Abstract:Warming of the climate system in recent 100 years is unequivocal.Under global warming,the amounts of snow and ice have diminished,the sea level has risen,and the extreme weather and climate events have increased.The climate system is facing severe challenges.2020 is becoming a special year on record for the bushfires in Australia,the locust plagues and the frequently extreme weather and climate events.How about the global warming in 2020?Based on the ERA5 reanalysis data,the global annual mean surface temperature (ANNT) in 2020 (ANNT-2020) is predicted.It suggests that the anomalies of the ANNT-2020 compared to the climatology during 1981-2010 and the interannual increment of the ANNT in 2020 will both be positive,since the interannual increment of the global winter surface temperature (DJFT) appears over 0.2℃ in 2020 and the signals of the anomalies in greenhouse gases,sea ice and sea surface temperature are positive for ANNT in 2020.Using the interannual increment approach,the quantitative prediction of ANNT-2020 shows that the ANNT-2020 will most possibly exceed the ANNT-2016 and 2020 will become the warmest year on record.

Abstract:The Weather Research and Forecasting model coupled to Chemistry(WRF-Chem model), coupled with an online BC source-tagging method, was used to study on the distribution, regional sources and diurnal variation of black carbon(BC) in autumn of October 2015 of Hunan and Hubei(Hunan-Hubei) basin in the middle reaches of the Yangtze river. The results show that, the contribution of local source and outside sources to BC at "Hunan-Hubei" varied greatly under different wind field conditions. In this study, there are three main BC source episodes in autumn in "Hunan-Hubei":(1)The type of import mainly controlled by north wind, with high wind speed and low BC concentration. The contribution to surface BC in "Hunan-Hubei" from upwind regions via transport was approximately 30.6%, and 61.7% from local source regions; (2)The type of stable under the condition of low surface wind speed and stable weather. The contribution of local BC was high, accounting for 79.6%; (3)The type of import mainly controlled by northeasterly wind. A high concentration of BC in "Hunan-Hubei" was maintained by the contributions from local and outside sources together, and the contribution of local sources was 64.1%. The contribution of outside sources mainly included the transport from Anhui, Shanxi-Shaanxi-Henan and Yangtze river delta. In the vertical direction, in the type of import, the local contribution to BC were mainly dominant under 300 m. Under the type of stable, the dominant contribution from local sources can be keep to more than 1 500 m(local source accounts for about 75% on surface and 50% at 1 500 m). In terms of diurnal variation, the change of contribution proportions of local and outside sources to BC in "Hunan-Hubei" was opposite. The proportion of local contribution remained high in the morning and night, while the contribution of external transport was low. In the afternoon, the local contribution decreased, while the contributions from outside was significantly enhanced. In the type of import, this feature of diurnal variation is more obvious.

Abstract:The previous genesis potential index (GPI) can be applied to accurately simulate the climate distribution of tropical cyclone (TC) genesis,yet performs poorly in the simulation of interannual variation of TC genesis.The present study attempts to improve the GPI over the western North Pacific (WNP),by considering the important impact of relative vorticity on interannual variation of TC genesis.Based on the best-track data from the Joint Typhoon Warning Center and NCEP/NCAR reanalysis data from 1979 to 2011,we substitute the absolute vorticity in the previous GPI with a modified relative vorticity.The Coriolis factor remains intact.The difference of tropical cyclone formation between the South China Sea (SCS) and WNP is also considered,and the GPI for the SCS (5°-25°N,100°-120°E) and WNP (5°-40°N,120°-180°E) are respectively developed.The modified GPI is shown to improve the simulation of the climate distribution of TC genesis.Moreover,compared with the previous GPI,the modified GPI greatly improves the simulation of the interannual variation of TC genesis,in particular in regard to weak tropical cyclones.

