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This study investigates the importance of convective systems for extreme rainfall along the northern coast of the Gulf of Guinea (GG) and their relationship with atmospheric and oceanic conditions. Convective system data (MCSs), daily precipitation, sea surface temperature (SST) and moisture flux anomalies from June to September 2007–2016 are used. The results show that 2/3 of MCSs crossing Abidjan are produced in June, which is the core of the major rainy season. Likewise, 2/3 of MCSs originate from continental areas, while 1/3 come from the ocean. Oceanic MCSs are mostly initiated close to the coast, which also corresponds to the Marine Heat Waves region. Continental MCSs are mostly initiated inland. The results also highlight the moisture flux contribution of three zones which have an impact on the onset and the sustaining of MCSs: (i) the seasonal migration of the intertropical convergence zone (ITCZ), (ii) the GG across the northern coastline, and finally (iii) the continent. These contributions of moisture fluxes coincide with oceanic warming off Northeast Brazil and the northern coast of the GG both two days before and the day of extreme rainfall events. The ocean contributes to moisten the atmosphere, and therefore to supply and sustain the MCSs during their lifecycle. [ABSTRACT FROM AUTHOR]

During the night of March 31st, 2017, a severe precipitation event affected the city of Mocoa, in the tropical Andes. Total 24-h accumulated precipitation during that day was the fourth largest on record. Satellite data shows that the event was associated with a Mesoscale Convective System (MCS) that formed over the Amazon and moved westward, reaching the tropical Andes. Reanalysis data suggests that a rapid intensification of the Orinoco Low-Level Jet (OLLJ) traveling southwestward parallel to the Andes was a precursor that favored the zones of convergence for MCS formation. Upstream intensification of the OLLJ was evident 8 h prior to the Mocoa precipitation event. Given the lack of a dense network of observations in this understudied region, we use the Weather Research and Forecasting model (WRF) to explore the plausible mesoscale structures in the OLLJ region associated with the initiation and development of the MCS. We study an ensemble of simulations with different grid spacings (12, 4 and 1.3 km) and Planetary Boundary Layer (PBL) schemes (YSU, MYNN and QNSE). The more realistic MCSs were obtained with the QNSE and YSU schemes, given that the corresponding simulations included a density current in the lowest levels moving parallel to the Andes, with a sharp line of convergence and large vertical velocities over the leading edge of the mesoscale disturbance. In contrast, the MYNN scheme produced a weaker OLLJ and no density current. It is suggested that the stronger vertical mixing in the MYNN scheme was associated with the vertical dilution of the OLLJ, and with a much weaker low-level traveling perturbation via the upward radiation of energy by gravity waves. Our results help to better understand flood-producing extreme events over the poorly studied Andes-Amazon region and provide the groundwork for improved predictability of such storms. [ABSTRACT FROM AUTHOR]

When the negatively buoyant air in the cloud downdrafts reaches the surface, it spreads out horizontally, producing cold pools. A cold pool can trigger new convective cells. However, when combined with the ambient vertical wind shear, it can also connect and upscale them into large mesoscale convective systems (MCS). Given the broad spectrum of scales of the atmospheric phenomenon involving the interaction between cold pools and the MCS, a parameterization was designed here. Then, it is coupled with a classical convection parameterization to be applied in an atmospheric model with an insufficient spatial resolution to explicitly resolve convection and the sub‐cloud layer. A new scalar quantity related to the deficit of moist static energy detrained by the downdrafts mass flux is proposed. This quantity is subject to grid‐scale advection, mixing, and a sink term representing dissipation processes. The model is then applied to simulate moist convection development over a large portion of tropical land in the Amazon Basin in a wet and dry‐to‐wet 10‐days period. Our results show that the cold pool edge parameterization improves the organization, longevity, propagation, and severity of simulated MCS over the Amazon and other different continental areas. Plain Language Summary: In nature, cold pools are formed by cold air masses descending from the low to mid‐troposphere in thunderstorms. When these drafts reach the surface, they spread out horizontally. A manifestation of cold pools is the relatively high speed at the gust front, which can lift environmental air producing new convective cells. Moreover, depending on ambient conditions, the cold pools may help organize the new convective cells, increasing their aggregation and forming the so‐called mesoscale convective systems (MCSs). MCSs, which cover hundreds to thousands of km2, significantly impact the global scale circulation, energy budget, hydrological cycle, and population safety. Forecasting MCSs is challenging for global circulation models (GCM) due to the broad spectrum of scales of the involved atmospheric phenomenon. The computational limitations, at present and for some time to come, do not allow running in real‐time GCMs, which explicitly solves all relevant scales of motion. This paper describes a methodology to account for essential interplays between cold pools edges and moist convection to be applied in the GCMs of weather and climate forecasting. We show that the method improves the model simulation of the main types of MCSs over the Amazon Basin and other continental areas. Key Points: A model scheme for including effect of cold pools edges in triggering new convective cells and storm propagation is presentedThe scheme is coupled with a convection parameterization and applied in the modeling of moist convective systemsThe method improves the organization, longevity, propagation, and severity of the simulated mesoscale convective systems [ABSTRACT FROM AUTHOR]

In December 2021, Super Typhoon Rai caused significant devastation to the South Philippines and East Malaysia. In the meantime, an unprecedented flood event occurred in Peninsular Malaysia at 2,000 km west of the typhoon's path, causing comparable socioeconomic impacts as Rai. Record‐breaking 3‐day precipitation was received by Peninsular Malaysia during 16–18 December. Based on the storm tracking results, this study identified two mesoscale convective systems (MCSs) that were directly responsible for the flooding. The two MCSs were directly initiated by a tropical depression and sustained by an elongated easterly water vapor corridor originating from the Super Typhoon Rai. The return period and joint frequency analysis of key drivers indicate that the 3‐day downpour was more severe than a "once‐in‐a‐century" event. Historical records suggest such anomalous moisture channel has become more frequent in Southeast Asia, which alarms heightened attention in forecasting winter flood. Plain Language Summary: On 16–18 December, Peninsular Malaysia received a record‐shattering 3‐day precipitation, resulting in catastrophic socioeconomic impacts. Due to the temporal coincidence with Super Typhoon Rai but far away in space, there were speculations that there might be a teleconnection between the two events. Our results reveal that their relationship could be more straightforward. Based on the analyses of storm tracking database and synoptic data records, we found that two consecutive mesoscale convective systems were responsible for the heavy precipitation, which were produced by a tropical depression that hovered over the peninsula. Meanwhile, Super Typhoon Rai provided a long‐range water vapor transport, akin to adding fuel (i.e., moisture) to the engine (i.e., the tropical depression), and therefore, the precipitation over the peninsula was significantly enhanced. Such long‐range moisture transport has become more frequent during the boreal winter season, posing an increasing risk of flooding in Southeast Asia. Key Points: A stretched moisture channel from Typhoon Rai and a strong tropical depression are key synoptic drivers for the flooding eventReturn period and joint probability of key drivers indicate that the 2021 Peninsular Malaysia flood was more severe than "once‐in‐a‐century"There is an increasing trend in such anomalous moisture channel, suggesting a rising risk of severe flooding in Southeast Asia [ABSTRACT FROM AUTHOR]

The monitoring of mesoscale convective systems (MCS) is typically based on satellite infrared data. Currently, there is limited research on the identification of MCS using true color composite cloud imagery. In this study, an MCS dataset was created based on the true color composite cloud imagery from the Fengyun-4B geostationary meteorological satellite. An MCS true color composite cloud imagery identification model was developed based on the Swin-Unet network. The MCS dataset was categorized into continental MCS and oceanic MCS, and the model's performance in identifying these two different types of MCS was examined. Experimental results indicated that the model achieved a recall rate of 83.3% in identifying continental MCS and 86.1% in identifying oceanic MCS, with a better performance in monitoring oceanic MCS. These results suggest that using true color composite cloud imagery for MCS monitoring is feasible, and the Swin-Unet network outperforms traditional convolutional neural networks. Meanwhile, we find that the frequency and distribution range of oceanic MCS is larger than that of continental MCS, and the area is larger and some parts of it are stronger. This study provides a novel approach for satellite remote-sensing-based MCS monitoring. [ABSTRACT FROM AUTHOR]

Abstract When the negatively buoyant air in the cloud downdrafts reaches the surface, it spreads out horizontally, producing cold pools. A cold pool can trigger new convective cells. However, when combined with the ambient vertical wind shear, it can also connect and upscale them into large mesoscale convective systems (MCS). Given the broad spectrum of scales of the atmospheric phenomenon involving the interaction between cold pools and the MCS, a parameterization was designed here. Then, it is coupled with a classical convection parameterization to be applied in an atmospheric model with an insufficient spatial resolution to explicitly resolve convection and the sub‐cloud layer. A new scalar quantity related to the deficit of moist static energy detrained by the downdrafts mass flux is proposed. This quantity is subject to grid‐scale advection, mixing, and a sink term representing dissipation processes. The model is then applied to simulate moist convection development over a large portion of tropical land in the Amazon Basin in a wet and dry‐to‐wet 10‐days period. Our results show that the cold pool edge parameterization improves the organization, longevity, propagation, and severity of simulated MCS over the Amazon and other different continental areas.

