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Tornadoes, as highly destructive weather events, require accurate detection for effective decision‐making. Traditional radar‐based tornado detection algorithms (TDA) face challenges with limited tornado feature extraction capabilities, leading to high false alarm rates and low detection probabilities. This study introduces the Multi‐Task Identification Network (MTI‐Net), leveraging Doppler radar data to enhance tornado recognition. MTI‐Net integrates tornado detection and estimation tasks to acquire comprehensive spatial and locational information. As part of MTI‐Net, we introduce a novel backbone network of Multi‐Head Convolutional Block (MHCB), which incorporates Spatial and Channel Attention Units (SAU and CAU). SAU optimizes local tornado feature extraction, while CAU reduces false alarms by enhancing dependencies among input variables. Experiments demonstrate the superiority of MTI‐Net over TDA, with a decrease in false alarm rates from 0.94 to 0.46 and an increase in hit rates from 0.23 to 0.81, highlighting the effectiveness of MTI‐Net in handling small‐scale tornado events. Plain Language Summary: Tornadoes, highly destructive small‐scale weather phenomena, demand accurate detection for informed decision‐making. Although meteorological radars are commonly utilized for tornado identification, current methods often suffer from false alarms or missed detections due to radar noise. In this study, we introduce the multi‐task learning‐based identification network (MTI‐Net), which not only enables tornado detection but also estimates tornado counts within radar data. We integrate Convolutional Neural Networks (CNNs) with Transformer techniques to enhance the model's ability to capture tornado information. CNNs detect local details using filters, while Transformers manage global connections through attention mechanisms. A series of experiments demonstrate significant improvements in tornado detection with MTI‐Net compared to traditional methods. Key Points: A tornado dataset with detailed radar features was created over China from 2017 to 2023Multi‐task learning was designed to simultaneously infer tornado detection and tornado number estimationIntegration of spatial and channel attention units can better extract tornado features from radar data [ABSTRACT FROM AUTHOR]

Understanding the diurnal variation of horizontal wind in the atmospheric boundary layer is important for weather and climate research and wind energy applications. Here we analyze the hourly data from 91 wind profiler radar sites in China and observe that the power spectral density of horizontal wind in lower troposphere approximately follows the −5/3 power law in the mesoscale range over the ocean and coastal areas. However, in inland areas, the slopes of the power spectra are significantly greater than −5/3. We characterize the temporal and spatial variations of maximum wind speed and low level jets and find that the thermal wind effect may partially contribute to the high percentage of low‐level jets observed in the southeastern coast of China and Hainan Island. While the ERA5 reanalysis reproduces wind spectrum well for time scales >1 day, its spectrum diverges significantly from that of profiler data at shorter time scales. Plain Language Summary: Understanding how the horizontal wind changes throughout the day in the lower part of the atmosphere is important for studying weather and climate and using wind energy. In this study, we looked at data from 91 radar sites in China that measure wind every hour. We found that the pattern of how the wind changes follows a specific mathematical relationship, called a power law, where the wind decreases in a particular way with decreasing spatial and temporal scales. This pattern holds true mostly over the ocean and coastal areas, but in areas further inland, the wind behaves a bit differently. We also studied how the low‐level jet (LLJ), which are fast winds at low altitudes, change over time and space. We discovered that the difference in temperature across the region contributes to the occurrence of these LLJs in coastal areas in southeast China and Hainan Island. Finally, we compare our findings with the ERA5 reanalysis, which demonstrates excellent agreement in reproducing the wind spectrum for time scales greater than 1 day. However, the spectrum derived from the ERA5 reanalysis diverges significantly from the profiler data at shorter time scales. Key Points: Wind spectrum density from wind profiler radars over China shows a less negative slope over inland sites than the −5/3 power law over oceanTemporal and spatial variation of maximum wind speed in the lower troposphere and low level jets are characterizedWind spectrum from ERA5 reanalysis is realistic (deficient) for time scales >1 day (<1 day) compared with profiler data [ABSTRACT FROM AUTHOR]

Since early 2019, the Lunar Penetrating Radar (LPR) onboard Chang'e‐4 (CE‐4)'s Yutu‐2 rover has been gathering data relating to the subsurface structure of the Von Kármán crater within the South Pole‐Aitken Basin (SPA) on the lunar farside. Low‐frequency radar data have the potential of carrying geological information of about 300 m worth of strata below the traversed path. Forty‐two days' data have revealed a bifurcated structure within the layered structure beneath the CE‐4 surveying area for the first time, affecting the overlying reflectors between 90 and 310 m. This study suggests that, based on the morphological characteristics, thickness, depth (timing sequence) and direction of the newly found structure, its origin might be linked to the deposition of ejecta from the Schrödinger impact. The local stratigraphy is interpreted as consisting of distinct geological layers, corresponding to the superposition of ejecta from different impact craters, paleo‐regolith, and basaltic lava flows. Plain Language Summary: A radar (the Lunar Penetrating Radar, or LPR), built to look at the rocks below the surface, is presently traveling across an area of the lunar farside onboard a rover, called Yutu‐2 sent by China to shed some light on the striking difference between the Earth‐facing side of the Moon and its farside. So far, the radar has revealed layered structures interpreted as distinct volcanic flows, thus helping to unravel their history. The rover has been surveying the floor of the Von Kármán crater inside one of the oldest and largest impact structures of the Moon, the South Pole‐Aitken (SPA) Basin. By analyzing 42 lunar days of data, we found a new layer with a hunched upper surface and a relatively flat bottom inserted into a multilayered structure. Based on the morphology, thickness, depth, and direction of the new feature, we argue that its source could represent the ejecta deposition from one of the ancient lunar impact basins: Schrödinger. The subsurface structure revealed by the radar shows a complicated geologic history on the farside including multiple lava eruption events, the deposition of ejecta from different impact craters and weathering layers that develop during the quiescent stage. Key Points: The CH‐1 Lunar Penetrating Radar data of Chang'e‐4 reveals ∼300 m deep subsurface stratigraphy of the lunar farsideA unique bifurcated structure that resembles an ejecta discontinuity affects the overlying and underlying strataThe geologic evolution of the Von Kármán crater and the ejecta layer might be connected to the Schrödinger basin [ABSTRACT FROM AUTHOR]

The impact of assimilating China's operational X‐band Phased‐Array radar's (X‐PAR) data on the analysis and warning forecast of the vortex structure and intensity of the June 8, 2018 Foshan, Guangdong province, tornadic storm was investigated for the first time using an Ensemble Kalman Filter (EnKF) data assimilation system. Both radar radial velocity (Vr) and reflectivity (Z) from two S‐band operational radars and one X‐PAR were assimilated. Deterministic forecasts were launched every 6 min from 05:42 UTC (20 min before the tornado touched down) to 06:00 UTC from the EnKF mean analysis field. Five experiments were conducted to examine the added capability of Z assimilation of the EnKF system, and to investigate the impact of assimilating X‐PAR data on the analysis and prediction of the tornadic storm. Compared to the experiment without Z assimilation, the assimilation of Z reduced the analysis error and greatly reduced the forecast error of Z. The assimilation of X‐PAR data greatly improved the vortex structure of the tornadic storm at low levels, and improved the intensity of the rear inflow of the tornadic storm, especially with a higher assimilation frequency. Compared to the experiments without X‐PAR data assimilation, assimilating X‐PAR data improved the predictability of tornadic storm. Plain Language Summary: Tornadoes are difficult to predict worldwide. However, the scan speed of current operational S‐band (10 cm wavelength) radar is too slow to capture the evolution of tornadoes. The newly built X‐band (3 cm wavelength) Phase‐Array radar (X‐PAR) network in Guangdong Province, China, are hopeful to fill in the gap with their higher scan frequency and higher spatial resolution, which can capture the fine‐scale structure and rapid evolution of small scale systems such as tornadic storms. This study focuses on a case where a tornado embedded within the typhoon Ewiniar was well captured by the X‐PAR network. It demonstrated for the first time the use of X‐PAR data on the prediction of a tornadic storm in China. We used ensemble‐based data assimilation techniques named Ensemble Kalman Filter to utilize the information provided by the X‐PAR data. With the improved information, the analyzed tornadic storm vortex structure at low levels was greatly improved, especially with a higher assimilation frequency. Compared to the experiments without X‐PAR data, the experiment using X‐PAR data successfully predicted the tornadic vortex a few minutes in advance. Key Points: The impact of assimilating China's X‐band Phased‐Array radar (X‐PAR) radar data on the analysis and forecast of a tornadic storm was first investigated using an Ensemble Kalman Filter systemThe assimilation of X‐PAR data helps to produce a more realistic‐looking tornadic storm structure, especially at low levelsIncreasing assimilation frequency of X‐PAR data reduces the analysis error and subsequently improves the 8‐min tornadic storm forecast [ABSTRACT FROM AUTHOR]

In this study, multi‐source data, especially weather radar data, were used in the analysis of structural features and evolution of a squall line‐like rainband (SLLR) of a linear mesoscale convective system (MCS) in the eastern slope of the Taihang Mountains on 12 and 13 August 2018 and reached the following conclusions: (a) The SLLR, located in north of the linear MCS, exhibited a significant horizontal gradient of reflectivity and large vertical extension. The front‐to‐rear flow that appeared between the surface and the stratosphere was lifted upward immediately in front of a cold pool that formed rearward‐tilting updrafts. (b) As the SLLR passed over, surface meteorological quantities changed drastically, coinciding with the heavy precipitation. (c) The SLLR, when propagating northeastward, showed a complex convective development of sequential intensification, weakening, and re‐intensification within a 2.5‐hr period. The temporal intensification was related not only to the development of a low‐level rear‐inflow jet but also to the dynamic interaction between the vertical environmental wind shear and the cold pool. The lifted rear‐inflow jet, which formed over a vertically stacked horizontal vorticity couplet behind the leading edge, provides a reasonable explanation for the intensification of the SLLR, resulting in the reduction of the cold pool circulation and enhancement of the convective updraft. Topographic forcing might play a crucial role in the re‐intensification of the SLLR, which suggests the importance of the cold pool and topography in structural features and convective evolution of the squall line‐like rain bands. Key Points: The squall line‐like rainband (SLLR) in a linear mesoscale convective system exhibited the characteristics of the typical squall lineThe SLLR was associated with a complex convective development of sequential intensification, weakening, and re‐intensificationThe cold pool and topography play crucial roles in structural features and convective evolution of the SLLR [ABSTRACT FROM AUTHOR]

