Explore the vast range of titles available.

South China experienced substantial rainfall from April 19 to April 22, 2024, with accumulated precipitation ranging from 200 mm to 350 mm. This significant precipitation was primarily driven by the combined synoptic influences of the southern branch trough, low‐level jet stream, and the Jiang–Huai cyclone, affecting northern and central‐eastern Guangxi as well as most parts of Guangdong. These synoptic conditions facilitated the initiation, development, and propagation of mesoscale convective systems (MCSs). Specifically, an MCS initiated in the evening over the eastern edge of the Yunnan–Guizhou Plateau (YGP), leading to the formation of a mesoscale vortex with closed cyclonic circulation at 850 hPa, which further promoted the merging of convection cells into an organized MCS. The intensified southerly winds appeared over the eastern parts of the mesoscale vortex, preceding the peak meridional component of moisture convergence by approximately 4–5 h. Moisture budget analysis revealed that the meridional component of horizontal moisture convergence was the primary contributor to the moisture increase over Guangxi and Guangdong provinces. Consequently, the enhanced mesoscale systems (vortices and MCSs) significantly increased horizontal convergence at lower levels, contributing substantially to the moisture accumulation over South China. The intensified low‐level southerly wind associated with mesoscale vortices can be considered a potential forewarning parameter for short‐range precipitation forecasting in such heavy rainfall events. Column‐integrated moisture budget analysis revealed that the meridional component of horizontal moisture convergence was the primary contributor to the moisture increase over South China during substantial rainfall event from April 19 to 22, 2024. The enhanced mesoscale systems (vortices and MCSs) significantly increased meridional horizontal convergence at lower levels, contributing substantially to the moisture accumulation. The low‐level intensified southerly wind associated with mesoscale vortices can be considered a potential forewarning parameter for short‐range precipitation forecasting in such heavy rainfall events.

The Southwest Vortex (SWV) is a mesoscale closed low-pressure system in Southwest China that significantly influences regional heavy rainfall. Understanding SWV characteristics and formation mechanisms is crucial for research in this field, with effective identification as the foundation. Currently, Chinese researchers lack a unified standard for SWV identification. Despite the availability of high spatiotemporal resolution reanalysis data, which provides a superior foundation for studying SWVs, existing methods struggle to fully exploit these datasets. Therefore, this study proposes PVSIA (Geopotential-Height-Field and Vector-Wind-Field based SWV Identification Algorithm), a method that integrates the geopotential height field and wind field characteristics. The PVSIA employs an innovative calculation method for wind vector rotation properties, enhancing identification speed and overcoming challenges posed by complex terrain. Furthermore, this study utilizes the ERA5 reanalysis dataset from 2019 to 2021 to systematically compare the performance of the PVSIA method with traditional geopotential height field methods in identifying SWVs, employing key evaluation metrics such as hit ratio, false alarm rate, and missing report rate. During this period, the PVSIA method achieved a hit rate of 94.25% in identifying SWVs, with a false alarm rate of 5.20% and a missing report rate of 5.74%. In contrast, the geopotential height field method, while achieving a higher hit rate of 98.85%, exhibited a significantly higher false alarm rate of 70.54%. In contrast, the PVSIA method maintains a high hit rate while significantly reducing the false alarm rate, demonstrating a more stable and reliable identification performance.

The southwest vortices (SWVs) are a unique type of mesoscale vortex that frequently induce torrential rainfall in China. In this study, we focused a long‐lived quasi‐stationary SWV, which was the primary system for producing an extremely heavy rainstorm within/around Sichuan (the maximum hourly precipitation was ~103.8 mm) in Mid July 2021. After reproduced the SWV's formation by using Weather Research and Forecasting model, we conducted trajectory analyses and topography sensitivity simulations to understand the effects of complicated topography on the vortex's formation. It is found that, the regions south and southwest of the SWV acted as the most important source regions for the air clusters that formed the SWV (proportion ≥ 65%), and the air clusters originated from the upper layer contributed the most (≥60%). Of these, the air clusters sourced from the upper layer southwest and south of the SWV played the most important role in the SWV's formation, as their increase in cyclonic vorticity and their contributions to trajectory number and vorticity were all much larger than those of the others. Sensitivity simulations indicated that, detailed topography features around the Sichuan Basin were crucial in determining the structure, intensity and precipitation of the SWV, whereas, the topography features were not a decisive factor for the SWV's formation. In summary, our findings are useful to enrich the current understanding of the SWVs' formation, which would be helpful to improve the related forecasts. The air particles sourced from the upper layer southwest and south of the southwest vortices (SWV) contributed the most to the SWV's formation, as their increase in cyclonic vorticity and their contributions to trajectory number and vorticity were all the largest. Although the detailed topography features were not a decisive factor for the SWV's formation, they exerted notable impacts on the structure, intensity, and precipitation of the SWV. The SWV's formation was the most sensitive to the topography south of the vortex, whereas, it was relatively insensitive to the topography southwest of the vortex.

