Assimilating All-sky Infrared Radiances from Himawari-8 Using the 3DVar Method for the Prediction of a Severe Storm over North China

Although radar observations capture storm structures with high spatiotemporal resolutions, they are limited within the storm region after the precipitation formed. Geostationary satellites data cover the gaps in the radar network prior to the formation of the precipitation for the storms and their environment. The study explores the effects of assimilating the water vapor channel radiances from Himawari-8 data with Weather Research and Forecasting model data assimilation system(WRFDA) for a severe storm case over north China. A fast cloud detection scheme for Advanced Himawari imager(AHI)radiance is enhanced in the framework of the WRFDA system initially in this study. The bias corrections, the cloud detection for the clear-sky AHI radiance, and the observation error modeling for cloudy radiance are conducted before the data assimilation. All AHI radiance observations are fully applied without any quality control for all-sky AHI radiance data assimilation. Results show that the simulated all-sky AHI radiance fits the observations better by using the cloud dependent observation error model, further improving the cloud heights. The all-sky AHI radiance assimilation adjusts all types of hydrometeor variables, especially cloud water and precipitation snow. It is proven that assimilating all-sky AHI data improves hydrometeor specifications when verified against the radar reflectivity. Consequently, the assimilation of AHI observations under the all-sky condition has an overall improved impact on both the precipitation locations and intensity compared to the experiment with only conventional and AHI clear-sky radiance data.

Satellite All-sky Infrared Radiance Assimilation:Recent Progress and Future Perspectives

Satellite infrared(IR)sounder and imager measurements have become one of the main sources of data used by data assimilation systems to generate initial conditions for numerical weather prediction(NWP)models and atmospheric analysis/reanalysis.This paper reviews the development of satellite IR data assimilation in NWP in recent years,especially the assimilation of all-sky satellite IR observations.The major challenges and future directions are outlined and discussed.

Assimilation of All-sky Geostationary Satellite Infrared Radiances for Convection-Permitting Initialization and Prediction of Hurricane Joaquin(2015)

Intensity forecasting is one of the most challenging aspects of tropical cyclone(TC) forecasting. This work examines the impact of assimilating high-resolution all-sky infrared radiance observations from geostationary satellite GOES-13 on the convection-permitting initialization and prediction of Hurricane Joaquin(2015) with an ensemble Kalman filter(EnKF)based on the Weather Research and Forecasting(WRF) model. Given that almost all operational global and regional models struggled to capture Hurricane Joaquin(2015)'s intensity, this study examines the potential in improving Joaquin's prediction when assimilating all-sky infrared radiances from GOES-13's water vapor channel. It is demonstrated that, after a few 3-hour cycles assimilating all-sky radiance, the WRF model was able to forecast reasonably well Joaquin's intensity,including its rapid intensification(RI). The improvement was largely due to a more realistic initial hurricane structure with a stronger, warmer, and more compact inner-core. Ensemble forecasts were used to further explore the important physical mechanisms driving the hurricane's RI. Results showed that the RI forecasts were greatly impacted by the initial inner-core vortex structure.

Evaluation of All-Sky Assimilation of FY-3C/MWHS-2 on Mei-yu Precipitation Forecasts over the Yangtze-Huaihe River Basin

All-sky (i.e., clear, cloudy, and precipitating conditions) assimilation of microwave observations shows potentially positive impacts on the improvement of the forecasts of cloud-associated weather processes. In this study, a typical mei-yu heavy precipitation event that occurred in 2017 was investigated, and the Weather Research and Forecasting data assimilation (WRFDA) as well as its 3D-Var assimilation scheme (excluding cloud and precipitation control variables) were applied to assimilate the Fengyun-3C (FY-3C) Microwave Humidity Sounder-2 (MWHS-2) observations under clear- sky (excluding the observations that are strongly affected by ice clouds and precipitation) and all-sky conditions. Three experiments including a control experiment without assimilating any observations, clear-sky, and all-sky experiments with only FY-3C/MWHS-2 observations assimilated were carried out. The results show that the all-sky assimilation approach that provides more cloud and precipitation information and increased more than 10% of the satellite data usage than the clear-sky experiment. Meanwhile, as compared with the control experiment, the all-sky assimilation reduced nearly 0.5% of the root mean square errors in the humidity fields, leading to more accurate forecast performances regarding the distribution and intensity of heavy rainfall;but it exhibited a neutral to negative impacts on the wind and temperature. Although the system used to conduct all-sky assimilation is only able to adjust control variables for moisture-, wind-, and temperature- related variables in the presence of cloud and does not benefit directly from cloud or precipitation information, the positive effects on heavy rainfall forecasts achieved in this study indicate a potential future benefit regarding disaster prevention and mitigation.

