Abstract:From March to April in 2023,10 dust weather processes occurred in China.The processes from 19 to 24 March and from 9 to 13 April reached the level of strong sandstorm and sandstorm respectively,bringing adverse impacts on population health,ecological environment and transportation.The anomalous Eurasian atmospheric circulations showed a zonal distribution from the late winter to early spring,the Siberian high and the East Asian trough were weak,and the area around Mongolia was controlled by the high pressure anomaly,which resulted in the continuous warm surface air temperature and soil temperature in the dust source area (the second highest since 1980).In addition,the lower troposphere also lacked water vapor transporting to the sand source,resulting in significantly less precipitation in the winter and spring of 2023 (the lowest in history since 1980).The continuous warm and dry climate conditions in winter and spring resulted in a large number of dry and loose gravel in the dust source area from February to March in 2023,which provided extremely favorable dust source conditions for the occurrence of sandstorms.The synoptic disturbance systems that triggered the sandstorms in March 19—24 and April 9—13 were both Mongolian cyclones.However,the two Mongolian cyclones and their configuration with the rear cold high were different,which directly caused the differences in the intensity,path and duration of the two sandstorms.From 19 to 24 March,the dust process reached the level of strong sandstorm,causing PM₁₀concentrations in Beijing and Harbin to exceed 2 000 and 3 600 μg·m^-3 respectively.The sandstorm from 9 to 13 April not only affected Northeast and North China,but also caused a significant increase in PM₁₀ concentration in cities south of the Yangtze River,such as Hangzhou and Fuzhou.Moreover,the research emphases of dust events from the aspects of climate cumulative effect and synoptic disturbance mechanism are analyzed,and the necessity and key points of conducting subseasonal-seasonal and interdecadal prediction of dust events are discussed.Furthermore,severe sandstorms in 2021 and 2023 also raise the scientific question,“Have dust events entered a new period of activity?”.To answer this question,it is necessary to study the interdecadal mechanism and prediction of dust change,and also to predict the future change of dust event trend to a certain extent.

Abstract:The summer of 2022 exhibits significant characteristics of high temperature,low humidity,and rainfall in South China.Previous studies have focused on extreme events of high temperature and low rainfall in summer,whereas attention to near-ground relative humidity,which is closely related to human comfort and crop growth,has been relatively insufficient.In this study,we define events of positive temperature anomaly,negative precipitation anomaly,and negative relative humidity anomaly exceeding one time of the interannual standard deviation between 1959 and 2022 are as compound events of summer high temperature,low humidity,and rainfall.Monthly ERA5 atmospheric reanalysis data of 1959—2022 are used in this study.We study the effect of spring soil moisture on the compound events in summer by composite analysis and a dynamic adjustment approach based on constructed circulation analogs,and the physical mechanism is analyzed.The results show that:1) The hot spots of the coupling between spring soil moisture and summer climate in south China are basically consistent with the high variability of summer temperature,precipitation,and relative humidity in 2022.2) When the soil in the Yangtze River Basin and Huang-Huai area is dry in spring and the southeast area is wet,the compound events of drying and heat will occur in summer.3) The effect of spring soil moisture on summer climate variability is mainly realized by adjusting the distribution of local evapotranspiration and net radiation energy.The study of the compound extreme events of high temperature,low humidity,and rainfall is of great significance in effectively preventing all kinds of disasters and safety accidents caused by them,protecting people's lives and property,and maintaining social production order.

Abstract:This study investigates the influence of large-scale atmospheric circulations on the historically extreme hot days in the mid-lower branches of the Yangtze River basin in peak summer (July—August) 2022.The results show that the hot weather is influenced by an anomalous anticyclone over extratropical East Asia and an anomalous cyclone over eastern Siberia.These meridional dipole circulation anomalies are related to both the positive phase of the North Atlantic Oscillation (NAO) and the British-Okhotsk Corridor (BOC) pattern.Concurrent with the positive phase of the NAO,a significant wave train propagates along the subtropical jet stream,contributing to the anomalous anticyclone over the mid-latitude region of East Asia.Additionally,the positive phase of the BOC pattern is usually coupled with the Silk Road pattern,which benefits the meridional dipole circulation over East Asia.Accompanying these meridional dipole circulation anomalies,both the South Asian high and the subtropical jet stream intensify and extend eastward in the upper troposphere,and the western North Pacific subtropical high also intensifies and extends westward in the lower and middle levels.Thus,the mid-lower Yangtze River basin is on the right side of the exit of the subtropical jet stream and is controlled by the anomalous high,which prohibits ascending motions and induces hot days by adiabatic warming,enhancing downward radiation at the surface.

