In this study, the effective radius of aerosol particles was experimentally retrieved using a self-developed dual-wavelength atmospheric aerosol lidar. A single-valued lookup table was first established, based on the OPAC database and the Gamma size distribution model, to define the relationship between the extinction coefficient ratio and the effective radius of atmospheric aerosol particles. The extinction coefficients corresponding to the 355 nm and 1064 nm wavelengths were then calculated using the echo signals retrieved horizontally by the lidar, in conjunction with the Mie scattering lidar equation. Subsequently, the lookup table was used to retrieve the real-time effective radius of aerosol particles by inputting the extinction coefficient ratio of the two wavelengths. Finally, the retrieval results were compared with the effective radii measured by an optical particle spectrometer, which had been corrected for relative humidity. An analysis over six months showed a coefficient of determination (R2) greater than 0.83. The results demonstrated that the dual-wavelength lidar exhibits a stable performance, the retrieval method is valid, and the detection results are accurate and reliable.

Meteorological radars, as remote sensing instruments, play a vital role in observing clouds and precipitation. However, due to the complexity of hydrometeors in shape, density, diameter, orientation, and particle size distributions, accurate quantification of the inner microphysical characteristics of a cloud/precipitation system is challenging for a single-frequency radar. Recently, the advancement in scattering theory of hydrometeors, computer science, and hardware manufacturing (such as millimeter-wave devices) has stimulated the application of multi-frequency radars, bringing novel observations for an improved understanding of cloud and precipitation microphysics. Over the past few years, the multi-frequency vertical detection techniques have evolved from the new retrieval methods being enlightened by scattering theory to a new stage of the crucial microphysical processes being revealed by field observations. In this paper, from the perspectives of liquid and frozen hydrometeor microphysics, we introduce the key techniques used for dual- and triple-frequency radar retrieval techniques based on the scattering and attenuation of hydrometeors. Meanwhile, enlightened by the scattering of hydrometeors, we propose that the multi-frequency radar detecting techniques are developing from the classical W/Ka/X wavelengths to a "triple-frequency plus" stage, involving radars with shorter wavelengths and/or longer wavelengths. With spaceborne radars being developed from single-frequency to dual-frequency radars, the improvement of ground-based multi-frequency radars is expected to provide crucial support to future spaceborne multi-frequency radar missions.

Significance Aerosol–cloud interaction affects the cooling of Earth’s climate, mostly by activation of aerosols as cloud condensation nuclei that can increase the amount of sunlight reflected back to space. But the controlling physical processes remain uncertain in current climate models. We present a lidar-based technique as a unique remote-sensing tool without thermodynamic assumptions for simultaneously profiling diurnal aerosol and water cloud properties with high resolution. Direct lateral observations of cloud properties show that the vertical structure of low-level water clouds can be far from being perfectly adiabatic. Furthermore, our analysis reveals that, instead of an increase of liquid water path (LWP) as proposed by most general circulation models, elevated aerosol loading can cause a net decrease in LWP.

This study developed a method of reconstructing the aerosol extinction coefficient based on hourly observations of the fine-particle (PM2.5) mass concentration, relative humidity (RH), and visibility at 9 stations in China between 2014 and 2015. First, we applied κ-Kӧhler theory to evaluate the number concentration distribution of the fine particles under ambient conditions from the PM2.5 mass and then used Mie theory to calculate the aerosol extinction coefficient. Second, we established the reconstruction model and identified reference values for the relevant parameters. After sensitivity tests confirmed good agreement between the extinction coefficients obtained through combinations of various values and those resulting from the reference values, linear regression was employed to reduce the discrepancy between the reconstructed and the observed coefficients. A closure study enabled us to determine the threshold of the extinction ratio (β/βObs) and identify haze and fog weather phenomena at the stations. Finally, we assessed the bias in the predicted number of hours with haze for 61 stations in China by comparing the estimates derived from different values for the model’s parameters with those derived from the reference values and found a relative bias of less than 15

