Detection of Precipitation Cloud over the Tibet Based on the Improved U-Net

Aiming at the problem of radar base and ground observation stations on the Tibet is sparsely distributed and cannot achieve large-scale precipitation monitoring.U-Net,an advanced machine learning(ML)method,is used to develop a robust and rapid algorithm for precipitating cloud detection based on the new-generation geostationary satellite of FengYun-4A(FY-4A).First,in this algorithm,the real-time multi-band infrared brightness temperature from FY-4A combined with the data of Digital Elevation Model(DEM)has been used as predictor variables for our model.Second,the efficiency of the feature was improved by changing the traditional convolution layer serial connection method of U-Net to residual mapping.Then,in order to solve the problem of the network that would produce semantic differences when directly concentrated with low-level and high-level features,we use dense skip pathways to reuse feature maps of different layers as inputs for concatenate neural networks feature layers from different depths.Finally,according to the characteristics of precipitation clouds,the pooling layer of U-Net was replaced by a convolution operation to realize the detection of small precipitation clouds.It was experimentally concluded that the Pixel Accuracy(PA)and Mean Intersection over Union(MIoU)of the improved U-Net on the test set could reach 0.916 and 0.928,the detection of precipitation clouds over Tibet were well actualized.

Vertical Distribution Characteristics of Precipitation Cloud in Tianjin Based on L-band Sounding Data

Based on L-band sounding data,threshold method of relative humidity was used to analyze vertical distribution characteristics of precipitation cloud system in Tianjin region.The results showed that main precipitation cloud system affecting Tianjin is cold and warm mixed cloud,followed by cold cloud,and precipitation of warm cloud is less.During May-November,precipitation of cold and warm mixed cloud is dominant,and it is dominant by precipitation of cold cloud from January to April.In four seasons,the precipitation frequency of double-layer cloud is the most,and precipitation of single-layer cloud mainly appears during March-November,and peak is in June.Peak of cloud system with three or more layers all appears in July and August.The cold cloud and warm cloud catalysts should be selected respectively for artificial precipitation enhancement in Tianjin.In winter,cold cloud catalyst operation is selected;in spring,summer and autumn,the cold cloud catalyst is spread in the cold cloud area,and the warm cloud catalyst is distributed in the warm cloud area according to the conditions of cloud layer.

A Comprehensive Observational Analysis for the Effects of Gas Cannons on Clouds and Precipitation

To analyze the effects of gas cannons on clouds and precipitation,multisource observational data,including those from National Centers for Environmental Prediction(NCEP)reanalysis,Hangzhou and Huzhou new-generation weather radars,laser disdrometer,ground-based automatic weather station,wind profiler radar,and Lin'an C-band dualpolarization radar,were adopted in this study.Based on the variational dual-Doppler wind retrieval method and the polarimetric variables obtained by the dual-polarization radar,we analyzed the microphysical processes and the variations in the macro-and microphysical quantities in clouds from the perspective of the synoptic background before precipitation enhancement,the polarization echo characteristics before,during and after enhancement,and the evolution of the fine three-dimensional kinematic structure and the microphysical structure.The results show that the precipitation enhancement operation promoted the development of radar echoes and prolonged their duration,and both the horizontal and vertical wind speeds increased.The dual-polarization radar echo showed that the diameter of the precipitation particles increased,and the concentration of raindrops increased after precipitation enhancement.The raindrops were lifted to a height corresponding to 0 to-20℃due to vertical updrafts.Based on the disdrometer data during precipitation enhancement,the concentration of small raindrops(lgN_(w))showed a significant increase,and the mass-weighted diameter D_(m)value decreased,indicating that the precipitation enhancement operation played a certain“lubricating”effect.After the precipitation enhancement,the concentration of raindrops did not change much compared with that during the enhancement process,while the Dm increased,corresponding to an increase in rain intensity.The results suggest the positive effect of gas cannons on precipitation enhancement.

Application of Cloud Precipitation Analysis System in Weather Modification in Fuxin

Based on Cloud Precipitation Analysis System(CPAS),the potential for weather modification during the four types of typical precipitation processes in Fuxin area in 2019 was analyzed,and the model forecast products before weather modification operation and the surface rainfall were compared.

Numerical Simulation on the Rainout-Removal of Sulfur Dioxide and Acidification of Precipitation from Stratiform Clouds

The rainout-removal of SO2 and the acidification of precipitation from stratiform clouds are simulated using a one-dimensional, time-dependent model, parameterized microphysically in which dissolution and dissociation of gaseous SO2 and H2O2, and oxidation reaction in aqueous phase are taken into account. The effects of dynamic factors, including updraft flow and turbulent transport, and the concentration of gaseous SO2 and H2O2 being transported into the clouds on pH value of the precipitation, the conversion rate S(Ⅳ)-S(Ⅵ) and the wet deposition rate of SO2 are discussed.