Abstract:Based on the monthly precipitation data of 160 meteorological observation stations in China,the 74 circulation indexes,HadISST monthly mean sea surface temperature data and NCEP/NCAR monthly mean reanalysis data,this paper compared and analyzed the differences of summer rainfall in eastern China and related atmospheric circulation in the decaying stage of two types of ENSO events,and discussed the possible mechanisms.The results are as follows:(1) In the following summer of EP type of El Niño (La Niña) events,precipitation in eastern China presents a three-pole-type of "+-+" ("-+-") inverse distribution from north to south,while precipitation during the following summer of CP type of El Niño(La Niña) events in eastern China presents a dipole-type of "+-" ("+-") inverse distribution from north to south.(2) The western Pacific subtropical high (WPSH) and the South Asia high (SAH) in the following summer of El Niño events are much stronger than the climatological normal.WPSH (SAH) of EP El Niño moves further westward (eastward).The area of WPSH of CP El Niño is larger than that of EP El Niño,and the intensity is stronger as well.During the following summer of La Niña events,WPSH and SAH of CP La Niña are stronger than those of EP La Niña but weaker than the climatological normal.(3) An anomalous anticyclone exists in the northwestern Pacific during El Niño events.The anticyclone of EP El Niño is southward and stronger,and lasts longer than that of CP El Niño,while the anticyclone of CP El Niño is northward and has larger range.However,during La Niña events,an anomalous cyclone exists in the northwestern Pacific region to southeastern China.The anomalous cyclone of CP La Niña is much stronger,with the area much larger than that of EP La Niña.(4) The difference of northwestern Pacific anomalous anticyclone between the two types of El Niño events may be related to the warming of the Indian Ocean Basin and the persistent abnormal cooling of SST in the Pacific Ocean.The difference of northwestern Pacific anomalous cyclone between two types of La Niña events may be related to the persistent abnormal warming of SST in tropical western Pacific Ocean.

Abstract:This study illustrates how aerosol affects the top of atmosphere (TOA)radiation flux in the NUIST model,using a hypothetical anthropogenic aerosol forcing determined by Coupled Model Intercomparison Project Phase 6.There are three ways by which anthropogenic aerosol affects TOA radiation flux.First,anthropogenic aerosol affects TOA radiation flux through the changes in aerosol optical properties,known as the aerosol radiative effect.This effect mainly depends on anthropogenic aerosol radiative forcing,and is not related to the Twomey effect.Second,anthropogenic aerosol affects TOA radiation flux through the changes in cloud optical properties,referred to as aerosol effects on cloud radiative forcing.These effects include the Twomey effect and semi-direct effect.Finally,anthropogenic aerosol affects TOA radiation flux via the changes in other optical factors.Compared with the first two ways,this third one is negligible.This study focuses on the second way,and discusses the methods used for estimating anthropogenic aerosol effects.In order to distinguish contributions to aerosol effects on cloud radiative forcing from semi-direct and indirect effects,we added two experiments:Rad and Tmy.The Rad experiment only considers the anthropogenic aerosol optical properties,which the Tmy experiment only considers the anthropogenic aerosol Twomey effect.Including the experiments used in Part 1,there are four experiments in total:Base,Rad,Tmy and Both.The results of the Rad and Base experiments show that anthropogenic aerosol semi-direct effect is estimated at 0.21 W·m^-2.Semi-direct effect could also be obtained as the difference between the aerosol effects on cloud radiative forcing from Both and Base experiments (i.e.semi-direct effect and Twomey effect)and the aerosol effects on cloud radiative forcing from Tmy and Base experiments (i.e.Twomey effect).This semi-direct effect is 0.09 W·m^-2,significantly less than those from the Bad and Base experiments.The difference between the Tmy and Base experiments shows that the effective radiative forcing (ERF)caused by anthropogenic aerosol Twomey effect is -0.22 W·m^-2.Meanwhile,the difference between the Both and Rad experiments shows that the ERF caused by the Twomey effect is -0.30 W·m^-2,which is stronger (more negative)than that caused by the difference between the Tmy and Base experiments.It is clear that the assessment results depend on experimental design.One likely reason for this is that aerosol semi-direct and indirect effects interact in a very complex manner,and the assumption of linear superposition is not reasonable.It is worth noting that the diagnosed Twomey effect not only includes the Twomey effect itself,but also cloud-relevant adjustments caused by the Twomey effect.Aerosol could make an obvious impact on quantifying cloud forcing,as aerosol also can scatter and absorb solar radiation.The short wave cloud forcing (SWCF)from Base experiments is -47.54 W·m^-2.Under no-aerosol conditions,the SWCF* (i.e.the SWCF calculated as a diagnostic with aerosol scattering and absorption neglected)from the Base experiment is -49.51 W·m^-2.The difference caused by the impact of aerosol is 1.98 W·m^-2.Compared with the Base experiment,this difference from the Rad experiment is increased by 0.38 W·m^-2,because anthropogenic aerosol is considered.In other words,for the same cloud optical properties,the SWCF diagnosed with aerosol optical properties may be shown to increase by~0.38 W·m^-2 after considering anthropogenic aerosol optical properties.Due to this obvious positive bias,the aerosol effects on cloud radiative forcing must be estimated from the change in SWCF* (diagnosed with aerosol scattering and absorption neglected),rather than SWCF (diagnosed using the traditional method).

Abstract:Through the WRF model and observational data,a numerical simulation was performed for a squall line process which had occurred in Guangxi Zhuang Autonomous Region of China.Based on the simulation results,the relationship of the MVs (mesoscale vortices) and the rear inflow in the squall with the surface high winds is analyzed.The Vorticity Budget and analysis of vortex line both show that there are east-west vortex couplets present in the bow echo,which are mainly caused by the divergence term.In addition,the relatively weak anticyclone vortex in the center is generated due to the conversation of horizontal vorticity to vertical vorticity,caused by the arch of the vortex line.Next,the contribution of the vortex couplet to the high winds on the ground is quantified by calculating cyclostrophic wind caused by the vortex couplet.The results show that the cyclostrophic winds account for 40%-50% of the ground winds in this squall line process.When the cyclostrophic winds are removed,then the intensity of the surface high winds will be weakened and the position will shift.It can be seen from the three-dimensional streamline that the subsidence of the rear inflow is another factor that produces the surface high winds.After completing the diagnosis of the buoyancy acceleration and dynamic acceleration,it is found that the sink of rear inflow jet is caused by the buoyancy acceleration.In addition,the uneven density in the horizontal direction is the main factor in generating the negative buoyancy acceleration,but the dynamic acceleration also has an obvious effect when the wind speed is suddenly strengthened.

Abstract:In this paper,the inconsistency index distribution and variation characteristics of the ECMWF surface air temperature forecasts over China were studied based on the surface 2 m air temperature forecast data of the ECMWF operational forecast model,during the period of December 1,2015 to November 30,2016,along with the calculation of the Jumpiness index of the forecast.The results revealed that the annual mean forecast inconsistency index of the surface air temperature forecasts over China decreased from north to south,with two areas of maximum values over Tibetan Plateau and eastern Inner Mongolia,respectively,thus indicating that the forecast jumpiness over these two areas is quite high.Among the four seasons of a year,the forecast inconsistency index of the surface air temperature is the greatest during the boreal winter,and smallest in the boreal summer,while there is little difference between the forecast inconsistency indexes in spring and autumn,the inconsistency indexes thereof lying between those in winter and summer.The inconsistency index of the surface air temperature forecast on a given day during boreal summer is slightly different from the summer average value of the inconsistency index,while that on a day during the boreal winter is significantly different from the winter average value of the inconsistency index.

Abstract:In this paper,using conventional observation data,NCEP 1°×1° reanalysis data,FY-2G satellite hourly TBB data,radar and AWS data,the potential and triggering characteristics of short-term heavy precipitation in southeastern Shanxi Province on the night of July 13,2018 were analyzed.The results reveal that the strong southwest airflow around subtropical high provide abundant water vapor conditions for the short-term heavy precipitation process.In addition,the stratification structure of "dry and cold under warm and wet" and the temperature differential advection of "high-level cold advection and low-level warm advection" provides the energy conditions required for the development of strong convection.The formation and maintenance of ascending motion are conducive to the release and enhancement of unstable energy.The meso-β scale convergence line on the ground develops into a meso-β scale vortex,thereby stimulating the consolidation and strengthening of the mid-β scale convective cloud mass,which in turn stimulates the merging and strengthening of meso-βscale convective clouds.The meso-γscale convective monomer embedded in the meso-βscale band echo of ≥ 35 dBZ,under the guidance of the 500 hPa southwest airflow,forms a slowly moving,highly organized multi-cell linear echo,which was the direct cause of the formation of short-duration heavy rainfall.The short-term heavy precipitation is located between 5 880 gpm and 5 840 gpm on the 500 hPa map,between the 850 hPa and 700 hPa shear line,and overlaps with 850 hPa and 700 hPa wet tongue,ground trunk line and mesoscale convergence line (near the 10 km range),as well as the cold air inflow side of the convective cloud mass TBB gradient high value area and TBB ≤ -60℃.

Abstract:Based on the high resolution numerical prediction products of China Meteorological Administration (CMA),the refined numerical prediction products of European Centre of Medium-range Weather Forecasts (ECMWF) and the data from national ground observation stations in China,the Northwest Intelligent Grid Temperature Objective Prediction Method (NWTM) has been developed by using wavelet analysis,sliding training,optimal fusion and other technologies,which can be used to deal with the time-frequency of the model error sequence and realize the correction of the model system error and local error.In order to test the forecast ability of the two model data,the data from March 2017 to February 2018 were used as training samples,the data of 239 national basic stations in Northwest China from March 2018 to January 2019 were tested.Results show that:(1) NETM can significantly improve the temperature forecast ability of CMA and ECMWF models.With the increase of forecast time,the errors of correction products of the two models increase.(2) Using the NWTM,the correction effect of ECMWF products on maximum temperature in Northwest China is obviously better than that of CMA,but the correction effect of CMA products on minimum temperature is more significant.Among them,for the 24 h maximum temperature,the correction effect of ECMWF in Ningxia is the best,and that of CMA in Qinghai is the best;for the forecast of 24 h minimum temperature,the correction effect of CMA in the four provinces of Northwest China is similar,and that of ECMWF in Shaanxi is the best.(3) The spatial error tests show that the correction ability of ECMWF correction products for the forecast of maximum temperature is obviously better than that of CMA,especially in the Hexi Corridor and the east-central region of Gansu,the north and south of Shaanxi,the south and central region of Ningxia,and most of Qinghai.In terms of the forecast of minimum temperature,CMA and ECMWF have better ability to correct the forecast of minimum temperature in Hedong region of Gansu and the south of Shaanxi.However,the correction ability of ECMWF correction products in the south-central region of Ningxia and the south of Qinghai is higher than that of CMA,while the correction ability of CMA correction products in the central region of Shaanxi is better.

Abstract:In recent decades,an increasing number of extreme climate events,especially extreme precipitation events,occurred under the background of global warming.Based on daily precipitation data from the US Climate Prediction Center,this paper analyzed spatial distribution and temporal variation of extreme precipitation events(including RX1day,RX5day,R10mm,R20mm,CDD) over the Eurasian continent during 1979 and 2018.The results was summarized as follows:1)As for the spatial distribution,large PRCPTOT prevailed over the South Europe,South Asia,Southeast Asia and East Asia,along with frequent extreme heavy precipitation events (i.e.,RX1day,RX5day,R10mm,R20mm) over these sub-regions.In addition,the Qinghai-Tibet Plateau,Central China and Mongolia in East Asia,the Indian subcontinent in South Asia and some parts of Central and West Asia,North Europe underwent high frequency of continuous drought and relatively fewer extreme heavy precipitation events.2)An interdecadal increase of PRCPTOT occurred in Southeast Asia,South Asia,East Asia,North Asia,West Asia and Southern Europe since the beginning of the 21st century with significant long-term upward trend during the whole period.Moreover,all RX1day,RX5day,R10 and R20 showed an interdecadal increase after the mid-1990s over South Asia,East Asia and central Asia with a long-term increasing tendency.Additionally,CDD showed a significant increase in South Asia,North Asia,East Asia and Central Asia in the 1980s,but the long-term trend was not obvious;It is notable that extreme heavy precipitation events significantly increased in Southeast Asia,South Asia and East Asia,while CDD occurred increasingly over North Europe since 2014.

Abstract:The present paper uses the Aircraft Meteorological Data Relay(AMDAR) data of flights from Xiamen and Jinjiang Airports in 2016 to test the wind field retrieval from dual-Doppler radars,then analyzes the total error of the wind field retrieved from the Xiamen and Quanzhou Doppler radars.The study results indicate the following:1)The mean absolute error of the wind field retrieval in the vicinity of the dual-Doppler radars connection is apparent.The mean absolute error of the retrieval result in the region where the angle between the two radars is less than 15 degrees and greater than 165 degrees is significantly higher than the annual average value.2)The wind direction field retrieval error decreases with increasing height.In addition,for the wind speed field retrieval,the error below 9 km is about 5 m/s,while that above 9 km is small.3) After eliminating the retrieval results in the area near the dual radar connection (i.e.the angle between the two radar connection is less than 15 degrees and greater than 165 degrees) and the reflectivity factor is less than 5 dBZ and equal to 100 dBZ (non-meteorological echo),the error of wind field retrieved by dual-Doppler radars is less significant.Furthermore,the annual mean absolute error of the wind direction relative to the AMDAR data is 29.4°,while that for the wind speed is 3.28 m/s.Overall,the retrieval results are close to the "true values",and the wind retrieval method is shown to be stable and reliable.

Abstract:In this study,using the daily precipitation data collected at 63 conventional meteorological observatories in Zhejiang Province from 1973 to 2017 and the sea surface temperature field,wind field,height field,humidity field and outgoing long-wave radiation (OLR) field provided by NCEP/NCAR,the EOF,anomalies Synthetic and t-test methods are used to analyze the time and space distribution of total rainy days in February to April in Zhejiang Province,as well as the atmospheric circulation field,previous sea surface temperature,and the distribution characteristics of the same OLR field in continuous rainy weather.Based on the analysis,we then explore the causes.The results show that the spatial distribution of the total number of rainy days in Zhejiang Province from February to April is generally divided into two categories:in the first,the distribution is the same around the province,while in the second the distribution is different between the north and south.When the high ridge of the Ural Mountains is strong (weak),the Okhotsk sea trough in the middle and high latitudes of the Eurasian continent and western Pacific subtropical high are also strong (weak),which causes the consistently strong (low)density rain in the province.OLR is a negative anomaly area in Zhejiang Province,which is prone to the same pattern of continuous rainy weather in the province.When the OLR is a positive anomaly area in Zhejiang Province,it is prone to cause the weather of consistently less rain than average in the province.In addition,when the weather of continuously more rain appears in the province,then the SST of the Equatorial Middle East Pacific in the early period and same period are significantly higher;otherwise,the SST of the Equatorial Middle East Pacific in the early period and same period are significantly lower.The SST in the western equatorial Pacific is the anti-phase.In the following year of El Niño,the weather phenomenon of continuously more rain typically appears in the province.In the following year of La Nina,the weather phenomenon of continuously less rain usually appears.

Abstract:The evolution of the "5·21" Mongolia wildfire in 2009 and the effect of fire-prevention isolation barrier along the China-Mongolia border were investigated by using WRF-Fire.The results showed that the model could reproduce the impacts of boundary winds on fire propagation.The simulation for fire area and propagation are shown to be broadly consistent with the observations:The first stage(1200 UTC 21st to 2200 UTC 21st),fire spread southwest slowly in the Mongolia because of low fuel loading on the near-bare surface with northeast wind.The second stage(2200 UTC 21 to 1100 UTC 22),wind direction turned to northwest,and fire spread southeast across flat and uniform grassland.Before the fire reached the border,the fire spread rapidly towards the isolation barrier because wind speed increased to reach around 8~10 m/s and wind direction was consistent with slope direction.The third stage(1100 UTC 22 to 2000 UTC 23),the barrier and firefighting was effective in preventing the fire entering Chinese territory.Then,the fire line spread north after wind direction turned to south.The fourth stage(2000 UTC 23 to 1200 UTC 24),wind speed reached more than 16 m/s and direction turned to northwest.However,fire spread south slowly due to the eastern isolation barrier and lake.When fire line reached the southern barrier,because of barrier and firefighting,the wildfire event ended at 0800 UTC 26.In the case that there was no barrier,sensitivity test showed that the fire would across the border and spread southeast and northeast following wind direction.In this situation,the main fuel type changed from grassland to needle forest,and the spreading fire would lead to a great loss of forest.

