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• Many techniques were applied in Beishan Exploration Tunnel to study EDZ. • Damage process was divided into blasting damage stage and progressive damage stage. • The mechanism of micro-cracks after blasting was analyzed by the feature of AE wave. • The shape of EDZ by blasting was delineated using GPR and p-wave velocity. • Techniques used for in-situ EDZ characterization were evaluated. Detailed characterization of the Excavation Damage Zone (EDZ) is an important issue for the high-level radioactive waste (HLW) geological disposal engineering, which is closely related to the long-term safety of the HLW repository. With drill-blast experiment in Beishan Exploration Tunnel (BET, a platform for the field experiment and validation of potential technologies used for China's HLW disposal engineering in crystalline rock), systematic field tests were carried out to evaluate the suitability of techniques in characterizing EDZ, and to study EDZ characteristic in crystalline tunnel. A series of investigation technologies were used to delineate EDZ and to examine the process of its formation, which includes: p-wave velocity measurement, ground penetrating radar (GPR), acoustic emission (AE) monitoring and borehole televiewer. P-wave velocity measurement along borehole reveal that wave velocity decreased significantly (more than 10%) in 30 cm to 50 cm from the excavation surface, and this zone is defined as EDZ. Clear images of borehole televiewer were obtained, which is helpful for EDZ delineation. GPR and borehole radar were also used for EDZ delineation. Strong reflection signals were detected in the range of 10 cm to 25 cm by GPR with high frequency antenna, indicating significant changes of physical properties of rock-mass in the zone, which is defined as Highly Damaged Zone (HDZ). Moreover, the formation process of EDZ induced by blast in crystalline rock tunnel was analyzed using AE monitoring. Damage process of surrounding rock was divided into blasting damage stage and progressive damage stage. AE events location show the induced cracking activities were clustering within 30 cm to 100 cm from excavation surface. With the experience from field investigation and result analysis, the feasibility and suitability of the techniques for EDZ characterization is evaluated. Finally a specialized EDZ characterization technique system is proposed for underground research laboratory construction in crystalline host rock in Beishan area. [ABSTRACT FROM AUTHOR]

Attenuation correction of measured reflectivity (Z H) and differential reflectivity (Z DR) is critical in short-wavelength radar applications, especially during extreme precipitation events such as heavy rain. This paper develops an improved self-consistent approach (improved ZPHI method) for attenuation correction in practical environment. In particular, a non-negative constraint is imposed on the specific attenuation, which is inferred from the monotonic increasing characteristic of differential propagation phase (Φ DP). The copolar correlation coefficient (ρ HV) is used to partition the Φ DP profiles into independent range segments, which are featured by different hydrometeor phases such as liquid rain or mixed-phase precipitation. Additional minimization constraint is imposed on the cost function of the difference between preprocessed Φ DP and reconstructed Φ DP to ensure its appropriate convergence. In addition, an exponential Z DR − Z H relation derived from local raindrop size distribution (DSD) data is applied in the procedure of Z DR correction. Polarimetric measurements from a C-band radar (CPOL) in Hangzhou of China during two extreme precipitation events are used to demonstrate the improved attenuation correction method. DSD observations from disdrometers and radar data from a nearby system operating at non-attenuated frequency (i.e., S-band) at Huangshan Mountain are used to evaluate the attenuation correction performance. This paper also studies the impact of attenuation correction on the radar-derived quantitative precipitation estimation (QPE) product, through cross-comparison with rain gauge observations. Results show that the polarimetric observations from CPOL radar are effectively enhanced and more consistent with collocated S-band measurements and the simulated radar moments based on DSD data. Hourly rainfall products derived from R (Z H) and R (Z H , Z DR) are significantly improved, which are comparable to R (K DP) after attenuation correction. • An improved attenuation correction method is proposed for C-band polarimetric radar applications. • The routinely operating C-band radar in Hangzhou, China is used to demonstrate the proposed attenuation correction scheme. • Cross-comparison with disdrometer data and collocated S-band observations shows great performance of this correction method. • The QPE products derived from R (Z H) and R (Z H , Z DR) are significantly improved after attenuation correction. [ABSTRACT FROM AUTHOR]