Numerical study of aerosol effect on three types of clouds and precipitation in Beijing area

Three types of rainfall （storm, moderate and slight rainfall） in the Beijing area were simulated by the Weather Research and Fore- cast （WRF3.2） model coupled with Milbrandt-two-moment cloud microphysics scheme, to explore the effect of aerosols on clouds and precipitation under continental and maritime aerosol scenarios. Results indicate that an increase of aerosols has various effects on clouds and precipitation. （1） The amount of surface precipitation is obviously affected. With an increase of aerosol con- centration, the 48-hr total precipitation of storm and moderate rainfall decreased by 23% and 16.6%, respectively, and the 24-hr total precipitation of slight rainfall decreased by 14.0%. （2） The distribution of surface precipitation is also clearly affected. The average precipitation for a rain storm increases in most parts of western Beijing and decreases by more than 20 mm in most parts of eastern Beijing with increasing aerosol concentration. The average precipitation of moderate rainfall decreases by 0.1-5 mm in most parts of the Beijing area. The effect of increased aerosol concentration is weak for slight rainfall distribution in the study area. （3） With an increase of aerosol concentration, a narrower width and lower precipitation peak value are found in the storm rainfall, and its duration is prolonged for the high aerosol concentration. An earlier precipitation termination of moderate rainfall is found with increasing aerosol concentration. （4） The upper-air hydrometeors vary with aerosol concentration, For storm and moderate rainfall, significantly higher cloud water concentration and lower rain water were found under the continental aerosol scenario.

A Precipitation Detection Method for MWTS-Ⅱ Radiance Assimilation in Typhoon Simulation

FY-3C Microwave Temperature SounderⅡ(MWTS-Ⅱ)lacks observations at 23.8 GHz,31 GHz and 89 GHz,making it difficult to remove the data contaminated by precipitation in assimilation.In this paper,a fast forward operator based on the Community Radiative Transfer Model(CRTM)was used to analyze the relationship between the observation minus background simulation(O-B)and the cloud fractions in different MWTS-Ⅱchannels.In addition,based on the community Gridpoint Statistical Interpolation(GSI)system,the radiation brightness temperature of the MWTS-Ⅱwas assimilated in the regional Numerical Weather Prediction(NWP)model.In the process of assimilation,Visible and Infrared Radiometer(VIRR)cloud detection products were matched to MWTS-Ⅱpixels for precipitation detection.For typhoon No.18 in 2014,impact tests of MWTS-Ⅱdata assimilation was carried out.The results show that,though the bias observation minus analysis(O-A)of assimilated data can be reduced by quality control only with|O-B|<3 K;however,the O-A becomes much smaller while the precipitation detection is performed with Fvirr<0.9(VIRR cloud fraction threshold of 0.9).Besides,the change of the environmental field around the typhoon is more conducive to make the simulated track closer to the observation.The 72-hour typhoon track simulation error also shows that,after the precipitation detection,the error of simulated typhoon track is significantly reduced,which reflects the validity of a precipitation detection method based on a double criterion of|O-B|<3 K and Fvirr<0.9.

Precipitation Microphysical Processes in the Inner Rainband of Tropical Cyclone Kajiki (2019) over the South China Sea Revealed by Polarimetric Radar

Polarimetric radar and 2D video disdrometer observations provide new insights into the precipitation microphysical processes and characteristics in the inner rainband of tropical cyclone(TC)Kajiki(2019)in the South China Sea for the first time.The precipitation of Kajiki is dominated by high concentrations and small(<3 mm)raindrops,which contribute more than 98%to the total precipitation.The average mass-weighted mean diameter and logarithmic normalized intercept are 1.49 mm and 4.47,respectively,indicating a larger mean diameter and a lower concentration compared to the TCs making landfall in eastern China.The ice processes of the inner rainband are dramatically different among different stages.The riming process is dominant during the mature stage,while during the decay stage the aggregation process is dominant.The vertical profiles of the polarimetric radar variables together with ice and liquid water contents in the convective region indicate that the formation of precipitation is dominated by warm-rain processes.Large raindrops collect cloud droplets and other raindrops,causing reflectivity,differential reflectivity,and specific differential phase to increase with decreasing height.That is,accretion and coalescence play a critical role in the formation of heavy rainfall.The melting of different particles generated by the ice process has a great influence on the initial raindrop size distribution(DSD)to further affect the warm-rain processes.The DSD above heavy rain with the effect of graupel has a wider spectral width than the region without the effect of graupel.

