Impact of GNSS radio occultation bending angle data assimilation in YH4DVAR system

Global Navigation Satellite System （GNSS） radio occultation measurements have been assimilated into the four- dimensional variational data assimilation system （YH4DVAR） using a one-dimensional bending angle operator （GBAO） as a new type of observation. For the sake of verifying the impact of GNSS radio occultation （RO） measurements to the data assimilation system, three experiments have been conducted. The statistical results of the analysis error experiment and forecast skill experiment show that the GNSS RO measurements have an impact on the analysis system. The typhoon forecast experiment shows the impact on the important weather process. They all have a positive impact on the weather forecast. Lastly, we look forward to future work on the observation system simulation experiment （OSSE） to investigate the impact of GNSS RO measurements as a function of observation number, which is an effective method to estimate the saturation of the observation number.

SST biases over the Northwest Pacific and possible causes in CMIP5 models

In this paper, the features and possible causes of sea surface temperature(SST) biases over the Northwest Pacific are investigated based on a mixed-layer heat budget analysis in 21 coupled general circulation models(CGCMs) from phase 5 of the Coupled Model Inter-comparison Project(CMIP5). Most CMIP5 models show cold SST biases throughout the year over the Northwest Pacific. The largest biases appear during summer, and the smallest biases occur during winter. These cold SST biases are seen at the basin scale and are mainly located in the inner region of the low and mid-latitudes. According to the mixed-layer heat budget analysis, overestimation of upward net sea surface heat fluxes associated with atmospheric processes are primarily responsible for the cold SST biases. Among the different components of surface heat fluxes, overestimated upward latent heat fluxes induced by the excessively strong surface winds contribute the most to the cold SST biases during the spring, autumn, and winter seasons. Conversely, during the summer, overestimated upward latent heat fluxes and underestimated downward solar radiations at the sea surface are equally important. Further analysis suggests that the overly strong surface winds over the Northwest Pacific during winter and spring are associated with excessive precipitation over the Maritime Continent region,whereas those occurring during summer and autumn are associated with the excessive northward extension of the intertropical convergence zone(ITCZ). The excessive precipitation over the Maritime Continent region and the biases in the simulated ITCZ induce anomalous northeasterlies, which are in favor of enhancing low-level winds over the North Pacific. The enhanced surface wind increases the sea surface evaporation, which contributes to the excessive upward latent heat fluxes. Thus, the SST over the Northwest Pacific cools.

An Application of Classical Test Theory and Manyfacet Rasch Measurement in Analyzing the Reliability of an English Test for Non-English Major Graduates

本研究以经典测验理论和多侧面Rasch测量模型为基础,运用SPSS和FACETS软件分析了一次"非英语专业研究生英语学位课程考试"的信度。经典测验信度分析结果表明,学生主客观部分的成绩没有显著相关性,三个主观考试题目的内部一致性也不够好,整体内部一致性信度不高。多侧面Rasch测量分析结果显示,两个评分员不同的严厉度、三个主观考试任务各不相同的难度、以及部分学生与某些考试任务的偏差交互作用是导致成绩内部一致性较差的主要因素。这些研究结果对考试设计和评分以及语言教学有如下启示:不仅要训练评分员保持自身一致而且要互相一致;教师应该系统学习和掌握基础的测量理论和考试设计知识,以设计内部一致性信度较高的考试题目或任务;教师在教学中要重视培养和提高学生的综合语言技能。

On the Local and Stratified Likelihood Approaches in Single-Index Hazards Model

We propose the single-index hazards model for censored survival data.As an extension of the Cox model and many transformation models,this model allows nonparametric modeling of covariate effects in a parsimonious way via a single index.In addition,the relative importance of covariates can be assessed via this model.We consider two commonly used profile likelihood methods for parameter estimation:the local profile likelihood method and the stratified profile likelihood method.It is shown that both methods may give consistent estimators under certain restrictive conditions,but in general they can yield biased estimation.Simulation studies are also conducted to demonstrate these bias phenomena.The existence and nature of the failures of these two commonly used approaches is somewhat surprising.