Abstract:Based on the content of Chapter 7 from the Sixth Assessment Report (AR6) contributed by the Intergovernmental Panel on Climate Change (IPCC) Working Group I (WGI),this paper presents the latest definition of effective radiative forcing (ERF) and its calculation method in AR6,and interprets the best estimations of ERF for each forcing agents from 1750 to 2019.According to the latest estimations in AR6,over the industrial era (1750—2019),the total anthropogenic ERF was 2.72(1.96 to 3.48) W·m^-2.This estimate has increased by 0.43 W·m^-2 compared to AR5 estimates for 1750—2011.Atmospheric concentration increases of greenhouse gases (GHGs) since 2011,and upwards revisions of their radiative efficiencies are the important contributors for the growth of total anthropogenic ERF.Changes in GHGs concentration contributed an ERF of 3.84(3.46 to 4.22) W·m^-2,of which Carbon dioxide continues to contribute the largest part (56％±16％).Aerosols have in total contributed an ERF of -1.1 (-1.7 to -0.4) W·m^-2 over 1750—2019.Aerosol-cloud interactions contributed approximately 75％—80％ of this ERF with the remainder due to aerosol-radiation interactions.There has been an increase in the estimated magnitude but a reduction in the uncertainty of the total aerosol ERF relative to AR5.However,there remains a considerable uncertainty in ERFaci as some of important adjustments are not considered.

Abstract:The increasing amount and intensity of extreme precipitation events due to global warming have had significant effects on the ecosystem,production,life,and society.This study uses precipitation data from 351 observation stations in Eastern China to explore the relationship between terrain factors and extreme hourly precipitation,which can be classified into single-peak and multi-peak precipitation based on diurnal variation characteristics,using the Multi-scale Geographically Weighted Regression model.The analysis of the spatial distribution of two peaks of extreme precipitation and topographic factors shows that the role of topographic factors in the two types of extreme rainfall is different.Topographic relief is the most important factor in the two types of peak-type precipitation,and the dominant areas are mainly the northern Zhejiang and the northern Zhejiang-Fujian Mountains.In single-peak precipitation,the topographic slope,besides topographic relief,is the most important factor,and the dominant area is in the southeast of the Zhejiang-Fujian Mountains.However,in multi-peak precipitation,the distance from the coastline has the greatest impact on extreme precipitation,and the dominant area is the coastal region.The mechanism analysis of the difference between these two types shows that convection dominates single-peak precipitation in the afternoon.The Convective Available Potential Energy (CAPE) value on the southeastern side of the Zhejiang-Fujian Mountains with a large topographic slope is higher,promoting convection.In multi-peak precipitation,advection dominates morning precipitation,and the water vapor transport is significantly larger than that of single-peak precipitation.Therefore,the distance from the coastline has a significant impact on this type of precipitation.Clarifying the relationship between terrain factors and extreme hourly precipitation under different diurnal variation characteristics can provide support for improving model simulation of extreme precipitation in regions with complex topography and disaster prevention and mitigation.