The mesoscale southwest vortices (SWVs) over the Sichuan Basin during the summer of 2000–2013 were detected and tracked based on a high‐resolution reanalysis data and station observations. Four types of SWV were classified according to dynamical and thermodynamical standards, and their main features were compared. This study presents the first analysis of the universal evolution mechanisms and energy conversion characteristics of long‐lived SWVs by using the vorticity and kinetic energy budgets, as well as a new composite method under a normalized polar coordinate. Also, this study is the first work to reveal the three‐dimensional shape of SWVs.

Dabie vortices (DBVs) are a type of heavy-rainfall-producing mesoscale vortices that appear with a high frequency around the Dabie Mountain over the Yangtze River Basin. For a long time, scholars have found that DBVs tend to form when a low-level jet (LLJ) appears in their neighboring regions. However, the underlying mechanisms of this phenomenon still remain vague. This study furthers the understanding of this type of event by conducting detailed analyses on a long-lived eastward-moving DBV that caused a severe flood in the 2020 summer. It is found that the LLJ in this event was belonged to a nocturnal LLJ type, with its maximum/minimum appeared around 2100/0600 UTC. The diurnal cycle of LLJ affected precipitation and intensity of the DBV notably: As the LLJ intensified, vortex’s precipitation and intensity both enhanced, and vice versa. The LLJ exerted two effects on the DBV’s formation that are opposite to each other. The more important effect is that the LLJ caused intense lower-level convergence around its northern terminus. This convergence directly produced cyclonic vorticity through vertical stretching, which dominates the DBV’s formation and enhances the convection-related upward cyclonic vorticity transport that acted as another favorable factor. The less important effect is that (i) the LLJ induced import of anticyclonic vorticity into the vortex’s central region, which decelerated the DBV’s formation; and (ii) the LLJ-related to strong ascending motions tilted horizontal vorticity into negative vertical vorticity, which reduced the growth rate of cyclonic vorticity.

A statistical analysis of the initial vortexes leading to tropical cyclone (TC) formation in the western North Pacific (WNP) is conducted with the ECMWF ERA5 reanalysis data from 1999 to 2018. It is found that TCs in the WNP basically originate from three kinds of vortexes, i.e., a mid-level vortex (MV), a low-level vortex (LV), and a relatively deep vortex with notable vorticity in both the lower and middle troposphere (DV). Among them, LV and DV account for 47.9% and 24.2% of tropical cyclogenesis events, respectively, while only 27.9% of TCs develop from the MV, which is much lower than that which occurs in the North Atlantic and eastern Pacific. Such a difference might be ascribed to the active monsoon systems in the WNP all year round. Due to the nearly upright structure of mid-level convergence in the early pre-genesis stage, TC genesis efficiency is the highest in DV. Compared with MV, LV generally takes a shorter time to intensify to a TC because of the higher humidity and the stronger low-level cyclonic circulation, which is related to air-sea interaction and boundary-layer convergence. Further examination of the relationship between tropical cyclogenesis and large-scale flow patterns indicate that the TC genesis events associated with LV are primarily related to the monsoon shear line, monsoon confluence region, and monsoon gyre, while those associated with MV are frequently connected with easterly waves and wave energy dispersion of preexisting TC. Compared with other flow patterns, tropical cyclones usually form and intensify faster in the monsoon confluence region.