Based on the concepts of cloud water resource (CWR) and related variables proposed in the first part of this study, this paper provides details of two methods to quantify the CWR. One is diagnostic quantification (CWR-DQ) based on satellite observations, precipitation products, and atmospheric reanalysis data; and the other is numerical quantification (CWR-NQ) based on a cloud resolving model developed at the Chinese Academy of Meteorological Sciences (CAMS). The two methods are applied to quantify the CWR in April and August 2017 over North China, and the results are evaluated against all available observations. Main results are as follows. (1) For the CWR-DQ approach, reference cloud profiles are firstly derived based on the CloudSat/CALIPSO joint satellite observations for 2007–2010. The NCEP/NCAR reanalysis data in 2000–2017 are then employed to produce three-dimensional cloud fields. The budget/balance equations of atmospheric water substance are lastly used, together with precipitation observations, to retrieve CWR and related variables. It is found that the distribution and vertical structure of clouds obtained by the diagnostic method are consistent with observations. (2) For the CWR-NQ approach, it assumes that the cloud resolving model is able to describe the cloud microphysical processes completely and precisely, from which four-dimensional distributions of atmospheric water vapor, hydrometeors, and wind fields can be obtained. The data are then employed to quantify the CWR and related terms/quantities. After one-month continuous integration, the mass of atmospheric water substance becomes conserved, and the tempospatial distributions of water vapor, hydrometeors/cloud water, and precipitation are consistent with observations. (3) Diagnostic values of the difference in the transition between hydrometeors and water vapor (Cvh − Chv) and the surface evaporation (Es) are well consistent with their numerical values. (4) Correlation and bias analyses show that the diagnostic CWR contributors are well correlated with observations, and match their numerical counterparts as well, indicating that the CWR-NQ and CWR-DQ methods are reasonable. (5) Underestimation of water vapor converted from hydrometeors (Chv) is a shortcoming of the CWR-DQ method, which may be rectified by numerical quantification results or by use of advanced observations on higher spatiotemporal resolutions.

The water in the air is composed of water vapor and hydrometeors, which are inseparable in the global atmosphere. Precipitation basically comes from hydrometeors instead of directly from water vapor, but hydrometeors are rarely focused on in previous studies. When assessing the maximum potential precipitation, it is necessary to quantify the total amount of hydrometeors present in the air within an area for a certain period of time. Those hydrometeors that have not participated in precipitation formation in the surface, suspending in the atmosphere to be exploited, are defined as the cloud water resource (CWR). Based on the water budget equations, we defined 16 terms (including 12 independent ones) respectively related to the hydrometeors, water vapor, and total water substance in the atmosphere, and 12 characteristic variables related to precipitation and CWR such as precipitation efficiency (PE) and renewal time (RT). Correspondingly, the CWR contributors are grouped into state terms, advection terms, and source/sink terms. Two methods are developed to quantify the CWR (details of which are presented in the companion paper) with satellite observations, atmospheric reanalysis data, precipitation products, and cloud resolving models. The CWR and related variables over North China in April and August 2017 are thus derived. The results show that CWR has the same order of magnitude as surface precipitation (P-s). The hydrometers converted from water vapor (C-vh) during the condensation process is the primary source of precipitation. It is highly correlated with P-s and contributes the most to the CWR over a large region. The state variables and advection terms of hydrometeors are two orders of magnitude lower than the corresponding terms of water vapor. The atmospheric hydrometeors can lead to higher PE than water vapor (several tens of percent versus a few percent), with a shorter RT (only a few hours versus several days). For daily CWR, the state terms are important, but for monthly and longer-time mean CWR, the source/sink terms (i.e., cloud microphysical processes) contribute the largest; meanwhile, the advection terms contribute less for larger study areas.

