Plateau Vortex Research Articles

Tibetan Plateau Vortex Activity and Its Relationship With the Tibetan Plateau Summer Monsoon and Precipitation

ABSTRACTThe unique topography and location of the Tibetan Plateau (TP) often result in extreme weather events, which have led to disastrous consequences for the TP and its downstream regions. The TP summer monsoon (TPSM) and the TP vortex (TPV) play key roles in the transfer and redistribution of water vapour during the summer months on the TP and are increasingly active in summer and disappear in winter. However, it remains uncertain if a relationship between these systems. Understanding the relationship between these two systems is crucial for uncovering precipitation patterns on the TP, improving weather forecasting accuracy and reducing socioeconomic losses resulting from weather‐related disasters. On the basis of GLDAS and ERA5 reanalysis data from 1996 to 2022, the relationships between TPVs and the TPSM were explored in terms of their intensity and spatial characteristics, and their impacts on the spatial distributions of precipitation across the TP were examined in this study. The results indicated that the monthly mean TPSM index agreed very well with the TPV in terms of the annual number formed, duration and intensity, especially in July and August. The investigation of the movement of the center of the TPSM from May to October revealed that the center of the TPSM moves westward when the TPV is active and moves eastward when the TPV is less active. In years with a strong TPSM, the precipitation location generated by TPVs was biased toward the east. This finding could be attributed to the greater number of TPV events and the fact that the TPVs in years with a stronger TPSM moved eastward across a greater distance than those in years with a weaker TPSM. These findings highlightthe contribution of the joint relationship between the TPSM and TPV to seasonal circulation changes and could provide a new perspective for the study and prediction of precipitation distributions on the TP.

Understanding the weakening patterns of inner Tibetan Plateau vortices

This study focuses on changes in the Tibetan Plateau vortices (TPVs) by using ERA5 reanalysis, covering the summers from 1979 to 2022 within the Tibetan Plateau (TP) region. These TPVs were identified using a geopotential height analysis. We discovered that the central-western TP had the most TPV activity and observed a clear decreasing trend in both the intensity and frequency of the TPVs in this region. This decrease was also accompanied by a decline in the strength of the associated vertical upward motion. To better understand this change, we employed the quasi-geostrophic omega equation. This allowed us to examine the dynamic, diabatic, and topographic factors contributing to the vertical motion during different phases of TPV activity in this region. Our results indicate that the main reason behind the weakened TPVs is the diminishing upper-level jet stream, which exerts dynamic forcing on the system. In the later stage, we observed that intensive moisture transport induces heightened diabatic vertical motion. However, this effect is not potent enough to counterbalance the diminishing dynamic influence. Therefore, our findings suggest a significant shift in TPV activity, transitioning from a dynamic-dominated regime to a latent heating-dominated diabatic regime. This new insight enhances our understanding of the complex mechanisms that influence TPV behavior.

Precipitation Characteristics at Different Developmental Stages of the Tibetan Plateau Vortex in July 2021 Based on GPM-DPR Data

The Tibetan Plateau vortex (TPV), as an α-scale mesoscale weather system, often brings severe weather conditions like torrential rain and severe convective storms. Based on the detections from the Global Precipitation Measurement (GPM) Core Observatory’s Dual-frequency Precipitation Radar (DPR) and the FY-4A satellite’s Advanced Geostationary Radiation Imager (AGRI), combined with ERA5 reanalysis data, the precipitation characteristics of a TPV moving eastward during 8–13 July 2021 at different developmental stages are explored in this study. It was clear that the near-surface precipitation rate of the TPV during the initial stage at the eastern Tibetan Plateau (TP) was below 1 mm·h−1, implying overall weak precipitation dominated by stratiform clouds. After moving out of the TP, the radar reflectivity factor (Ze), precipitation rate, and normalized intercept parameter (dBNw) significantly increased, while the proportion of convective clouds gradually rose. Following the TPV movement, the distribution range and vertical thickness of Ze, mass-weighted mean diameter (Dm), and dBNw tended to increase. The high-frequency region of Ze appeared at 15–20 dBZ, while Dm and dBNw occurred at around 1 mm and 33 mm−1·m−3, respectively. Near the melting layer, Ze was characterized by a significant increase due to the aggregation and melting of ice crystals. The precipitation rate of convective clouds was generally greater than that of stratiform clouds, whilst both of them increased during the movement of the TPV. Particularly, at 01:00 on 12 July, there was a significant increase in the precipitation rate and Dm of convective clouds, while dBNw noticeably decreased. These findings could provide valuable insights into the three-dimensional structure and microphysical characteristics of the precipitation during the movement of the TPV, contributing to a better understanding of cloud precipitation mechanisms.