During the night of March 31st, 2017, a severe precipitation event affected the city of Mocoa, in the tropical Andes. Total 24-h accumulated precipitation during that day was the fourth largest on record. Satellite data shows that the event was associated with a Mesoscale Convective System (MCS) that formed over the Amazon and moved westward, reaching the tropical Andes. Reanalysis data suggests that a rapid intensification of the Orinoco Low-Level Jet (OLLJ) traveling southwestward parallel to the Andes was a precursor that favored the zones of convergence for MCS formation. Upstream intensification of the OLLJ was evident 8 h prior to the Mocoa precipitation event. Given the lack of a dense network of observations in this understudied region, we use the Weather Research and Forecasting model (WRF) to explore the plausible mesoscale structures in the OLLJ region associated with the initiation and development of the MCS. We study an ensemble of simulations with different grid spacings (12, 4 and 1.3 km) and Planetary Boundary Layer (PBL) schemes (YSU, MYNN and QNSE). The more realistic MCSs were obtained with the QNSE and YSU schemes, given that the corresponding simulations included a density current in the lowest levels moving parallel to the Andes, with a sharp line of convergence and large vertical velocities over the leading edge of the mesoscale disturbance. In contrast, the MYNN scheme produced a weaker OLLJ and no density current. It is suggested that the stronger vertical mixing in the MYNN scheme was associated with the vertical dilution of the OLLJ, and with a much weaker low-level traveling perturbation via the upward radiation of energy by gravity waves. Our results help to better understand flood-producing extreme events over the poorly studied Andes-Amazon region and provide the groundwork for improved predictability of such storms.

Abstract In December 2021, Super Typhoon Rai caused significant devastation to the South Philippines and East Malaysia. In the meantime, an unprecedented flood event occurred in Peninsular Malaysia at 2,000 km west of the typhoon's path, causing comparable socioeconomic impacts as Rai. Record‐breaking 3‐day precipitation was received by Peninsular Malaysia during 16–18 December. Based on the storm tracking results, this study identified two mesoscale convective systems (MCSs) that were directly responsible for the flooding. The two MCSs were directly initiated by a tropical depression and sustained by an elongated easterly water vapor corridor originating from the Super Typhoon Rai. The return period and joint frequency analysis of key drivers indicate that the 3‐day downpour was more severe than a “once‐in‐a‐century” event. Historical records suggest such anomalous moisture channel has become more frequent in Southeast Asia, which alarms heightened attention in forecasting winter flood.

Torrential rain with the greatest social impact in Chongqing in the year of 2021 occurred in the central and eastern parts of Sichuan basin from August 7 to August 8. Using multi-source observation and ERA5 reanalysis data, the characteristics of mesoscale convective systems during the heavy rain process were analyzed. The heavy rainfall occurred under the background of the warm Southwest Vortex induced by the trough moving into the Sichuan basin, and had evident characteristics of stages, bounds, and extremes. The heavy rainfall formed successively in the southeast of the Southwest Vortex center and near the boundary layer convergence line in the east and south of the Southwest Vortex. The heavy rainfall of each stage was produced by mesoscale-β convective systems which moved slowly and maintained for 3~6 h. Warm and humid instability and weak vertical wind shear provided favorable environment for the development of mesoscale convective systems. Vorticity analysis showed that the development of the Southwest Vortex was mainly due to the low-level convergence and vertical vorticity transport. However, the development of positive vorticity in the rainstorm area was not exactly the same as that of the Southwest Vortex, and the horizontal vorticity tilting effect was relatively significant. The positive vorticity of the heavy rainstorm area in the first stage was mainly due to the significant low-level convergence, vertical vorticity transport, and horizontal vorticity tilting effect near the Southwest Vortex center in the middle and low level troposphere. The positive vorticity of the heavy rainstorm area in the second and third stages were mainly due to the horizontal vorticity tilting effect above the boundary layer and the convergence in the boundary layer. The boundary convergence triggered mesoscale convective activities in the warm and humid atmosphere, which promoted the heavy rain in the second and the third stages.

This study investigates the importance of convective systems for extreme rainfall along the northern coast of the Gulf of Guinea (GG) and their relationship with atmospheric and oceanic conditions. Convective system data (MCSs), daily precipitation, sea surface temperature (SST) and moisture flux anomalies from June to September 2007–2016 are used. The results show that 2/3 of MCSs crossing Abidjan are produced in June, which is the core of the major rainy season. Likewise, 2/3 of MCSs originate from continental areas, while 1/3 come from the ocean. Oceanic MCSs are mostly initiated close to the coast, which also corresponds to the Marine Heat Waves region. Continental MCSs are mostly initiated inland. The results also highlight the moisture flux contribution of three zones which have an impact on the onset and the sustaining of MCSs: (i) the seasonal migration of the intertropical convergence zone (ITCZ), (ii) the GG across the northern coastline, and finally (iii) the continent. These contributions of moisture fluxes coincide with oceanic warming off Northeast Brazil and the northern coast of the GG both two days before and the day of extreme rainfall events. The ocean contributes to moisten the atmosphere, and therefore to supply and sustain the MCSs during their lifecycle.

The monitoring of mesoscale convective systems (MCS) is typically based on satellite infrared data. Currently, there is limited research on the identification of MCS using true color composite cloud imagery. In this study, an MCS dataset was created based on the true color composite cloud imagery from the Fengyun-4B geostationary meteorological satellite. An MCS true color composite cloud imagery identification model was developed based on the Swin-Unet network. The MCS dataset was categorized into continental MCS and oceanic MCS, and the model’s performance in identifying these two different types of MCS was examined. Experimental results indicated that the model achieved a recall rate of 83.3% in identifying continental MCS and 86.1% in identifying oceanic MCS, with a better performance in monitoring oceanic MCS. These results suggest that using true color composite cloud imagery for MCS monitoring is feasible, and the Swin-Unet network outperforms traditional convolutional neural networks. Meanwhile, we find that the frequency and distribution range of oceanic MCS is larger than that of continental MCS, and the area is larger and some parts of it are stronger. This study provides a novel approach for satellite remote-sensing-based MCS monitoring.

An extreme torrential rain event occurred in the Jianshi Canyon in the mountainous area of Southwest Hubei on 26 July 2020, which was mainly caused by quasi-stationary mesoscale convection system (MCS). Using conventional observations, the data from regional automatic weather stations, radar data and ERA5 reanalysis data, we have performed analysis on the atmospheric circulation and the evolution and formation mechanism of quasi-static MCS in this event. Results are as follows. (1) Affected by the continental high and the Mongolian cold vortex moving eastward and southward and the stable subtropical high, the MCS forms in the north of the subtropical high and near the low-level convergence line. The mid-and low-level convergence line and the southerly jet in front of the low vortex provide favorable environmental conditions for the development and maintenance of the MCS. (2) The MCS in the Jianshi Canyon shows the characteristics of quasi-stationary with backward propagation, whose direction is consistent with the canyon trend, and it experienced two stages: quasi-stationary backward propagation and quasi-stationary merging. (3) Under the complex terrain of Jianshi Canyon and Enshi "bell mouth", the interaction between cold outflow and continuously strengthened and sinking low-level southerly jet has a significant effect on the formation and development of the MCS. The low-level jet is forced to rise on the windward slope for sustained weak cold outflow, forming a stable lifting condition in front of the mountain, which is the main reason for the maintenance of quasi-stationary backward propagation. The blocking effect of the low-level jet and the terrain in the south of Jianshi on the cold pool, and the merging of convective cells moving northward, are the reasons for the formation of quasi-stationary merging of the MCS. (4) The complex terrain plays an important role in the evolution of the MCS. The canyon wind effect and the topographic lifting effect of windward slope result in the enhanced development of the MCS. The cold outflow guided by the slope terrain of Jianshi Canyon quickly descends the mountain to form the convergence zone with the southerly lifted by the windward slope at front of the mountain, which speeds up the backward propagation of the MCS. The γ-mesoscale topography in the south of Jianshi Canyon blocks the downhill cold outflow and makes it move slowly southward, resulting in the propagation speed of the MCS to slow down and show a quasi-stationary state.

