<div><div>This study investigates the microphysical processes of lightning-producing convective clouds over Northeast India during September 2009, using unique in-situ measurements from an instrumented aircraft in conjunction with near-simultaneous Tropical Rainfall Measuring Mission (TRMM) satellite overpass observations. TRMM measurements revealed isolated convective cells with reflectivity up to 45 dBZ, storm tops near 14 km, and frequent lightning flashes (2–250 s<sup>−1</sup>), indicative of mature mixed-phase cumulonimbus systems. Aircraft-based droplet size distribution (DSD) measurements showed progressive spectral broadening with altitude and drizzle onset near the 0 °C isotherm level. Large values of liquid water content (LWC) near it promote the formation of supercooled water in colder regimes. The coexistence of supercooled droplets, ice, and graupel at sub-zero temperatures creates favorable conditions for charge separation. The hydrometeor axis ratio and diameter relationship is evaluated.</div><div>Vertical profiles of droplet concentration, LWC, ice water content, effective radius (<span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span>), and autoconversion rates further highlight active droplet growth through collision–coalescence processes. The autoconversion rate was modulated by updraft transport and feedbacks from droplet depletion on drizzle formation. Scatter plot and normalized DSD analyses revealed distinct microphysical regimes: cloud-only (positive <span><math><mi>μ</mi></math></span>, high <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>w</mi></mrow></msub></math></span>, where <span><math><mi>μ</mi></math></span> is the shape parameter and <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>w</mi></mrow></msub></math></span>, the intercept parameter of normalized Gamma DSD) and cloud–drizzle (negative <span><math><mi>μ</mi></math></span>, reduced <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>w</mi></mrow></msub></math></span>). In warm, droplet-dominated clouds (2 <span><math><mrow><mo><</mo><mi>D</mi><mo><</mo><mn>50</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, <span><math><mrow><mi>T</mi><mo>></mo><mn>0</mn><mspace></mspace><mo>°</mo><mi>C</mi></mrow></math></span>), the relationships between <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span>–LWC and <span><math><mi>μ</mi></math></span>–LWC become more pronounced. When both cloud droplets and drizzle are included (2 <span><math><mrow><mo><</mo><mi>D</mi><mo><</mo><mn>50</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>), these relationships weaken. In cold clouds (<span><math><mrow><mi>T</mi><mo><</mo><mn>0</mn><mspace></mspace><mo>°</mo><mi>C</mi></mrow></math></span>), a strong coupling between <span><math><mi>μ</mi></math></span> and <span><math><mi>λ</mi></math></span> emerges. Considering only larger hydrometeors (50 <span><math><mrow><mo>&l
{"title":"Cloud microphysical processes of lightning-producing convective clouds over Northeast India: Insights from in-situ and TRMM observations","authors":"Mahen Konwar , B. Abida Choudhury , Imolemba Longkumer , Duncan Axisa","doi":"10.1016/j.atmosres.2025.108704","DOIUrl":"10.1016/j.atmosres.2025.108704","url":null,"abstract":"<div><div>This study investigates the microphysical processes of lightning-producing convective clouds over Northeast India during September 2009, using unique in-situ measurements from an instrumented aircraft in conjunction with near-simultaneous Tropical Rainfall Measuring Mission (TRMM) satellite overpass observations. TRMM measurements revealed isolated convective cells with reflectivity up to 45 dBZ, storm tops near 14 km, and frequent lightning flashes (2–250 s<sup>−1</sup>), indicative of mature mixed-phase cumulonimbus systems. Aircraft-based droplet size distribution (DSD) measurements showed progressive spectral broadening with altitude and drizzle onset near the 0 °C isotherm level. Large values of liquid water content (LWC) near it promote the formation of supercooled water in colder regimes. The coexistence of supercooled droplets, ice, and graupel at sub-zero temperatures creates favorable conditions for charge separation. The hydrometeor axis ratio and diameter relationship is evaluated.</div><div>Vertical profiles of droplet concentration, LWC, ice water content, effective radius (<span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span>), and autoconversion rates further highlight active droplet growth through collision–coalescence processes. The autoconversion rate was modulated by updraft transport and feedbacks from droplet depletion on drizzle formation. Scatter plot and normalized DSD analyses revealed distinct microphysical regimes: cloud-only (positive <span><math><mi>μ</mi></math></span>, high <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>w</mi></mrow></msub></math></span>, where <span><math><mi>μ</mi></math></span> is the shape parameter and <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>w</mi></mrow></msub></math></span>, the intercept parameter of normalized Gamma DSD) and cloud–drizzle (negative <span><math><mi>μ</mi></math></span>, reduced <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>w</mi></mrow></msub></math></span>). In warm, droplet-dominated clouds (2 <span><math><mrow><mo><</mo><mi>D</mi><mo><</mo><mn>50</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>, <span><math><mrow><mi>T</mi><mo>></mo><mn>0</mn><mspace></mspace><mo>°</mo><mi>C</mi></mrow></math></span>), the relationships between <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span>–LWC and <span><math><mi>μ</mi></math></span>–LWC become more pronounced. When both cloud droplets and drizzle are included (2 <span><math><mrow><mo><</mo><mi>D</mi><mo><</mo><mn>50</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span>), these relationships weaken. In cold clouds (<span><math><mrow><mi>T</mi><mo><</mo><mn>0</mn><mspace></mspace><mo>°</mo><mi>C</mi></mrow></math></span>), a strong coupling between <span><math><mi>μ</mi></math></span> and <span><math><mi>λ</mi></math></span> emerges. Considering only larger hydrometeors (50 <span><math><mrow><mo>&l","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"333 ","pages":"Article 108704"},"PeriodicalIF":4.4,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785330","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-17DOI: 10.1016/j.atmosres.2025.108705