Abstract:The response of North Africa (NA) summer monsoon precipitation to stabilized global warming of 1.5 ℃ at the end of the 21th century is investigated using the SSP1-2.6 scenario from Coupled Model Intercomparison Program Phase 6 (CMIP6).The multi-model ensemble mean suggests the NA summer monsoon precipitation will be increased by 0.26 mm/d relative to 1985—2014 under stabilized global warming of 1.5 ℃,yields the monsoon hydrological sensitivity of 4.8％/℃.The change of monsoon precipitation is more pronounced over the northern part of the NA monsoon region.The moisture budget analysis revealed that the thermodynamics processes increase the atmospheric temperature and enhance moisture transport,leading to the higher atmospheric precipitable water relative to 1985—2014 in the whole NA monsoon region.In the dynamic perspective,the significant warming over the Sahara region increases the land-sea thermal contrast and alters the zonal mean temperature structure.The former enhances the low-troposphere monsoon circulation,and the latter pushes the African Easterly Jet northward,resulting in enhanced monsoon precipitation over the northern part of the NA monsoon region.It is partially canceled by the weakened upper Tropical Easterly Jet,especially over the southern NA monsoon region.Thus,the dynamic processes shape the inhomogeneous change of monsoon precipitation.Therefore,the thermodynamic processes increase the regional mean monsoon precipitation,and the dynamic processes contribute to the spatial pattern of precipitation changes.

Abstract:In 2018,the precipitation in the first rainy season in South China (Guangdong Province and Guangxi Zhuang Autonomous Region) is abnormally low,with the regional average total precipitation of 410.9 mm,which is about 40％ less than the average climate.The results of this study show that the precipitation negative anomaly in the first rainy season in South China in 2018 is related to the warm sea temperature in the tropical northern Pacific (TNP).The SST positive anomaly in the tropical North Pacific results in the cyclonic circulation anomaly in the Northwest Pacific and the east wind anomaly in the South China Sea through the Mastuno-Gill response,which weakens the South China Sea summer monsoon.Abnormal anticyclonic circulation exists in the lower troposphere from South China to South China Sea.There is an abnormal transport of water vapor from the mid-latitude North Pacific Ocean to the tropical Pacific Ocean via the Kuroshio Sea Area,the South China Sea,and the Philippine Islands,and South China is an abnormal divergence region of water vapor.On the other hand,the warm sea temperature anomaly in the TNP region causes abnormal convergence in the lower layer,abnormal divergence in the upper layer,and abnormal upward movement in the region,leading to abnormal convergence in the upper layer,abnormal divergence in the lower layer,and abnormal subsidence movement in South China.This circulation arrangement is not conducive to the production of precipitation in South China,resulting in unusually little precipitation in South China's first rainy season in 2018.The physical mechanism of the TNP regional warm sea temperature anomaly causing the negative precipitation anomaly in South China's first rainy season in 2018 is also verified by the average test results of 30 member sets of the ECHAM5 model.

Abstract:To achieve China’s national target of carbon neutrality by 2060,significant development of clean energy such as wind power is required.However,future usage of wind resources is subject to large uncertainties due to climate change.This study utilizes the Artificial Neural Network (ANN) method to calibrate the simulated surface wind speed from 16 CMIP6 climate models and then projects changes in wind power density in China for the 2030s,2060s,and 2100s under low (SSP1-2.6) and high (SSP5-8.5) emission scenarios relative to the present day (2000—2014).The results show that the ANN,on average,reduces the root mean square error of the CMIP6 climate models by (39.93％±9.57％) and increases the correlation coefficient from 0.56 to 0.83 between the multi-model ensemble mean simulations and observations.This suggests that the ANN-based calibration can better replicate the spatial distribution and seasonal variation of surface wind in China at the present day.The ensemble projected wind power density by the 2060s (2050—2064) is,on average,reduced by (1.01±0.94) W·m^-2 (2.62％±2.27％) and (1.11±1.45) W·m^-2 (1.90％±2.51％) relative to the present day under the two scenarios,respectively.For the temporal variation,the wind power density is reduced by (1.16±1.14) W·m^-2 and (1.43±1.58) W·m^-2 under the two emission scenarios in spring,the largest season for wind power.For the spatial variation,wind power density in southeastern China decreases by (0.56±0.53) W·m^-2 under the SSP1-2.6 scenario but increases by (0.40±0.29) W·m^-2 under the SSP5-8.5 scenario.In the near term (2025—2039),the national average wind power density is projected to reduce by (0.52±0.83) W·m^-2 and (0.54±1.12) W·m^-2 relative to the present day under the two scenarios.In the long term (2085—2099),the wind power density is projected to decrease by (0.98±1.17) W·m^-2 and (1.83±1.17) W·m^-2.The correction of CMIP6 data using the eXtreme Gradient Boosting (XGB) method shows smaller projection magnitudes but similar tendencies.This suggests that the decreasing trend of wind power density in China becomes more significant with strengthened global warming.