Variability and trends of near-surface wind speed over the Tibetan Plateau: The role played by the westerly and Asian monsoon

Near-surface wind speed exerts profound impacts on many environmental issues, while the long-term (≥60 years) trend and multidecadal variability in the wind speed and its underlying causes in global high-elevation and mountainous areas (e.g., Tibetan Plateau) remain largely unknown. Here, by examining homogenized wind speed data from 104 meteorological stations over the Tibetan Plateau for 1961–2020 and ERA5 reanalysis datasets, we investigated the variability and long-term trend in the near-surface wind speed and revealed the role played by the westerly and Asian monsoon. The results show that the homogenized annual wind speed displays a decreasing trend (−0.091 m s−1 per decade, p < 0.05), with the strongest in spring (−0.131 m s−1 per decade, p < 0.05), and the weakest in autumn (−0.071 m s−1 per decade, p < 0.05). There is a distinct multidecadal variability of wind speed, which manifested in an prominent increase in 1961–1970, a sustained decrease in 1970–2002, and a consistent increase in 2002–2020. The observed decadal variations are likely linked to large-scale atmospheric circulation, and the correlation analysis unveiled a more important role of westerly and East Asian winter monsoon in modulating near-surface wind changes over the Tibetan Plateau. The potential physical processes associated with westerly and Asian monsoon changes are in concordance with wind speed change, in terms of overall weakened horizontal air flow (i.e., geostrophic wind speed), declined vertical thermal and dynamic momentum transfer (i.e., atmospheric stratification thermal instability and vertical wind shear), and varied Tibetan Plateau vortices. This indicates that to varying degrees these processes may have contributed to the changes in near-surface wind speed over the Tibetan Plateau. This study has implications for wind power production and soil wind erosion prevention in the Tibetan Plateau.

Connections between different characteristics of the Tibetan Plateau vortices

AbstractTibetan Plateau vortices (TPVs) are major rainfall triggers over the Tibetan Plateau (TP), which often cause heavy rainfalls in eastern China when moving off the TP. Although previous studies have revealed the climatic characteristics of TPVs at different timescales, the relationships between the different activity characteristics of TPVs are unclear. In this study, TPVs during May to August during 1998–2020 are objectively identified based on ERA5 reanalysis data, and connections between the initial states of TPVs and their subsequent activities, as well as the connections between the states of TPVs before moving off the TP and those after moving off are investigated. It is reported that the TPVs generated over the central and western TP north of 32° N, particularly near 84° E, 35° N, are always stronger, maintain longer and move further in their subsequent life, and the TPVs generated near 95° E over the eastern TP move eastwards the fastest. The initial intensity of most TPVs is smaller than 1.1 × 10−4 s−1; regarding these TPVs, their average duration, movement distance and movement speed exhibit an initial decrease followed by an increase as the initial intensity rises. The stronger the TPVs initially are, the stronger they are in their entire lifetime. The majority of the moving‐off TPVs are generated over the eastern TP; generally, TPVs generated further east with a large initial intensity are more likely to move off the TP. After moving off the TP, most TPVs remain in the same movement direction as before; if the TPVs are strong when they are over the TP, they tend to be strong, last long and move eastwards further after moving off the TP, and vice versa.

