Application of a hybrid multiscalar indicator in drought identification in Beijing and Guangzhou,China

The Palmer drought severity index(PDSI) is physically based with multivariate concepts, but requires complicated calibration and cannot easily be used for multiscale comparison. Standardized drought indices(SDIs), such as the standardized precipitation index(SPI) and standardized precipitation evapotranspiration index(SPEI), are multiscalar and convenient for spatiotemporal comparison, but they are still challenged by their lack of physical basis. In this study, a hybrid multiscalar indicator, the standardized Palmer drought index(SPDI), was used to examine drought properties of two meteorological stations(the Beijing and Guangzhou stations) in China, which have completely different drought climatologies. The results of our case study show that the SPDI is correlated with the well-established drought indices(SPI, SPEI, and PDSI) and presents generally consistent drought/wetness conditions against multiple indicators and literature records. Relative to the PDSI, the SPDI demonstrates invariable statistical characteristics and better comparable drought/wetness frequencies over time and space. Moreover,characteristics of major drought events(drought class, and onset and end times) indicated by the SPDI are generally comparable to those detected by the PDSI. As a physically-based standardized multiscalar drought indicator, the SPDI can be regarded as an effective development of the Palmer drought indices, providing additional choices and tools for practical drought monitoring and assessment.

Characteristics of super drought in Southwest China and the associated compounding effect of multiscalar anomalies

In recent decades,Southwest China(SWC)has suffered from frequent super droughts,leading to severe economic losses and ecological degradation.This study investigates the characteristics of super droughts in SWC during 1961-2022,reveals the compounding effect of multiscalar anomalies,and explores the plausible atmospheric circulation mechanisms responsible.The nature of super drought is a compound drought caused by the superposition of extreme drought events across multiple time scales.By contrasting the typical drought cases in 2006 and 2022,the decisive role of multiscalar drought compounding is confirmed.Based on the Comprehensive Multiscalar Index(CMI),multiple super drought events in SWC were identified to be temporally clustered during 2006-2014.Among them,the decadal background of enhanced evaporation and precipitation deficit at long time scales is a necessary condition for shaping the overall pattern of super droughts,while the precipitation and evaporation anomalies at short time scales trigger the outbreak of super droughts,determining the exact timing of occurrence.These events include August-September 2006,November 2009 to May 2010,July-October 2011,April-May 2012,January-April 2013,etc.Statistical results suggest that the contribution of superposed precipitation anomalies to super drought is 2.4 times that of evaporation.As regards the circulation mechanisms affecting multiscalar precipitation,the anomalous spatial patterns at short-term and long-term scales are similar,featuring the cyclonic circulation over the South China Sea and the northeasterly wind anomalies together with the subsidence center over SWC.During 2006-2014,the possible causes for the cross-seasonal persistent precipitation reduction in SWC are the extreme negative phase of the Pacific Decadal Oscillation(PDO)in the North Pacific as well as the pronounced warming of the warm pool in the western Pacific.The key dynamic processes are outlined as follows.On the one hand,the negative PDO phase generates anomalous anticyclonic circulation in the North Pacific,with the northeasterly winds on its southwest flank extending to Southeast Asia,hindering moisture transport into SWC.On the other hand,the warming of the warm pool excites anomalous cyclonic circulation to its northwest,also giving rise to northeasterly wind anomalies over SWC.Meanwhile,the ascending motion over the warm pool region diverges at upper levels with outflows converging aloft over SWC,which further induces compensating downward motion there.The combined effect of the above two remote forcings establishes a climatic background state unfavorable for precipitation over SWC at long time scales,thus constituting a crucial prerequisite for the superimposition of short-term precipitation anomalies to develop into super droughts.

综合自适应阈值与多尺度的TV图像修复方法

基于TV模型的图像修复算法具有较好的修复效果,但其对参数的选取较敏感,且运算量较大。该文提出了一种综合自适应阈值与多尺度的TV图像修复算法,该方法不仅可以提高TV图像修复模型的修复稳定性,还可以进一步压缩运算量,提高修复速度。

SMA:一种新的多线程处理器模型

本文提出了一种新的多线程处理器模型，它结合了前瞻性执行机制和多线程执行机制，既能从更大的指令窗口中开发出更多的ＩＬＰ，又能屏蔽各种长延迟操作，达到较高的资源利用率。本文深入讨论了ＳＭＡ模型及其特点，并进行了初步的性能分析。

采用多标量模型的感应电机简化模型预测转矩控制算法

模型预测转矩控制(model predictive torque control,MPTC)基于定子磁链和定子电流预测值间接获取转矩预测值,会造成转矩预测误差,引起转矩纹波。且其价值函数中,转矩与磁链的量纲不同,需引入加权因子加以调整。该文引入定子磁链与定子电流矢量的矢积和标积,选择新的状态变量,导出新的感应电机多标量模型,并将其与模型预测转矩控制相结合,提出一种多标量模型预测转矩控制方法。运用该文所提方法直接预测转矩和无功转矩,能够简化算法,减小转矩预测误差,提高转矩响应速度,抑制转矩纹波。此外,该文定义一个统一加权因子的价值函数,构成价值函数的转矩与无功转矩的量纲相同,避免繁琐的加权因子选取设计。最后,通过实验验证所提方法的有效性和可行性。