Deep convection plays a vital role in transporting Asian pollutants from the planetary boundary layer (PBL) into the Asian summer monsoon anticyclone (ASMA). However, the efficiency and effectiveness of transporting pollutants with various chemical and physical properties to the ASMA remain unclear. In this study, we use the global atmospheric chemistry and climate model EMAC to investigate the deep convective transport of trace gases such as CO, NH3 and SO2 from the PBL to the ASMA over the years 2010-2020. We quantify the deep convective transport efficiency of different trace gases into the ASMA. We show that the strongest convective transport tendency occurs over northern India and the southern edge of the Tibetan Plateau for CO (0.2-0.5 ppbv h-1), over the south and eastern parts of the Tibetan Plateau for NH3 (0.02-0.05 ppbv h-1), and over central India and eastern China for SO2 (0.002-0.005 ppbv h-1). We find that, in contrast to CO and NH3, the SO2 enhancements within the ASMA are very weak, and there can even be a decrease in SO2 over the southern Tibetan Plateau relative to the surroundings. Our analysis indicates that gas-liquid partitioning in clouds and subsequent wet deposition over South Asia are more effective at reducing SO2 than NH3 reaching the Tibetan Plateau and the ASMA. In view of ongoing changes in regional emissions, the effects of deep convective transport of various pollutants and associated gas-aerosol-cloud interactions on the chemical features of the ASMA require continued investigation.

The paper outlines research achievements of Chinese Academy of Meteorological Sciences (CAMS) in the development of new multi-band weather radar detection technologies, field experiments, radar data quality control, generation of secondary products, studies of cloud-precipitation processes and structures. In response to scientific frontiers and national requirements, CAMS has successively developed a C-band transportable dual-polarization radar, an X-band phased-array weather radar, a multi-band cloud radar observation system, and a C-band continuous-wave vertically pointing radar. Cloud-precipitation observation bases and severe convective weather observation bases have been established at Longmen, Shenzhen, and Foshan in Guangdong, as well as cloud-precipitation observation bases at Naqu and Mêdog on the Tibetan Plateau. Long-term field experiments are carried out focusing on rainstorms, typhoons, microphysical structures of clouds and precipitation at these sites. Utilizing these field experiment data together with observations from the national weather radar network, studies have been conducted on data quality control methods for W/Ka/Ku multi-band cloud radars, C-band vertically pointing continuous-wave radar, wind profilers, dual-polarization weather radars, and phased-array dual-polarization weather radars, aiming to remove non-meteorological echoes, reduce attenuation effects, and mitigate systematic biases in radar measurements. Mosaic and integration methods for S-, C-, and X-band weather radars have been developed to extend the spatial coverage of radar data, reduce biases in X-band radar data, and produce high-quality gridded radar data with high spatiotemporal resolution. Employing dual-band Doppler power spectrum analysis technique, methods have been investigated for retrieving vertical air velocity, raindrop size distributions, and drop size distributions of solid precipitation particles of different shapes, as well as vertical profiles of water content and rainfall intensity from multi-band cloud radars. Quantitative precipitation estimation, hydrometeor classification, tornado and mesocyclone identification, and networking approaches for multi-band weather radars have also been studied. Furthermore, nowcasting research based on artificial intelligence has been conducted, thereby enhancing the capability of radar systems to detect cloud and precipitation microphysical and dynamical parameters. Using field experiment data, the fine microphysical structure and evolution of clouds and precipitation in regions such as South China and the Tibetan Plateau have been investigated, providing more detailed data and products for cloud physics and severe weather monitoring and early warning. Many of these research results have been operationally applied to severe weather monitoring and warning services in China. Enhancing the detection capabilities, optimizing the accuracy of observation modes, and expanding the application of phased array weather radar technology, as well as advancing detection techniques using shorter wavelengths and their application in cloud process observation, will remain key research directions for CAMS in the future.

