Abstract:Deep convections have a great impact on the vertical distribution of atmospheric pollutants.Combined with the Multi-resolution Emission Inventory for China (MEIC),the Weather Research and Forecasting model coupled with Chemistry model (WRF-Chem) was used to simulate a deep convective weather process and the change of atmospheric chemical gases composition in Guangdong Province on 6 May 2016,focusing on the influence of the deep convective system on the redistribution of atmospheric chemical gases composition.Results show that the simulation reproduces the convective weather process and the temporal and spatial distributions of atmospheric pollutants.Analysis of scavenging efficiencies (SEs) of different soluble species shows that the impact of wet scavenging on species of low solubility (CO,NO₂ and O₃) could be neglected,while the SEs of SO₂,H₂O₂ and HNO₃ are 50.8%,98.5% and 38.2%,respectively.However,the SEs do not necessarily increase with the increase of solubility because of the combined physical and chemical processes of atmosphere.

Abstract:Based on the 1-7 days ensemble forecasts of the European Centre for Medium-Range Weather Forecasts (ECMWF),US National Centers for Environmental Prediction (NCEP),and the Japan Meteorological Agency (JMA),the UK Met Office (UKMO) as well as the Korea Meteorological Administration (KMA) in the TIGGE datasets,the multimodel ensemble forecasts of the surface air temperature in China and its adjacent area during the period from 1 January to 30 September 2015 were conducted by using long-term memory (LSTM) neural networks,neural networks (NN),bias-removed ensemble mean (BREM) and the superensemble (SUP) with sliding training period for the forecast period from September 5 to 30,2015.The results showed that the BREM forecast was no better than the ECMWF forecast due to the impact of low skill model forecasts among the five models.The forecast skill of SUP was better than that of all the single models.For 24-144h forecasts,the root mean square error (RMSE) of SUP was significantly smaller than that of ECMWF forecast.As the forecast lead-time increased,the RMSE increased as well.The forecast skill of NN was roughly equivalent to that of SUP.Overall,the LSTM approach showed the best forecast performance,especially when the forecast lead-time was longer than 72 h,the RMSE of the LSTM forecast was considerably smaller than that of ECMWF,BREM,NN,and SUP forecasts.The LSTM neural networks approach significantly reduced the forecast RMSE of the surface air temperature in the northwestern,northern,northeastern,southwestern,and southern China.However,the RMSE of the LSTM forecast was relatively larger in southern Xinjiang area compared with ECMWF forecast.

Abstract:In this study,the MCS process under the background of Northeast Cold Vortex is simulated using the WRF model.A Barnes filter is used to decompose the model data into three scales,which are then substituted into the corresponding energy equation for calculation.Next,the development process of MCS,energy conversion of multi-scale system,and relationship between kinetic energy and precipitation are studied from the perspective of energy.The research results show that in this process a large amount of potential energy is transferred to kinetic energy,which provides energy for the development of the system.During the development of convection cell to MCS forming,the large scale kinetic energy in the middle and lower layers decreased,while the large-scale kinetic energy changed the small-and medium-scale kinetic energy,which in turn promoted the development of the convective monomer.The enhancement of large-scale kinetic energy in the upper layer corresponds to that of the upper jet stream,and promotes the development of the convection system.The β mesoscale system performs kinetic energy transfer to the α mesoscale system in the middle layer,which promotes the formation of the MCS.During the formation and development of the MCS,the conversion of potential energy at various scales to kinetic energy at the α and β mesoscales reached its maximum.During the MCS weakening phase,the large-scale system and the α mesoscale system have a certain inhibitory effect on the β mesoscale system at the middle and upper levels,thus weakening the development of the β mesoscale system.In this process,the β mesoscale scale system acts as the direct cause of precipitation,while the positive center of kinetic energy change corresponds to the large precipitation center.

