Structure and evolution of a midwestern storm during VORTEX-95 as determined from airborne Doppler data

A midwestern squall line which occurred on 2 June 1995 near the border of New Mexico and Texas was observed and sampled by NWS WSR-88D and two airborne radars, namely, NOAA P-3 Lower Fuselage Radar and NCAR ELDORA. Within a four-hour time span, the squall line initially formed from a convective cell close to a surface dryline, through the subsequent “secondary development” and merging processes, these storms eventually organized into a squall line moving toward the east. Interestingly, cells within the squall line posses their major convective activities at the western end of the storm body. This structural feature together with the three-dimensional characteristics of each cell within the line are different from those observed in a traditional quasi two-dimensional squall line in the Mid-west. Our findings reveal that the presence of a larger directional and speed shear in the lower troposphere, due to the approaching mid-tropospheric large-scale short wave, played a key role in the formation and development of this convective system being investigated. The environmental conditions and storm evolution agree well with those reported in the previous numerical simulation studies using a cloud model. These numerical studies consistently showed that the combined effects of large-scale low-level wind shear and atmospheric thermal instability (i.e., a bulk Richardson number) uniquely determine the structure and evolution of a midwestern mesoscale convective system, such as a squall line.; A dual-Doppler synthesis was conducted to study some structural features of two individual cells, embedded within the squall line, using ELDORA data. The differences between this line structure and the traditional squall line are identified and explained. With the aid of ELDORA high resolution data set, a detailed three-dimensional wind field was derived at every analysis level. The thermodynamic retrieval method was then employed to recover the pressure field from the detailed wind field. Subsequently, the derived wind and pressure fields were used to investigate the kinematic and dynamic structures of a mid-level mesocyclone associated with one of the storms embedded within the three-dimensional squall line.