Abstract:Based on daily temperature and precipitation data from 91 meteorological stations in Guangxi from 1961 to 2025, climate and annual evaluation indicators suitable for Guangxi were constructed. This indicator is divided into two evaluation periods: flood season (April to September) and non flood season (January to March, October to December). By introducing dynamic weights to amplify the impact of key catastrophic events such as extreme high and low temperatures, floods, and droughts, and using a ten day standardized anomaly weighted accumulation method, the climate annual index is finally obtained. Using the percentile method, climate scenes are classified into five levels. The results show that from 1961 to 2020, the climate annual index in Guangxi significantly increased at a rate of 1.2·10a-1, and the overall climate annual index deteriorated. The frequency of "bad" years significantly increased after the 1990s. By comparing and verifying with historical records of major weather processes and disaster loss assessments, it has been proven that the index is reliable and applicable to business, and has performed well in commercial applications from 2021 to 2025. At the same time, this indicator has also shown good results in the application at the city and county levels, and can be used for climate and annual landscape evaluation at the three levels of Guangxi Autonomous Region, city, and county.

Abstract:Using conventional observations, satellite and radar observations, and ERA5 reanalysis data, this study analyzed the heavy precipitation characteristics, environmental conditions, and mesoscale system evolution associated with the localized extreme torrential rainfall event in the western Sichuan Basin on 11 July 2023. Furthermore, through analyses of orographic lifting velocity, mesoscale dynamical diagnostics, and latent heating effects, it explored the possible physical mechanisms responsible for convective initiation, organization, and maintenance. This rainstorm was a warm-sector event on the plateau slope under weak large-scale synoptic forcing, caused by a meso-β-scale convective system originating from a multi-cell linear storm. It differs from large-scale basin-wide rainstorms driven by significant synoptic-scale forcing. The precipitation featured a narrow, quasi-stationary band with a notable train echo effect. Short-duration heavy rainfall lasted for 8-9 hours, with a maximum hourly rainfall intensity of 83.7 mm·h-1 and a 12 h accumulated rainfall of 371.9 mm. Heavy precipitation was concentrated in the canyon terrain and steep windward slopes of the northern Longmen Mountain, highlighting the prominent role of topography. After nightfall, mountain breezes accumulated at the valley bottom, forming a cold pool. The warm and moist southeasterly flow within the boundary layer rides up over this cold pool, initially triggering localized weak convection.At midnight, the establishment of the southeasterly low-level jet enhances the orographically forced lifting rate on the windward slopes, resulting in intensified convection. Simultaneously, influenced by topographic blocking, a northeasterly diverted flow develops in front of the mountains, forming a shear line with the ambient southeasterly wind, which facilitates the organized development of convection along the terrain. On the other hand, the nocturnal thermal contrast between the plateau and the basin generates a pronounced horizontal temperature gradient that reinforces the low-level vertical wind shear in the piedmont region. That is, the orographic thermal forcing favors the acceleration of the boundary-layer southeasterly flow in the foothill area, thereby further promoting the organized development of convection. The synergy of three processes—a positive feedback between convective latent heat release and vorticity development that enhanced upward motion, cold/warm advection at upper/lower levels that amplified instability, and continuous moisture supply by the southeasterly.

Abstract:Taking the Jianghuai Meiyu precipitation event on 19–20 June 2025 as a case study, this paper investigates the microphysical characteristics and latent heat structure of Meiyu precipitation using the three-dimensional observations and retrieved precipitation and latent heat products from the Precipitation Measurement Radar onboard Fengyun-3G (FY-3G), with ERA5 reanalysis data employed for joint verification and mechanism analysis. The results show that Meiyu precipitation is a mixture of stratiform and convective precipitation across different scales, primarily originating from widespread stratiform precipitation, followed by embedded deep convective cloud clusters. The bright band corresponds well with stratiform precipitation. The upward motion above the bright band promotes the melting and collision–coalescence of ice particles, forming a cloud water accumulation zone that produces persistent stratiform precipitation. Convective precipitation echoes mainly originate from low-level cloud systems and are accompanied by strong vertical motion. In stratiform precipitation, the scatter distributions of particle diameter and concentration are relatively concentrated, both showing a decreasing trend with increasing height. In convective precipitation, the particle concentration and diameter exhibit pronounced discrete distributions, scattering toward larger diameters and higher concentrations at low altitudes and toward smaller diameters and lower concentrations at high altitudes. During stratiform precipitation, the particle concentration ranges in the warm and cold regions are similar, but some particle diameters in the warm region are noticeably larger than those in the cold region. During convective precipitation, compared with the cold region, the particle diameter and concentration scatter in the warm region exhibits a discrete pattern toward smaller diameters and higher concentrations. The latent heat data indicate that the greatest latent heat release occurs near the melting layer, with the greatest latent heat absorption in the lower atmosphere, and a pronounced latent heat absorption zone exists within 1 km below the melting layer. The ERA5 data confirm the reasonableness of the FY-3G latent heat data, with a correlation coefficient of 0.64 and a root-mean-square error of 2.0 K·hr?1. The statistical consistency in vertical distribution between the ERA5 apparent heat source Q1 and the FY-3G latent heat verifies the physical mechanism of latent heat release through water vapor phase transitions in the melting layer. The results of this paper provide key observational evidence for understanding the fine-scale structural characteristics of Meiyu, and the revealed vertical differences in stratiform/convective precipitation particle spectra and the vertical structure characteristics of latent heat can provide observational constraints for the parameter settings of relevant processes in microphysical parameterization schemes.

