Abstract:Using the rain drop size distribution (DSD) data obtained from OTTParsivelⅡlaser optical disdrometer in 4-23 August 2014 in Xinzhou, Shanxi Province, the moments method for estimating Gamma DSD parameters is studied in this paper. The precipitation clouds are divided into three categories: stratiform, cumuliform and stratiform mixed with cumuliform. Comparing the observed and estimated DSD data in 1 min, 5 min average and moving 5 min average, root mean square error (RMSE) and error distribution of DSD are computed with the method of least square and moments. A new method of moments is put forward involving M0, M3 and M6 which respectively represent the moments of raindrop number concentration, liquid water content and radar reflectivity. The analysis shows that using moments to estimate rain DSD, the M036 (M0, M3 and M6) is the best among the moment methods because the averaged RMSE in 1 min, 5 min average and moving 5 min average is minimum and the error distribution is concentrated. The parameters of DSD estimated from threekind precipitation clouds decrease with the increase of rainfall intensity R. The fitting DSD parameters (N0, μ, λ) satisfy binomial distribution and their correlation coefficient is good.

Abstract:Based on the data of several instruments applied in the 2014 Yangjiang and Tibetan experiments, the sensitivity, liquid water content (LWC or ice water content, IWC) can be detected and difference between different mode echoes of a new solidstate millimeter wave radar (SMMR) constructed by State Key Laboratory of Severe Weather (LaSW) and 23th Institute of Aerospace Science and Technology are contrasted. Also, difference between this radar and microrain radar (MRR) echo is contrasted. The results show: (1) differences between different modes of SMMR are in reasonable agreement with theoretical results. All the status and cumulus in nearsurface layer can be observed by boundary layer mode and precipitation mode. Cirrus mode can observe cirrus which ice water content is over 0.0007 g·m-3. Observation capability of all three modes decreased with the increase of height. (2) Differentials between three mode echoes are mostly less than 3.5 dB. (3) MRR echo and Pasivel2 laser optical disdrometer echo are almost same, system difference existed between MRR and SMMR echo.

Abstract:The threshold of extreme precipitation is defined by the method of percentile method in this paper. Based on Bayesian theory, probabilistic forecasting of extreme precipitation is discussed and we do the Bayesian extreme precipitation experiment and verification. Experiments which are based on observational and modal extreme precipitation threshold show the following conclusions. False prediction of extreme precipitation is proved to be more when the threshold is based on the observational extreme precipitation. The forecast of main rain band is stronger. False prediction is less while the threshold is based on the modal extreme precipitation and the early warning to the heavy rain is obvious as well. By contrast, the probabilistic forecasting based on the prior probability is smaller. The verification result shows that the accuracy of the extreme precipitation is improved by the Bayesian method, but the false prediction ratio has increased.

Abstract:Using conventional meteorological data, regional automatic station precipitation data, NCEP 1°×1° reanalysis data and FY2E satellite cloud image, evolution characteristics of the circulation situation, causes of the rainstorm and mesoscale features of the continual torrential rain process in Jilin Province from 14 to 17 in August 2013 were analyzed. The results show that in the unusually stable largescale circulation background, the torrential rain was mainly caused by two upper troughs which moved to the east along the same path on the middle latitude frontal zone and repeated impacting Jilin Province.The precipitation process was divided into two major stages. In the first stage, it was severe convective precipitation. θse frontal zone tilted to the south along height unstably and water vapor was abundant, forming large convective available potential energy. In the second stage, however, the rainfall gradually turned to mixed severe precipitation. θse frontal zone tilted to the north with height, the intensity of water vapor transport, precipitation duration and total rainfall amount were significantly stronger than in the first stage. During heavy rainfall, αmesoscale convective cloud cluster or MCC was formed successively and divided into 3 stages, impacting Jilin. In the developing stage of cloud cluster, there was a vertical structure of cyclonic vorticity with the mesoscale convergence on low altitude, anticyclone vorticity with the mesoscale divergence on high altitude, and the rising velocity was obvious. At the same time, the recurring of the wind speed convergence which was in the front of a ultralowlevel jet at 925 hPa was also the possible mesoscale triggering mechanism of the continual heavy rain.

Abstract:LambJenkinson atmospheric circulation classification scheme is used to classify daily circulation types. The major types, their catalogues and the relationship between the surface atmospheric circulation and the concentration of pollutants in Wuhan from 2004 to 2013, are explored. The results show that six major types (A, C, E, AE, NE and SE) occur most frequently, and the major types are A, AE and E in winter and autumn, A, C and E occur frequently in spring, C and E are the major types in summer. For air pollution days, major types are A, AE, E, SE, C and NE, and the major types that impact air pollution in different seasons are different. The Type C is mainly in spring and summer, being controlled by weak low pressure. The four major types (A, SE, E, AE) are relevant to severe air pollution in Wuhan. Severe air pollution occurs easily under the control of high pressure system or easterly. The impact of the circulation types on the concentration of air pollutants is different.