Weather radar has demonstrated the ability to monitor wildfires and associated smoke plumes. However, the long-range, S-band operational radar network has severe limitations in providing high-resolution observations in the lower atmosphere due to the earth curvature. This paper presents an innovative technique of using shorter-range, low-power, fast scanning X-band radar for monitoring wildfires. Sample observations from wildfire events in southern China show that the polarimetric radar correlation coefficient of wildfire echoes varies from 0.55 to 0.75, with an average value of 0.61; the differential reflectivity varies from 2.28 to 5.08 dB with an average value of 3.99 dB; the differential propagation phase varies from 40.27° to 69.27°, with an average value of 56.66°; and all observables exhibit subtle changes at different scanning elevation angles. In addition, changes in echo intensity observed by higher elevation scans lag behind those observed by lower elevation scans, and the change of wildfire area lags behind the variation of echo intensity. Given the emerging interest in deploying such compact, cheaper X-band systems for urban hydrometeorological applications, it is expected that these radars, customized with flexible scan strategy, will provide new opportunities and advantages in wildfire detection and mitigation. • Weather radar has demonstrated the ability to monitor wildfires and associated smoke plumes • The operational long-range, S-band radar has severe limitations in providing high-resolution low-level measurements • The compact and low-power X-band dual-polarization radar is more efficient in monitoring wildfire and its evolution • The polarimetric observables, especially the correlation coefficient, can effectively identify the wildfire smoke plumes [ABSTRACT FROM AUTHOR]

Abstract Elucidating the vertical structures of clouds is key to reducing the uncertainty in cloud-induced climate forcing; however, we do not yet know explicitly about the cloud structures that form over Beijing, China, and how they vary. In this paper, we document vertically resolved cloud structures and their climatological variation based on three-year (1 January 2015 to 31 December 2017) ground-based Ka-band (35 GHz) millimeter-wave cloud radar (MMCR) measurements. Cloud top height (CTH) and radar reflectivity are higher in summer and autumn than in spring and winter. We verified the MMCR measurements of the CTH and cloud base height (CBH) independently based on observations from the Himawari-8 and CL51 ceilometer at the same station, respectively. The CTH decreased as the thickness of the cloud layer increased. This may have been due to the mechanism used to determine the CTH, which was based on data from the satellite infrared channel. There were two peaks in the CBH distribution, located at 0–1 km and 5–6 km, whereas the frequency of the CTH peaked at an altitude of 9–10 km, between 1200 and 1800 LST. Precipitating clouds tended to be located at lower altitudes and exhibited stronger radar reflectivities than non-precipitating clouds. The cloud frequency tended to peak in autumn and reached a minimum in winter. In terms of the seasonality of clouds at various levels, middle- and high-level clouds were dominant over Beijing, with high and low (precipitating) clouds concentrated between May and October. Mid-altitude clouds occurred more frequently in winter and spring. CTH peaked in summer due to the strong solar radiation received by the surface. In contrast, minimum CBH occurred in winter. The cloud heights were higher and radar reflectivities larger than reported in previous studies. These results are correlated with urban warming effects. Understanding the properties of clouds will not only be of benefit to researchers carrying out cloud forcing studies, but will also provide key validation data for climate model simulations. Graphical abstract Unlabelled Image Highlights • The cloud vertical structures in Beijing are elucidated using 3-year observations • Cloud structures from MMCR, Himawari-8 and ceilometer agree with each other very well • Cloud top heights are shown to decrease as the cloud layer thickness increases [ABSTRACT FROM AUTHOR]

