Abstract:Secondary circulation plays an important role in the intensifying and maintenance of typhoon. The SawyerEliassen (SE) equation derived based on gradient wind balance is usually used to diagnose the secondary circulation of typhoon. However, the gradient wind balance has large errors within and near the boundary layer, which leads to large errors of the secondary circulation solved by SE equation within the boundary layer. Based on the full formation of the radial momentum equation, a novel SE equation is derived in this paper. The supergradient force including the radial friction of boundary layer is therefore considered in the novel SE equation. And it turns out that the supergradient force can modulate the secondary circulation by affecting the coefficients related to baroclinicity in SE equation. The diagnostic analysis of the typhoon Sinlaku (2008) shows the novel SE equation can improve the solved secondary circulation remarkably without subjective modifying the flow structure near boundary layer. The novel SE equation can avoid the false convection at the out flank of the eyewall in and near the boundary layer, and can reduce the false strong boundary layer inflow.

Abstract:In this paper, four multimodel ensemble methods, namely ensemble mean (EMN), weighted ensemble mean (WEMN), biasremoved ensemble mean (BREM) and weighted biasremoved ensemble mean (superensemble, SUP) have been constructed based on TIGGE datasets, from which four single model forecasts of recent three years from CMA, ECMWF, JMA and NCEP are selected to conduct multimodel ensemble combination and comparison. Single and multimodel ensemble forecasts on the tracks and central pressure of tropical cyclone over Western Pacific with forecast lead time 24 h, 48 h, 72 h, 96 h and 120 h are evaluated and compared. The results show that different single models have different forecast skills. The CMA forecast has the worst performance during the three years, and the best single model forecast in 2010 and 2011 is ECMWF while NCEP is the best one in 2012. Generally, multimodels have significant superiority over the single models within 120 h forecast lead times. As the simplest method within all the four multimodels, EMN shows limited superiority. WEMN has better skill than EMN because it can give different weights to the member models, while the BREM exhibits superiority for the systematic bias is removed. Because of considering both the weights of member models and bias elimination, the SUP has a better skill in general.

Abstract:Based on station data and NCEPFNL 1°×1° reanalysis data from 2008 to 2012, the developing Yellow River cyclones passing over Bohai Sea are classified into Summertype and Springtype. In this paper, the structures and impact factors of the two types of cyclones, especially the moisture, thermal and dynamic effects of the HuangBohai Sea are compared and analyzed. It is shown that the Summertype cyclones are related to the wide area of heavy rainfall, while the Springtype cyclones are related to large gale area instead of rain. The structures of the cyclones are baroclinic, but Summertype cyclone is with a warm center, while Springtype cyclone has remarkable baroclinicity. Upperlevel jet is at the south of cyclone in spring, the cyclonic wind shear at the jet left side keeps the cyclone, and the upper level momentum passes down into the back of Springtype cyclone, and meets the cold front secondary circulation and the flat sea surface, which is conducive to rapidly increasing lowlevel cyclonic winds. In comparison, the upper level jet is at the north of cyclone in summer, and the upperlevel divergence of the jet right side and lowlevel convergence strengthen together the ascending motion of summer cyclone, favoring strong cyclonic precipitation and condensation latent heat release. There is conversion of perturbation potential energy to kinetic energy when cyclones develop through the Bohai Sea that maintains and strengthens the cyclone momentum. In addition MPV calculations show that Summertype cyclones are with the deep and thick dry air sinking, which is favorable for the formation of heavy precipitation, but in Springtype the drywet gradient is small and distributes in scattered patterns, corresponding to the smallscale precipitation. HuangBohai Sea is the main vapor transport channel of cyclones which transports abundant moisture in summer because of the higher sea surface temperature than in spring, but the water vapor transport is deficiency in spring. The low level wind speed of Springtype cyclone is significantly enhanced by sea surface dynamic effect, while the effect does not work in Summertype cyclone. Diabatic heating analysis over Bohai Sea indicates that latent heat plays an important role in Summertype cyclone, while the sensible heat is more significant in Springtype cyclone.

Abstract:Based on the NCEP/NCAR 1°×1° FNL data, satellite TBB data from Japan Meteorological Agency and dense surface observation data of China Meteorological Administration, this paper investigated a severe snow process in Southern Tibetan Plateau. The results show that (1) the snowstorm is mainly related to the impact from residual cloud systems of northwardmoving cyclonic storm phailin over the Bay of Bengal. (2) The southerly lowlevel jet between the storm and high pressure circulation is beneficial to the northward movement of Storm phailin and its impact. (3) The cyclone provides unstable energy via southerly lowlevel jet and the strong ascending airflows to Southern Tibetan Plateau, which creates favorable dynamic and thermodynamic conditions for the snowstrom. (4) The frontogenesis formed by the cold air from the westerly trough and warm air from the storm and the forced ascending caused by the terrain effect of Tibetan Plateau also enhance the dynamical conditions of snowstorm. (5) The unstable energy advection by the storm is the main energy source for the snowstorm. High elevation, dry and cold underlying surface and low 0℃ height over Southern Tibetan Plateau are important factors for the continuity of the snowstorm.