Abstract:Based on the daily mean temperature data from 753 stations in China during 1960 and 2013,the extreme cooling events in eastern China during winter monsoon period was defined and its temporal and spatial characteristics were studied.Results showed that extreme cooling events occurred most frequently in the south of Northeast China,most part of North China and the north of Middle China while it seldom occurred in the south of Middle China.In the past 53 winter monsoon periods,extreme cooling events in eastern China were generally decreasing and the decreasing trends were most obvious in the south of Northeast China,southern and eastern parts of North China,northern parts of Middle China and East China at a rate of 0.4-0.8 times per decade.In addition,the frequencies of extreme cooling events in Northeast China,North China,and Middle China experienced sudden decreases in 1980,1973 and 1969,respectively.A spatial difference in the average intensities of extreme cooling events was also found out with a strong-weak-strong pattern from north to south.These results are helpful to deepen our understanding of the characteristics of extreme cooling events in China in recent decades and to provide a scientific basis for decision-making of chilling injury prevention.

Abstract:Using a new methodology,namely,Multiscale Window Transform(MWT),and the MWT-based multiscale energetics analysis,the cold center of the Atlantic blockings in the lower stratosphere is studied for an understanding of its generation mechanism. It is found that the generation is due to the canonical transfer of Available Potential Energy(APE) to the blocking scale window from both the processes shorter than 16 days and those longer than 64 days; the gained APE is then transported away northwestward and southeastward,and then converted into the blocking-scale Kinetic Energy(KE),causing the enhancement or persistence of the high-pressure centers.These processes are particularly conspicuous in the northwest,which could account for the northwestward extension of the blocking highs.Traditionally it is believed that,in the atmosphere,APE is transferred downward from large scale to smaller scales,but here we find that,when blockings occur,both the low-frequency and high-frequency processes transfer toward the blocking-scale window.Also,different from the previous finding that,in the troposphere the blocking-scale KE is converted into the APE on the same scale window to make the blocking decay,here in the lower stratosphere the conversion is in the opposite direction,i.e.,it is from APE to KE,making the blockings enhanced. Recent numerical experiments indicate that the dynamical processes around the tropopause are crucial for the development and maintenance of the blockings;this study will facilitate a deeper understanding of these processes.

Abstract:As forcing factors of land surface,the snow cover and frozen soil play important roles in the climate system.Based on the monthly snow cover days of 81 meteorological stations and the observation data of the lower boundary of the first frozen layer of 45 stations in the Tibetan Plateau from 1971 to 2016,the temporal and spatial variation characteristics of snow cover and frozen soil in the Tibetan Plateau and their relationships with NDVI (Normalized Difference Vegetation Index) were analyzed.The possible influence of changes in the underlying surface of snow cover and frozen soil on the vegetation and desertification in the Tibetan Plateau were also discussed.Results show that:(1)The distribution of snow cover days in the Tibetan Plateau is extremely uneven.The Bayan Har and Tanggula mountains are high value areas of snow cover days in the plateau,and their interannual variabilities are large.(2)There is a decreasing trend of snow cover days in the Tibetan Plateau from 1971 to 2016,and the average reduction rate is 3.5 d/(10 a).A sudden change of the snow cover days occurs around 1998,and the reduction rate is further accelerated to 5.1 d/(10 a).(3)The lower boundary of the first frozen layer in the Tibetan Plateau from 1971 to 2016 shows an upward trend,reaching -3.7 cm/(10 a),which is closely related to the warming of the Tibetan Plateau.(4)NDVI in the Tibetan Plateau is increasing slowly,which is consistent with the increasing trend of temperature and precipitation.The effect of snow cover and frozen soil changes on NDVI in different regions of the Tibetan Plateau has significant difference.Under the background of climate warming,the warm and humid environment promotes the melting of snow and the lifting of the lower boundary of the first frozen layer.Further,the water content of shallow soil layers increases,which is conductive to vegetation restoration and growth.The results have a certain role in the study of land desertification on the Tibetan Plateau.

