Airborne Observations of Cloud Condensation Nuclei Spectra and Aerosols over East Inner Mongolia

A set of vertical profiles of aerosol number concentrations, size distributions and cloud condensation nuclei（CCN）spectra was observed using a passive cloud and aerosol spectrometer（PCASP） and cloud condensation nuclei counter, over the Tongliao area, East Inner Mongolia, China. The results showed that the average aerosol number concentration in this region was much lower than that in heavily polluted areas. Monthly average aerosol number concentrations within the boundary layer reached a maximum in May and a minimum in September, and the variations in CCN number concentrations at different supersaturations showed the same trend. The parameters c and k of the empirical function N = c S^kwere 539 and1.477 under clean conditions, and their counterparts under polluted conditions were 1615 and 1.42. Measurements from the airborne probe mounted on a Yun-12（Y12） aircraft, together with Hybrid Single-Particle Lagrangian Integrated Trajectory model backward trajectories indicated that the air mass from the south of Tongliao contained a high concentration of aerosol particles（1000–2500 cm^（-3）） in the middle and lower parts of the troposphere. Moreover, detailed intercomparison of data obtained on two days in 2010 indicated that the activation efficiency in terms of the ratio of NCCNto N_a（aerosols measured from PCASP） was 0.74（0.4 supersaturations） when the air mass mainly came from south of Tongliao, and this value increased to 0.83 on the relatively cleaner day. Thus, long-range transport of anthropogenic pollutants from heavily polluted mega cities,such as Beijing and Tianjin, may result in slightly decreasing activation efficiencies.

Case Studies of the Microphysical and Kinematic Structure of Summer Mesoscale Precipitation Clouds over the Eastern Tibetan Plateau

Three cases of microphysical characteristics and kinematic structures in the negative temperature region of summer mesoscale cloud systems over the eastern Tibetan Plateau(TP)were investigated using X-band dual-polarization radar.The time-height series of radar physical variables and mesoscale horizontal divergence δderived by quasi-vertical profiles(QVPs)indicated that the dendritic growth layer(DGL,-20°C to-10°C)was ubiquitous,with large-value zones of K_(DP)(specific differential phase),Z_(DR)(differential reflectivity),or both,and corresponded to various dynamic fields(ascent or descent).Ascents in the DGL of cloud systems with vigorous vertical development were coincident with large-value zones of Z_(DR),signifying ice crystals with a large axis ratio,but with no obvious large values of K_(DP),which differs from previous findings.It is speculated that ascent in the DGL promoted ice crystals to undergo further growth before sinking.If there was descent in the DGL,a high echo top corresponded to large values of K_(DP),denoting a large number concentration of ice crystals;but with the echo top descending,small values of K_(DP) formed.This is similar to previous results and reveals that a high echo top is conducive to the generation of ice crystals.When ice particles fall to low levels(-10℃ to 0℃),they grow through riming,aggregation,or deposition,and may not be related to the kinematic structure.It is important to note that this study was only based on a limited number of cases and that further research is therefore needed.

Aircraft Observation and Simulation of the Supercooled Liquid Water Layer in a Warm Conveyor Belt over North China

This paper studied a snow event over North China on 21 February 2017,using aircraft in-situ data,a Lagrangian analysis tool,and WRF simulations with different microphysical schemes to investigate the supercooled layer of warm conveyor belts(WCBs).Based on the aircraft data,we found a fine vertical structure within clouds in the WCB and highlighted a 1-2 km thin supercooled liquid water layer with a maximum Liquid Water Content(LWC) exceeding0.5 g kg^(-1) during the vertical aircraft observation.Although the main features of thermodynamic profiles were essentially captured by both modeling schemes,the microphysical quantities exhibited large diversity with different microphysics schemes.The conventional Morrison two-moment scheme showed remarkable agreement with in-situ observations,both in terms of the thermodynamic structure and the supercooled liquid water layer.However,the microphysical structure of the WCB clouds,in terms of LWC and IWC,was not apparent in HUJI fast bin scheme.To reduce such uncertainty,future work may focus on improving the representation of microphysics in bin schemes with in-situ data and using similar assumptions for all schemes to isolate the impact of physics.

Microphysical Characteristics of Precipitation during Pre-monsoon,Monsoon, and Post-monsoon Periods over the South China Sea

Raindrop size distribution (RSD) characteristics over the South China Sea (SCS) are examined with onboard Parsivel disdrometer measurements collected during marine surveys from 2012 to 2016. The observed rainfall is divided into premonsoon, monsoon, and post-monsoon periods based on the different large-scale circumstances. In addition to disdrometer data, sounding observation, FY-2E satellite, SPRINTARS (Spectral Radiation-Transport Model for Aerosol Species), and NCEP reanalysis datasets are used to illustrate the dynamical and microphysical characteristics associated with the rainfall in different periods. Significant variations have been observed in respect of raindrops among the three periods. Intercomparison reveals that small drops (D < 1 mm) are prevalent during pre-monsoon precipitation, whereas medium drops (1?3 mm) are predominant in monsoon precipitation. Overall, the post-monsoon precipitation is characterized by the least concentration of raindrops among the three periods. But, several large raindrops could also occur due to severe convective precipitation events in this period. Classification of the precipitation into stratiform and convective regimes shows that the lg(Nw) value of convective rainfall is the largest (smallest) in the pre-monsoon (post-monsoon) period, whereas the Dm value is the smallest (largest) in the pre-monsoon (post-monsoon) period. An inversion relationship between the coefficient A and the exponential b of the Z?R relationships for precipitation during the three periods is found. Empirical relations between Dm and the radar reflectivity factors at Ku and Ka bands are also derived to improve the rainfall retrieval algorithms over the SCS. Furthermore, the possible causative mechanisms for the significant RSD variability in different periods are also discussed with respect to warm and cold rain processes, raindrop evaporation, convective activities, and other meteorological factors.

Microphysical Processes of a Stratiform Precipitation Event over Eastern China:Analysis Using Micro Rain Radar data

Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.

Aircraft Measurements of the Microphysical Properties of Stratiform Clouds with Embedded Convection

The presence of embedded convection in stratiform clouds strongly affects ice microphysical properties and precipitation formation.In situ aircraft measurements,including upward and downward spirals and horizontal penetrations,were performed within both embedded convective cells and stratiform regions of a mixedphase stratiform cloud system on 22 May 2017.Supercooled liquid water measurements,particle size distributions,and particle habits in different cloud regions were discussed with the intent of characterizing the riming process and determining how particle size distributions vary from convective to stratiform regions.Significant amounts of supercooled liquid water,with maxima up to 0.6 g m−3,were observed between−3℃ and−6℃ in the embedded convective cells while the peak liquid water content was generally less than 0.1 g m−3 in the stratiform regions.There are two distinct differences in particle size distributions between convective and stratiform regions.One difference is the significant shift toward larger particles from upper−15℃ to lower−10℃ in the convective region,with the maximum particle dimensions increasing from less than 6000μm to over 1 cm.The particles larger than 1 cm at−10℃ are composed of dendrites and their aggregates.The other difference is the large concentrations of small particles(25–205μm)at temperatures between−3℃ and−5℃ in the convective region,where rimed ice particles and needles coexist.Needle regions are observed from three of the five spirals,but only the cloud conditions within the convective region fit into the Hallett-Mossop criteria.

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.

Simulations of Microphysics and Precipitation in a Stratiform Cloud Case over Northern China:Comparison of Two Microphysics Schemes

Using the Weather Research and Forecasting(WRF)model with two different microphysics schemes,the Predicted Particle Properties(P3)and the Morrison double-moment parameterizations,we simulated a stratiform rainfall event on 20–21 April 2010.The simulation output was compared with precipitation and aircraft observations.The aircraft-observed moderate-rimed dendrites and plates indicated that riming contributed significantly to ice particle growth at the mature precipitation stage.Observations of dendrite aggregation and capped columns suggested that aggregation coexisted with deposition or riming and played an important role in producing many large particles.The domain-averaged values of the 24-h surface precipitation accumulation from the two schemes were quite close to each other.However,differences existed in the temporal and spatial evolutions of the precipitation distribution.An analysis of the surface precipitation temporal evolution indicated faster precipitation in Morrison,while P3 indicated slower rainfall by shifting the precipitation pattern eastward toward what was observed.The differences in precipitation values between the two schemes were related to the cloud water content distribution and fall speeds of rimed particles.P3 simulated the stratiform precipitation event better as it captured the gradual transition in the mass-weighted fall speeds and densities from unrimed to rimed particles.

