Crucial roles of eastward propagating environments in the summer MCS initiation over the U.S. Great Plains

Journal Article · Fri Aug 27 00:00:00 EDT 2021 · Journal of Geophysical Research: Atmospheres

DOI:https://doi.org/10.1029/2021JD034991· OSTI ID:1821865

Song, Fengfei ^[1]; Feng, Zhe  ^[1]; Leung, Lai-Yung  ^[1]; Pokharel, Binod ^[2]; Wang, Simon ^[2]; Chen, Xingchao ^[3]; Sakaguchi, Koichi ^[1]; Wang, Chichia ^[2]

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1. BATTELLE (PACIFIC NW LAB)
2. Utah State University
3. Pennsylvania State University

Mesoscale convective systems (MCSs) frequently occur over the U.S. Great Plains during summer. An analysis using self-organizing map is conducted to identify four types of summer MCS initiation environments during 2004-2017. The first two types feature favorable large-scale environments at both upper and low levels, while Type-3 has favorable lower-level and surface conditions but unfavorable upper-level circulation, and Type-4 features the most unfavorable large-scale environments for MCS initiation. Despite the unfavorable large-scale environment, the convection-centered environments in Type-4 are favorable for MCS initiation and similar to the first two types, suggesting a role of sub-synoptic disturbances as an MCS precursor. All four types of the MCS initiation delineate a clear eastward propagating feature in many fields, such as upper-level potential vorticity/geopotential height, surface pressure and surface equivalent potential temperature, upstream up to 25°-longitude west of and ~36 hours before the MCS initiation. The propagating environments and local, non-propagating low-level moisture are found to be important in MCS initiation at the foothill of the Rocky Mountains, but over the central Great Plains, it is the coupling of dynamical and moisture anomalies associated with propagating waves that results in the MCS initiation. By tracking MCSs and mid-tropospheric perturbations (MPs), a type of sub-synoptic disturbances with Rocky Mountains origin, ~30% of MPs is 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, suggesting MPs to be a source of intense MCSs in summer.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1821865
• Report Number(s): PNNL-SA-157771
• Journal Information: Journal of Geophysical Research: Atmospheres, Vol. 126, Issue 16
• Country of Publication: United States
• Language: English