Abstract:Intra-seasonal Oscillation (ISO) with a time scale between 10 and 90 days is one of the most significant climatic phenomena.Abundant observation researches have proved that the ISO of diabatic heating over the Tibetan Plateau (TP) is active,which is not only affected by the low-frequency activity from mid-and high-latitude,but is also affected more significantly by the inter-seasonal thermal forcing of tropics.It is more likely to be an important source of predictability for intra-seasonal prediction.Therefore,it is necessary to understand the ISO of the TP's thermodynamic effect and its propagation.Based on the daily reanalysis data of NCEP/NCAR from 1979 to 2017,the atmospheric heat source is estimated.The characteristics and propagation pathway of Quasi-BiWeekly Oscillation (QBWO) of the atmospheric heat source over the TP in summer are investigated.Results show that the first two leading modes of the quasi-biweekly atmospheric heat source over the TP and its surrounding areas,i.e.the uniform pattern with the load center in the southeast of the TP and the dipole pattern with the southeast-northwest antiphase change in the TP,reflect two different states of QBWO of the atmospheric heat source over the TP during its propagation from east to west in summer.This is mainly because in the middle and upper troposphere of the mid-latitude area,the activities of the quasi-biweekly atmospheric circulation are shown as the propagation of large anomalous cyclones and anticyclones from Northeast China to West Asia from east to west through the TP.When they move near the TP,they increase rapidly,and when they move away from the TP in the west,they decrease obviously.In addition,QBWO of the heat source over the TP modulates the precipitation anomalies in the TP and its surrounding areas,the Bay of Bengal and the Indian Peninsula.However,the further study is needed to explain the physical mechanism of the precipitation anomalies caused by thermodynamic effect from the TP.

Abstract:The ultimate purpose of this study is to estimate anthropogenic aerosol effects on the planetary energy balance based on hypothetical anthropogenic aerosol forcings given by Coupled Model Intercomparison Project Phase 6(CMIP6).In order to achieve the confidence of these estimates,we also analyzed how natural variability contributes to uncertainty in these estimates.The climate model used in this study is NESM,which is an Earth system model developed by Nanjing University of Information Science and Technology(NUIST).The anthropogenic aerosol forcing officially recommended by CMIP6 is a hypothetical dataset derived from the second version of the Max Planck Institute Aerosol Climatology(MACv2-SP).MACv2-SP is implemented into the NESM model to represent anthropogenic aerosol optical properties and an associated Twomey effect.The NESM model results show that the global annual mean anthropogenic aerosol optical depth (AOD) in the visible band and the normalized change in cloud droplet number(dNovrN) calculated from MACv2-SP are 0.025 and 1.075,respectively.The anthropogenic aerosol forcings used in this study are similar to those in the paper which introduces MACv2-SP.This indicates that the MACv2-SP is used correctly in the NESM model.In the present study,the fixed-SST method is used to diagnose the aerosol effective radiative forcing (ERF).We set up two experiments:Base and Both.The Base experiment turns off MACv2-SP,while the anthropogenic aerosol optical properties and Twomey effect described by MACv2-SP are used in the Both experiment.The Base and Both experiments results show that anthropogenic aerosol ERF is estimated at -0.45 W·m^-2.The contribution to this ERF from direct radiative effect is -0.34 W·m^-2,which is significantly greater than its corresponding standard deviation (0.01 W·m^-2).The contribution to this ERF from aerosol-induced changes in clouds (i.e.semi-direct effect and Twomey effect) is -0.10 W·m^-2,which is only one third of its corresponding standard deviation (0.30 W·m^-2).These indicate that climate model is capable of achieving high confidence in estimating direct radiative effect,yet only very low confidence in estimating aerosol effects on cloud radiative forcing.The Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5),using expert judgment,assessed the ERF to be -0.9 W·m^-2,with a 5 to 95% uncertainty range of -1.9 to -0.1 W·m^-2 (moderate confidence).Compared with IPCC AR5,the ERF described in this study is in the uncertainty range,although it is weak (less negative).The second phase of the Aerosol Comparisons between Observations and Models (AeroCom II) model results provide a direct radiative effect estimate of -0.35 W·m^-2,with a model range of about -0.60 to -0.13 W·m^-2.The direct radiative effect estimate from our model results is similar to that of AeroCom II.This also suggests that the aerosol effects on cloud radiative forcing are the main sources of the difference in ERF between this study and IPCC AR5.CMIP6 only considers the Twomey effect,ahilw other aerosol indirect effects are not included.This may be the reason for which the aerosol effects on cloud radiative forcing in this study are weaker than those of IPCC AR5.