Dual‐frequency radar (DFR) could improve the accuracy of estimating the microphysical properties of rain profiles. Unfortunately, factors that cause inaccuracies in retrieved rain profiles include uncertainties in raindrop size distribution (DSD) parameterizations, DFR retrieval methods and radar measurement errors. The primary objective of this study was to assess the uncertainties in retrieving rain profiles to offer insight into application considerations for ground‐based DFRs in China. The uncertainties caused by DSD models are assessed by comparing attenuation coefficients and rain rates from DFR algorithms with those directly derived from DSD spectra from disdrometers. Then, based on a DSD model, the impacts of retrieval methods, radar range resolution, measurement error and errors in temperature on DFR retrievals are explored by comparing the rain profiles obtained using DFR algorithms with those directly output from the Weather Research and Forecasting model. Overall, the impact of measurement error on the DFR retrievals is relatively significant for both the forward retrieval method and the iterative backward retrieval method and should be eliminated in practical applications. At an individual uncertainty level, the impact of DSD parameterizations on the retrievals from the dual‐frequency technique is less than ±10% bias when the shape factor μ of the gamma distribution ranges from 2 to 4. The retrieved rain profiles from the forward retrieval method are relatively sensitive to radar range resolution and the retrieval performance can be improved with increasing the range resolution, while the iterative backward retrieval method exhibits stable retrieval performance. The impact of temperature errors on the retrieved rain profiles is negligible. [ABSTRACT FROM AUTHOR]

This study examines the impacts of humidity adjustment in a cloud analysis system on the analysis and forecast of a squall line that occurred in southeast China on 23–24 April 2007. Radial velocity data are assimilated using the ARPS three‐dimensional variational system while reflectivity data are assimilated by a cloud analysis system. Experiments with two different humidity adjustment schemes are performed, with the original and enhanced versions. Another experiment does not adjust moisture. Both schemes generally decrease the humidity in front of the convective line and increase the humidity within the convective and stratiform regions of squall line compared to no humidity adjustment, and the original scheme produces the higher humidity within precipitation regions, especially the stratiform region. Both schemes improve the forecast of squall line structure, including the leading convective line, a transition zone, and a trailing stratiform region. Among the three experiments, the enhanced scheme produces the highest precipitation forecast skill. The latent heating rates are also diagnosed to investigate the microphysical responses to the humidity adjustment. The cooling outside of the observed precipitation regions corresponding to the humidity reduction also acts to suppress spurious precipitation. Water vapor condensation into cloud water and cloud water evaporation generally dominate the latent heating/cooling below the freezing level. Compared to the enhanced scheme, the original scheme releases much more latent heat in the middle troposphere, causing more warming. This is linked to the higher cloud water condensation rate, due to the higher amount of moisture addition/adjustment by the original scheme. Key Points: An enhanced vertical velocity‐dependent moisture adjustment scheme produces better squall line structures in both analysis and forecastThe "overwarming" issue associated with the original scheme is linked to more latent heat release associated with higher condensation rateCondensation into and evaporation of cloud water dominates latent heating/cooling below the freezing level [ABSTRACT FROM AUTHOR]

Thunderstorm identification from weather radar data remains a fundamental problem in lightning nowcasting. In this study, a novel thunderstorm identification method combining the area of graupel distribution region and weather radar reflectivity is proposed. To optimize identification parameters of the identification method, the radar echoes with 312 thunderstorms in 17 weather processes in Nanjing area, China, from 2014 to 2015 were identified and tested to obtain the optimal identification parameters. The results indicate that the optimal parameter combination is to set the storm region identification reflectivity threshold at 0°C isothermal level to 30 dBZ and set the area of graupel distribution region to 2 km2. With such a parameter combination, the optimal identification results with the probability of detection of 91%, false alarm rate of 6.9%, and critical success index of 85.3% could be obtained. Moreover, the proposed thunderstorm identification method can also provide effective means for thunderstorm nowcasting. Plain Language Summary: Thunderstorm is a kind of disastrous weather that often brings us great losses. If thunderstorms can be timely detected, we can take appropriate means to deal with them. Weather radar is considered as an efficient tool for detecting thunderstorms. It is an important problem in the application of weather radar to identify thunderstorms from radar echoes. In the present study, a new method for identifying thunderstorms using dual‐polarization weather radar is proposed, which combines reflectivity with the integral area of graupel related to thunderstorm electrification to identify thunderstorms. The method is tested by 312 thunderstorms in 17 weather processes in Nanjing area, China, from 2014 to 2015. The test results show that the method has good thunderstorm identification performance. Key Points: A novel thunderstorm identification method combining the area of graupel distribution region and weather radar reflectivity is proposedThe area of graupel distribution region at certain isothermal levels is the key parameter of the thunderstorm identification methodA detection probability of 91% and a false alarm rate of 6.9% can be achieved by the proposed method [ABSTRACT FROM AUTHOR]

Deep learning models based on radar echo extrapolation have been widely used in precipitation nowcasting. However, they face the challenge of insufficient input information when extending the forecast lead time, requiring the incorporation of physics‐based numerical weather prediction (NWP). Given that the strengths of radar and NWP data vary depending on the forecast time, effectively fusing these two data sources in a unified deep learning model remains an open research problem. In this study, we propose a Time‐aware Adaptive Feature Fusion Network (TAFFNet) for very short‐term precipitation forecasts up to 12 hr. TAFFNet fuses features adaptively according to their relative contributions to forecast skill at different times. Experimental results demonstrate that TAFFNet performs the best for very short‐term precipitation forecasts. The case studies show that adaptively fusing NWP with radar can improve the accuracy of precipitation forecasts, especially for predicting the initiation and dissipation of storms at longer lead times. Plain Language Summary: Very short‐term precipitation forecasting aims to predict precipitation for a couple of hours, which is crucial for public safety and emergency management in cities. Recently, deep learning models have been widely used for precipitation nowcasting (0–2 hr) based on observation extrapolation. However, as the forecast time increases, extrapolating historical observations alone is inadequate without incorporating physical constraints. On the contrary, traditional NWP can provide essential physical background, but the prediction accuracy still needs improvement for early forecasting periods. In this study, we proposed a novel deep learning model named TAFFNet to combine both advantages of radar and NWP for very short‐term precipitation forecasts up to 12 hr. The features of radar and NWP are first extracted, respectively. Their features are fused adaptively in the forecasting part through a time‐aware adaptive feature fusion (TAFF) module, according to their relative contributions to forecast skill at different lead times. The feature fusion approach can be optimized adaptively through model training. The proposed model is evaluated on the radar and NWP model data set covering southeast China. Results demonstrate that incorporating NWP into a radar‐based deep learning model can improve very short‐term precipitation forecasts. TAFFNet can better capture the storm's initiation and dissipation during forecasting. Key Points: A novel deep learning model termed Time‐aware Adaptive Feature Fusion Network (TAFFNet) is proposed for very short‐term precipitation forecasts up to 12 hrFeatures from radar and numerical weather prediction are fused adaptively in deep levels based on their relative contributions to forecast at different lead timesTAFFNet can improve very short‐term precipitation forecasts, especially for predicting storms initiation and dissipation at longer times [ABSTRACT FROM AUTHOR]

A mesoscale convective system (MCS) over East China on June 5, 2009 was thoroughly analyzed using an Advanced Regional Prediction System (ARPS) ensemble square root filter (EnSRF) system. The analyzed reflectivity structure, location and intensity compared well with observation, and were substantially better than an experiment without radar data assimilation. The cold pool and wind speed in the convective regions were strengthened. With improved initial conditions, the impact of single‐moment (SM), double‐moment (DM) and triple‐moment (TM) microphysics parameterization (MP) schemes on ensemble forecasts of MCSs was evaluated. The use of multi‐moment (MM) MP schemes showed some improvements in neighborhood ensemble probability for reflectivity and precipitation. Quantitative reflectivity and precipitation forecast skills were also improved in MM forecasts, with those of the TM forecast the best. [ABSTRACT FROM AUTHOR]