During the boreal summer, the westerlies of the South Asian monsoon prevail over Southwest China, flowing perpendicularly to the north–south-oriented mountains. However, the initiation mechanism of nocturnal convection under weak synoptic forcing in this region remains unclear. This study combines radar observations, convection-resolving Weather Research and Forecasting (WRF) simulations, and terrain sensitivity experiments to investigate the influence of low-level winds and complex terrain on nocturnal convection initiation (CI) around Cangshan Mountain, a typical north–south-oriented range in Southwest China. Diagnostic analysis of vertical velocity acceleration indicates that CI is associated with persistent dynamic forcing and rapid enhancement of thermal buoyancy forcing, and the terrain oriented perpendicular to the flow plays a crucial role in this process. Thermodynamically, the topography of Cangshan Mountain depresses the level of free convection (LFC) and lifting condensation level (LCL) to below 700 hPa via moisture accumulation and enhanced instability in the western valleys, resulting in pronounced thermal asymmetry between the eastern and western flanks of the mountain. Dynamically, low-level winds influenced by Cangshan Mountain and a mountain range to its west generate persistent convergence within the thermally favorable environment, which induces ascending motion above both the LFC and LCL. During the hour before CI, the LFC within the western valleys gradually decreases, while the convergence above the LFC and LCL persistently intensifies, forcing the maintenance and enhancement of ascending motion. This process simultaneously promotes water vapor condensation, thereby enhancing thermal buoyancy forcing and ultimately leading to CI. Terrain sensitivity experiments reveal that scaling down the Cangshan Mountain elevation weakens its topographic barrier effect, raising the LFC and reducing low-level convergence at the CI location, thereby suppressing CI. This study identifies a terrain-elevated convection mechanism, where parallel mountains lower the LFC thermodynamically while raising the convergence layer dynamically. The proposed mechanism provides a reference for improving convection forecasting in complex terrain under weak synoptic forcing.

To address the scarcity of observational data constraining in-depth research on topographic precipitation, the Cangshan Mountain Precipitation Experiment (CAMPEX) was launched by the Chinese Academy of Meteorological Sciences and Yunnan Provincial Meteorological Bureau. Focused on the quasi-north–south-oriented Dali Cangshan Mountain, a region with a pronounced precipitation enhancement effect in Southwest China, CAMPEX aims to elucidate how steep meso-γ-scale terrain modulates large-scale systematic precipitation and locally triggered convection. For this purpose, three core observation zones across the mountain peak and the eastern and western valleys are equipped with X-band and Ka-band radars, microwave radiometers, disdrometers, Doppler wind lidars, and other advanced instruments. The 5-yr experiment has completed 2 intensive observing periods to date (20 June–31 October 2024 and 1 May–31 October 2025), capturing 17 systematic precipitation events and 14 locally triggered convective processes under dominant weather conditions such as shear lines, typhoon remnants, frontal systems, southern branch troughs, and weak synoptic-forcing scenarios. Advances in cross-instrument quality control, multi-radar mosaics, and three-dimensional (3D) wind-field retrieval over complex terrain, have enabled comprehensive monitoring of precipitation evolution, filling previous radar blind zones. The campaign has produced high-resolution datasets including 3D winds, thermodynamic profiles, and cloud microphysics. Another distinct feature of CAMPEX is a hectometer-resolution numerical forecasting system designed particularly for the Cangshan region, operating synchronously with the field campaign. Preliminary analysis confirms the reliability of the acquired data and has provided potential insights into how the Cangshan terrain enhances precipitation of different types. This paper outlines the design and implementation of CAMPEX, and presents the dataset and early scientific findings obtained thus far.

