Initial analysis of the Los Alamos Sferic Arrays in North-central Florida and Great Plains

In the spring of 2004 Los Alamos National Laboratory deployed a new electric field change array (LASA) in north central Florida. This eight station array is capable of locating over 3000 events per minute, during active storms. Initial analysis of the system has found that for events within the array, we have excellent location accuracy and sensitivity. LASA can detect low current signals of a couple of kilo-amps, and locate events better than .5 km within 100 km of the center. For events 600 km away our minimum detectable signal increases to about 25 kilo-amps, with radial errors increasing up to 25 km. Classification of waveforms into cloud-to-ground (CG) and intra-cloud (IC) events shows that there are at least three times more IC's than CG's. Different storms have different ratios and different types of lightning. With the new smaller baselines it is possible to locate the sferics in 3-D. This method locates return strokes close to the ground and IC events in the upper part of the storm. The 3-D locations can track the development of individual storms by locating a few points per flash. In April, 2005, an additional six-station array was deployed in the Great Plains. The Great Plains network (GPN) form a much larger array of ~1000 km diameter, and predominately produces 2-D lightning location except for some temporally isolated IC events for which the ionospheric reflection can be used to determine the heights of the sources.