Abstract:Convectiveallowing ensemble forecasting experiments were applied for an extreme precipitation event in North China in 18-20 July 2016. Uniform initial condition and boundary condition were used for ensemble simulations with 13 members based on varied WRFARW microphysics at 4 km horizontal resolution. The intensity and spatiotemporal distribution of simulated precipitation were similar to precipitation observation, and significant uncertainties were proved to be among ensemble members. Accuracy of rainfall simulation was improved compared with global numerical model, and members with Morrison scheme and WSM6_P2 scheme achieved better results verified by methods of neighborhood ETS, correlation, and RMSE. Rainfall’s probability density function showed that bias of excessive rainfall dominates below 50 mm rainfall prediction, and deficient bias of precipitation dominates above 100 mm. Significant spread was found in the intensity of upperlevel jet and path of surface cyclone in the ensemble simulation experiments. Correlation analysis between precipitation and diagnosed variables including precipitable water, lowlevel relative vorticity and vertical motion proved that ensemble members could be divided into severe precipitation and weak precipitation. The subdivision with severe precipitation features severe convective echoes, strong subsidence, intense cool pool, and significant positive potential vorticity anomaly in midlower level due to latent heating which takes effect on subsequent evolution of weather system. Warm cloud process plays an important role in weak precipitation with relatively weak radar echoes, weak cool pool which is much more close to the steady stratiform precipitation process in fact. Radar reflectivity simulated by several kinds of 2moment microphysics schemes is characterized by “bright belt” echoes around 0℃ level, and separation between convection and stratiform cloud is more realistic compared with simulation results of 1moment microphysics schemes. With different settings of several key parameters in the WSM6 scheme, two types of precipitation processes were identified as severe convective storm and intense warm cloud precipitation, so uncertainties in the convectivescale physical process could be estimated for specific synoptic event which indicates the superiority of ensemble forecasting based on varied microphysics.

Abstract:An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in midhigh latitude. The abnormal development of Huanghuai cyclone, southwest and southeast lowlevel jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly lowlevel jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at midlevel and the strong warm and wet advection at lowlevel jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cutoff vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the longlasting rainfall process.

Abstract:Radar echo characteristics of the vortexshaped mesoscale convective system (MCS) that produced heavy rain in Jianghan Plain of Hubei Province on 18 June 2011 and the possible causes of MCS structure are analyzed by using Doppler radar data, conventional observations and dense surface observations and the radar 4DVar wind retrieval data. The results show that: (1) Heavyrainproducing vortexshaped MCS echoes in mature stage showed multiple spiral convective echo belts with cyclonic curvature, surrounded by stratiform cloud echoes and evolving into the cold and warm frontal structure as a result of invasion of cold air. Echo merger and vorticity train effect are the main characteristics of motion in producing severe precipitation. (2) The vortexshaped MCS which was in favorable environment was the result of severe development of boundary layer mesoscale vortex system in the transition zone of western Hubei mountain and Jianghan Plain. (3) The formation of the mesoscale vortex system was closely related to the development of the surface reverted warm trough, rainfall in the front of the southwest vortex and special terrain. Strong convergence of airflows from different directions was the main mechanism of the development in its earlier stage. The late development might be related to latent heat release, for the vortex circulation developed upward to 700 hPa.

Abstract:The new improved retrieval data of cloud water, rain water and ice water detected by the TRMM (Tropical Rainfall Measuring) satellite TMI (TRMM Microwave Imager) are applied to quantitatively verify the performance of six microphysical schemes of WRF (Weather Research and Forecasting) model for hydrometeors over Jiangsu offshore and surrounding areas. The statistical verification results of 19 cases show that the six schemes can predict the magnitude and approximate range of the hydrometeors. For cloud water content forecasting there is a large deviation in NSSL 2mom scheme but little deviation in other schemes. CAM5.1 scheme has a better performance in forecasting rain water when the content is larger, but worse performance when the content is small. Lin scheme is better in forecasting ice water than other schemes compared to the observation. On the basis of quantitative verification, the ensemble forecasting experiments are carried out by the two methods of ensemble mean (EMN) and the biasremoved ensemble mean (BREM). The results show that both methods can reduce the error of prediction, and the BREM is better than the EMN.

