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1. Can Pre-Storm Errors in the Low-Level Inflow Help Predict Spatial Displacement Errors in MCS Initiation?

   https://doi.org/10.3390/atmos12010007  

   Vertz, Nicholas J.; Gallus, William A.; Squitieri, Brian J. (January 2021, Atmosphere)

   null (Ed.)

   The Great Plains low-level jet (LLJ) is a contributing factor to the initiation and evolution of nocturnal Mesoscale Convective Systems (MCSs) in the central United States by supplying moisture, warm air advection, and a source of convergence. Thus, the ability of models to correctly depict thermodynamics in the LLJ likely influences how accurately they forecast MCSs. In this study, the Weather Research and Forecasting (WRF) model was used to examine the relationship between spatial displacement errors for initiating simulated MCSs, and errors in forecast thermodynamic variables up to three hours before downstream MCS initiation in 18 cases. Rapid Update Cycle (RUC) analyses in 3 layers below 1500 m above ground level were used to represent observations. Correlations between simulated MCS initiation spatial displacements and errors in the magnitude of forecast thermodynamic variables were examined in regions near and upstream of both observed and simulated MCSs, and were found to vary depending on the synoptic environment. In strongly-forced cases, large negative moisture errors resulted in simulated MCSs initiating further downstream with respect to the low-level flow from those observed. For weakly-forced cases, correlations were weaker, with a tendency for smaller negative moisture errors to be associated with larger displacement errors to the right of the inflow direction for initiating MCSs. 

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2. Understanding mesoscale convective processes over the Congo Basin using the Model for Prediction Across Scales-Atmosphere (MPAS-A)

   https://doi.org/10.5194/egusphere-2025-3591  

   Zhao, Siyu; Fu, Rong; Núñez_Ocasio, Kelly; Nystrom, Robert; He, Cenlin; Zhang, Jiaying (August 2025, EGU)

   Abstract. The Congo Basin in Central Africa is one of three convective centers in the tropics, characterized by a high proportion of precipitation produced by mesoscale convective systems (MCSs). However, process-level understanding of these systems and their relationship to environmental factors over the Congo Basin remains unclear, largely due to scarce in-situ observations. This study employs the Model for Prediction Across Scales–Atmosphere (MPAS-A), a global cloud-resolving model, to investigate MCSs in this region. Compared to satellite-observed brightness temperature (Tb), MPAS-A realistically simulates key MCS features, allowing a detailed comparison between two mesoscale convective complex (MCC) cases: one over the southern mountainous region (MCC-south) and the other over the northern lowland forests (MCC-north). MCC-south is larger, longer-lived, and moves a longer distance than MCC-north. Our analysis shows that MCC-south is supported by higher thermodynamic energy and more favorable vertical wind shear ahead of the system. The shear extends up to 400 km, explains up to 65 % of the Tb variance, and is well balanced by a moderately strong cold pool. In contrast, MCC-north features weaker, localized shear near the center and a stronger cold pool. The African Easterly Jet helps maintain the shear in both cases, but an overly strong jet may suppress low-level westerlies and weaken convection. These results show how latitude and topography modulate environmental influences on Congo Basin MCS developments. The findings underscore the value of global cloud-resolving models in data-sparse regions for understanding convective systems and their impacts on weather extremes and societal risks. 

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3. Impacts of Coastal Terrain on Warm-Sector Heavy-Rain-Producing MCSs in Southern China

   https://doi.org/10.1175/MWR-D-21-0190.1  

   Zhang, Murong; Rasmussen, Kristen L.; Meng, Zhiyong; Huang, Yipeng (March 2022, Monthly Weather Review)

