The Mechanism and Predictability of an Elevated Convection Initiation Event in a Weak-Lifting Environment in Central-Eastern China

Abstract

An elevated convection initiation (CI) of a quasi-linear mesoscale convective system (MCS) that occurred in a weak-lifting environment in the early morning on 23 June 2016 in central-eastern China was investigated using observational analysis and convection-permitting numerical simulations. This MCS gradually developed into a surface-based MCS and eventually produced a strong supercell that spawned an EF4 tornado in Yancheng City of Jiangsu Province and killed 98 people. This elevated MCS was initiated ahead of a surface front without identifiable boundaries at the surface. An elevated moist absolutely unstable layer (MAUL) was found to be conducive to the CI. The MAUL provided negligible convective inhibition and contributed to CI without strong-lifting mechanisms. Numerical simulation results showed that the formation of the elevated MAUL was mainly attributed to adiabatic cooling by weak vertical ascent and sufficient horizontal moisture transport near the terminus of a low-level jet. The weak vertical ascent before the CI was sloping and was likely to be relevant to the layer-lifting process associated with the realization of potential instability. The results showed that the MAUL in this weak-lifting environment was characterized by a shallower depth, a weaker lapse rate, and a longer sustaining period than the conditions in a strong-lifting environment. The predictability of this elevated CI case was examined using a 10-member ensemble forecast. A total of 80% of the ensemble members captured the CI. Rather than a difference in lifting, whether having an elevated MAUL or not was the major difference between CI and non-CI members in the present case.

Convection Initiation Resulting From the Interaction Between a Quasi‐Stationary Dryline and Intersecting Gust Fronts: A Case Study

“…It is a process in which a potentially unstable air parcel passes through its level of free convection (LFC) to initiate buoyant updraft growth with the release of instability. The ability to forecast when and where a new convective system will be initiated is important for disaster preparedness; therefore, CI has been extensively researched in recent decades (e.g., Campbell et al, ; Markowski et al, ; Peters & Hohenegger, ; Su & Zhai, ; Trier et al, ; Weckwerth & Parsons, ; Wilson & Roberts, ; Zhang et al, ; Ziegler & Rasmussen, ). However, predicting the precise location and timing of CI remains a challenge partly due to the lack of spatially and temporally dense observations, especially in the planetary boundary layer (PBL).…”

Initiation of an Elevated Mesoscale Convective System With the Influence of Complex Terrain During Meiyu Season

“…In this study, following the widely used MCS and CI definition based on radar reflectivity (Romatschke et al., 2010; Trier et al., 2017; Xiao et al., 2017; Zhang et al., 2019), the value of 40 dBZ is used as the reflectivity threshold for the convective precipitation; MCS is identified by a continuous or quasi‐continuous band of 40dBZ reflectivity that extends for at least 50 km in at least one direction; and CI is determined when and where the radar echo first reaches 40 dBZ.…”

“…Zhang et al. (2019) unveiled mechanisms of an elevated CI by analyzing the thermodynamic environment. They found that the existence of an elevated moist absolutely unstable layer was conducive to the elevated CI, but the dynamic mechanisms were not thoroughly discussed.…”

Atmospheric Structure for Convective Development in the Events of Cloud Clusters over the Korean Peninsula

“…In this subsection, we compare major features of atmospheric environment for CCs over the Korean peninsula with those for elevated MCSs over the central US (e.g., Moore et al 2003;Wilson and Roberts 2006;etc. ) and central East China (He et al 2018;Zhang et al 2019). Convection over the front in CCML events may be classified as elevated convection over the cold side of surface boundary.…”

“…Recently, He et al (2018) found an occurrence of elevated convection in an event of a nocturnal squall line along the Meiyu Front over central East China, in which the main convection was initiated along a mesoscale convergence line above a stable boundary layer. Zhang et al (2019) showed an elevated MCS that was initiated ahead of a surface front without identifiable boundaries at the surface, and demonstrated that an elevated moist absolutely unstable layer (i.e., a saturated layer within which θ e decreases with height) was found to be conducive to the elevated CI.…”