Ensemble Kalman Fitting Paleo-Reanalysis Version 2 (EKF400_v2)

EKF400 version 2 is a monthly resolved paleo-reanalysis covering the period 1603 to 2003. Early instrumental temperature, surface pressure and precipitation (new in version 2) observations, temperature indices derived from historical documents and temperature and moisture sensitive tree-ring measurements (largely increased number in version 2) were assimilated into an atmospheric general circulation model ensemble using a Kalman filtering technique. This data set combines the advantage of traditional reconstruction methods of being as close as possible to observations with the advantage of climate models of being physically consistent and having 3-dimensional information about the global state of the atmosphere at 2x2 degree resolution for various variables and at all points in time.
While version 1 was using time-dependent covariances from the 30-member ensemble, version 2 uses a blended covariance matrix. It consists of 50% time-dependent and 50% climatological covariances. This leads to a better covariance estimation, not only between various locations in space but in between various variables, too.

EKF400版本2是一项每月更新的古气候再分析数据集，涵盖了1603年至2003年的时间段。该数据集整合了早期仪器测量的温度、地表气压和降水（版本2新增）观测数据，以及源自历史文献的温度指数和温度及湿度敏感的树木年轮测量数据（版本2中数量大幅增加），通过卡尔曼滤波技术将这些数据同化于大气环流模型集合中。该数据集融合了传统重建方法的优势，即尽可能接近观测数据，同时结合了气候模型的优势，确保物理一致性，并提供了全球大气状态在2x2度分辨率下关于各种变量的三维信息，适用于所有时间点。版本1采用30成员集合的时间相关协方差，而版本2则使用混合协方差矩阵，其中包含50%的时间相关协方差和50%的气候协方差。这一改进不仅提升了空间各位置之间的协方差估计，也提高了不同变量之间的协方差估计。