Release of positive charges producing sprite halos

The occurrence of sprite halos has been found almost solely in association with cloud-to-ground lightning flashes due to the release of positive charges (Miyasato et al., Geophysical Research Letters 29(21), 2033). Here, a numerical simulation method is used to study the positive charges producing sprite halos. A particle model, combined with the quasi-electrostatic (QE) model, is used to take account of the positive charges centered at two altitudes of 5 and 10 km. The altitude of 10 km is a typical position of positive charge in thunderstorm convective regions. The choice of an altitude of 5 km is based on observations for the positive sprite-producing charges, which are located at the altitude range of 4-7 km. Results show that sprite halos can be produced by positive charges at both altitudes. The region where sprite halos occur is determined mostly by the values of the released positive charges, which is in good agreement with the previous observations. The variation of the region of positive charges is approximately equivalent to the variation of the value of positive charge. The time when positive charge is released determines the intensity of optical emission from a sprite halo. Typically, the positive charge of 100 or 200 C released at an altitude of 10 or 5 km, respectively, within a time of 0.6 ms will produce a sprite halo with a maximum optical intensity of ∼1×107 R. The estimated threshold of positive charges at which sprite halos are produced is consistent with the value estimated from the observed sprite halos.