Kinematic and thermodynamic conditions related to convective systems with a bow echo in Poland

Abstract

Severe wind events are often related to the occurrence of mesoscale convective systems with arch-shaped radar reflectivity, i.e., a bow echo. In this research, the kinematic and thermodynamic conditions associated with 91 bow echo cases which occurred in the warm season (i.e., from early April until late September) in Poland (2007-2014) were analyzed. The environmental conditions were determined primarily based on the upper air soundings, and additionally on data obtained from ERA-Interim reanalysis. The results indicate that there is a relatively wide range of shear and instability environments associated with bow echoes over Poland. The identified cases occurred both in weakly forced environments, and as well developed in dynamic synoptic patterns with low instability. We have also found cases with strong instability and significantly increased shear values. The combination of a moist boundary layer and steep mid-tropospheric lapse rate usually resulted in moderate to high CAPE values for identified bow echo cases. The median of surface-based CAPE was equal to 1594 J/kg (Mean Layer CAPE = 1038 J/kg) for soundings, and to 1622 J/kg (Mean Layer CAPE = 1275 J/kg) for ERA-Interim. Bow echo environments also showed significantly increased potential for strong downdrafts and damaging outflow winds (the median Downdraft CAPE reached 849 J/kg for soundings and 734 J/kg for ERA-Interim). Bow echoes were usually associated with the occurrence of strong air flow in the troposphere. The presence of a jet stream in the middle and upper troposphere contributed to the development of increased vertical wind shear values. The median of 0-6-km shear exceeded 15 m/s, whereas for 0-3-km shear, it was approximately equal to 12.5 m/s and to 7 m/s for 0-1-km shear. 1 Introduction Mesoscale convective systems (MCSs) can pose a significant risk to human life and health, as well as huge losses in the economy. Every year across Europe, several thousand destructive wind, tornado, hail, or heavy rain events cause temporary disorganization of life. These phenomena are frequently connected with the movement of strong meso-β-scale convective systems with arch-shaped radar reflectivity, i.e., bow echo. According to Klimowski et al. (2003), at least 29% of all severe wind reports recorded in the USA (Northern High Plains) during the warm seasons of 1996-1999 were caused by the activity of convective systems with a bow echo (24% of fatal/deadly nontornadic convective wind storms in the USA from 1998 to 2007 (all seasons)-Schoen and Ashley 2011). Gatzen (2013), in turn, pointed out that 58% of severe wind reports (≥ 26 m/s) in Germany were related to a bow echo (for the warm season between 1997 and 2011). Research on the spatial and temporal variability of bow echo occurrence focused primarily on the area of the USA and Central Europe. They included both warm season

Derecho Evolving from a Mesocyclone—A Study of 11 August 2017 Severe Weather Outbreak in Poland: Event Analysis and High-Resolution Simulation

“…4). Such values are known to be conducive to the development of linear MCSs capable of producing damaging wind gusts when combined with sufficient thermodynamic instability (Doswell and Evans 2003;Cohen et al 2007;Weisman et al 2013;Celi nski-Mysław et al 2018). Similar estimates of a wind shear have been confirmed by sounding measurements taken at 1200 UTC in Prague and Prostejov in the Czech Republic (airflow of 20-25 m s 21 at 700-500 hPa).…”

“…Long-lived MCSs that are persistent in producing widespread damaging winds are known as derechos (Johns and Hirt 1987). European studies on derecho have focused mainly on the analysis of environmental conditions (Gatzen 2004;Punkka et al 2006;López 2007;Pú cik et al 2011;Simon et al 2011;Hamid 2012;Gospodinov et al 2015;Toll et al 2015;Mathias et al 2017;Celi nski-Mysław et al 2018) and multiannual summaries (Gatzen et al 2011;Gatzen 2013; Celi nski-Mysław and Matuszko 2014; Celi nski-Mysław and Palarz 2017). The results from these studies indicate that a few such events occur each year in Europe including Poland.…”

“…The most common ingredients for a wellorganized MCS are sufficient amounts of moisture in the boundary layer, steep low and midlevel temperature lapse rates, strong vertical wind shear, a persistent lifting mechanism, and a parallel orientation between deeplayer wind and shear vectors leading to a fast system propagation (Evans and Doswell 2001;Kuchera and Parker 2006;Cohen et al 2007;Coniglio et al 2010;Pú cik et al 2015;Taszarek et al 2017). A wind shear with a magnitude of approximately 15 m s 21 in a 0-3-km layer is considered conducive for a long-lived linear MCS capable of producing widespread wind damage (Coniglio and Stensrud 2001;Weisman and Rotunno 2004;Weisman et al 2013;Mathias et al 2017;Celi nski-Mysław et al 2018). Depending on the environmental conditions, we can distinguish a progressive derecho typical for high thermodynamic instability, a serial derecho where the wind shear and synoptic-scale lift play a dominant role, and a hybrid derecho that is a mixture of both (Johns and Hirt 1987;Johns 1993).…”

“…Baseline circulation patterns are identified for 500 hPa, 850 hPa, and mean sea level pressure fields. Kinematic and thermodynamic conditions are assessed within the use of parameters that in the previous studies have been considered valuable for forecasting deep moist convection and well-organized MCSs (Doswell et al 1996;Evans and Doswell 2001;Craven and Brooks 2004;Cohen et al 2007;Coniglio et al 2007Coniglio et al , 2011Weisman et al 2013;Pú cik et al 2015;Taszarek et al 2017;Celi nski-Mysław et al 2018). These include: mostunstable (MU) convective available potential energy (CAPE), 0-6 km above ground level (AGL) deep-layer shear (DLS), 0-3 km AGL midlevel shear (MLS), 800-500-hPa vertical temperature lapse rate, 0-500 m AGL mixed-layer mixing ratio, and precipitable water.…”

VDRAS and Polarimetric Radar Investigation of a Bow Echo Formation After a Squall Line Merged With a Preline Convective Cell

“…The lifted condensation level (LCL, 899 hPa) and level of free convection (LFC, 899 hPa) were at ~0.8 km AGL, and the atmosphere was relatively dry above ~700 hPa. Notably, the convective available potential energy (CAPE, 1,266 J kg −1 ) in this case was smaller than that of bow echoes in central Europe (~1,600 J kg −1 ) (Celiński‐Mysław et al, 2019) and in the central part of North America (2,000~2,500 J kg −1 ) (Atkins et al, 2005; Bluestein & Jain, 1985; Wakimoto et al, 2014) but was comparable with those in the subtropics (~700–1,300 J kg −1 ) (Chen & Chou, 1993; Meng et al, 2012) and the midlatitudes (~1,200–1,600 J kg −1 ) (Parker & Johnson, 2000; Wyss & Emanuel, 1988).…”