Renmin Yuan

Lidar Based Remote Sensing of Atmospheric Boundary Layer Height Over Land and Ocean

Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of the ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and the ABL vertical structure over ocean and land are analyzed. The new methods are then applied to satellite lidar measurements. The aerosol-derived global marine boundary layer heights are evaluated with marine ABL stratiform cloud top heights and results show a good agreement between them.

The Effect of Coordinate Rotation on the Eddy Covariance Flux Estimation in a Hilly KoFlux Forest Catchment

The Gwangneung KoFlux supersite, located in a rugged mountain region, is characterized by a low wind speed due to a mountain-valley circulation and rolling terrain. Therefore, it is essential to understand the effect of coordinate rotation on flux measurements by the eddy-covariance method. In this paper, we review the properties of three orthogonal coordinate frames (i.e., double, triple, and planar fit rotations) and apply to flux data observed at the Gwangneung supersite. The mean offset of vertical wind speed of sonic anemometer was inferred from the planar fit (PF) coordinate rotation, yielding the diurnal variation of about . Double rotation

Global dust distribution from improved thin dust layer detection using A‐train satellite lidar observations

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Recent Trends of Summer Convective and Stratiform Precipitation in Mid-Eastern China.

A new dust detection algorithm was developed to take advantage of strong dust signals in the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) 532 nm perpendicular channel to more accurately identify optically thin dust layer boundaries. Layer mean particulate depolarization ratios and improved thin ice cloud detections by combining CALIPSO and CloudSat products were used to further refine the dust mask. Three year global mean results show that the new method detects dust occurrences total detected dust case numbertotal observation number of 0.12 and 0.028 below and above 4 km altitudes, while CALIPSO Level 2 products reported 0.07 and 0.012, respectively. The improvements are mainly in weak source and transporting regions, and the upper troposphere, where optically thin, but significant dust layers from the point of view of aerosol-cloud interactions are dominated. The results can help us to better understand global dust transportation and dust-cloud interactions and improve model simulations.

On Factors Controlling Marine Boundary Layer Aerosol Optical Depth

Many studies have reported on the trends of precipitation in Mid-Eastern China (EC). However, the trends of convective and stratiform precipitation are still unknown. Here, we examine the trends of summer convective and stratiform precipitation in EC from 2002 to 2012 on the basis of the TRMM observations. Results revealed that the rain frequency (RF) for both convective and stratiform precipitation increased in majority regions of Southern EC (SEC), but decreased in Northwest part of Northern EC (NEC). The decreasing rate of RF for stratiform precipitation in NEC is twice as much as that for convective precipitation, while the increase of convective precipitation in SEC is more evident than stratiform precipitation. The rain rate (RR) exhibited a decreasing trend in most portions of EC for both convective and stratiform precipitation. In SEC, neither PW nor WVT has good ability in explaining the precipitation variability. However, in NEC, PW is closely correlated to convective RF and WVT is more closely related to stratiform RF.

Grid-cell aerosol direct shortwave radiative forcing calculated using the SBDART model with MODIS and AERONET observations: An application in winter and summer in eastern China

Sea spray aerosol is one of the largest natural contributors to the global aerosol loading and thus plays an important role in the global radiative budget through both direct and indirect effects. Previous studies have shown either strong or weak relationships between marine boundary layer (MBL) aerosol optical depth (τ) and the near-surface wind speed. However, the marine τ is influenced by a wide range of factors. This study attempts to examine extra contributing factors beyond wind to better characterize MBL τ variations over the global ocean by using 4 year A-train data (2006–2010). The results show that among many factors controlling MBL τ, surface wind speed and MBL depth are the two most important factors. This suggests that not only mechanical production of sea spray particles driven by near-surface wind processes but also vertical redistribution driven by turbulent and shallow convective mixing in the MBL controls MBL τ variations. A new two-parameter parameterization of τ was derived based on satellite measurements. Evaluations with independent data show that the new parameterization improves the prediction of MBL τ. The comparisons between the Fu-Liou radiative transfer model calculations and Aqua Clouds and the Earths Radiant Energy System observations showed that the new parameterization improves the estimation of aerosol radiative forcing.

Vertically resolved separation of dust and other aerosol types by a new lidar depolarization method