On 7 July 2023, a large-scale heavy precipitation event takes place in northwestern Liaoning, influenced by the Northeast cold vortex. An extreme hourly precipitation of 95.9 mm is recorded from 1800 BT to 1900 BT at Fangshan, Heishan County. A multi-scale analysis of this hourly extreme precipitation event is conducted using ERA5 reanalysis data, upper-air observations, automatic weather station observations, FY-4A satellite data, 3-dimensional mosaic products of weather radar base data (V3.0) and dual polarization radar data. The analysis focuses on large-scale environmental characteristics of this extreme hourly precipitation event, the development and evolution of mesoscale convective systems, and evolution characteristics of dual-polarization radar parameters during the event. These approaches reveal the role of the surface cold pool in the initiation and development of mesoscale convective systems that produced the heavy precipitation, as well as the relationship between 3-dimensional vertical structure and microphysical characteristics of convective systems and the extreme precipitation. Results indicate that during this process, an occluded front exists near the Northeast cold vortex. The heavy precipitation area is located near the occluded front system, within the southeast quadrant of the mature cold vortex. Fangshan, where extreme hourly rainfall occurs, is situated close to the warm front of the occluded front system. At the same time, there is a continuously strengthening southwest low-level jet in the lower layers, which transports warm and moist water vapor to the heavy precipitation area, providing favorable dynamic and moisture conditions for this hourly extreme precipitation event. Under combined effects of cold pool outflow generated by evaporative cooling of surface precipitation, the topography of the Yiwulü Mountains, as well as warm and moist environmental airflow, convective cells are continuously triggered in areas with high temperature gradient. The train effect formed by continuously emerging cells is the core cause for this hourly extreme precipitation event. The heavy rainfall belt shows a southwest-northeast distribution, closely aligns with the terrain, and continuously passes through Fangshan, causing an extreme hourly precipitation of 95.9 mm and accumulated rainfall of 190.3 mm in 5 h. During the extreme hourly precipitation period, there are two main convective storms affecting Fangshan, resulting in two precipitation peaks. Both strong convective storms are characterized by high values of reflectivity (Z), differential reflectivity (ZDR), and specific differential phase (KDP) values, accompanied by ZDR and KDP columns developing above -20 ℃ level, indicating abundant ice-phase particles. However, there are also differences, the first precipitation peak is mainly due to raindrop coalescence and growth, featuring large diameters and low concentrations; the second precipitation peak had high raindrop concentration, smaller drop diameters, and is accompanied by incompletely melted ice-phase particles.

The raindrop size distribution (RSD) plays a crucial role in study of microphysical processes related to precipitation. Discrepancies in the derived microphysical characteristics of precipitation arise when different models are adopted to fit RSD, thereby affecting accuracy of precipitation microphysical studies. Consequently, a comprehensive examination of RSD fitting models is warranted. Due to limitations of the instrument, the disdrometer is prone to underestimating small raindrops and medium-size raindrops.The full RSD is constructed through the combination and observations from micro rain radar and disdrometer at Mêdog (4 April, 13 September and 29 September in 2021) and Longmen (10 May, 9 June and 10 June in 2022). Generalized Gamma model is implemented to characterize full RSD, with comparative analyses being conducted against the standard Gamma model. Results indicate that rain rates calculated from full RSD are better agreement with the ground rain gauge measurements, exhibiting higher correlation coefficients and smaller biases. Based on full RSD data of different rainfall intensities obtained from different regions, double-moment normalization is adopted by choosing the 3rd and the 6th moments to achieve the fitting of generalized Gamma model with two shape parameters(μ and c). The raindrop number concentration N(D), generalized diameter parameter D'm and rain rate obtained are shown to be closer to observations than those fitted by standard Gamma model, and it can be used to describe the drizzle pattern, the precipitation pattern, and the region between them simultaneously. Judging from results of quantitative comparison, it shows that the fitting of generalized Gamma model demonstrates a smaller bias and a higher model efficiency coefficient compared to standard Gamma model. Based on the raindrop size distribution of precipitation influenced by various microphysical processes (diameter-controlled type and quantity-controlled type) at Mêdog and Longmen, the fundamantal shape h(x) of the raindrop size distribution is derived through double-moment normalization. Even for raindrop size distributions that exhibit significant microphysical differences, the function h(x) continues to demonstrate remarkable stability. Especially in the central part of the normalized diameter range, this relative stability is demonstrated to have important practical application value for the retrieval of raindrop size distribution from dual-polarization weather radar data by applying the generalized Gamma model.