Aerosol–meteorology feedback diminishes the transboundary transport of black carbon into the Tibetan Plateau

Abstract. Black carbon (BC) exerts potential effects on climate, especially in the Tibetan Plateau (TP), where the cryosphere and environment are very sensitive to climate change. The TP saw a record-breaking aerosol pollution event during the period from 20 April to 10 May 2016. This paper investigates the meteorological causes of the severe aerosol pollution event, the transboundary transport flux of BC, the aerosol–meteorology feedback, and its effect on the transboundary transport flux of BC during the severe aerosol pollution event using observational and reanalysis datasets as well as simulation based on a coupled meteorology and aerosol/chemistry model, Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). By analyzing weather maps derived from the reanalysis dataset, it is found that the plateau vortex and southerly winds were key factors that contributed to the severe aerosol pollution event. Subsequently, due to the good performance of the WRF-Chem model for the spatiotemporal characteristics of meteorological conditions and aerosols, the transboundary transport flux of BC during the pollution event was investigated. The results show that the vertically integrated cross-Himalayan transport flux of BC decreases from west to east, with the largest transport flux of 20.8 mg m−2 s−1 occurring at the deepest mountain valley in southwestern TP. Results from simulations with and without aerosol–meteorology feedback show that aerosols induce significant changes in meteorological conditions in the southern TP and the Indo-Gangetic Plain (IGP), with the atmospheric stratification being more stable and the planetary boundary layer height decreasing in both regions, and the 10 m wind speed increasing in the southern TP but decreasing in the IGP. Changes in meteorological conditions in turn lead to a decrease in the surface BC concentration in the southern TP of up to 0.16 µg m−3 (50 %) and an increase in the surface BC concentration in the IGP of up to 2.2 µg m−3 (75 %). In addition, it is found that the aerosol–meteorology feedback decreases the vertically integrated transboundary transport flux of BC from the central and western Himalayas towards the TP. This study not only provides crucial policy implications for mitigating glacier melt caused by aerosols over the TP but is also of great significance for the protection of the ecological environment of the TP.

Interdecadal change of Tibetan Plateau vortices during the past 4 decades and its possible mechanism

The Tibetan Plateau vortices (TPVs) are mesoscale weather systems active at the near-surface of the Tibetan Plateau (TP), which are one of the major precipitation-producing systems over the TP and its surrounding areas. TPVs mainly occur in the warm season from May to September. In this paper, we investigated the interdecadal change of TPVs in the warm seasons of 1979–2020 with the six widely used reanalysis datasets. A significant change of the TPVs frequency appears around the mid-1990s, associated with less TPVs during 1979–1995 and more TPVs during 1996–2020, which is constant among the multiple reanalysis datasets. The abrupt change of TPVs is caused by a transition of the Atlantic Multi-decadal Oscillation (AMO) from a cold phase to a warm phase in the mid-1990s. The shift of AMO leads to a silk-road pattern-like wave train and a spatially asymmetric change of tropospheric temperature. It modifies the intensity of the subtropical westerly jet and the TP heating, leading to the interdecadal change of TPV activities.

Mechanism of Diabatic Heating on Precipitation and the Track of a Tibetan Plateau Vortex over the Eastern Slope of the Tibetan Plateau

Mechanism of Diabatic Heating on Precipitation and the Track of a Tibetan Plateau Vortex over the Eastern Slope of the Tibetan Plateau

Benefit of assimilating satellite all‐sky infrared radiances on the cloud and precipitation prediction of a long‐lasting mesoscale convective system over the Tibetan plateau