The climate system of the Third Pole region, including the (TP) and its surroundings, is highly sensitive to global warming. Mesoscale convective systems (MCSs) are understood to be a vital component of this climate system. Driven by the monsoon circulation, surface heating, and large-scale and local moisture supply, they frequently occur during summer and mostly over the central and eastern TP as well as in the downstream regions. Further, MCSs have been highlighted as important contributors to total precipitation as they are efficient rain producers affecting water availability (seasonal precipitation) and potential flood risk (extreme precipitation) in the densely populated downstream regions. The availability of multi-decadal satellite observations and high-resolution climate model datasets has made it possible to study the role of MCSs in the under-observed TP water balance. However, the usage of different methods for MCS identification and the different focuses on specific subregions currently hamper a systematic and consistent assessment of the role played by MCSs and their impact on precipitation over the TP headwaters and its downstream regions. Here, we review observational and model studies of MCSs in the TP region within a common framework to elucidate their main characteristics, underlying mechanisms, and impact on seasonal and extreme precipitation. We also identify major knowledge gaps and provide suggestions on how these can be addressed using recently published high-resolution model datasets. Three important identified knowledge gaps are 1) the feedback of MCSs to other components of the TP climate system, 2) the impact of the changing climate on future MCS characteristics, and 3) the basin-scale assessment of flood and drought risks associated with changes in MCS frequency and intensity. A particularly promising tool to address these knowledge gaps are convection-permitting climate simulations. Therefore, the systematic evaluation of existing historical convection-permitting climate simulations over the TP is an urgent requirement for reliable future climate change assessments.

Extreme rainfall occurred over the South African east coast during 10–12 April 2022, leading to over 500 deaths and massive damage. This study seeks to understand a key feature, namely the progression of the rainfall maxima from the northern KwaZulu-Natal (KZN) coast during the night of 10–11 April by ~550 km to the Eastern Cape coast about 48 h later. The large-scale circulation was dominated by a cut-off low over the South African interior with a strong ridging anticyclone southeast of the country in the South Indian Ocean. Satellite, rain gauge, and ERA5 reanalysis are used to show that the timing and location of the heaviest rainfall are closely tied to, firstly, the formation of a Mesoscale Convective System (MCS) at ~0300UTC April 11 on the northern KZN coast which tracked south and then offshore, and secondly, a meso-trough which formed a coastal meso-low by ~2100 UTC April 11. The meso-low tracked south over the warm waters of the Agulhas Current before strengthening into Subtropical Depression Issa. Mesoscale interaction between the MCS and coastal meso-low determined the positioning and timing of the strongest onshore low-level jet, moisture convergence and uplift, and hence the progression of the heavy rainfall down the coast. Such mesoscale interaction has not previously been documented in southern Africa or the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

An event‐based assessment of the sea surface temperature (SST) threshold at the genesis of tropical mesoscale convective systems (MCSs) is performed in this study. We show that this threshold (SSTG) has undergone a significant warming trend at a rate of ∼0.2°C per decade. The SSTG shows a remarkable correspondence with the tropical mean SST and upper‐tropospheric temperature on interannual and longer timescales. Using a high‐resolution global climate model that permits realistic simulations of tropical MCSs, we find that the observed features of SSTG are well simulated. Both observation and model simulations demonstrate that the upward tendency in SSTG primarily results from the environmental SST warming over MCS genesis regions rather than the changes in MCS genesis location. A continuous increase in SSTG is projected in a warming simulation, but the relationship between SSTG and upper‐tropospheric temperature remains unchanged, suggesting that the tropical tropospheric temperature generally follows a moist‐adiabatic adjustment. Plain Language Summary: The development of tropical ocean showers and thunderstorms requires a warm ocean surface as an energy source fueling the storm. As a good example, a sea surface temperature (SST) threshold of 26.5°C has long been recognized as a necessary condition for tropical cyclone genesis. Here we examine the SST threshold at the genesis of tropical mesoscale convective systems, which occur so frequently throughout the tropics that they play an important role in shaping the general circulation of the atmosphere as they redistribute moisture and energy in the atmosphere. Using satellite observations and a high‐resolution global climate model, we show that this threshold has undergone a significant warming trend during the past several decades and will continue to increase in the future. This warming trend is closely related to the changes in the tropical mean SST. A constant relationship between the SST threshold and upper‐tropospheric temperature is found in both the current climate and a warming climate, which corroborates the argument that tropospheric temperatures in the tropics approximately follow a moist adiabatic adjustment. Key Points: A significant warming trend in sea surface temperature at the genesis of tropical mesoscale convective systems (MCSs) sea surface temperature threshold (SSTG) has been observedA global climate model that can explicitly simulate MCSs captures the observed features of SSTG and projects a continuous increaseA constant relationship between SSTG and upper‐tropospheric temperature indicates the existence of a moist‐adiabatic adjustment [ABSTRACT FROM AUTHOR]

Based on Himawari-8 satellite observations, the mesoscale convective system (MCS) behaviors of two successive but distinct warm-sector rainfall episodes (EP1 and EP2) on 6–7 May 2018 over southeastern China were compared, with the latter episode being a record-breaking rainfall event. Results showed that MCSs played a dominant role in EP2, but not in EP1, by contributing over 80% of the extreme rainfall total and all the 10-min rainfalls over 20 mm. MCS occurrences were more frequent in EP2 than EP1, especially in the coastal rainfall hotspots, along with more frequent merging processes. Overall, the MCS samples in EP2 were larger in size, more intense, and moved slower and more in parallel to their orientation, which facilitated local rainfall accumulation. Two new indices are proposed—the overlap index (OLI) and merging potential index (MPI)—to evaluate two MCS processes vital for rainfall production: the repeated passage of an individual MCS over given areas and the merging between MCSs, respectively. Both OLI and MPI in EP2 were significantly larger than in EP1, which tended to produce larger maximum rainfall amount and stronger 10-min rain rates in the following hour. These results demonstrate the potential value of satellite-based MCS information for heavy rainfall nowcasting, which is particularly significant for warm-sector rainfall with its limited predictability. [ABSTRACT FROM AUTHOR]

Abstract Mesoscale convective systems (MCS) contribute about half of the world's precipitation and create flash flooding as well as other extreme weather events. Despite steady progress in research of these systems in the last several decades, better theoretical understanding is still needed to understand their dynamical organizations and to improve their forecasts in numerical models. By using the Moncrieff‐Green horizontal vorticity equation, this paper presents an analytical model of one type of MCS, the steady‐state squall lines. It describes the organization, propagation, and properties of mesoscale circulations of two‐dimensional steady‐state convective systems under sheared environment. Far‐side solutions are formulated to illustrate the underlying physical processes of squall line flows. Numerical procedures are described to solve the model under general environmental conditions. The model leads to the following prediction of squall line properties: Given the environmental profiles of wind and convective available potential energy (CAPE), the propagation speed, the depths and mass fluxes of the tilted ascending front‐to‐rear flow, the overturning updraft, and the descending rear inflow of the squall line can be all determined from the cold pool buoyancy or CAPE. The squall lines are therefore self‐organized dynamical systems that have limited degrees of freedom in their properties. The model advances the theoretical understanding of how mesoscale flow components interact to sustain organized convection. It provides a new tool to interpret squall line systems in high resolution models and to parameterize them in climate models.

Transient luminous events (TLEs) are electrical discharges in the upper atmosphere caused by vigorous thunderstorms. Six sprites, which are part of TLEs, were observed on 22 July 2013 from Mt. Fuji (3776 m above sea level), Japan. All the six sprites were associated with intense positive cloud-to-ground strikes (+CGs), whose causative positive charges can reside in the stratiform region. Consequently, we assumed that the main sprites causative charges could generate an in situ charging mechanism, accompanied by precipitation growth in the extensive stratiform region. Thus, we supposed that there can be a relationship between the time sequence of surface precipitation intensity and the sprite emissions. In this study, we conclude that time sequences and horizontal evolution of Mesoscale Convective Systems (MCSs) precipitation are associated with sprites. As the result, prior to sprites 1–5, the areal amount of strong precipitation (≥8 mm/h) increased considerably, and only a small increase occurred during sprite 6. Analyzing the time sequence of the percentage of strong and weak precipitation with respect to the total precipitation, it was found that sprites 1–6 occurred within 20 min after the local peaks with respect to strong precipitation compared to total precipitation. In particular, sprites 2–5 occurred very close to local peaks. The rise time to the first peak of the strong precipitation rate associated with the first sprite was 80 min, while the rise time to the last peak associated with sprite 6 was 30 min. The temporal differences until the peaks suggest that the charging speeds, or mechanisms, related to precipitation differ between sprites 1–5 and sprite 6 in parent MCSs. [ABSTRACT FROM AUTHOR]

