RETRIEVING ATMOSPHERIC SOUNDING PROFILES AROUND TYPHOON YUNNA USING INFRARED HYPERSPECTRAL MEASUREMENTS AIRS

In this study,we derived atmospheric profiles of temperature,moisture,and ozone,along with surface emissivity,skin temperature,and surface pressure,from infrared-sounder radiances under clear sky (cloudless) condition.Clouds were detected objectively using the Atmospheric Infrared Sounder under a relatively low spatial resolution and cloud-mask information from the Moderate Resolution Imaging Spectroradiometer under a high horizontal resolution;this detection was conducted using space matching.Newton’s nonlinear physical iterative solution technique is applied to the radiative transfer equation (RTE) to retrieve temperature profiles,relative humidity profiles,and surface variables simultaneously.This technique is carried out by using the results of an eigenvector regression retrieval as the background profile and using corresponding iterative forms for the weighting functions of temperature and water-vapor mixing ratio.The iterative forms are obtained by applying the variational principle to the RTE.We also compared the retrievals obtained with different types of observations.The results show that the retrieved atmospheric sounding profile has great superiority over other observations by accuracy and resolution.Retrieved profiles can be used to improve the initial conditions of numerical models and used in areas where conventional observations are sparse,such as plateaus,deserts,and seas.     

应用ATOVS资料反演大气温湿廓线

本文用牛顿迭代的方法反演NOAA-15极轨气象卫星ATOVS资料，求解大气温度廓线和水汽廓线，本文利用一阶变分原理从辐射传输方程中得到了大气温度、水汽权重函数的解析形式，并改进了传统使用的线性迭代方法，利用牛顿非线性迭代方法求解大气表层温度，大气温度廓线及大气水汽廓线，并根据大气参量的自相关性，将大气温度廓线、大气水汽廓线用经验正交函数（EOF）的线性组合表示，减少了要反演的参数，提高了反演稳定性和迭代速度。     

The implementation of reverse Kessler warm rain scheme for radar reflectivity assimilation using a nudging approach in New Zealand

Reverse Kessler warm rain processes were implemented within the Weather Research and Forecasting Model (WRF) and coupled with a Newtonian relaxation, or nudging technique designed to improve quantitative precipitation forecasting (QPF) in New Zealand by making use of observed radar reflectivity and modest computing facilities. One of the reasons for developing such a scheme, rather than using 4D-Var for example, is that radar VAR scheme in general, and 4D-Var in particular, requires computational resources beyond the capability of most university groups and indeed some national forecasting centres of small countries like New Zealand. The new scheme adjusts the model water vapor mixing ratio profiles based on observed reflectivity at each time step within an assimilation time window. The whole scheme can be divided into following steps: (i) The radar reflectivity is firstly converted to rain water, and (ii) then the rain water is used to derive cloud water content according to the reverse Kessler scheme; (iii) The cloud water content associated water vapor mixing ratio is then calculated based on the saturation adjustment processes; (iv) Finally the adjusted water vapor is nudged into the model and the model background is updated. 13 rainfall cases which occurred in the summer of 2011/2012 in New Zealand were used to evaluate the new scheme, different forecast scores were calculated and showed that the new scheme was able to improve precipitation forecasts on average up to around 7 hours ahead depending on different verification thresholds.     

TROPOSPHERIC WATER VAPOR OBSERVATIONS USING A RAMAN LIDAR OVER HEFEI*

This paper presents a Raman lidar for measuring tropospheric water vapor profiles over Hefei(31.9°N,117.17°E),China.Intercomparisons of water vapor mixing ratio obtained by this Raman lidar and GZZ-59 type radiosonde observations show the good agreements when relative humidity is higher than 20%.Typical vertical profiles and seasonal variations of water vapor mixing ratio distribution are reported.Many observation eases indicate that the high moisture layer corresponds to large aerosol scattering ratios in the lower troposphere.     