   Abstract Warm-sector heavy rainfall in southern China refers to the heavy rainfall that occurs within a weakly forced synoptic environment under the influence of monsoonal airflows. It is usually located near the southern coast and is characterized by poor predictability and a close relationship with coastal terrain. This study investigates the impacts of coastal terrain on the initiation, organization, and heavy rainfall potential of MCSs in warm-sector heavy rainfall over southern China using quasi-idealized WRF simulations and terrain-modification experiments. Typical warm-sector heavy rainfall events were selected to produce composite environments that forced the simulations. MCSs in these events all initiated in the early morning and developed into quasi-linear convective systems along the coast with a prominent back-building process. When the small coastal terrain is removed, the maximum 12-h rainfall accumulation decreases by ∼46%. The convection initiation is advanced ∼2 h with the help of orographic lifting associated with flow interaction with the coastal hills in the control experiment. Moreover, the coastal terrain weakens near-surface winds and thus decreases the deep-layer vertical wind shear component perpendicular to the coast and increases the component parallel to the coast; the coastal terrain also concentrates the moisture and instability over the coastal region by weakening the boundary layer jet. These modifications lead to faster upscale growth of convection and eventually a well-organized MCS. The coastal terrain is beneficial for back-building convection and thus persistent rainfall by providing orographic lifting for new cells on the western end of the MCS, and by facilitating a stronger and more stagnant cold pool, which stimulates new cells near its rear edge. 

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4. Dynamics Governing a Simulated Bow-and-Arrow-Type Mesoscale Convective System

   https://doi.org/10.1175/MWR-D-22-0091.1  

   Zhang, Shushi; Parsons, David B.; Xu, Xin; Sun, Jisong; Wu, Tianjie; Abulikemu, Abuduwaili; Xu, Fen; Chen, Gang; Shen, Wenqiang; Liu, Lihang; et al (March 2023, Monthly Weather Review)

   Abstract The bow-and-arrow Mesoscale Convective System (MCS) has a unique structure with two convective lines resembling the shape of an archer’s bow and arrow. These MCSs and their arrow convection (located behind the MCS leading line) can produce hazardous winds and flooding extending over hundreds of kilometers, which are often poorly predicted in operational forecasts. This study examines the dynamics of a bow-and-arrow MCS observed over the Yangtze–Huai Plains of China, with a focus on the arrow convection provided. The analysis utilized backward trajectories and Lagrangian vertical momentum budgets to simulations employing the WRF‐ARW and CM1 models. Cells within the arrow in the WRF-ARW simulations of the MCS were elevated, initially forming as convectively unstable air within the low-level jet (LLJ), which gently ascended over the cold pool and converged with the MCS’s mesoscale convective vortex (MCV) at higher altitudes. The subsequent ascent in these cells was enhanced by dynamic pressure forcing due to the updraft being within a layer where the vertical shear changed with height due to the superposition of the LLJ and the MCV. These dynamic forcings initially played a larger role in the ascent than the parcel’s buoyancy. These findings were bolstered by idealized simulations employing the CM1 model. These results illustrate a challenge for accurately forecasting bow-and-arrow MCSs as the updraft magnitude depends on dynamical forcing associated with the interaction between vertical shear associated with the environment and due to convectively generated circulations. 

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5. Dynamics and Energetics Associated With Two East Pacific Easterly Waves During the OTREC Campaign in August 2019

   https://doi.org/10.1029/2024JD042266  

   Zhou, Yihao; Maloney, Eric_D (April 2025, Journal of Geophysical Research: Atmospheres)

   Abstract This study investigates the vertical structure and related dynamical and energy conversion processes that aided the development of two east Pacific easterly waves (EWs) during the 2019 OTREC (Organization of Tropical East Pacific Convection) campaign period. The initial mesoscale convective systems (MCSs) that seeded both disturbances formed near the Panama Bight and developed into EWs near the Papagayo jet exit region. In the MCS stage, both disturbances were characterized by top‐heavy vertical motions and midlevel vorticity near the maximum vorticity center. The deep convection caused strong latent heating and eddy available potential energy (EAPE) generation and conversion to eddy kinetic energy (EKE) in the upper levels. When the disturbances moved to the south of the Papagayo jet, they interacted with the low‐level shear vorticity there, enhancing low‐level stretching and vorticity. Subsequently, the top‐heavy upward motion intensified and led to enhanced stretching and vorticity intensification at midlevels. The enhanced stretching on the southwest side also favored the formation of southwest‐northeast tilted vorticity at midlevels that characterizes EWs. After the EWs formed near the jet exit, the vertical motion weakened and became more bottom‐heavy, with the maximum vorticity shifting to lower levels. This change in the vertical motion profile near the jet exit region is likely modulated by the lower sea surface temperature, reduced moisture, and weaker convective instability. While EAPE‐to‐EKE conversion weakened during this period, the low‐level barotropic conversion of EKE in the jet exit served as the primary energy source for the EWs. 

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