AbstractThis study reports a study trying to find the dominant factor on streamer initiation from an isolated hydrometeor in thundercloud fields at 7 km altitude corresponding to an atmosphere pressure of about 0.453 atm. Three parameters are considered including hydrometeor size, shape, and electric quantity. The simulation results indicate that a larger hydrometeor is more likely to initiate a streamer discharge at a lower ambient field for noncharged hydrometeors. The charge on hydrometeor plays a prominent role when a charged hydrometeor has a smaller size, and it is easier to initiate a streamer in this case. At 0.25 Ek, a positive streamer discharge has been presented for a charged hydrometeor with a radius of 0.5 mm. The critical field to form streamer discharge for a column shape hydrometeor without charge is much smaller than that for a spherical hydrometeor. If smaller hydrometeors are charged, the critical field for a spherical hydrometeor becomes lower than that for a column one. The electric quantity charged on hydrometeor has little effect on the critical field for both spherical and column hydrometeors, when the hydrometeor size is larger enough. The charge on hydrometeor plays a dominant role in streamer initiation when hydrometeor is smaller, but hydrometeor shape becomes more important for larger hydrometeor. Streamer discharge can be predicted by Meek number, but stable streamer cannot be ensured. Streamer branch will be met when ambient field is lower than 0.25 Ek.