雷达资料同化对2016年6月23日阜宁龙卷模拟的改进

基于GSI（Community Gridpoint Statistical Interpolation）同化系统和WRF（Weather Research and Forecasting）模式,探讨了多部多普勒雷达的反射率因子和径向速度资料同化对2016年6月23日江苏阜宁龙卷模拟的改进效果和影响过程。结果表明:（1）仅同化雷达反射率因子和仅同化径向速度均能在一定程度上改进模式对阜宁龙卷及其环境场的模拟,且雷达径向速度同化的改进作用更大;同时同化两种资料改进效果最佳。（2）雷达反射率因子同化是利用复杂云分析技术,直接修正了水凝物含量,增加了潜热释放,对低层大气热力场进行了正温度扰动调整,从而主要改进了初始场的水汽条件和热力条件;而雷达径向速度同化通过三维变分技术直接修正了风场,进而引起水汽输送变化影响水凝物的调整和大气热力场的变化,对初始场的动力条件和热力条件修正较大;同时同化两种资料修正了初始场的动力和热力结构,保证了两者物理上的协调,综合了两者的改进作用,从而取得最佳模拟效果。（3）同时同化雷达反射率因子和径向速度后,模式在阜宁附近模拟出了明显的涡旋结构,尽管涡旋强度和龙卷结构与实况仍有一定差距,但涡旋发生发展过程、路径、地面小时极大风和降水等模拟与实况吻合度均明显高于对照试验。      

Classification and Diurnal Variations of Precipitation Echoes Observed by a C-band Vertically-Pointing Radar in Central Tibetan Plateau during TIPEX-III 2014-IOP

This study investigates classification and diurnal variations of the precipitation echoes over the central Tibetan Plateau based on the observations collected from a C-band vertically-pointing frequency-modulated continuous-wave (C-FMCW) radar during the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-III) 2014-Intensive Observation Period (2014-IOP). The results show that 51.32% of the vertical profiles have valid echoes with reflectivity >–10 dBZ, and 35.06% of the valid echo profiles produce precipitation at the ground (precipitation profiles); stratiform precipitation with an evident bright-band signature, weak convective precipitation, and strong convective precipitation account for 52.03%, 42.98%, and 4.99% of the precipitation profiles, respectively. About 59.84% of the precipitation occurs in the afternoon to midnight, while 40.16% of the precipitation with weaker intensity is observed in the nocturnal hours and in the morning. Diurnal variation of occurrence frequency of precipitation shows a major peak during 2100–2200 LST (local solar time) with 59.02% being the stratiform precipitation; the secondary peak appears during 1300–1400 LST with 59.71% being the weak convective precipitation; the strong convective precipitation occurs mostly (81.83%) in the afternoon and evening with two peaks over 1200–1300 and 1700–1800 LST, respectively. Starting from approximately 1100 LST, precipitation echoes develop with enhanced vertical air motion, elevated echo top, and increasing radar reflectivity. Intense upward air motion occurs most frequently in 1700–1800 LST with a secondary peak in 1100–1400 LST, while the tops of precipitation echoes and intense upward air motion reach their highest levels during 1600–1800 LST. The atmospheric conditions in the early morning are disadvantageous for convective initiation and development. Around noon, the convective available potential energy (CAPE) increases markedly, convective inhibition (CIN) is generally small, and a super-dry-adiabatic layer is present near the surface (0–400 m). In the early evening, some larger values of CAPE, level of neutral buoyancy, and total precipitable water are present, suggesting more favorable thermodynamic and water vapor conditions.     

Influences of Two Convective Schemes on the Radiative Energy Budget in GAMIL1.0

The Grid-point Atmospheric Model of IAP LASG version 1.0 (GAMIL1.0) is used to investigate the impacts of different convective schemes on the radiative energy budget.The two convective schemes are Zhang and McFarlance (1995)/Hack (1994) (ZM) and Tiedtke (1989)/Nordeng (1994) (TN).Two simulations are performed:one with the ZM scheme (EX_ZM) and the other with the TN scheme (EX_TN).The results indicate that during the convective process,more water vapor consumption and temperature increment are found in the EX_ZM,especially in the lower model layer,its environment is therefore very dry.In contrast,there is a moister atmosphere in the EX_TN,which favors low cloud formation and large-scale condensation,and hence more low cloud fraction,higher cloud water mixing ratio,and deeper cloud extinction optical depth are simulated,reflecting more solar radiative flux in the EX_TN.This explains why the TN scheme underestimates the net shortwave radiative flux at the top of the atmosphere and at surface.In addition,convection influences longwave radiation,surface sensible and latent heat fluxes through changes in cloud emissivity and precipitation.     