Abstract:Using daily precipitation and temperature of 86 meteorological observation stations in Guangdong from 1961 to 2017,along with meteorological drought index data DI,the objective and quantitative assessment methods for annual climate status in Guangdong were established,with comprehensive consideration of the four aspects of rain-waterlogging,low temperature,drought and high temperature.The annual climate status in Guangdong was objectively and quantitatively assessed,and actual disaster situations were used to verify the evaluation results.The results show that the trend of the annual climate status index of the rain-waterlogging and drought in Guangdong has not changed significantly over the past 57 years;however,the annual climate status index of low temperature decreased dramatically,while the annual climate status index of high temperature increased substantially.The annual climate status index of the rain waterlogging in Guangdong decreased at a rate of 0.06/10 a over the past 57 years,but the trend was not obvious.The evaluation results of the annual climate status were consistent with the disaster situation.The evaluation results reveal that there were five poor climate years,namely 1963,1969,1993,2001 and 2008.The research results provide a technical basis for the objective and quantitative climate assessment business and decision-making services performed in Guangdong.

Abstract:In this study,the outflow-jet interaction of tropical cyclone Roke (2011) is preliminarily analyzed by using four atmospheric reanalysis datasets (CFSv2,ERA-I,MERRA2 and JRA-55),along with CIMSS high-resolution satellite images and three Best-Track datasets (JTWC,CMA and JMA).It is observed that,during the outflow-jet interaction period,the poleward outflow jet and divergence were enhanced.Meanwhile,the positive PV anomaly extending from the southern side of the upper-level jet stream gradually approached and partially superposed with the positive PV region of Roke (2011),thereby leading to the rapid intensification (RI) of Roke (2011).Among the four atmospheric reanalysis datasets,in CFSv2 the wind and divergence field of Roke (2011) during the process of outflow-jet interaction are similar to the distribution and evolution in CIMSS images.Moreover,CFSv2 accurately described the transmission process of the weak positive PV extending from the southern side of the jet stream to Roke (2011).As a result,the track and intensity changes of Roke (2011) in CFSv2 are most similar to the observations.

Abstract:Using radar data and mesoscale numerical model (WRF) to analyses the background field characteristics,cloud microstructures,and evolution characteristics of microphysical processes in the clouds during the two hailfall events in the southern mountainous region of Ningxia.The results show that the formation of hail clouds in this area mainly depends on the unstable stratification of "upper dry and lower wet" and local heating.The environmental moisture content of the two cases is different,but the hailfall processes are both formed.The water content in hail clouds is mainly concentrated on snow and graupel.The main growth of graupel is mainly through the process of vapor sublimation and riming of supercooled cloud water.The hail particle is conversed from graupel particle above the 0℃ level and collects supercooled cloud water to grow.The auto-conversion from cloud to rain in hail clouds of this area is very faint.The rain is mainly formed by the melting of snow,graupel and hail particles during the falling process,and the effect of rain evaporation is significant during precipitation.

Abstract:The anthropogenic ammonia emission inventory in Anhui Province from 2006 to 2017 was made by using the emission factor method.The anthropogenic ammonia emission level,trend and spatial distribution characteristics were also analyzed.The results showed that Fuyang City and Lu'an City were the two areas with higher anthropogenic ammonia emissions in Anhui Province in 2017,while Ma'anshan had the smallest emission amount,accounting for 1.83% of the total in Anhui Province.The average ammonia emission intensity in Anhui Province was 5.34 t·km^-2.The ammonia emission intensity in Fuyang,Huainan and Bengbu were all over 7 t·km^-2.Ammonia emissions from livestock and poultry breeding sources increased from 2006 to 2017,especially from pigs,broilers and ducks,which accounted for 34.49%-38.39%,20.31%-32.8% and 10.40%-16.42% of the total ammonia emissions from livestock and poultry sources respectively.The ammonia emission from nitrogen fertilizer showed a trend from increase to decrease,and the amount in 2017 was 28.71 kt lower than that in 2013.Biomass combustion,human emissions and nitrogen fertilizer production were the main sources of ammonia emissions among non-agricultural sources,but the contribution of ammonia produced by motor vehicles showed a significant increasing trend.For example,the percentage of ammonia emission from motor vehicles increased from 1.86% in 2006 to 7.47% in 2017,which was related to the increasing vehicle ownership in Anhui Province in recent years.