Abstract This study evaluates the performance of latest version 5B (V5B) Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) Final Run products during a 60-year return extreme precipitation storm on 7 May 2017 over southern China with gauge observations as the reference dataset. Version 4 (V4) Global Satellite Mapping of Precipitation (GSMaP) products and quantitative precipitation estimates derived from a local ground-based S-band dual polarization weather radar (radar, hereafter) were used for parallel comparisons. The satellite-only products (IMERGUncal and GSMaP_MVK) and gauge-corrected products (IMERGCal, GSMaP_Gauge) were selected for this study. The results showed that: 1) GSMaP_MVK, IMERGUncal, GSMaP_Gauge and IMERGCal generally capture the spatio-temporal patterns of storm-accumulated rainfall with correlation coefficient (CC) values about 0.76, 0.70, 0.68 and 0.72, respectively, while radar was well correlated with gauge measurement (CC about 0.94); 2) The GSMaP_Gauge (−19.38%), IMERGCal (−40.23%), GSMaP_MVK (−57.12%), IMERGUncal (−58.77%) satellite-based precipitation products all underestimated the storm-accumulated precipitation, while ground radar overestimated by 27.48%; 3) Both IMERGCal and IMERGUncal outperformed their GSMaP counterparts in capturing the time-series with much higher CC (0.50 vs. -0.21, 0.51 vs. 0.17); 4) Among the satellite-based QPE products, when the rainfall rates are <5 mm/h, IMERGCal performs best with highest CSI. The V4 GSMaP standard products and latest V5B IMERG final run products still had resolution and accuracy limitations in estimating extreme precipitation for this type of warm sector rainfall storm. These findings will help developers of rainfall retrieval products to understand the errors and also help improve modeling of hydrological extremes. Highlights • V5B IMERG performed better than V4 GSMaP during extreme rainfall storm • All satellite-based QPE products generally captured the spatial patterns • IMERG outperformed GSMaP for hourly series of rainfall • Radar can serve as a good tool for extreme rainfall monitoring. [ABSTRACT FROM AUTHOR]

Based on vertically pointing observations of Ka-band frequency-modulated continuous millimeter wave cloud radar (MMCR) in 2020, we investigate cloud vertical structures at Wuhan in central China. Case comparison indicates that the cloud top locations in the MMCR observation are largely consistent with those in satellite data. The precipitation has the occurrence frequency of 9.5% over the year, with the maximum value of 16.3% in July and the submaximal value of 14.7% in January, showing the significant influences of monsoons on precipitation at Wuhan. As the humid, cloudy and rainy climate, the probability of precipitation and non-precipitation clouds increases gradually from 53.9% in January to a large value of 71.5% in July. The non-precipitation clouds have the probability of 44.5% in the year, with two prominent peaks at the reflectivities of −35 to −30 dBZ around 12 km in summer and − 37– −32 dBZ around 10 km in spring. The cloud top can reach the heights of 14.49, 16.62, 13.38 and 11.73 km from spring to winter, respectively. The monthly mean cloud layer thickness is the largest (2.18 km) in May and September, and the smallest (1.36 km) in November. The seasonally averaged base and top heights and thickness of clouds have small diurnal variations. The high cloud is predominant in the warm months from May to September, and in the other cool months, the middle cloud has the most fraction. The quantitative investigation of clouds is helpful in improving the cloud parameterization in climate models. • Ka-band MMCR observations reveal the seasonal, monthly and diurnal variations of clouds at Wuhan in central China. • Precipitation is clearly impacted by monsoons, and cloud shows a response to seasonal and diurnal variations of temperature. • Probability of clouds and precipitation increases from 53.9% in January to 71.5% in July, showing cloudy and rainy at Wuhan. [ABSTRACT FROM AUTHOR]

In remote sensing–based forest aboveground biomass (AGB) estimation research, data saturation in Landsat and radar data is well known, but how to reduce this problem for improving AGB estimation has not been fully examined. Different vegetation types have their own species composition and stand structure, thus they have different data saturation values in Landsat or radar data. Optical and radar data also have different characteristics in representing forest stand structures, thus effective use of their features may improve AGB estimation. This research examines the effects of Landsat Thematic Mapper (TM) and ALOS PALSAR L-band data and their integrations in forest AGB estimation of Zhejiang Province, China, and the roles of textural images from both datasets. The linear regression models of AGB were conducted by using (1) Landsat TM alone, (2) ALOS PALSAR data alone, (3) their combination as extra bands, and (4) their data fusion, based on non-stratification and stratification of vegetation types, respectively. The results show that (1) overall, Landsat TM data perform better than PALSAR data, but the latter can produce more accurate estimates for bamboo and shrub, and for forests with AGB values less than 60 Mg/ha; (2) the combination of TM and PALSAR data as extra bands can greatly improve AGB estimation performance, but their fusion using the modified high-pass filter resolution-merging technique cannot; (3) textures are indeed valuable in AGB estimation, especially for forests with complex stand structures such as mixed forests and pine forests with understories of broadleaf species; (4) stratification of vegetation types can improve AGB estimation performance; and (5) the results from the linear regression models are characterized by overestimation and underestimation for the smaller and larger AGB values, respectively, and thus, selecting non-linear models or non-parametric algorithms may be needed in future research. [ABSTRACT FROM AUTHOR]