A 62‐day "extremely violent Meiyu" occurred in the Yangtze River basin from June to July in 2020, and its abnormal precipitation caused serious losses to the social economy. In this paper, the characteristics of newly formed mesoscale convective systems (MCSs) and the environmental conditions affecting the MCS formation during this abnormal precipitation event are investigated based on hourly datasets, including the temperature of brightness blackbody (TBB) data derived from the FY‐2F geostationary meteorological satellite, and the three‐source merged precipitation products from China Meteorological Administration. The results show that there were 31,778 times of short‐duration heavy precipitation (hourly precipitation exceeding 20 mm) occurred in the Yangtze River basin from June to July in 2020. The 69.3% of short‐duration heavy precipitation (hourly precipitation exceeding 20 mm) are closely related to the MCSs. The increase of newly formed MCSs leaded to more short‐duration heavy precipitation. The abnormal precipitation in the Yangtze River basin from June to July is mainly caused by elongated MCSs with an average lifetime of 6 h. The number of the newly formed MCSs presents obvious diurnal variations, with the most frequent at 20:00 (Beijing Time, the same below). The newly formed MCSs are prone to appear near the Yangtze–Huaihe shear line, and the magnitude of southerly wind at 500 hPa determines the distance between the MCSs and the shear line. The enhancement of vorticity advection at 500 hPa and water vapor convergence are conducive to the MCS formation. The weakening of low‐level jet corresponds to the increase of newborn MCS. [ABSTRACT FROM AUTHOR]

Modern global reanalysis products have greatly accelerated meteorological research in synoptic‐to‐planetary‐scale phenomena. However, their use in studying tropical mesoscale convective systems (MCSs) and their regional‐to‐global impact has mostly been limited to supplying initial and boundary conditions for MCS‐resolving simulations and providing information about the large‐scale environments of MCSs. These limitations are due to difficulties in resolving tropical MCS dynamics in the relatively low‐resolution global models and that tropical MCSs often occur over poorly observed regions. In this work, a Tropical MCS‐resolving Reanalysis product (TMeCSR) was created over a region with frequent tropical MCSs. This region spans the tropical Indian Ocean, tropical continental Asia, Maritime Continent, and Western Pacific. TMeCSR is produced by assimilating all‐sky infrared radiances from geostationary satellites and other conventional observations into an MCS‐resolving regional model using the Ensemble Kalman Filter. The resulting observation‐constrained high‐resolution (9‐km grid spacing) data set is available hourly during the boreal summer (June‐August) of 2017, during which widespread severe flooding occurred. Comparisons of TMeCSR and European Center for Medium Range Weather Forecast Reanalysis version 5 (ERA5) against independent satellite retrievals indicate that TMeCSR's cloud and multiscale rain fields are better than those of ERA5. Furthermore, TMeCSR better captured the diurnal variability of rainfall and the statistical characteristics of MCSs. Forecasts initialized from TMeCSR also have more accurate rain and clouds than those initialized from ERA5. The TMeCSR and ERA5 forecasts have similar performances with respect to sounding and surface observations. These results indicate that TMeCSR is a promising MCS‐resolving data set for tropical MCS studies. Plain Language Summary: Thunderstorms provide much of the rainfall over the Tropics and have important impacts on global weather and climate. However, these important systems often occur over regions with sparse in‐situ observations. Hence, it is difficult to use in‐situ observations to study the detailed dynamics and thermodynamics of these thunderstorm systems. While combining observations with computer simulation data can produce three‐dimensional data sets over the Tropics, the currently available combination data sets have difficulty resolving these thunderstorm systems. In this study, we combined high‐resolution satellite measurements with high‐resolution weather simulations to produce a high‐resolution four‐dimensional data set. This new data set can capture tropical thunderstorm systems over an area spanning the tropical Indian Ocean to the western edge of Pacific Ocean. We compared the accuracy of our new data set against a gold standard global data set. Using independent satellite‐derived radiation and rainfall data, we found that our new data set has more accurate storm characteristics compared to the gold standard. These characteristics include clouds and rainfall. Furthermore, simulations initialized from our new data set had a similar advantage over simulations initialized from the gold standard. These promising results suggest that our new data set might be better at capturing tropical thunderstorm systems than the gold standard. Key Points: Tropical mesoscale convective systems (MCSs) research can benefit from an observation‐constrained MCS‐resolving reanalysis data setWe produced such a data set using all‐sky satellite infrared radiances, MCS‐resolving regional simulations, and ensemble data assimilationCompared to European Center for Medium Range Weather Forecast Reanalysis version 5, the new data set better captured cloud, rainfall, and frequency of tropical MCSs and produced better short‐term forecasts [ABSTRACT FROM AUTHOR]

Vertical wind shear is known to play a key role in the organization and intensity of mesoscale convective systems (MCSs) in West and Central Africa. A decadal increase in vertical wind shear has recently been linked to a decadal increase in intense MCSs over the Sahel. Here, the effects of vertical wind shear on MCSs over West and Central Africa have been investigated using a 10‐year (1998–2007) MCS dataset. Strong vertical shear is associated with long‐lived, moderate speed, moderate size and cold (deep) storms with high rain rates. The observed cloud top heights of storms over the oceans are closer to their level of neutral buoyancies (LNBs) compared to their land counterparts on the same latitudes. We hypothesize that this is due to greater entrainment dilution over land compared to storms over the ocean. Vertical shear allows storm anvils to reach higher altitudes relative to their LNB, this is consistent with the colder top storms over the Sahel (a region with a high vertical shear) compared to the Congo, despite a higher LNB in the Congo. It is not possible to diagnose the exact mechanisms for this impact of vertical shear from the data, but it is consistent with recent work showing that shear reduces entrainment dilution of squall‐line updrafts. We conclude that modelling impacts of vertical shear, which are normally missed in convection parameterizations, are not only important for predictions of high impact weather, but also for modelling the mean distribution of storm heights across Africa. [ABSTRACT FROM AUTHOR]

Using routine meteorological observations, intensive observations from the automatic weather stations, satellite images, radar products, NCEP reanalysis data, fine grid model data and regional mesoscale model data, we have conducted an examination on the reasons for the miss of forecast and the predictability of a short-term extreme precipitation event occurred in the Shaying River Basin at the night on 18 August 2017. The results indicate that this event occurs under the circulation of a high in the west and a low in the east. The stability and continuance of shear lines in the low-level and boundary layer and the establishment of the ultra-low level southwest jet provide the water vapor transport and convergence conditions for the occurrence of severe precipitation. The weak cold air spreads southwards along the south of North China and gradually intrudes into the inverted trough forming a mesoscale convergence line (convergence center) in the Shaying River Basin and maintaining such condition for a long time to trigger the release of unstable energy, which is a good indicator in predicting the occurrence of rainstorm. The two mesoscale convective cloud clusters reinforced and developed jointly into a Meso-β scale Convective System (MβCS) with a quasistatic state. It maintains for 6 hours in the lower reaches of the Shaying River Basin, which is the direct reason that leads to the enhancement of precipitation. The mesoscale convective system is triggered by the cold pool and its front surface mesoscale convergence line, and the strong echo continuously develops and maintains in the high value zone of temperature gradient in front of the cold pool, resulting in short-term extreme precipitation. The weak dynamic condition, the water vapor being mainly concentrated in the boundary layer and the extremely favorable thermal instability condition during this event, as well as the limited capture ability of the numerical model in forecasting this kind of convective rainstorm, all these factors are the causes of the miss of forecast of the rainstorm. The insufficient estimation of numerical models and operational forecasts in the precipitation intensity and its extreme, and the lack of forecasters'experience in forecasting extreme weather, are also some of the reasons for the forecast errors.

Based on conventional meteorological observations, observational data from the regional automatic weather stations, NCEP reanalysis data with spatial resolution of 1°×1° and temporal resolution of 6 h, satellite images, Doppler weather radar and wind profiler data, as well as the retrieval results from BeijingVariational Doppler Radar Analysis System (VDRAS), we have conducted analysis of the precipitation characteristics, atmospheric circulation, mesoscale system evolution features and the causes of a regional warm-sector torrential rain event in the Beijing-Tianjin-Hebei region on 12 August 2020. The results show that the event occurs in the warm air mass below 500 hPa at the edge of the subtropical high, and the main influencing systems are the low-level jet and the warm shear line at the 850 hPa. The whole severe precipitation event presented clearly the phased characteristics; it can be divided into two stages corresponding to the two different rainstorm areas, i.e., the southern Hebei and the north part of the Beijing-Tianjin-Hebei region with different formation mechanisms. The severe precipitation in the first stage is caused by a meso-α-scale convective system (MαCS), which is triggered by the surface convergence line. Before the precipitation starts, the local water vapor and unstable energy is rich. When the surface convergence line triggers the release of unstable energy, a strong linear echo is formed. The severe precipitation is mainly caused by the continuous development of convective cells in the spiral echo corresponding to the surface cyclonic circulation. The severe precipitation in the second stage is generated by several β-scale cloud clusters, and the southerly low-level jet strengthened northward provides sufficient water vapor and better dynamic conditions for the occurrence of torrential rain. The low-level jet in the boundary layer and the mesoscale low vortex system are the crucial influence systems at the second stage of this event. The hourly extremely severe precipitation of 125.9 mm at a station in Xiongan New Area is caused jointly by the warm cloud precipitation at the tail of comma-shaped radar echo and the "train effect".

