基于SBDART辐射传输模型的夜间辐射雾自动检测及时间序列分析

如何确定合适的阈值来区分夜间辐射雾、晴空地表和中高云一直是雾检测研究的重点。圣巴巴拉DISORT大气辐射传输模型(Santa Barbara DISORT atmospheric radiative transfer,SBDART)可模拟雾顶亮度温度。基于该模型获取MODIS B20与B31波段的亮温差(brightness temperature difference,BTD),将其用于夜间辐射雾检测。以MODIS卫星数据为可行性试验数据,用国家卫星气象中心提供的地面验证数据进行验证,结果表明,使用该模型监测夜间雾的准确率达78.3%,误判率为21.7%,可靠性指标为0.643,Kappa系数为0.730。为进一步验证方法的稳定性,选取8景卫星序列图像进行时间序列分析,结果显示Kappa系数均值为0.744,说明应用当前阈值方法对MODIS夜间雾检测具有可适用性。该方法为夜间雾预报和夜间雾参数反演提供了有效的参考。

西北地区气溶胶光学特性及辐射影响

利用SACOL(兰州大学半干旱气候与环境观测站)2006~2012年AERONET(全球气溶胶自动监测网)level 2.0和太阳短波辐射计资料,分析了中国西北地区气溶胶的光学特性与辐射影响。利用辐射传输模式SBDART(平面平行大气辐射传输模式)检验TOA(大气层顶)处辐射强迫为正的原因。BOA(地表)、TOA、Atmosphere(大气)的辐射强迫年均值分别是-59.43 W m^(-2)、-17.03 W m^(-2)、42.40 W m^(-2),AOD(光学厚度,550nm)年均值0.37,α(波段的波长指数,440~675 nm)年均值0.91,变化趋势与AOD位相相反,当AOD为0.3~2.2时,α很小(0.0~0.2),表明粒子尺度很大。SSA(单次散射反照率,675 nm)年均值0.93,g(不对称因子,675 nm)年均值0.68,复折射指数(675 nm)实部年均值1.48,虚部0.007。复折射指数实部的年变化趋势与AOD一致,虚部与AOD反位相,所以西北地区多为粗模态散射性气溶胶。气溶胶对大气的加热率最大值出现在0~2km,随高度递减。冬、夏半年在地表加热率分别是2.6 K d^(-1)和0.6 K d^(-1);季节变化中,冬季、秋季、春季和夏季,在地表的加热率依次是2.5 K d^(-1)、1.4 K d^(-1)、1.2 K d^(-1)和0.2 K d^(-1),主要因为秋季气溶胶的吸收性大于春季。地表反照率和SSA对TOA正辐射强迫贡献率分别是22.5%和77.5%。

Aerosol optical properties and its direct radiative forcing over Tibetan Plateau from 2006 to 2017

Studies on optical properties of aerosols can reduce the uncertainty for modelling direct radiative forcing(DRF)and improve the accuracy for discussing aerosols effects on the Tibetan Plateau(TP)climate.This study investigated the spatiotemporal variation of aerosol optical and microphysical properties over TP based on OMI and MERRA2,and assessed the influence of aerosol optical properties on DRF at NamCo station(30°46.44′N,90°59.31′E,4730 m)in the central TP from 2006 to 2017 based on a long measurement of AERONET and the modelling of SBDART model.The results show that aerosol optical depth(AOD)exhibits obvious seasonal variation over TP,with higher AOD500nm(>0.75)during spring and summer,and lower value(<0.25)in autumn and winter.The aerosol concentrations show a fluctuated rising from 1980 to 2000,significant increasing from 2000 to 2010 and slight declining trend after 2013.Based on sensitivity experiments,it is found that AOD and single scattering albedo(SSA)have more important impact on the DRF compared withαvalues and ASY.When AOD440nm increases by 60%,DRF at the TOA and ATM is increased by 57.2%and 60.2%,respectively.When SSA440nm increases by 20%,DRF at the TOA and ATM decreases by 121%and 96.7%,respectively.

Accurate Shortwave Radiation Simulation with a Two-Layer Aerosol Model in Xinjiang Region

To harness the rich solar energy resources in Xinjiang Region of Northwest China,this study tries to address the issue of lack of downward surface shortwave radiation(DSSR)observations and the need to improve the accuracy of satellite retrieval and numerical simulation of DSSR under varied sky and meteorological conditions.(1)A two-layer aerosol model specific to Xinjiang was developed to capture the vertical distributions of aerosols based on multiple data sources including lidar,GPS sounding,ground meteorological observations,and profiles from the ECMWF reanalysis version 5(ERA5)data.The results show that the ERA5/PBLH(planetary boundary layer height)and ERA5/ALH(aerosol layer height)could be used to establish the two-layer aerosol model and characterize the vertical distribution of aerosols in Xinjiang Region.(2)Using the Santa Barbara Discrete Atmospheric Radiative Transfer(SBDART)model,a localized inverse model of clear-sky DSSR was established.After parameter adjustment and using the optimal combination of input parameters for DSSR simulation together with the two-layer aerosol model,the model-simulated DSSR(DSSRSBD)under clear-sky conditions improved significantly compared to the initial results,with all fitting indices greatly improved.(3)In addition,the study demonstrated that the impact of the two-layer aerosol model on DSSR was more pronounced under dust conditions than clear-sky conditions.(4)Using the localized clear-sky DSSR inversion model and its required parameters,simulations were also conducted to capture the spatiotemporal distribution of DSSR under clear-sky conditions in Xinjiang from 2017 to 2019.The annual average DSSR_(SBD)under clear-sky conditions in Xinjiang during 2017–2019 was 606.78 W m^(-2),while DSSR from CERES(DSSR_(CER))under the same conditions was generally higher(703.95 W m^(-2)).(5)It is found that satellite remote sensing products experienced data loss in high-altitude snow areas,where numerical simulation technology could serve as a valuable complement.

基于激光雷达和SBDART模式的大气散射辐射亮度计算

为给辐射传输方程求解提供足够的气溶胶状态信息,提出了一种双波长拉曼-米激光雷达探测技术和系统。首先,设计了高性能4通道分光系统,用于提取中心波长分别为354.7 nm和1064.2 nm以及386.7 nm和852.7 nm的米-瑞利散射回波信号和氮气拉曼散射回波信号,实现对大气气溶胶的精细探测和反演。然后,在不同天气条件下利用该系统开展了探测实验,通过反演的气溶胶多参量廓线构建了由33层光学厚度、单次散射反照率、散射相函数组成的实际大气气溶胶状态参数列表,并将其作为平面平行辐射传输(SBDART)模式的实际大气自定义气溶胶输入文件。最后,求解辐射传输方程,得到33层实际大气散射辐射亮度分布以及太阳直接和散射辐射亮度的计算结果。通过分析不同天气条件下的实际大气散射辐射亮度,验证了大气气溶胶状态对大气散射辐射亮度的决定性影响。实验结果表明,该系统与地面气象站测量的总辐射亮度平均相对误差为8.2%,相关性系数达到0.98。