Taking winter and summer in eastern China as an example application, a grid-cell method of aerosol direct radiative forcing (ADRF) calculation is examined using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model with inputs from MODIS and AERONET observations and reanalysis data. Results show that there are significant seasonal and regional differences in climatological mean aerosol optical parameters and ADRF. Higher aerosol optical depth (AOD) occurs in summer and two prominent high aerosol loading centers are observed. Higher single scattering albedo (SSA) in summer is likely associated with the weak absorbing secondary aerosols. SSA is higher in North China during summer but higher in South China during winter. Aerosols induce negative forcing at the top of the atmosphere (TOA) and surface during both winter and summer, which may be responsible for the decrease in temperature and the increase in relative humidity. Values of ADRF at the surface are four times stronger than those at the TOA. Both AOD and ADRF present strong interannual variations; however, their amplitudes are larger in summer. Moreover, patterns and trends of ADRF do not always correspond well to those of AOD. Differences in the spatial distributions of ADRF between strong and weak monsoon years are captured effectively. Generally, the present results justify that to calculate grid-cell ADRF at a large scale using the SBDART model with observational aerosol optical properties and reanalysis data is an effective approach.摘要本文利用SBDART模式, 结合MODIS和AERONET提供的气溶胶数据以及再分析数据, 并以中国东部冬、夏季节为例, 提出了一种模拟计算格点尺度上气溶胶直接辐射强迫的方法.结果表明, 气溶胶光学参数和直接辐射强迫存在明显的季节变化和区域差异.对于光学厚度而言, 夏季的值要明显高于冬季, 且夏季时中国东部存在两个明显的高值区. 对于单次散射反照率来说, 夏季的值也高于冬季, 这主要与夏季时弱吸收性的二次气溶胶增多有关, 且从空间分布上来看, 夏季时中国北方的单次散射反照率值高于南方, 冬季时正相反. 对于中国东部冬、夏季而言, 气溶胶在大气顶和地面层都会造成负的辐射强迫, 且在地面的辐射强迫为大气顶辐射强迫的四倍. 气溶胶的辐射强迫对地面层有明显的降温增湿效果. 除季节变化外, 气溶胶光学厚度和辐射强迫也都表现出明显的年际变化, 且夏季时年际变化比冬季时剧烈. 但是受到单次散射反照率影响, 辐射强迫的年际变化情况并不总是与光学厚度的完全对应. 本文还研究了气溶胶辐射强迫与季风活动的关系, 结果表明气溶胶辐射强迫的空间分布在季风强弱年时存在明显差异. 总体而言, 本文的研究结果表明在较大尺度的区域内, 利用SBDART模式并结合气溶胶观测资料和再分析资料进行格点尺度上气溶胶直接辐射强迫模拟计算的方法是有效的.

The momentum flux‐gradient relations derived from field measurements in the urban roughness sublayer in three cities in China

This paper developed a new retrieval framework of external mixing of the dust and non-dust aerosol to predict the lidar ratio of the external mixing aerosols and to separate the contributions of non-spherical aerosols by using different depolarization ratios among dust, sea salt, smoke, and polluted aerosols. The detailed sensitivity tests and case study with the new method showed that reliable dust information could be retrieved even without prior information about the non-dust aerosol types. This new method is suitable for global dust retrievals with satellite observations, which is critical for better understanding global dust transportation and for model improvements.

A Study of the Distribution and Variability of Cloud Water Using ISCCP, SSM/I Cloud Product, and Reanalysis Datasets

Field measurements of the momentum flux and wind velocity gradient were carried out at three urban sites in the cities of Nanjing, Changzhou, and Suzhou, China. The observational data in the urban roughness sublayer are analyzed to derive the momentum flux-gradient relations in terms of framework of the local similarity theory with a least squares fit, and the relations are then compared to the classical similarity relations of Businger et al. (1971). The results show that the momentum flux varies with height; thus, the constant-flux assumption in the Monin-Obukhov Similarity Theory is not met in the urban roughness sublayer. However, the dimensionless wind velocity gradient may be described by the local similarity theory, and the derived flux-gradient relations have the same form as the classical similarity relations do. Under stable conditions, the coefficient βm in the fitted relations increases with height and gradually approaches the value of 4.7 in the classical similarity relations. The trend suggests that the turbulent flow may be described by the classical similarity relations once the height increases and reaches the top of the urban roughness sublayer, and thus, the height of the top of the urban roughness sublayer may be estimated by linear extrapolation of the derived relations in this study. The relation between the critical Richardson number Ric and the coefficient βm is derived as Ric = Prt/βm, where Prt is the turbulent Prandtl number. In the urban roughness sublayer, the value of Ric is larger than 0.2.

Simulation study on light propagation in an isotropic turbulence field of the mixed layer.

AbstractIn this paper, the global distribution of cloud water based on International Satellite Cloud Climatology Project (ISCCP), Moderate Resolution Imaging Spectroradiometer (MODIS), CloudSat Cloud Profiling Radar (CPR), European Center for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim), and Climate Forecast System Reanalysis (CFSR) datasets is presented, and the variability of cloud water from ISCCP, the Special Sensor Microwave Imager (SSM/I), ERA-Interim, and CFSR data over the time period of 1995 through 2009 is discussed. The results show noticeable differences in cloud water over land and over ocean, as well as latitudinal variations. Large values of cloud water are mainly distributed over the North Pacific and Atlantic Oceans, eastern ITCZ, regions off the west coast of the continents as well as tropical rain forest. Cloud water path (CWP), liquid water path (LWP), and ice water path (IWP) from these datasets show a relatively good agreement in distributions and zonal means. The...