Radar and lightning analyses of gigantic jet‐producing storms

Abstract

[1] An analysis of thunderstorm environment, structure, and evolution associated with six gigantic jets (five negative polarity, one positive) was conducted. Three of these gigantic jets were observed within detection range of very high frequency lightning mapping networks. All six were within range of operational radars and two-dimensional lightning network coverage: five within the National Lightning Detection Network and one within the Global Lightning Detection (GLD360) network. Most of the storms producing the jets formed in moist tropical or tropical-like environments (precipitable water ranged from 37 to 62 kg m À2 , and 0-6 km shear from 3.5 to 24.8 m s À1 ), featuring high convective available potential energy (1200-3500 J kg À1 ) and low lifted indices (À2.8 to À6.4). The storms had maximum radar reflectivity factors of 54 to 62 dBZ, and 10 dBZ echo contours reached 14-17 km. Storms covered by three-dimensional lightning mappers were near peak altitude of lightning activity (modes of the vertical distributions of radio sources were at altitudes colder than À50 C) and vertical reflectivity intensity, with overshooting echo tops around the times of their jets. Two of the other three jet-producing storms produced their jet around the time of a convective surge as indicated by radar data and likely featured overshooting tops. The observations suggest a link between convective surges, overshooting tops, and the occurrence of gigantic jets, similar to prior modeling studies.

A Thermodynamic, kinematic and microphysical analysis of a jet and gigantic jet‐producing Florida thunderstorm

“…For these types of storms, one might anticipate that negative GJs would tend to occur during the explosive storm development phase when the updraft is most intense. Yet this does not always appear to be the case with some reports in the literature of negative GJs occurring during the later stages of a thunderstorm's life cycle [e.g., Soula et al, 2011;Meyer et al, 2013]. Under these circumstances, it is possible that upper level shear may also play a role by enhancing the mixing at storm top or by differentially advecting the upper charge region downstream of the main central charge [van der Velde et al, 2010].…”

“…They report relatively large ranges in a number of standard convection-related parameters including CAPE (1200-3500 J/kg), PWAT (37-62 mm), tropopause height (12.5-17 km), melting level (3.5-5.1 km), and 0-6 km shear (3.5-25 ms À1 ). Only one of the ground-based jet events reported by Meyer et al [2013] is, unambiguously, a supercell as indicated by the 0000 UTC 17 April 2011 Morehead City N.C. sounding (taken about 3 h prior to the positive GJ event). As a measure of the deep layer (0 to 6 km) shear, the Bulk Richardson Number shear (BRNSHR) [Weisman and Klemp 1982;Stensrud et al, 1997] -the 25th percentile reported for tornadic storms [Thompson et al, 2003] and the northern Mexico storm of 13 May 2005, described as a high precipitation supercell by Meyer et al [2013], has a well-defined mesocyclone [van der Velde et al, 2007a] but is embedded in a relatively low-shear environment (SRH of 70 m 2 s À2 and BRNSHR of 6 m 2 s À2 ).…”

“…The deep layer shear (BRNSHR) is on the order of supercell magnitudes for three of the jet events-one of which is a remnant tropical disturbance. The 28 September 2010 Florida event is associated with deep convection (over the Gulf Stream) ahead of an early season cold front-with strong westerly flow aloft (>60 kt) and is not tropical storm related as reported in Meyer et al [2013]. ) are listed (from left to right, respectively) below the MUCAPE.…”

“…If the Krehbiel et al [2008] hypothesis is right about their origin being between screening charge and strong upper positive charge, then apparently some storms may have weak enough mixing at their top to make this possible. Conversely, overshoots and turbulent mixing at thunderstorm cloud top are fairly ubiquitous and thus not necessarily a unique signature for GJ production [Meyer et al, 2013]. The overshoot itself can be somewhat ephemeral, especially in weaker single/multicell convection where short lived, but intense, convective pulses (surges) are the norm.…”

“…Lu et al [2011] document two different GJ events (Florida and Oklahoma) but do not report on their meteorology. However, radar and satellite data from these two cases along with four other GJ events are presented by Meyer et al [2013]. They report relatively large ranges in a number of standard convection-related parameters including CAPE (1200-3500 J/kg), PWAT (37-62 mm), tropopause height (12.5-17 km), melting level (3.5-5.1 km), and 0-6 km shear (3.5-25 ms À1 ).…”