Abstract:Accurate forecasting of precipitation phase transitions is a key focus and challenge in winter meteorological services. Using multi-source observational data, including ground-based automatic weather stations, ERA5 reanalysis data, wind profiler radar, microwave radiometer, cloud radar, and X-band dual-polarization radar, this study comprehensively analyzes the evolution characteristics of phase transitions during two heavy rain-snow events in Shenyang: from November 5 to 7, 2023 (Event I) and from February 18 to 19, 2024 (Event II). The study also extracts indicative metrics for phase transitions based on multi-source observations. The results show: (1) Event I was controlled by a deep, slowly moving cold vortex system, with stronger dynamic and moisture conditions (maximum vertical velocity > 8m/s, liquid water content reaching up to 12 g·m?3), resulting in large cumulative precipitation and a relatively gradual phase transition process. Temperatures retrieved by the microwave radiometer agreed well with the operational phase transition thresholds. In contrast, Event II was dominated by a fast-moving upper-level trough, with rapid cold air intrusion, leading to a more abrupt phase transition. Furthermore, the microwave radiometer-retrieved temperatures were lower than those from sounding, causing a 1–2 hour deviation in precipitation phase identification based on traditional thresholds. (2) Observations from cloud radar and wind profiler radar indicate that both events exhibited a significant weakening of vertical updrafts (decreasing to 1–2m/s), a sharp decline in liquid water content retrieved by the microwave radiometer, and a continuous drop in the 0°C layer height during the rain-to-snow transition phase. The descent of the 0°C layer bright band and the low correlation coefficient region (0.8–0.92) to the ground, as detected by X-band dual-polarization radar during the rain-to-snow transition, represents the most intuitive and reliable near-term warning indicator for phase transitions. (3) Based on the above multi-source observational characteristics, this study proposes an analytical framework consisting of "dynamic attenuation diagnosis—thermal stratification tracking—dual-polarization radar phase identification," shifting the forecasting mindset from "threshold-based" to "trend-based" analysis. This provides a more operationally feasible technical pathway for the nowcasting of winter precipitation phase transitions.

Abstract:The raindrop size distribution reflects the variation of raindrop number concentration per unit volume with particle size, and its study is of great significance for revealing precipitation formation mechanisms and deepening the understanding of cloud physical processes. This paper presents a detailed typical cases analysis of the raindrop size distribution on November 5, 2023, based on atmospheric measurement devices such as micro rain radar and disdrometer. The results indicate that, 1) The trends of rainfall rate variation show good consistency among micro rain radar，rain gauge and disdrometer.Compared to the other two detection devices, the micro rain radar shows a significant underestimation of near-surface rainfall rate at 400m height. 2) The raindrop size distribution width during convective cloud precipitation is larger than that during stratiform cloud precipitation. Furthermore, whereas the normalized intercept parameter differs only marginally between stratiform and convective precipitation, it is the mass-weighted mean diameter that governs the magnitude of the rainfall rate..3) From the vertical evolution of raindrop size distribution below the bright band, it can be observed that as raindrops fall, the number of small raindrops decreases while the number of large raindrops increases. The raindrop size distribution spectrum gradually broadens, with convective precipitation exhibiting a wider spectrum than its stratiform precipitation. Minute-scale vertical evolution of raindrop spectra indicates evident coalescence microphysical processes in stratiform precipitation. Furthermore, the number of large particles in convective precipitation is significantly greater than that in stratiform precipitation at all heights.4) The classification of precipitation type in the vertical direction(snow-mix-rain)is relatively distinct throughout the precipitation process, with the height of the mix layer gradually decreasing over time,the zero degree layer height progressively lowers. This aligns with the gradual drop in ground-level air temperature during the precipitation process.

