanced upwelling and vertical mixing yielded more significant SST cooling in the CE region at the RW stage due to the CE and low translation speed (<2 m/s). The differences between the RI and RW regions were remarkable when using the Hybrid Coordinate Ocean Model (HYCOM) global ocean model output.

Labor Activity of Convicts in Conditions of Humanization of Imprisonment in Late 18&lt;sup&gt;th&lt;/sup&gt; — Early 21&lt;sup&gt;st&lt;/sup&gt; Centuries (Western Siberia)

The experience of attracting convicts to work in West Siberian prisons, including those located on the territory of the Arctic zone of Yugra in the late 18th — early 21st centuries, is considered. It is noted that this experience was introduced as part of the humanization of the penitentiary system according to the European model. The authors introduce the concept of “three-phase model” of humanization of the prison. The thesis is substantiated that in the history of Russia this model was implemented three times and necessarily included new principles for organizing the work of prisoners. The results of the last reform, which took place in 2010—2020 are compared with previous reforms and general patterns characteristic of Russia are identified. The purpose of the article is to determine the relationship between the model of work in places of detention and the stages of weakening / strengthening of political power. The study is carried out through the analysis of the organization of work of prisoners, since this factor is an indicator of the state of the law enforcement system, and it reflects the degree of stability of state power as a whole. The study concluded that in the conditions of Russia, the principles of organizing the work of prisoners should correspond to the ideas of justice that are characteristic of the Russian people. The authors argue that the “three-phase model” implemented several times for the humanization of the prison according to the European model always entails negative consequences for the Russian statehood.

Analysis of Extreme Rainstorms Associated with Tropical Cyclone Rammasun (2014) over Guangxi Province of China

The tropical cyclone (TC) Rammasun (1409) successively caused three extreme rainstorms centered in Hepu, Fangcheng, and Lingshan in Guangxi. In this study, a set of datasets, including the China Meteorological Administration (CMA) TC best-track data, rain gauge stations, radar products, and the latest ERA5 reanalysis, were used to investigate the spatial–temporal characteristics and causes of the three rainstorms. Overall, there are apparent discrepancies among them regarding the triggering and maintenance mechanisms. Prior to its landfall in Guangxi, the rainstorm surge (hourly precipitation 136.9 mm) around Hepu was triggered by the approaching low-level jet and northward intrusion of convective instability in the context of abundant vapor supply and vigorous convection. At the weakening stage, Rammasun gradually crossed over the Shiwan Mountains, with a strong convection zone in the western eyewall moving to Fangcheng, which enhanced the precipitation there under the help of topographic uplift. The friction effect slowed down the TC, and contributed to accumulation of the precipitation, which, however, was somewhat suppressed (hourly precipitation less than 50 mm) by the low-level stratification. In the decaying stage, the Lingshan rainstorm was triggered under the combined efforts of the high-level divergence due to the expansion of the South Asian high and the surface convergence between the southeasterly and southerly winds, accompanied by the westward expansion of the high-energy zone. Finally, the corresponding conceptual models for the three rainstorms are summarized and should provide important implications to both research and forecasting for TC-related heavy precipitation.

Investigating the Deterioration of Pavement Skid Resistance Using an Accelerated Pavement Test

Stone matrix asphalt (SMA) mixture has been widely used in pavement engineering for its preferable in-service performance. However, deterioration of SMA pavement in skid resistance is apparent under traffic loading. There remains lacking attention on skid resistance attenuation of SMA pavement, which in turn is important for skid durability design in practice. Hence, this study aims to perform a thorough investigation to reveal the skid resistance attenuation law of SMA pavement. Multiple types of SMA-13 mixtures prepared by different material designs were selected to conduct a kneading test that simulates real surface states of in-service SMA pavement. Pressure-sensitive film and a 3D laser scanner were utilized for evaluating anti-skid performance and skid durability. The finite element (FE) method is introduced to simulate vehicle braking distance for skid-resistance evaluation. The results show that skid resistance attenuation of SMA pavement consists of two stages: In the first stage, the skid resistance of SMA pavement experiences a short enhancement, followed by a long-term weakening stage. Abundant surface texture of SMA helps to mitigate the impact of traffic load on skid resistance. The FE analysis and pressure-sensitive film results demonstrate the potential of skid durability design of SMA pavement based on the skid resistance attenuation law.