Abstract:In recent years, the eastern part of China, especially the JingJinJi (shortly for BeijingTianjinHebei Region) has suffered increasingly severe pollution of PM2.5. A case of PM2.5 pollution over the JingJinJi Region during the autumn of 2014 is studied with WRFChem model in this paper. The results show that the pollution was caused by a stable weakhigh pressure system with the dominant southerly wind on the surface. The temperature inversion layer further suppressed the diffusion of pollutants in the vertical direction. High concentration of PM2.5 mainly spread in southern Beijing, Tianjin and northern Hebei Province, where the contribution of secondary PM2.5 was higher than that of primary PM2.5 to most of the pollution areas. Vertically, the secondary inorganic particles accumulated around Beijing, then became a high concentration region affixed to the ground surface. On the other hand, there was a zone of high pollutants over 1.2-1.6 km, and primary pollutants only had one high value area near the surface. The vertical distribution height of PM2.5 showed a similar trend with the boundary layer height.

Abstract:A sustained foghaze event that occurred in early December 2013 in Yancheng was analyzed based on surface meteorological parameters, NCEP reanalysis data (1°×1°), and air pollutants concentration. The study focus lies in circulation background, surface meteorological elements and atmospheric stratification feature, as well as thermodymamic condition and pollution. The results show that there were weak cold air forces in middlehigh level in early December with zonal circulation at 500 hPa. The breezed surface layer was the favorable circulation background for the formation of foghaze. The maintenance of stable stratification characteristics, high inversion intensity and continuous lower mixed layer were responsible for the sustained foghaze briefly. In addition, the weak sinking motion, positive divergence and negative vorticity were the dynamic factors for the sustain development of foghaze. The longdistance transport of pollutants played a certain role in the concentration increase of pollutant particulates according to the backward trajectory types and the monitored fire spots. Finally, the nonlinear regression formula of visibility, humility and PM2.5 concentration was established, which is better for visibility forecasting and provides a favorable basis for the operation of foghaze forecasting.

Abstract:Combined with the geographic information data, a data set of 27 stations over the Pearl River Delta Region including all of ordinary and national basic climatological stations was used to analyze the annual and seasonal trend and urbanization effect for mean temperature, mean minimum temperature, mean minimum temperature and diurnal temperature range, respectively. The main results are as follows. In 1963-2012, all the weather stations underwent evident warming in terms of annual mean temperature, annual mean maximum temperature and annual mean minimum temperature, and witnessed significant decrease in annual mean diurnal temperature range except Conghua, Zengcheng, Zhuhai and Shangchuandao. In Guangzhou, Foshan and Huizhou, the contribution of the annual urban warming was positive for the mean temperature and mean maximum temperature. However, the contribution rate of urbanization was negative for the diurnal temperature range, indicating that the reduction of daily temperature range is mainly caused by the urbanization. As for the season, urbanization effect in fall is the strongest. Since the reform and opening policy was implemented, the range of warming areas has become expanded and the strength of warming become much stronger than the counterpart in the recent 50 years in the respect of annual mean temperature, mean maximum temperature and mean minimum temperature. Especially the warming of annual mean maximum temperature is much evident. For the diurnal temperature range, the positive regions have also increased, mainly distributing in northern area of the Pearl River Delta with maximum rate of 0.25 ℃·(10 a)-1. Compared with the situation in the recent 50 years, the annual mean temperature, mean maximum temperature and mean minimum temperature has decreased in Guangzhou while the annual mean temperature and mean minimum temperature has increased in Foshan and Huizhou.

Abstract:By using the daily observation data of acid rain from 32 stations from 2007 to 2014 as well as Yichang and Wuhan Stations during 1990-2014, we studied the variation of acid rain in Hubei Province. The results indicated that the precipitation of the region shows weak acidity and the mean pH is 4.68. The intensity has been in the trend of getting weak since 2008, maintaining a weak level between 2007 and 2014. The areas with pH less than 4.5 are located in the Three Gorges Valley, some areas of western part, the west of southeastern part, and the southern part of Hubei. The average annual frequency of acid rain and strongacid rain is 69.5% and 24.4% respectively. The frequency tends to decline while the strong acidrain shows the trend of decreasing significantly since 2009. The areas where acid rain occurs frequently are located in most southern part and the east of northwestern part of Hubei. The average annual electrical conductivity is 50.3 μs·cm-1, showing a pattern of high in central part and low in west and east part. The pH value is lower in winter than in summer while the frequency and electrical conductivity are higher in winter than in summer. The intensity of acid rain in Wuhan has been inclining to increase since 2005, retaining a strong during 2006-2012 while the electrical conductivity has a increasing trend. Both the intensity and pollution level are higher in Yichang than in Wuhan. In addition, the content of nitrogen oxides over Hubei Province tended to spread and increase. The sulphur dioxide content in Wuhan tends to decline while the nitrogen dioxide content tends to increase. Because of this change the acid rain components in Hubei may transform from sulfate to sulfate combined with nitric acid.

