Preliminary Breakdown Process of Winter Positive Cloud-To-Ground Lightning and Its Relation to the Following First Return Stroke

We have studied the preliminary breakdown (PB) process and its relation to the following positive first return stroke (RS) for 60 winter positive cloud-to-ground (+CG) lightning flashes using their 3D mapping data by Discone Antenna Lightning Mapping Array in conjunction with the E-field change information by Fast Antenna Lightning Mapping Array. 31 (52%) PBs are found to propagate upward, 27 (45%) downward, and the remaining 2 (3%) with some initial progression direction reversal features. The winter +CG PBs can be characterized with an initiation height from 0.9 to 4.4 km, a propagation distance from 0.2 to 2.6 km, a propagation speed from 3.5x105 $3.5\times {10}<^>{5}$ to 5.4x106 $5.4\times {10}<^>{6}$ m/s without significant differences between upward and downward PBs. The time interval and the 2D displacement distance from the PB initiation to the first RS range from 6.1 to 603.7 ms, from 0 to 39.2 km, respectively. Return strokes with strongest intensities tend to have shorter intervals and 2D displacements between PB and RS. We also found some weak correlations between the PB characteristic parameters. All 60 +CGs involved multiple charge regions with opposite polarities and small separations. Finally, we have discussed our findings.