Abstract:Using NCEP/NCAR (2.5°×2.5°) reanalysis data, conventional and unconventional data and based on the environmental and mesoscale characteristics, this paper analyzes the impact of the superstorm “Phailin” in the Bay of Bengal on the severe precipitation in Tibet. The results show that after Phailin’s landing, it weakens into a low pressure. The development of the low pressure clouds is divided into two stages, forming three mesoscale convective cloud cluster, which controls the Tibetan Plateau severely under the influence of southern branch. The occurrence of severe precipitation has direct corresponding relations with the speed of southern winds. The southern part of Tibet does not see severe precipitation until the establishment of the lowlevel southwestern jet while the establishment of the lowlevel jet results from the contribution of the southern branch. The important relationship between the speed of southern winds and severe precipitation is quite conductive to forecasting such weather events.

Abstract:Based on Tianshui Doppler radar data, characteristics of radar reflectivity, Doppler velocity and PUP products during a warm area rainstorm in Southeastern Gansu Province in 19-20 June 2013 are analyzed. The results show that the characteristics of radar reflectivity are extremely similar with the characteristic of warmarea torrential rains in eastern and southern China. The “train effect” of local strong echo is obvious. Strong echoes are generally lower than 45 dBz, and mainly distribute in below 0℃ layer. It was advantageous to the generation of strong echo and highfrequency “train effect” that warm advection and wind convergence structure in boundary layer to middlelower level, lowlevel jet maintaining showed on Doppler velocity characteristics. The mesoγ scale vortex has indicative significance for the nowcasting of severe precipitation.

Abstract:Analysis of the hail echo artificial in Anhui in spring and summer is important for hail prevention. By using the hail data collected in Anhui during 2002-2013, CINRAD data, the Storm Cell Identification and Tracking (SCIT) algorithm, we got 59 hail processes from March to August and analyzed statistically the echo intensity and height of hail clouds, and VIL. The results show that hail probability is the greatest in June and July, especially in from afternoon to evening (15:00-18:00 BT). Over the Anhui Region, hail echo intensity of spring and summer is at least 55 dBz, mostly is 60-70 dBz, VIL is at least 30 kg·m-2, mostly is 40-80 kg·m-2. The varying trend of VIL is similar with the maximum reflectivity, and their maximum values tend to occur near the onset time of hail. The average echo top of hail storm is 13.6 km in spring and summer, average top storm height of 30 dBz is 12.1 km and the maximum echo top height is above 17 km.

Abstract:Based on the complex terrain and large city characteristics, the geographic information of Beijing was cut into 6458 grids and corresponding channels. Focused on the urban hydrodynamic and hydrographic process, the Beijing Urban Waterlogging (BUW) numerical model was built to simulate the ponding depth. Driven by highresolution precipitation observation, BUW can simulate the spatial distribution of the 21 July 2012 urban ponding in Beijing well, and the variation and max depth under concave bridges are close to actual condition too. In the scene of 2yr Return Period (2RP), there are some isolated ponding points inside the 4Ring Road. The depth and range of ponding increase in 10RP and 50RP. Under 100RP, there is servere pondings within the whole 5Ring Road with most exceeding 50 cm in the south. Facing the rainfall at the 21 July 2012 level, urban drainage will not be improved obviously with 20% of pipe diameter (20%+PD) broadening. The ponding gets relieved distinctly between the Roads of 4Ring and 5Ring and slightly inside the 4Ring in 60%+PD experiment. When the pipe diameter is broadened continuously, there is only shallow ponding between the 2Ring and the 4Ring in 100%+PD experiment and no ponding insides the 6Ring in 140%+PD experiment.

Abstract:Using hourly precipitation observation data from 124 stations during the period from June to August, 2011-2012, TRMM estimated precipitation data with 0.25°×0.25° resolution, DEM elevation data, the correlation coefficient, relative error and accuracy index, the TRMM precipitation estimate ability in Tibetan and the elevation effect on precipitation estimation are analyzed. The results show that TRMM precipitation estimation trend in the plateau is consistent with larger precipitation intensity and more frequency. The average accuracy without precipitation is much higher than mean accuracy rate of precipitation, the missing rate is lower and false alarm is higher. The TRMM data have better estimate ability on the observation station with more rains. The observing sites of Tibetan are mostly located in relatively lowlying area (valley). When the elevation error between observating stations and surrounding areas is small, the precipitation error between TRMM and observation is small. On the contrary, precipitation error becomes larger when the elevation error is larger.

Abstract:Based on the 53 a (1961-2013) daily precipitation data in Meiyu flood period over YangtzeHuaihe Basin, the threshold of extreme precipitation for each station is defined by percentile method, and the spatial and temporal distribution and mutation features are analyzed. The results show that the 95% thresholds of extreme precipitation are more than 50 mm, and their high value centers are mainly located from eastern Hubei to southern Anhui. The average intensity distribution of extreme precipitation is similar to the distribution of thresholds. Both the extreme precipitation and extreme rainfall days present decreasing features from southern Anhui to its surrounding areas, while the former accounts for about 1/4 to 1/3 of total Meiyu precipitation. In addition, stations of extreme precipitation for each pentad show single peak type with the maximum centered in the 5th pentad of June to the 2nd pentad of July. The extreme precipitation, extreme rainfall days and the extreme precipitation perecntage of the total precipitation in Meiyu period have obvious interannual variability with ascending trends, and the mutations of the extreme precipitation and rainfall stations occur in 1980.