Krishnaveni R B , Jyotirmayee Satapathy , Buddhi Prakash Jangid
Different atmospheric regimes, primarily governed by Cloud dynamics, have significant influence on the atmospheric radiative properties which, over a long term eventually modifies the regional climate. To study these effects, eleven years (2012−2022) of Clouds and the Earth's Radiant Energy System (CERES) observations of long-wave and short-wave radiation fluxes have been analyzed over India for different atmospheric conditions. Study includes different cloud properties, macro and microphysical parameters as well as optical nature such as cloud cover, Cloud Optical Depth (COD) and Cloud Top Pressure (CTP) along with cloud liquid and ice content and their evolution and distribution in connection with the radiative fluxes. Seasonal studies and their contribution in governing the radiative dynamics of the atmosphere have been emphasized. This case study is intended to provide insight into the cloud and radiation coupled with atmospheric thermodynamics and its sensitivity, independently as well as co-dependently based on statistical analysis through machine learning tools as well. The increased cloud cover, LW absorption and SW reflection is evident over Indian region signifying the modification in the radiation budget in the recent times. Further, more ice, liquid amount, lower cloud temperature, and bigger particles have been responsible for the rise of LW and SW reflected TOA fluxes as well.
{"title":"Cloud radiative effects over Indian regional atmosphere using CERES observations and machine learning regressions","authors":"Krishnaveni R B , Jyotirmayee Satapathy , Buddhi Prakash Jangid","doi":"10.1016/j.atmosres.2025.108705","DOIUrl":"10.1016/j.atmosres.2025.108705","url":null,"abstract":"<div><div>Different atmospheric regimes, primarily governed by Cloud dynamics, have significant influence on the atmospheric radiative properties which, over a long term eventually modifies the regional climate. To study these effects, eleven years (2012−2022) of Clouds and the Earth's Radiant Energy System (CERES) observations of long-wave and short-wave radiation fluxes have been analyzed over India for different atmospheric conditions. Study includes different cloud properties, macro and microphysical parameters as well as optical nature such as cloud cover, Cloud Optical Depth (COD) and Cloud Top Pressure (CTP) along with cloud liquid and ice content and their evolution and distribution in connection with the radiative fluxes. Seasonal studies and their contribution in governing the radiative dynamics of the atmosphere have been emphasized. This case study is intended to provide insight into the cloud and radiation coupled with atmospheric thermodynamics and its sensitivity, independently as well as co-dependently based on statistical analysis through machine learning tools as well. The increased cloud cover, LW absorption and SW reflection is evident over Indian region signifying the modification in the radiation budget in the recent times. Further, more ice, liquid amount, lower cloud temperature, and bigger particles have been responsible for the rise of LW and SW reflected TOA fluxes as well.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"332 ","pages":"Article 108705"},"PeriodicalIF":4.4,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785332","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-16DOI: 10.1016/j.atmosres.2025.108710
Yihua He , Wei Lou , Cheng Sun , Menghao Dong , Zichen Song , Linfeng Shi , Yibing Tong
Summer precipitation in Central China (CC) is typically influenced by ocean-atmosphere coupling processes. However, the mechanisms through which land surface processes in surrounding regions affect CC precipitation, particularly those over the Indochina Peninsula (ICP), remain poorly understood. We propose that extreme heat events (TX90P) over the ICP during March–April-May (MAM) enhance June–July-August (JJA) precipitation in CC. ICP MAM TX90P establishes a self-reinforcing feedback loop through energy and moisture exchange processes at the land-atmosphere (L-A) interface, thereby amplifying the intensity of extreme heat events. Extreme heat events are accompanied by high-pressure systems with anomalous subsidence of airflow that suppress precipitation and reduce soil moisture (SM). The resulting dry soil establishes a positive feedback mechanism with precipitation, enabling the anomalous SM reduction to persist into JJA. This soil moisture memory effect-induced drought leads to weakened vertical motion over the ICP, promoting the formation of an anticyclonic circulation pattern spanning the ICP and Western Pacific (WP), which subsequently strengthens southwesterly winds that transport moisture toward CC, resulting in enhanced precipitation. Simulations using a Linear Baroclinic Model (LBM) confirm that ICP extreme heat events generate southwesterly wind anomalies, facilitating northeastward moisture transport to CC. A multiple linear regression model incorporating MAM TX90P, preceding winter El Niño-Southern Oscillation (ENSO), and preceding winter Indian Ocean Dipole (IOD) effectively reproduces observed JJA CC precipitation (r = 0.62). This result demonstrates that incorporating extreme heat-related land surface processes significantly improves precipitation prediction skill compared to models relying solely on oceanic variability.