Abstract A 62‐day “extremely violent Meiyu” occurred in the Yangtze River basin from June to July in 2020, and its abnormal precipitation caused serious losses to the social economy. In this paper, the characteristics of newly formed mesoscale convective systems (MCSs) and the environmental conditions affecting the MCS formation during this abnormal precipitation event are investigated based on hourly datasets, including the temperature of brightness blackbody (TBB) data derived from the FY‐2F geostationary meteorological satellite, and the three‐source merged precipitation products from China Meteorological Administration. The results show that there were 31,778 times of short‐duration heavy precipitation (hourly precipitation exceeding 20 mm) occurred in the Yangtze River basin from June to July in 2020. The 69.3% of short‐duration heavy precipitation (hourly precipitation exceeding 20 mm) are closely related to the MCSs. The increase of newly formed MCSs leaded to more short‐duration heavy precipitation. The abnormal precipitation in the Yangtze River basin from June to July is mainly caused by elongated MCSs with an average lifetime of 6 h. The number of the newly formed MCSs presents obvious diurnal variations, with the most frequent at 20:00 (Beijing Time, the same below). The newly formed MCSs are prone to appear near the Yangtze–Huaihe shear line, and the magnitude of southerly wind at 500 hPa determines the distance between the MCSs and the shear line. The enhancement of vorticity advection at 500 hPa and water vapor convergence are conducive to the MCS formation. The weakening of low‐level jet corresponds to the increase of newborn MCS.

Abstract Vertical wind shear is known to play a key role in the organization and intensity of mesoscale convective systems (MCSs) in West and Central Africa. A decadal increase in vertical wind shear has recently been linked to a decadal increase in intense MCSs over the Sahel. Here, the effects of vertical wind shear on MCSs over West and Central Africa have been investigated using a 10‐year (1998–2007) MCS dataset. Strong vertical shear is associated with long‐lived, moderate speed, moderate size and cold (deep) storms with high rain rates. The observed cloud top heights of storms over the oceans are closer to their level of neutral buoyancies (LNBs) compared to their land counterparts on the same latitudes. We hypothesize that this is due to greater entrainment dilution over land compared to storms over the ocean. Vertical shear allows storm anvils to reach higher altitudes relative to their LNB, this is consistent with the colder top storms over the Sahel (a region with a high vertical shear) compared to the Congo, despite a higher LNB in the Congo. It is not possible to diagnose the exact mechanisms for this impact of vertical shear from the data, but it is consistent with recent work showing that shear reduces entrainment dilution of squall‐line updrafts. We conclude that modelling impacts of vertical shear, which are normally missed in convection parameterizations, are not only important for predictions of high impact weather, but also for modelling the mean distribution of storm heights across Africa.

Córdoba Province in Argentina is a global hotspot for deep hail-producing storms. Previous studies of hail formation and detection largely relied on satellite snapshots or modeling studies, but lacked hail validation, relying instead on proxy metrics. To address this limitation, this study used hail collected in the mountainous Córdoba region in collaboration with the citizen science program "Cosecheros de Granizo 2018–2020" including from a record-breaking hail event and from the 2018–2019 RELAMPAGO field campaign. Three cases including a MCS and two supercells, which have verified hail in different environment locations relative to the Sierras de Córdoba, were analyzed for multi-spectral signatures in GOES-16 satellite data. Brightness temperatures decreased over time after convective initiation, reaching values cooler than the tropopause with variations around those values of different magnitudes. Overall, all cases exhibited a slight weakening of the updraft and strong presence of smaller ice crystal sizes just prior to the hail report, especially for the larger hailstones. The results demonstrate promise in using satellite proxies for hail detection in multiple environments for different storm modes. The long-term goal is to better understand hail-producing storms and unique challenges of forecasting hail in this region. [ABSTRACT FROM AUTHOR]

Using routine upper-air and surface weather observations, satellite images, Doppler weather radar products, the observations from regional automatic weather stations and NCEP 6-hourly reanalysis data with 1°×1° resolution, we have conducted an analysis of the mesoscale system evolution and environmental field characteristics of a warm-sector heavy rainfall event occurred in the southeast of Fanjing Mountain from July 3 to 4 in 2016. Results are as follows. (1) This event, whose main influencing systems are westerly trough at 500 hPa and warm shear line at 850 hPa, occurred in the upper trough area to the northwest of the subtropical high, the south side of low-level warm shear, the left front of low-level jet and the divergence zone at 200 hPa. As a result, this event is a warm-sector extreme heavy rainfall event in Guizhou without the affecting of obvious cold air in the ground level. (2) This warm-sector heavy rainfall event is directly caused by four continuous convective cloud clusters, in which the severe precipitation occurred near the center of the convective cloud clusters and in the area of big values of TBB gradient at their back side. (3) The heavy rain was caused by the mixed precipitation echoes of cumuliform clouds. Favorable environmental conditions causing such a high efficient precipitation include warm clouds, deep wet layer, low-level abundant water vapor transport, abnormal low level of free convection (LFC) and level of condensation lifting (LCL), and "thin high" distribution of convective effective potential energy with moderate intensity. (4) The zones with great value of water vapor flux and the water vapor convergence centers are concentrated in southeast side of Fanjing Mountain because of the blocking effect of terrain. The easterly wind in the boundary layer turned south in front of the mountain and met the southerly airflow in the rainstorm area, forming an east-west stable mesoscale convergence line. The convections were triggered, merged, strengthened and then moved eastward near the convergence line, which is the important cause for the heavy rain forming. The meso-and micro-scale dynamical forcing by windward slope and the trumpet-shaped topography are favorable to the transport and uplift condensation of water vapor in the boundary layer.

Precipitation over tropical oceans rapidly increases when the environmental column saturation fraction (CSF) increases past a critical value of ∼0.7. Past studies suggested that increased stratiform rainfall greatly contributes to the rapid rainfall enhancement. In this study, the sequential roles of non‐deep convection, deep convection, and mesoscale convective system (MCS) in precipitation‐moisture interactions are examined using 19 years of satellite observations. When CSF is below ∼0.5, non‐deep convection dominates total rainfall, and predominantly contributes to moistening of the environment. Between the CSF range of 0.5–0.7, transition to deep convective rainfall begins. Meanwhile, MCS contribution to total rain rapidly increases, and the environment is further moistened. MCS becomes the major rainfall type above the critical CSF value (∼0.7), with the rapid increase of total rain mostly explained by the rapid increase in MCS rain area. Rainfall reduction at high CSF values is jointly contributed by MCS and non‐deep convection. Plain Language Summary: Over tropical oceans, atmospheric moisture is a dominant factor that determines the occurrence of heavy rainfall. Past studies have suggested that rainfall over tropical oceans quickly intensifies when the atmospheric moisture content is beyond a critical value. This phenomenon can be mostly explained by the rapid increase of stratiform precipitation when the environment is getting close to saturation. Using a novel global cloud classification and tracking data set, we show that mesoscale convective systems (MCSs) play a crucial role in the precipitation‐moisture coupling over tropical oceans. When the atmosphere is ∼50% saturated, the contribution of MCS to total precipitation begins to rapidly increase. MCS becomes the most important rainfall type after the atmosphere is ∼70% saturated. During the process, MCSs also contribute to the moistening of the large‐scale environment. The rapid total rainfall increase beyond the critical saturation value can be almost entirely explained by the enhancement of MCS rainfall, and more specifically MCS rain area. Key Points: When the environment is dry, shallow convection and congestus dominate total rain and gradually moisten the atmosphereWhen the environment is ∼50% saturated, the contribution of deep convective rainfall to total rainfall begins to increaseWhen the environment is >70% saturated, mesoscale convective system becomes the major rain type, leading to rapid increase of total rain [ABSTRACT FROM AUTHOR]

The influence of a mesoscale convective system (MCS) in the evolution of two wildfires that started during the afternoon of 17 June 2017 in Pedrógão Grande, Central Portugal is discussed and analysed using weather radar data, weather stations, video images and fire spread analysis. As the MCS approached the region, its convectively driven flows started to influence the fires. The overturning flows were formed by two main limbs: one organised as front-to-rear deep layer inflows that propagated over the convective region of the MCS and the other as rear-to-front mid-level inflows that descended below the anvil structure of the MCS. The rear-to-front inflows, while accelerating and descending to lower levels, contributed to modify the fires' intensity and plume characteristics. After the two fires merged, the resulting junction fire became very intense and impossible to control. Then, a firestorm was generated, causing the deaths of 66 people. The main goal of this study is to detail the influence of the MCS in the fire spread, thus contributing to the general knowledge of outstanding fire behaviour modifications due to the influence of atmospheric convective processes. [ABSTRACT FROM AUTHOR]