Based on the WRF-3DVar system, different momentum control variables in radar data assimilation are investigated for their effects on the analysis and forecast of strong convective weather systems in the study. The single observation assimilation tests are performed besides three cycling data assimilation experiments based on U-wind/ V -wind (UV) and stream-function and velocity potential (ψχ) that are scalar representations of flow fields for their irrotational and divergence components. The wind field increments for both control variables in single observation tests show that when UV are the control variables, the wind field increments have a smaller range of influence that it better reflects the characteristics of the observed information itself at the convective scale than ψχ. When ψχ are used as control variables, negative increments are generated in the analyzed wind field because ψχ have the property of maintaining the integrated value of the wind field. In addition, radar data from 5 Doppler radars in northeast China are assimilated. The cycling assimilation experiments show that CV_UV produces enhanced forecast than CV_ ψχ in terms of radar reflectivity and precipitation. Another case also proves this conclusion. In particular, CV_UV improves the dynamics field and water vapor convergence, which lead to better intensity and structure prediction of the strong convection process. In contrast, CV_ ψχ yields relative discontinuous wind field structure, which tends to reduce the organization of the forecast strong echoes. Another set of experiments are further designed with only radar reflectivity assimilated with CV_UV. The results show that assimilating radial velocity is helpful to improve the forecasting skill. • Different control variables are studied for their effects on the analysis and forecast of strong convective systems. • CV_UV is relatively more localized in terms of analysis increments and is applicable to the convective scale. • CV_UV improves the dynamics field and water vapor convergence for the strong convection process. • CV_UV produces enhanced forecast than CV_ψχ in terms of radar reflectivity and precipitation. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of raindrop size distributions (RSDs) and polarimetric radar parameters retrieved by T-matrix for stratiform and convective precipitation in Beijing and Zhangbei (northern China), and Yangjiang (southern China) are studied and compared based on RSD data observed with PARSIVEL disdrometers in these three different climatic regions. The effects of observed and fitted RSD on scattering simulation are also discussed. The conclusions further confirm the obvious variation of RSDs in different climatic regions and rain types. There is significant regional difference in rainfall microphysical parameters for convective precipitation, and small regional difference for stratiform precipitation, instead. Convective precipitations from Beijing and Yangjiang both have higher mass-weighted mean diameter D m and log10 N w (N w : normalized intercept parameter) values than stratiform precipitations. The averaged RSDs from both rain types in Beijing and Yangjiang are in good agreement with gamma distribution while those in Zhangbei cannot be well fitted either by gamma or M–P (Marshall–Palmer) distribution. It is essential to take into account the effect of air density on raindrop fall velocity in highlands far away from sea level, such as Zhangbei. The μ–Λ relation varies with location. For a given Λ value, the fits to the data in the three regions have higher μ values than Florida relation (Zhang et al., 2003). It is robust to retrieve polarimetric radar parameters by T-matrix. There is an exponential relationship between differential reflectivity Z DR and radar reflectivity factor Z H , as well as the relation between specific differential phase K DP and Z H . The variation of the relations in different climate regions and rain types results from RSD's sensitivity to climatic regions and rain types. Observed RSD is superior to the fitted one in retrieving polarimetric radar parameters. [Copyright &y& Elsevier]

