Total lightning characteristics of storms: supercells and cells within mesoscale convective systems

The Lightning Detection and Ranging (LDAR II) network has shown the capability to increase situational awareness for thunderstorm forecasts (both severe and non-severe) in the Dallas-Fort Worth, TX region. In combination with radar and cloud-to-ground (CG) lightning information, the LDAR II gives an excellent view into the 3-D evolution of thunderstorm processes. Cell-based lightning characteristics, especially lightning height information, were related to storm intensity (updraft strength) in many of the storms examined.

LDAR II source density patterns indicated dynamical storm processes. A lightning hole (an annulus of large source density surrounding a small region (< 10 km diameter) of weaker density values) was observed in the 6 April 2003 supercell case. This feature infers the location of an intense updraft; however, maximum 40 dBZ echo height was not collocated with the hole. The hole was persistent for over an hour of the storm's lifetime, and its diameter was consistent with that of an updraft. Another distinct feature noticed with both the 6 April 2003 and 13 October 2001 supercells was a double maximum in negative CG flash density. Each maximum was located where one might expect downdrafts to occur within a supercell (rear and front flanks). Straight-line severe wind events associated with the 13 October 2001 and 27 May 2002 storm systems revealed comma-shape/bow source density structures. These are analogous to the radar-detected bow echo.

The relationship between lightning cell characteristics and severe wind reports was inconsistent. The 13 October report occurred while the storm was weakening and the 27 May storm was intensifying during a wind report. Each of these wind events were associated with a reflectivity bow echo embedded within a mesoscale convective system (MCS). It is likely that system processes (rear inflow jet development) determined the time and location of the severe surface winds, not individual cell processes. Hence, a relationship between cell characteristics and high wind events in an MCS can be expected to be weak and/or inconsistent.

In comparison to these organized thunderstorm events, a pulse thunderstorm was examined with this data. Two isolated cells merged on 27 June 2001. Intensification of the storm was clearly shown using total lightning and radar data during and immediately after the merger. Flash rates increased from 56 to 180 flashes (5 minutes)-1 and the lightning top (95th percentile source altitude) elevated over 2 km in a 25 minute period.

Using total lightning data in conjunction with radar data can aid forecasters in diagnosing and predicting storm intensity. An advantage of data like LDAR II is that its data stream is practically continuous. As opposed to radar data, images and characteristics of storms can be updated every minute. As with radar data, there is a limit on the useful range of the data (150 km from the network center) as source detection efficiency decreases rapidly and location errors increase with distance. The detection of multimodal vertical distributions of LDAR II sources is also affected by a storm's range from the network.