Atmospheric and Space Electricity Posters
Presiding: H Kikuchi, Institute for Environmental Electromagnetics; S Pulinets, Instituto de Geofisica
AE11A-01 0830h
Spatio-temporal variability of lightning activity over the Indian region
Spatio-temporal variability of lightning activity over the Indian land mass region (8o-33oN, 73o-86oE) has been studied by using monthly satellite based lightning flash grid (5 deg. x 5 deg) data for 5-year (1998-2002) period. These data have been examined for depicting the annual, seasonal and spatial distribution of the lightning activity. The study revealed the positive relationship between lightning flash density and latitude on the annual time scale. There exists a positive relationship of lightning flash density with latitude and it is linked with the convective activity, large-scale circulations, land mass gradient and orography of the region under study. On the seasonal time scale, the positive relationships were observed in the pre-monsoon and monsoon seasons where as a negative relationship is observed in the post monsoon season. The comparison of flash density with maximum surface air temperature shows the existence of nonlinear relationship between the two parameters giving an approximate increasing rate of flash density as 32% per 1oC rise in temperature. The lightning flash density shows a pronounced semi annual oscillation over the latitude belts 8-28 deg. N.
http://www.tropmet.res.in
AE11A-02 0830h
Overview of Initial Performance of BOLTEK Storm Tracker : A Lightning Detector
This paper discusses the technical details and functioning of the newly installed lightning detector, a Boltek Storm Tracker. It is installed at the terrace of the Institute building nearly 40 ft above the ground level. The potential of the instrument is judged by operating the same during the premonsoon season (March - May) thunderstorms of the year 2004 occurred over the Pune region. From the records it is seen that the instrument is capable of detecting the lightning strokes (IC and CG of either polarities) up to the radial distance of 300 miles. The detected lightning events are also confirmed through electric field records taken at the same location and at the same time.
http://www.tropmet.res.in
AE11A-03 0830h
Modern Protection Against Lightning Strikes
The application of science to provide protection against lightning strikes began around 1750 when Benjamin Franklin who invented the lightning rod in an effort to discharge thunderclouds. Instead of preventing lightning as he expected, his rods have been quite successful as strike receptors, intercepting cloud-to ground discharges and conducting them to Earth without damage to the structures on which they are mounted. In the years since Franklin's invention there has been little attention paid to the rod configuration that best serves as a strike receptor but Franklin's original ideas continue to be rediscovered and promoted. Recent measurements of the responses of variously configured rods to nearby strikes indicate that sharp-tipped rods are not the optimum configuration to serve as strike receptors since the ionization of the air around their tips limits the strength of the local electric fields created by an approaching lightning leader. In these experiments, fourteen blunt-tipped rods exposed in strike-reception competitions with nearby sharp-tipped rods were struck by lightning but none of the sharp-tipped rods were struck.
AE11A-04 0830h
Thunderstorm Electric Potential Profiles: Electrical Evolution and Lightning Energy
From a balloon sounding of electric field through a thunderstorm, one can calculate the vertical profile of potential, V, within the storm. In this presentation we investigate thunderstorm electrical evolution by examining V profiles through various stages of a storm's life. We present data from New Mexico mountain thunderstorms in which we made a series of 4 to 6 balloon soundings. Several of the successive V profiles in the same storm are quite similar, in spite of the numerous lightning flashes that occurred during the balloon flights. These similarities suggest that the V profiles are reasonable estimates of the in-cloud potential. The similar profiles occur during the mature phase of the storm, and mature phase profiles are even similar from one storm to another. This is true despite different lightning flashing rates and, presumably, different charge generation rates in the different storms. Another result of this work is that potential profiles during the early and late stages of the storm do not resemble those from the mature stage. Recently, Coleman et al. [2003] showed that intra-cloud (IC) flashes connect potential extrema of opposite polarity and that normal (negative) cloud-to-ground (CG) flashes connect a potential minimum to ground. Thus we can use the V profiles to estimate the potential difference spanned by lightning flashes during the evolution of the storm and, with this, estimate the lightning energy. Typical potential differences spanned by IC and CG flashes will be presented from four storms. Reference: Coleman, L.M., T.C. Marshall, M. Stolzenburg, T. Hamlin, P.R. Krehbiel, W. Rison, and R.J. Thomas, Effects of charge and electrostatic potential on lightning propagation, J. Geophys. Res., 108, doi:10.1029/2002JD002718, 2003.