Calibration and Validation of an All-Sky Imager

The automatic all-sky imager developed by the Institute of Atmospheric Physics,Chinese Academy of Sciences,provides all-sky visible images in the red,green,and blue channels.This paper presents three major cali-bration experiments of the all-sky imager,geometric an-gular calibration,optical calibration,and radiometric calibration,and then infers an algorithm to retrieve rela-tive radiance from the all-sky images.Field experiments show that the related coefficient between retrieved radi-ance and measured radiance is about 0.91.It is feasible to use the algorithm to retrieve radiance from images.The paper sets up a relationship between radiance and the im-age,which is useful for using the all-sky image in nu-merical-simulations that predict more meteorological pa-rameters.

Preliminary Retrieval of Aerosol Optical Depth from All-sky Images

The relationship between the radiance ratio （radiance at wavelength 450 nm to 650 nm） and aerosol optical depth （AOD） is analyzed in this paper by numerical simulation and a ＂LUT＂ （look-up table） approach is then presented for the retrieval of AOD from the radiance ratio. In this LUT approach, the AOD retrieval error depends mainly on the assumption of aerosol types. From the preliminary simulation, a typical error of 15%–20% in AOD obtained from the radiance ratio is estimated, due to neglecting changes in the ground albedo and background atmosphere. At its worst, the AOD error reached a maximum of around 50%, which will be refined in the future. In the latter part of the paper, comparisons are made between AOD from the imager and from the CE-318 sun photometer, both located at Xianghe observatory in Hebei Province （39.75° N, 116.96° E）. This field experiment shows that AOD from the imager is highly correlated with AOD from the sun photometer, with a correlation coefficient of 0.95 and an average retrieval error of around 7%. A contrast experiment confirms the feasibility of retrieving AOD from all-sky images, but more analysis and future research are required to improve the accuracy.

Occurrence characteristics of branching structures in equatorial plasma bubbles:a statistical study based on all-sky imagers in China

Branching structure(BS)is a very important phenomenon in the evolution of equatorial plasma bubbles(EPBs),the mechanism of which is widely studied from observation and from simulation.However,occurrence characteristics of branching structure of equatorial plasma bubbles(BSEPBs)have not been well addressed.In this work,we used seven-years(2012-2018)of observations from two all-sky imagers to study occurrence of BSEPBs in detail.These data reveal a high incidence of BS in EPB cases;in particular,most EPBs occurring on days with geomagnetic disturbances exhibited BS.Periods when all EPBs exhibited BS increased significantly in the 2014 solar maximum.Occurrence times of BSEPBs varied with local time;most of the BSEPBs began to appear between 21:00 and 22:00 LT.During the solar maximum,some BSEPBs were observed after midnight.The data also reveal that BSEPBs are characterized primarily by two branches or three branches.Multi-branching appeared only in the solar maximum.EPB events with different coexisting branching structures increased from 2012 to 2014 and decreased from 2014 to 2018.These results strongly suggest that BSEPB occurrence is related to solar activity and geomagnetic activity,and thus provide a new perspective for future studies of EPBs as well as enriching our understanding of ionospheric irregularity.

Impact of EnKF assimilating Himawari-8 all-sky infrared radiance on the forecasting of a warm-sector rainstorm event

Warm-sector rainstorms are highly localized events, with weather systems and triggering mechanisms are not obvious,leading to limited forecasting capabilities in numerical models. Based on the ensemble Kalman filter(PSU-En KF) assimilation system and the regional mesoscale model WRF, this study conducted a simulation experiment assimilating all-sky infrared(IR)radiance for a warm-sector rainstorm in East China and investigated the positive impact of assimilating the Himawari-8 moisture channel all-sky IR radiance on the forecast of the rainstorm. Results indicate that hourly cycling assimilation of all-sky IR radiance can significantly improve the forecast accuracy of this warm-sector rainstorm. There is a notable increase in the Threat Score(TS), with the simulated location and intensity of the 3-hour precipitation aligning more closely with observations. These improvements result from the assimilation of cloud-affected radiance, which introduces more mesoscale convective information into the model's initial fields. The adjustments include enhancements to the moisture field, such as increased humidity and moisture transport, and modifications to the wind field, including the intrusion of mid-level cold air and the strengthening of lowlevel convergent shear. These factors are critical in improving the forecast of this warm-sector rainstorm event.

