Abstract:In view of the uncertainty of dust emission in source regions, several representative dust-emission schemes are applied to simulate the dust emission by wind erosion during a strong dust storm weather process in East Asia, using the high-resolution output from MM5V3.7.The simulated results are compared with the surface observations and the satellite images, and the differences among these simulated schemes are also compared.Results show that two schemes have better simulation effect and steadier performance.

Abstract:The anthropogenic aerosols(sulfate, black carbon and organic carbon) and their effects on the East Asian summer monsoon have been simulated by using a regional climate model RegCM3 coupled with a chemistry aerosol model.Results show that aerosol can change summer 850 hPa wind over East Asia.A cyclonic anomaly circulation center appears on the estuary of the Yangtze River and the northerly air flow on its west will weaken the summer southwestly monsoon in East Asian.Investigation has been conducted on the relationship between spring and summer aerosol column burden over China and summer 850 hPa meridional wind in East Asia.Evidence shows that the aerosol column burden in both spring and summer bears a close negative correlation with summer 850 hPa meridional wind in East Asia.The summer southerly monsoon in East China weakens when the spring aerosol column burden over North China or the summer aerosol column burden over South China increases.The reasons may be the short wave radiative forcing caused by aerosol effects on the top of the atmosphere and the surface, which leads to the change of air pressure and potential height between sea and land.

Abstract:Based on the difference in precipitation between the station over the Yellow Mountain and those in Huangshan District, Jixi and Huangshan city, which is defined as the orographic enhancement factor(R₀), as well as the change of visibility during 1960 and 2009, the possible ways that air pollution aerosols influenced orographic precipitation were studied.During 1960 and 1979, the increasing trend of R₀ matched well with the decreasing visibility and increasing aerosols.Different stations presented different change trends for R₀ while the visibility was increasing and aerosol was decreasing during 1980 and 1989.With decreasing visibility and increasing aerosols, R₀ decreased significantly during 1990 and 2009.The effect of aerosols on the orographic precipitation was relevant with background concentration of aerosols.When the background concentration of aerosols was low, increasing aerosols would promote orographic precipitation.When the background concentration of aerosols was high, air pollution aerosols would suppress orographic precipitation significantly and the corresponding visibility threshold was about 10 km.When the aerosols suppressed orographic precipitation, the inhibition effect was negatively correlated with the wind speed and positively correlated with wind frequency and average precipitation in each wind direction.

Abstract:Based on the encryption sounding data, the automatic meteorological observing data and other conventional observing data, we analyzed a severe sandstorm occurring in the Midwest Inner Mongolia autonomous region on 23—24 April 2009.The ground meteorological elements and its internal dynamical and thermal changes in the process were studied.The result showed that:1)Before the sandstorm, the temperature lapse rate was big, the relative humidity was large, the wind speed near the ground was small and the wind direction was easterly;when the dust storm occurred, there was an inversion in the atmosphere temperature, the relative humidity was small, the wind speed increased obviously and the wind direction was westerly and stable;when the sandstorm ended, the temperature decreased, the relative humidity increased fast and the wind velocity reduced rapidly in all layers;2)The atmospheric stratification had been conditionally unstable before the sandstorm took place and turned to be stable in the low layer and neutral between 800 hPa and 600 hPa when the dust storm occurred, and the low layer atmosphere was extremely dry at the time.Then the humidity became large when the sandstorm ended.So "3θ"curve could provide a valuable reference for the monitoring and forecast of dust storms;3) The relative storm helicity(RSH), which was available when the dust storm occurred, was of the maximum value compared with all the other observation times, and it had a good correlation with the sandstorms in intensity.That was to say, the bigger the RSH was, the severer the sandstorm would be;4) The intensity of the sandstorm was not only closely related to the surrounding velocity, but also to the values of the tangential and vertical velocities in the sandstorm.

Abstract:With the rapid development of the urbanization and industrialization, heat island effect in Nanjing has been more striking.The air pollution of particulate matters has a bad impact on the atmospheric environment, climate change and citizens.This paper analyses variation characteristics of heat island intensity under different particulate matters concentration levels with the observations in Nanjing.The OPAC(optical properties of aerosols and clouds) and TUV(troposphere ultraviolet-visible) models are used to calculate optical thickness and radiation forcing of aerosols as well as study the physical mechanism of the aerosols affecting the heat island intensity.The heat island intensity of Nanjing, which is stronger in winter than in summer, changes between -0.5 K and 1.3 K.The fine particle mass concentration ranges from 32 to 135 μg/m³, which is higher in winter than in summer.The aerosols have an extinction effect on the heat island.The higher aerosols mass concentration, the lower heat island intensity.There is an apparent difference in different seasons.The optical thickness of aerosols in the suburb in Nanjing changes between 0.28 and 1.01 and the radiation forcing ranges from -3.88 W·m^-2 to -4.72 W·m^-2.Due to the differences of underlying surface, anthropogenic heat and particulate matter concentration, the surface temperature declines differently in urban and rural area.In general, the particulate matter weakens the urban heat island as 0.1 K in summer and 0.2 K in winter.

