Lightning Activity in a Hail-Producing Storm Observed with Phased-Array Radar (AMS weblink)
Study cautions use of lightning trends alone to diagnose severe weather potential
Researchers from NSSL and CIMMS have published the first study to combine rapidly updating phased-array radar data with high-resolution lightning data to study lightning behavior in a hail storm. Frequent scans from phased array radar revealed relationships between lightning and storm growth not able to be seen with current radar update rates. Though total lightning flash rates are expected to increase as storm updrafts intensify, in this case a short-lived decrease in total lightning flash rate (upper-left) was observed during the simultaneous development of an updraft surge (2234 UTC). This decrease in flash rate occurred as wet hail formed in the new updraft (based on three-body scatter spike signature; right-side of Figure). Such wet growth is not conducive to charging of cloud particles and likely contributed to the formation of a "lightning hole", which is more commonly seen in supercells. This short-lived decrease in lightning rate is followed by a sharp increase in lightning rate (top-left of Figure) coincident with continued updraft growth (right-side of Figure). This finding cautions forecasters in the use lightning mapping observations alone to diagnose an increase or decrease in updraft intensity and the potential for severe weather.
Funding for this research was provided by NSF Grants ATM-0813767 and ATM-0233268. Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the National Science Foundation.
Upper left image: Lightning flash rate. Lower left image: Charge structure. Right image: Vertical reflectivity cross sections of hail storm during Period 2.
Adaptive DSP Algorithm for PAR Timely Scans
Animation of ADAPTS data collection on 6 April 2009. Green and orange dots indicate active beam positions; white dots inactive beam positions. The horizontal axis depicts a 90 deg sector, while the vertical axis depicts the elevation angles. Image courtesy of Sebastian Torres.
Working at NOAA/NSSL gives meteorologists the opportunity to collaborate with Radar and Software Engineers, and vice versa. An example is the new adaptive scanning cability of ADAPTS. The ADAPTS, which stands for Adaptive DSP (Digital Signal Processing) Algorithm for PAR Timely Scans, periodically (~5 min) completes a volumetric surveillance scan, which is used to determine where weather echoes are located. Following a surveillance scan, data collection continues contiguously at low elevation angles (e.g., 0.5–2.5°) and is then limited to areas with weather echoes (green dots in figure to the left) and a neighborhood around them (orange dots in figure to the left). The scanning positions with the neighborhood helps to capture storm advection, growth, and decay between surveillance scans. A detailed description of ADAPTS is published in the AMS Journal of Applied Meterology and Climate (AMS weblink).