Abstract:Based on the synoptic environment analysis of 15 thunderstorm cases in the area of Dongting Lake from 2013 to 2015, the weather situation can be divided into the following categories: lowlevel warm advection forcing category, baroclinic frontogenesis category, quasibarotropic category and upper cold advection forcing category. According to the strength of cold advection in the north of lowlevel shear line, the lowlevel warm advection forcing category can also be classified into strong cold and warm advection forcing, strong warm advection forcing and middle category. Summarizing the synoptic situation configuration characteristics of thunderstorms in different stages, the radar echo characteristics and the forecast focus could offer references for shortrange, shorttime and nowcasting weather forecasts.

Abstract:A technique for estimating tropical cyclone (TC) intensity over the Western North Pacific utilizing FY3C Microwave Temperature Sounding (MWTSII) data was developed. First, the limbadjustment was conducted to correct the data of Channels 5-8 to the values they would have in a vertical view, and the corrected deviations were all smaller than the instrument sensitivity. Then the radiance anomaly (core value minus an average environmental value) was used to analyze the characteristics of the TC warm core, and the magnitude and shape feature of the warm core were found related to the TC intensity. As TC intensity gets stronger, the magnitude increases and the shape feature gets clearer and more complete. Finally, an estimation model was estabished using the maximun radiance anomaly of Channel 6 and Channel 7. The standard deviation was 13.0 hPa. After the correction of the bias resulted from the unevenly distribution of MWTSII footprints, the standard deviation was reduced to 12.0 hPa, and, then further reduced to 11.1 hPa after the latitude was taken into account.

Abstract:Digital gridded weather forecast is the developing trend of weather forecasting operation in China. Based on NWP model products, meteorological observation data and an evaluation on subjective and objective forecast, a diurnal extreme temperature Multimodel Consensus Gridded Forecast (McGF) system was developed. Statistical results show that there are significant seasonal forecast error differences in both subjective and objective forecasts, and forecasters have more forecasting skills in summer, when the NWP systemaitc errors are more stable. NWP model shows a flow dependent (conditional bias) characteristic. When the temperature is higher (lower), the nagative (positive) forecast error is bigger. Both subjective and objective forecasts are affected by topography and there are relatively significant forecast errors in the northern mountainous areas. As the lead time of forecast extends, the growth of forecast errors is, not big and the subjective forecasting skills are stable relatively. Based on these results, McGF interpretation application system was devloped with four modules, including realtime verification, stationbased interpretation, gridded application and performanceweighted averages. The results showed that Tmax forecasts of McGF are better than subjective and objective forecasts, with its mean absolute errors less than 2℃ within 72 h. Relatively speaking, Tmin forecast errors are much lower and the enhancements of McGF are relatively small. The cases of extreme high/low temperature showed that McGF gridded forecasts in Guangdong Province can more reasonably reflect the spatial distribution and intensity feature.

Abstract:The purpose of this study is to investigate boundary layer heights calculated by Richardson number method, inversion method and potential temperature gradient method, and compare them with Nozaki’s method based on Lband radar sounding data in Beijing in November and December 2014. The similarities and differences of the boundary layer results calculated by the four methods during the two heavy pollution periods in 27 November to 1 December and 15-20 December 2014 are analyzed in details by using vertical profiles of meteorological elements and PM2.5 data in the same periods. The results show that the boundary layer heights calculated by Richardson number method, inversion method and potential temperature gradient method are 653 m, 1152 m and 1296 m in Beijing in November and December 2014 respectively, and the calculated boundary layer heights are negatively correlated with PM2.5 concentration in some degrees. The statistical probability results show that distribution of boundary layer heights below 500 m has the biggest probability, but there are some differences in other height ranges. Through the two typical heavy pollution periods, we found that different methods have applicability and limitation. Therefore, it is necessary to combine the vertical profiles of meteorological factors and pollutant concentrations with subjective judgment, which would help to determine the height of boundary layer.