{"title":"Spring extreme heat in the Indochina Peninsula enhances the prediction skill of summer precipitation in Central China","authors":"Yihua He , Wei Lou , Cheng Sun , Menghao Dong , Zichen Song , Linfeng Shi , Yibing Tong","doi":"10.1016/j.atmosres.2025.108710","DOIUrl":"10.1016/j.atmosres.2025.108710","url":null,"abstract":"<div><div>Summer precipitation in Central China (CC) is typically influenced by ocean-atmosphere coupling processes. However, the mechanisms through which land surface processes in surrounding regions affect CC precipitation, particularly those over the Indochina Peninsula (ICP), remain poorly understood. We propose that extreme heat events (TX90P) over the ICP during March–April-May (MAM) enhance June–July-August (JJA) precipitation in CC. ICP MAM TX90P establishes a self-reinforcing feedback loop through energy and moisture exchange processes at the land-atmosphere (L-A) interface, thereby amplifying the intensity of extreme heat events. Extreme heat events are accompanied by high-pressure systems with anomalous subsidence of airflow that suppress precipitation and reduce soil moisture (SM). The resulting dry soil establishes a positive feedback mechanism with precipitation, enabling the anomalous SM reduction to persist into JJA. This soil moisture memory effect-induced drought leads to weakened vertical motion over the ICP, promoting the formation of an anticyclonic circulation pattern spanning the ICP and Western Pacific (WP), which subsequently strengthens southwesterly winds that transport moisture toward CC, resulting in enhanced precipitation. Simulations using a Linear Baroclinic Model (LBM) confirm that ICP extreme heat events generate southwesterly wind anomalies, facilitating northeastward moisture transport to CC. A multiple linear regression model incorporating MAM TX90P, preceding winter El Niño-Southern Oscillation (ENSO), and preceding winter Indian Ocean Dipole (IOD) effectively reproduces observed JJA CC precipitation (<em>r</em> = 0.62). This result demonstrates that incorporating extreme heat-related land surface processes significantly improves precipitation prediction skill compared to models relying solely on oceanic variability.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"333 ","pages":"Article 108710"},"PeriodicalIF":4.4,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-16DOI: 10.1016/j.atmosres.2025.108697
Xishu Huang , Chaohui Chen , Yuan Sun , Zhihao Feng , Wei Zhong , Hongrang He
Relatively little is known about the role of upper-tropospheric factors in monitoring and predicting tropical cyclone (TC) intensity, despite their significant contribution to TC development. Using data from the International Best Track Archive for Climate Stewardship (IBTrACS) and cloud-top height (CTH) products from the Fengyun-4 A (FY-4 A) satellite, this study found that the mean CTH within a radius of 0–200 km from the TC center exhibited a correlation of 0.47 with TC intensity. This correlation was significantly higher than that of conventional predictors such as sea surface temperature (SST), which showed a correlation of 0.32. Moreover, changes in CTH typically preceded changes in TC intensity by approximately 12 to 15 h, suggesting that CTH may serve as a leading indicator of TC intensity. The study also examined the mechanisms through which CTH influences TC intensity. Results indicated that an increase in CTH was generally associated with enhanced TC outflow, which in turn strengthened the TC's secondary circulation. This process improved the efficiency of the TC Carnot heat engine and ultimately favored TC intensification.