A Multiscale Analysis of a Nocturnal Extreme Rainfall Event of 14 July 2017 in Northeast China Gaili Wang1, Da-Lin Zhang2,1, and Jisong Sun11State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Science, Beijing, China46 South Street Zhongguancun, Beijing, China 1000812 Department of Atmospheric and Oceanic Science, University of Maryland, College Park, College Park, Maryland AbstractA 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-a-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-b-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 BST 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-b-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.

Mêdog, located at the entrance of the water vapour channel of the Yarlung Zangbo Grand Canyon, and it has the highest rainfall and lowest elevation on the Tibetan Plateau (TP). The droplet size distribution (DSD) and microphysical processes associated with rainfall usually exhibit different characteristics under different synoptic patterns. In this study, an objective classification method is used to categorize the synoptic patterns that affect heavy rainfall (daily rainfall amounts > 10 mm) in Mêdog into four patterns: southwest airflow (SWA), southern-branch trough (SBT), intense baroclinicity (IBC), and terrain-forced precipitation (TFP). SWA occurs most frequently (approximately 70

The Second Tibetan Plateau Scientific Expedition and Research Program tasked a research team with the “Investigation of the water vapor channel of the Yarlung Zsangbo Grand Canyon (INVC)” in the southeastern Tibetan Plateau (TP). This paper summarizes the scientific achievements obtained from the data collected by the INVC observation network and highlights the progress in investigating the development of heavy rainfall events associated with water vapor changes. The rain gauge network of the INVC can represent the impacts of the Yarlung Zsangbo Grand Canyon (YGC) topography on precipitation at the hourly scale. The microphysical characteristics of the precipitation in the YGC are different than those in the lowland area. The GPM-IMERG (Integrated Multi-satellitE Retrievals for Global Precipitation Measurement) satellite precipitation data for the YGC region should be calibrated before they are used. The meridional water vapor flux through the YGC is more important than the zonal flux for the precipitation over the southeastern TP. The decreased precipitation around the YGC region is partly due to the decreased meridional water vapor flux passing through the YGC. High-resolution numerical models can benefit precipitation forecasting in this region by using a combination of specific schemes that capture the valley wind and water vapor flux along the valley floor.

Mêdog is located at the entrance of the water vapor channel of the Yarlung Tsangpo Great Canyon on the southeastern Tibetan Plateau (TP). In this study, the seasonal variation in the microphysical vertical structure of stratiform precipitation at the Mêdog site in 2022 was investigated using micro rain radar (MRR) observations, as there is a lack of similar studies in this region. The average melting layer height is the lowest in February, after which it gradually increases, reaches its peak in August, and then gradually decreases. For lower rain categories, the vertical distribution of small drops remains uniform in winter below the melting layer. The medium-sized drops show slight increases, leading to negative gradients in the microphysical profiles. Slight or evident decreases in concentrations of small drops are observed with decreasing height in the premonsoon, monsoon, and postmonsoon seasons, likely due to significant evaporation. The radar reflectivity, rain rate, and liquid water content profiles decrease with decreasing height according to the decrease in concentrations of small drops. With increasing rain rate, the drop size distribution (DSD) displays significant variations in winter, and the fall velocity decreases rapidly with decreasing height. In the premonsoon, monsoon, and postmonsoon seasons, the concentrations of large drops significantly decrease below the melting layer because of the breakup mechanism, leading to the decreases in the fall velocity profiles with decreasing height during these seasons. Raindrops with sizes ranging from 0.3–0.5 mm are predominant in terms of the total drop number concentration in all seasons. Precipitation in winter and postmonsoon seasons is mainly characterized by small raindrops, while that in premonsoon and monsoon seasons mainly comprises medium-sized raindrops. Understanding the seasonal variation in the vertical structure of precipitation in Mêdog will improve the radar quantitative estimation and the use of microphysical parameterization schemes in numerical weather forecast models over the TP.