• Quantified the uncertainty in the radar and GSMaP QPEs in a China's hilly humid region. • Investigated the radar and GSMaP QPEs utility for integrated flood and landslide forecasting. • Developed a dynamic bias correction method to improve the radar and GSMaP QPEs. • Explored the impacts of time interval and spatial resolution on the bias-correction performance. It is important to develop the integrated flood and landslide modeling system driven by radar and satellite to predict these hazards to mitigate their damages. In this study, we investigated the utility of the C-band, one-polarization radar quantitative precipitation estimation (QPE) and the Global Satellite Mapping of Precipitation (GSMaP) satellite QPE for the integrated prediction of floods and landslides in two hilly basins of southern Shaanxi Province of China. We further developed a dynamic bias correction to reduce uncertainty in radar and satellite QPEs using gauge observations and explored the impacts of gauge density and spatial resolution of QPE on the effectiveness of bias correction. Our results show that the radar and GSMaP QPEs have respective large negative and positive biases. The bias-correction method has significantly improved the quality of both radar and GSMaP QPEs and the associated accuracies in the simulated hydrological processes and slope stability. The bias-correction method with a correction time interval of 24 h can achieve the optimal results for both radar and GSMaP QPEs. Although gauge density and spatial resolution impact the accuracy of the bias-corrected methods for both radar and GSMaP, inclusion of the observations from even a small number of rain gauges will be helpful for reducing the uncertainty in the radar and satellite QPEs. [ABSTRACT FROM AUTHOR]

Abstract: Across-The-Road (ATR) radar is the most common type of traffic speed measurement devices used in China for traffic law enforcement. Its speed measurement accuracy is highly concerned by drivers, lawyers, policemen and metrologists as well. Among those influence factors, antenna horizontal beamwidth is an important one, which has not been taken into account in the current verification regulation of ATR radar in China. In this paper, the current verification methods of ATR radar in China are firstly introduced, and the reason for the field measurement error of ATR radar is analyzed. The speed measurement error of ATR radar related to antenna horizontal beamwidth is investigated in details, and theoretically calculated in various combinations of installation angles and horizontal beamwidths. Field tests with three equal-distanced piezo sensors each lane as triggering reference have also been performed on two ATR radar samples with horizontal beamwidth 5° and 10° respectively. The results of theoretical analysis and field tests verify that antenna horizontal beamwidth smaller than 6° is a precondition for accurate and reliable field measurements, which has also been added to the newly published pattern approval regulation of ATR radar in China. [Copyright &y& Elsevier]

Abstract: Five years of CALIPSO lidar layer products are used to study transpacific transport of Asian dust. We focus on possible changes to dust intrinsic optical properties during the course of transport, with specific emphasis on changes to particulate depolarization ratio (PDR). PDR distributions for Asian dust transported across the Pacific are compared to previously reported PDR distributions for African dust transported across the Atlantic. African dust shows a slight decreasing trend in PDR during westward transport across the Atlantic during its most active long-range transport season in summer. Asian dust, on the other hand, shows some spatial variability in PDR over the Pacific during its most active long-range transport season in spring. The dust PDR is generally smaller over the ocean than over the Tarim basin and nearby downwind regions. PDR also shows a decreasing trend with latitude moving northward toward the Arctic, together with an increasing trend in the dust aerosol optical depth (AOD) when passing over polluted Asian regions. Possible explanations include (i) the mixing of dust externally or internally with other types of aerosol over the heavily developed industrial regions in East Asia, and (ii) the downstream mixing of dust plumes from different source regions (i.e., Tarim and Gobi). Dust from different source regions exhibits relatively large differences in PDR, with mean values of 0.34±0.07, 0.28±0.06, and 0.30±0.08, respectively, over the Tarim basin, Gobi Desert and Northwest African source regions. Different transport mechanisms are seen for African dust and Asian dust. Asian dust transport is originated by cold fronts and driven by westerly jets. In contrast, summer African transatlantic dust transport is driven by trade winds and is generally well confined in altitude in the free troposphere throughout the tropics and subtropics. [Copyright &y& Elsevier]