{"title":"Cloud-top height as a leading indicator of tropical cyclone intensity in the Western North Pacific","authors":"Xishu Huang , Chaohui Chen , Yuan Sun , Zhihao Feng , Wei Zhong , Hongrang He","doi":"10.1016/j.atmosres.2025.108697","DOIUrl":"10.1016/j.atmosres.2025.108697","url":null,"abstract":"<div><div>Relatively little is known about the role of upper-tropospheric factors in monitoring and predicting tropical cyclone (TC) intensity, despite their significant contribution to TC development. Using data from the International Best Track Archive for Climate Stewardship (IBTrACS) and cloud-top height (CTH) products from the Fengyun-4 A (FY-4 A) satellite, this study found that the mean CTH within a radius of 0–200 km from the TC center exhibited a correlation of 0.47 with TC intensity. This correlation was significantly higher than that of conventional predictors such as sea surface temperature (SST), which showed a correlation of 0.32. Moreover, changes in CTH typically preceded changes in TC intensity by approximately 12 to 15 h, suggesting that CTH may serve as a leading indicator of TC intensity. The study also examined the mechanisms through which CTH influences TC intensity. Results indicated that an increase in CTH was generally associated with enhanced TC outflow, which in turn strengthened the TC's secondary circulation. This process improved the efficiency of the TC Carnot heat engine and ultimately favored TC intensification.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"332 ","pages":"Article 108697"},"PeriodicalIF":4.4,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785298","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Differential reflectivity (ZDR) observations from dual-polarimetric radars are directly related to the mean diameter of raindrops. To leverage this one-to-one relationship, the present study develops a mean diameter update (MDU) approach based on a local ensemble transform Kalman filter radar data assimilation system for ZDR assimilation, which enables the explicit updating of the mass-weighted mean diameter (Dm) of raindrops. A series of assimilation experiments using both pseudo and real radar observations is conducted to examine the feasibility of the MDU approach. The results of the scalar assimilation experiment indicate that explicitly updating Dm by the assimilated pseudo ZDR observation further enhances the accuracy of the Dm analysis. The single-pseudo-observation assimilation experiment reveals that the MDU approach effectively leverages the strong correlation between simulated ZDR and Dm, and more corrections are propagated to the grid points near the pseudo ZDR observation. In the observation system simulation experiments (OSSEs) for the Mei-Yu front case, assimilating pseudo ZDR observations with the MDU approach reduces analysis errors of simulated ZDR and rainwater state variables in each cycle. The forecast performance is the most favorable in terms of the forecast skill score and the rainfall probability when the forecast is initiated with more accurate microphysical states obtained by the MDU approach. Regarding the real-observation experiments, the analysis and forecast results are consistent with those of the OSSEs. The application of the MDU approach to both pseudo and real observations confirms its ability to exploit the intrinsic relationship between ZDR and Dm, improving the accuracy of analyses and forecasts.
{"title":"An innovative approach to ZDR data assimilation using an ensemble Kalman filter: a proof-of-concept study","authors":"Bing-Xue Zhuang , Kao-Shen Chung , Wei-Yu Chang , Chih-Chien Tsai , Yi-Chiang Yu","doi":"10.1016/j.atmosres.2025.108703","DOIUrl":"10.1016/j.atmosres.2025.108703","url":null,"abstract":"<div><div>Differential reflectivity (<em>Z</em><sub><em>DR</em></sub>) observations from dual-polarimetric radars are directly related to the mean diameter of raindrops. To leverage this one-to-one relationship, the present study develops a mean diameter update (MDU) approach based on a local ensemble transform Kalman filter radar data assimilation system for <em>Z</em><sub><em>DR</em></sub> assimilation, which enables the explicit updating of the mass-weighted mean diameter (<em>D</em><sub><em>m</em></sub>) of raindrops. A series of assimilation experiments using both pseudo and real radar observations is conducted to examine the feasibility of the MDU approach. The results of the scalar assimilation experiment indicate that explicitly updating <em>D</em><sub><em>m</em></sub> by the assimilated pseudo <em>Z</em><sub><em>DR</em></sub> observation further enhances the accuracy of the <em>D</em><sub><em>m</em></sub> analysis. The single-pseudo-observation assimilation experiment reveals that the MDU approach effectively leverages the strong correlation between simulated <em>Z</em><sub><em>DR</em></sub> and <em>D</em><sub><em>m</em></sub>, and more corrections are propagated to the grid points near the pseudo <em>Z</em><sub><em>DR</em></sub> observation. In the observation system simulation experiments (OSSEs) for the Mei-Yu front case, assimilating pseudo <em>Z</em><sub><em>DR</em></sub> observations with the MDU approach reduces analysis errors of simulated <em>Z</em><sub><em>DR</em></sub> and rainwater state variables in each cycle. The forecast performance is the most favorable in terms of the forecast skill score and the rainfall probability when the forecast is initiated with more accurate microphysical states obtained by the MDU approach. Regarding the real-observation experiments, the analysis and forecast results are consistent with those of the OSSEs. The application of the MDU approach to both pseudo and real observations confirms its ability to exploit the intrinsic relationship between <em>Z</em><sub><em>DR</em></sub> and <em>D</em><sub><em>m</em></sub>, improving the accuracy of analyses and forecasts.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"332 ","pages":"Article 108703"},"PeriodicalIF":4.4,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-16DOI: 10.1016/j.atmosres.2025.108706
