Los Alamos National Laboratory

FORTE Compact Intra-cloud Discharge Detection Parameterized by Peak Current


M J Heavner, D. M. Suszcynsky, A. R. Jacobson, B. D. Heavner, and D A Smith

LAUR-02-5759

GPS Lightning Observations


The GPS observations of lightning were the motivation for the FORTE/LASA study presented below. The GPS/LASA time tags for events were compared, and a tight temporal correlation window provided a strong separation from background (chance coincident) events. The window used was a GPS time stamp 300 us before to 100 us after the LASA time stamp. For events within this window, the LASA estimated peak current histograms for all events, independent of LASA classification, just CG events, and just CID/NBE events are shown below. All LASA events and just GPS/LASA events are plotted. For all events, -CGs dominate the LASA data set, while the +NBs dominate the GPS/LASA coincident events. For just CG events, both LASA and GPS/LASA coincident events are dominated by -CGs. GPS/LASA events may have an improved detection efficiency with greater LASA estimated peak current dependent, but the GPS/LASA CGs have relatively poor statistics. For the CID/NB events, LASA has an almost equal number of both +NB and -NB events, while the GPS/LASA NBs are dominated by +NBs. The GPS/LASA +NBs also show a distinct esimated peak current threshold of ~45.

I GPS All Peak Current Histogram

II GPS CG Peak Current Histogram

III GPS NBE Peak Current Histogram

FORTE Lightning Observations

The FORTE/LASA coincident events are similar to the GPS/LASA coincident data set. As illustrated in A below, the coincident event time window (including the corrections for time of flight delays), determined independently for the two coincident sets, have the same -300 us to +100 us size. Plot B below, shows the estimated peak current for all LASA events and all FORTE/LASA events, similar to I above. For FORTE/LASA coincidents, the results are similar to the general LASA population, but much more strongly dominated by CGs. The negative events are slightly skewed towards weaker peak currents. This is most likely due to the fact that the LASA population is dominated by -CGs, while the FORTE/LASA population is dominated by -NBs, for which the peak currents are probably under-estimated. As shown in C, and similar to the GPS/LASA results in III above, the LASA NBs are nearly equivalent in total number, while the FORTE/LASA coincident events are more dominated by +NBs. The +NBs in the FORTE/LASA coincident events do not show any strong evidence of the estimated peak current threshold affect seen in III above. Plot D, below, shows the histogram for all LASA NBEs that occurred when FORTE was overhead and armed, but for which no coincident FORTE event was recorded. A priori, a tendency towards lower peak currents for non-FORTE detected NBEs was expected, as evidence of some threshold effect. However, no such tendency is apparent in the data.

A FORTE/LASA Event Time Differences

B FORTE/LASA

C FORTE

D FORTE

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