Aerosol radiative properties are key factors in the process of aerosol radiative forcing calculation.The scattering phase function and asymmetry factor facilitate the illustration of the direction of radiative transfer and the estimation of parameters in remote sensing.In the early summer of 2014,aerosol radiative parameters are obtained at Raoyang Meteorology Administration (an agricultural district) with a latest three-wavelength polar nephelometers (Aurora 4000)developed by EcoTech,Australia.Compared with the previous model,the instrument is unique in that it can measure the volume scattering coefficient from () through to 170° degrees and () is 10°,15°,…,90°.Based on the volume scattering coefficient,the scattering phase function can be computed with the traditional formula between them.What's more,one improved approach is proposed to calculate the asymmetry factor with the combination of scattering phase function and backscattering ratio.The backscattering ratio used can be calculated from the backscattering coefficient and total scattering coefficient as defined.Aerosol radiative properties of PM2.5 including calculated scattering phase function and the fitted asymmetry factor are presented during the observation between 16 June and 18 August in 2014.The result suggests that the improved HG aerosol particle phase function can fit the aerosol scattering phase function observed at Raoyang Meteorology Administration of Hebei well.Observed results of forward scattering phase function (15°-20°) and the backscattering ratio are all in good agreement with the numerical results.The average asymmetry factors at the wavelength of 635 nm,525 nm and 450 nm are 0.53,0.57 and 0.57,respectively,with no significant difference possibly due to the size distribution of aerosol.The value of it at 525 nm are accordant with analysis of previous experiments,which indicate the asymmetry factor of dry aerosol are in the range of 0.55 and 0.63 (550 nm).Two examples of different pollution status (dirty period and clean one) are chosen,depending on the scattering coefficient,and the radiative properties are different.During two dirty periods,values of asymmetry factor are between 0.55 and 0.63,which is larger than those in clean periods.For asymmetry factor,mean values at 635 nm,525 nm and 450 nm wavelength are in the range of 0.51-0.53,0.54,0.54,respectively.Such results provide more details and supports for further study of radiative effects of aerosol.

Lidar, radiosonde, and ground-based in situ nephelometer measurements made during an intensive field campaign carried out from July to September 2014 at the Xinzhou meteorological station were used to determine the aerosol hygroscopic growth effect in a cloud-capped, well-mixed boundary layer. Aerosol hygroscopic properties at 355 and 532 nm were examined for two cases with distinct aerosol layers. Lidar-derived maximum enhancement factors in terms of aerosol backscatter coefficient derived using a relative humidity (RH) reference value of 85% were 1.19 at 532 nm and 1.10 at 355 nm for Case I and 2.32 at 532 nm and 1.94 at 355 nm for Case II. To derive the aerosol particle hygroscopic growth factor at specific RH values, the Kasten and Hänel models were used. A comparison of the goodness of fit for the two models showed that the Kasten model performed better. The hygroscopic growth curve for RH>90% was much steeper than that for RH in the range of 85–90%. The slopes of the lidar-derived enhancement factor curve (measured from 85% to 95% RH) and the nephelometer-derived enhancement factor curve (measured from 40% to 62% RH) in Case I show similar trends, which lends confidence to using lidar measurements for studying aerosol particle hygroscopic growth. Data from a ground aerosol chemical speciation monitor showed that the larger values of aerosol hygroscopic enhancement factor in Case II corresponded to greater mass concentrations of sulfate and nitrate in the atmosphere.

针对全球范围内大气参数实时监测技术需求，以地表30千米内与人类活动密切相关的大气空间为探测对象，依据大气分子的拉曼散射原理，开展具有自主知识产权的紫外域波长激光雷达探测大气水汽、温度和气溶胶特性的系统及实验研究，主要涉及拉曼激光雷达系统探测技术、微弱信号提取技术与方法、大动态范围的数据拼接与校正技术、多参量并行精细探测及反演技术和模块化系统集成技术与对比实验研究等多学科交叉技术。结合多年来研究大气水汽和温度拉曼激光雷达技术的积累，研制了以特殊分色片和窄带干涉滤光片为核心的高性能拉曼分光系统，实现了大气分子的振动和转动拉曼信号的高效精细提取技术，构建了拉曼激光雷达系统，实现了对大气水汽、温度与气溶胶廓线的精细探测。长期实验探测性能稳定，可靠性高，可作为区域性大气和空间环境地基激光雷达监测基地继续开展长期观测实验研究。

The total column-averaged volume mixing ratio of atmospheric carbon dioxide (\( {\text{X}}_{{{\text{CO}}_{ 2} }} \)) has been retrieved with high spectral resolution solar absorption data obtained from ground-based Fourier transform spectrometer (FTS) measurements at Xichong, a coastal site in the district of Shenzhen in southern China. Based on differential optical absorption spectroscopy (DOAS) theory, the \( {\text{X}}_{{{\text{CO}}_{ 2} }} \) was retrieved by finding the best match of observed high spectral resolution solar absorption data and monochromatic radiation transfer model calculations. The averaged \( {\text{X}}_{{{\text{CO}}_{ 2} }} \) in the whole observation period was about 394.9 ppm. The uncertainty of the retrieval was estimated to be 2.0 ppm (0.51 %) by comparing retrievals at two bands. The preliminary results show that \( {\text{X}}_{{{\text{CO}}_{ 2} }} \) retrieved by this method can be used to validate satellite remote sensing of \( {\text{X}}_{{{\text{CO}}_{ 2} }} .\)

以布设在天津的由13部地基GPS组成的高密度小尺度探测网为基础,对蒙特卡罗层析算法中GPS平均站距、层析时间间隔以及蒙特卡罗随机次数3个影响层析算法的关键参数进行敏感性实验和分析.实验表明,层析解算精度随着平均站距的降低和蒙特卡罗次数的增加而提高,增加层析时间间隔对提高层析算法结果的精度作用不明显.同时提出采用“最优+次优”的两组残差最小水汽场的平均作为最终层析场的方法,使得水汽场绝对偏差较前人所采用的只取残差最小水汽场的方法减少约30％.

黑体为目标的能见度测量是从科西米德定律出发,通过工业相机对黑体目标物进行拍摄,建立黑体和背景天空的数学模型,求得能见度.分析表明:当能见度小于30 km,黑体黑度和CCD(change coupled device)工业相机的面非均匀性对该方法测得的能见度造成的误差约为3.7％.该方法与前向散射能见度仪测量进行对比,能见度变化趋势上具有一致性;但在高能见度时,黑体能见度测量值大于前向散射能见度测量值,低能见度时,黑体测量值小于前向散射能见度测量值.

The PM10 mass concentration from 428 ground sites in Eastern China in 2011 were used to investigate the temporal representative of satellites carrying MODIS for air quality monitoring.The daily,monthly,seasonal and yearly averaged ground measurements of PM10 mass concentration at the time when the satellite data is available(SATPM) were compared with the corresponding 24 hours averaged ground measurements(ALLPM).The data with the Aqua-MODIS time are more close to ALLPM than those with Terra-MODIS time,and most relative errors fall into the range of ±20%,indicating a high reliability of temporal representative on Aqua time.Data from both satellites were incorporated together through a linear fitting to get the validated daily and yearly SATPM.The results show a better correlation and own lower root mean square errors(RMSE) with ALLPM.Because PM2.5 is more correlated with optical observations,the results are also of significant implications for the reliability of PM2.5 retrieval from satellite.

Based on the principle that the reflectivity at a water(or ice) absorbing band primarily depends on cloud particle size,the comparison of effective particle radius of water cloud is made,retrieved from the data of channel 3(3.7μm) of FY-3A Visible and Infrared Radiometer(VIRR) and the data of channel 6 (1.64μm) and channel 7(2.13μm) of FY-3A Medium Resolution Spectral Imager(MERSI)using SBDART radiation transfer mode.The results show that the effective particle radius can be quantitatively retrieved by any of the three channels of 1.64,2.13 and 3.7μm.The reflectivity of channel 1.64 and 2.13μm is more sensitive to the larger particles while channel 3.7μm shows better sensitivity when optical thickness is smaller.The retrieve product of effective particle radius of the three channels have better correlations with the effective particle radius products of MODIS.