AbstractHeavy rainfall events in the warm season (May–September) over the Tibetan Plateau (TP) region and its downstream areas are often closely related to eastward‐propagating Tibetan Plateau Vortices (TPVs). Hence, improving the prediction of TPVs and their associated convective activity is of paramount importance, given the significant potential impacts they can have on densely populated downstream regions, including but not limited to flooding and damages. In this study, a typical long‐lived TPV that occurred in July 2008 was used for the first time to explore the benefit of assimilating satellite all‐sky infrared radiances on the cloud and precipitation prediction of the TPV‐induced eastward‐propagating mesoscale convective system (MCS). The all‐sky infrared radiances from the water vapor (WV) channel of the geostationary Meteosat‐7 and other conventional observations were assimilated into a 4‐km grid spacing regional model using the ensemble Kalman filter. The results revealed that the all‐sky infrared data assimilation improved the cloud, precipitation, dynamical, and thermodynamical analyses as well as 0–12‐hr deterministic and ensemble forecasts. Compared with the experiment in which the all‐sky infrared radiances were not assimilated (non‐radiance experiment), the experiment with assimilated all‐sky infrared radiances yielded clearly improved initial wind and cloud fields, 1–12‐hr cloud forecasts, and 1–6‐hr precipitation forecasts. This study indicates that assimilation of all‐sky satellite radiances has the potential for improving the operational cloud and precipitation forecasts over the TP and its downstream areas.

Increasing amounts of midwestern Tibetan Plateau vortices and their response to soil moisture distribution coupled with different synoptic systems

AbstractTibetan Plateau Vortices (TPVs) are important synoptic systems that affect precipitation over the Tibetan Plateau (TP) and downstream weather. By using daily reanalysis data provided by ECMWF and the objective identification methods, the study identified the basic spatiotemporal changes of TPVs, clustered the TPVs by different dynamic circulation types and explored the dynamic circulation background of the classified TPVs in the midwestern TP and their relationship with thermal factors, such as sensible heat and soil moisture. The results show that TPVs in the midwestern TP exhibited an increasing trend from May to August, resulting from the coupling of dynamics with thermal forcing. The related synoptic circulations were divided into four types according to the dynamic circulations: the shortwave trough, the longwave trough, the shear line and the plateau anticyclone type. Among the TPVs, the percentage of TPVs in the shortwave and longwave trough type was relatively large, accounting for 48.7% and 31.5%, respectively, both of which were dominated by the coupling of increased sensible heat and decreased soil moisture. The shear line type was less affected by thermal factors, and mainly driven by dynamic factors, whereas the soil moisture gradient was responsible for the plateau anticyclone type. The simulation experiment also proved this conclusion.

Two types of Tibetan Plateau vortex genesis in June and the associated mechanisms

The Tibetan Plateau vortex (TPV) is a key system triggering rainfall over the Tibetan Plateau (TP) during the boreal summer. The TPV genesis mechanisms are complicated and its classification is a great challenge. This study attempts to elucidate these aspects. By introducing the standardized index of 24-h increment of equivalent potential temperature Delta_{24h} theta_{{text{e}}} at 500 hPa, all the TPV cases generated in June between 1980 and 2016 are classified as either positive or negative. Composite analysis is subsequently applied to the extremes of these two types, i.e., the first and last fifth-percentile cases with extremely negative and positive standardized Delta_{24h} theta_{{text{e}}}, respectively. Results indicate that 70% of them occur in relatively warmer and wetter environments, with diabatic heating dominating the positive type and the dynamic effect of large-scale circulation dominating the negative type. For the extremely positive cluster, the geopotential-height increment over the TP exhibits a negative/west–positive/east dipole, which enhances the southerly flow over the western TP, while forming surface water–vapor convergence. Consequently, strong condensation heating occurs near the sub-cloud level, resulting in the development of potential vorticity below and eventually TPV genesis. For the negative cluster, local shear lines at 500 hPa and upstream troughs at 250 hPa occur at the TPV genesis location. In conjunction with anomalous westerlies, positive potential vorticity is generated in situ due to zonal advection. The retardation caused by the Kunlun Mountains on the impinging westerly flow associated with side-boundary friction also contributes to TPV genesis southeast of the mountains.

