The role of charged ice hydrometeors in lightning initiation

In connection with the lightning initiation problem, we consider positive streamer formation around charged, needle-shaped ice hydrometeors in an external electric field. We present results of numerical simulations of the streamer discharges that include the ice dielectric polarization and conductivity, and determine the external field intensity, at which stable streamer development is possible for different hydrometeor sizes and charge magnitudes. We find that the required charge is within the range of measured precipitation charges while the required external field is higher than observed in thunderclouds. We conclude, therefore, that a second mechanism for amplification of thundercloud fields is required for the streamer inception.