The Yarlung Zsangbo Grand Canyon (YGC) is an important pathway for water vapor transport from southern Asia to the Tibetan Plateau (TP). This area exhibits one of the highest frequencies of convective activity in China, and precipitation often induces natural disasters in local communities, which can dramatically affect their livelihoods. In addition, the produced precipitation gives rise to vast glaciers and large rivers around the YGC. In 2018, the Second Tibetan Plateau Scientific Expedition and Research Program tasked a research team to conduct an "investigation of the precipitation process in the water vapor channel of the Yarlung Zsangbo Grand Canyon" (INVC) in the southeastern TP. This team subsequently established a comprehensive observation system of land-air interaction, water vapor, clouds, and rainfall activity in the YGC. This paper introduces the developed observation system and summarizes the preliminary results obtained during the first two years of the project. Using this INVC observation network, herein, we focus on the development of rainfall events on the southeastern TP. This project also helps to monitor geohazards in the key area of the Sichuan-Tibet railway, which traverses the northern YGC. The observation datasets will benefit future research on mountain meteorology.

Raindrop size distribution (DSD) is a basic characteristic for describing the microphysical process of rainfall. A better understanding of DSD and its variations is not only crucial for improving microphysical parameterization schemes in numerical weather forecasting models, but also important for radar quantitative precipitation estimation. It shows that DSD characteristics are not only related to geographical location, climate, terrain, and humidity, but also vary among different rainfall types and rain rate in the same region. At present, there are still some uncertainties and limitations in the understanding of microphysical characteristics of rainfall in Northeast China, and the microphysical parameterization scheme still lacks accurate description of rainfall microphysical process. Based on observations of the precipitation phenomenon instrument at Xinmin of Liaoning Province in summer, DSD characteristics of different rainfall rate classes are investigated and compared with those of other regions in China. Spectral width of DSD increases with an increase in rain rate ( R). The spectral width of raindrops is close to 8 mm when R>20 mm·h-1. Small drops are predominant in rainfall of Xinmin, but moderate drops make the most significant contribution to total rainfall. Observed DSD samples are also categorized into convective and stratiform rainfall types. The convective rainfall at Xinmin has large raindrop size and low raindrop concentration. Convective rainfall can be identified as continental clusters, with average Dm and lg Nw of 2.14 mm and 3.40, while average Dm and lg Nw of stratiform rainfall at Xinmin are 1.23 mm and 3.30, respectively. The μ- Λ and Z- R relationships for convective and stratiform rainfall at Xinmin are thus fitted. Fitted μ- Λ relationship at Xinmin is similar to that in other regions fitted with data observed by PARSIVEL disdrometers, but different from the empirical relationship fitted from two-dimensional video raindrop spectrometers (2DVD) observations in other regions, and the difference of instruments is the main cause for the discrepancies of μ- Λ relationships. Compared with East China and North China, Xinmin rainfall has larger Dm, lower lg Nw, and higher exponent value of fitted Z- R power-law relationship for convective rainfall, indicating that the radar reflectivity factor at Xinmin increases more rapidly with the increase of rain rate. Using the Z- R empirical formula fitted at Xinmin can reduce the error of radar-based quantitative precipitation estimation. Results would contribute to the understanding of microphysical characteristics of rainfall in Northeast China and the accuracy of radar quantitative precipitation estimation.