Ying Li , Yunbin Yuan , Wenwu Ding , Xinyu Zhang
Sudden stratospheric warming (SSW) events in the southern hemisphere were found to have strong influences on the Earth's atmosphere. However, statistical evaluations of such events were rarely carried out. This study introduces a new definition to detect and monitor SSW events in the southern hemisphere from a statistical point of view. The new method accounts characteristics of such events and uses three metrics to monitor stratospheric warmings in the three altitude layers of 20–25 km, 25–30 km and 30–35 km. If one of the metrics is continuously larger than a minimum threshold for more than 5 days, then an SSW event is detected and a main warming phase is recorded. Subsequently, the onset date, warming strength, duration, mean warming area and location of an event are recorded. The new method is applied to 42 years' reanalysis data from 1980 to 2021. Results show that the new definition can detect both strong and weak events. The frequency of all SSW events is 0.38/year and of strong events is 0.26/year in this study. Seasonally, SSW events occur most often in the three months from July to September and geographically most often in the eastern longitude side of southern polar region. It is also found that the number, strength and duration of SSW events from the latter two decades of 2001–2020 are larger than that of the previous two decades of 1981–2000 in this study though further studies are required to consolidate this conclusion.
{"title":"A statistical evaluation of sudden stratospheric warming events in the southern hemisphere based on a new definition","authors":"Ying Li , Yunbin Yuan , Wenwu Ding , Xinyu Zhang","doi":"10.1016/j.atmosres.2025.108706","DOIUrl":"10.1016/j.atmosres.2025.108706","url":null,"abstract":"<div><div>Sudden stratospheric warming (SSW) events in the southern hemisphere were found to have strong influences on the Earth's atmosphere. However, statistical evaluations of such events were rarely carried out. This study introduces a new definition to detect and monitor SSW events in the southern hemisphere from a statistical point of view. The new method accounts characteristics of such events and uses three metrics to monitor stratospheric warmings in the three altitude layers of 20–25 km, 25–30 km and 30–35 km. If one of the metrics is continuously larger than a minimum threshold for more than 5 days, then an SSW event is detected and a main warming phase is recorded. Subsequently, the onset date, warming strength, duration, mean warming area and location of an event are recorded. The new method is applied to 42 years' reanalysis data from 1980 to 2021. Results show that the new definition can detect both strong and weak events. The frequency of all SSW events is 0.38/year and of strong events is 0.26/year in this study. Seasonally, SSW events occur most often in the three months from July to September and geographically most often in the eastern longitude side of southern polar region. It is also found that the number, strength and duration of SSW events from the latter two decades of 2001–2020 are larger than that of the previous two decades of 1981–2000 in this study though further studies are required to consolidate this conclusion.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"332 ","pages":"Article 108706"},"PeriodicalIF":4.4,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145766046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-16DOI: 10.1016/j.atmosres.2025.108709
Priya Kumari , B. Preethi , M. Mujumdar
The Intertropical Convergence Zone (ITCZ) is a zonally oriented tropical band where trade winds converge, triggering deep convection and heavy rainfall, and produces about 32% of global precipitation. Studies indicate that the migration of ITCZ significantly influences the climate of tropical regions and adjacent areas. It is to be noted that during the summer monsoon (June–September) season, the ITCZ undergoes a pronounced northward shift in the South Asian monsoon region which is attributed to the displacement of zero absolute vorticity contour northward of the equator. However, changes in local precipitation are not necessarily correlated with the position of the zonal mean ITCZ, which point towards the importance of analyzing ITCZ dynamics on both regional and seasonal scales. A comparative analysis of various metrics based on precipitation, convection, moisture, and circulation reveals notable differences in estimating the ITCZ location. To address this, a multivariate probabilistic approach, combining precipitation and mean meridional mass flux, has been applied. This method effectively captures the seasonal migration of the ITCZ from boreal winter to boreal summer season, and also resolves its regional variations, providing a clearer picture of onset, peak, and withdrawal phases of South Asian Summer monsoon season.
