Lightning in a strong multicell storm: Positive and negative leaders are represented by the yellow and white contours, respectively. Thus, white leaders to ground indicate -CG flashes and yellow leaders to ground show +CG flashes. The red diamond-shapes indicate where lightning was initiated in the model. Each frame shows 2 minutes of lightning activity. The brown surfaces are mixing ratio of precipitation greater than 1 g/kg, whereas light gray and blue-gray indicate the cloud boundary (small droplets and ice crystals, respectively). The surface color contour shows reflectivity from weak (blue) to strong (red). The view is from the south.

This simulation used the Gardiner noninductive charging parameterization (fixed reversal temperature of -15 C) and no inductive charging, but a minimum ice crystal concentration up to 100 per liter. The initial lightning activity is purely intracloud between a main negative charge region at midlevels and a positive charge region above. A lower postive charge (LPC) region develops when some graupel and meltwater rain are ingested into a new updraft cell. The strengthening of the LPC is seen in the surface electric field: the outermost solid line (0 kV/m) bends inward, away from the base of the new cell, and soon more strongly negative values appear (negative contours are dashed). The LPC is involved in IC and -CG flashes, both of which have downward negative leaders and upward positive leaders. The +CG flashes from the forward flank region occur as negatively charged graupel descends out of the storm (notice the positive Ez at the surface below).

The simulation used a Weisman and Klemp (1982) analytical sounding. The horizontal resolution is 500 m and is stretched in the vertical from 200  at the surface to 500 m aloft.