Helicity characteristics of cyclonic vortexes and their effect on convection in a wide‐ranging extreme rainstorm in China

AbstractOn 20–22 July 2012, a severe rainstorm occurred in the Sichuan basin of Southwest China and in the Beijing area of North China. This rainstorm was related to the activities of a Tibetan Plateau vortex (TPV) and Southwest China vortex (SWCV). By using radiosonde, satellite brightness temperature, and NCEP_FNL data, we investigated the helicity characteristics nearly the vortexes and their effect on convection. Results showed that (1) strong precipitation in the Sichuan basin was mainly related to the interaction between the TPV and SWCV, while strong precipitation in the Beijing area was related to the northward movement of a cyclonic vortex caused by a split in the SWCV. (2) During the occurrence of the rainstorm, four mesoscale convection systems (MCSs) were observed. Their vertical structure showed a positive vorticity–negative divergence in the lower levels, and negative vorticity–positive divergence in the upper levels, accompanied by vertical upward movement. This was an important factor in the development and maintenance of MCSs, as well as one of the mechanisms for producing heavy precipitation. On this basis, we further discussed the effect of helicity on the MCSs in the atmospheric environment with rotational characteristics. Results showed that the increase in negative water vapour helicity and storm‐relative helicity were more likely to cause a strong development of MCSs.

Causation of the heavy rainfall in Kyushu in early July 2020: A perspective of the depression that originated over the Tibetan Plateau

Heavy rain fell in Kyushu, Japan, in early July 2020, which caused huge life and economic losses. The present work reports that a Tibetan Plateau vortex (TPV) generated over the Tibetan Plateau transformed into a trough at the eastern edge of the Tibetan Plateau, and the trough continued to move eastward and was responsible for the heavy rainfall in Kyushu. Accordingly, the maintenance and eastward movement of the trough and the influencing mechanism of the trough on the rainfall in Kyushu are explored based on the final analysis data (FNL) from NCEP and the JRA-55 reanalysis from JMA. Diagnoses of the potential vorticity (PV) tendency equation indicate that the horizontal PV flux convergence east of the trough is the primary contributor to the eastward movement and maintenance of the trough. Furthermore, the trough is proved to have important effects on the moisture condition and the ascending motion around Kyushu. That is, the trough increases the moisture in Kyushu by intensifying the eastward moisture transportation to Kyushu; the positive vorticity and warm center, as well as the wind perturbation related to the trough, are in favor of stronger ascending motion in Kyushu. The findings in this work provide extended knowledge on the causation of rainfall in Japan, which is beneficial for further precipitation prediction.

Characteristics and changes in the atmospheric water cycle of the Tibetan Plateau Vortex

The Tibetan Plateau Vortex (TPV) is an important low-pressure system that affects the weather and climate in the Qinghai-Tibet Plateau. It is of great importance to study the water cycle of the TPV to further understand the TPV and its resulting disastrous weather. This study is different from the previous studies of TPV cases or of the atmospheric water cycle of the Qinghai Tibet Plateau. Focusing on the moving TPV weather system, from the perspective of climatology, the characteristics of the atmospheric water cycle of the TPV and the atmospheric circulation that affects the activity of the TPV water cycle are studied using statistical methods based on the reanalysis data. The results show that the TPV water cycle is mainly affected by external circulation. The overall water vapour utilization efficiency of the TPV water cycle first decreases and then increases, and its activity degree first decreases and then increases. The high-value area of TPV precipitation is located in the middle of the plateau and annual TPV precipitation has a good correlation with TPV water cycle activity. The large-scale system is closely related to the vortex water cycle of the plateau. When the intensity of the South Asian high (SAH) is relatively strong, the West Pacific subtropical high (WPSH) advances westward, and there is a stronger warm rising area over the main body of the plateau. When the southerly airflow on the south side of the low-level plateau is strong, the water cycle of the TPV is more active, easily moves eastward and produces more precipitation, and vice versa.