{"title":"Climatological characteristics of ITCZ over the South Asian monsoon domain: Using multivariate probabilistic approach","authors":"Priya Kumari , B. Preethi , M. Mujumdar","doi":"10.1016/j.atmosres.2025.108709","DOIUrl":"10.1016/j.atmosres.2025.108709","url":null,"abstract":"<div><div>The Intertropical Convergence Zone (ITCZ) is a zonally oriented tropical band where trade winds converge, triggering deep convection and heavy rainfall, and produces about 32% of global precipitation. Studies indicate that the migration of ITCZ significantly influences the climate of tropical regions and adjacent areas. It is to be noted that during the summer monsoon (June–September) season, the ITCZ undergoes a pronounced northward shift in the South Asian monsoon region which is attributed to the displacement of zero absolute vorticity contour northward of the equator. However, changes in local precipitation are not necessarily correlated with the position of the zonal mean ITCZ, which point towards the importance of analyzing ITCZ dynamics on both regional and seasonal scales. A comparative analysis of various metrics based on precipitation, convection, moisture, and circulation reveals notable differences in estimating the ITCZ location. To address this, a multivariate probabilistic approach, combining precipitation and mean meridional mass flux, has been applied. This method effectively captures the seasonal migration of the ITCZ from boreal winter to boreal summer season, and also resolves its regional variations, providing a clearer picture of onset, peak, and withdrawal phases of South Asian Summer monsoon season.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"332 ","pages":"Article 108709"},"PeriodicalIF":4.4,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-16DOI: 10.1016/j.atmosres.2025.108707
Yongle Liu , Chenchao Zhan , Leyuan Zhao , Yangjinxi Ge , Tianliang Zhao
Tropical cyclones (TCs) can significantly influence tropospheric ozone (O3) in coastal regions, with impacts closely tied to TC tracks. Based on long-term observational records, this study examined O3 formation and sources in Nanjing under TCs from July to October over 2014–2023. During this period, the number of O3-polluted days increased from 43 to 80. Notably, between July and October, TCs and O3 pollution episodes frequently coincided, with ∼49 % of O3 pollution occurring on TC days. Applying a finite mixture algorithm, TCs affecting Nanjing were classified into three tracks: northwest track (NT), turning track (TT) and westward track (WT). NT occurred earliest; TT had the fewest TC days; WT was most frequent but developed latest. NT TCs located near (128°E, 21°N), about 800 km from Nanjing with intensities above severe tropical storm, were most frequently associated with O3 pollution, whereas TT and WT corresponded to TCs near (126°E, 24°N) and (111°E, 21°N) with varying intensities. Across all TC tracks, O3 formation and accumulation were favored (46.6 % to 61.6 %) by higher temperature (5.1 % to 20.8 %), lower relative humidity (−25.8 % to −16.6 %), reduced cloud cover (−21.0 % to −14.1 %), lower wind speed (−24.5 % to −7.6 %), and elevated concentrations of NO2 (14.1 % to 15.2 %) and CO (12.3 % to 18.5 %). However, O3 pollution varied with the TC's location. In the early phases, southeastern peripheral airflow transported O3 and its precursors from the Shanghai–northern Zhejiang–Nanjing corridor, contributing over 50 % of the total. As TCs moved, NT TCs facilitated short-range transport from central Anhui (∼23.4 %), TT TCs enhanced northward transport from Shandong and Jiangsu (∼54.0 %), and WT TCs drove long-range transport from Jiangxi and even Guangzhou (∼19.6 %). These findings suggest that the movement and positioning of TCs can significantly influence O3 pollutions, providing valuable insights for O3 pollution control in coastal cities.
