A Laboratory in the Sky
The Tashkent TV Tower, at 375 meters (1,230 feet), is the tallest structure in Central Asia. Completed on January 15, 1985, its primary function is television and radio broadcasting, with signals reaching across the Tashkent region and into southern Kazakhstan. The tower also houses a complex hydrometeorological station. Its steel lattice structure, supported by three massive legs, was engineered to withstand a magnitude 9 earthquake. This robust design makes it an ideal platform for a unique field of atmospheric physics: the study of upward lightning.
Unlike typical cloud-to-ground lightning, upward lightning initiates from a tall, grounded object and propagates toward the storm cloud above. The extreme height of the Tashkent Tower increases the local electric field at its tip, creating the necessary conditions to launch these upward flashes. This phenomenon allows scientists to observe the development of the initial lightning channel, known as a leader, from a fixed, instrumented point. Studying leader propagation is difficult with natural lightning, which strikes unpredictably. Research at similar tall structures uses high-speed cameras (recording up to 100,000 frames per second), electric field meters, and lightning mapping arrays to analyze this process in detail.
Decoding the Upward Flash
Most upward lightning events involve an upward propagating positive leader, which effectively lowers negative charge to the ground. These are often triggered by a preceding, nearby lightning flash—sometimes as far as 60 kilometers away—that rapidly alters the charge distribution in the storm cloud. Data from triggered lightning experiments show that the average two-dimensional speed of these upward positive leaders is around 1.0 × 10^5 meters per second, though speeds can vary significantly as the leader ascends.
The process begins with the formation of streamers ahead of the leader tip, which then merge to extend the main channel. By measuring the channel-base currents and electric field changes, scientists can correlate physical processes happening hundreds of meters in the air with precise electrical data. This research has direct applications for improving protection systems for tall infrastructure, including skyscrapers, wind turbines, and communication towers, which are all susceptible to upward lightning strikes. The data gathered helps refine models of lightning physics and improves safety standards for structures that regularly interact with thunderstorms.