Radar data assimilation (DA) can improve short-term precipitation forecasts. However, assimilating radar observations into a numerical prediction model may produce spurious precipitation and large errors in the position and magnitude of precipitation, and high-frequency cyclic assimilation may exacerbate this problem. In this paper, a severe convection case that occurred on 27 June 2018 over eastern China was used to investigate the impacts of the radar DA frequency and large-scale constraint on precipitation forecasts. The Weather Research and Forecasting (WRF) three-dimensional variational (3D-Var) DA system was used to assimilate radial velocity and reflectivity data. The sensitivity of the DA frequency using 15-min and 1-h assimilation intervals was examined first, revealing that the 15-min DA interval produced a greater overprediction bias of precipitation. A diagnosis of the analysis fields showed that higher-frequency DA cycling produced excessive wind speed and water vapor convergence at low levels and exaggerated upward movement. Then, the large-scale constraint was imposed on the regional model by the spectral nudging (SN) technique, which assimilated Global Forecast System (GFS) forecast field data during the forecast periods. The results demonstrated that the application of SN could significantly reduce the positional deviation of the precipitation forecast and the magnitude of overpredicted precipitation. SN could effectively adjust large-scale circulation fields, thereby improving the conditions of water vapor convergence. Moreover, SN also improved the forecasts of surface variables such as wind, temperature, and humidity. • The impacts of the radar data assimilation frequency and large-scale constraint on precipitation forecasts are investigated. • A higher frequency of radardata cyclic assimilation leads to a larger overprediction bias of precipitation. • Using the spectral nudging to assimilate GFS forecast data in the forecast periods can improve precipitation forecasting. [ABSTRACT FROM AUTHOR]

Abstract: We used 50-MHz ground-penetrating radar to detect the boundary of permafrost in Xidatan region, the northern limit of the marginal and sporadic permafrost area on the Tibetan Plateau, China. We interpreted the lower limit of permafrost from nine radar profiles to determine the boundary between the permafrost and non-permafrost region. We also sketched the locations of permafrost table along the nine profiles and acquired the lower alpine limit of permafrost in this area. Based on the lower alpine limit of permafrost determined in this field survey, a new permafrost distribution map was drawn with the help of GIS analyses. Comparing with the research work in 1975, permafrost in Xidatan is reduced 12% in area and the lower alpine limit has increased by 25 m. The situation of global warming, apparent climatic warming recorded at two stations near Xidatan, could be responsible for permafrost degradation in this area. [Copyright &y& Elsevier]

Currently, high-resolution severe storm observations obtained by vehicle-mounted mobile X-band dual-polarization radar (X-pol) are widely used in severe storm structure and dynamics studies; however, the identification of hailstones based on X-pol is still rare, leading to the limited application of X-pol in identifying hydrometeors in the microphysical processes of severe storms. Based on previous works, this study constructs an improved X-pol hydrometeor identification (HID) method for hailstorms; the hydrometeor categories include a rain-hail mixtures (RH) category indicating hailstones are melting or experiencing wet growth, and the correlation coefficient between horizontally and vertically polarized echoes (ρ HV) is used to locate the local mixed phase region in storms to avoid misclassifications of hydrometeors resulted by environmental temperature in this local mixed phase region. The improved HID method can see liquid water information above the melting layer; it provides a possibility to observe the microphysical process of hailstones wet growth above the melting layer. Furthermore, this improved HID method was utilized to study the high spatiotemporal resolution data collected by the Institute of Atmospheric Physics of Chinese Academy of Sciences (IAP) X-pol for one summer hailstorm over northern China. The results indicate that the identified RH is consistent with the surface hail record of National weather observatory of China Meteorological Administration (CMA), the specific differential phase (K DP) column is more sensitive than the differential reflectivity (Z DR) column for indicating the updraft zone movement, and we considered that the relative position between the key area of hail (KAH, where above the Z DR column, Z DR ~ −2 to 0 dB, Z H ~ ≥ 50 dB Z) and the updraft zone (indicated by the Z DR , K DP column) will determine the evolution of hail. Furthermore, high-density graupels (HDGs) in the upper layer of the KAH may be the source of RH embryos, and these HDGs collect liquid droplets from the liquid water-rich (LWR) area located behind the KAH to form a large number of RH in the lower layer of the KAH. These characteristics are important for hailstone forecasting and warnings. • Constructing an improved X-band dual-polarization radar (X-pol) hydrometeor identification (HID) method for hailstorms. • This improved method showed its superiority in observing liquid water information above the melting layer within storms. • The results reveal how the polarization parameters of X-pol indicate the generation and extinction of hail. [ABSTRACT FROM AUTHOR]

