Chuanhong Zhao

How aerosols modulate warm-sector extreme rainfall over South China by altering mesoscale convective system (MCS) organization remains poorly understood. We investigate a coastal warm-sector extreme-rainfall event on 10–11 May 2022 using five WRF v4.3.3 sensitivity experiments with different water-friendly aerosol concentrations. Multiscale responses are diagnosed using a two-dimensional discrete cosine transform, hydrometeor mass budgets, and buoyancy analysis. All experiments reproduce the inland frontal and coastal warm-sector rainbands, while aerosol sensitivity is concentrated in coastal MCS continuity, convective-scale hydrometeor activity, and rainwater production. As aerosol loading increases from low to moderate levels, condensational growth and cloud-water collection by raindrops intensify, establishing a more persistent warm-rain water source. Increased supercooled cloud water further promotes snow and graupel riming and melting, strengthening cold-rain processes. Meanwhile, low-level inflow, ascent, and hydrometeor columns become better aligned, favoring sustained MCS regeneration and a more continuous coastal rainband. At higher aerosol loading, smaller mean cloud-droplet sizes suppress warm-rain production, while evaporative cooling and low-level cold anomalies intensify, coinciding with greater spatial separation of newly triggered convection from the primary rainband and increased rainband fragmentation. Although cold-rain compensation occurs in a few intense cores late in the highest-concentration experiment, it does not restore regionally averaged rainwater generation or rainband continuity. These results reveal a non-monotonic aerosol sensitivity in which precipitation depends not only on local microphysical enhancement but also on whether microphysical and dynamical responses remain spatially coupled to the MCS regeneration zone within this coastal warm-sector convective system over South China.

How aerosols modulate warm-sector extreme rainfall over South China by altering mesoscale convective system (MCS) organization remains poorly understood. We investigate a coastal warm-sector extreme-rainfall event on 10–11 May 2022 using five WRF v4.3.3 sensitivity experiments with different water-friendly aerosol concentrations. Multiscale responses are diagnosed using a two-dimensional discrete cosine transform, hydrometeor mass budgets, and buoyancy analysis. All experiments reproduce the inland frontal and coastal warm-sector rainbands, while aerosol sensitivity is concentrated in coastal MCS continuity, convective-scale hydrometeor activity, and rainwater production. As aerosol loading increases from low to moderate levels, condensational growth and cloud-water collection by raindrops intensify, establishing a more persistent warm-rain water source. Increased supercooled cloud water further promotes snow and graupel riming and melting, strengthening cold-rain processes. Meanwhile, low-level inflow, ascent, and hydrometeor columns become better aligned, favoring sustained MCS regeneration and a more continuous coastal rainband. At higher aerosol loading, smaller mean cloud-droplet sizes suppress warm-rain production, while evaporative cooling and low-level cold anomalies intensify, coinciding with greater spatial separation of newly triggered convection from the primary rainband and increased rainband fragmentation. Although cold-rain compensation occurs in a few intense cores late in the highest-concentration experiment, it does not restore regionally averaged rainwater generation or rainband continuity. These results reveal a non-monotonic aerosol sensitivity in which precipitation depends not only on local microphysical enhancement but also on whether microphysical and dynamical responses remain spatially coupled to the MCS regeneration zone within this coastal warm-sector convective system over South China.

The differential reflectivity ( Z _DR ) column is a notable radar signature in thunderstorms, serving as a proxy for updrafts and an early indicator of storm intensity. However, a quantitative relationship among the Z _DR column morphology, related microphysical characteristics, and dynamic structures based on sufficient field observations has not yet been reported. To explore these quantitative relationships, we develop a three-dimensional Z _DR column identification method based on 100 Z _DR columns within severe thunderstorms (primarily supercells) in the Pearl River delta region of South China from April to July in 2021 and 2024. The 3D-connected component labeling with horizontal and vertical tolerance mechanisms is integrated into the method to ensure the structural independence and integrity of multiple Z _DR columns coexisting within the same thunderstorm. This method shows that Z _DR columns in severe thunderstorms exhibit mean depths of approximately 2 km, mean widths of approximately 6 km, mean volumes of approximately 30 km ³ , 30–70-min life cycles, and high liquid water contents (mean = 2.23 g m ⁻³ ). Quantitative relationships between three morphological parameters (volume, width, and depth) of Z _DR columns and updraft volumes retrieved from multiradar wind fields using 1–11 m s ⁻¹ thresholds were also determined. All three morphological parameters of the Z _DR column outperform the traditional 35-dB Z echo-top height in indicating updraft intensity. In addition, the distribution of hydrometeors was explored. Our results, derived from extensive observations, quantitatively highlight the strong relationship between Z _DR column morphology and thunderstorm dynamic structure, providing a theoretical foundation for improving severe weather warnings and forecasts. Significance Statement: Differential reflectivity ( Z _DR ) columns observed by dual-polarization radar are known indicators of updrafts in thunderstorms, but they have rarely been quantitatively characterized on the basis of abundant observational datasets, which are needed for objective operational use. This study introduces an automated three-dimensional method to identify Z _DR columns and demonstrates that their depths, widths, and volumes are strongly related to updraft intensities. Compared with traditional updraft indicators such as the echo-top height, Z _DR column morphology provides a more accurate representation of updraft intensity within severe thunderstorms. These results show that Z _DR columns can be used as practical radar-based tools to improve real-time monitoring and nowcasting of severe convective storms.