In this study, a three-dimensional mesoscale model was used to numerically simulate the well-known “98.7” heavy rainfall event that affected the Yangtze Valley in July 1998. Two experiments were conducted to analyze the impact of moist processes on the development of meso- β scale vortices (M β V) and their triggering by mesoscale wind perturbation (MWP). In the experiment in which the latent heat feedback (LHF) scheme was switched off, a stable low-level col field (i.e., saddle field—a region between two lows and two highs in the isobaric surface) formed, and the MWP triggered a weak M β V. However, when the LHF scheme was switched on as the MWP was introduced into the model, the M β V developed quickly and intense rainfall and a mesoscale low-level jet (mLLJ) were generated. The thickness of the air column and average temperature between 400 and 700 hPa decreased without the feedback of latent heat, whereas they increased quickly when the LHF scheme was switched on, with the air pressure falling at low levels but rising at upper levels. A schematic representation of the positive feedbacks among the mesoscale vortex, rainfall, and mLLJ shows that in the initial stage of theM β V, the MWP triggers light rainfall and the latent heat occurs at low levels, which leads to weak convergence and ageostrophic winds. In the mature stage of theM β V, convection extends to the middle-to-upper levels, resulting in an increase in the average temperature and a stretching of the air column. A low-level cyclonic circulation forms under the effect of Coriolis torque, and the mLLJ forms to the southeast of the M β V.

Mesoscale convective vortices (MCVs) often cause rainstorms. To deepen our understanding of MCV formation mechanisms, reanalysis data from the National Centers for Environmental Prediction and the Weather Research and Forecasting model were used to simulate MCV activity in East China in August 2009. The simulations could reproduce the MCV and associated convective activities well. The vorticity budget and MCV formation mechanisms were then analyzed. The results show that the planetary vorticity advection is much smaller than other terms of the vorticity equation. The MCV initiates in the convective precipitation region and below 800 hPa. When the MCV initiates, there are vorticity-variation couplets within the vortex, and the MCV moves towards the positive vorticity-variation direction. In positive vorticity-variation areas, the divergence term and the tilting term are the vorticity source. The equilibrium response to diabatic heating is one of the forming mechanisms of this MCV. The latent-heating level is relatively low in this MCV case, and the MCV-forming level is also relatively low. Another forming mechanism of this MCV is the tilting of the horizontal vortex tube caused by the upward motion. At the MCV initiation, the perturbation scale of the vortex is found to be larger than the Rossby deformation radius, and thus the MCV could have a long duration.

Tropical cyclones of the Bay of Bengal (BoB) that formed near the synoptic-scale dryline usually intensified over a distance of 600–800 km within 3 days and caused severe destruction after landfall. High-resolution simulations of very severe cyclonic storms in association with dryline indicate that the meridional shear aids in the development of a linear-shaped group of convective cells that mature as an east–west oriented quasi-linear convective system (QLCS) within the boundary between the dry-moist air masses. The leading edge deep convections are supported by low-level moist southwesterly inflow; however, the typical mid-level mesoscale convective vortex (MCV) associated with these QLCS is unremarkable due to a very narrow trailing stratiform region within the QLCS. Supercells are likely to be organized within the QLCS due to extremely unstable atmospheric conditions resulting from a strong vertical shear of 27–39 m s−1 between 0 and 6 km and large convective available potential energy of > 3000 J kg−1. The vertical shear veering with height causes several numbers of low-level mesovortices having diameters less than 10 km at the leading edge in the different convective stages of the QLCS. The dryline aloft in the BoB produces horizontal positive shear vorticity of the order 10–5 s−1 with higher values in the levels 850–600 hPa. The advection of intense cloud-scale cyclonic mesovortices (~ 10–3 s−1) assists and enhances a cyclonic vortex to the rear side of the QLCS that performs as an MCV for cyclogenesis over the BoB.

The WRF-ARW regional atmosphere circulation model has been used to reproduce a few episodes of cold intrusion and the Novorossiysk bora accompanied by the formation of the mesoscale cyclonic vortex over the Black sea, which can be clearly observed from satellite images of cloudiness. It has been shown that the vortex development is associated with the specific features of air flow around the northwestern edge of the Caucasus Mountains. We have estimated the vertical vorticity associated with the alongshore horizontal gradient of temperature. We have considered the field structure of wind velocity and temperature of the axisymmetric quasi-two-dimensional vortex generated in the coastal zone and displaced seaward after separating from the coast. With the background northerly wind, the coastal cyclonic circulation is not accompanied by the vortex separation from the coast. The specific feature of the development of the cyclonic vortex is the southeastern wind with velocities of up to 10 m/s in the Caucasus coastal area from Sochi to Sukhum.