Abstract:The weather research and forecasting(WRF) model, coupled with a multi-layer urban canopy model BEP(building energy parameterization), is used to investigate a high temperature episode occurred in the Yangtze River Delta region on 13 August 2013.A southeasterly breeze, consistent with the direction of Suzhou-Wuxi-Changzhou urban cluster, is prevailed over the Yangtze River Delta region during the episode.Simulating results show that significant urban heat island(UHI) effects occur in the urban cluster, and the UHI intensity increases from Suzhou to Changzhou.Under the impact of the southeasterly breeze, the UHI effects of the three individual cities merge together, forming a stronger UHI circulation.In the night, the UHI circulation is weakened by the stable planetary boundary layer, which is favorable for the downstream transport of the UHI effect.The urban planetary boundary layer height is significantly increased by the UHI effect.During the daytime, a strong lake breeze between Lake Taihu and land has great impacts on the UHI of the nearby cities.Air temperature over Wuxi and Changzhou is significantly decreased by the cold air from Lake Taihu, and the upward extension of the UHIs over the two cities are suppressed.Connections of the UHIs between Wuxi and Changzhou are weakened by Lake Taihu.The planetary boundary layer height over Wuxi and Changzhou is more significantly decreased by the lake breeze during daytime.

Abstract:The microphysical properties and boundary layer characteristics of three icing processes that took place at Enshi radar station in the winter of 2008 and 2009 was simulated by using the Weather Research and Forecasting(WRF) mesoscale model coupled with the Thompson microphysical scheme, and the results were compared with the observational data.The results showed that the simulations could well reflect the appearance of inversion layer over the radar station.The mean absolute errors of mass concentrations of cloud water and median volume diameter of cloud/fog droplets between simulations and observations were 10^-2 g·m^-3 and 3.8 μm, respectively.There was a high center whose mass concentration was 0.3 g·m^-3 over the radar station, and it moved to the ground gradually, bringing sufficient droplets and precipitation to the ice accretion processes.

Abstract:Based on the weather and data from meteorological satellites and radars, the macrophysical and microphysical characteristics of the stratiform cloud in Shanxi Province on 11 March 2009 were analyzed by using droplet measurement technology(DMT).The results showed that precipitation clouds were composed of altostratus and stratocumulus.Content of liquid water ranged from 0 to 0.42 g/m³.Particle concentrations observed by cloud droplet probe(CDP)and cloud imaging probe(CIP)were large, whose maximum values were 451.93 cm^-3 and 162.78 L^-1 respectively.Suitable temperature ranges for seeding were from -11.4 to -7℃ and from -4.4 to 0℃.The upper portion of altostratus was the nucleating and sublimation growth area.The mid and lower portions of altostratus was the active growth layer of ice crystals.Ice crystals from altostratus grew up by sublimation and coagulation in the stratocumulus.The spatial distribution of stratiform cloud microphysical parameters was uneven.The cloud droplet spectra were mainly of two-peak and multi-peak distributions.In the middle and top portions of stratocumulus, the spectra were exponential.When liquid water concentration(LWC) was less than 0.03 g/m³ or larger than 0.1 g/m³, the spectra were unimodal.

Abstract:The precipitation of a convective-stratiform mixed cloud in Zhangjiakou during 18—19 April 2009 is simulated using the mesoscale numerical model WRF-ARW(V3.2) and comparatively analyzed with the observation data in different scales.Results show that the west wind trough at 700 hPa and the low vortex at 850 hPa are the main weather systems responsible for convective-stratiform mixed cloud.The warm wet air from the southern and the low vortex from northwest Inner Mongolia are main water vapor suppliers, which converge in Zhangjiakou region and thus are conducive to cloud system development and precipitation formation.The cloud system shows a NE-SW banded distribution, which is 1000 km long and 300 km wide, and has lots of cloud water centers, which are about tens of kilometers.The cloud system has the echo characteristics of typical convective-stratiform mixed cloud precipitation, such as columnar echo of cumulus cloud embedded in uniform echo layer.The cross-section of radar echo shows that the cloud water content is heterogeneous either horizontally or vertically.The centers of rainwater are corresponding with the centers of graupel and snow in the upper layer, with horizontal range of 10—20 km.

Abstract:The drizzle plays an important role in determining the cloud lifetime and evolution.Millimeter wave radar is suitable for detecting non-precipitating and weak precipitating clouds.It is of great valuement to know whether the drizzle occurs or not by the millimeter wave radar measurements.In this paper, the radar reflectivity factor of drizzle is calculated based on the dataset of cloud droplet distribution observed by aircraft.In comparison with the simultaneous radar observations, there is a good agreement between the two reflectivities.The result shows that the reflectivity factor threshold of drizzle derived from in-situ measurements can be used by the radar to diagnose the occurrence of the drizzle.The threshold of reflectivity factor to distinguish drizzle and cloud particles is derived by analyzing the probability distribution function of reflectivity factor due to cloud particles and drizzle drops.Usually, the reflectivity factor of cloud particles is below -5 dBz while the value of drizzle is above -20 dBz.A value between -15 and -12 dBz can be used as the threshold of drizzle.

Abstract:Based on the data of raindrop size distributions(RSDs) and lightening over the Leizhou peninsula in August 2007, this paper analyzed the(RSDs) of a thunderstorm at Suixi and Zhanjiang on 6 August 2007 and the relationship between lightening and precipitation.The results showed that the RSDs were mostly bi-peak or multi-peak spectra at Suixi while they were mainly single-peak spectra at Zhanjiang.The spectra were all fitted with Gamma distribution.The lightning strokes were higher in heavy rain(I>10 mm/h) than in the precipitation with lower rain rate.The strokes of lightning also increased when it got closer to the station in heavy rain(I>10 mm/h).The positive ground flash frequency rose obviously with increasing rain rates.The relationship between lightning frequency and distance-normalized current intensity in the precipitation suggested that a higher occurrence frequency of cloud-ground(CG) lightning in shorter distance was associated with broader raindrop size spectrum and higher rain rates.

Abstract:Huai'an and surrounding area experienced a serious fog-haze event during June 9—11, 2012.The concentrations of PM_2.5, NO_x, CO, SO₂ increased remarkably during this period.Based on the air pollution monitor data and the synoptic observation information, the air pollution characteristics, influence factors and the sources were analyzed.The results showed that the SO₂ concentration was always lower than 0.049 mg/m³, NO_x, PM_2.5, CO concentration was inversely related with visibility and had two peaks when the visibility was lower than 1 000 m in the whole process.During the fog-haze progress, inversion layers maintained at the low-level, whose bottom was at 975 hPa and the top near 925 hPa.The stable structure restrained the atmospheric turbulences, vertical exchanges of water vapor as well as vertical diffusion of pollutants, and thus created good thermal conditions for the maintenance of the fog-haze process.There remained easterly winds during the whole progress and the visibility changed with the wind speed synchronically.By tracking the air mass from the simulations of the HYSPLIY4.8 model, we found that this fog-haze process over the lower reaches of Huaihe River was mainly caused by the weather condition and crop residue burning.

Abstract:Based on the online observed concentration of H-1301, HCFC-22, CFC-11 and SF6 at Shangdianzi background station during 7—12 September 2012, a typical case about short-term fluctuation of halogenated greenhouse gases is analyzed by means of trajectory, footprint and flow field analysis methods.The trajectory analysis results show that, before occurrence of pollution, air masses mainly come from the further north and northwest at 1200 UTC 7 September 2012, with a long horizontal transport distance, rapid moving speed and high vertical height.Meanwhile, the corresponding volume fractions of halogenated greenhouse gases are relatively low, which are 4×10^-12, 350×10^-12, 260×10^-12 and 10×10^-12 for H-1301, HCFC-22, CFC-11 and SF6, respectively.However, in 9—10 September 2012, a certain percentage of air masses convolute over the south of the station with a short horizontal transport distance and low vertical height, moving slowly in the boundary layer, which hinders the spread of pollutants in the boundary layer and results in the relatively high concentrations of halogenated greenhouse gases.Such situation contributes a lot to the short-term rapid growth of concentration levels.The peak volume fractions of H-1301, HCFC-22 and CFC-11 reach 45×10^-12, 1200×10^-12 and 310×10^-12 at 1200 UTC 9 September, respectively, and that of SF6 does 28×10^-12 at 0300 UTC 10 September.On 11 September, the convoluting air mass in the southwest direction disappears.On 12 September, air masses all come from the far northwest and have rapid moving trajectories.The footprint analysis results are the same as the trajectory analysis results, which are that the regions with high sensitivity coefficient are mainly located in the north of the station in 7—8 September, and in the south of the station in 9—10 September.Then the regions with high sensitivity coefficients in the south of the station disappear in 11—12 September.In addition, the flow field analysis results show that the circulation pattern in 9—10 September is favorable for the accumulation of pollutants in the observed region, resulting in the short-term lift of pollutants' concentrations.