Up to now, all analysis of the distribution of water vapor over the Taklimakan desert area only depends on limited ground measurements and radio soundings setting mostly on the outer margin area. This paper establishes an approach to retrieve the water vapor over the desert at high temporal and spatial resolutions by the use of FY2C geostationary satellite split-window channels in cooperation with ground-based GPS water vapor measurement. Results show that the water vapor distribution over the Taklimakan desert is affected highly by topography and surface properties. The outer margin area has generally more water vapor than the inner area. Over the outer margin area, the western part has more water vapor than the eastern part, and the northern part has more than the southern part. The driest area lies to the south of Tazhong, east of Hotan River, and extended to the south boundary of the desert. Similar to elsewhere, water vapor over the desert area shows diurnal, monthly, seasonal and annual variations even at the driest inner area of the desert. In summer, the water vapor is transported from west to east over a long distance along the westerlies at a height between 700–400 hPa and with the average speed of 50 km h−1.

A UV vibrational Raman lidar has been built and used to make quantitative measurements of water vapor and aerosol optical properties over Xi'an, China. Vertical profiles of the water vapor mixing ratio and aerosol extinction coefficient are retrieved. The water vapor mixing ratio is calibrated with radiosonde data. The diurnal variations of the water vapor mixing ratio, aerosol extinction coefficient, and aerosol optical depth are obtained. The results obtained in the form of a time-height indicator (THI) display clearly showed the relationship between water vapor and aerosols, in which the gradual enhancement of water vapor density results in aerosol accumulation in the early morning, in particular in the lower troposphere. The seasonal variations of the water vapor mixing ratio and aerosol optical depth over Xi'an were observed and analyzed using the average monthly distribution obtained by lidar for the first time, which will provide useful scientific data and real-time monitoring methods for studying local climate change.

Solar ultraviolet (UV) radiation plays a significant role in climate, atmospheric chemical processes, and ecosystem balance. Aerosol optical depth (AOD) at UV wavelengths, the UV-AOD, is an important quantity for studying the extinction of UV radiation in the atmosphere. Ground-based UV-AOD observations, such as those from the AErosol RObotic NETwork (AERONET), are limited in spatial coverage. Current space derived UV-AOD from the Total Ozone Mapping Spectrometer (TOMS) or the Ozone Monitoring Instrument (OMI), on the other hand, are subject to large errors associated with low resolution, cloud contamination, assumed height of aerosol layer, and low sensitivity to aerosols in the lower troposphere. In this study, a new UV-AOD product is derived for the year 2009 by extrapolating the Moderate Resolution Imaging Spectra-radiometer (MODIS) visible bands AOD product (VIS-AOD) to 380 and 340 nm. Results are evaluated against UV-AOD measurements taken at AERONET sites. Over the oceans, four extrapolating methods are investigated by using two to five wavelengths. The best result, which has a correlation coefficient (R) of 0.90 at both wavelengths and root mean square errors (RMSE) of 0.062 and 0.068 at 380 and 340 nm, respectively, is achieved by combining a linear-extrapolation and a second-order polynomial fitting that takes into account the wavelength dependence of the Ångström exponent. Moreover, more than 80% of the data fall within the uncertainty range of ±0.05 ± 0.20τ. Over land, UV-AOD is extrapolated using the Ångström exponent derived from VIS-AODs at 470 and 660 nm, the only two wavelengths available from the MODIS AOD product. Compared with AERONET observations, the correlation coefficient is about 0.90 at both 380 and 340 nm, while the RMSE increases to 0.152 at 380 nm and 0.174 at 340 nm, due to the larger uncertainty of MODIS AOD over land. With the relatively low biases, this UV-AOD product will be valuable for climate and atmospheric chemistry research. Copyright 2012 American Association for Aerosol Research