HR: 11:20h
AN: AE51B-04 INVITED     [PDF]
TI: Results of Rocket-Triggered Lightning Studies at Camp Blanding, Florida: An Update
AU: * Rakov, V A
EM: rakov@ece.ufl.edu
AF: Department of Electrical and Computer Engineering, University of Florida, 553 Engineering Building #33, PO Box 116130, Gainesville, FL 32611-6130 United States
AB: In this review, we present selected results of triggered-lightning experiments at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida. After a general update, the following three topics will be covered in more detail. (1)Mechanism of cutoff and re-establishment of current in rocket-triggered lightning. We will present evidence (electric and magnetic fields, channel-base current, time-resolved optical records) that the gap resulting from the vaporization of the triggering wire by the upward positive leader current is bridged by a leader/return-stroke type process (Rakov et al., 2003). Characterization of the attempted interruption and following re-establishment of current to ground in rocket-triggered lightning may have important implications for the understanding of channel current cutoff in natural lightning flashes and may provide new insights into the formation of strokes occurring in the same channel within a millisecond or less. (2)Estimation of input energy in rocket-triggered lightning. In 2000, the electric fields in the immediate vicinity (within 0.1 to 1.6 m) of the triggered lightning channel were measured with Pockels sensors (Miki et al., 2002). We used these fields and associated currents measured at the base of a 2-m strike object to compute power and energy, each per unit channel length and as a function of time (up to 10 ms), associated with return strokes in rocket-triggered lightning. In doing so, we assumed that the vertical component of the electric field at horizontal distances of 0.1 to 1.6 m from the lightning attachment point is not much different from the longitudinal electric field inside the channel (Borovsky, 1995). The estimated mean input energy over the first 50 ęs or so is between 1 and 10 kJ/m, consistent with predictions of gas dynamic models. (3)Multiple-station measurements of electric and magnetic fields and their time derivatives produced by close natural lightning discharges. In 2002, the field measuring network established at the ICLRT in 1997 was upgraded to include field derivative measurements, optical coverage, and measurements of current in a grounded structure in response to nearby lightning strikes. The network currently includes measurements at 11 locations and covers an area of approximately 0.5 sq. km. In 2002, data were obtained for 11 cloud-to-ground flashes, including a three-stroke bipolar flash. This bipolar flash consisted of two positive strokes in separate channels followed by a negative stroke along the second-stroke channel. Selected data acquired in 2002 and 2003 will be presented. References Borovsky, J.E. 1995. An electrodynamic description of lightning return strokes and dart leaders: guided wave propagation along conducting cylindrical channels. J. Geophys. Res. 100: 2697-726. Jerauld, J., V.A. Rakov, M.A. Uman, D.E. Crawford, B.A. DeCarlo, D.M. Jordan, K.J. Rambo, and G.H. Schnetzer. Multiple-station measurements of electric and magnetic fields due to natural lightning, in Proc. Int. Conf. on Lightning and Static Electricity, Blackpool, United Kingdom, 2003. Miki, M., V.A. Rakov, K.J. Rambo, G.H. Schnetzer, and M.A. Uman. Electric fields near triggered lightning channels measured with Pockels Sensors. J. Geophys. Res., 107(D16), 10.1029/2001JD001087, 2002. Rakov, V.A., D.E. Crawford, V. Kodali, V.P. Idone, M.A. Uman, G.H. Schnetzer, and K.J. Rambo. Cutoff and re-establishment of current in rocket-triggered lightning. J. Geophys. Res., submitted, 2003.
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting