冰核浓度变化对云辐射的模拟试验

NUMERICAL SIMULATION EXPERIMENTS FOR THE EFFECTS OF CHANGES OF ATMOSPHERIC ICE NUCLEI CONCENTRATIONS ON RADIANT PROPERTIES OF CLOUD

文中利用中国气象科学研究院 2 0 0 0年版三维对流云模式 ,假设冰核浓度比现在模式中通常用来计算实际降水量的Fletcher给出的冰核浓度增大了 5倍 ,对北京地区 1996年 6～ 9月 18次降水过程作了模拟的对比分析。结果发现 ,80 %的模拟云在冰核浓度增大后都出现降水减小 ,云顶卷云毡面积扩大 ,云顶升高 ;95%的模拟云出现冰晶尺度变小 ,数量增多的现象。说明冰核浓度增大后 ,云的物理特性会有一些改变 。

Research on the possible effects of Cloud Condensation Nuclei (CNN) on radiant p roperties of cloud and climate has been investigated in many papers, but the effects of Ice Nuclei (IN) have not been well analyzed. In fact, ice nuclei ar e very import ant in many weather events for the reason that IN can affect the initial concent rations of ice particles in cold cloud and then change the physical characterist ics of cold cloud. Recently, with more and more human activities, numerical conc entrations of IN have increased a lot in atmosphere in some places. Observations in Beijing show that the concentrations of IN in Beijing have increased a lot i n about 32 years from 1963 to 1995. The IN concentrations which can been activat ed at -20 ℃ increase about 15 times. Since, ice nuclei concentrations at high altitudes and the concentrations and scales of ice crystal in cloud can not be observed synchr onous easily now, so the relation between concentrations of IN a nd ice crystal by observation we can not be tested in reality. Thus, numerica l simulations are adopte d. In this thesis, all simulations used 3-D convective cloud model of CAMS (Chin ese Academy of Meteorological Sciences, version 2000). First of all, a single te st which used the sounding data of June, 10, 1996 was completed. In the simulati on, it is supposed that the concentration of IN had increased 5 times and 1 0 ti mes and got the same results that ice particles concentration increased and the size of them decreased. What is more, cloud tops heightened when IN concentratio ns increased although the change ranges were not entirely the same. Then numeric al simulations of 18 precipitation days from June to September in 1996 were cond ucted. The conclusions were that when ice nuclei concentrations increased, in 80 percents simulated precipitation processes, the amounts of precipitation decrea sed, the cloud tops heightened and the areas of cloud top height increased. rath er more, in 95 percents processes, the scales of ice crystal in the cloud d ecre ased and the quantities increased. That is, physical properties of cold cloud ch anged when IN concentrations changed. From some analysis including a simulation using SBDART radiative model, some results could be achieved. That is, cloud ref le ctance increased when cloud top increased, ice particles concentration increased and size of them decreased when cloud reflectance increased. In conclusion, rad iant properties of cloud changed when IN concentrations increased. For the reaso n that cold cloud plays an important role in global radiative balance, the clima tic effects caused by cold cloud can be modified directly and indirectly.