Correction of ted field weakening switching diagram for mainline diesel locomotives of te type

The processes are considered when the stages of weakening of the TED magnetic field are switched on on diesel locomotives of the TE10 type. The analysis of the unstable operation and automatic switching on of the transition relay at partial loads corresponding to the locomotive's speed at the rated load in operation is carried out. TED current algorithms are proposed for correcting the scheme for switching on the relay of transitions from a full field to a weakened field. A variant of the correction circuit is proposed to check its operation during operation. This principle has been violated since the creation of the TE10 diesel locomotive. It is still violated on TE10 diesel locomotives, except for diesel locomotives equipped with the USTA system.

Contribution of deformation and reaction of amphiboles to the weakening of the middle continental crust: A case study from sheared diorites along the Shuiyu shear zone in Northern Beijing

How the deformation of amphiboles and their involvement in metamorphic reactions during shearing affect the rheology of the middle crust remains controversial. Middle crustal fault rocks are exposed along the Shuiyu shear zone (SYSZ) in Yunmeng Shan, Northern Beijing, which was formed by the exhumation of the Yunmeng Shan metamorphic core complex during the Early Cretaceous tectonic extension of the North China Craton. Various deformation structures, optical microstructures, dislocation submicrostructures and fabrics during the transition from brittle to ductile deformation in the middle crust are observed in the sheared diorites. In particularly, two types of amphiboles, i.e., the A-type with brown cores and green mantles as porphyroclasts and the B-type of green-colored fine grains in the matrix, distributed biotite grains and interconnected fine biotite zones, are observed in the deformed diorites. Geothermometer analysis reveals that the amphibole grains in the sheared diorites were crystallized at temperatures over c. 720 °C, deformed at c. 680 °C–600 °C and transformed into biotite at c. 600 °C–520 °C. During these processes, fluid not only enhanced crystal plasticity and governed the deformation of the amphibole grains, but was also involved in their metamorphic transformation into biotite. Our results show that the diorites along the Shuiyu shear zone experienced three stages of middle crustal shearing and weakening, i.e., an early stage of fluid-enhanced crystal plasticity followed by rigid body rotation, a middle stage of transformation from a strong phase (amphibole) to a weak phase (fine-grained biotite and quartz) and a late stage of weak phase interconnection.

Identification of synoptic patterns for extreme rainfall events associated with landfalling typhoons in China during 1960–2020

Extreme rainfall associated with landfalling typhoon (ERLTC) can cause severe disasters and economic impacts throughout China. Improving the accuracy of ERLTC forecasts is therefore crucial in disaster prevention and mitigation. The top 26 ERLTC events in China during 1960–2020 are investigated based on multi-source datasets. These ERLTC events are categorized into five main types according to the geographical location of the extreme precipitation and its position relative to the tropical cyclone (TC) center, namely: the typhoon inner-core rainfall in Taiwan (TWIC), typhoon inverted trough rainfall in Taiwan (TWIT), weak typhoon rainfall in Hainan (HNWK), strong typhoon rainfall in Zhejiang (ZJST) and inland typhoon remnant rainfall (ILRM). All the ERLTC events occurred in the weakening stage of TC after reaching its lifetime maximum intensity in convective cloud (TBB ≤ −32 °C) regions over complex local terrain. The translational speeds of 20 TCs (76.9% of the total) were smaller than the climatological average (20.6 km h−1) during the extreme precipitation events. The differences are as follows: the TWIC and TWIT types are featured with different season, track and water vapor channel although both occurred in Taiwan. The other three types are distinguished by spinning track and strong convective cloud for HNWK type, strong TC intensity and binary TC interactions for ZJST type; and stagnation and strong westerly trough activity for ILRM type, respectively. These results are expected to provide useful clues for an in-depth understanding of ERLTC events over China.