AE11A-05 0830h
On the Initiation of Upward Lightning Discharges Above Thunderstorms
A simple cylindrical charged disk model has been used to study the occurrence of lightning in thunderstorms. The model uses three-dimensional lightning mapping data to estimate the heights, thicknesses, and diameters of the charge regions in an actual storm, and assumes an exponential decrease in the lightning breakdown threshold with altitude. The storm charging currents and charge amounts are estimated by matching the predicted and observed flashing rates for both intracloud and ground flashes. The model was developed as a means of quantitatively interpreting and simulating balloon-borne electric field soundings and lightning mapping data in storms but provides additional insights into the occurrence of lightning discharges. For example, the model simulations clearly show the importance of lower positive charge in initiating cloud-to-ground (CG) lightning; the presence of such charge enhances the electric field to breakdown values between the main negative and lower positive charge regions of normal polarity storms, whereas without lower positive charge the electric field strengths do not reach breakdown values in the presence of ongoing intracloud activity. A similar, surprising result of the model calculations concerned the effect of the negative screening charge attracted to the cloud top by the upper positive charge region of the storm. The screening charge enhances the electric field between it and the upper positive charge to the point that would initiate a discharge between the two regions. Because the magnitude of the positive charge is greater than that of the screening charge, the discharge would develop vertically upward above the storm top, just as a CG flash usually travels on through the lower positive charge to ground. Observations show that such discharges usually do not occur, implying that the upper screening charge is somehow removed, probably by being dissipated into the upper positive charge. In the absence of such dissipation, or in the presence of some extraordinary triggering event (such as an energetic cosmic ray), upward discharges would or could be initiated. This is likely to be the cause of blue jets, blue starters, and other luminous phenomena observed at and above the tops of thunderstorms. The conditions for triggering upward discharges are enhanced by the occurrence of CG discharges, which remove negative charge from storm mid-levels and suddenly enhance the electric field between the upper positive charge and the screeing charge. Upward discharges are therefore likely to occur relatively soon after negative polarity CG flashes in a storm. Upward discharges from normal polarity storms would transport positive charge upward and be generative of the atmospheric electric potential.
AE11A-06 0830h
Investigating Nitric Oxide Production by Lightning Using Fully-Coupled Radiation Transport, Hydrodynamics and Chemistry
Numerical simulations [Goldenbaum & Dickerson, JGR, 1993] and laboratory experiments [Navarro-González et al., GRL, 2001] indicate that nitric oxide (NO) is produced in the high temperature lightning return-stroke channel. As the channel temperature and density drop, a "freeze-out" point is reached where the reactions that produce and destroy NO become too slow to further alter the ambient NO concentration. Exactly when and why this freeze-out point occurs is a matter of concern and debate. Goldbenbaum & Dickerson, using a purely hydrodynamic model with 18 chemical reactions, find that after a few microseconds a rapid drop in channel air density triggers the freeze-out. This finding is in opposition to the phenomenological models of Borucki and Chameides [RGSP, 1984] and Bhetanabhotla et al. [AE, 1985] which invoke a slower temperature decay---driven by turbulent and radiative cooling---to arrive at a temperature driven freeze-out that occurs after hundreds of microseconds of channel evolution. In this talk, we present results from a new model of the lightning return-stroke channel that incorporates fully-coupled radiation transport, hydrodynamics and chemistry. Our model extends the work of Goldenbaum & Dickerson in the following important ways: (i) we include a multispectral dynamical equation for radiation that is directly coupled to the local concentration and radiative properties of chemical species, (ii) a total of 687 chemical reactions are modeled including the important NO self-destruction reaction NO + NO ⇒ N2O + O, and (iii) we use an eddy-diffusivity model to incorporate the effects of turbulent mixing. Using our fully-coupled dynamical model we revisit the origin and nature of NO freeze-out during the complex evolution of the return-stroke channel.