Numerical simulation of negative streamers at different pressures

In order to study the characteristics of negative streamers about lightning initiation at different heights in the thunderclouds, a cylindrically symmetrical two-dimensional model was used to simulate negative streamers between planar parallel plates in nitrogen. In the model, a flux-corrected transport (FCT) technique was used to solve the continuity equations and an adaptive grid refinement strategy was used to increase computing efficiency. The simulation results indicate that, after the initial stage of adjustment the streamers propagate in a steady-state mode, the characteristics of steady-state are decided by background ionization frequency which is determined by pressure and background electric field together. A logarithmic linear relationship can be found between average streamer velocity and the background ionization frequency. Under the same background electric field, the background ionization frequency increases with the decrease in pressure, and streamers develop faster, implying they are more likely to initiate in the region with a relatively lower pressure. At the same pressure, the background ionization frequency increases as the intensity of the background electric field increases and streamers develop faster, and streamers tend to initiate in the region with a stronger background electric field.