偏振云粒子谱仪(CAS-DPOL)的数据处理和应用

Development of data processing methods for the cloud aerosol spectrometer with depolarization (CAS-DPOL) and their application

摘要:

对小云粒子（粒径<50 μm）的相态进行检测是云物理飞机测量领域的一个难点，而利用云粒子的偏振信息对云粒子相态进行鉴别是目前云物理研究领域比较认可的一种方法。本文针对偏振云粒子谱仪（cloud aerosol spectrometer with depolarization，CAS-DPOL）所测云粒子偏振参量的应用需求展开研究，通过对现有方法的比较分析，整合出一套适合于该仪器的方法和阈值。基于所整合出的方法和阈值以及该仪器在2021年5月23日东北冷涡天气的一次航测结果，探讨了该仪器在人工影响天气和飞机自然结冰探测领域的应用，此次航测发现温度在-1~-8 ℃的云内过冷云滴数对总云粒子数占比的平均值可达到80.18%，云相以混合相为主，间有纯过冷水云相存在;此次航测以云粒子谱仪所测数浓度大于5 cm^-3作为过冷滴存在的下限判定指标是比较可信的;此外，飞机在此次航测中的自然结冰强度为微量结冰，没有探测到符合《运输类飞机适航标准》附录C曲线要求的结冰气象条件。

Abstract:

Accurate knowledge of the phase of small cloud particles (d<50 μm) is crucial for understanding cloud microphysical processes and radiative effects,which remain major sources of uncertainty in weather and climate models.In situ measurements provide an effective means of obtaining cloud particle phase information;however,detecting the phase of small particles in airborne cloud physics observations has long been challenging.Utilizing the polarization properties of cloud particles to distinguish their phase has recently become recognized as an effective approach.This study focuses on the processing and application of polarization parameters measured by the Cloud Aerosol Spectrometer with Depolarization (CAS-DPOL),a commercial instrument developed by Droplet Measurement Technologies (DMT),USA.The CAS-DPOL was recently introduced into China's meteorological observation system and developed—together with other cloud microphysical probes—aboard the Inner Mongolia weather modification aircraft Y-12.Despite its operational use,no prior studies in China have reported the application of polarization information from CAS-DPOL,primarily due to the absence of dedicated data processing methods.
To address this limitation,this study integrates and refines a set of algorithms and threshold criteria suitable for processing CAS-DPOL polarization parameters to retrieve cloud particle phase states and related microphysical quantities.Additionally,the inter-arrival time (IAT) and transit time (TT) of detected particles are analyzed to identify shattered and coincidence particles,respectively.
Based on these methods and thresholds,the CAS-DPOL data collected during an airborne campaign over Northeast China,23 May 2021—under a cold vortex synoptic pattern—were analyzed.The results show that,the temperature in the detected clouds was between -1 ℃ and -8 ℃,supercooled cloud droplets accounted for approximately 80.18% of the total particle number concentration.The cloud phase was predominantly mixed-phased,although some regions consisted entirely of supercooled water clouds.For this weather system,a particle number concentration greater than 5 cm^-3 was found to be a reliable lower threshold indicating the presence of supercooled droplets,providing a practical reference for determining cloud-seeding suitability.Furthermore,analysis of in-flight natural icing intensity indicated only minimal icing,with no conditions meeting the CCAR-25 Appendix C criteria.The preliminary results demonstrate that supercooled liquid droplets can be effectively distinguished from ice crystals using the proposed processing methods in conjunction with CAS-DPOL measurements.Although further validation is needed,the findings highlight the strong potential of CAS-DPOL and the developed algorithms for applications in cloud microphysics research,artificial weather modification,and aircraft icing detection.