Aircraft Measurements of Cloud–Aerosol Interaction over East Inner Mongolia

To investigate the potential effects of aerosols on the microphysical properties of warm clouds, airborne observational data collected from 2009 to 2011 in Tongliao, Inner Mongolia, China, were statistically analyzed in this study. The results demonstrated that the vertical distribution of the aerosol number concentration（N_a） was similar to that of the clean rural continent. The average aerosol effective diameter（D_e） was maintained at approximately 0.4 μm at all levels. The data obtained during cloud penetrations showed that there was a progressive increase in the cloud droplet concentration（N_c） and liquid water content（LWC） from outside to inside the clouds, while the Nawas negatively related to the Ncand LWC at the same height. The fluctuation of the N_a, Ncand LWC during cloud penetration was more obvious under polluted conditions（Type 1） than under clean conditions（Type 2）. Moreover, the wet scavenging of cloud droplets had a significant impact on the accumulation mode of aerosols, especially on particles with diameters less than 0.4 μm. The minimum wet scavenging coefficient within the cloud was close to 0.02 under Type 1 conditions, while it increased to 0.1 under Type 2 conditions,which proved that the cloud wet scavenging effect under Type 1 conditions was stronger than that under Type 2 conditions.Additionally, cloud droplet spectra under Type 1 conditions were narrower, and their horizontal distributions were more homogeneous than those under Type 2 conditions.

Microphysical characteristics of precipitating cumulus cloud based on airborne Ka-band cloud radar and droplet measurements

Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018,the microphysical structural characteristics of cumulus(Cu)cloud at the precipitation stage were investigated.The cloud droplets in the Cu cloud were found to be significantly larger than those in stratiform(STF)cloud.In the Cu cloud,most cloud particles were between 7 and 10μm in diameter,while in the STF cloud the majority of cloud particles grew no larger than 2μm.The sensitivity of cloud properties to aerosols varied with height.The cloud droplet effective radius showed a negative relationship with the aerosol number concentration(Na)in the cloud planetary boundary layer(PBL)and upper layer above the PBL.However,the cloud droplet concentration(Nc)varied little with decreased Na in the high liquid water content region above 1500 m.High Na values of between 300 and 1853 cm-3 were found in the PBL,and the maximum Na was sampled near the surface in August in the Hebei region,which was lower than that in autumn and winter.High radar reflectivity corresponded to large FCDP(fast cloud droplet probe)particle concentrations and small aerosol particle concentrations,and vice versa for low radar reflectivity.Strong updrafts in the Cu cloud increased the peak radius and Nc,and broadened cloud droplet spectrum;lower air temperature was favorable for particle condensational growth and produced larger droplets.

Evaluating the performance of a WRF microphysics ensemble through comparisons with aircraft observations

observation data obtained in a mesoscale convective system are compared to Weather Research and Forecasting(WRF)model simulations using four microphysics schemes(Morrison,WSM6,P3,SBM)with different complexities.The main purpose of this paper is to assess the performance of the microphysics ensemble in terms of cloud microphysical properties.Results show that although the vertical distributions of liquid water content(LWC)and ice water content(IWC)simulated by the four members are quite different in the convective cloud region,they are relatively uniform in the stratiform cloud region.Overall,the results of the Morrison scheme are very similar to the ensemble average,and both of them are closer to the observations compared to the other schemes.Besides,the authors also note that all members still overpredict the LWC by a factor of 2–8 in some regions,resulting in large deviation between the observation and ensemble average.

Observational Evidence of High Ice Concentration in a Shallow Convective Cloud Embedded in Stratiform Cloud over North China

In this study we observed the microphysical properties, including the vertical and horizontal distributions of ice particles,liquid water content and ice habit, in different regions of a slightly supercooled stratiform cloud. Using aircraft instrument and radar data, the cloud top temperature was recorded as higher than -15℃, behind a cold front, on 9 September 2015 in North China. During the flight sampling, the high ice number concentration area was located in the supercooled part of a shallow convective cloud embedded in a stratiform cloud, where the ambient temperature was around -3℃. In this area,the maximum number concentrations of particles with diameter greater than 100 μm and 500 μm（N_（100） and N_（500）） exceeded 300 L-（-1） and 30 L-（-1）, respectively, and were related to large supercooled water droplets with diameter greater than 24 μm derived from cloud–aerosol spectrometer probe measurements. The ice particles types in this region were predominantly columnar, needle, graupel, and some freezing drops, suggesting that the occurrence of high ice number concentrations was likely related to the Hallett–Mossop mechanism, although many other ice multiplication processes cannot be totally ruled out.The maximum ice number concentration obtained during the first penetration was around two to three orders of magnitude larger than that predicted by the Demott and Fletcher schemes when assuming the cloud top temperature was around-15℃.During the second penetration conducted within the stratiform cloud, N_（100） and N_（500） decreased by a factor of five to ten, and the presence of columnar and needle-like crystals became very rare.