基于一维变分算法的红外高光谱(IASI)卫星遥感大气温湿廓线研究

大气温湿度廓线是大气重要参数,在数值天气预报及天气预警中具有重要的应用价值。为获得高精度的大气温度与水汽混合比廓线数据,研究了基于Metop-A/IASI红外高光谱资料的大气温度与水汽混合比廓线变分反演方法。利用IASI高光谱传感器温度和水汽探测通道资料,结合CRTM模式和WRF模式预报技术,使用一维变分方法,研究了卫星资料质量控制、背景误差协方差本地化、观测误差协方差计算等方法,构建了大气温度及水汽混合比廓线变分反演系统,并在北京、青岛、沈阳3个地区开展了反演试验。以探空为标准的反演结果对比显示,使用WRF模式预报值作为背景场,温度的平均误差绝对值小于0.6 K,均方根误差为0.89 K;水汽混合比的平均误差绝对值小于0.021 g/kg,均方根误差为0.02 g/kg。试验结果表明:基于一维变分方法,可以利用Metop-A/IASI红外高光谱资料进行大气温度与水汽混合比廓线高精度探测。     

基于特征向量法的地基红外高光谱反演大气温湿廓线附加影响因子分析

在地基高光谱遥感中,特征向量法获取的温湿廓线以初值的方式对物理反演进行约束,其反演精度对物理反演结果有着重要的影响。利用AERI的观测辐射资料和同站点的探空数据,基于特征向量法分析了温度廓线与湿度廓线反演的异同点;研究了主成分个数的选择问题,综合考虑反演精度和特征向量中包含的信息将反演温度廓线和湿度廓线的最优主成分个数定为7。为提高反演精度,引入地面温度、湿度、气压作为影响因子,试验结果表明,考虑反演精度和稳定性,地面气压的引入相比于其他2种单一气象要素以及3种气象要素组成的因子集表现更好,尤其是对边界层中下部的温湿廓线有着明显的提升,并随着高度的降低提升作用更明显,温度廓线RMSE降低最高达到1.5K,湿度廓线RMSE降低最高达到0.42g/kg。同时,分析了对数反演形式对湿度廓线的影响,结果表明,以水汽混合比的形式反演时取自然对数对反演精度的影响较小;将反演得到的水汽混合比转化为相对湿度后,取自然对数对反演精度有12%以上的提升。     

长江三角洲城市群对夏季降水影响机制的模拟研究

利用耦合了单层城市冠层模型UCM的中尺度模式WRF,对长江三角洲城市群夏季城市化效应进行了5 a(2003—2007年)高分辨数值模拟,并作了长江三角洲地区有无城市的对比试验。结果表明,城市化使得长三角城市群及其邻近地区,夏季近地层水汽混合比呈明显减少趋势,而850~700 h Pa层的水汽混合比有所增大。通过对比有与无城市各等级降水日所对应的2 m水汽混合比,得出小雨降水日对应的2 m水汽混合比差异与总降水日对应的差异最为接近。通过分析环流场、散度场和垂直速度场发现,水汽混合比的垂直变化是由于城市群的存在使得近地层辐合、850~700 h Pa层辐散的配置增强,以及在城市群上空增强了的垂直上升运动,从而增强城区对流活动,水汽的垂直输送也更为活跃,由此可能导致对流性降水的增加。     

集合卡尔曼滤波同化多普勒雷达资料的数值试验

利用集合卡尔曼滤波(EnKF)在云数值模式中同化模拟多普勒雷达资料,并考察了不同条件下EnKF同化方法的性能.结果显示,经过几个同化周期后,EnKF分析结果非常接近真值.单多普勒雷达资料EnKF同化对雷达位置不太敏感,双雷达资料同化结果在同化的初期阶段比单雷达资料同化结果准确.同化由反射率导出的雨水比直接同化反射率资料更有效,联合同化径向速度和雨水有利于提高同化分析效果.协方差对EnKF同化效果起着非常重要的作用,考虑模式全部预报变量与径向速度协方差的同化效果比仅考虑速度场与径向速度协方差的同化效果好.雷达资料缺值降低了同化效果,此时增加地面常规观测资料的同化可以明显提高同化分析效果.EnKF同化技术对雷达观测资料误差不太敏感.初始集合对同化分析有较大影响.EnKF同化受集合大小和观测资料影响半径.同化对模式误差较敏感.利用EnKF同化双多普勒雷达资料,分析了一次梅雨锋暴雨过程的中尺度结构.结果表明,EnKF同化技术能够从双多普勒雷达资料反演暴雨中尺度系统的动力场、热力场和微物理场,反演的风场是较准确的,反演的热力场和微物理场分布也是基本合理的.中低层切变线是此次暴雨的主要动力特征,对流云表现为低层辐合、高层辐散并有垂直上升运动伴随,其热力特征表现为低层是低压区,高层为高压区,中部为暖区而上、下部为冷区,水汽、云水和雨水分别集中在对流云体内、上升气流区和强回波区.     