{"title":"Formation and source apportionment of ozone in Nanjing affected by tropical cyclones with different tracks","authors":"Yongle Liu , Chenchao Zhan , Leyuan Zhao , Yangjinxi Ge , Tianliang Zhao","doi":"10.1016/j.atmosres.2025.108707","DOIUrl":"10.1016/j.atmosres.2025.108707","url":null,"abstract":"<div><div>Tropical cyclones (TCs) can significantly influence tropospheric ozone (O<sub>3</sub>) in coastal regions, with impacts closely tied to TC tracks. Based on long-term observational records, this study examined O<sub>3</sub> formation and sources in Nanjing under TCs from July to October over 2014–2023. During this period, the number of O<sub>3</sub>-polluted days increased from 43 to 80. Notably, between July and October, TCs and O<sub>3</sub> pollution episodes frequently coincided, with ∼49 % of O<sub>3</sub> pollution occurring on TC days. Applying a finite mixture algorithm, TCs affecting Nanjing were classified into three tracks: northwest track (NT), turning track (TT) and westward track (WT). NT occurred earliest; TT had the fewest TC days; WT was most frequent but developed latest. NT TCs located near (128°E, 21°N), about 800 km from Nanjing with intensities above severe tropical storm, were most frequently associated with O<sub>3</sub> pollution, whereas TT and WT corresponded to TCs near (126°E, 24°N) and (111°E, 21°N) with varying intensities. Across all TC tracks, O<sub>3</sub> formation and accumulation were favored (46.6 % to 61.6 %) by higher temperature (5.1 % to 20.8 %), lower relative humidity (−25.8 % to −16.6 %), reduced cloud cover (−21.0 % to −14.1 %), lower wind speed (−24.5 % to −7.6 %), and elevated concentrations of NO<sub>2</sub> (14.1 % to 15.2 %) and CO (12.3 % to 18.5 %). However, O<sub>3</sub> pollution varied with the TC's location. In the early phases, southeastern peripheral airflow transported O<sub>3</sub> and its precursors from the Shanghai–northern Zhejiang–Nanjing corridor, contributing over 50 % of the total. As TCs moved, NT TCs facilitated short-range transport from central Anhui (∼23.4 %), TT TCs enhanced northward transport from Shandong and Jiangsu (∼54.0 %), and WT TCs drove long-range transport from Jiangxi and even Guangzhou (∼19.6 %). These findings suggest that the movement and positioning of TCs can significantly influence O<sub>3</sub> pollutions, providing valuable insights for O<sub>3</sub> pollution control in coastal cities.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"333 ","pages":"Article 108707"},"PeriodicalIF":4.4,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785338","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-15DOI: 10.1016/j.atmosres.2025.108702
A. Di Bernardino , S. Argentini , E. Brattich , M. Campanelli , G. Casasanta , A. Cecilia , M. Erriu , S. Falasca , A. Faggi , A.M. Siani
Urban Heat Island (UHI) and Urban Pollution Island (UPI) processes shape urban climate and air quality, yet their interaction remains insufficiently quantified, particularly in Mediterranean coastal cities. Existing research often examines these phenomena separately or over short time spans, leaving uncertainties regarding the meteorological drivers governing the UHI-UPI co-evolution. This study provides a multi-year, observation-based assessment of the coupled dynamics between Urban Heat Island Intensity (UHII) and Urban Pollution Island Intensity (UPII) in Rome (Italy), focusing on the atmospheric conditions that modulate their relationship. Air temperature, humidity, and wind speed, together with major air pollutants (PM10, PM2.5, NO2, NO, and O3), were analysed using an integrated statistical framework. Lag-correlation analysis revealed that the strongest UHII-UPII relationship occurs when nocturnal UHII is shifted backward by one day, reflecting daytime pollutant accumulation and nighttime trapping. Regression results highlighted daily mean air temperature and wind speed as the primary drivers modulating the UHII-UPII association. Spearman correlations showed negative associations between UHII and NO (−0.60), PM10 (−0.45), NO2 (−0.35), and PM2.5 (−0.34), alongside positive correlations with O3 (0.54) and NO2/NO (0.42). These correlations intensified during heatwaves and calm wind conditions, suggesting enhanced interactions under extreme weather and stagnant atmospheric conditions. UHII peaks in summer, while UPII maximizes in winter for all pollutants except for O₃, which exhibits an opposite pattern. These findings reveal a complex interplay between urban warming and pollutant accumulation, highlighting the need for integrated urban planning to address joint UHII-UPII challenges under ongoing urbanization and intensifying severe heat episodes.