Mêdog County, with its mountains and valleys, is located in the southeastern Tibetan Plateau (TP) and at the lower reaches of the Yarlung Zangbo River. This area has the highest annual rainfall amount over the TP, and in situ measurements are very scarce due to frequent debris flows and transportation difficulties. A monitoring campaign focused on cloud and precipitation observations was established in Mêdog in 2019 as a part of the Second Tibetan Plateau Scientific Expedition and Research Program. This paper evaluates the accuracy of micro rain radar (MRR) measurements and investigates the variations in precipitation vertical structure in Mêdog using observations collected from the MRR, disdrometer, and rain gauges in summer 2021. The measurements from the three instruments show a strong consistency, with correlation coefficients exceeding 0.93. Although the profiles of integral rain parameters for different rain rate categories in Mêdog are similar to those in other regions, the vertical evolution of raindrop size distributions shows significant differences. For lightest rain, the evaporation of small raindrops and breakup of large raindrops are clear during their descent. For the rainfall rate category of 0.2–2.0 mm h−1 (2.0–20.0 mm h−1), concentrations of small and medium (large) drops show almost uniform vertical structures, while the large (medium) drop number displays a positive (negative) gradient. A disturbance at height of 1.5–2.0 km above ground level (AGL) is observed in the heavy rainfall due to strong updrafts. In general, the MRR measurements in Mêdog are robust. The raindrop breakup process is more apparent in Mêdog than in other regions, resulting in high concentration of size-limited raindrops. In addition, it is found that the interaction between steep terrain and Mêdog convective rain causes the strong updrafts between 1.5 and 2.0 km AGL.

Precipitation is particularly important for the earth's climate system. Understanding the structural characteristics, microphysical processes and drop size distribution (DSD) of precipitation is very important for quantitative precipitation estimation with radar and improving microphysical parameter schemes of numerical weather prediction models. With the launch of the Second Tibet Plateau Scientific Expedition and Research(STEPS), Chinese Academy of Meteorological Sciences has deployed Ka-band cloud radar (KaCR), X-band dual polarization phased array radar (X-PAR), disdrometer, micro rain radar (MRR) and other detection equipment in Mêdog, filling the gap of cloud and precipitation observation in this area and provides data basis for studying the physical characteristics of clouds and precipitation. Mêdog is located at Yarlung Zangbo Grand Canyon, the entrance of the water vapor channel in southeastern Tibet. Influenced by the warm and humid airflow brought by the Indian Ocean monsoon, the precipitation of Mêdog during the monsoon period exceeds 60% of the annual precipitation. MRR is a low-cost, miniaturized vertical directional Doppler rain radar that can more accurately analyze the vertical structural changes of precipitation. Based on observation of the rain gauge, MRR and disdrometer set up at Mêdog National Climate Observatory from 1 June to 30 September in 2021, the consistency of different instruments is studied. The observed rainfall is classified into convective, stratiform and shallow precipitation types, and the average vertical distribution characteristics of different precipitation types are studied from the aspects of raindrop size distribution, falling speed, rain rate, liquid water content and radar reflectivity. The results show that the measurement of rain gauge, MRR and distrometer are highly consistent. The correlation coefficient of daily rainfall is above 0.89, and the highest correlation coefficient between MRR and rain gauge is 0.96. However, MRR overestimates weak precipitation and underestimate strong precipitation. There are significant differences in the vertical structure of different precipitation types during the monsoon period of Mêdog. Values of each microphysical quantity of convective precipitation are larger. The collision and growth process of raindrop is significant during the falling process below 3 km height, and the raindrop number concentration increases rapidly. There is significant updraft at a height of 1-2 km. The echo intensity of stratiform cloud precipitation is weak below the height of the melting layer. The radar reflectivity, rain rate and liquid water content increase with altitude decrease, the falling speed of raindrops remains basically stable in the vertical direction. The concentration of medium-sized raindrops remains constant with height, and the evaporation, fragmentation, and coalescence processes are in a relatively balance. Values of each microphysical quantity of shallow precipitation are relatively small but vary significantly with height and show negative slops in the vertical direction. The shallow precipitation is dominated by the collision process of raindrops.