SENSITIVITY OF SEA SURFACE TEMPERATURE RETRIEVAL TO SEA SURFACE EMISSIVITY

To estimate sea surface temperature(SST)with high accuracy from radiometrie measure-ments,it is no longer acceptable to assume that sea surface emissivity is unity or any other con-stant.This note presents an investigation of the desirable emissivity accuracy in relation to re-trieval.It was found that 1% error in surface emissivity can cause up to 0.7 K error in the re-trieved SST,although this sensitivity is often reduced to about 0.5 K on average because of thedownward atmospheric radiation at surface partially compensates for the emissivity error.Since thedownward atmospheric radiation ratio is controlled to a large extent by the integrated water vaporin the atmosphere and,secondarily,by view angle,the sensitivity of SST retrieval to surface emis-sivity has been computed as a function of these two parameters.     

大气中水汽混合比的Raman激光雷达探测

介绍了作者自行研制的L625Raman激光雷达系统的结构和主要技术参数,叙述了Raman激光雷达探测水汽混合比的基本原理和数据处理方法。使用这台激光雷达在合肥地区进行了水汽混合比垂直分布的探测,对获得的水汽混合比垂直廓线进行了初步的分析和研究。最后就L625Raman激光雷达探测水汽混合比的误差进行了分析和讨论。     

Application of Radar Reflectivity Factor in Initializing Cloud-Resolving Mesoscale Model. Part Ⅰ: Retrieval of Microphysical Elements and Vertical Velocity

Assuming that cloud reaches static state in the warm microphysical processes, water vapor mixing ratio(qv), cloud water mixing ratio (qc), and vertical velocity (w) can be calculated from rain water mixing ratio (qr)- Through relation of Z-qr, qr can be retrieved by radar reflectivity factor (Z). Retrieval results indicate that the distributions of mixing ratios of vapor, cloud, rain, and vertical velocity are consistent with radar images, and the three-dimensional spatial structure of the convective cloud is presented. Treating q,v saturated at the echo area, the retrieved qr is about 0.1 g kg-1, qc is always less than 0.3 g kg-1, w is usually below 0.5 m s-1, and rain droplet terminal velocity (vr) is around 5.0 m s-1 in the place where radar reflectivity factor is about 25 dBz; in the place where echo is 45 dBz, the retrieved qr and qc are always about 3.0 g kg-1, w is greater than 5.0 m s-1, and vr is around 7.0 m s-1. In the vertical, the maximum updraft velocity is greater than 3.0 m s-1 at the height of around 5.0 kin, the maximum cloud water content is about 3.0 g kg-1 above 5 km and the maximum rain water content is about 3.0 g kg-1 below 6 kin. Due to the assumption that the cloud is in static state, there will be some errors in the retrieved variables within the clouds which axe rapidly growing or dying-out, and in such cases, more sophisticated radar data control technique will help to improve the retrieval results.     

The Construction of SCM in GRAPES and Its Applications in Two Field Experiment Simulations

A Single Column Model(SCM) for Global and Regional Atmospheric Prediction Enhanced System (GRAPES) is constructed for the purpose of evaluating physical process parameterizations.Two observational datasets including Wangara and the third Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study(GABLS-3) SCM field observations have been applied to evaluate this SCM.By these two numerical experiments,the GRAPES_SCM is verified to be correctly constructed.Furthermore, the interaction between the land surface process and atmospheric boundary layer(ABL) is discussed through the second experiment.It is found that CASE3(CoLM land surface scheme coupled with ABL scheme) simulates less sensible heat fluxes and smaller surface temperature which corresponds with its lower potential temperature at the bottom of the ABL.Moreover,CASE3 simulates turbulence that is weaker during the daytime and stronger during nighttime,corresponding with its wind speed at 200 m which is bigger during daytime and smaller during nighttime.However,they are generally opposite in CASE2(SLAB coupled with ABL).The initial profile of the water vapor mixing ratio is artificially increased by the experiment setup which results in the simulated water vapor mixing becoming wetter than actually observed.CASE1 (observed surface temperature taken as lower thermal forcing) and CASE2 have no soil moisture prediction and simulate a similar water vapor mixing ratio,while CASE3 has a soil moisture prediction and simulates wetter.It is also shown that the time step may affect the stabilization of the ABL when the vertical levels of the SCM are fixed.     