The Urumqi Institute of Desert Meteorology under the China Meteorological Administration (CMA) launched an observational experiment with a boundary layer wind-profiling radar in Urumqi City in February to March 2010. As described in this paper, wind profiles from the experiment were used to first compare with radiosonde data measured simultaneously to verify the confidence of wind-profiling radar data, which was used to analyse the wind field characteristics and other related issues in a snowstorm process that took place in Urumqi on 28 March 2010. Both wind direction and speed derived from wind-profiling radar data have good consistency with those from radiosonde data (wind velocity coefficient: 0.85; wind direction coefficient: 0.78). Before the snowstorm, a surface wind shear occurred. After outbreak of the event, the local weather was dominated by northwesterly and northerly winds at increasing velocities, while temperature was dropping and air pressure increased. Through in-depth analyses of the time-height profiles of the snowstorm process, it can be determined on a preliminary basis that the snowstorm was induced by a cold front system that entered the area around 2200-2300 LST on 27 March. A shear line that developed from a lower to a higher altitude represented both height and location of the frontal zone, and the cold front motion was broadly in a northeast-southwest direction. The wind direction in the process changed counterclockwise with height: this was mainly governed by cold advection, and baroclinic instability was established soon after the overpass of the cold front, eventually leading to the snowstorm. During the weather event, the equivalent reflectivity factor Ze was consistent with the onset and end of the snowstorm, the height at which rain (snow) particles were formed and snowfall intensity. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Previous theoretical simulations showed the generation of double‐layer structures of E‐region field‐aligned irregularities (FAIs). In this study, we report the double‐layer structures of E‐region FAIs observed by an all‐sky radar at low latitude Ledong (18.4°N, 109°E), China. These FAIs appeared at the altitudes ∼90 and 110 km respectively. Both layers displayed quasi‐periodic patterns with synchronized spatial features, that is, being manifested as spatially separated patches or wavelike structures over similar longitudes at the two layers simultaneously. The neutral wind observations revealed the existence of wind shears at two separated altitudes where the double FAI layers occurred. The two wind shears created two vertically separated sporadic E layers and possibly drove the generation of the double‐layer FAIs via gradient drift instability. The synchronized spatial features of the FAIs at the two layers could be modulated by gravity waves. Plain Language Summary: The E‐region field‐aligned irregularities (FAIs) were observed usually in a form of single layer. Due to the limited field of view of narrow‐beam radars which were traditionally employed for observing ionospheric irregularity, the spatial morphology and evolution of E‐region FAIs in a small region were resolved. Owing to the recently developed capability of all‐sky radars in observing E‐region irregularities, the spatial features of E‐region irregularities over a larger zonal region up to hundreds of kilometers in the horizontal plane can be derived. Further, the spatial features of E‐region irregularities in the vertical direction can be unambiguously determined. Utilizing an all‐sky radar at low latitude Ledong, China, a case of double‐layer structures of E‐region FAIs, which occurred at ∼90 and 110 km altitudes respectively, was observed. The double layers of FAIs spanned a zonal coverage ∼250 km, showing as synchronized spatially separated quasi‐periodic patches or wavelike structures in two layers. Especially, the wavelike structures synchronized in the two layers could provide solid evidence for the crucial role of gravity waves in modulating E‐region irregularities. In combination with the collocated ionosonde Es and neutral wind observations, the physical mechanisms responsible for the generation of the double‐layer E‐region FAIs were discussed. Key Points: Double layer structures of E‐region field‐aligned irregularity (FAI) were observed at low latitude by an all‐sky radarBoth layers of FAIs were quasi‐periodic type and synchronously manifested as spatially separated patches or wavelike structuresThe double‐layer FAIs were likely generated by wind shear driven gradient drift instability and modulated by gravity waves [ABSTRACT FROM AUTHOR]

This study presented an intuitive approach to derive large‐scale tidal flat's Digital Elevation Model (DEM). We first developed an automated method for accurately extracting the waterline from Synthetic Aperture Radar images acquired in Subei Sandbanks along the Yellow Sea coast of China between 2015 and 2020 based on deep convolutional neural networks. The statistical results show this method has appreciable accuracy for efficient waterline extraction even under complex imaging conditions with a mean recall and precision of 0.90 and 0.80, respectively. Then the pixel‐level extracted waterlines are calibrated with a global tide model to construct the large‐scale tidal flat's DEM in the study region. The comparison against in situ topographic data shows an error of 29 cm, demonstrating the usefulness of monitoring the morpho‐sedimentary evolution in intertidal areas. Furthermore, the Subei Sandbanks remained stable from 2015 to 2020, while the coastal region changed drastically due to human activities. Plain Language Summary: Monitoring the geomorphological evolution of tidal flats is critical for coastal development and wetland conservation. Compared to traditional surveying approaches, the waterline method can provide topographic maps more frequently with a lower cost and higher coverage. However, both the signal returned from the sea surface and the exposed tidal flats on radar images change drastically under different sea conditions. Benefiting from the development of deep learning, especially the deep convolutional neural networks, waterlines of tidal flats on complex Synthetic Aperture Radar images can now be automatically and accurately extracted. Furthermore, with a calibrated ocean tide model that can make the tidal evaluation instantly, we develop an automatic approach to topographic map the large‐scale tidal flats, which may provide timely information for stakeholders related to coastal management and ecosystem protection. Key Points: A deep‐learning‐based technique was developed to extract waterline from synthetic aperture radar imagesA combination of the deep‐learning model and tidal analysis is used for automatic topographic mapping of large‐scale tidal flatsMulti‐year digital elevation model series in the study region are obtained with morpho‐sedimentary evolution analysis [ABSTRACT FROM AUTHOR]

Using a clustering algorithm based on cloud‐to‐ground (CG) lighting data, 72,974 thunderstorms were identified and tracked in the middle reaches of the Yangtze River Basin from May to September of 2016–2020. Thunderstorms predominantly occur in the southeast region and move to the northeast at a speed of 16–64 km/hr. Most thunderstorms have short durations (98.3%, ≤3 hr) and low CG flash frequencies (90.0%, ≤64). Thunderstorms with longer durations are mainly triggered near the mountains and tend to occur (end) earlier (later) in the afternoon (evening). The peak composite reflectivity (CR) corresponding to CG flashes from all thunderstorms is 50 dBZ. Approximately 70% (20%) of CG flashes occur in convective (stratiform) areas. The first CG flash of a thunderstorm tends to occur in convective areas with a higher CR than that of the last CG flash. The average and maximum CRs of CG flashes increase significantly with thunderstorm duration. Plain Language Summary: Thunderstorms are known as a type of weather system that is typically accompanied by the presence of lighting and other hazardous weather (high winds, heavy rain, hail and tornadoes). Cloud‐to‐ground (CG) lighting produced by thunderstorms is a highly dangerous weather phenomenon that occurs between a thundercloud and the ground and often causes wildfires, explosions and severe damage to buildings. The middle reaches of the Yangtze River Basin in China are a transition zone between plateaus and plains, with dense urban agglomerations, rivers and lakes. However, thunderstorm activity in such complex underlying surfaces is poorly understood. Based on ground‐based radar and lightning observations, the statistical characteristics of thunderstorm activity in this region during the warm seasons (May to September) of 2016–2020 are analyzed using a lightning clustering method. The CG lighting number, area and displacement of thunderstorms increase with thunderstorm duration. Thunderstorms that last longer are mostly triggered near the mountains and often start earlier in the afternoon and end later in the evening. In addition, CG lighting produced by thunderstorms is associated with high radar echo intensity. These findings are useful for improving the nowcasting of lightning and other hazardous weather caused by thunderstorms. Key Points: The cloud‐to‐ground (CG) flash number, area, displacement, etc., of thunderstorms based on lightning data change with increasing thunderstorm durationThunderstorms with longer durations, mostly triggered near the mountains, occur earlier in the afternoon and end later in the eveningRadar echo characteristics of CG flashes from thunderstorms with different durations show certain regularities [ABSTRACT FROM AUTHOR]

Using 5‐year dual‐polarization radar observations, variations of convective and microphysical characteristics of extreme precipitation features (EPFs) with increasing rainfall extremity over a monsoon coastal region (Pearl River Delta; PRD) in South China are investigated through comparing three groups of EPFs (ER1, ER2, and ER3). The more extreme rainfall shows a notable increase and decrease in the fractions of "intense" convection and "weak" convection, respectively. The higher rainfall extremity is accompanied by statistically significant increases in ice and liquid water contents but a roughly equal fraction of coalescence in liquid‐phase processes. While the raindrop size distributions of ER1 to ER3 similarly feature a mean size larger than "maritime‐like" droplets and a concentration much higher than "continental‐like" raindrops, the mean size and concentration of raindrops tend to increase slightly with the increasing rainfall extremity. Two sensitivity experiments on EFP definition confirm the robustness and representative of the above results. Plain Language Summary: Extreme precipitation could induce flooding and severe hazards and may increase in the warming climate. It has recently been shown that extreme precipitation can be produced by very intense convection with presence of large solid precipitating particles such as graupel and hail, or by weak convection with much shorter vertical extension through rapid growth of many raindrops, or by moderate convection in between. However, we do not know well to what extent extreme precipitation overlaps with intense convection and how the convective and microphysical characteristics change with increasing rainfall extremity. To answer these questions, we use 5‐year dual‐polarization radar observations over a monsoon coastal region combined with distrometer observations, and comparatively analyze the convective and microphysical characteristics of rainfall with three different extreme levels. Results show that, with higher rainfall extremity, probability distribution of the extreme rainfall‐producing convection tends to shift toward stronger convective intensity, producing larger liquid and ice water contents (significant at 0.01 confidence level) and also slightly higher concentration with larger mean size of raindrops. Key Points: With more extreme rainfall, the extreme precipitation features tend to grow in horizontal size from the meso‐γ‐ to meso‐β‐scaleOverlap between extreme precipitation and extreme convection increases substantially with more extreme rainfallEnhanced mixed‐phase processes, larger liquid/ice water contents, slight changes in liquid‐phase processes are with more extreme rainfall [ABSTRACT FROM AUTHOR]

