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During the natural icing test flight of an aircraft, capturing icing weather conditions, selecting optimal meteorological conditions, and processing compliance data have been long-standing challenges. This article analyzes the background and limitations of the formation of the icing meteorological standard in Appendix C of CCAR25, and proposes a flight method for ice detection using an icing experimental research aircraft. This method includes the selection and modification of icing experimental research aircraft, detection target area determination, flight operation strategy, flight safety management, data processing, etc. Based on statistical analysis of detection data, the selection criteria for meteorological conditions for natural icing flight test of civil aircraft are determined. A series of data processing methods and compliance criteria for icing meteorology are standardized, including cloud gaps, liquid water content, total water collection rate, icing rate, icing thickness, and degree of ice shedding. Domestic icing meteorological prediction algorithms are calibrated and verified, and safety control strategies and risk degradation measures for natural icing flight test are explored. A large number of flight tests have shown that this method has strong versatility and significant effects. It has been successfully applied to the certification of C919 aircraft, and strongly supports the independent development of domestic icing airworthiness standards.

The matric suction of saline soil is the driving force that causes water migration, and it is of great significance for exploring the mechanism of water and salt migration in saline frozen soil. In order to investigate the effect of phase transition of soil pore solution induced by temperature on the matric suction of saline soil, the matric suction of different types of saline soils was measured by pF meter under different temperature conditions. The natural soil was first washed to obtain the desalinized soil, then different salt mass ratios of sodium chloride and sodium sulfate (0:6, 4:2, 2:4, 6:0) were added into the desalinized soil to model the composite saline soil, the salt content and water content were set to 6% and 20%, respectively. Subsequently, the remolded saline soil was compacted into the test chamber (0.37 m×0.25 m×0.22 m), and its dry density was controlled at 1.6 g/cm³. Hydra Probe II and pF meter were embedded at 11cm of the sample to measure the liquid water content and matric suction versus temperature. Freezing-thawing box (TMS 9 018-R30), produced by Zhejiang Tomos company, was employed to control the experimental temperature by step cooling method. The temperature range was from 30 to -24 °C, and the temperature interval was 3 °C. The data was collected by CR300 at an interval of 6 h. When the experiment was complete, the temperature effect of saline soil matric suction was analyzed and the effect of water/salt phase transition was explored. The experimental results reveal that the matric suction of saline soil increases almost linearly with the decrease of temperature when no phase transition occurs, which is caused by surface tension and wetting coefficient. Different types of saline soils have different effects on the phase transition process of pore solution, resulting in significant differences in the matric suction of different types of saline soils. The mirabilite crystallizes at 19 °C and the second phase transition occurs at -9 °C for the composite saline soil with 2% NaCl+4% Na2SO4, and the phase transition of composite saline soil with 4% NaCl+2% Na2SO4 occurs at 11 and -16 °C.Sodium chloride can inhibit the occurrence of ice formation, then the matric suction caused by ice formation is reduced, and the segregated frost heave caused by water migration is restrained indirectly. Besides, sodium sulfate is prone to crystallization at positive temperatures, and ice is also produced in the secondary phase transition process, both salt crystallization and ice formation increase the matric suction in sodium sulfate soil, and water and salt redistribute in this process, salt expansion and frost heave are induced. For composite saline soil, sodium sulfate mainly affects the salt crystallization of the soil at a positive temperature, while sodium chloride mainly affects the ice formation of the soil at a negative temperature. The different proportions of the two salts cause significant differences in the salt crystallization temperature and the secondary phase transition temperature, resulting in more complex phase transition laws in composite saline soil, and it is more difficult to predict the matric suction of composite saline soil. In addition, this paper further explores the contribution of ice and salt crystallization to the variation of matric suction, providing effective references for a deeper understanding of the relationship between phase transition processes and matric suction in saline soils. [ABSTRACT FROM AUTHOR]