Estimation of Hourly Solar Radiation at the Surface under Cloudless Conditions on the Tibetan Plateau Using a Simple Radiation Model

In this study,the clear sky hourly global and net solar irradiances at the surface determined using SUNFLUX,a simple parameterization scheme,for three stations(Gaize,Naqu,and Lhasa) on the Tibetan Plateau were evaluated against observation data.Our modeled results agree well with observations.The correlation coefficients between modeled and observed values were > 0.99 for all three stations.The relative error of modeled results,in average was < 7%,and the root-mean-square variance was < 27 W m 2.The solar irradiances in the radiation model were slightly overestimated compared with observation data;there were at least two likely causes.First,the radiative effects of aerosols were not included in the radiation model.Second,solar irradiances determined by thermopile pyranometers include a thermal offset error that causes solar radiation to be slightly underestimated.The solar radiation absorbed by the ozone and water vapor was estimated.The results show that monthly mean solar radiation absorbed by the ozone is < 2% of the global solar radiation(< 14 W m 2).Solar radiation absorbed by water vapor is stronger in summer than in winter.The maximum amount of monthly mean solar radiation absorbed by water vapor can be up to 13% of the global solar radiation(95 W m 2).This indicates that water vapor measurements with high precision are very important for precise determination of solar radiation.     

An evaluation of the surface radiation budget over North America for a suite of regional climate models against surface station observations

Components of the surface radiation budget (SRB) [incoming shortwave radiation (ISR) and downwelling longwave radiation (DLR)] and cloud cover are assessed for three regional climate models (RCM) forced by analysed boundary conditions, over North America. We present a comparison of the mean seasonal and diurnal cycles of surface radiation between the three RCMs, and surface observations. This aids in identifying in what type of sky situation simulated surface radiation budget errors arise. We present results for total-sky conditions as well as overcast and clear-sky conditions separately. Through the analysis of normalised frequency distributions we show the impact of varying cloud cover on the simulated and observed surface radiation budget, from which we derive observed and model estimates of surface cloud radiative forcing. Surface observations are from the NOAA SURFRAD network. For all models DLR all-sky biases are significantly influenced by cloud-free radiation, cloud emissivity and cloud cover errors. Simulated cloud-free DLR exhibits a systematic negative bias during cold, dry conditions, probably due to a combination of omission of trace gas contributions to the DLR and a poor treatment of the water vapor continuum at low water vapor concentrations. Overall, models overestimate ISR all-sky in summer, which is primarily linked to an underestimate of cloud cover. Cloud-free ISR is relatively well simulated by all RCMs. We show that cloud cover and cloud-free ISR biases can often compensate to result in an accurate total-sky ISR, emphasizing the need to evaluate the individual components making up the total simulated SRB.     

用单站探空资料分析对流层气柱水汽总量

使用北京地区１９９６,１９９７年７月中至８月上旬常规探空（标准层和特性层）资料,计算了各层气柱的水汽混合比,绘制了水汽垂直分布的廓线,并据水汽廓线分布把大气分为四种类型,通过对各层水汽混合比积分,算出该时段每日０８,２０时的北京单站对流层气柱累积水汽量,研究气柱水汽总量与降水的关系,为预报降水量级,降水范围提供依据,这一分析结果可与辐射仪遥感水汽技术得到的结果进行比较,并为应用其它新的探测技术（如     

晴空时大气红外遥感及其反演问题研究 II. 反演试验研究

前文给出了卫星红外观测资料的反演处理方法，并对方法作了理论上的分析，在本文中，我们将此方法应用到TOVS、GOES-8实际资料及AIRS模拟观测资料处理中并重点对TOVS资料进行试验。在反演中，我们将大气温度廓线和水汽混合比（lnq）廓线用各自的经验正交函数（EOF）表示以提高反演的稳定性并缩短计算时间，同时采用一种过滤操作以加速迭代的收敛速度。除了用本文提出的方法对TOVS资料进行处理外，还用国际TOVS处理软件包（ITPP-4.0）对同样的资料进行反演。试验表明，本文方法的反演结果优于ITPP的结果。AIRS模拟反演结果表明，高分辨率红外垂直探测器的遥感精度能够达到温度1 K、水汽10%。     

Physical explanation of the weakened brightness temperature difference signal over the yellow sea during a dust event: Case study for March 15–16, 2009

This paper attempts to explain the cause of weakening or disappearing brightness temperature difference (BTD) signatures, in particular, over the Yellow Sea during the March 15–16, 2009 dust event. Using a simple correction approach that removes the effects of emissivity difference and water vapor effect difference, we confirmed that the weakening or disappearing BTD signatures noted over the Yellow Sea are largely due to the spectral emissivity contrast between land and ocean. The weakening or disappearing dust is hypothesized to be pronounced when the dust loading is weak because of the surface contribution to the top of atmosphere radiance, and that it is mainly due to the difference in spectral emissivity over the window band between land and ocean. It is further suggested that water vapor may be considered as a correction factor in spite of its smaller contribution.