A numerical study of the effects of varing ice nuclei concentration on severe precipitation of a large area in north China

Ice nuclei play an important role in cold cloud precipitation. In order to analyze the influence of ice nuclei-temperature spectra on the large-scale heavy precipitation process, the ice nuclei-temperature spectra measured in fields in North China are used to simulate the process. Two sets of experiments were simulated: (1) the high ice nucleus concentration ice nuclei-temperature spectrum (HIN) observed in the 1990s and (2) the low ice nucleus concentration ice nuclei-temperature spectrum (LIN) observed in the 2010s. The results show that the two sets of experiments can reproduce the temporal and spatial evolution of the extreme precipitation event and the convective system. The change of ice nucleus concentration has no obvious effect on the overall precipitation process and the regional average precipitation. The increase of ice nucleus concentration would increase the precipitation in the early precipitation period (southern and northern precipitation) but weaken the precipitation in the later precipitation period (middle precipitation), which had a significant impact on the local precipitation intensity. The significant impact may be related to the higher background ice nucleus concentration in North China. In terms of the whole process, the contents of rainwater, cloud water, and ice phase in the HIN test with high ice nucleus concentration are slightly higher than those in the LIN test with low ice nucleus concentration. However, the high ice nucleus concentration in the early precipitation period (southern precipitation) and the low ice nucleus concentration in the later period (middle precipitation) make the rain content higher, which is mainly due to the influence of change of ice nucleus concentration on the two conversions of cloud water to rain water. This study shows that under the background of high ice nucleus concentration, the change of ice nucleus concentration has little effect on the precipitation intensity and the overall temporal and spatial distribution of the falling area, but it can cause the temporal and spatial changes of local precipitation.