Mêdog and Nagqu are two typical climate regions of the Tibetan Plateau, with different atmospheric conditions and local orography. This may lead to different diurnal variation patterns of clouds and precipitation. This paper investigates the diurnal variations of clouds and precipitation in Mêdog and Nagqu, using ground-based measurements from Ka-band cloud radar and a Particle Size and Velocity (PARSIVEL) disdrometer. High frequencies of cloud cover and precipitation occur from 23:00 local solar time (LST) to 05:00 LST in Mêdog, while low frequencies appear from 11:00 LST to 17:00 LST. The occurrence frequencies in Nagqu maintain high values from 13:00 LST to 21:00 LST. In terms of mean rain rate, heavier rainfall appears in the evening and at night in Mêdog, with peaks at 00:00 LST and 18:00 LST, respectively. In Nagqu, the heaviest rainfall occurs at 12:00 LST. In addition, the afternoon convective rainfall in Nagqu is characterized by a much higher concentration of large drops, which can be classified as continental-like. The morning rainfall has the lowest concentration of large drops and can be classified as maritime-like. Finally, the mechanisms of diurnal variations in the two regions are discussed. The diurnal cycle of clouds and precipitation in Mêdog may be associated with the nocturnal convergence of moisture flux and mountain–valley wind circulation. Diurnal variations in Nagqu have a high correlation with the diurnal cycle of solar radiation. The high nocturnal frequency of clouds and precipitation in the two regions at night is closely related to the convergence of moisture flux.

Mêdog, located in the southeastern Tibetan Plateau（TP） and the valley of the lower reaches of the Yarlung Zangbo River, is the main water vapor channel from the Indian Ocean to the TP. Mêdog is also an important part of the TP precipitation system because it has the largest annual average precipitation amount over the TP. Based on the Ka-band cloud radar（KaCR） observation data of the Mêdog National Climate Observatory in 2020, this study first preprocessed the power spectrum data of the KaCR, which were verified by comparing with measurements from a collocated precipitation phenomenometer. Then, two weak stratiform precipitation processes that occurred on March 6 and August 24, 2020, were selected, and the raindrop size distribution（RSD） was retrieved from the power spectrum data of the KaCR to explore the microphysical characteristics of weak precipitation in the dry and rainy seasons in Mêdog. Results showed that the systematic error of the reflectivity factor reached approximately 12 dB between KaCR measurements and theoretical values of KaCR calculated from the observations using the precipitation phenomenometer. Good consistency between the two datasets is evident after KaCR was corrected. Furthermore, the near-surface RSDs retrieved from KaCR was close to those observed from the precipitation phenomenometer. The heights of the bright band in Mêdog varied with the seasons and were low in the dry season（i.e., approximately 1.5 km above ground level） and high in the rainy season（i.e., approximately 4 km above ground level）. The spectral width of the RSD of the weak stratiform precipitation cases was narrow, and the diameter of the raindrop did not exceed 3 mm in Mêdog. Above the bright band, the diameter of small ice particles gradually increased with the decrease in height according to the spectrum skewness and kurtosis.However, the growth of ice particles in the dry season is more obvious than that in the rainy season. Below the bright band, the ice particles converted into liquid water drops, whose concentration decreased as the height decreased in the process of falling, probably due to the coalescence and evaporation of raindrops. The smaller the diameter is, the faster the concentration of raindrops decreases. Near the ground, the significant decrease in the concentration of raindrops can be attributed to enhanced evaporation.

Mêdog is located at the entrance of the water vapor channel in the Yarlung Zangbo Grand Canyon (YGC). This area has the largest annual accumulated rainfall totals and precipitation frequency on the Tibetan Plateau (TP). This paper investigates the seasonal variation in raindrop size distribution (DSD) characteristics in Mêdog based on disdrometer observations from 1 July 2019 to 30 June 2020. The DSD characteristics are examined under six rain rate classes and two rainfall types (stratiform and convective) in the winter, premonsoon, monsoon and postmonsoon periods. The highest (lowest) concentration of small raindrops is observed in monsoon (winter) precipitation, whereas large raindrops predominate in premonsoon precipitation. For stratiform rainfall, the mean mass-weighted mean diameter (Dm) exhibits overlooked differences in the four periods, while the mean normalized intercept parameter (Nw) is significantly higher in the monsoon period than in the other three periods. The convective rainfall in the monsoon and postmonsoon periods is characterized by a high concentration of limited-size drops and can be classified as maritime-like. This is probably attributed to abundant warm and humid airflow transported by the Indian Ocean monsoon into Mêdog. The westerly winds prevail over the TP during the premonsoon period, and thereby the premonsoon convective rainfall in Mêdog has a larger mean Dm and a lower mean Nw. In addition, the relationships of radar reflectivity Z and rain rate R for different precipitation types in different periods are also derived. A better understanding of the seasonal variation in the microphysical characteristics of precipitation in Mêdog is important for improving the microphysical parameterization scheme and the precipitation forecast of models on the TP.