Two methods for separating the magnetospheric solar wind charge exchange soft X-ray emission from the diffuse X-ray background

Solar wind charge exchange(SWCX)is the process of solar wind high-valence ions exchanging charges with neutral components and generating soft X-rays.Recently,detecting the SWCX emission from the magnetosphere is proposed as a new technique to study the magnetosphere using panoramic soft X-ray imaging.To better prepare for the data analysis of upcoming magnetospheric soft X-ray imaging missions,this paper compares the magnetospheric SWCX emission obtained by two methods in an XMM-Newton observation,during which the solar wind changed dramatically.The two methods differ in the data used to fit the diffuse X-ray background(DXB)parameters in spectral analysis.The method adding data from the ROSAT All-Sky Survey(RASS)is called the RASS method.The method using the quiet observation data is called the Quiet method,where quiet observations usually refer to observations made by the same satellite with the same target but under weaker solar wind conditions.Results show that the spectral compositions of magnetospheric SWCX emission obtained by the two methods are very similar,and the changes in intensity over time are highly consistent,although the intensity obtained by the RASS method is about 2.68±0.56 keV cm^(-2)s^(-1)sr^(-1)higher than that obtained by the Quiet method.Since the DXB intensity obtained by the RASS method is about 2.84±0.74 keV cm^(-2)s^(-1)sr^(-1)lower than that obtained by the Quiet method,and the linear correlation coefficient between the difference of SWCX and DXB obtained by the two methods in diffe rent energy band is close to-1,the diffe rences in magnetospheric SWCX can be fully attributed to the diffe rences in the fitted DXB.The difference between the two methods is most significant when the energy is less than 0.7 keV,which is also the main energy band of SWCX emission.In addition,the difference between the two methods is not related to the SWCX intensity and,to some extent,to solar wind conditions,because SWCX intensity typically va ries with the solar wind.In summary,both methods are robust and reliable,and should be considered based on the best available options.

基于深度学习的全天空相机成像日间云量计算研究

云量是天文领域中地基光电望远镜站址选择的重要评价参数之一。针对全天空相机成像的日间云量计算存在的问题,提出一种基于深度学习的全天空相机成像日间云量计算模型。云检测层,模型通过构建通道加权-特征融合(channel weighting-feature fusion,CWFF)结构,从而加强对云层记忆能力和深层特征的提取能力以完成云检测任务;云量计算层,模型提出一种基于云检测模型的云量计算方法,有效提高云量计算的误差率。实验表明,该方法在云检测任务中的综合准确率超过95%,在云量计算任务中的平均绝对误差不超过5%。

GOES-16 ABI观测和ERA5全天空模拟亮温揭示的热带对流水平特征尺度对比分析

本研究通过将GOES-16 ABI观测亮温和ERA5再分析资料的全天空模拟亮温进行对比分析,发现观测亮温和模拟亮温对流低值区位置大体接近,也能够定性反映出对流从发展到减弱的日变化过程,但亮温低值区域的强度存在较大差异。即使把高分辨率ABI通道13观测亮温平均到ERA5分辨率(0.25°×0.25°),在热带对流区的低亮温强度仍然高于ERA5全天空模拟亮温。因此利用主成分分析(Principal Component Analysis,PCA)和离散傅里叶变换(Discrete Fourier Transform,DFT)对任意选择的两对流区域内的观测和模拟亮温进行了尺度分析和对比。在其中对流较强的区域内,当ABI观测亮温的主成分分量从1增加到9时,水平特征尺度从700 km逐渐减小到150 km。ERA5全天空模拟亮温从主成分1增加到4时,水平特征尺度从950 km减小到270 km空间尺度,但当主成分4增加到9时,特征尺度几乎不变。在对流较弱的另一区域也能够发现ERA5模拟亮温对对流水平特征尺度有明显高估。ERA5模拟亮温各主成分的相位和观测亮温存在2 h以内的误差。由于ERA5全天空模拟亮温低值区与ERA5云冰路径大值区吻合度较高,由此可以推测ERA5云冰路径误差是造成ERA5全天空模拟亮温与ABI观测亮温差别的主要原因之一。

