| Multi-layer stratiform clouds system generated by cold front weather system is the main precipitation cloud system at Sanjiangyuan National Nature Reserve in autumn and is the job object of artificial rainfall. Making use of data of PMS (Particle Measuring Systems) data observed during the airborne observation experiment over the Sanjiangyuan National Nature Reserve, the structure of microphysical feature in vertical layers, the phase of cloud particles at different heights and the distribution of particle spectrum, the microphysical characteristics of the multi-layer stratiform clouds in autumn are studied. In the meantime,the growth mechanism of cloud particles is discussed. By analyzing the horizontal transport of aircraft sowing the AgI flame agent, microphysical effects are studied, First, the effective area before and after the operation are compared and got the distinguishing of cloud particle’s phase state, then the variation of total number concentration of liquid cloud particles and ice crystal,cloud particle spectrum and f1(fraction of liquid water) are analyzed. This results can provide a microphysical theoretical basis for quantitative index of the artificial rainfall and effect of test in this region. The main results are as follows.(1) The vertical structure and microphysical characteristics of autumn multi-layer stratiform clouds system (Cs-As-Sc) are analyzed in this paper. The clouds system of development consists of four layers. The Cs(cirrostratus) and the upper-level of As(altostratus) are ice-phase cloud, while the lower level of As and Sc(stratocumulus) are supercooled mixed-phase cloud. The particle concentration and the supercooled water content of the lower level As are the largest in the cloud system. The average particle concentration which the radius larger than50μm is gradually increased from the top of Cs down. The Cs particle size and spectral width of the lowest layers are the largest in the cloud system, which has a clear regional characteristics. Ous results was compared with the observation analysis of other area in northern China. It is found that:the value of LWCFSSP (Liquid Water Content by Forward Scattering Spectrometer Probe)and particle concentration of As and Sc are larger is our observation; besides, the breadth of cloud particle spectrum are wider. The particle concentration which observed by FSSP(Forward Scattering Spectrometer Probe) had remarkable negative correlation with its diameters and the area of high concentration corresponds to high moisture content. The difference between the high and the lower supercooled water in the cloud particles spectrum are distinguished. The high supercooled water area of Sc has an obvious rime growth phenomenon.(2) According to the2DC(Two-Dimensional Cloud Probe) image and gray projection data, the phase of particle radius D large than50μm is judged in this paper. In the meantime, based on the correlations about the instantaneous spectrum of FSSP cloud particle, the value of liquid water content calculated from FSSP and the observation of supercooled water content obverted with King detector, the particle phase in the mixed-phase cloud are also judged. The median diameter of cloud particles between3.5～18.5μm (3.5～21.5μm) in the Sc (lower As and convective bubble) is liquid phase while median diameter of cloud particles greater than21.5μm (24.5μm) is ice phase. The droplets effective radius of high supercooled water area increased with the increasing cloud height in the bottom of Sc and As. The supercooled water content mean ratio of the high subcooled water area are related to the supercooled water content in Sc while it is opposited in lower As of cloud.(3) The features of particles spectrum at different heights are analyzed and the growth mechanism of cloud particles is discussed. The cloud particle spectrum in the mixed-phase cloud observed by the FSSP and observed by the2DC are respectively in single-peak Γ distribution and in the negative exponential distribution. In ice cloud and lower layer As, the growth of ice crystal may be limited to growth of condensation and coagulation, which make it is difficult to generate ice phase particles larger than400μm. At lower layer As, the vapor needed in condensation is not only from the ice-water transformation occurred in cloud, but also from the updraft which can transport vapor from outside. Strong updraft can be an advantage for broadening cloud particle spectrum and increasing concentration.(4) At the leeword of routine in the scope of36km about2-23min later after seeding, the variation of concentration and diameter detected by FSSP&2DC in test region, which is not out of the range of normal floating compared with pre-test. However, in the high supercooled water area(HSWA) where the SLWC(supercooled liquid water content) larger than0.01g/m3, the concentration of cloud particles for liquid phase decrease obviously and the density of ice crystal particles increased. The mean value of f1reduced from68.3±23.1%to34.2±12.4%. The effects of seeding is remarkably in high supercooled water area, but not obviously in low supercooled water area and routine cross points which just influenced by original seeding that effects in comparison. |
PDF Full Text Request