In June 2019, an earthquake sequence comprising five M > 5 events occurred in a region of southwest China with fluid injection for both hydraulic fracturing and salt mining, which raised an extensive controversy on the cause. Here we use interferometric synthetic aperture radar (InSAR) observations to determine the source parameters of the sequence and to investigate the relationship with local injection activities. Both Sentinel‐1 and Advanced Land Observing Satellite 2 SAR images are collected to measure coseismic and preseismic surface deformation. Geodetic inversions with coseismic observations show that the sequence ruptured a previously unmapped southwest‐dipping thrust fault above 3 km depth, which intersects with the open‐hole sections of wells for solution mining of salt. In the 4 months before the sequence, cumulative line‐of‐sight displacements near the wells are around 1–2 cm after correcting seasonal‐like deformation. Our results indicate that water injection likely enhanced pore pressure within the fault zone and thus contributed to inducing the sequence. Plain Language Summary: Earthquakes are seldom reported in relation to fluid injection for salt mining. Here, we present a unique case of an earthquake sequence probably induced by such human activity in Changning (southwest China). The sequence began with a Ms 6.0 earthquake, which is an unprecedented magnitude and larger than the historical records of earthquakes induced by wastewater disposal and hydraulic fracturing. Due to the sparse distribution of seismic stations and the failure of a key station closest to injection wells for salt mining before the Ms 6.0 earthquake, available seismic data are not enough to constrain the spatial locations of events in the earthquake sequence. Here we instead use high spatial‐resolution interferometric synthetic aperture radar observations of coseismic surface deformation to image the causative fault of the sequence. We find that the open‐hole sections of injection wells intersect the seismogenic fault. Moreover, the cumulative surface displacements near the salt mine in the ~4 months before the sequence are 1–2 cm, which was mainly caused by ground uplift. Accordingly, we hypothesize that fluid injection increased pore pressure within the fault zone and brought it to rupture. Our interferometric synthetic aperture radar observations and inversion results present significant evidence toward the causality between salt mining and the earthquake sequence. Key Points: InSAR observations show significant ground deformation due to the Changning earthquake sequence near the salt mineInSAR inversions reveal that the Changning earthquake sequence ruptured a southwest‐dipping thrust fault above the depth of 3 kmThe open‐hole sections of wells injecting for solution mining of salt intersect the InSAR‐inferred seismogenic fault [ABSTRACT FROM AUTHOR]

Mars' surface is characterized by a weathered layer of regolith and exposed rock exposures that are the results of long‐term geological processes. The Mars Rover Penetrating Radar (RoPeR) on board the Zhurong rover of China's first Mars mission (Tianwen‐1) has been investigating the fine structure and dielectric properties of the martian regolith in the southern Utopia Planitia. The permittivity of the regolith within 5 m of the landing zone is 3.6−2.0+3.1 ${3.6}_{-2.0}^{+3.1}$, and the average loss tangent is 0.0174−0.0053+0.0053 ${0.0174}_{-0.0053}^{+0.0053}$. The high lossy parameter suggests the possible cause for the missing subsurface reflectors in the landing region detected by either in‐situ radar or orbiter radars. The permittivity distribution map has been derived to show permittivity varying with depth and location. The high dispersion of both permittivity and loss tangent values along the traverse path indicates relatively heterogeneous material distribution on the landing site compared to an airless body such as the Moon. Plain Language Summary: A layer of regolith covers the surface of Mars, which is the result of geologic processes that occurred over millions to billions of years. Compared to the observations from satellites, the Zhurong rover of China's first Mars mission (Tianwen‐1) had a closer look at the properties of the regolith layer in the explored region within southern Utopia Planitia. There is evidence that the exposed materials might be related to aqueous activities. Local landforms on the surface suggest the possible presence of buried volatiles, like water ice. The radar instrument (RoPeR) on board the rover can expose subsurface structures and the dielectric properties of the regolith layer at high‐resolution, to assess their composition. The loss tangent results suggest that water ice is not the main component of the local martian regolith at some depth. The scattering distribution of radar profile along the traveling path and heterogeneous subsurface features show more diverse surface processes and weaker space weathering effects on Mars than those on the airless Moon. Key Points: The dielectric properties of martian regolith at the Tianwen‐1 landing site suggest that water ice is not the dominant componentThe radar image and permittivity and loss tangent distribution maps show a high heterogeneity of subsurface materialsCompared to the lunar regolith, the martian regolith shows more diverse surface processes and weaker space weathering effects [ABSTRACT FROM AUTHOR]

Light detection and ranging (LiDAR) data can provide 3D structural information of objects and are ideal for extracting individual tree parameters, and individual tree segmentation (ITS) is a vital step for this purpose. Various ITS methods have been emerging from airborne LiDAR scanning (ALS) or unmanned aerial vehicle LiDAR scanning (ULS) data. Here, we propose a new individual tree segmentation method, which couples the classical and efficient watershed algorithm (WS) and the newly developed connection center evolution (CCE) clustering algorithm in pattern recognition. The CCE is first used in ITS and comprehensively optimized by considering tree structure and point cloud characteristics. Firstly, the amount of data is greatly reduced by mean shift voxelization. Then, the optimal clustering scale is automatically determined by the shapes in the projection of three different directions. We select five forest plots in Saihanba, China and 14 public plots in Alpine region, Europe with ULS or ALS point cloud densities from 11 to 3295 pts/m2. Eleven ITS methods were used for comparison. The accuracy of tree top detection and tree height extraction is estimated by five and two metrics, respectively. The results show that the matching rate (Rmatch) of tree tops is up to 0.92, the coefficient of determination (R2) of tree height estimation is up to.94, and the minimum root mean square error (RMSE) is 0.6 m. Our method outperforms the other methods especially in the broadleaf forests plot on slopes, where the five evaluation metrics for tree top detection outperformed the other algorithms by at least 11% on average. Our ITS method is both robust and efficient and has the potential to be used especially in coniferous forests to extract the structural parameters of individual trees for forest management, carbon stock estimation, and habitat mapping. [ABSTRACT FROM AUTHOR]

The dielectric permittivity is one of the most significant properties of lunar material. For the past decades, researchers have assumed or used an indirect density versus depth relation to constrain the subsurface permittivity on the Moon. On 3 January 2019, Chang'E‐4 (CE‐4) rover‐borne lunar penetrating radar (LPR) successfully landed on the Von Kármán crater on the Moon's farside. CE‐4 LPR is the first surface radar on the Moon's farside for exploring regolith thickness and geological structure. Numerous parabolic‐shaped diffractions (PSD), which indicate subsurface objects, are identified in LPR data. We estimate the permittivity of the first ~50 m at the landing region using these PSDs based on a hyperbolic fitting method. A best‐fit permittivity/density versus depth relation is obtained, and this relation could be used at different areas on the Moon. Plain Language Summary: Currently, rover‐deployed/spaceborne radar systems are frequently employed in lunar exploration. The depth and thickness of lunar subsurface structure observed from radar data are completely influenced by the dielectric properties of subsurface materials. The dielectric properties also provide vital clues on compositions and origin of subsurface materials. However, except the results measured with returned sample from lunar surface, we have no more information about dielectric properties of global and deeper lunar subsurface materials. In January, China's CE‐4 spacecraft softly landed on the farside of the Moon for the first time and released the lunar penetrating radar (LPR). In this study, we estimate the dielectric permittivity of the first ~50 m at the landing region with LPR data and propose a best‐fit permittivity/density versus depth relation which could be used at different areas on the Moon. Key Points: The permittivity of lunar subsurface materials at CE‐4 landing site is estimatedA best‐fit permittivity/density versus depth relation is obtainedThe obtained best‐fit relation can be used at different areas on the Moon [ABSTRACT FROM AUTHOR]

Utilizing the measurements and retrievals from the Global Precipitation Measurement dual‐frequency precipitation radar data during the summer of 2014–2020, this study analyzes the precipitation microphysics for summer rainfall over the Yangtze‐Huai River Valley (YHRV) region in China with respect to the precipitation efficiency index (PEI). The results show that the mean near‐surface rain rate and PEI for convective precipitation are generally larger than that for stratiform precipitation. There are larger raindrops in near‐surface rainfall for convective precipitation than that for stratiform precipitation. The High PEI precipitation is characterized by the larger ratio of convective precipitation samples compared to that for the other two categories of precipitation. The mean mass‐weighted mean diameter (Dm) of the near‐surface raindrops increase along with the precipitation top height (PTH) in Moderate PEI precipitation for convective and stratiform precipitating clouds. The larger PEI indicates the larger occurrence of the heavy raindrops and strong radar echoes near the ground. The growth process of raindrops falling below the melting layer in the High PEI precipitation is dominated by collision‐coalescence while the collisional break up is the dominant process below the melting layer in Low PEI precipitation. It is further verified that the microphysical characteristics and mechanisms of summer rainfall over the YHRV region are similar to that of precipitation derived from tropical cyclones over the ocean during the monsoon period. Key Points: The near‐surface raindrops increase along with the precipitation top height in the moderate precipitation efficiency index (PEI) precipitationThe higher PEI indicates the larger occurrence of near‐surface heavy raindrops and strong radar echoesThe microphysical mechanisms in the summer precipitation process are analyzed in terms of various PEI [ABSTRACT FROM AUTHOR]

In this study, we examine the evolution of ice‐phase microphysics [polarimetric radar signatures and identified graupel and hail (GH) (hereafter, GH) distributions] and raindrop characteristics [drop size distribution (DSD) and rainfall intensity] in a warm‐sector extreme rainfall case during the Meiyu period in Eastern China. Deep convection is identified in this rainstorm, raindrop characteristics are found to be deeply affected by the GH distribution condition, heavy rainfall (rain rate >20 mmh−1 $\mathrm{m}\mathrm{m}\,{\mathrm{h}}^{-1}$) is basically contributed by convective samples with GH identified aloft. As GH height rises, number concentration and mean size of raindrops increase accordingly, leading to the growth of rainfall intensity. Extreme rainfall (rain rate >100 mmh−1 $\mathrm{m}\mathrm{m}\,{\mathrm{h}}^{-1}$) is majorly induced by deep convection with hail or widespread (over 10 km level) graupel, melting of the abundant highly‐rimed particles plays a dominant role in generating high concentration raindrops. By revealing the link between GH distribution conditions and raindrop characteristics, the study helps to understand the specific role of ice‐phase processes to the formation of low‐level raindrops in deep convection. Plain Language Summary: Ice‐phase microphysics governs surface rainfall intensity and drop size distribution of raindrops in deep convection. Owing to the lack of direct observation in deep convection, the specific role of ice‐phase microphysics to raindrop formation remains a struggle. Here we use polarimetric radar and surface instruments, to link ice‐physics microphysics to raindrop characteristics from a warm‐sector deep convection case producing extreme rainfall in Eastern China. We found that the contribution of ice‐phase microphysics to raindrop formation is enhanced as the growth of graupel and hail (GH) distribution depth. To a certain extent, low‐level drop size distribution characteristics and rainfall intensity are dependent on the distribution condition of GH. These current findings are helpful to improve the microphysical understanding of deep convection. Key Points: Microphysics of a warm‐sector extreme rainfall rainstorm caused by deep convection in Eastern China is revealedLow‐level drop size distribution and rainfall intensity are deeply affected by graupel and hail distribution condition in the deep convectionLink between ice‐phase microphysics and raindrop characteristics in deep convection is preliminarily established [ABSTRACT FROM AUTHOR]

