Record-breaking summer-autumn drought in southern China in 2022:Roles of tropical sea surface temperature and Eurasian warming

From summer to autumn in 2022,a severe drought lasted in southern China,posing serious effects on economic growth and ecological systems.This study explored the atmospheric circulations accounting for this persistent drought event.It shows that the drought in southern China during the summer of 2022 was strongly linked to the divergence of water vapor flux and descending motions,which were respectively caused by the anomalous anticyclone over the western North Pacific and the northward movement of the East Asian subtropical jet(EASJ).Differently,the atmospheric background responsible for the sustained drought in autumn is manly featured by a cyclonic circulation anomaly over the region from the Bay of Bengal to the South China Sea,which led to decreased moisture and descending motions in southern China.Further investigation suggests that the rarely strong surface warming over northern Eurasia and the extreme La Nina-like pattern over the tropical Pacific jointly resulted in the anomalous anticyclone over the western North Pacific and the northward shift of the EASJ in the summer of 2022,while the cyclonic circulation anomaly prevailing over the region from the Bay of Bengal to the South China Sea in autumn was largely attributed to the extremely negative anomalies of the tropical Indian Ocean sea surface temperature.

Active Disturbance Rejection Position Servo Control of PMSLM Based on Reduced-order Extended State Observer

To enhance the control accuracy of permanent magnet synchronous linear motor(PMSLM)servo systems affected by disturbances,such as time-varying parameters and abrupt load changes,an active disturbance rejection control(ADRC)algorithm based on a reduced-order extended state observer(ESO)is adopted to suppress the disturbances on the control system.First,the system’s ability to estimate disturbances is enhanced by linearizing the ESO.Second,the pole placement method is used for the construction of a reduced-order ESO that can reduce the influence of the number of adjustment parameters and the phase lag.The parameters of the reduced-order ADRC are adjusted,the optimal control parameters are selected,and the stability of controller is proved.Finally,practical experiments prove that the proposed method can improve control accuracy under multiple working conditions and features strong anti-interference ability.There is a smaller steady-state error,and no overshoot is observed.