Observation of thermal plasmas in contact with saline water

Understanding how a lightning channel interacts with the sea surface requires interdisciplinary knowledge and diagnostic tools. We establish a physical model to simulate a lightning strike on water. A 0.06 C electrostatic charge is released through an exploding wire into grounded saline water, resulting in intense interactions between the thermal plasma channel and condensed states surface. High-speed photography and electrophysical diagnostics indicate that the pulsed electrical-thermal-mechanical loading from the plasma lasts several microseconds, while liquid surface deformation happens several milliseconds later. Varying the conductivity of saline water from 500 to 50 000 μS/cm, increases the discharge current from 0.2 to 6.5 kA, resulting in stronger plasma expansion and interface displacement. The broadening of the spark channel above the water surface is soon overshadowed by the expanded plasma channel. Shock waves are observed in air, although only a small portion is transmitted into the water. Therefore, surface deformation results from the pressure exerted by long-lasting ionized gases. The morphology of the arc-root above the surface does not exhibit obvious cathode spots (electron emission), and current density is stabilized on the order of 10 A/mm² of the contact area. There are several electromagnetic wave bursts during the discharge, which correspond to a sudden change in the circuit parameters and plasma dynamics. A time-frequency analysis suggests that the radiation is mainly concentrated in the radio frequency region. It has a strong energy distribution in the ranges of 104-181 and 312-729 MHz. The characteristics will enable the recognition and monitoring of marine lightning.