Typhoon Lekima (2019) possessed a double‐eyewall structure before making landfall in eastern China, with its outer eyewall showing quasi‐periodic convective intensification. Several physical mechanisms that may cause eyewall convection asymmetries were examined. The upshear occurrence of the strongest convection could not be explained by either the typhoon's motion or the effect of descending inflow from outer rainbands. Radar reflectivity analysis showed that phase locking occurred between the wavenumber‐2 vortex Rossby waves (VRWs) propagating radially outward from the inner eyewall and the azimuthally propagating wavenumber‐1 VRWs on the inner edge of the outer eyewall. Additional phase locking further arose between the aforementioned wavenumber‐1 VRWs and the azimuthally propagating wavenumber‐2 VRWs on the outer edge of the outer eyewall. These two phase‐locking processes led to the pronounced quasi‐periodic intensification of the convective asymmetry in the western semicircle of Lekima's outer eyewall. Plain Language Summary: Tropical cyclone eyewalls are commonly accompanied by torrential rainfall that tends to cause flooding and devastation. In particular, precipitation prediction becomes more challenging when the eyewall convective activity exhibits a markedly asymmetric structure. This work focuses on the repeated occurrence of strong convection in the outer eyewall of Typhoon Lekima (2019) before it made landfall in China. The coastal ground‐based radar observations show that phase locking between waves associated with the double eyewalls serves as a plausible mechanism for the presence of the repeated strong precipitation in Lekima's outer eyewall. The findings in this study highlight the merit of coastal ground‐based radar observations in examining physical processes of tropical cyclone structure evolution, particularly in regions without aircraft reconnaissance. Key Points: Radar observations revealed quasi‐periodic intensification of convective asymmetries in the outer eyewall of Typhoon LekimaThe strongest convection in the outer eyewall occurred upshearPhase locking between vortex Rossby waves in the concentric eyewalls led to the occurrence of quasi‐periodic asymmetric convection [ABSTRACT FROM AUTHOR]

Microphysical signatures relevant to the asymmetric convection in the outer eyewall of Super Typhoon Lekima (2019) before its landfall in China were analyzed from ground‐based radar observations. The results indicate that the microphysical characteristics varied in quadrants. In the upshear‐left outer eyewall, the convection was deepened on the inner edge due to the phase locking between vortex Rossby waves (VRWs), and warm rain was the predominant process contributing to the enhancement of rainfall. In contrast, the strongest precipitation occurred on the outer edge of the upshear‐right outer eyewall. In this region, exuberant riming processes and graupel formation prevailed above the melting layer due to the strongest and more outward tilted updrafts induced by the phase locking between the VRWs. A good deal of graupel melted into raindrops, along with significant accretion processes, produced intense rainfall with larger drop sizes. Plain Language Summary: Accurate forecasting of tropical cyclone precipitation requires a deep‐depth understanding of the complex microphysical processes within the storm. Using ground‐based radar observations, we found significant variation in the number, shape, and size of raindrops in the outer eyewall of Super Typhoon Lekima (2019) before its landfall in China. Warm rain processes governed the intensification of rain below the melting layer in both upshear‐left and upshear‐right outer eyewalls. However, in the upshear‐right quadrant, interactions of vortex Rossby waves significantly enhanced updrafts on the outer edge of the outer eyewall, boosting riming processes and graupel formation above the melting layer and generating the heaviest rainfall. These current findings may be used to weigh up and improve numerical tropical cyclone forecasting models. Key Points: Asymmetry of microphysical signatures was found in the outer eyewall of Lekima (2019)Accretion governed the intensification of rain below the melting layer in both upshear‐left and upshear‐right outer eyewallsPhase locking of vortex Rossby waves in the outer eyewall could produce the most active ice processes and heaviest rainfall [ABSTRACT FROM AUTHOR]

Monsoon coasts are characterized by active convection, but the features of associated convection initiation (CI) are not well understood. An analysis of kilometer‐resolution radar observations in South China reveals a distinct dependence of CI on monsoon activity, land‐sea contrast, and coastal orography. The CI occurrence becomes highly active after the monsoon onset and extends northward in summer. Several CI hotspots appear on tropical islands, peninsulas, and windward slopes of coastal mountains. Daytime CI occurrences are concentrated on land within 100 km of the coastline. The nocturnal CI maxima are located on coastlines and in the offshore areas with adjacent mountains. CI shows an offshore propagation after midnight prior to rainfall, probably due to the convergence of land breezes or downslope winds with diurnally enhanced onshore monsoon flows. The improved understanding of CI may provide additional benefit for forecasting severe weather because CI foretells the development of full‐fledged deep convection. Plain Language Summary: A large fraction of global rainfall occurs in the coastal areas of summer monsoon which are highly populated. Characterizing convective activity along monsoon coasts has been an important issue in regional/global climate and hydrological studies. For the first time, this study presents a long‐term radar climatology of convection initiation (CI) on the monsoon coasts of South China which have dense observation networks. The results show that CI becomes highly active after the summer monsoon onset. Most CI occurrences are concentrated within 100 km of the coastline, and the local maxima are strongly affected by topography and land‐sea contrast. The triggering of coastal convection also shows strong diurnal cycles with a daytime maximum on land and an offshore propagation after midnight. The findings provide key information to improve our understanding of how convective activity emerges in monsoon coastal areas. Key Points: We present the first long‐term climatology of convection initiation on the coasts where monsoon flows interact with local circulationsConvection initiation is highly active within 100 km of the coastline, with maxima near local mountains during onshore southwesterliesThe triggering of convection is dominant on land in the afternoon and off the coast after midnight, particularly in the monsoon season [ABSTRACT FROM AUTHOR]

This study analyzes microphysical signatures relevant to the short‐cycle lightning activity in the inner core of Typhoon Hato (2017) before landfall in China. Observations reveal that the lightning bursts were accompanied by enhanced inner‐core convection with a behavior cycle of about 3 hr. The coupling between wavenumber‐2 vortex Rossby waves (VRWs) and shear‐forced convective asymmetries resulted in a local updraft enhancement. Furthermore, supercooled liquid water droplets invigorated a striking enhancement of graupel via riming immediately above the freezing level, further enhancing charge separation and lightning generation outside the eyewall. Furthermore, when similar phase‐locking was associated with other propagating VRWs, graupel and updraft volumes were significantly boosted, leading to short‐cycle lightning outbreaks in the inner core. Plain Language Summary: Lightning behavior is one of the well‐defined indicators of convection within the Tropical cyclone (TC) circulation. Before the landfall of Typhoon Hato (2017), we found short‐cycle lightning outbreaks in the inner core of this typhoon. The interaction between the internal structures of the storm and changes in wind speed and direction with height could strikingly reinforce convection, thereby favorable for the short‐cycle electrification enhancement. This scenario is distinct from diurnal lightning bursts within TCs, which were found in previous studies. The diurnal lightning activity is thermodynamically governed by radiation, while vortex‐environment interactions in the inner core of Hato dynamically force the short‐cycle lightning outbreaks revealed here. Therefore, the findings presented in this case study suggest that interactions between the internal structures of a TC and the environment warrant an adequate focus in the short‐range forecasting of inner‐core convection in landfalling TCs. Key Points: Short‐cycle lightning outbreaks were found in the inner core of Typhoon Hato (2017)Interactions between vortex Rossby waves and the shear‐induced convective enhancement likely led to the quasi‐periodic lightning behaviorStrengthened updrafts and the significant growth of graupel enhanced the charge separation and lightning outbreaks [ABSTRACT FROM AUTHOR]

A tornado/waterspout associated with a supercell thunderstorm was observed in the adjacent waters of southern China on the evening of 18 April 2019. The case was documented using surface weather observations and Doppler radar data. A weather station near the tornado/waterspout, recorded wind gusts corresponding to hurricane intensity for a few seconds, never observed before in the region. The Doppler velocity associated with the tornado/waterspout was analysed and the vertical profile of the velocity could be very useful for wind engineering applications in the region. Dual‐polarization observations also were analysed and exhibited some similar signatures documented in supercell tornadoes in other parts of the world. Predictability of the tornado/waterspout was studied using a numerical weather prediction model. It showed that the location and timing of the waterspout/tornado could be roughly reproduced, and the model might be used to give earlier alerting to the vessels operating in the south China coastal waters. [ABSTRACT FROM AUTHOR]