Multiscale Perspectives on an Extreme Warm-Sector Rainfall Event over Coastal South China

On 22 June 2017, an extreme warm-sector rainfall event hit the western coastal area of South China, with maximum hourly and 12-h rainfall accumulations of 189.4 and 464.8 mm, respectively, which broke local historical records. Multisource observations were used to reveal multiscale processes contributing to the extreme rainfall. The results showed that a marine boundary layer jet (BLJ) coupled with a synoptic low-level jet (LLJ) inland played an important role in the formation of an extremely humid environment with a very low lifting condensation level of near-surface air. Under the favorable pre-convective conditions, convection was initialized at a mesoscale convergence line, aided by topographic lifting in the evening. During the nocturnal hours, the rainstorm developed and was maintained by a quasi-stationary mesoscale outflow boundary, which continuously lifted warm, moist air transported by the enhanced BLJ. When producing the extreme rainfall rates, the storm possessed relatively weak convection, with the 40 dBZ echo top hardly reaching 6 km. The extreme rainfall was produced mainly by the warm rain microphysical processes, mainly because the humid environment and the deep warm cloud layer facilitated the clouds’ condensational growth and collision–coalescence, and also reduced rain evaporation. As the storm evolved, the raindrop concentration increased rapidly from its initial stage and remained high until its weakening stage, but the mean raindrop size changed little. The extreme rain was characterized by the highest concentration of raindrops during the storm’s lifetime with a mean size of raindrops slightly larger than the maritime regime.

Experimental Study on Replacing Coal Seam CH4 with CO2 Gas.

In recent years, many studies have reported the mechanism of CH4 stimulation by gas injection. However, the studies have focused only on monitoring CH4 and CO2 in the tail gas. Thus, it is difficult to distinguish the adsorbed and free gas in the coal and rock and accurately calculate the CO2/CH4 replacement ratio in the displacement process. The low-field NMR technology can effectively overcome the drawbacks of the traditional displacement experiments and distinguish the free and adsorbed gas in the coal and rock. In the present study, the NMR technology analyzed the T2 spectrum for the CH4 desorption amount and CO2/CH4 displacement efficiency in the replacement of methane with gaseous CO2. The results suggested the following: (1) the process of CO2 gas replacing CH4 can be divided into three stages: the initial stage of competitive adsorption, the dominant stage of competitive adsorption, and the weakening stage of competitive adsorption. (2) The cumulative desorption of CH4 gas increases with the increase in replacement time. With the increase in temperature, it first increases and then decreases, and the extreme value is obtained at about 40 °C. Additionally, the greater the CO2 injection pressure is, the greater the cumulative desorption of CH4 is. (3) The cumulative replacement ratio is positively correlated with the replacement time, and with the increase in replacement time, the increment in the cumulative replacement ratio decreases gradually and the upward trend tends to be stable. Overall, the cumulative displacement ratio would increase with an increase in the CO2 injection pressure. With the increase in temperature, the maximum value of the cumulative replacement ratio first increases and then decreases, and the extreme value obtained is about 5.49 at 40 °C.

Dissociation experiment and dissociation rate model of CO2 hydrate

Applying CO2 hydrate (referred to as hydrate) to CO2 storage and sequestration can alleviate global greenhouse effect, which is currently a hot spot of hydrate research. In order to explore the dissociation mechanism and rate, this paper carries out hydrate dissociation experiments under different working conditions of depressurization stage, temperature and initial hydrate volume fraction by using the reactor. Then, based on the experimental results, the influences of pressure, temperature, hydrate volume fraction, mass exchange and energy exchange on the dissociation rate are analyzed. Finally, a hydrate dissociation rate model considering the influences of intrinsic dissociation dynamics, mass transfer and other comprehensive mechanisms is established. And the following research results are obtained. First, two dissociation phenomena appear in the process of hydrate dissociation, including adsorption of gas bubble and shedding of flaky hydrate from the edge. Second, hydrate dissociation is a process of intrinsic dissociation dynamic driving, mass and heat transfer. According to the dissociation rate variation, it can be divided into two stages, i.e., stable dissociation stage and dissociation weakening stage. In the stable dissociation stage, the dissociation rate is maintained constant. And in the dissociation weakening stage, the dissociation rate decreases gradually with the increase of dissociation resistance (mass exchange). Third, both pressure and temperature drive the dissociation by influencing the difference between the actual hydrate surface fugacity and the phase equilibrium fugacity. The increase of depressurization range can lead to the increase of dissociation rate while the duration of stable dissociation is extending. The increase of temperature can also lead to the increase of the dissociation rate, but its influence is less than that of depressurization. In conclusion, this newly established dissociation rate model can well predict the value and variation trend of hydrate dissociation rate. And under the working condition of 2.0 MPa, the maximum relative error of the experimental results is 5.1%.

