Electrical structure in thunderstorm convective regions: 1. Mesoscale convective systems

Abstract

Abstract. Electric field (E) soundings through convective regions of mesoscale convective systems (MCSs) are examined in this paper. Ten E soundings through updrafts in MCS convective regions and five soundings in MCS convective regions outside updrafts are used to show that a typical electrical structure exists in this region. These 15 E soundings plus one other previously published sounding, which is included in this analysis, comprise all known soundings in the convective region of MCSs. The basic charge structure identified in MCS updrafts consists of four charge regions, alternating in polarity, with the lowest region positive and the highest region negative. The basic charge structure outside updrafts in MCS convective regions has six charge regions, alternating in polarity, with a positive charge region lowest. Maximum E magnitudes of both polarities are larger and are located at lower heights in soundings outside updrafts compared to those within updrafts. Excepting the upper positive charge, inferred charge regions are shallower and have larger charge densities outside updrafts. The center of the main negative charge is lower and warmer outside updrafts (5.5 km,-6.2øC) than within updrafts (6.9 km,-15.7øC). These features inside and outside updrafts are incorporated in a new conceptual model of MCS convective region charge structure. Also, an expanded conceptual model is developed, using previously published data from other parts of MCSs. This more complete conceptual model shows the typical electrical charge, airflow, and reflectivity features in the stratiform region, the transition zone, and the convective region of midlatitude mesoscale convective systems.

Serial soundings of electric field through a mesoscale convective system

“…As in previous studies [e.g., Stolzenburg et al, 1998aStolzenburg et al, , 1998b] the altitude and density of net charge in the cloud are determined from the vertical E z sounding using a one-dimensional approximation to Gauss's law. Depths in the sounding through which the slope of E z is quasilinear with height correspond to regions of charge, the polarity of the slope yields the charge polarity, and the magnitude of the slope is proportional to the average charge density.…”

“…One of the goals of MEaPRS was to make electric field soundings across a symmetric leading line/trailing stratiform MCS so that we could test how well the conceptual model of Stolzenburg et al [ 1998a] fits with data from a single MCS. Unfortunately, the system on June 5, 1998, was not an ideal symmetric leading line/trailing stratiform MCS because it had significant motion parallel to the convective line and because the trailing stratiform region was underdeveloped at the time and place of our last two soundings.…”

Electric field values observed near lightning flash initiations

“…[13] For the sounding shown in Figure 2b (91153), the radiosonde data end at time of the lightning flash, although the E data continue and the balloon ascends for another 17.5 min (subsequent E data are not shown; see Stolzenburg et al [1998] for complete sounding). The E before the flash was À331 kV m À1 (scaled), or 118% of RB th .…”

Transient luminous events above two mesoscale convective systems: Storm structure and evolution

“…[4] However, balloon-borne electric field meter measurements have established that multiple positive charge layers can exist with the stratiform region of an MCS [Chauzy et al, 1985;Schuur et al, 1991;Marshall and Rust, 1993;Stolzenburg et al, 1994Stolzenburg et al, , 1998Stolzenburg et al, , 2001. In addition, the number and altitudes of the positive charge layers appear to depend on MCS morphology, with differences seen between asymmetric and symmetric MCSs [Schuur and Rutledge, 2000a], as well as between bow echo, "squall line," and predominantly stratiform MCSs [Marshall and Rust, 1993].…”