The surface slope and roughness of the Moon have been investigated extensively over a wide baseline range except millimeter to decimeter scales. In this study, we present for the first time millimeter‐to decimeter‐scale surface slope and roughness of the Moon at China's Chang'e‐4 landing regions (∼20 m across) using the Digital Terrain Model (DTM) with a resolution of 5 mm/pixel. The bidirectional slope at the 7 mm scale can be larger than 40° with a median value of ∼10°. The root‐mean‐square (RMS) height within a window size of 125 mm varies from ∼1 mm to ∼18 mm with a median value of ∼4 mm. Both the bidirectional slope and RMS height show scale‐dependent behaviors and the parameter of scale dependence, the Hurst exponent, is ∼0.6–0.85. We also synthesized the bidirectional slope at baseline from micrometer to kilometer, showing that bidirectional slope decreases from ∼60° at micrometer to ∼1° at a kilometer. At millimeter‐scale, surface roughness is mainly controlled by small impact craters, rocks, and regolith properties. Our roughness results not only bridge the gap in understanding surface roughness from traditional topographic data sets to radar and thermal observations, but also provide valuable information about lunar regolith characteristics, and small‐scale geological processes. Plain Language Summary: The roughness of a planetary body quantitively describes terrain surface topographic undulation at a horizontal scale and is widely used in geological and geomorphological studies. Roughness is an important parameter in radar observations due to its modulation of radar wave behaviors. Lunar surface roughness at a wide baseline range has been investigated before, but not in the baseline range of millimeter to decimeter. The Panoramic Camera onboard the Yutu‐2 rover collected millimeter‐scale resolution stereo images over China's Chang'e‐4 landing region. We generated a 5 mm/pixel resolution DTM covering an area of ∼20 m wide and then calculated three roughness parameters. We found that small impact craters, rocks, and regolith properties are the controlling factors affecting the millimeter‐scale roughness of the lunar surface. Combining with previous roughness results, we obtained lunar surface roughness versus baseline at scales ranging from micrometer to kilometer, which can be applied in a variety of studies. Key Points: We investigated millimeter to decimeter scale topographic roughness of the Moon in the Chang'e‐4 exploration region of ∼20 m wideThe median bidirectional slope is ∼10° at 7 mm scale and the median RMS height is ∼4 mm at 125 mm window size, and both show scale dependent behaviorsSmall impact craters, rocks, and regolith properties mainly affect millimeter‐scale topographic roughness of the Moon [ABSTRACT FROM AUTHOR]

The surface slope and roughness of the Moon have been investigated extensively over a wide baseline range except millimeter to decimeter scales. In this study, we present for the first time millimeter‐to decimeter‐scale surface slope and roughness of the Moon at China's Chang'e‐4 landing regions (∼20 m across) using the Digital Terrain Model (DTM) with a resolution of 5 mm/pixel. The bidirectional slope at the 7 mm scale can be larger than 40° with a median value of ∼10°. The root‐mean‐square (RMS) height within a window size of 125 mm varies from ∼1 mm to ∼18 mm with a median value of ∼4 mm. Both the bidirectional slope and RMS height show scale‐dependent behaviors and the parameter of scale dependence, the Hurst exponent, is ∼0.6–0.85. We also synthesized the bidirectional slope at baseline from micrometer to kilometer, showing that bidirectional slope decreases from ∼60° at micrometer to ∼1° at a kilometer. At millimeter‐scale, surface roughness is mainly controlled by small impact craters, rocks, and regolith properties. Our roughness results not only bridge the gap in understanding surface roughness from traditional topographic data sets to radar and thermal observations, but also provide valuable information about lunar regolith characteristics, and small‐scale geological processes. Plain Language Summary: The roughness of a planetary body quantitively describes terrain surface topographic undulation at a horizontal scale and is widely used in geological and geomorphological studies. Roughness is an important parameter in radar observations due to its modulation of radar wave behaviors. Lunar surface roughness at a wide baseline range has been investigated before, but not in the baseline range of millimeter to decimeter. The Panoramic Camera onboard the Yutu‐2 rover collected millimeter‐scale resolution stereo images over China's Chang'e‐4 landing region. We generated a 5 mm/pixel resolution DTM covering an area of ∼20 m wide and then calculated three roughness parameters. We found that small impact craters, rocks, and regolith properties are the controlling factors affecting the millimeter‐scale roughness of the lunar surface. Combining with previous roughness results, we obtained lunar surface roughness versus baseline at scales ranging from micrometer to kilometer, which can be applied in a variety of studies. Key Points: We investigated millimeter to decimeter scale topographic roughness of the Moon in the Chang'e‐4 exploration region of ∼20 m wideThe median bidirectional slope is ∼10° at 7 mm scale and the median RMS height is ∼4 mm at 125 mm window size, and both show scale dependent behaviorsSmall impact craters, rocks, and regolith properties mainly affect millimeter‐scale topographic roughness of the Moon [ABSTRACT FROM AUTHOR]

Convection is highly active on tropical islands. Based on a 3‐year radar climatology over Hainan Island, a mountainous tropical island in South China, we identified a distinct spatial dependence of convection initiation (CI) on the speed of the large‐scale low‐level flow. Convection initiates most prominently over the lee‐side plains in high‐wind conditions while over mountains in low‐wind conditions. Quasi‐idealized numerical simulations suggest that mountain ridges stimulate the formation and growth of horizontal convective rolls (HCRs) over the lee‐side plains in high‐wind conditions. These HCRs subsequently intersect with sea‐breeze fronts, which enhances the low‐level convergence favoring CI on the lee‐side plains of the island. During low‐wind conditions, thermally driven circulations control and favor CI over the mountains during the day. The findings highlight that the response of local circulations to the lower‐troposphere ambient flow and diurnal thermal heating is an important aspect of convection initiation on the island. Plain Language Summary: Skillfully predicting the location and timing of the formation of thunderstorms in the tropics is a challenging problem. Using radar observations, this study investigates how the key characteristics of low‐level winds influence the formation of thunderstorms on a mountainous tropical island (Hainan Island in South China). Modeling results demonstrate that the spatial occurrence of the thunderstorm formation is sensitive to the speed of low‐level winds. The thunderstorm formation occurs most prominently on the downwind plains and over the upwind mountain regions under the high‐wind and low‐wind conditions, respectively. During the high‐wind condition, the perturbed ambient flows downwind of ridges help to enhance the convergence in the boundary layer, and thus contribute to the thunderstorm formation in the plain region in the afternoon. Under low‐wind conditions, the local daytime heating is responsible for the frequent formation of thunderstorms over mountains. Considering that large‐scale circulations can be predicted reasonably well by numerical models, the findings of this study may assist operational forecasts of the formation of thunderstorms on tropical islands. Key Points: The location of convection initiation on the mountainous Hainan Island depends on the speed of the large‐scale low‐level flowConvection initiates most prominently over the lee‐side plains in high‐wind condition and over the mountainous region in low‐wind conditionHorizontal convective rolls (HCRs), generated on mountain lee sides, interact with sea‐breeze fronts and enhance low‐level updrafts during high‐wind conditions [ABSTRACT FROM AUTHOR]

The Gao Fen 7 (GF‐7) satellite is China's first submeter, high‐resolution Earth observation and remote sensing satellite for natural resource monitoring, land surveying, and other industrial applications in China. The GF‐7 laser altimeter system is the successor of the ZiYuan3‐02 (ZY3‐02 satellite) laser altimeter. The key objective of the GF‐7 laser altimetry system is to provide high‐precision ground elevation control points that assist in optical imaging to achieve 1:10000 mapping in China. This paper introduces the GF‐7 laser altimeter system payload specifications, mission objectives, in‐orbit calibration plan, data products, and service policy. In the future, the GF‐7 laser altimeter system will also serve multidisciplinary and professional applications through its precise elevation measurement capabilities. In addition, it will play a vital role in Earth observation, climate change monitoring, and environmental protection. Plain Language Summary: Spaceborne laser altimeters are widely used for planet surface measurements due to their high range accuracy. This paper details the GF‐7 laser altimeter system, which is China's first formal spaceborne laser altimeter system for Earth observations. This laser altimeter system will be used in scientific experiments for the first time in China. GF‐7 laser altimeter system is the first to be equipped with laser footprint cameras and a laser optical axis surveillance camera. The GF‐7 satellite will be launched in October 2019, and the scientific experiments will begin in November. All the data it gets will be released globally. In the future, these data will help researchers from different disciplines around the world to conduct scientific experiments and monitor the Earth's resources. The GF‐7 laser altimeter system will play a vital role in global climate change monitoring, environmental protection, disaster warning, etc. The content presented in this article will help students, researchers, and engineers in the fields of geography, oceanography, and glaciology understand and use GF‐7 satellite laser data, which will be of great significance. Key Points: A new laser altimeter system design consisting of a laser altimeter, two laser footprint cameras, and a laser optical axis surveillance camera equipped with the Gao Fen 7 satellite is introducedThe application of the Gao Fen 7 laser altimeter system including ground control point measurement, polar ice sheet monitoring, and forest biomass estimation is presentedScientific experiments on the Gao Fen 7 laser altimeter system to be performed in November 2019 are given. Six levels of data products are listed and will be provided to users worldwide [ABSTRACT FROM AUTHOR]