Abstract:Based on conventional meteorological observation data and NCEP reanalysis data as well as hourly pollutant concentration data, seasonal characteristics of consecutive haze events in Xuzhou in 2013 are analyzed, including circulation background, surface meteorological characteristics, pollution forming and maintaining mechanism. The findings are as follows. Consecutive haze events are prone to occur when the cold advection at high level, warm high ridge at low level, and back of surface high or saddle pattern occur in autumn and winter, and southwest wind at high and low level, south airflow in the back of high pressure and the surface wind are not very weak in spring and summer. Wind speed in autumn and winter is very slow at night, slightly increasing during the day, but in spring and summer wind speed is stable relatively, being 2-3 m·s-1. Wind direction is northerly and easterly mainly in autumn and winter, but easterly to southeasterly in spring and summer. Temperature stratifications are stable with obvious surfacelayer thermal inversion during the consecutive haze events in autumn and winter. In contrast, inversion layers are higher in spring than in autumn and the summer stratification is unstable without obvious inversion. Shallow upward motion exists at low level， and downdraft at the upper level in winter and summer while it is downdraft in most cases during the spring and autumn nights.

Abstract:Surface observation, CMA PM2.5 concentration, Lband sounding second data and other information are used to analyze surface wind characteristics and mass concentration of PM2.5 on fog，haze and clear days in Beijing, Shijiazhuang and Taiyuan from January to February 2013. Typical foghaze processes are selected to analyze vertical structure of boundary layer and inversion layer characteristics, which are also compared with those of clear days. Dynamical and thermal differences in boundary layer are summarized according to different intensities in foghaze processes. Analysis result shows that inversion intensity has a negative correlation with visibility, which has some indicating importance in fog and haze predictions.

Abstract:In meteorological observation services, artificial methods are usually used to determine the occurrence of dew and frost phenomena. Manual observation has strong subjectivity, fewer observing times and low efficiency and it can not fully and continuously reflect the characteristics of dew and frost process. This article describes a dew and frost automatic observation device. The device works by detecting changes in capacitance of capacitive sensors in high humidity and low humidity conditions and measuring frequency changes caused by the change in capacitance. Then the recognition software is used to judge occurrence of dew phenomenon and frost phenomenon combined with freezing temperature information and icing information in order to achieve the dew and frost automatic observation. Through a lot of dew and frost comparative tests, we found the automatic observation device can accurately identify the occurrence of dew and frost process and the device can be extended to the practical use.

Abstract:Using the 2010-2014 FY2 and FY3 meteorological satellite data and radar data, conventional observations and numerical forecasting products as well as multithreshold method, and area overlap method, the cloud identification tracking method for Hubei rainstorm is studied. Besides shortterm forecasting method for Hubei 6 h rainstorm is studied by using batching method. Wuhan Central Meteorological Observatory has established a torrential rain monitoring and forecasting system in the form of web page. Forecasters can quantitatively monitor and forecast the occurrence and development of torrential rains by the system. The application and test in 2014 results show that this system plays a guide role in monitoring and forecasting torrential rains in Hubei Province.

Abstract:This paper analyzes the key technique of product generation of regional meteorological decision service in meteorological emergency operations. First, interpolation method of smallvalue automatic station is discussed, and then zerovalue automatic weather station interpolation method is proposed. Verification shows that this method can effectively improve the accuracy of precipitation interpolation. Second, model construction technique based on ArcGIS ModelBuilder is proposed. Components of hourly accumulated precipitation, interpolation of meteorological observation data, generation of graphic products are developed by ArcObjects. Combined with spatial analysis components provided by ArcGIS, an hourly accumulated precipitation process and graphic generation model are constructed. Finally, highefficiency and highprecision graphics are generated automatically.

Abstract:The following are the main characteristics of the general circulation of atmosphere in June 2015. There are two polar vortex centers in the Northern Hemisphere, which is a little bit stronger than normal years. The strength of subtropical high is close to climatological normal. The monthly mean temperature over China is 20.3℃, 0.3℃ higher than the corresponding period of normal years. The monthly mean temperature in southern (northern) China is mainly higher (lower) than the same period of normal years. The mean precipitation (104.8 mm) is 5.5% more than normal (99.3 mm). Eight rainfall processes appear in June 2015. Severe precipitation events happen in Yangtze River and Huaihe river and the northern part of South Yangtze River Region and many showery rains occur in Northeast China. Drought gets mitigated in Hainan, but strengthened in western Yunnan Province. High temperature events are observed at 64 stations. Gale and hail disasters hit 21 provinces this month. No.8 Typhoon, lands in Guangdong, which is the first landing typhoon in China this year.