The signature of the low-latitude mesosphere response to the February 2017 minor sudden stratosphere warming (SSW) was detected using the observations of a meteor radar at Fuke (19.5°N, 109.1°E) a low-latitude station in China and ERA-5 data. Radar detected the zonal wind reversal in the mesosphere three days before the SSW event, whereas the ERA-5 does not reproduce the mesospheric wind response at low-latitudes during the 2017 SSW and large discrepancies are found between the mesospheric zonal winds derived from the Fuke radar and ERA-5. The quasi oscillatory pattern was noted in the meridional winds before the SSW event, afterward, the northward winds are significant. We observed the existence of 20–28-day planetary waves (PWs) in the Fuke meteor radar measured mesospheric zonal winds before the SSW and the 2-12-days period PWs before and after the SSW in the meridional winds. The zonal structure and periodicity of the PWs have been verified with the other meteor radar at the Indian tropical station Tirupati (13.63°N, 79.4°E). However, ERA-5 does not capture the PW activity in the mesosphere as radar. The similarities and dissimilarities among the different techniques have been discussed. Therefore, the present study re-emphasizes the strong response of the low-latitude mesosphere to the 2017 minor SSW in a manner similar to the major SSW event. • The Fuke meteor radar along with ERA-5 were used to study the low-latitude mesospheric signatures during the 2017 SSW. • Large discrepancies are found between the mesospheric winds derived from the Fuke radar and ERA-5 during the 2017 SSW. • Mesospheric wind measurements from Fuke and Tirupati radars reveal PW oscillations at low-latitudes during the SSW. • ERA-5 does not capture the PW activity in the mesosphere as a meteor radar. [ABSTRACT FROM AUTHOR]

• Optimized retrieval of DSDs and rainfall from polarimetric radar data. • Attenuation correction considering the DSD variabilities. • Optimized attenuation correction and retrieval using a uniform framework. A variational approach for optimized drop size distribution (DSD) retrieval, attenuation correction, and rainfall estimation from polarimetric radar measurements (horizontal reflectivity factor Z H , differential reflectivity Z D R , and differential phase shift Φ D P) is proposed in this study. The spatial continuity of rain is guaranteed by introducing the radial B-spine filter and azimuthal Kalman filter, which helps to mitigate the impact of the random errors in Z D R and Φ D P. The approach is evaluated using a simulated experiment and two real cases observed by a mobile C-band and an operational S-band polarimetric radar in south China. The comparative results demonstrate that the proposed variational approach can correct attenuation more accurately than the conventional method using assumed linear relationships between specific attenuation and specific differential phase. The rainfalls derived from the DSD estimates based on this proposed approach agree well with the rain gauge measurements. It is also shown that the proposed method has a better performance than the existing variational retrieval and the composite estimator. [ABSTRACT FROM AUTHOR]

• The UHF radar is applied to detect water-surface velocities to be used as the boundary condition for flow measurement. • The Reynolds-Averaged Navier-Stokes (RANS) is proposed to analyze cross-section velocity distribution. • The suggested methodology performs better than the power law and the log law especially in the narrow channel region. Non-contact flow measurement method plays an increasingly important role in river discharge measurement. However, most channel cross-section velocity distribution models proposed by researchers have certain limitations in application, underwater velocities are always necessary when applied in narrow channels, which makes it challenging to calculate natural river discharge using water-surface velocities measured by remote sensing instruments. This letter takes water-surface velocities detected by UHF radar as boundary conditions and a new velocity distribution model is derived based on the Reynolds-Averaged Navier-Stokes (RANS) equations. UHF radar measures surface velocities of the cross-section, and velocities on the river bed of the cross-section are considered to be 0. The RANS equations are simplified to be a two-dimensional Poisson equation and the cross-section velocity distribution is solved by using the closed boundary conditions. Some field experiments were conducted in the Hanjiang River at Xiantao, Hubei, China in September 2017 and April–July 2018, the processing results of which show that the proposed model is superior to the power law and the log law models, especially near the side wall (narrow channel region). River discharges calculated by this method are highly consistent with those provided by Hubei Xiantao hydrologic station, which verifies the reliability of the model and the feasibility of using UHF radar to measure natural river discharge continuously and automatically. [ABSTRACT FROM AUTHOR]