This study examined synoptic impacts on the occurrence of boundaries and their associated convection during summers from 2012 to 2016 over Hetao Irrigation District in North China, where there is a sharp vegetation contrast. Objective synoptic‐pattern classification showed that boundary days, especially convective boundary days, were more frequent under a mid‐troposphere high‐pressure ridge or pre‐trough pattern. Such patterns featured a warmer near‐surface environment, stronger southerly winds, larger convective available potential energy (CAPE), and low‐level moisture convergence. Relative to unfavorable patterns, boundaries under favorable patterns showed more apparent arid‐area dependence, more dominant orientation along the line of vegetation contrast, more moved northward, formed and matured earlier, and triggered convection more dispersedly. Under each pattern, compared with nonboundary days, boundary days possessed higher near‐surface temperatures and stronger ambient flows against the vegetation‐contrast‐induced circulations near the surface; plus, compared with nonconvective boundary days, convective boundary days possessed stronger updrafts, larger CAPE, and higher moisture and K index. Plain Language Summary: Boundary layer convergence lines (boundaries), which often manifest as fine lines of clear‐air radar echoes, are an important mesoscale mechanism of convective initiation. Mesoscale boundaries induced by vegetation heterogeneity are far less well understood than those induced by the contrast between sea or lakes and land, particularly in terms of synoptic impacts on the occurrence of such boundaries and their associated convection. Based on a boundary data set during the five summers from 2012 to 2016 over Hetao Irrigation District (HID)—an area in North China with a sharp contrast in vegetation, mainly between desert and irrigation areas—the aim of the present study was to link these boundaries and their associated convection with different synoptic features via objective synoptic‐pattern classification. Results showed that the boundaries were more likely to occur and trigger convection on days when HID was under a high‐pressure ridge or pre‐trough pattern. The favorable patterns had a warmer environment with stronger southerly flows for boundaries to develop, along with larger convective available potential energy and moisture convergence for boundaries to trigger convection. Their associated boundaries showed more apparent arid‐area dependence, more dominant orientation along the vegetation interface, more northward movements, earlier formation and maturity, and more dispersed convection initiation timing. Key Points: Boundaries and their convection over Hetao Irrigation District prefer mid‐level high‐pressure‐ridge or pre‐trough synoptic patternsThe favorable patterns have a warmer boundary layer with more frequent southerly flows, larger CAPE, and stronger moisture convergenceInstability and moisture effectively distinguish convective from nonconvective boundary days but not boundary from nonboundary days [ABSTRACT FROM AUTHOR]

The microphysical processes of cloud and precipitation in the Tianshan Mountains still remain unclear due to the complex terrain and the lack of ground-based observational data. In this study, the characteristics of summer raindrop size distribution (RSD) in the western and central Tianshan Mountains of China were investigated in 2020 and 2021. According to the average raindrop spectra, the RSD characteristics exhibit significant differences that the concentration of medium and large particles is relatively higher at Zhaosu than that at Tianchi. Weak precipitation prevails in the Tianshan Mountains most of the time, yet moderate rainfall and heavy rainfall have a great impact on the accumulated rainfall amount. For each rainfall rate class, raindrops of diameter less than 0.75mm have a lower concentration and raindrops of diameter greater than 3 mm have a higher concentration at Zhaosu as compared to those at Tianchi. Compared with Tianchi, Zhaosu has a larger mass-weighted mean diameter (Dm) and a lower normalized intercept parameter (log10Nw). Compared with the classical convective spectrum, the RSDs at both Zhaosu and Tianchi are similar to the continental convective cluster. The relationships between the shape and slope (μ–Λ), and radar reflectivity and rainfall rate (Z– R) exhibit a significant difference in the western and central Tianshan Mountains of China. [ABSTRACT FROM AUTHOR]

The data of lightning flash count, rainfall, radar reflectivity, vertical wind shear (WS), surface dew point temperature (DP) and particulate matter up to 10 μm in size (PM10) over Guilin, China from July 2010 to December 2019 were studied to check whether aerosol invigoration effect (AIV) exists in the study area. It was found that convective rainfall fluctuates less when compared with lightning in convective system. A hypothesis was put forward that the difference in fluctuations between convective rainfall and lightning is attributed to AIV. To test this hypothesis, lightning yield, which is defined as the ratio between lightning and rainfall, was analyzed. It was found that lightning yield has a positive correlation with PM10 when WS is low and DP is high for convective precipitation. It was also found that for the weak WS cases, when aerosol conditions are shifted from super pristine to the optimal concentration (Nop), lightning yield increases with increasing PM10; whereas for concentrations greater than Nop, lightning yield decreases with increasing PM10. Nop would be larger for higher DP. The results are in line with the previous studies showing that AIV depends strongly on weak wind shear and/or warm cloud base. This suggests that AIV exists in the study area, and suggests that the hypothesis is reasonable, and lightning yield can be used as a surrogate to study AIV. [ABSTRACT FROM AUTHOR]

The rainfall distribution associated with landfalling tropical cyclones (TCs) along the South China coast are examined using radar data from Hong Kong Observatory (HKO). This preliminary study relates the landfall direction, and possible rotations/transitions of TC rainfall asymmetries before and after the landfall. Three types of landfalling TCs on the South China coast are categorized: from the east, normal to the coast and from the southwest. For those from the east, the rainfall maximum rotates anticyclonically from the southwest before later landfall to the northwest. TCs making landfall perpendicular to the coast have a rainfall maximum remaining in the southwest quadrant throughout the landfall process. For TCs making landfall from the southwest, the rainfall maximum rotates cyclonically from the southeast before later landfall to the northeast. The relative importance of the impact of land properties and vertical wind shear on these rainfall asymmetries is investigated by using a numerical model. Sensitivity tests show that the rotations/transitions of landfalling TC rainfall asymmetry appear to be insensitive to land properties (e.g. moisture availability, surface friction and topography), but result primarily from changes in the orientations of the vertical wind shear in the environment. However, the surface friction of the landmass appears to contribute to the enhancement of rainfall intensity. The rainfall distribution associated with landfalling tropical cyclones (TCs) along the South China coast are examined using radar data. Three types of landfalling TCs are categorized based on the landfall direction, and possible rotations/transitions of TC rainfall asymmetries before and after the landfall. The rotations/transitions of landfalling TC rainfall asymmetry appear to be insensitive to land properties (e.g. moisture availability, surface friction and topography), but result primarily from the orientations of the vertical wind shear in the environment. [ABSTRACT FROM AUTHOR]

This study evaluates how clouds evolve into thunderstorms in terms of the turbulence characteristics producing the first flash. Observations of 57 (39) isolated thunderstorm (non‐thunderstorm) cells during 2016/2017 in Southern China are provided by an S‐band polarimetric radar and three independent lightning location systems. The vertical turbulence characteristics of clouds associated with thunderstorms are obviously different from non‐thunderstorms. For thunderstorms, the maximum of the eddy dissipation rate (mean value in each height layer) in the entire height is 0.19 m2 s−3, which occurs at the first flash stage, and the achievable height of turbulence exceeds the −30°C layer. For non‐thunderstorms, however, the maximum is 0.12 m2 s−3, and the achievable turbulence height hardly exceeds the −10°C layer. Additionally, the turbulence intensities of the locations where the initial discharge pulse events of the first flashes occur are weak. These turbulence characteristics are useful for lightning nowcasting. Plain Language Summary: The first flash is a significant indicator of the development of a thunderstorm. Hence, studying how clouds evolve into thunderstorms producing the first flash is an interesting topic. Understanding the occurrence of the first flash is valuable for developing nowcasting tools and lightning parameterizations in numerical weather prediction models. However, the role of turbulence in producing the first flashes in the development of thunderstorms is poorly understood. Turbulence indicating the disorder in clouds provides the relative speed differences for hydrometeors with different masses and inertias. Consequently, it is essential for electrification process and the occurrence of the first flash. The vertical turbulence characteristics are both demonstrated in thunderstorms from the initial generation to the occurrence of the first flashes and in non‐thunderstorms. The resulting turbulence characteristics may provide useful information for lightning nowcasting. Key Points: This study evaluates how clouds evolve into thunderstorms in terms of the turbulence characteristics producing the first flashThe vertical turbulence characteristics of clouds show obvious differences between thunderstorms and non‐thunderstormsThe turbulence intensities of the locations where the initial discharge pulse events of the first flashes occur are weak [ABSTRACT FROM AUTHOR]

The middle reaches of the upstream of Jinsha River (MRUJR) is located in the eastern segment of the Jinsha River suture zone on the southwest of China. A study of the MRUJR based on tectonic geomorphology is noteworthy for providing a profound understanding of the tectonic transition between the Sichuan‐Yunnan and Qamdo blocks and active tectonics in various subbasins. Based on the global digital elevation model Shuttle Radar Topography Mission 1 (30 m resolution) data and geographic information system techniques, four geomorphic indices, the hypsometric integral, stream length‐gradient, drainage basin asymmetry, and drainage basin shape were calculated and analysed. Combined with geologic evidence from field surveys and fault slip rates estimated, the tectonic activities and mechanisms were discussed. Through the specific analytical comparisons, the variations in the geomorphic indices were unlikely affected by lithology and climate but showed changes in relevant tectonic activity. The analysis results of geomorphic index value manifested related strong activities in the northwestern and southeastern regions of MRUJR, tilt directions are mainly SW–NE and NE–SW, respectively. The MRUJR is undergoing rapid uplift. These results are consistent with the field evidence. [ABSTRACT FROM AUTHOR]

Triggered or induced earthquakes have been widely reported as resulting from various human activities, yet seismicity triggered by small‐scale infrastructure construction is rare. Here, we report on an investigation of an extremely shallow Mw4.1 earthquake which occurred on 11 August 2016 in the Sichuan Basin (China), a region with historically low seismicity. Our seismic waveform analyses indicate an almost pure thrust focal mechanism at a centroid depth of ~1 km. Furthermore, 18 Sentinel‐1 synthetic aperture radar interferograms, stacked to obtain subcentimeter accuracy, reveal up to 3 cm line‐of‐sight deformation which overlaps with an automotive testing site constructed in 2014. Removal of 10 m of a surface rock layer during the construction may have produced an unloading effect and resulted in up to 0.11 MPa Coulomb stress changes on a blind fault, larger than the 0.01 MPa threshold typically invoked in studies of tectonic earthquakes. However, the delayed triggering still requires further investigation. Plain Language Summary: While induced earthquakes in the shallow part of the crust have been observed globally, a remaining knowledge gap is whether small‐scale infrastructure construction can trigger earthquakes or not. We investigate these questions on an extremely shallow Mw4.1 earthquake in the eastern Sichuan Basin (China). To determine earthquake source parameters, we combine seismological data with satellite imaging. We find this thrust event ruptured at the depth of ~1 km, located just beneath an automotive testing site constructed in 2014. Crucially, we note the testing site construction involved removal of a large volume of surface rock. We further analyze the stress changes produced by the unloading of the surface rock. We find a possible triggering relationship between the infrastructure construction and the occurrence of this shallow earthquake. Our results thus shed new light on the causes of shallow earthquakes associated with small‐scale infrastructure construction. Key Points: The 11 August 2016 Mw4.1 Dianjiang earthquake was an extremely shallow thrust event (~1 km)Stacking of Sentinel‐1A SAR interferograms with subcentimeter resolution reveals LOS deformation of up to 3 cm produced by the earthquakeThe earthquake was likely triggered by the unloading effect after surface rock layer was removed during infrastructure construction [ABSTRACT FROM AUTHOR]