Spatial differences in pressure and heat transfer characteristics of CO2 hydrate with dissociation for geological CO2 storage

The submarine CO2 hydrate-based geological storage is an effective method for carbon capture and storage, which is significant for mitigating the greenhouse effect. The pressure and temperature variation can affect the storage stability of CO2 hydrate. In order to investigate the spatial differences in pressure and heat transfer characteristics of CO2 hydrate mixed system and the morphological evolvement process with dissociation during depressurization stage, a 100 L high-pressure reactor is used to take comprehensively experimental study. Furthermore, the effects of environmental heat flux and hydrate volume fraction on dissociation behavior and hydrate stability are also analyzed. The results indicate that the energy of hydrate mixed system is spatially inhomogeneous during dissociation and the heat flux flows to the region where the sensible heat is greatly consumed. And the bottom temperature is approximately 1.4-fold versus upper temperature. The depressurization dissociation process can be divided into dissociation stable stage (DSS) and dissociation weakening stage (DWS). The duration of DSS at depressurization stage of 1.5–1.2 MPa is around 3-fold versus stage of 2.5–2.0 MPa.

Effects of the East Asian subtropical westerly jet on winter persistent heavy pollution in the Beijing–Tianjin–Hebei region

AbstractBased on the daily average concentration of PM2.5, 15 typical persistent heavy pollution episodes (PHPEs) in the Beijing–Tianjin–Hebei (BTH) region during the winters of 2013–2019 are identified. And then the impact of the intra‐seasonal variations of the 200‐hPa subtropical westerly jet (SWJ) on the PHPEs is investigated. The results show that the SWJ affects the lifecycle of the PHPEs in the BTH region mainly through the meridional shift and intensity variation. In particular, the intensity variation has a closer relationship with the vertical velocity and low‐level meridional wind to affect the PHPEs. In the developing stage of the PHPEs, the SWJ shifts northward and strengthens. The BTH region is on the left side of the entrance of the SWJ and the vertical secondary circulation intensifies the descending motion in situ. As a result, the atmospheric boundary layer is compressed to sink rapidly, a temperature inversion in the lower levels appears and the atmospheric stability is enhanced. Finally, the atmospheric environment is favourable for the rapid accumulation of pollutants and the occurrence of the PHPEs. In the peak stage, the southward withdrawal and weakening of the SWJ favour the anomalous ascending motion and low‐level southerly anomalies over the BTH region. The dominant role of the dynamic descending motion is replaced by the low‐level southerly anomalies to enhance the PHPEs, by transporting more warm‐humid air to the BTH region. In the weakening stage, the SWJ moves northward and intensifies again. The low‐level southerly anomalies weaken to contribute to the dissipation of the pollutants.

A Comparative Modeling Study of Supertyphoons Mangkhut and Yutu (2018) Past the Philippines with Ocean-Coupled HWRF

The ocean-coupled Hurricane Weather Research and Forecasting (HWRF) system was used to investigate the evolution of Supertyphoons Mangkhut and Yutu (2018) over the Philippines Sea and near landfall in the northern Philippines. The simulation results indicate that Mangkhut at a deepening stage has a smaller track sensitivity to the use of different physics schemes but greater intensity sensitivity, which becomes reversed for Yutu at a weakening stage. When both upstream tracks are well simulated with some specific suite of physics schemes, sensitivity experiments indicate that both track deviations near the northern Philippines are only weakly modified by the air–sea interaction (ocean-coupled or uncoupled processes), the topographic effects of the Philippines terrain (retained or not), and the initial ocean temperature change along both typhoon tracks. The interactions between the internal typhoon vortex and the large-scale flow play an important role in the overall movement of both typhoons, which were explored for their structural and convective evolutions near the terrain. The wavenumber-one potential vorticity (PV) tendency budget of the typhoon vortex was analyzed to explain the induced typhoon translation from different physical processes. The west-northwestward translation for the stronger Mangkhut near the northern Philippines is primarily induced by both horizontal and vertical PV advection but with the latter further enhanced to dominate the northward deflection when closing in to the terrain. However, the northwestward translation and track deflection near landfall for the weaker Yutu are driven by the dominant horizontal PV advection. Differential diabatic heating is relatively less important for affecting the movement of both typhoons near landfall.