During July 4 to 10, an extreme heavy rainfall occurred in the Yangtze River Basin. By using high temporal and spatial resolution FY-4A blackbody temperature (TBB) data and the China hourly merged precipitation analysis combining observations from automatic weather stations with CMORPH products, an automatic identification and tracking method of convection is applied to analyze the identification, tracking and classification of the mesoscale convective system (MCS) in the secondary terrain and the east region (105°-125°E, 25°-35°N) in Yangtze river basin. The western, eastern and east-moving types of MCS are classified, and their spatial and temporal distribution characteristics and the physical parameters are studied. Results showed that the number of MCS generated in the western region increased significantly, remain unchanged in the eastern region, and occurred mostly in the east-moving type in July 5 to 6. The initiation peak of western and eastern types generally occurs in the afternoon and early morning, while the east-moving type mainly occurs in the early morning. The east-moving type is more easterly than that of the western type MCS, which is more favorable for east moving to affect the downstream area. Compared with western and eastern type MCS, lower TBB, greater rainfall intensity, longer life duration, more rapidly development, larger rainfall area and convective cloud area, longer moving path and wider influence range are presented in east-moving MCS, indicating that the east-moving MCS is more vigorous. Meanwhile, with the increase of life duration, the number of MαCS increases, while the number of MβCS decreases gradually.

Based on weather radar data, precipitation data from densified rainfall stations, hydrological data at Wucha hydrological station in Qijiang Catchment and ERA5 reanalysis data, we have conducted the analysis of a record-breaking flood event occurred in Qijiang Catchment from June 19 to 22 in 2020 including the spatial-temporal distribution of precipitation, the circulation background, the water vapor sources and the evolutional characteristics of mesoscale convective systems (MCSs). The results indicate that (1) this event is a persistent severe precipitation event with concentrated range and characterized by obvious periodic and diurnal variation. It can be divided into three stages. Severe precipitation mainly occurs at night. (2) Persistent heavy rainfall occurs under the circulation pattern of cold air guided by east-moving cold low pressure in the Ural Mountains moving southward to the northeast of Sichuan Basin, low trough in the mid-latitude maintaining for a long time in the eastern Sichuan-Chongqing-Guizhou area and the Western Pacific subtropical high being stable. (3) Low-level warm and moist southwest jet further increases the atmospheric stratification instability between northern Guizhou and southern Chongqing, and it conveys water vapor from South China Sea and Bengal Bay to Qijiang River Basin, providing abundant water vapor for the generation and persistence of heavy rainfall. (4) The occurrence and development of MCSs at the three severe precipitation stages show different features. At the first stage, MCSs in coherence with the strong radar echoes are situated in roughly north-south direction, moving eastward to affect the Qijiang Catchment, and the duration of heavy rainfall is therefore relatively short. Next, the MCSs present southwest-northeast direction, affecting Qijiang Catchment for a longer time, but the echo intensity is weak. At last stage, the MCSs present massive. And they are linearly distributed in the northwest-southeast direction when they mature, exhibiting "train effect", which affects Qijiang Catchment longest and cause the greater precipitation intensity.

Extreme rainfall events have posed several serious threats to many populated and urbanized areas in the world including the Indian subcontinent. Therefore, accurate predictions of their intensity and areas of influence are important for flood‐prone risk assessments. On 14 July 2016, heavy to exceptionally heavy rainfall occurred in Yamunanagar (30.16° N, 77.29° E), located in the state of Haryana in North India, which led to widespread disruption of communication, electricity, inundation of houses, and so forth. The present paper aims at examining observational, synoptic, thermo‐dynamical, and numerical features associated with this devastating rainfall episode. The analysis found that during extreme rainfall episodes, a trough in mid‐tropospheric westerlies and a strong low‐level atmospheric monsoonal flow seem to have strongly interacted with each other, creating a strong convergence zone near study areas that led to a severe rainstorm. The quasi‐stationary supercells were also noticed due to continuous moisture incursions from the Bay of Bengal and orographic uplift over the Himalayas near Yamunanagar. A deep layer of wind shear interacts dynamically with the convergence zone and leads to a potential rainstorm. Thermodynamic indices indicate high instability over the heavy rainfall area. The dynamics of this event were studied in detail by using three‐dimensional variational data assimilation within the weather research and forecasting model, configured with triple two‐way nesting domains (27, 9, and 3 km). The model results show that the weather research and forecasting model satisfactorily captures the quantitative precipitation (300 mm) in 24 h over the Yamunanagar region as compared with observation (365 mm). [ABSTRACT FROM AUTHOR]

The ability of an observationally‐constrained cloud‐system resolving model (Weather Research and Forecasting; WRF, 4‐km grid spacing) and a global climate model (Energy Exascale Earth System Model; E3SM, 1‐degree grid spacing) to represent the precipitation diurnal cycle over the Amazon basin during the 2014 wet season is assessed. The WRF model coupled with a 3‐D variational data assimilation scheme reproduces the spatial variability of the precipitation diurnal cycle over the basin and the lifecycle of westward propagating MCSs initiated by the coastal sea‐breeze front. In contrast, a single morning peak in rainfall is produced by E3SM for simulations despite the nudging of large‐scale winds toward global reanalysis, indicating precipitation in E3SM is largely controlled by local convection associated with diurnal heating. The role of propagating MCS on the environment are discussed by using a multivariate perturbation analysis. We also find that the advection of moisture perturbations from ocean to inland regions have a higher correlation with the occurrence of MCSs in the Amazon than the intensity of colder air intrusion associated with sea breezes along the coast. Moreover, the presence of large cold pools over the central Amazon basin are responsible for the maintenance of propagating deep convection. Plain Language Summary: The Amazon basin in South America is one of the regions over land that has the highest occurrence of large‐size and deep cloud systems (also called "Mescoscale Convective System" [MCS]). Since they have a wide coverage and produce much heavier rainfall than the other types of cloud, the regional climate and even the earth system are tied closely with their behaviors. However, current global atmospheric models are unable to reproduce realistic diurnal variation of precipitation in the Amazon and the poor representation of those MCSs is responsible for the deficiency. We use various observations as the reference to understand how accurate the physical processes related to MCS are represented by both the cloud‐system resolving (higher‐resolution) and global climate (lower‐resolution) models. The results show the diurnal variation of local precipitation in the basin is mostly reproduced by cloud‐system resolving model but not the global climate model, because the propagating MCSs and many related processes can only be simulated by using higher‐resolution model. We also found the advection of moisture perturbation from ocean to inland regions have a higher correlation with the occurrence of MCS in the Amazon than intensity of colder air intrusion associated with sea breezes along the coast. Key Points: Spatial variability of the precipitation diurnal variation in the Amazon is mostly reproduced by WRF but not E3SMRepresentation of propagating convective systems is the key to simulate accurate diurnal cycle of precipitationOcean to inland advection of moisture perturbations into the Amazon control the occurrence of propagating MCS [ABSTRACT FROM AUTHOR]

Mesoscale convective systems (MCSs) are one of the most climatically significant forms of convection because of their large role in water and energy cycles. The mesoscale features associated with MCS are difficult to represent in climate models because the relevant dynamics and physics are absent or poorly represented with coarse model resolution (∼100 km). Using a regionally refined model (RRM) with 0.25° grid spacing embedded in the Energy Exascale Earth System Model (E3SM), we explore the impact of cloud microphysics parameterizations on the simulation of precipitation, particularly MCS precipitation over the contiguous United States. The Predicted Particle Properties (P3) cloud microphysics scheme has been modified and implemented into E3SM to overcome the limitations of the default Morrison and Gettelman (MG2) scheme in which rimed precipitating ice particles (graupel/hail) are absent and frozen particles are artificially partitioned into cloud ice and snow. We show that P3 improves the simulation of precipitation statistics including frequency distribution compared with MG2 with a limited effect on the diurnal cycle. P3 predicts higher hourly rain rates, resulting in 20% more MCSs and a higher total MCS precipitation (4.4%) compared to MG2, agreeing better with observations. The improvements with P3 mainly result from improved representations of ice microphysics, which not only produces higher rain rates through melting but also leads to a stronger large‐scale ascending motion by releasing more latent heating. This study suggests that improving microphysics parameterization is important for simulating MCS precipitation as future climate model resolutions continue to increase. Plain Language Summary: Mesoscale convective systems (MCSs) are large storms playing an important role in regulating the precipitation and climate, which are difficult to simulate in global climate models because of inaccurate physics parameterization and coarse model resolution. The regionally refined model (RRM) allows high‐resolution regional simulation embedded in a coarse‐resolution global model, enabling the simulation of MCSs. The representation of small‐scale cloud microphysical processes in models impacts MCS precipitation. A relatively new cloud microphysics scheme—Predicted Particle Properties (P3)—has been modified and implemented into the Department of Energy's climate model—Energy Exascale Earth System Model (E3SM), to overcome the limitations of the original scheme. Here we examine how cloud microphysics parameterizations can impact MCS simulations over the contiguous United States using the RRM framework. We show that the P3 scheme notably improves the simulations of precipitation, particularly MCS precipitation. The improvement mainly results from improved representations of ice microphysics in P3, which helps to produce more realistic heavy precipitation rates. Key Points: The new microphysics scheme employed in E3SM improves the simulation of precipitation and PDF of precipitation rateP3 notably improves the simulation of MCS number and precipitation by predicting higher frequencies of large precipitation ratesLarge biases in precipitation and its diurnal cycle still exist, which might not be caused by cloud microphysics in resolved clouds [ABSTRACT FROM AUTHOR]