In the morning of 5 March 2010, an aircraft experienced tail strike when it departed from the south runway of the Hong Kong International Airport to the west. This paper documents the meteorological conditions in the tail strike event, and discusses the alerting and the forecasting aspects of the event. Based on the analysis of the aircraft manufacturer, the tail strike is believed to arise from significant wind shear (headwind loss) experienced by the aircraft. By analysing the surface and the LIDAR observations, it appears that the significant wind shear is related to disruption of the background southwesterly flow by the complex terrain near the airport. From the surface observations, there is a microscale cyclone at the western part of the south runway. The radial velocity image of the LIDAR also depicts an area of reverse flow in that region against the background southerly flow. The alerting of the wind shear based on the two wind shear alerting algorithms developed by the Hong Kong Observatory is discussed, and it turns out that the anemometer-based wind shear algorithm could successfully capture this wind shear occurring close to the ground. On the other hand, due to geometrical constraint, the LIDAR does not pick up the headwind loss experienced by the aircraft. The forecasting of this wind shear event is considered by performing high resolution (down to a horizontal resolution of 50 m) using a mesoscale numerical weather prediction model. The simulated headwind profile at the event time is generally consistent with the aircraft data, though the headwind loss in the simulation is smaller than the reality. Together with the forecast wind gusts, it may be possible to alert the aviation weather forecaster at an earlier time about the occurrence of terrain-induced wind shear over the south runway in this particular event. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

A tornado that occurred in eastern China on June 23, 2016 was simulated with the Weather Research and Forecasting (WRF) model (version 3.9) using three different microphysical schemes (WRF single‐moment 6‐class [WSM6] scheme, Morrison double‐moment scheme, and Milbrandt–Yau [MY] scheme). The results showed that the Morrison scheme's simulation result was the best among the three schemes. The Morrison scheme simulated a better structure of three layers, including a cold pool near the ground, thick heating layer in the middle levels, and cooling again above 14 km. From the microphysical processes, the possible formation mechanism was that the convective activity was first evoked by the near‐ground cold pool, and then the horizontal vortex tube was raised and vertically stretched before turning in the vertical direction by the release of latent heat caused by the water vapor condensation. Thereafter, the vortex tube was cut off by the downward movement caused by the cloud water evaporation and the snow melting in the front of the convection system, causing the violent vertical lift of the rear vortex tube, forming the tornado. The radar reflectivity (units: dBZ) from (a) observation, (b) the Morrison scheme, (c) the MY scheme, and (d) the WSM6 scheme at 0600 UTC; and the 1‐hr total rainfall (units: mm) from (e) observation, (f) the Morrison scheme, (g) the MY scheme, and (h) the WSM6 scheme during 0600–0700 UTC June 23, 2016. [ABSTRACT FROM AUTHOR]

In the evening of 11 April 2011, vortex/wave shedding from a mountain to the south of the Hong Kong International Airport (HKIA) appeared to occur following the establishment of fresh to strong easterly airflow in Hong Kong. This paper documents the observations by the various meteorological instruments of the event and discusses the possibility of forecasting the vortex/wave shedding using a high resolution numerical weather prediction (NWP) model. The vortex/wave shedding was well observed by the Light Detection and Ranging (LIDAR) system at HKIA. The vortex/wave appeared as an area of reversed flow against the background east to southeasterly airflow in the airport area. It was detached from the mountain and moved to the northwest with the background southeasterly flow, with a gradual decrease of the spatial extent in the area of reversed flow. The vortex/wave brought about significant wind shear to both arrival flight paths to the west of HKIA, as evidenced from the headwind profile data measured by the LIDARs and the aircraft data. It had rather large vertical extent, reaching the top of the boundary layer, but did not extend downward to the surface, as shown from the vertical scans of the LIDAR and the surface wind observations. The shedding event is successfully captured by high-resolution NWP model with a spatial resolution of 50 m. The model output has a lead time of 6-7 h ahead of the event, indicating the possible occurrence of terrain-induced wind shear in the form of vortex/wave shedding from a mountain. As a result, the numerical simulation could be useful in giving an early alert to the aviation weather forecaster about the significant wind shear event, which could be hazardous to the landing aircraft. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

A significant wind shear event occurred in the early morning of 27 December 2009 at the Hong Kong International Airport (HKIA), leading to the diversion of three aircraft to the airport of Shenzhen (about 39 km to the north-northwest of HKIA). This paper documents the meteorological observations and predictions for the event. The significant wind shear arose from disruption of the prevailing easterly to southeasterly flow by the complex terrain to the south of the airport. It was well captured by the Doppler Light Detection and Ranging (LIDAR) systems at HKIA and, as such, the aircraft were given sufficient warning about the occurrence of significant wind shear. The headwind changes along the glide paths as measured by the LIDAR were consistent with the aircraft measurements. The observations of the remote-sensing instruments during the event, including the LIDAR, are described in the paper. Moreover, this paper discusses the possibility of including wind shear forecast information for flight planning purpose for this particular case. The forecast wind field near HKIA based on a high-resolution numerical weather prediction (NWP) model is described. For the present wind shear event, it appears that the occurrence of terrain-disrupted airflow near HKIA may be forecast about 6 h ahead. The timing of significant wind shear is, however, not reproduced well in the NWP forecast. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Surface solar radiation (SSR), as a primary component of heat budget between land and atmosphere, controls both water and energy exchanges. However, the sub‐grid terrain radiative effect (STRE) which exerts critical influences on SSR simulation is usually extremely simplified or even ignored in most current land surface models (LSMs) due to the heavy computational burden. In this study, we developed a physically realistic and computationally efficient three dimensional (3D) STRE scheme and implemented it into the Common Land Model (CoLM) to indicate its quantitative influences on surface energy budget, land surface temperature (LST), soil temperature, and moisture simulations over the Heihe River Basin, Tibetan Plateau. Results show that the CoLM coupled with 3D‐STRE scheme shows more realistic description of SSR and improves the simulation of soil thermal and moist features at both single‐point and regional scales. Compared to the results without 3D‐STRE, the inclusion of 3D‐STRE scheme efficiently diminishes the overestimation of SSR, which leads to the root mean square error (RMSE) of LST simulation reduced by 17.1% due to significant improvements in valley areas. Adopting 3D‐STRE scheme also improves the pattern and amplitude of temporal variability of simulated soil temperature (moisture) at 37 sites with the mean Taylor score increased by 3.6–3.7% (14.0–14.3%). These results emphasize the importance of considering the 3D‐STRE scheme in LSMs and are significantly helpful to deepen our understanding of surface heat exchanges and improve the representations of land surface processes over complex terrain. Plain Language Summary: Topography exerts remarkable influences on the land surface solar radiation (SSR) over complex terrain, which controls both water and energy exchanges between land and atmosphere. However, the parameterization of sub‐grid topographical effects on SSR are usually extremely simplified or even ignored in most current numerical models due to the heavy computational burden. In this study, we developed a parameterization with much more real physical processes, simple parameters and high computational efficiency to consider the impact of sub‐grid topography on SSR, it tends to show widely potential application in land process and climate modeling. Taking the Heihe River Basin in China as an example, we found that the land surface model coupled with this scheme shows more realistic description of SSR and significantly improves the simulations of soil thermal and moist features. These results highlight the necessity of considering the sub‐grid topographical effects on SSR simulation in land surface modeling and are obviously helpful to advance our understanding of the surface heat exchanges and improve the representations of land surface processes over complex terrain areas. Key Points: A 3D sub‐grid terrain radiative effect (STRE) scheme is developedThe 3D STRE scheme can show more realistic description of the land surface solar radiationThe CoLM coupled with the 3D STRE scheme significantly improved the simulation of soil thermal and moist features over complex terrain areas [ABSTRACT FROM AUTHOR]

Extreme summer precipitation often associated with flash floods has devastating impact on the local economies and livelihood of millions of people over East China. Tracking down the drivers of those extreme events will help to understand their formation mechanisms and to improve forecasts. Here the synoptic patterns associated with summer extreme precipitation events over East China during 1961-2018 have been identified systematically and quantitatively using a circulation clustering method. The results show that regional events over East China are dominated by the Eastern Asian summer monsoon associated Meiyu front, landfalling tropical cyclones and low-pressure vortices. Most sub-regions have seen increasing trends of extreme rainfall events during the past 6 decades with comparable contributions from the two main drivers. There was a decreasing trend over the North China Plain driven by the lowlevel southeasterly winds. Plain Language Summary Closely linked to flash floods, extreme precipitation is one of the high impacts but low probability weather phenomena that challenge modern numerical predictions. However, models are generally more skillful in predicting synoptic weather systems than precipitation itself. Taking East China as an example, this paper demonstrates the links between extreme precipitation events and synoptic weather systems using circulation clustering. Two major weather systems, the Eastern Asian Summer Monsoon and landfalling tropical cyclones are responsible for most extreme precipitation events (about 70%) over East China during the summer season. If models can accurately predict the strength and position of these weather systems, there may be enhanced potential of predicting regional precipitation extremes. Such implications are not regionally limited. [ABSTRACT FROM AUTHOR]