Qilian Mountains are an important ecological barrier in Northwest China. The precipitation in Qilian Mountains is mainly caused by topographical cloud system. Aircraft detection in Qilian Mountains is of great significance for deepening the understanding of cloud microphysical processes, and for scientifically and effectively carrying out artificial precipitation operations to improve the ecological environment. Using the airborne observations of a topographic cloud precipitation process in Qilian Mountains on 29 August 2020, the microphysical characteristics of the summer cloud precipitation process in Qilian Mountains are studied. The cloud system presents an obvious layered structure. The height of the cloud base is 4000 m, and the water content of the whole layer is relatively rich. The liquid water content (L) is between 0.65 and 1.1 g·m-3, and the cloud water large value area appears at 4500-5300 m altitude, which has a high concentration of cloud droplets. The water content of cloud water is mainly contributed by cloud droplets between 15 and 20 μm. The average concentrations of small cloud particles and large cloud particles are 7.54 cm-3 and 0.86 cm-3. The average effective diameters of small cloud particles and large cloud particles are 11.02 μm and 198.11 μm. The cloud particles in Qilian Mountains have the characteristics of small concentration and large diameter. There are obvious differences in cloud microphysical characteristics between the north and south slopes of Qilian Mountains. Affected by the topography, the concentration and diameter of cloud droplets on the northern slope are larger than those on the southern slope, and L on the northern slope are significantly larger than those on the southern slope too. The spectra of cloud droplets at different heights in Qilian Mountains are respectively unimodal distribution. The spectrum of cloud droplets with a diameter less than 50 μm can be fitted by Gamma distribution, while the spectrum of cloud droplets with a diameter greater than 50 μm shows a power exponent distribution. The ice crystals in the ice layer are mainly grown through the process of sublimation and coalescence. The growth mechanism of the ice crystals in the mixed layer is mainly the Bergeron process, and accompanied by attachment and aggregation growth.

Based on the cloud microphysical detection data of 10-sortie aircraft over southern Sichuan Basin in 2015 and 2017, the liquid water content measured by DMT (Droplet Measurement Technologies) hot-wire liquid water content sensor is examined, and abnormal values in maximum, minimum and negative values are found.There are 4 possible causes for the abnormal maximum, minimum and negative values of liquid water content. First, the errors are caused by multiple parameters such as temperature, air pressure and vacuum velocity, which may lead to the error superposition of calculated values. Second, the on-board operators didn't calibrate the zero before entering the cloud. Third, the on-board operators only calibrate the zero once before entering the cloud during the whole flight. Fourth, the interval between cloud entry and exit is too short, so that the manual zero calibration is inaccurate.Using cloud particle spectrum data from cloud droplet probe (CDP), cloud imaging probe (CIP) and precipitation imaging probe (PIP), three solutions are proposed for calibrating hot-wire liquid water content sensor. Solution 1 is to set the criteria for entering cloud as the concentration of particle above a certain size from CDP probe greater than 0. Solution 2 is to set the criteria for entering cloud as the number concentration of cloud particles greater than 10 cm-3 from CDP probe. Solution 3 is to set the criteria for entering cloud as the number concentration from CDP, CIP and PIP probe greater than 0. The results show that when the number concentration is 0 from CDP, CIP and PIP probe, the original non-zero liquid water content problems are corrected by these solutions.To avoid the influence of ice phase particles on CDP number concentration, the verification is carried out in the positive temperature zone. All the test results show that the negative proportion of liquid water content is also significantly reduced compared with the original data. Solution 1 reduces the negative proportion of liquid water content, and make the minimum and maximum more reasonable than other scales. The liquid water content measured by Solution 1 are more reasonable than Solution 2 and 3.

To develop the method of retrieving cloud liquid water content by using both radar and microwave radiometer, the present study analyzes the data from the dual band cloud radar and microwave radiometer in the comprehensive observation test that was carried out in Longmen by the Chinese Academy of Meteorological Sciences from April to September 2019. Firstly, the temperature (T), relative humidity (RH), liquid water content (LWC) and liquid water path (LWP) retrieved by microwave radiometer zenith observation and off-zenith observation during precipitation events is tested, and then the difference between LWC and LWP retrieved by two kinds of detection equipment is analyzed. The results are as follows: (1) The products retrieved by microwave radiometer in off-zenith observation mode are less affected by precipitation, and the retrieval results are obviously better than those of zenith observation mode. (2) The LWP retrieved by the two detection devices has good correlation and is consistent over time. However, the LWP retrieved by cloud radar is significantly correlated with average echo intensity. With the increase of radar echo, the ratio of LWP retrieved by cloud radar to microwave radiometer increases. (3) The correlation of LWC retrieved by the two detection devices is poor and there is a significant deviation. When the melting layer is not considered, the LWC retrieved by single band cloud radar and microwave radiometer has a similar change trend with height, and the retrieval results of dualband cloud radar and microwave radiometer are significantly different in the range of 1km and above. [ABSTRACT FROM AUTHOR]