[1] The location accuracy of the New Mexico Tech Lightning Mapping Array (LMA) has been investigated experimentally using sounding balloon measurements, airplane tracks, and observations of distant storms. We have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network. The model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique. Sources over the network are located with an uncertainty of 6-12 m rms in the horizontal and 20-30 m rms in the vertical. This corresponds well with the uncertainties of the arrival time measurements, determined from the distribution of chi-square values to be 40-50 ns rms. Outside the network the location uncertainties increase with distance. The geometric model shows that the range and altitude errors increase as the range squared, r 2 , while the azimuthal error increases linearly with r. For the 13 station, 70 km diameter network deployed during STEPS the range and height errors of distant sources were comparable to each other, while the azimuthal errors were much smaller. The difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations. The overall results are shown to agree well with hyperbolic formulations of time of arrival measurements [e.g., Proctor, 1971]. Two appendices describe (1) the basic operation of the LMA and the detailed manner in which its measurements are processed and (2) the effect of systematic errors on lightning observations. The latter provides an alternative explanation for the systematic height errors found by Boccippio et al. [2001] in distant storm data from the Lightning Detection and Ranging system at Kennedy Space Center.

Instrumented aircraft and radar were used to investigate the microphysical, electrical, and dynamic evolution of the life cycle of a small thunderstorm which occurred in southeastern Montana. The observations commenced as precipitation development was just beginning, continued through the active stage of growth as the cloud produced graupel up to 8 to 9 mm diameter and reflectivities aloft of 45 dBZ, through the dissipation stage when only an anvil with a trail of light precipitation remained. The largest particles and the primary development of precipitation were found to occur in the fringes of the updraft. The electric fields inside the cloud did not exceed 100 V m−1 until 5 mm graupel, ice particle concentrations of 10 L−1, and reflectivities of 35 dBZ were already present, but then rapidly electrified to produce a single intracloud discharge 8 min later, near the peak of microphysical development. Early in the electrical development of the cloud when observed electric fields were only 200 V m−1, negative charge accumulation was observed near the 7 km (−20°C) level and was associated with the high reflectivity region. In the early stages of precipitation fallout, particle charge measurements near 4.5 km showed primarily negatively charged particles which appeared to be associated with precipitation falling from the cloud. Less than 5 to 10% of the observed particles larger than 100 μm were carrying charges larger than 5 pC, the detection limit of the instrument. These observations are discussed from the point of view of charge generation in thunderstorms, particularly, charge transfer between colliding ice particles.

We designed an instrument to measure the charge and vertical velocity of individual precipitation particles inside thunderclouds. A balloon carried the particle charge instrument, an electric field meter, and a standard meteorological radiosonde upward into thunderclouds over Langmuir Laboratory in central New Mexico. During one balloon flight the instruments encountered two regions of positive charge below the main negative charge center. We identify these positive regions with the lower positive charge centers that have been described in the literature for many years. We find the following points: (1) One region had an estimated total charge of 0.4 C. The other had 2 C. (2) The charge resided on precipitation particles. The particles' charges typically ranged between 10 and 200 pC, but a few particles had charges up to 400 pC. Their diameters lay between an estimated 1–3 mm. The charges were too large to be explained by the polarization induction mechanism. We favor the hypothesis that lightning provided the positive charge in the lower positive charge centers. (3) The motion of the lower positive charge centers enhanced the electrical energy of the storm, but their contribution to the overall electrical budget was small. (4) The field excursions (at the ground) associated with precipitation (FEAWPs) described by C. B. Moore and B. Vonnegut are probably caused by lower positive charge centers descending on precipitation. The larger (2 C) lower positive charge center caused a FEAWP. Negatively charged precipitation particles passed through our instrument near the top of its trajectory just before the balloon was struck by lightning. The charge density on precipitation particles was substantial, but we do not have enough information to comment on the role the particles may have had in generating the main region of negative charge.

A model is presented to describe the propagation of positive corona streamers in the low field region of a non-uniform field gap in atmospheric air. It has been assumed that the growth is a property solely of the streamer tip, uninfluenced by the channel conductivity. Calculations from the model indicate that the criterion for propagation of a streamer in zero external field is that the number of ions in the tip be l0 s and the radius about 3 • 10 -3 cm. It is proposed that the streamer ceases to propagate as a result of the loss of energy of the tip due to the formation of ion pairs in the channel. The results of previous experimental observations of streamers are compared with calculations derived from the model, and a prediction from the model of the lifetime of streamers after voltage removal is discussed.

Aircraft, radar, and surface observations were used to study the relationship between precipitation development and the onset of electrification in thunderstorms which formed near or over the Magdalena Mountains of New Mexico. The study included storms which were electrically active as well as ones in which no electrical enhancement was observed. Electric fields inside these clouds showed negligible enhancement and did not exceed 1 kV m−1 until reflectivities at 6 km above mean sea level (msl) (about −10°C) exceeded approximately 40 dBZ and cloud tops exceeded 8 km. The onset of electrification occurred during or immediately after convective growth within the cloud.