In this paper, non-typhoon heavy rain research in Taiwan for the past 30 years is reviewed. Since 1987 TAMEX experiment, Taiwan heavy rain research and forecast operation have been experienced a significant change, i.e., from qualitative description transfer into quantitative analysis and simulation. Many new measurement instrumentations and numerical weather prediction systems have been installed. Due to great challenge caused by climate change and frequent occurrence of extreme weather events, in order to provide timely information for emergency response and disaster risk reduction, technology development on quantitative precipitation forecast (QPF) has become world-wide common requirements. In this paper, efforts from Taiwan meteorology community to strengthen the knowledge of basic understanding of heavy rainfall events and to improve the forecast capability are reviewed.

Abstract Mesoscale convective systems (MCSs) are one of the most climatically significant forms of convection because of their large role in water and energy cycles. The mesoscale features associated with MCS are difficult to represent in climate models because the relevant dynamics and physics are absent or poorly represented with coarse model resolution (∼100 km). Using a regionally refined model (RRM) with 0.25° grid spacing embedded in the Energy Exascale Earth System Model (E3SM), we explore the impact of cloud microphysics parameterizations on the simulation of precipitation, particularly MCS precipitation over the contiguous United States. The Predicted Particle Properties (P3) cloud microphysics scheme has been modified and implemented into E3SM to overcome the limitations of the default Morrison and Gettelman (MG2) scheme in which rimed precipitating ice particles (graupel/hail) are absent and frozen particles are artificially partitioned into cloud ice and snow. We show that P3 improves the simulation of precipitation statistics including frequency distribution compared with MG2 with a limited effect on the diurnal cycle. P3 predicts higher hourly rain rates, resulting in 20% more MCSs and a higher total MCS precipitation (4.4%) compared to MG2, agreeing better with observations. The improvements with P3 mainly result from improved representations of ice microphysics, which not only produces higher rain rates through melting but also leads to a stronger large‐scale ascending motion by releasing more latent heating. This study suggests that improving microphysics parameterization is important for simulating MCS precipitation as future climate model resolutions continue to increase.

Abstract The ability of an observationally‐constrained cloud‐system resolving model (Weather Research and Forecasting; WRF, 4‐km grid spacing) and a global climate model (Energy Exascale Earth System Model; E3SM, 1‐degree grid spacing) to represent the precipitation diurnal cycle over the Amazon basin during the 2014 wet season is assessed. The WRF model coupled with a 3‐D variational data assimilation scheme reproduces the spatial variability of the precipitation diurnal cycle over the basin and the lifecycle of westward propagating MCSs initiated by the coastal sea‐breeze front. In contrast, a single morning peak in rainfall is produced by E3SM for simulations despite the nudging of large‐scale winds toward global reanalysis, indicating precipitation in E3SM is largely controlled by local convection associated with diurnal heating. The role of propagating MCS on the environment are discussed by using a multivariate perturbation analysis. We also find that the advection of moisture perturbations from ocean to inland regions have a higher correlation with the occurrence of MCSs in the Amazon than the intensity of colder air intrusion associated with sea breezes along the coast. Moreover, the presence of large cold pools over the central Amazon basin are responsible for the maintenance of propagating deep convection.

Abstract Extreme rainfall events have posed several serious threats to many populated and urbanized areas in the world including the Indian subcontinent. Therefore, accurate predictions of their intensity and areas of influence are important for flood‐prone risk assessments. On 14 July 2016, heavy to exceptionally heavy rainfall occurred in Yamunanagar (30.16° N, 77.29° E), located in the state of Haryana in North India, which led to widespread disruption of communication, electricity, inundation of houses, and so forth. The present paper aims at examining observational, synoptic, thermo‐dynamical, and numerical features associated with this devastating rainfall episode. The analysis found that during extreme rainfall episodes, a trough in mid‐tropospheric westerlies and a strong low‐level atmospheric monsoonal flow seem to have strongly interacted with each other, creating a strong convergence zone near study areas that led to a severe rainstorm. The quasi‐stationary supercells were also noticed due to continuous moisture incursions from the Bay of Bengal and orographic uplift over the Himalayas near Yamunanagar. A deep layer of wind shear interacts dynamically with the convergence zone and leads to a potential rainstorm. Thermodynamic indices indicate high instability over the heavy rainfall area. The dynamics of this event were studied in detail by using three‐dimensional variational data assimilation within the weather research and forecasting model, configured with triple two‐way nesting domains (27, 9, and 3 km). The model results show that the weather research and forecasting model satisfactorily captures the quantitative precipitation (300 mm) in 24 h over the Yamunanagar region as compared with observation (365 mm).

Extreme rainfall occurred over the South African east coast during 10–12 April 2022, leading to over 500 deaths and massive damage. This study seeks to understand a key feature, namely the progression of the rainfall maxima from the northern KwaZulu-Natal (KZN) coast during the night of 10–11 April by ~550 km to the Eastern Cape coast about 48 h later. The large-scale circulation was dominated by a cut-off low over the South African interior with a strong ridging anticyclone southeast of the country in the South Indian Ocean. Satellite, rain gauge, and ERA5 reanalysis are used to show that the timing and location of the heaviest rainfall are closely tied to, firstly, the formation of a Mesoscale Convective System (MCS) at ~0300UTC April 11 on the northern KZN coast which tracked south and then offshore, and secondly, a meso-trough which formed a coastal meso-low by ~2100 UTC April 11. The meso-low tracked south over the warm waters of the Agulhas Current before strengthening into Subtropical Depression Issa. Mesoscale interaction between the MCS and coastal meso-low determined the positioning and timing of the strongest onshore low-level jet, moisture convergence and uplift, and hence the progression of the heavy rainfall down the coast. Such mesoscale interaction has not previously been documented in southern Africa or the Southern Hemisphere.

Based on Himawari-8 satellite observations, the mesoscale convective system (MCS) behaviors of two successive but distinct warm-sector rainfall episodes (EP1 and EP2) on 6–7 May 2018 over southeastern China were compared, with the latter episode being a record-breaking rainfall event. Results showed that MCSs played a dominant role in EP2, but not in EP1, by contributing over 80% of the extreme rainfall total and all the 10-min rainfalls over 20 mm. MCS occurrences were more frequent in EP2 than EP1, especially in the coastal rainfall hotspots, along with more frequent merging processes. Overall, the MCS samples in EP2 were larger in size, more intense, and moved slower and more in parallel to their orientation, which facilitated local rainfall accumulation. Two new indices are proposed—the overlap index (OLI) and merging potential index (MPI)—to evaluate two MCS processes vital for rainfall production: the repeated passage of an individual MCS over given areas and the merging between MCSs, respectively. Both OLI and MPI in EP2 were significantly larger than in EP1, which tended to produce larger maximum rainfall amount and stronger 10-min rain rates in the following hour. These results demonstrate the potential value of satellite-based MCS information for heavy rainfall nowcasting, which is particularly significant for warm-sector rainfall with its limited predictability.

Transient luminous events (TLEs) are electrical discharges in the upper atmosphere caused by vigorous thunderstorms. Six sprites, which are part of TLEs, were observed on 22 July 2013 from Mt. Fuji (3776 m above sea level), Japan. All the six sprites were associated with intense positive cloud-to-ground strikes (+CGs), whose causative positive charges can reside in the stratiform region. Consequently, we assumed that the main sprites causative charges could generate an in situ charging mechanism, accompanied by precipitation growth in the extensive stratiform region. Thus, we supposed that there can be a relationship between the time sequence of surface precipitation intensity and the sprite emissions. In this study, we conclude that time sequences and horizontal evolution of Mesoscale Convective Systems (MCSs) precipitation are associated with sprites. As the result, prior to sprites 1–5, the areal amount of strong precipitation (≥8 mm/h) increased considerably, and only a small increase occurred during sprite 6. Analyzing the time sequence of the percentage of strong and weak precipitation with respect to the total precipitation, it was found that sprites 1–6 occurred within 20 min after the local peaks with respect to strong precipitation compared to total precipitation. In particular, sprites 2–5 occurred very close to local peaks. The rise time to the first peak of the strong precipitation rate associated with the first sprite was 80 min, while the rise time to the last peak associated with sprite 6 was 30 min. The temporal differences until the peaks suggest that the charging speeds, or mechanisms, related to precipitation differ between sprites 1–5 and sprite 6 in parent MCSs.