多波段鱼眼镜头相机实验室几何定标方法

鱼眼镜头因其独特的曲率和光学特性,使用非相似成像模型拟合后,仍有接近10像素的径向残余畸变。研究了多波段鱼眼相机的定标原理、定标流程,在非相似成像模型基础上,提出了基于分离式精密二维转台的鱼眼镜头定标方法,并通过相机姿态位置精密调整与方位转台360°旋转,光斑像素位置始终不变的方法,确定相机主点。为分析色差对鱼眼镜头径向畸变的影响,采取不同波段单独定标的方法。利用不同时刻的太阳角度数据来验证镜头定标系数,结果显示天顶角与方位角的均方根误差分别为0.226°和0.487°。该方法有效实现了鱼眼镜头相机在不同波段的几何定标,提高了像素点与入射光线角度之间的匹配精度。

风云三号C星微波湿度计资料全天候同化对台风玛莉亚预报的影响

随着风云三号系列卫星的成功发射,越来越多的卫星微波直接观测资料应用于数值天气预报的资料同化系统。并且由于卫星微波全天候同化技术可以充分利用晴天及云雨区微波观测资料,在增加同化使用的观测数据的基础上,有效提高数值天气预报准确率,该技术在卫星资料同化领域也颇受瞩目。本研究选取2018年7月的台风玛莉亚,利用WRF(Weather Research and Forecasting)模式及其同化系统WRFDA(WRF Data Assimilation)中三维变分方法,探讨风云三号C星微波湿度计观测资料的全天候同化技术在区域模式中的适用性,以及其在不同模式驱动场中的预报表现。通过对比仅同化晴空区域卫星资料的试验和全天候同化的试验结果发现,全天候条件下更多的云雨区域观测资料被有效利用,能够更好地模拟出台风玛莉亚核心区域的暖心和对称风速结构,有效改善湿度场的预报,对台风路径的预报误差平均降低了大约34%~62%,且这种正面影响均能在不同模式驱动场中得到体现。

Intensity correction in all-sky auroral image projection transform

BY using all-sky(fish-eye)lens and highly sensitive TV camera,the effective monitoring ra-dius and time resolution of ground aurora observation have now been raised to 600 km and1/30 s(for instance,SIT-TV camera recording in NTSC format).By incorporating high-sen-sitivity imaging device(integrated from image intensifier and CCD(charge coupled device)

Assimilation of All-Sky Radiance from the FY-3 MWHS-2 with the Yinhe 4D-Var System

Compared with traditional microwave humidity sounding capabilities at 183 GHz,new channels at 118 GHz have been mounted on the second generation of the Microwave Humidity Sounder(MWHS-2)onboard the Chinese FY-3C and FY-3D polar orbit meteorological satellites,which helps to perform moisture sounding.In this study,as the allsky approach can manage non-linear and non-Gaussian behavior in cloud-and precipitation-affected satellite radiances,the MWHS-2 radiances in all-sky conditions were first assimilated in the Yinhe four-dimensional variational data assimilation(YH4DVAR)system.The data quality from MWHS-2 was evaluated based on observation minus background statistics.It is found that the MWHS-2 data of both FY-3C and FY-3D are of good quality in general.Six months of MWHS-2 radiances in all-sky conditions were then assimilated in the YH4DVAR system.Based on the forecast scores and observation fits,we conclude that the all-sky assimilation of the MWHS-2 at 118-and 183-GHz channels on FY-3C/D is beneficial to the analysis and forecast fields of the temperature and humidity,and the impact on the forecast skill scores is neutral to positive.Additionally,we compared the impacts of assimilating the 118-GHz channels and the equivalent Advanced Microwave Sounding Unit-A(AMSUA)channels on global forecast accuracy in the absence of other satellite observations.Overall,the impact of the 118-GHz channels on the forecast accuracy is not as large as that for the equivalent AMSUA channels.Nevertheless,all-sky radiance assimilation of MWHS-2 in the YH4DVAR system has indeed benefited from the 118-GHz channels.

