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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.

To clarify the relationship between material transport, photosynthesis, fluorescence dynamics and cold tolerance of winter turnip rape (Brassica rapa L.) and to further provide theoretical basis for rape breeding and evaluation of cold resistance, 2 cultivars Longyou 7 (strong freezing-tolerance) and Tianyou 4 (weak freezing-tolerance) were determined in natural temperature falling. Effects of low temperature on dry matter distribution, photosynthetic performance and kinetic curve of chlorophyll fluorescence induction were investigated under field conditions. It was shown that dry matter and distribution rates of dry matter in roots of both cultivars increased, but photosynthetic rate, transpiration rate, Fo (fluorescence at O-step at 20 microseconds), Fk (fluorescence at K-step, 300 microseconds), Fj (fluorescence at J-step at 2 millisecond) and Fm (dark-adapted maximum fluorescence at P-step) of chlorophyll fluorescence induced kinetics curves of O-J-I-P decreased, with the decreasing temperature. Thus the decline of photosynthetic performance might help accumulation of dry matter in roots at low temperature. Photosystem damage and photo inhibition occurred, which presented with falling of PSII receptors (area), photosynthetic performance index (PI), maximum fluorescence (Fm) and maximum photochemical efficiency (Fv/Fm), except the rising of initial fluorescence (Fo). Longyou 7 had lower Pn, Fm, Fv/Fm, and had lower potential activity of PSII (Fv/ Fo) and reduced capacity of QA and QB. It showed weaker photosynthetic capacity and stronger photo inhibition in Longyou 7 than those of Tianyou 4 under low temperatures. These indicated that the photosynthetic capacity of Longyou 7 decreased at low temperature before winter, which might be due to non-stomatal factors, and low temperature might lead to enhanced photoinhibition. In summary mary, the cold resistance of winter turnip rape was related to leaf photosynthetic characteristics and dry matter accumulation under low temperature. Weak photosynthesis could reduce growth activity of aboveground parts and root matter consumption, which was conducive to dry matter accumulation of rape root to enhance its cold resistance. [ABSTRACT FROM AUTHOR]

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