{"title":"Influence of atmospheric parameters on the interaction between Urban Heat and Pollution Islands in a Mediterranean coastal city","authors":"A. Di Bernardino , S. Argentini , E. Brattich , M. Campanelli , G. Casasanta , A. Cecilia , M. Erriu , S. Falasca , A. Faggi , A.M. Siani","doi":"10.1016/j.atmosres.2025.108702","DOIUrl":"10.1016/j.atmosres.2025.108702","url":null,"abstract":"<div><div>Urban Heat Island (UHI) and Urban Pollution Island (UPI) processes shape urban climate and air quality, yet their interaction remains insufficiently quantified, particularly in Mediterranean coastal cities. Existing research often examines these phenomena separately or over short time spans, leaving uncertainties regarding the meteorological drivers governing the UHI-UPI co-evolution. This study provides a multi-year, observation-based assessment of the coupled dynamics between Urban Heat Island Intensity (UHII) and Urban Pollution Island Intensity (UPII) in Rome (Italy), focusing on the atmospheric conditions that modulate their relationship. Air temperature, humidity, and wind speed, together with major air pollutants (PM<sub>10</sub>, PM<sub>2.5</sub>, NO<sub>2</sub>, NO, and O<sub>3</sub>), were analysed using an integrated statistical framework. Lag-correlation analysis revealed that the strongest UHII-UPII relationship occurs when nocturnal UHII is shifted backward by one day, reflecting daytime pollutant accumulation and nighttime trapping. Regression results highlighted daily mean air temperature and wind speed as the primary drivers modulating the UHII-UPII association. Spearman correlations showed negative associations between UHII and NO (−0.60), PM<sub>10</sub> (−0.45), NO<sub>2</sub> (−0.35), and PM<sub>2.5</sub> (−0.34), alongside positive correlations with O<sub>3</sub> (0.54) and NO<sub>2</sub>/NO (0.42). These correlations intensified during heatwaves and calm wind conditions, suggesting enhanced interactions under extreme weather and stagnant atmospheric conditions. UHII peaks in summer, while UPII maximizes in winter for all pollutants except for O₃, which exhibits an opposite pattern. These findings reveal a complex interplay between urban warming and pollutant accumulation, highlighting the need for integrated urban planning to address joint UHII-UPII challenges under ongoing urbanization and intensifying severe heat episodes.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"332 ","pages":"Article 108702"},"PeriodicalIF":4.4,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-13DOI: 10.1016/j.atmosres.2025.108680
Sree Anusha Ganapathiraju , Utkarsh Kanth , Madhuri Sai Latha V. , Maheswaran Rathinasamy , Niranjan Kumar Kondapalli , Sara M. Vallejo-Bernal , Norbert Marwan , Sukhwinder Kaur
In 2023, the coastal town of Kayalpattinam in Tamil Nadu recorded an extraordinary rainfall exceeding 950 mm on December 17 and 18, resulting in severe flash floods and devastation to livelihoods in the community. This study critically examines the physical mechanisms driving this event across scales. Employing regional reanalysis datasets, we elucidate the localized characteristics responsible for extreme precipitation and systematically address the associated uncertainties. The investigation revealed that the spatiotemporal dynamics of moisture transport played a vital role in the increased moisture influx over the region. In particular, the local convection combined with heightened atmospheric instability and intensified advection in the surrounding areas played a pivotal role in the formation of significant mid-tropospheric cyclones. These developed atmospheric phenomena are rarely observed in this region, which typically experiences tropical cyclones and depressions more frequently. This study emphasizes the necessity of conducting meticulous investigations to improve risk assessments and preparedness for future climatological phenomena of similar magnitude.
{"title":"Spatiotemporal dynamics of moisture influx and their role in precipitation extremes: A study of December 2023 in Kayalpattinam","authors":"Sree Anusha Ganapathiraju , Utkarsh Kanth , Madhuri Sai Latha V. , Maheswaran Rathinasamy , Niranjan Kumar Kondapalli , Sara M. Vallejo-Bernal , Norbert Marwan , Sukhwinder Kaur","doi":"10.1016/j.atmosres.2025.108680","DOIUrl":"10.1016/j.atmosres.2025.108680","url":null,"abstract":"<div><div>In 2023, the coastal town of Kayalpattinam in Tamil Nadu recorded an extraordinary rainfall exceeding 950 mm on December 17 and 18, resulting in severe flash floods and devastation to livelihoods in the community. This study critically examines the physical mechanisms driving this event across scales. Employing regional reanalysis datasets, we elucidate the localized characteristics responsible for extreme precipitation and systematically address the associated uncertainties. The investigation revealed that the spatiotemporal dynamics of moisture transport played a vital role in the increased moisture influx over the region. In particular, the local convection combined with heightened atmospheric instability and intensified advection in the surrounding areas played a pivotal role in the formation of significant mid-tropospheric cyclones. These developed atmospheric phenomena are rarely observed in this region, which typically experiences tropical cyclones and depressions more frequently. This study emphasizes the necessity of conducting meticulous investigations to improve risk assessments and preparedness for future climatological phenomena of similar magnitude.</div></div>","PeriodicalId":8600,"journal":{"name":"Atmospheric Research","volume":"331 ","pages":"Article 108680"},"PeriodicalIF":4.4,"publicationDate":"2025-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145759435","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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