Cirrus clouds play a crucial role in the energy balance of the Earth-atmosphere system.We investigated the spatiotemporal variations of cirrus over the South China Sea(SCS)using satellite data(MOD08,MYD08,CALIPSO)and ...Cirrus clouds play a crucial role in the energy balance of the Earth-atmosphere system.We investigated the spatiotemporal variations of cirrus over the South China Sea(SCS)using satellite data(MOD08,MYD08,CALIPSO)and reanalysis data(MERRA-2)from March 2007 to February 2015(eight years).The horizontal distribution reveals lower cirrus fraction values in the northern SCS and higher values in the southern region,with minima observed in March and April and maxima sequentially occurring in August(northern SCS,NSCS),September(middle SCS,MSCS),and December(southern SCS,SSCS).Vertically,the cirrus fraction peaks in summer and reaches its lowest levels in spring.Opaque cirrus dominates during summer in the NSCS and MSCS,comprising 53.6%and 55.9%,respectively,while the SSCS exhibits a higher frequency of opaque cirrus relative to other cloud types.Subvisible cirrus clouds have the lowest frequency year-round,whereas thin cirrus is most prominent in winter in the NSCS(46.3%)and in spring in the MSCS(45.3%).A case study from September 2021 further explores the influence of ice crystal habits on brightness temperature(BT)over the SCS.Simulations utilizing five ice crystal shapes from the ARTS DDA(Atmospheric Radiative Transfer Simulator Discrete Dipole Approximation)database and the RTTOV 12.4 radiative transfer model reveal that the 8-column-aggregate shape best represents BT in the NSCS and SSCS,while the large-block-aggregate shape performs better in the SSCS.展开更多
为了研究南海海气湍流热通量的高频日内变化过程,本文利用2020年9月30日至11月12日国产新型漂流式海气界面浮标(Drifting Air-sea Interface Buoy,DrIB)的现场观测数据,估算了南海西部海气湍流热通量。结果显示:观测期间潜热通量均值为1...为了研究南海海气湍流热通量的高频日内变化过程,本文利用2020年9月30日至11月12日国产新型漂流式海气界面浮标(Drifting Air-sea Interface Buoy,DrIB)的现场观测数据,估算了南海西部海气湍流热通量。结果显示:观测期间潜热通量均值为125 W/m2,感热通量均值为15 W/m2。此外,发现平静天气条件与极端天气条件下湍流热通量控制因素有所变化,极端天气条件下风速异常项对湍流热通量异常的影响增强。本文还利用DrIB观测结果评估了现今较为先进的两种高分辨率再分析通量产品———欧洲中期天气预报中心(European Centre for MediumRange Weather Forecasts,ECMWF)第五代再分析产品(ECMWF Reanalysisv5,ERA5)和现代回顾分析的研究与应用第2版数据(Modern-Era Retrospective analysis for Research and Applications,version 2,MERRA2),发现ERA5与DrIB的相关性略高于MERRA2,但ERA5与MERRA2估算极端天气条件下海气湍流热通量的结果与直接观测结果仍有较大差异。展开更多
海冰密集度是描述海冰特征的重要参数,准确获取海冰密集度对研究全球气候变化具有重要意义。针对北极夏季海冰密集度反演精度较低的问题,本文通过对微波辐射传输模型中的海冰发射率和初始海冰密集度进行优化估算,改善了微波辐射传输模...海冰密集度是描述海冰特征的重要参数,准确获取海冰密集度对研究全球气候变化具有重要意义。针对北极夏季海冰密集度反演精度较低的问题,本文通过对微波辐射传输模型中的海冰发射率和初始海冰密集度进行优化估算,改善了微波辐射传输模型对夏季观测亮温的大气校正效果,从而优化被动微波海冰密集度的反演结果,本研究采用2019年6—9月的FY-3D/MWRI亮温数据,分别利用优化前和优化后的ASI2算法(ASI2和ASI2E),结合固定系点(FTP)与动态系点(DTP),分别获得了4套夏季北极海冰密集度数据(ASI2-FTP、ASI2-DTP、ASI2E-FTP、ASI2E-DTP),并利用14景MODIS影像对结果进行了精度验证。研究结果表明,本研究提出的优化方法可有效提高北极夏季海冰密集度的反演精度,其中该优化方法对基于固定系点的反演改进尤为明显,其优化后的均方根误差(root mean square error,ERMSE)由21.9%减小到15.43%,偏差(bias,|B_(bias)|)由-12.40%下降到-6.01%。4种反演方法中,基于动态系点的算法优化后(ASI2E-DTP)表现尤为明显,其E_(RMSE)和B_(bias)分别为14.33%和-4.53%。展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42027804,41775026,and 41075012)。