Abstract:In view of the limitation that the traditional historical frequency matching method (Hist-FMM) cannot effectively correct the positional deviation of precipitation areas, an improved frequency matching correction scheme based on low-level circulation similarity (Sim-FMM) is proposed, which uses wind direction and speed at 925 hPa as dynamic constraints. By analyzing the coupling relationship between precipitation and the wind field at 925 hPa, together with sensitivity experiments, the optimal parameter scheme for Sim-FMM was established. For general precipitation correction, a wide tolerance window (30° for wind direction and 4 m·s?1 for wind speed) without seasonal constraints is adopted to ensure sample representativeness. For heavy rainfall correction, a narrower tolerance window (10° for wind direction and 1 m·s?1 for wind speed) combined with seasonal constraints is applied to balance circulation similarity and climatological characteristics. Based on surface observations and ECMWF forecast data from December 2023 to May 2026, the correction performance of Sim-FMM was evaluated. The results show that Sim-FMM outperforms Hist-FMM in precipitation correction. For winter rainfall events, Sim-FMM effectively reduces widespread false alarms by matching analogous circulation samples, increasing the rain/no-rain accuracy by 1.9% relative to Hist-FMM. For local heavy rainfall events in spring and summer, Sim-FMM alleviates the systematic underestimation of rainstorm magnitude, improving the rainstorm threat score (TS) by 8.4% relative to Hist-FMM during 2024-2026. Nevertheless, Sim-FMM performs slightly worse for autumn heavy rainfall, which may be attributed to the highly concentrated seasonal features of autumn rainfall over Hainan Island and the inability of the regional mean wind field at a single time to fully depict the heterogeneous structures of complex systems such as typhoons and shear lines.

Abstract:Based on the Local Climate Zone (LCZ) framework, this study systematically analyzes the characteristics of temperature differences across various underlying surface types and their response mechanisms to meteorological conditions. Using hourly temperature, wind speed, and precipitation data (2010–2021) from 37 meteorological stations within the Fifth Ring Road of Beijing, combined with field surveys and satellite imagery, the stations were classified into five LCZ types. The results indicate that the main urban area exhibits a temperature gradient dominated by building density. The compact high-rise zone (LCZ 1) serves as a stable heat center, with average temperatures significantly higher than those of vegetated zones. Thermal differences among LCZ types follow a seasonal pattern of intensifying in autumn and winter while weakening in spring and summer, with the most pronounced disparities occurring during winter nights. Furthermore, precipitation significantly reduces thermal differences between LCZs through evaporative cooling, while simultaneously highlighting the dominant role of surface properties. Finally, weak wind conditions favor the maintenance of thermal gradients, whereas strong wind environments promote the homogenization of the temperature field.

Abstract:Based on observation data from 76 national meteorological stations in Hubei Province and ERA5 reanalysis data during 2000-2024, 108 rain-snow events are classified by means of the T-mode principal component analysis (TPCA). The temporal distributions, circulation configurations, and impact characteristics of the rain-snow events under different circulation types are then analyzed. The results show that over the 25 years (2000—2024), Hubei Province experienced 4.3 rain-snow events on average annually, with a clear inter-annual variability. These events occurred mainly in January and February, accounting for 74% of the total. Based on the circulation patterns at 500 hPa, these rain-snow events are classified into three types: the Lake Baikal High-Ridge Type (48.1%), Lake Baikal Low-Trough Type (30.6%), and Lake Baikal Northwesterly Flow Type (21.3%). In the composite mean fields of the three circulation types, the Lake Baikal High-Ridge Type features the deepest southern-branch trough at 500 hPa and the strongest influence of the surface cold high. The Lake Baikal Low-Trough Type is characterized by the strongest southwesterly jet at 700 hPa, with a maximum wind speed of 20 m·s?1, and the most favorable dynamical conditions. The Lake Baikal Northwesterly Flow Type has the weakest southern-branch trough. The three circulation types of rain-snow events produces distinct impacts in Hubei Province. The Lake Baikal Low-Trough Type has a higher daily average maximum precipitation (15.34 mm) and deeper average maximum snow depth (9.33 cm) than the other two types and is more prone to produce deep snow cover. The Lake Baikal High-Ridge Type has the largest average value of total precipitation (19.63 mm), the highest mean numbers of snow-covered and wire-icing stations, and the greatest wire-icing intensity with a mean maximum wire-icing diameter of 3.83 mm. It also has the longest duration of rain-snow event, lasting for 2.22 d on average. The Lake Baikal Northwesterly Flow Type generally generates smaller precipitation amount, the weakest snow accumulation and wire icing, and the shortest event duration. These findings could provide a reference for circulation-pattern-based forecasting of rain-snow events and disaster risk assessment in Hubei Province.