Abstract:In this paper, subcatchments of small rivers in Hunan are determined based on DEM data and D8 algorithm. According to the network propagation model for flood forecast of main rivers in Hunan Province, a directed graph related to the subcatchments has been built, which represents the topological relationship among these areas both in temporal and spatial dimension. To build the relation between precipitation and runoff in a reasonable space, the concept of valid rainarea related to the flood graph is proposed. By using the valid rainarea data series and runoff series, the hidden Markov model is built to calculate critical rainarea threshold of flood disasters at different time scales in the subcatchments in Hunan Province. Finally, the observed flood warning data (collected in 2010-2015) are used to test the proposed method. The results show that the new method has similar performance to traditional statistical ways but is more accurate and stable. In addition, the successful application of the new method to the operation of forecasting flood disaster on 13 June 2015 further proved that the new method is suitable for flood forecasting.

Abstract:Highquality wind observation on sea surface is the foundation of marine meteorological monitoring and forecasting. The accuracy of satellite retrieved winds along coast is low. The exponent law representing wind profile near surface layer is used to retrieve winds on sea surface around islands or mudflats on which automatic weather stations have been set up. Then objective analysis method is used to transform retrieved winds at discrete points into regular mesogrid to get complete wind field with high resolution. The accuracy of retrieved winds is determined by the parameter α in exponent law which is influenced by the status of underlying surface and atmosphere structure. The influence of the latter is more significant than the former. Experiments are performed to verify the error of retrieved winds calculated with different wind profile variation rates (parameter α). The results show that the accuracy of retrieved winds using multiple wind profile variation rates is better than that using single one. By using hybrid wind profile variation rates, mean error (ME), mean absolute error (MAE) and root mean square error (RMSE) of the overall sample are obtained, being 0.04 m·s-1, 1.51 m·s-1 and 2.01 m·s-1, respectively. Through optimizing retrieved winds on sea surface, MAE and RMSE are respectively reduced to 1.28 m·s-1 and 1.68 m·s-1.

Abstract:By using the meteorological observation data from 91 weather stations in Jiangxi province during 1981-2014 and the late rice yield data of the corresponding time period, and combining physiological characteristics of late rice and climatic features of Jiangxi, the suitability models for temperature, precipitation and sunshine in the Jiangxi area are constructed. Moreover, according to the correlation between rice yield and suitability, the climate suitability index is determined. Then based on the index, the dynamic prediction model of the late rice in Jiangxi is constructed and tested so as to diagnose the climate suitability of the late rice in Jiangxi and to do dynamic prediction of the late rice yield. The results indicate that the method has high prediction accuracy of the bumper or poor harvest trend and the actual yield in the model test and forecasting test, and it could satisfy the needs of operational services.

Abstract:In winter 2015/2016, the Arctic Oscillation (AO) showed a remarkable subseasonal variation with the positive phase in December 2015 while strong negative phase in January 2016, which resulted in the southward invading of the super cold wave from the polar region to the midlatitudes in the Northern Hemisphere. The temperature in the Northern Hemisphere including China changed from positive anomaly in December to negative anomaly in January. The phase transition of the AO from positive to negative was mainly associated with the North Atlantic storm activity. At the end of December 2015, a strong cyclonic storm appeared over the North Atlantic. This storm conveyed huge quantities of warm air into the polar region, which quickly warmed the Arctic up. The geopotential height anomaly over the Arctic region changed from negative in December 2015 to positive in January 2016, eventually leading to the transition of the AO from positive phase to negative phase.

Abstract:The following are the main characteristics of the general circulation of atmosphere in April 2016. There were two polar vortex centers in the Northern Hemisphere, and the strength of main polar vortex center was weaker than normal. There were four waves around the earth in middlehigh latitudes. The position and strength of East Asia trough and south branch were close to normal annual means. The area and strength of subtropical high in the Northern Hemisphere were stronger than annual means and the northern boundary of Northwestern Pacific subtropical high maintained near 20° N. Moreover, shortwave trough in low latitudes was active than usual. In April, the monthly mean temperature of China is 12.6℃, 1.6℃ higher than usual, being the second highest value in record for the same period. The mean precipitation of China is 62.2 mm in April, 39.1% higher than usual. There were three cold air events over the country, and four sanddust events in the north of China in April. Rainfalls were seen frequently in the south of China, and 10 heavy rain processes occurred during the month. In addition, several severe convective weather events such as shorttime severe precipitation, thunderstorm and gales in Jiangnan Region and Huanan Region of China.