Abstract:Based on the chemical composition of precipitation data in Waliguan from 2007 to 2009, the pH value, conductivity and distribution characteristics of Cl^-, NO₃^-, SO₄^2-, NH₄⁺, K⁺, Na⁺, Ca²⁺ and Mg²⁺ are analyzed.Results show that the annual mean of pH and conductivity are 6.60 and 21.26 μs/cm, respectively, and they have rising trends from 2007 to 2009.In terms of the pH value, the frequency of neutral-based precipitation is the most(65.13%), followed by the alkaline precipitation, and the acid rain is the least.The ion concentrations from high to low are Ca²⁺, SO₄^2-, Na⁺, NH₄⁺, Cl^-, Mg²⁺, NO₃^- and K⁺, respectively, which have obvious seasonal variations.The K⁺, Na⁺, Ca²⁺, and Mg²⁺ have similar sources.The value of SO4^2-/NO^3- in the precipitation varies from 0.35 to 16.48, and the mean value is 3.07.The value of SO4^2-/NO^3- has a falling trend from 2007 to 2009.The annual variation of SO4^2-/NO^3- has two peak values in April, and September-October, respectively.

Abstract:By using ECWMF and NCEP/NCAR monthly mean reanalysis data(from September 1957 to August 2002), characteristics of interannual potential predictability of SLP, 500 hPa geopotential height, 200 hPa zonal wind and 850 hPa meridional wind in winter and summer are analyzed respectively.The results show that the potential predictability is high in the tropics, especially the equatorial area and eastern Pacific.In contrast, the potential predictability is relatively low over the middle and high latitudinal areas.After comparing the differences between these two sets of reanalysis data, we find that the difference in the Southern Hemisphere is more obvious than that in the Northern Hemisphere, especially around the South Pole.The difference in low-level variables is larger than those in middle-and high-level variables.There exists some potential predictability in East Asian in both winter and summer.East Asian winter monsoon described by all the variables in both two sets of reanalysis data has high potential predictability with little difference.Only the East Asian summer monsoon described by 500 hPa geopotential height shows high potential predictability with little difference.There are obvious differences in East Asian summer monsoon's potential predictability with low-level variables including SLP and 850 hPa meridional wind between the two sets of reanalysis data.

Abstract:Interannual change of summer temperature in Qingdao was analyzed based on the monthly average temperature data during June and August in 1951—2010 by using the method of principal component analysis and cluster analysis through SAS software.According to principal component analysis, the first principal component was the summary of summer temperature departure in Qingdao.The positive(negative) direction reflected the positive(negative) anomaly of temperature and the strength reflected its degree.The second principal component reflected the temperature difference among each month of the same year.The larger the absolute value of the second principal component was, the greater the temperature difference among each month was.Cluster analysis showed that the change of average monthly temperature in summer in Qingdao could be divided into three categories.The first type was that the temperature was low in June and July and warmed up in August.The second type was that the average temperature in July was the highest while in June and August it was relatively low.The third category was that the temperature in June was low and it got high in both July and August.The year of 1993 and 2003 were of the first type, 2005 of the second type and the other years of the third type.

Abstract:Urban heat island circulation(UHIC) and sea breeze circulation(SBC) usually coexist in coastal urban areas;they play a crucial role in transport and dispersion of air pollutants, and have a significant effect on convection initiation.With the development of urbanization, environmental problems such as air pollution become more and more serious, and disaster induced by severe convective weather becomes more and more serious too.Therefore, the study of UHIC and SBC interaction receives increasing and extensive attention.In this paper, the history of numerical studies of UHIC and SBC interaction in last 30 years is overviewed;The current research status and some problems are analyzed;Some important results are outlined;Some issues and topics are addressed for further study.