Characteristics of two different types of thunderstorms in summer over the Nagqu area in China

To investigate further the characteristics of thunderstorms on the Qinghai–Tibet plateau, a plateau vortex (PV) thunderstorm and a local thermoconvective (TC) thunderstorm over the Nagqu area are analyzed using cloud-radar, microwave-radiometer, and raindrop-spectrometer data, and their macrophysical and microphysical evolution characteristics are discussed in terms of thermodynamic processes, microphysical processes, and lightning activities. The results show the following. 1) The cloud layer was deeper in the PV thunderstorm, but the TC thunderstorm had a stronger short-time updraft with a radial velocity exceeding 10 m/s, and the warming from the strong updraft action and latent heat release from the hydromorphic phase change was about twice that of the PV thunderstorm. 2) The water vapor density increased significantly when the thunderstorm cloud passed, and the liquid water content in the middle and lower layers exceeded 4 g/m3. The maximum ice water content in the TC thunderstorm was twice bigger than that in the PV thunderstorm. The trends of raindrop number concentration and rain intensity of the PV thunderstorm were similar, and the average particle size of raindrops was smaller than that of the TC thunderstorm. 3) Both types of thunderstorms accounted for more than 90% of negative cloud-to-ground (CG) lightning, and the regions with black-body temperature (TBB) less than −40 °C and a larger TBB gradient were more favorable for the occurrence of CG lightning. 4) Thermodynamic fields bring water vapor and lift for microphysical processes, and microphysical changes release latent heat to enhance the dynamic effects, which together promote the development of lightning activities. The peak radial velocity and ice-phase particle concentration were more than 10 min ahead of the active peak of the CG lightning. This study reveals the macrophysical and microphysical evolution characteristics of different types of thunderstorms and provides a certain scientific basis for disaster prevention and mitigation regarding thunderstorms over the Nagqu area.

Extreme precipitation events over the Tibetan Plateau and its vicinity associated with Tibetan Plateau vortices

Extreme precipitation events (EPEs) often bring disastrous consequences, such as floods, urban waterlogging and landslides. Understanding the effects of weather systems on EPEs can help improve the accuracy of weather forecasts. The Tibetan Plateau vortex (TPV) is a mesoscale weather system that is active near the surface of the Tibetan Plateau (TP). Though the crucial role of TPVs on the TP precipitation has been widely known, the influence of TPVs on EPEs is not yet clear. In this study, the quantitative impacts of TPVs on the EPEs over the TP and its surrounding areas are investigated based on the TPV datasets from the ECMWF Reanalysis v5 (ERA5) and four precipitation datasets from the ERA5, NOAA Climate Prediction Center (CPC), Integrated Multi-satllitE Retrievals for the Global Precipitation Measurement (GPM) Mission (IMERG) and in-situ rain gauges. The results show that the TPVs have remarkable positive contribution to the EPEs over the TP and its adjacent regions for all four precipitation datasets. The TPVs induce more than half of the daily EPEs over the central TP, while the number of days influenced by TPVs only accounts for <20% of the total days over this region. A higher frequency of EPEs is identified over the central TP, and a higher ratio of the TPVs tends to be associated with EPEs after they move out of the TP. The EPEs tend to occur near the center and the southeastern quadrant of TPVs. For the TPVs associated with EPEs (EPE-TPVs) and those having no relation to EPEs (NEPE-TPVs), the structure of TPVs and related large-scale circulation are significantly different at the upper- and lower-level of the troposphere. The EPE-TPVs tend to be larger, stronger, thicker, and move farther than the NEPE-TPVs. The TPVs inducing EPEs usually consist of some specific synoptic components, including the southwest monsoon current along the southern side of TPVs, the shear line near the surface of the TP, and the South Asia high in the upper-troposphere. EPE-TPVs related atmospheric circulations and the climatology of circulations are analyzed in detail to provide a better understanding for forecast service.

Climatic characteristics of Tibetan Plateau vortex precipitation based on observations