Abstract:Since 2024, the operational operation of most new-generation weather radars in China has adopted three observation modes: precipitation mode 1 (VCP11D), precipitation mode 2 (VCP21D), and clear-air mode (VCP31D). However, a systematic evaluation of their specific data quality differences and the scientific validity of the automatic switching strategy is still lacking. This study uses 11,965 sets of observation data from 117 dual-polarization operational radars nationwide, collected before and after mode switching from April to July 2024, to compare and analyze the performance of the three observation modes in terms of ground clutter suppression capability, sensitivity, and measurement accuracy. Furthermore, by statistically calculating the proportion of effective precipitation echoes in newly added/missing elevation layers before and after mode switching, the study quantitatively evaluates the rationality of the current automatic switching strategy, which is based on thresholds of composite reflectivity (CR), echo top (ET), and vertically integrated liquid water content (VIL). The results show that: (1) In terms of data quality, the three modes exhibit comparable ground clutter suppression capabilities, but the clear-air mode significantly increases the area of ground clutter identification due to its longer pulse width. The clear-air mode has the highest sensitivity, followed by the precipitation modes; however, differences in radar models and refined modifications can reduce sensitivity. The number of pulse accumulations in different observation modes primarily affects the measurement accuracy of differential reflectivity (ZDR) and correlation coefficient (ρhv); fewer accumulations lead to greater dispersion of these two parameters. (2) Regarding switching strategies, the current fixed-threshold strategy fails to effectively capture the vertical structural changes in precipitation, resulting in low utilization of elevation resources. Taking the CINRAD/SAD radar as an example, the switching threshold between the two precipitation modes is set too low, resulting in a median effective precipitation echo proportion of only 27.13% in the newly added elevation layers of VCP11 (5.2°, 7.5°, 8.7°, 12°, and 16.7°), thus failing to fully leverage the advantages of vertical dense observations. Conversely, the threshold for switching from precipitation to clear-air mode is set too high, resulting in a median of 15.66% of precipitation echoes remaining in the missing elevation layers (6.0°, 9.9°, 14.6°, 19.5°) of VCP31 after switching. (3) To address the above issues, considering the limited computational capacity of the Radar Data Acquisition (RDA) subsystem, this paper proposes a simple switching indicator based on the spatial proportion of echoes in common elevation layers. Comparative verification shows that this indicator significantly improves the accuracy of mode switching and the utilization of elevation resources. This study provides a scientific basis for optimizing the observation strategies of China’s new-generation weather radars and enhancing the capability of severe weather monitoring and early warning.

Abstract:This study investigates the decadal modulation of ENSO’s impact on intraseasonal summer precipitation over eastern China. During 1991–2024, early summer (June) following an El Ni?o event tends to see increased precipitation over the middle and lower reaches of the Yangtze River and regions to the south, whereas late summer (August) experiences a decrease in these same regions. This inverse-phase relationship underwent a significant decadal shift around the early 2000s. A comparison between the periods 1991–2003 and 2004–2024 reveals that in the latter period, the relationship between ENSO and precipitation in August of the following year in the middle and lower reaches of the Yangtze River and regions to the south weakened, making it less likely for widespread negative precipitation anomalies to occur in this region. By examining the concurrent changes in sea surface temperature (SST) and atmospheric circulation associated with ENSO events, this study finds that over the western North Pacific in August 2004–2024, weakened easterly anomalies lead to reduced latent heat flux from evaporation, resulting in a shift from negative to positive SST anomalies. Meanwhile, positive SST anomalies over the northern Indian Ocean are comparatively weaker. Consequently, the anomalous anticyclone over the western North Pacific is unable to persist and transitions into a cyclonic circulation, which is detrimental to precipitation deficits over the middle and lower reaches of the Yangtze River and adjacent southern regions. In terms of circulation configuration, at the 500 hPa level, the East Asia–Pacific/Pacific–Japan teleconnection pattern shifts from a “+-” to a “-+” pattern in August 2004–2024; at the 200 hPa level, the East Asian subtropical westerly jet weakens. Both changes are unfavorable for precipitation deficits over the middle and lower reaches of the Yangtze River and southern regions. This research clarifies the decadal modulation of ENSO’s influence on intraseasonal summer precipitation in eastern China, providing a theoretical basis for improving intraseasonal precipitation prediction.