The Yarlung Zangbo Grand Canyon (YGC) is an important pathway for water vapor transport from south Asia to the Tibetan Plateau (TP). This area exhibits one of the highest frequencies of convective activity in China, and precipitation often brings natural disasters to local communities that can dramatically affect their livelihoods. In addition, the produced precipitation has produced vast glaciers and large rivers around the YGC. In 2018, the Second Tibetan Plateau Scientific Expedition and Research Programme tasked a research team to conduct an "Investigation of the water vapor channel of the Yarlung Zangbo Grand Canyon" in the southeastern Tibetan Plateau. This team subsequently established a three-dimensional comprehensive observation system of land-air interaction, water vapor transport, cloud cover, and rainfall activity in the YGC. This paper introduces the developed observation system and summarizes preliminary results obtained during the first two years of the project. Using this observation network, we focus herein on the development of heavy rainfall events in southeast Tibet that are associated with water vapor transported from the south. This project also helps to monitor geohazards in the key area of the Sichuan-Tibet railway that traverses the northern YGC.

The civilian airplane is a common transportation mode for the local people in the Qinghai-Tibet Plateau (QTP). Due to the profound dynamic and thermal effects, the QTP can trigger strong windstorms during the warm season, during which downbursts can cause severe low-level wind shear and threaten aviation safety. However, the study of downbursts over QTP has not been given much attention. This study analyzes and interprets a typical traveling dry microburst line that happened at the Xining Caojiapu International Airport (ZLXN) on 14 May 2020, intending to show a better understanding of the dry downbursts over QTP and explore the synergetic usage of different remote sensing technologies for downburst detection and warning in plateau airports. Specifically, the characteristics of synoptic conditions, the convective system formation process, and the structure and evolution of downbursts and relevant low-level winds are comprehensively investigated. The results show that, under the control of an upstream shallow trough, features of the local atmosphere state, including a dry-adiabatic stratification, a shallow temperature inversion, increases in solar radiation heating, and strong vertical shears of horizontal winds, can be favorable atmospheric prerequisites for the formation and development of dry storms and downbursts. Low-reflectivity storm cells of the Mesoscale Convective System (MCS) organize to form narrow bow echoes, and downbursts show features of radial wind convergences and rapid descending reflectivity cores with hanging virga as observed by a Doppler weather radar. Moreover, details of gales, gust fronts, convergences, turbulences, wind collisions, and outflow interactions triggered by the downburst line are also detected and interpreted by a scanning Doppler wind lidar from different perspectives. In addition, the findings in this work have been compared with the results observed in Denver, U.S., and some simulation studies. Finally, a few conceptual models of low-level wind evolutions influenced by the dry downburst line are given.

Mêdog and Nagqu 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 Mêdog and Nagqu. The DSD characteristics are studied under five different rainfall rate categories and two precipitation types (stratiform and convective). For the total datasets, the number concentrations of drops with diameters D > 0.6 (D < 0.6) mm are higher (lower) in Nagqu than in Mêdog. The fitted normalized gamma distributions of the averaged DSDs for the five rainfall rate categories show that Nagqu has a larger (lower) mass-weighted mean diameter Dm (normalized intercept parameter, lgNw) than does Mêdog. The difference in Dm between Nagqu and Mêdog increases with the rainfall rate. Convective clusters in Nagqu could be identified as continental-like, while convective precipitation in Mêdog 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 lower concentrations of larger drops observed in Nagqu, whereas warm rain prevails in Mêdog, producing abundant small drops.