AbstractTibetan Plateau vortices (TPVs) are important rainfall producers generated over the Tibetan Plateau (TP), which can move off the TP under certain conditions. The TPVs greatly affect both local and downstream rainfall, but the characteristics of TPV precipitation are not yet fully understood. Accordingly, the climatic characteristics of TPV precipitation during May–August of 1998–2018 are explored in this work from multiple aspects, based on observational TPV and precipitation data sets. Generally, maximums of precipitation amount are observed over the eastern TP and in Sichuan Basin, and the TPVs contribute more than 40% of the precipitation in certain areas within the TP. For the TPVs located over the TP, the precipitation is distributed zonally with a relatively small intensity; for the TPVs beyond the TP, the associated precipitation is distributed in the southwest–northeast direction with a larger intensity. TPVs tend to be responsible for intense rainfall, that is, heavy and torrential rainfalls, and are suggested to be the major intense rainfall producers at certain stations over and downstream from the TP. Meanwhile, TPV precipitation exhibit distinctive features in separate month, for example, TPV precipitation account for the largest percentage of the total precipitation in June and the smallest in August; more than half, even 75% of the torrential rain days downstream from the TP in Sichuan Basin and the regions around 35°N in central and eastern China in May, and in the regions over the TP and its eastern flank in June, July and August are attributed to TPVs.

Heavy precipitation events in northwestern China induced by northeastward plateau vortex: Two cases comparison

The plateau vortex is one of the dominant weather systems that modulate summer rainfall in northwestern China, a typical arid/semi-arid area worldwide. Two heavy rainfall cases in the summer of 2012 and 2013, accompanying the northeastward movement of plateau vortexes, are selected here. The role of plateau vortexes in these two cases is explored by diagnosing their moist potential vorticity, helicity, and convective clouds characteristics, using numerous data (ERA-Interim reanalysis, multi-sourced precipitation data, FY-2E satellite images). The plateau vortexes enhanced convective instability in the rainfall area by entraining upper-level dry and cold air, manifested as salient vertical gradients of moist potential vorticity and steep pseudo-equivalent potential temperature isolines. The rainfall occurred eastward relative to the vortex movement track and intensified on the left of cloud black body temperature (TBB) with larger gradients at the middle to late stages of the vortex life span. The generation of moisture helicity is dictated by the water vapor transportation, with the negative value concentrated in the water vapor-rich areas. Notably, the two cases differ in tracks, life spans, water vapor sources, and precipitation amounts, which may be attributed to large-scale circulation background, vertical vortex structure, and moisture condition.

The characteristics and formation mechanism of double-band radar echoes formed by a severe rainfall occurred in the Sichuan Basin under the background of two vortices coupling

During 29–30 UTC June 2013, a severe rainfall event with a long and narrow region of strong precipitation occurred in the central of the Sichuan Basin (SCB). Under the combined influence of a Tibetan Plateau vortex (TPV) and a southwest vortex (SWV), two banded strong radar echoes existed and developed simultaneously over the SCB. The analysis reveals that the vertical wind shear (VWS) caused by the circulations of the TPV and the SWV was the dominant factor of the formation and development of the radar echoes over the SCB. During the coupling period of the two vortices, the SWV provided abundant water vapor at the middle and lower levels over the SCB and the updrafts of the two vortices break through that formed deep convection, which made the precipitation in the SCB reach the maximum intensity. The enhancement of horizontal vorticity caused by the baroclinicity and the secondary circulation related to the two vortices created conditions for the formation of the double-band radar echoes. The matching degree of water vapor and heating conditions accompanying the circulation of the two vortices could affect the developments of convective storms and precipitation.

Effects of Atmospheric Heat Source on the Tibetan Plateau Vortex in Different Stages: A Case Study in June 2016

The Tibetan Plateau (TP) vortex (TPV), one of the crucial weather systems triggering rainfall, plays a key role in modulating precipitation over TP and downstream regions. The role of atmospheric heat source in TPV development is explored by a case study in June 2016, using high-resolution ERA5 reanalysis, black-body temperature (TBB) obtained from the Fengyun-2E (FY-2E) satellite, and precipitation amount from the Tropical Rainfall Measurement Mission (TRMM). The evolutions of TPV can be split into three stages, i.e., generation, development, and pre-moving-off stage. The intensity of TPV increases with fluctuations, with weaker and shallower TPV in the generation stage, strongest in the development stage and deepest in the pre-moving-off stage. Importantly, the genesis of TPV is related to the surface warming center driven by surface sensible heating while its development is primarily dependent on the latent heat of condensation. The main contributor of the latent heat of condensation is further analyzed as a vertical transport of the water vapor that promotes TPV development.