Revisiting the size of nonspherical particles recorded by optical array probes with a new method based on the convex hull

In recent years,the Cloud Imaging Probe(CIP)and Precipitation Imaging Probe(PIP)produced by Droplet Measurement Technologies(DMT)have been introduced by a number of meteorological research and operation centers in China.The supporting software provided by DMT,i.e.,PADS(Particle Analysis and Display System),cannot output detailed information on each individual particle,which definitely limits the in-depth utilization of cloud and precipitation particle image data in China.In this paper,particle-by-particle information was extracted by decompressing the CIP and PIP original particle image data,based on which a new definition of the dimension for nonspherical particles is proposed by using the area of the convex hull enclosing a particle to obtain the equivalent diameter of a circle with equal area.Based on the data detected during one flight in Inner Mongolia,the particle size distribution obtained using the new particle size definition and that used by the other four existing definitions are compared.The results show that the particle number concentration calculated using different particle size definitions can vary by up to an order of magnitude.The result obtained based on the new particle size definition is closest to that calculated with the area-equivalent diameter definition.

A Modified Double-Moment Bulk Microphysics Scheme Geared toward the East Asian Monsoon Region

Representation of cloud microphysical processes is one of the key aspects of numerical models.An improved double-moment bulk cloud microphysics scheme(named IMY)was created based on the standard Milbrandt-Yau(MY)scheme in the Weather Research and Forecasting(WRF)model for the East Asian monsoon region(EAMR).In the IMY scheme,the shape parameters of raindrops,snow particles,and cloud droplet size distributions are variables instead of fixed constants.Specifically,the shape parameters of raindrop and snow size distributions are diagnosed from their respective shape-slope relationships.The shape parameter for the cloud droplet size distribution depends on the total cloud droplet number concentration.In addition,a series of minor improvements involving detailed cloud processes have also been incorporated.The improved scheme was coupled into the WRF model and tested on two heavy rainfall cases over the EAMR.The IMY scheme is shown to reproduce the overall spatial distribution of rainfall and its temporal evolution,evidenced by comparing the modeled results with surface gauge observations.The simulations also successfully capture the cloud features by using satellite and ground-based radar observations as a reference.The IMY has yielded simulation results on the case studies that were comparable,and in ways superior to MY,indicating that the improved scheme shows promise.Although the simulations demonstrated a positive performance evaluation for the IMY scheme,continued experiments are required to further validate the scheme with different weather events.

Observational Characteristics of Cloud Vertical Profiles over the Continent of East Asia from the CloudSat Data

The CloudSat satellite data from June 2006 to April 2011 are used to investigate the characteristics of cloud vertical profiles over East Asia （20°-50°N, 80°- 120°E）, with particular emphasis on the profiles of precipitative clouds in comparison with those of nonprecipitative clouds, as well as the seasonal variations of these profiles. There are some obvious differences between the precipitative and nonprecipitative cloud profiles. Generally, precipitative clouds mainly locate below 8 km with radar refiectivity in the range of-20 to 15 dBZ and maximum values appearing within 2-4-km height, and the clouds usually reach the ground; while nonprecipitative clouds locate in the layers of 4 12 km with radar refiectivity between -28 and 0 dBZ and maximum values within 8-10-km height. There are also some differences among the liquid precipitative, solid precipitative, and possible drizzle precipitative cloud profiles. In precipitative clouds, radar reflectivity increases rapidly from 11 to 7 km in vertical, implying that condensation and collision-coalescence processes play a crucial role in the formation of large-size drops. The frequency distribution of temperature at -15℃ is consistent with the highest frequency of radar reflectivity in solid precipitative clouds, which suggests that the temperatures near -15℃ are conductive to deposition and accretion processes. The vertical profiles of liquid precipitative clouds show almost the same distributions in spring, summer, and autumn but with differences in winter at mainly lower levels. In contrast, the vertical profiles of solid precipitative clouds change from spring to winter with an alternate double and single high-frequency core, which is consistent with variations of the frequency distribution of temperature at 15℃. The vertical profiles of nonprecipitative clouds show a little change with season. The observations also show that the precipitation events over East Asia are mostly related to deep convective clouds and nimbostratus clouds. These results are expected to be useful for evaluation of weather and climate .models and for improvement of microphysical parameterizations in numerical models.