Crucial Roles of Eastward Propagating Environments in the Summer MCS Initiation Over the U.S. Great Plains. Issue 16 (16th August 2021)

• Record Type: Journal Article
• Authors: Song, Fengfei; Feng, Zhe; Leung, L. Ruby; Pokharel, Binod; Wang, S.‐Y. Simon; Chen, Xingchao; Sakaguchi, Koichi; Wang, Chi‐chia
• Is Part Of: Journal of geophysical research. Volume 126:Issue 16(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-08-16
• Subjects: mesoscale convective systems -- eastward propagating environments -- mid‐tropospheric perturbations -- large‐scale environments -- convection initiation -- local moisture; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD034991
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: This study aims to further understand the environments supporting summer mesoscale convective system (MCS) initiation in the U.S. Great Plains. A self‐organizing map analysis is conducted to identify four types of summer MCS initiation environments during 2004–2017: Type‐1 and Type‐2 feature favorable large‐scale environments, Type‐3 has favorable lower‐level and surface conditions but unfavorable upper‐level circulation, while Type‐4 features the most unfavorable large‐scale environments. Despite the unfavorable large‐scale environment, convection‐centered composites reveal the presence of favorable sub‐synoptic scale environments for MCS initiation in Type‐3 and Type‐4. All four types of MCS initiation environments delineate clear eastward propagating features in many meteorological fields, such as potential vorticity, surface pressure, and equivalent potential temperature, upstream up to 25° west of and ∼36 h before MCS initiation. While the propagating environments and local, non‐propagating low‐level moisture are important to MCS initiation at the foothill of the Rocky Mountains, MCS initiation in the Great Plains is supported by the coupled dynamical and moisture anomalies, both associated with eastward propagating waves. Hence, MCSs initiated in the plains can produce more rainfall than those initiated at the foothill due to a more abundant moisture supply. By tracking MCSs and mid‐tropospheric perturbations (MPs), a unique type of sub‐synoptic disturbances with Rocky Mountains origin, it is shown that ∼30% of MPs are associated with MCS initiation, mostly in Type‐4. Although MPs are related to a small fraction of MCS initiation, MCSs that are associated with MPs tend to produce more rainfall in a larger area with a stronger convective intensity. Plain Language Summary: During spring and summer, organized and traveling thunderstorms are commonplace in the U.S. Great Plains. While these thunderstorms contribute considerably to the seasonal rainfall, the summertime thunderstorm initiation is less well understood because the large‐scale meteorological patterns are substantially weaker in summer than spring and the smaller‐scale perturbations become more important but are harder to capture by the sparse observation network. Here, we combine newly developed tracking records of these traveling thunderstorms with a modern atmospheric data set to examine the thunderstorm initiation environments in summer. We find that eastward propagating environment exist several days before the thunderstorm initiation. The relative importance of the ingredients in the propagating environments to thunderstorm initiation changes from the foothill of the Rocky Mountains to the central plains as the coupling between moisture and wind pattern becomes increasingly critical. Hence, at the beginning several hours of thunderstorms, their rainfall is heavier in the plains due to more moisture supply, compared to thunderstorms initiated at the foothill. With available data of a unique type of weather disturbances originated from the Rocky Mountains, we are able to quantify the contribution of this type of disturbances to the summertime thunderstorm initiation. Key Points: Summer mesoscale convective systems (MCSs) in the U.S. Great Plains can initiate under unfavorable large‐scale environments when favorable sub‐synoptic forcing is present Eastward propagation is found for both large‐scale and sub‐synoptic environments, up to 25° west of and 36 h prior to MCS initiation About 30% of mid‐tropospheric perturbations originated from the Rocky Mountains initiate intense MCSs under weak large‐scale forcing