Positive Leaders Propagate Slower at Higher Altitudes: Experimental Evidence and Theoretical Explanation

We provide the clearest experimental evidence to date that positive leader velocity decreases with decline of air density in troposphere. The experiments are conducted at altitudes 4,300 m Tibet and 53 Beijing using long gap discharge technique. Rigorous comparative studies performed synchronized measurement current under different densities similar temperature humidity conditions. effect reduced on is analyzed a detailed thermal-hydrodynamic model. It found widely used similarity law setting initial radius inversely proportional does not hold estimating speeds