Tropical mesoscale convective system formation environments

Abstract

Mesoscale convective systems (MCSs) in the tropics play an integral role in the water cycle, are associated with local hazardous weather conditions, and have significant remote impacts on the midlatitude jet stream. Although it is known that MCSs occur in relatively moist environments, it is unclear how far in advance favorable ingredients (lift, instability, and moisture) in the mesoscale environment precede MCS formation. In this study, an automated MCS tracking algorithm and global reanalyses are used to examine the pre-MCS environment for 3295 MCSs that occurred in the tropics in a 3-month period. Results showed that increased water vapor and mesoscale ascent implied by low-level convergence and upper-level divergence preceded MCS formation by up to 24 h. Regional variations in pre-MCS environment conditions were apparent and are discussed. Future work will study to what extent these moisture and wind anomalies can be used to predict MCS formation.

Synoptic Control on the Initiation and Rainfall Characteristics of Warm‐Season MCSs Over the South China Coast

“…The correlation analysis was also performed using the fields 2.5 hr prior to the initiation of MCSs, and the results are presented in Figures 14-16. Previous studies have documented that favorable environments can precede MCS formation by several hours (e.g., Galarneau Jr. et al, 2023). Nevertheless, we also tested the environmental fields at different leading times of MCS initiation, Figure 14 shows that MCS rainfall characteristics (i.e., the maximum area, maximum hourly rainfall, and maximum hourly heavy rainfall) over the SCC are significantly correlated with the synoptic-scale dynamic and thermodynamic conditions under P1.…”

“…The correlation analysis was also performed using the fields 2.5 hr prior to the initiation of MCSs, and the results are presented in Figures 14–16. Previous studies have documented that favorable environments can precede MCS formation by several hours (e.g., Galarneau Jr. et al., 2023). Nevertheless, we also tested the environmental fields at different leading times of MCS initiation, and the results showed minimal differences, indicating the relative stability of the large‐scale environment on the timescale of MCSs.…”

Influence of sea stratification and troposphere stability over the Coastal Squall Lines of Eastern Amazon

“…Environmental variables of the troposphere were obtained from ERA5, which is distributed by The European Centre for Medium-Range Weather Forecasts (ECMWF - (Hersbach et al, 2020)). Including a series of improvements from the previous ERA-Interim dataset, ERA5 was used in previous studies about convective systems in tropical regions (Angulo-Umana and Kim, 2023;Galarneau Jr et al, 2023). The variables used in this work were air temperature, wind velocity (zonal and meridional), and specific humidity.…”

Environmental Controls on MCS Lifetime Rainfall Over Tropical Oceans

“…Recent studies indicated that the lifecycles of MCSs dominate the precipitation‐moisture coupling process over the tropical oceans. High lower‐free‐tropospheric moisture content seems to be a necessary condition for the organization of tropical oceanic MCSs (Ahmed & Schumacher, 2015; X. Chen, Leung, Feng, & Yang, 2022; Galarneau et al., 2023; Schiro et al., 2020; Wolding et al., 2020).…”

“…High lower-free-tropospheric moisture content seems to be a necessary condition for the organization of tropical oceanic MCSs (Ahmed & Schumacher, 2015;X. Chen, Leung, Feng, & Yang, 2022;Galarneau et al, 2023;Schiro et al, 2020;Wolding et al, 2020).…”