文摘Cirrus clouds play a crucial role in the energy balance of the Earth-atmosphere system.We investigated the spatiotemporal variations of cirrus over the South China Sea(SCS)using satellite data(MOD08,MYD08,CALIPSO)and reanalysis data(MERRA-2)from March 2007 to February 2015(eight years).The horizontal distribution reveals lower cirrus fraction values in the northern SCS and higher values in the southern region,with minima observed in March and April and maxima sequentially occurring in August(northern SCS,NSCS),September(middle SCS,MSCS),and December(southern SCS,SSCS).Vertically,the cirrus fraction peaks in summer and reaches its lowest levels in spring.Opaque cirrus dominates during summer in the NSCS and MSCS,comprising 53.6%and 55.9%,respectively,while the SSCS exhibits a higher frequency of opaque cirrus relative to other cloud types.Subvisible cirrus clouds have the lowest frequency year-round,whereas thin cirrus is most prominent in winter in the NSCS(46.3%)and in spring in the MSCS(45.3%).A case study from September 2021 further explores the influence of ice crystal habits on brightness temperature(BT)over the SCS.Simulations utilizing five ice crystal shapes from the ARTS DDA(Atmospheric Radiative Transfer Simulator Discrete Dipole Approximation)database and the RTTOV 12.4 radiative transfer model reveal that the 8-column-aggregate shape best represents BT in the NSCS and SSCS,while the large-block-aggregate shape performs better in the SSCS.
文摘为了研究南海海气湍流热通量的高频日内变化过程,本文利用2020年9月30日至11月12日国产新型漂流式海气界面浮标(Drifting Air-sea Interface Buoy,DrIB)的现场观测数据,估算了南海西部海气湍流热通量。结果显示:观测期间潜热通量均值为125 W/m2,感热通量均值为15 W/m2。此外,发现平静天气条件与极端天气条件下湍流热通量控制因素有所变化,极端天气条件下风速异常项对湍流热通量异常的影响增强。本文还利用DrIB观测结果评估了现今较为先进的两种高分辨率再分析通量产品———欧洲中期天气预报中心(European Centre for MediumRange Weather Forecasts,ECMWF)第五代再分析产品(ECMWF Reanalysisv5,ERA5)和现代回顾分析的研究与应用第2版数据(Modern-Era Retrospective analysis for Research and Applications,version 2,MERRA2),发现ERA5与DrIB的相关性略高于MERRA2,但ERA5与MERRA2估算极端天气条件下海气湍流热通量的结果与直接观测结果仍有较大差异。
文摘海冰密集度是描述海冰特征的重要参数,准确获取海冰密集度对研究全球气候变化具有重要意义。针对北极夏季海冰密集度反演精度较低的问题,本文通过对微波辐射传输模型中的海冰发射率和初始海冰密集度进行优化估算,改善了微波辐射传输模型对夏季观测亮温的大气校正效果,从而优化被动微波海冰密集度的反演结果,本研究采用2019年6—9月的FY-3D/MWRI亮温数据,分别利用优化前和优化后的ASI2算法(ASI2和ASI2E),结合固定系点(FTP)与动态系点(DTP),分别获得了4套夏季北极海冰密集度数据(ASI2-FTP、ASI2-DTP、ASI2E-FTP、ASI2E-DTP),并利用14景MODIS影像对结果进行了精度验证。研究结果表明,本研究提出的优化方法可有效提高北极夏季海冰密集度的反演精度,其中该优化方法对基于固定系点的反演改进尤为明显,其优化后的均方根误差(root mean square error,ERMSE)由21.9%减小到15.43%,偏差(bias,|B_(bias)|)由-12.40%下降到-6.01%。4种反演方法中,基于动态系点的算法优化后(ASI2E-DTP)表现尤为明显,其E_(RMSE)和B_(bias)分别为14.33%和-4.53%。
