| Studying the cloud microphysical parameters such as the particles' average diameter,concentration, distribution and content that are the key to describe the atmospheric state in cloud scale is significant for the change of climate, the change of weather and the security of aviation.The layered structure of stratiform cloud is uniform and obvious, so we will use the stratiform cloud that based on stratiform cloud layered structure theory (studied by Mr Gu) to study the raindrop in the low height. The inversion theory, using the radar reflectivity observed by weather radar to calculate the raindrop spectrum parameters, will be given. Besides, the calculation algorithm will be designed.According to the relationship between radar reflectivity factor and particle's average diameter, in the drop size distribution is known, we adopt the least squares method to establish the inversion model based on the radar reflectivity factor to retrieve the particles' average diameter in the stratiform cloud. We will carry out the simulation test to verify the applicability of the proposed inversion theory and the designed calculation method.The first simulation test is using the radar reflectivity factor without considering the radar observation error as the observation data. The second simulation test is using the radar reflectivity factor without considering the radar observation error as the observation data. The final one is the sensitivity test between the retrieved results like average diameter and DSD and the different situations such as the shape parameter (gamma), the cloud water content et al. It has found that we can get the inversion average diameter by the inversion method proposed in this paper whatever containing radar observation error or not. And if the deviation of the absolute value of radar observations added bigger (smaller), the inversion average diameter values will be farther (closer) compared with the "true value" of average diameter. When the random error is bigger, the difference between the retrieved average diameter and "true value" will exit, but this difference is small, so this error has little effect on the retrieval result. Finally, the retrieval raindrop average diameter is not sensitive to the shape parameter (gamma),he cloud water content and the initial average diameters. The calculated DSD is sensitive to both the shape parameter (gamma) and the cloud water content, but not sensitive to the initial average diameters.After verifying the proposed inversion theory and calculation method, we will use this method to carry out the inversion experiments with observation data observed by weather radar,one is in July 13, 2011 Yitong Changchun,anthor one is July 13 2012, in Jurong Zhenjiang. Then,the inversion results are analyzed and discussed. Firstly, in the first case, the trend between the drop-size distribution calculated with the inversion algorithm and the observation is almost the same. The magnitude and value of drop-size distribution between calculations and observations are almost equal. The radar reflectivity factor profiles calculated from the average raindrop diameter and the number concentration values are in good agreement with the reflectivity profiles. Besides,there is different between the result of retrieval DSD and the DSD observation,the reasons why they are different as following, ?The difference in sampling space. ?There are microphysical processes like the coagulation, broken and evaporation in the different sampling space. ?The DSD observation and the gamma distribution function are incomplete conformity.In the second case, the different period of the radar reflectivity calculated by inversion average diameter and number concentration inversion are closer to each period of radar reflectivity observations. We can find that the drop-size distribution between calculations and observations are almost equal form the inversion result of the case one. So, though lacking of the observation data for comparing,we will believe that it has a certain reference value in raindrop average diameter, number concentration and DSD calculated with the retrieval method. |
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