Abstract:In this paper, a quality control system was established based on the AMDAR quality control method from NCEP. Using oneyear AMDAR dataset, the system was tested and the characteristics of each AMDAR data quality type were examined. The main conclusions are as follows. (1) The hourly rejection rate of AMDAR data through year 2014 is 5.79%, and most of the rejections occur in near duplicate check. (2) There is a significant diurnal variation feature for both quantity and quality of AMDAR data. Duplicate reports increase with the growth of data quantity, while suspicious and disorderly reports decrease with the growth of data quantity. (3) The characteristics of the data quality are different in different height layers. Quality problems mainly occur in the nearsurface layer, and the heights where the power or the phase of aircraft are adjusted. (4) The result of near duplicate check is highly sensitive to the threshold of lat/lon, which mainly occurs in the upper layers, and the impact of height threshold happens in the lower layers. (5) The averaged global temperature after data quality control is higher than original reports at each height, while the averaged wind speed becomes lower than the original.

Abstract:In the present study, the WRF model with the incorporation of a Single Layer Urban Canopy Model is used to investigate the cooling effect of roof greening in Nanjing. Sensitivity tests of albedo, heat capacity, thermal conductivity and humidity are conducted for the time period from 28 to 29 July 2013. The simulation results show that: (1) the albedo of roofs is reduced to approximately 0.15 after greening, which is smaller than the albedo values of the roofs built with cement or other reflective materials. This result may lead to the increase of city temperature by 0.2℃ in daytime. (2) The heat capacity of roofs increases significantly after greening, leading to the decline of temperature by 0.33℃ in daytime while the temperature at night increases by about 0.21℃. (3) Due to the existence of vegetation and soil layer, the thermal conductivity of roofs is weakened. As a result, the net radiation on roofs is more easily converted to sensible heat rather than being transferred downwards, warming the overlying ambient air. (4) The change of soil humidity enhances the release of latent heat from the net radiation on roofs. Therefore, temperatures in daytime and nighttime are reduced by about 1.23℃ and 0.44℃, respectively. In addition, the statistical analysis of the simulation results for different seasons shows that the reduction of temperature by roof greening is the strongest in summer, which can reach 1.22℃. In comparison, the temperature decreases by about 0.96℃ in spring, 0.75℃ in autumn and only 0.38℃ in winter.

Abstract:Based on the daily sensible temperature in Huangshi City, Hubei Province from 2007 to 2013, the trend of electric load rate and its response to the meteorology factors were discussed. The results showed that the sensible temperature and the human comfort index have good applicability in analyzing the impact of weather factors on the electric load rate, and the sensible temperature is shown to be the highest correlation factor. As to the power load rate, it has a linear growth from 2007 to 2013 but decreases during the financial crisis. What’s more, the meteorological load rate in working days was higher before 2011. Since then, the phenomenon has appeared to reverse, and the difference has increased. Finally, it is found that the sensible temperature higher than 22.9℃ (weekdays) or 21.5℃ (holidays) would produce the sensitive load, while 1℃ increase of sensible temperature could bring up to 6% additional meteorological load rate.

Abstract:The performance of mediumrange forecast is verified and compared for the models of T639, ECMWF and Japan from December 2016 to February 2017. The results show that all of the three models can predict the variation and adjustment of the atmospheric circulation over Asian middle and high latitude areas well, of which ECMWF model performs the best. The three models perform well in predicting the transitions of temperature at 850 hPa, as they all have smaller biases for southern China than for northern China. Temperature forecasts for northern China, produced by T639 model are lower while temperatures forecasted by Japan model for southern China are higher, and ECMWF model performs better than the other two models in general. For the surface high pressure forecasting during the nationwide cold wave process in February 2017, T639 model performs better in forecasting the intensity of cold high pressure than ECMWF and Japan models. ECMWF model does well in forecasting the location of high center, while T639 and Japan models produce obvious bias.

Abstract:The main characteristics of the general atmospheric circulation in February 2017 are as follows. There was one polar vortex center in the Northern Hemisphere and stronger than usual. The circulation in Eurasian middlehigh latitudes showed a threewave pattern. The strength of western Pacific subtropical high was near climatological normal. The south branch trough was a little weaker than normal years. The monthly mean temperature was 0℃, which is 1.7℃ higher than normal, while the monthly mean precipitation amount was 14.4 mm, which is 17.1% less than normal. Two waves of strong cold air processes and three rainfall processes occurred during this month. Because of the second wave of strong cold air process, a snowstorm event was seen in Xinjiang, with the daily precipitation breaking the historical extremum. Meanwhile, two foghaze weather events appeared in the central and eastern part of China.