How aerosols modulate warm-sector extreme rainfall over South China by altering mesoscale convective system (MCS) organization remains poorly understood. We investigate a coastal warm-sector extreme-rainfall event on 10–11 May 2022 using five WRF v4.3.3 sensitivity experiments with different water-friendly aerosol concentrations. Multiscale responses are diagnosed using a two-dimensional discrete cosine transform, hydrometeor mass budgets, and buoyancy analysis. All experiments reproduce the inland frontal and coastal warm-sector rainbands, while aerosol sensitivity is concentrated in coastal MCS continuity, convective-scale hydrometeor activity, and rainwater production. As aerosol loading increases from low to moderate levels, condensational growth and cloud-water collection by raindrops intensify, establishing a more persistent warm-rain water source. Increased supercooled cloud water further promotes snow and graupel riming and melting, strengthening cold-rain processes. Meanwhile, low-level inflow, ascent, and hydrometeor columns become better aligned, favoring sustained MCS regeneration and a more continuous coastal rainband. At higher aerosol loading, smaller mean cloud-droplet sizes suppress warm-rain production, while evaporative cooling and low-level cold anomalies intensify, coinciding with greater spatial separation of newly triggered convection from the primary rainband and increased rainband fragmentation. Although cold-rain compensation occurs in a few intense cores late in the highest-concentration experiment, it does not restore regionally averaged rainwater generation or rainband continuity. These results reveal a non-monotonic aerosol sensitivity in which precipitation depends not only on local microphysical enhancement but also on whether microphysical and dynamical responses remain spatially coupled to the MCS regeneration zone within this coastal warm-sector convective system over South China.

This study develops a novel framework within the Weather Research and Forecast Model for modeling aerosol‐cloud‐lightning interactions. The framework explicitly represent aerosol‐cloud interactions by prescribing aerosols with two configurations: an idealized setup, where both cloud condensation nuclei (CCN) and ice nucleating particles (IN) are assumed to have a single chemical composition and spatially uniform distributions; and a quasi‐realistic configuration, with multi‐species aerosols assigned spatially varying distributions, where hygroscopic components act as CCN, dust particles act as IN, and all aerosol species influence radiative transfer. Cloud microphysics is coupled with detailed charge‐to‐discharge processes to simulate lightning. The framework is evaluated using two thunderstorms in Guangdong, China. For an isolated storm, the model reproduces a tripolar charge structure similar to observations, demonstrating its capability in simulating electrification. For a frontal storm, the model reproduces the observed precipitation, and lightning is broadly simulated in the correct regions of the storm but substantially underestimated. This requires further investigation. The results further show that increasing CCN concentration suppresses rainfall while enhancing lightning. Higher CCN concentrations produce more numerous but smaller cloud droplets, which suppresses the coalescence into rain, allows more droplets to loft into the upper level, and forms more but smaller cloud ice particles. This boosts graupel‐ice collisions, intensifies non‐inductive charging, strengthens the upper positive charge and the vertical electric‐field gradient, ultimately increasing the lightning frequency. In contrast, no significant aerosol‐induced updraft invigoration is observed. These results suggest that microphysical effects may dominate the dynamical invigoration effect in aerosol modulating thunderstorm electrification and lightning.

Convective impulses (CIs) occur in thunderstorms and are strongly associated with severe convection, often contributing to hazardous weather events. However, the underlying physical mechanisms governing CIs remain poorly understood. In this study, multiple CI events were identified in two selective thunderstorms and analysed from the perspective of the cloud life cycle using polarimetric radar and lightning observations. We investigated the roles of environmental conditions and cloud microphysics in CI events. Our results indicate a pronounced increase in supercooled liquid water and graupel content prior to CI occurrence. The breakup of raindrops is closely linked to the observed increase in supercooled raindrops, suggesting that the fragmentation of large raindrops below the melting layer contributes to raindrop multiplication at subfreezing temperatures. These smaller raindrops subsequently freeze into graupel-like particles, releasing latent heat that may enhance convection and/or lightning activity. This hypothesized physical mechanism is further supported by idealized numerical simulations, which demonstrate that the updraft intensity varies with the efficiency of raindrop breakup. Additionally, large raindrops involved in the breakup process originate from the coalescence of raindrops during the initial pre-CI event, whereas graupel melting or shedding plays a role in subsequent pre-CI events. This improves the understanding of CIs following precipitation loading, melting, and evaporation within a near-stationary thunderstorm cell. These findings reveal a likely physical mechanism contributing to CI events and offer new insights into thunderstorm microphysics and dynamics.