Abstract:This paper,based on the index of Jiangsu Meiyu,analyzes the characteristics of Meiyu precipitation in Nanjing in 2018,and the associated circulation causing the anomaly Meiyu,by using the daily precipitation data of Nanjing and daily NCEP/NCAR reanalysis data.The results show the following:1) The Meiyu in Nanjing in 2018 was characterized by the later beginning date,nonuniform distribution of Meiyu precipitation in space,and a significantly lesser amount of Meiyu precipitation (80% less than the climatic mean in the southern Nanjing).2) The previous trough in westerlies was active,and this caused the Northwest Pacific Subtropical High (NPSH) to occur more southerly than normal.In such a case,the seasonal northward of NPSH occurred late,which in turn resulted in a late beginning date of Meiyu.Meanwhile,the South Asia High (SAH) in 2018,which was stronger and more northeastward than the climatic mean,was conducive to a late beginning of Meiyu.3) During the Meiyu period,the ridge of NPSH jumped to north sharply and the SAH was stronger and more northeastward than the climatic mean.These circulations,together with the weak activities of the Northeast China cold vortex,led to a northward conglomeration between cold air and warm air,as well as significantly less rainfall during the Meiyu period in the region along the Yangtze River.4) The amount of Meiyu precipitation in Nanjing shows a negative correlation with the north-south span of the NPSH from June to July.5) In the years of strong East Asia summer monsoon,the Meiyu precipitation in the central and northern parts of Nanjing was less than the climatic mean.These insights will be useful in the forecast of Nanjing Meiyu.

Abstract:In the present study,based on the CN05.1 gridded rainfall data and the NCEP/NCAR reanalysis for the period of 1961-2016,the interdecadal change of autumn rainfall in western China (WCAR) is investigated.The results reveal that the WCAR shifted from a positive phase to a negative phase in the mid-1980s.After entering the 2010s,the WCAR tends to increase again,with the increasing amplitude becoming even greater than that before the mid-1980s.Next,the physical mechanism responsible for the interdecadal change in the WCAR is further explored from the perspective of large-scale atmospheric circulations,in particular focusing on the similarities and differences in the atmospheric circulations for the increase of the WCAR after the 2010s and before the mid-1980s.During these two periods,in comparison with the negative phase of the WCAR,both the Lake Balkhash trough and Asian sea level pressure are strengthened,favoring the southward outbreak of cold air from the high latitudes into western China.Meanwhile,the southerly anomalies prevail in the lower troposphere of East Asia,thereby benefiting from the transport of water vapor from the low latitudes toward western China.In addition,the East Asian jet stream shifts northward,providing favorable dynamical conditions for the occurrence of the WCAR.Under such a configuration,the WCAR is strengthened.With respect to the counterparts before the mid-1980s,the blocking over Europe and trough over Lake Balkhash are both much stronger,which may cause more cold air from the high latitudes to invade western China.At the same time,more warm-moist airflows from the Indian Ocean in the Southern Hemisphere are transported toward western China.Finally,it is shown that more cold air and warm-moist airflows which are encounter in the targeted region contribute to the greater rainfall occurring after the 2010s than before the mid-1980s.

Abstract:Based on the 2017-2018 high-resolution numerical forecast products of China Meteorological Administration (CMA),real-time urban forecast products of Gansu Province and data of national ground-based observation stations,the intelligent grid high and low temperature objective correction products of Gansu Province are developed by using wavelet analysis,sliding training,optimal fusion and other technologies.The test results show that the three correction products (urban forecast products,sliding training correction products and optimal fusion products) have the ability to correct CMA forecast,and the maximum temperature correction ability of the three objective correction products is stronger than the minimum temperature correction ability.The prediction results of the high and low temperature correction products produced by the sliding training method and the optimal fusion method are better than those of the model objective prediction in the areas with obvious systematic errors (Gannan,Longnan,etc.),while the high and low temperature urban prediction products have advantages in the areas with strong temperature localization or poor model objective prediction ability.The prediction ability of the high and low temperature products generated by the optimal fusion prediction method is slightly higher than that of the sliding training correction products,and is basically the same as that of the urban prediction products produced by the existing forecasters,which initially has the ability to replace the subjective prediction.