Abstract:Based on the three-dimensional lightning location data of VLF/LF in Yunnan Province from 2017 to 2018 and the data of artificial observation thunderstorm days in Yunnan Province from 1987 to 2006,and using mathematical statistics,spatial interpolation and other methods,this paper studied the spatial and temporal distribution characteristics of lightning activity in Xishuangbanna area,known as a thunderstorm capital.The grid method was used to transform the lightning location data into a grid lightning activity days,to study the correlation between artificial observation thunderstorm days and lightning location monitoring data.Results show that the lightning activity in Xishuangbanna area begins to increase gradually from March,and the peak appears from July to August.The lightning frequency of intra-cloud flash is less than that of cloud-to-ground flash,the lightning frequency of positive flash is less than that of negative flash,and the lightning frequency of positive cloud-to-ground flash in Xishuangbanna area is significantly more than that in other areas of Yunnan Province.In November,the lightning intensity is larger,but the frequency is less.In July,the lightning frequency is more,but the intensity is smaller.Most intra-cloud flashes occur below 8 km,with an average height of 4.914 km.The density distribution of cloud-to-ground flash and intra-cloud flash is the same,higher in the north and lower in the south and east-west.The intensity of intra-cloud flash is significantly higher than that of cloud-to-ground flash,but the spatial distribution is weak in the north and strong in the south and east-west.The monthly distribution characteristics of the observed thunderstorm days are consistent with those of the grid lightning activity days.The study also shows that Xishuangbanna is the area with the most observed thunderstorm days and the area with the most grid lightning activity days in Yunnan Province.

Abstract:In the present study,based on the observed cloud-to-ground(CG) lightning location data from the period of 2007 to 2013 and the new observed intracloud(IC) lightning location data for 2013 in Jiangsu Province,the temporal and spatial pattern of CG and IC lightning activities along the expressways in southern Jiangsu were investigated.The following results were observed:(1)There were a greater number of CG lightning activities along the western expressways than the eastern ones.The highest frequency appeared along the Yangzhou-Liyang Expressway,the peak period of CG lightning activities in a given year was from June to August,and the peak time (July) along the western expressways was earlier than in the eastern region(August).However,the peak time (13:00 BST-16:00 BST) in the CG lightning frequency along the eastern expressways was slightly earlier than in the western region(14:00 BST-18:00 BST).(2)The CG lightning current(peak current) was mainly concentrated in the range of 20~50 kA,while the overall lightning current trend in the east was greater than in the west.The regions where CG lightning activities occurred most frequently were Nanjing-Zhenjiang Hills,Taihu Lake and the Yangtze River Valley.Among these,the expressway near Nanjing City,the Zhenjiang part of the Yang-Liyang Expressway,the Nanjing part of the Nanjing-Hangzhou Expressway,the Wuxi part of the Expressway along the Yangtze River,and the Shanghai-Nanjing Expressway were the highest CG lightning density sections.(3)The IC lightning activities in 2013 occurred mainly from May to September.The IC lightning frequencies along the western expressways fluctuated significantly in a distribution type of double peak months.The IC lightning activities along the eastern expressways were relatively concentrated,and exhibited a distribution type of a single peak month.The time of IC lightning along the western expressways(13:00 BST-18:00 BST) was earlier than along the eastern expressways (17:00 BST-18:00 BST).