Convective impulses (CIs) occur in thunderstorms and are strongly associated with severe convection, often contributing to hazardous weather events. However, the underlying physical mechanisms governing CIs remain poorly understood. In this study, multiple CI events were identified in two selective isolated thunderstorms and analyzed from the perspective of the cloud life cycle using polarimetric radar and lightning observations. We investigated the roles of environmental conditions and cloud microphysics in CI events. Our results indicate a pronounced increase in supercooled liquid water and graupel content prior to CI occurrence. The breakup of raindrops is closely linked to the observed increase in supercooled raindrops, suggesting that the fragmentation of large raindrops below the melting layer contributes to raindrop multiplication at subfreezing temperatures. These smaller raindrops subsequently freeze into graupel-like particles, releasing latent heat that may enhance convection and/or lightning activity. This hypothesized physical mechanism is further supported by idealized numerical simulations, which demonstrate that the updraft intensity varies with the efficiency of raindrop breakup. Additionally, large raindrops involved in the breakup process originate from the coalescence of raindrops during the initial pre-CI event, whereas graupel melting or shedding plays a role in subsequent pre-CI events. This improves the understanding of CIs following precipitation loading, melting, and evaporation within a near-stationary thunderstorm cell. These findings reveal a likely physical mechanism contributing to CI events and offer new insights into thunderstorm microphysics and dynamics.

Convective impulses (CIs) occur in thunderstorms and are strongly associated with severe convection, often contributing to hazardous weather events. However, the underlying physical mechanisms governing CIs remain poorly understood. In this study, multiple CI events were identified in two selective isolated thunderstorms and analyzed from the perspective of the cloud life cycle using polarimetric radar and lightning observations. We investigated the roles of environmental conditions and cloud microphysics in CI events. Our results indicate a pronounced increase in supercooled liquid water and graupel content prior to CI occurrence. The breakup of raindrops is closely linked to the observed increase in supercooled raindrops, suggesting that the fragmentation of large raindrops below the melting layer contributes to raindrop multiplication at subfreezing temperatures. These smaller raindrops subsequently freeze into graupel-like particles, releasing latent heat that may enhance convection and/or lightning activity. This hypothesized physical mechanism is further supported by idealized numerical simulations, which demonstrate that the updraft intensity varies with the efficiency of raindrop breakup. Additionally, large raindrops involved in the breakup process originate from the coalescence of raindrops during the initial pre-CI event, whereas graupel melting or shedding plays a role in subsequent pre-CI events. This improves the understanding of CIs following precipitation loading, melting, and evaporation within a near-stationary thunderstorm cell. These findings reveal a likely physical mechanism contributing to CI events and offer new insights into thunderstorm microphysics and dynamics.

Convective impulses (CIs) occur in thunderstorms and are strongly associated with severe convection, often contributing to hazardous weather events. However, the underlying physical mechanisms governing CIs remain poorly understood. In this study, multiple CI events were identified in two selective isolated thunderstorms and analyzed from the perspective of the cloud life cycle using polarimetric radar and lightning observations. We investigated the roles of environmental conditions and cloud microphysics in CI events. Our results indicate a pronounced increase in supercooled liquid water and graupel content prior to CI occurrence. The breakup of raindrops is closely linked to the observed increase in supercooled raindrops, suggesting that the fragmentation of large raindrops below the melting layer contributes to raindrop multiplication at subfreezing temperatures. These smaller raindrops subsequently freeze into graupel-like particles, releasing latent heat that may enhance convection and/or lightning activity. This hypothesized physical mechanism is further supported by idealized numerical simulations, which demonstrate that the updraft intensity varies with the efficiency of raindrop breakup. Additionally, large raindrops involved in the breakup process originate from the coalescence of raindrops during the initial pre-CI event, whereas graupel melting or shedding plays a role in subsequent pre-CI events. This improves the understanding of CIs following precipitation loading, melting, and evaporation within a near-stationary thunderstorm cell. These findings reveal a likely physical mechanism contributing to CI events and offer new insights into thunderstorm microphysics and dynamics.