基于机器学习的地基云图分类研究进展

基于机器学习的地基云图分类是光伏发电功率预测的关键技术。该技术主要通过传统机器学习和深度学习方法对地基云图特征提取提升地基云图分类准确率。全文归纳了地基云图分类标准和云图采集设备;简要介绍了地基云图分类数据集;从传统机器学习和深度学习两方面详细论述了典型的地基云图分类方法;比较了不同方法在Kiel F和MGCD地基云图分类数据集上的性能;最后对现有地基云图分类方法进行了总结,并针对目前地基云图分类面临的挑战进行了展望。

一种星辐射模式下全天区星图识别算法及FPGA实现

针对在DSP中实现全天区星图识别算法耗时长导致实时性差,提出并实现了一种基于FPGA的星辐射模式下的全天区星图识别算法。该方法利用FPGA并行性、高主频等特性,在保证算法高精度、高准确度的前提下,解决了全天区星图识别耗时长的问题。首先,根据星点信息构建星辐射模式;其次,基于FPGA实现了星辐射模式下对应特征向量的计算;最后,提出了一种可预读、流水化的星辐射模式匹配算法,极大地缩短了星辐射模式匹配的时间。在Xilinx公司的Xc7a75tfgg484-2平台上进行实验验证,结果表明,在相同时钟主频下,基于FPGA的星图识别算法速度比基于DSP的算法速度快10.95倍以上,而且在使用三组特征向量同时进行匹配时,识别率超过99%。

可见光/红外全天空成像仪和云雷达联合反演云高

为解决大部分设备无法单独获取全天空云底高度的问题,基于中国气象局大气探测基地可见光/红外天空成像仪和毫米波云雷达2019年6月的灰度值与云底高度数据,利用辐射传输模式计算地面8~14μm波段向下红外辐射随天顶角的变化关系,并根据红外波段测得的天顶云底灰度值与非天顶位置的天顶角余弦灰度值之间的线性关系,从而反演得到全天空云底高度。结果表明:(1)相比于全天无云的情形,在一天的相同时间时,全天有云时的天顶灰度值较高。(2)当云底高度为2000 m以上且云层较厚时,云底高与红外模块所测灰度值的相关性明显好于云层较薄的低云。(3)2019年8月12日的个例验证结果显示,反演云高与通过云雷达测得的实际云高相关系数为0.956,而与取天顶附近约30°天顶角得到的云高相关系数为0.9508。

中国上空夜间电离层等离子体泡群演化过程的多设备观测

利用子午工程富克站(19.5°N,109.1°E)全天空气辉成像仪、VHF雷达、三亚站(18.4°N,109.6°E)数字测高仪及C/NOFS卫星观测数据,对2014年3月30日中国上空的等离子体泡进行了研究。结果表明,当天夜间观测到一个等离子体泡群,约由9个等离子体泡组成,发生在日落后,一直持续到午夜后。其自西向东运动,南北向最大尺度超过1200 km,东西向绵延超过1400 km,在演化中部分结构融合在一起。等离子体泡被气辉成像仪观测到的同时,数字测高仪及VHF雷达观测到了相应扩展F及羽毛状不规则结构。同时,C/NOFS卫星检测到相应电子密度耗散。这表明,该等离子体泡同时被地基光学观测、无线电探测及C/NOFS卫星观测到。研究结果给出了多仪器同时观测到的等离子体泡群演化过程,丰富了多仪器融合研究电离层不规则体的内容。

浅析全固态中波发射机天调网络的工作原理及应用创新

随着科学技术的发展,目前,中波广播技术所采用的硬件设备基本上是全固态中波发射机。相比于传统的中波发射机,全固态中波发射机具有效率高、能耗低、性能优、绿色环保等优势。从全固态中波发射机与天调网络的工作原理出发,探析了全固态中波发射机天调网络应用过程中的影响因素及其存在的问题,并有针对性地提出了一些创新型的应用方法与措施。旨在促使全固态中波发射机与天调网络的结合应用效用达到最大化,进一步保障整个系统高效稳健的运营。