Radar and Lightning Observations of the 3 June 2000 Electrically Inverted Storm from STEPS

Abstract

This study addresses the kinematic, microphysical, and electrical evolution of an isolated convective storm observed on 3 June 2000 during the Severe Thunderstorm Electrification and Precipitation Study field campaign. Doppler-derived vertical velocities, radar reflectivity, hydrometeor classifications from polarimetric radar, and Lightning Mapping Array (LMA) charge structures are examined over a nearly 3-h period. This storm, characterized as a low-precipitation supercell, produced modest amounts of hail, determined by fuzzy-logic hydrometeor classification as mostly small (<2 cm) hail, with one surface report of large (≥2 cm) hail. Doppler-derived updraft speeds peaked between 20 and 25 m s?1, and reflectivity was never greater than 60 dBZ. The most striking feature of this storm was its total lack of cloud-to-ground (CG) lightning. Though this storm was electrically active, with maximum flash rates near 30 per minute, no CG flashes of either polarity were detected. The charge structure inferred from the LMA observations was consistent with an inverted dipole, defined as having a midlevel positive charge region below upper-level negative charge. Inverted charge structures have typically been considered conducive to producing positive CG lightning; however, the 3 June storm appeared to lack the lower negative charge layer below the inverted dipole that is thought to provide the downward electrical bias necessary for positive CG lightning.