Idealized numerical simulation experiment of ice seeding in convective clouds using a bin microphysics scheme

A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud seeding with an ice concentration of 1000 Lin a regime that has relatively high supercooled liquid water can obtain a positive effect,the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment.In no-shear environment,the change in the microphysical thermodynamic field after seeding shows that,although more graupel is produced via riming and this can increase the surface rainfall intensity,the larger drag force and cooling of melting graupel is unfavorable for the development of cloud.On the contrary,when the cloud develops in a wind shear environment,since the main downdraft is behind the direction of movement of the cloud,its negative effect on precipitation is much weaker.

Impact of Soil Moisture Uncertainty on Summertime Short-range Ensemble Forecasts

To investigate the impact of soil moisture uncertainty on summertime short-range ensemble forecasts（SREFs）, a fivemember SREF experiment with perturbed initial soil moisture（ISM） was performed over a northern China domain in summertime from July to August 2014. Five soil moisture analyses from three different operational/research centers were used as the ISM for the ensemble. The ISM perturbation produced notable ensemble spread in near-surface variables and atmospheric variables below 800 h Pa, and produced skillful ensemble-mean 24-h accumulated precipitation（APCP24） forecasts that outperformed any single ensemble member. Compared with a second SREF experiment with mixed microphysics parameterization options, the ISM-perturbed ensemble produced comparable ensemble spread in APCP24 forecasts, and had better Brier scores and resolution in probabilistic APCP24 forecasts for 10-mm, 25-mm and 50-mm thresholds. The ISM-perturbed ensemble produced obviously larger ensemble spread in near-surface variables. It was, however, still under-dispersed, indicating that perturbing ISM alone may not be adequate in representing all the uncertainty at the near-surface level, indicating further SREF studies are needed to better represent the uncertainties in land surface processes and their coupling with the atmosphere.

Evaluation of the Predicted Particle Properties (P3) Microphysics Scheme in Simulations of Stratiform Clouds with Embedded Convection

To evaluate the ability of the Predicted Particle Properties(P3)scheme in the Weather Research and Forecasting(WRF)model,we simulated a stratiform rainfall event over northern China on 22 May 2017.WRF simulations with two P3 versions,P3-nc and P3-2ice,were evaluated against rain gauge,radar,and aircraft observations.A series of sensitivity experiments were conducted with different collection efficiencies between ice and cloud droplets.The comparison of the precipitation evolution between P3-nc and P3-2ice suggested that both P3 versions overpredicted surface precipitation along the Taihang Mountains but underpredicted precipitation in the localized region on the leeward side.P3-2ice had slightly lower peak precipitation rates and smaller total precipitation amounts than P3-nc,which were closer to the observations.P3-2ice also more realistically reproduced the overall reflectivity structures than P3-nc.A comparison of ice concentrations with observations indicated that P3-nc underestimated aggregation,whereas P3-2ice produced more active aggregation from the self-collection of ice and ice-ice collisions between categories.Efficient aggregation in P3-2ice resulted in lower ice concentrations at heights between 4 and 6 km,which was closer to the observations.In this case,the total precipitation and precipitation pattern were not sensitive to riming.Riming was important in reproducing the location and strength of the embedded convective region through its impact on ice mass flux above the melting level.

Review of Chinese atmospheric science research over the past 70 years: Atmospheric physics and atmospheric environment

Since the founding of the People’s Republic of China 70 years ago,the subject of atmospheric physics and atmospheric environment has developed rapidly in China,providing important support for the development of atmospheric science and guarantee for the development of national economy.In this paper,the general advancement of atmospheric physics and atmospheric environment in last 70 years was described.The main research progress of atmospheric physics and atmospheric environment in the past 40 years of reform and opening-up was reviewed,the outstanding research achievements since the 21 st century were summarized,the major problems and challenges are pointed out,and the key directions and suggestions for future development are put forward.