Abstract:This study evaluates the prediction capability of the Global Ensemble Prediction System in the China Meteorological Administration (CMA-GEPS) for the extreme Meiyu process over China in 2020.Results show that during the Meiyu season,the strong and stable western Pacific subtropical high (WPSH) and the gradually strengthened East Asian summer monsoon provide favorable dynamic and moisture conditions for strong rainfall.The CMA-GEPS can skillfully forecast the evolution trend of the WPSH index with 7—9 leading days.The prediction skills of the WPSH strength and area are about the same level as the results from the NCEP ensemble prediction system,and the WPSH strength presents a weaker bias compared with the observation.The CMA-GEPS prediction skills for the ridge line and the western ridge point index are comparable to the results from the ECMWF ensemble prediction system,and the forecasting bias is mainly attributed to the more southward location of the ridge line and the more eastward center position of the western boundary.For the East Asian summer monsoon,CMA-GEPS can skillfully predict the index with 9 leading days,which is two days earlier than the control forecast.The CMA-GEPS control forecasting bias is mainly attributed to the weaker precipitation intensity and more southward location of the strong rainfall belt;it also fails to predict heavy rain in some regions in the middle and lower reaches of the Yangtze River.The Time-Spatial Weight Ensemble Probability (TSWNP) scheme improves the prediction skills related to heavy rain with CMA-GEPS,and the scheme reduces the occurrence of missing precipitation predictions.The results of precipitation probability prediction are verified by observation and Brier scores,indicating that the TSWNP scheme is superior to the original single-point ensemble probability forecast method and the control forecast,and also has good application value for heavy storm prediction in the Meiyu period.

Abstract:Different model parameterization schemes affect the simulation of weather and climate,but their effect on the simulated land-atmosphere coupling is still unclear.In this study,16 different physical parameterization schemes are used with the WRF 4.0 model to simulate the climate in northern China during the summer of 2013.The simulated mean precipitation is found to be most affected by cumulus schemes,least affect by microphysics schemes,and affected in between by shortwave radiation schemes.The correlation coefficients between soil moisture and latent heat flux (R_(SM,LH)) and between latent heat flux and lifting condensation level height (R_(LH,LCL))are used to represent land-atmosphere coupling,and their sensitivities to different parameterization schemes are investigated.The study shows that R_(SM,LH)decreases with precipitation and relative humidity and increases with downward shortwave radiation,while the change in R_(LH,LCL)is opposite.The changes in both metrics are similar and are related to the mean wetness changes.As the soil moisture tends to saturate,evapotranspiration is limited gradually by solar radiation,and the influence of land processes on the atmosphere weakens.Besides,the strength of the simulated land-atmosphere coupling varies with the physical parameterization schemes,including the cumulus schemes,microphysics schemes,and shortwave radiation schemes.These differences in coupling are also closely related to the different mean climates simulated by different parameterization schemes.Therefore,this study has important guidance for choosing parameterization schemes in WRF 4.0,especially cumulus schemes.