Based on observation data, NCEP/NCAR (1°×1°) 6 h interval FNL reanalysis data、NCEP GFS (0.5°×0.5°) 6 h interval data, Doppler radar and mesoscale ground automatic station data, the environmental condition, triggering mechanism and the evolution of the convection system in the typhoon "Matmo" rainstorm in 2014 were analyzed. The numerical sensitivity experiments for intrusion of cold air intensity were also conducted. The results are as follows. (1) Rainstrom occurred during the process of typhoon transition. The invasion of cold air makes the thermal structure of the typhoon change, atmospheric baroclinic enhance in the periphery of typhoon and the stratification become more unstable, which is beneficial to the development of the mesoscale convective system. (2) The trigger of the convective system is caused by the intrusion of cold air in the boundary layer. The confrontation between cold air and warm air masses causes a strong convergence in the Eastern JiangHuai, which makes the precipitation echo persist. (3) The results of numerical sensitivity experiments show that the intrusion of cold air makes the outer region of the typhoon more statically unstable, which is conducive to the formation of deep vertical motion, prolonging and strengthening mesoscale convective systems. If cold air were too weak, the vertical motion in the convective system would be weak and so would the convection intensity. If cold air were too strong, although strong vertical motion could be developed in the convective system, the life span of the mesoscale convective system would be short, because the short time vertical motion could not be conducive to persistent strong precipitation.

Abstract Two different mesoscale convective system (MCS) events that produced the heavy rainfall over the Greater Jakarta (GJ) during 15–18 January 2013 period were investigated. The purpose of the present study is to analyze the atmospheric conditions of two different MCSs during the heavy rainfall. Data consist of 3 hourly rainfalls of meteorological stations, infrared satellite, sounding, 6-hourly surface wind and reanalysis data. The first MCS was developed at 16:00 LT on 14 January 2013 over the eastern coast of Sumatra covered an area of 249,732 km2 at maximum size, with about 16 h durations. The next MCS was developed at 22:00 LT on 16 January 2013 over the northern coast of the GJ in 9 h of duration, and maximum covered area around 55,829 km2. A warmer and moist air was observed on the low-level layer in the evening of 16 January 2013 (prior of second MCS), in comparison to 14 January 2013 event. Combination of both the surface strong wind perturbation and equivalent potential temperature in the second MCS might be contributed to heavy rainfall over the GJ than the first one.

Tulisan ini merupakan studi awal yang membuktikan pengaruh Mesoscale Convective System (MCS) terhadap curah hujan (CH) ekstrem di pesisir barat Sumatra dengan menggunakan citra rapidscan 10 menit Himawari-8 kanal IR1. Untuk mendapatkan data yang berkualitas, penulis melakukan koreksi data CH penakar Hellman terhadap data standar CH di Moelaboh (MLH), Sibolga (SBG), Teluk Bayur (TBR) dan Bengkulu (BKL) serta koreksi paralaks data citra Himawari-8. Dalam mengidentifikasi MCS, penulis menggunakan kriteria brightness temperature (BT) ≤ 221 derajat kelvin (K), luasan BT ≥ 10.000 km2 dan durasi ≥ 3 jam. Hasil penelitian mengindikasikan bahwa CH ekstrem bersamaan dengan keberadaaan MCS yang membuktikan bahwa CH ekstrem diakibatkan oleh MCS di MLB, SBG, TBR dan BKL. MCS tersebut sangat dipengaruhi oleh kemunculan Westerly Wind Burst (WWB) yang terhalangi oleh Bukit Barisan untuk kasus CH ekstrem di SBG dan TBR atau berinteraksi dengan angin pasat tenggara dari Samudra Hindia sebelah barat daya Sumatra untuk kasus CH ekstrem di BKL. Untuk kaus CH ekstrem di MLB, MCS terbentuk akibat interaksi angin pasat di Samudra Hindia sebelah barat Sumatra dan aliran siklonik sebelah barat MLB. This paper was a preliminary study that proved the impact of the mesoscale convective system (MCS) on extreme rainfall on the west coast of Sumatra using rapid scan imagery of 10 minutes Himawari-8 channel IR1. To get qualified data, we conducted the correction of rainfall data of Hellman gauge to the rainfall standard data in Moelaboh (MLH), Sibolga (SBG), Teluk Bayur (TBR), and Bengkulu (BKL) and the parallax correction to Himawari-8 imagery data. To identify MCS, we used brightness temperature (BT) ≤ 221 K, BT area ≥ 10.000 km2 and duration ≥ 3 hours as the criteria. The results indicated that extreme rainfall occured simultaneously with MCS proved that the extreme rainfall caused by MCS in MLB, SBG, TBR, and BKL. The MCS was greatly influenced by the appearance of westerly wind burst (WWB) which was blocked by Bukit Barisan for extreme rainfall cases in SBG and TBR or interacted with the southeast trade winds of the Indian Ocean in the southwest of Sumatra for extreme rainfall case in BKL. For extreme rainfall case in MLB, MCS was formed due to the interaction of trade winds of the Indian Ocean in the west of Sumatra and cyclonic flow in the west of MLB.

The influence of a mesoscale convective system (MCS) in the evolution of two wildfires that started during the afternoon of 17 June 2017 in Pedrógão Grande, Central Portugal is discussed and analysed using weather radar data, weather stations, video images and fire spread analysis. As the MCS approached the region, its convectively driven flows started to influence the fires. The overturning flows were formed by two main limbs: one organised as front-to-rear deep layer inflows that propagated over the convective region of the MCS and the other as rear-to-front mid-level inflows that descended below the anvil structure of the MCS. The rear-to-front inflows, while accelerating and descending to lower levels, contributed to modify the fires’ intensity and plume characteristics. After the two fires merged, the resulting junction fire became very intense and impossible to control. Then, a firestorm was generated, causing the deaths of 66 people. The main goal of this study is to detail the influence of the MCS in the fire spread, thus contributing to the general knowledge of outstanding fire behaviour modifications due to the influence of atmospheric convective processes.

Mesoscale convective systems (MCSs) can bring up to 60% of summer rainfall to the central United States but are not simulated by most global climate models. In this study, a new empirical orthogonal function based index is developed to isolate the MCS activity, similar to that developed by Wheeler and Hendon (2004) for the Madden-Julian Oscillation. The index is applied to compactly compare three conventional- and super-parameterized (SP) versions (3.0, 3.5, and 5.0) of the National Center for Atmospheric Research Community Atmosphere Model (CAM). Results show that nocturnal, eastward propagating convection is a robust effect of super-parameterization but is sensitive to its specific implementation. MCS composites based on the index show that in SP-CAM3.5, convective MCS anomalies are unrealistically large scale and concentrated, while surface precipitation is too weak. These aspects of the MCS signal are improved in the latest version (SP-CAM5.0), which uses high-order microphysics. Key Points A new EOF based index compactly evaluates the mid-latitude MCS signal in GCMs Central US summer MCS physics is a robust effect of cloud super-parameterization The MCS signal is most realistic in SP-CAM5.0 that uses high-order microphysics ©2013. American Geophysical Union. All Rights Reserved.

A region under rainfall is a contiguous spatial area receiving positive precipitation at a particular time. The probabilistic behavior of such a region is an issue of interest in meteorological studies. A region under rainfall can be viewed as a shape object of a special kind, where scale and rotational invariance are not necessarily desirable attributes of a mathematical representation. For modeling variation in objects of this type, we propose an approximation of the boundary that can be represented as a real valued function, and arrive at further approximation through functional principal component analysis, after suitable adjustment for asymmetry and incompleteness in the data. The analysis of an open access satellite dataset on monsoon precipitation over Eastern Indian subcontinent leads to explanation of most of the variation in shapes of the regions under rainfall through a handful of interpretable functions that can be further approximated parametrically. The most important aspect of shape is found to be the size followed by contraction/elongation, mostly along two pairs of orthogonal axes. The different modes of variation are remarkably stable across calendar years and across different thresholds for minimum size of the region. for this article, including a standardized description of the materials available for reproducing the work, are available as an online supplement. [ABSTRACT FROM AUTHOR]