Abstract:Aerosols have great impacts on the environment,meteorology,and human health.These effects are closely related the physical and chemical properties of aerosols (particle size distribution,chemical composition,mixing state,etc.).In this paper,we develop an online,comprehensive aerosol observation system and report the results of comprehensive observation experiments of Beijing,Shanghai,and Guangzhou using this system to study aerosol environmental and climate effects.Through comparative analysis,it is found that Guangzhou has highest aerosol number concentration,but the pattern of its particle size distribution is similar to that of Beijing,both of which are dominated by smaller nuclear modes.However,the aerosol concentration in Shanghai is low in all modes.The comparison of new particle formation (NPF) in three megacities suggests that the occurrence frequency of NPF in Beijing is lower than that in Guangzhou,mainly due to more large-size aerosols in the atmosphere of Beijing,which inhibited the occurrence and development of NPF because of the higher coalescence sink.The results also show that aerosol hygroscopicity in Beijing and Shanghai is stronger than that in Guangzhou.Anthropogenic emissions could significantly weaken aerosol hygroscopicity in megacities,with the diurnal variation of aerosol hygroscopicity being closely related to anthropogenic activities and aerosol ageing processes.In addition,there are significant differences in the diurnal variation of the aerosol optical absorption coefficient in the three megacities,such that the absorption coefficient in Beijing is higher during the daytime than at night,while it is reversed in Guangzhou.This is likely caused by the differences in the environment surrounding the observation stations and the diverse characteristics of the atmospheric boundary layer.

Abstract:A wind profiler radar is a new type of Doppler wind radar designed to measure the horizontal wind vectors, and are able to provide wind profiles at various elevations with high temporal and spatial resolution. It plays an increasingly important role in China's Meteorological business. However, the quality of wind profiler radar data varies widely considering the different types of radars deployed in China. To better utilize these data in numerical weather prediction (NWP), this study assesses the data quality from five different types of wind profiler radars (i.e., CFL-06, GLC-24, TWP8-L, CFL-03 and CLC-11-D) at 20 stations in North China from June to September 2019. Results show that each type of profiler has strong detection ability, but different profilers have great differences in data acquisition rate and effective detection height. Without considering the influence of precipitation, the data quality of V-wind is better than that of U-wind for all types of profilers. In all air conditions, the quality of u-wind data from TWP8-L profiler is relatively the best, followed by CFL-03 radar, the quality of U-wind data from GLC-24 radar is the worst. The differences in V-wind data is not noticeable, while bias correction and quality control are necessary for U-wind data. The data quality of wind profile radar is quite sensitive to precipitation, which reduces the data acquisition rates at low levels and increases the data acquisition rates at the middle and high levels, with the maximum increase of 53％. The statistical results indicate precipitation is responsible for the large mean errors and root mean square errors (RMSEs) of u wind data. GLC-24 and CLC-11-D profilers are the most sensitive to precipitation. The RMSEs are increased by 5.5 m/s in precipitation regions as compared to non-precipitation regions. The U-wind and V-wind data in precipitation regions requires further quality control procedure.

Abstract:The observational stability,observational ability,and rationality of both the base data and products of the millimeter cloud radar (MCR) installed at Shanghai Meteorological Service during “The study and experiment of vertically integrated meteorological observation technology in mega-cities” (MCME) are evaluated using observations from a ground-based lidar distrometer,a micro-rain radar,a radiosonde,FY-4A's products,and a surface rain gage.The results show that the observational stability of the MCR is considerably high,with only one software failure during the MCME and a data acquisition rate greater than 95％.The minimal detectable reflectivity of the MCR is generally distributed within -40 to -20 dBZ and has an exponential distribution in the vertical direction,which fits well with the theory.The minimal detectable reflectivity of the MCR changes little (less than 2 dB for heights lower than 9 km) during the MCME.A false “No Cloud” region is seen in the MCR's observation when the rain rate is larger than 4—5 mm/h.Although the raw data of the two MCRs have certain differences,the pattern of reflectivity in the time-height cross-section is highly reasonable,as indicated by comparisons between the reflectivity from the MCR's observation,the reflectivity calculated with the lidar distrometer's observation,and the reflectivity from the micro-rain radar's observation.The cloud top height and cloud base height retrieved by the MCR are also evaluated by the cloud top and base height calculated by the radiosonde and the cloud top height retrieved by the FY-4A satellite,and the results show a certain degree of consistency among the three observations.The inconsistency of reflectivity caused by the merging of multiple pulses with different pulse widths used in the MCR's base data processing and the false “clear sky area” caused by strong attenuation are two evident issues that may have significant impacts on the operational usage of the MCR.The paper concludes with recommendations on how to improve the current MCR in light of the requirements for the development of the Shanghai Meteorological Service.