Abstract:Diabatic heating is closely related to the occurrence and development of weather system and is closely related to weather processes such as precipitation. Diabatic heating plays an important role in atmospheric motion and has drawn more and more attention in recent years. Study and understanding of diabatic heating can help improve numerical weather forecasting model and enhance the forecasting ability of numerical weather forecasting model. This paper systematically analyzes the basic contents of diabatic heating and the research results of diabatic heating in recent decades, mainly including concept and characterization of diabatic heating, spatiotemporal distribution characteristics of diabatic heating, relationship between diabatic heating and monsoon, relationship between diabatic heating and weather systems such as subtropical high over western Pacific, tropical cyclone, temperate cyclone and jet streams, and relationship between diabatic heating and precipitation as well as the characterization of diabatic heating in the numerical model, etc. Then, we point out that diabatic heating should be further studied.

Abstract:To investigate the application effect of stochastic kinetic energy backscatter (SKEB) perturbation scheme, a regional ensemble forecast system (REFS) is constructed based on the WRF model. Sensitivity experiments on perturbation amplitude are conducted to find the functional characteristic of SKEB. Additionally, a synthetic model perturbation scheme which combines multiphysics (namely MPHY) and SKEB, called SKEBMPHY, is developed, and the forecast effects of the three schemes of SKEB, MPHY and SKEBMPHY are compared and evaluated. The results show that the SKEB scheme can estimate the stream function and temperature perturbation through a constant kinetic dissipation rate, and the exhibited difference of model integration is correlated to the amplitude of the kinetic dissipation rate. Perturbing the vertica1 structure is not helpful to the difference growth. The comparison results of SKEB, MPHY and SKEBMPHY schemes indicate that the SKEB has advantage on upperair wind spread growth compared to MPHY while MPHY has larger spread for lowlevel temperature than SKEB. The SKEBMPHY scheme exhibits the best perturbation growth characteristic of the three schemes not only for upperair variables but also for lowlevel variables. In addition, the SKEBMPHY scheme has the most skillful performance of the three schemes in terms of ensemble verifications. Furthermore, compared with single MPHY scheme, applying the SKEB scheme will improve precipitation forecast skill of heavy rain. All the results from this study indicate that the SKEB scheme and the SKEBbased synthetic scheme are promising.

Abstract:Track forecasting is the greatest progress over past decades in numerical weather prediction (NWP) regarding the tropical cyclones (TCs). But the landfalling TC precipitation prediction capability of NWP models is still very limited. Focusing on combining dynamical and statistical methods, a new method named tracksimilaritybased Landfalling Tropical cyclone Precipitation (LTP) DynamicalStatistical Ensemble Forecast (LTP_DSEF) model has been developed. The LTP_DSEF model includes five steps: TC track prediction, identification of analogue TC tracks, identification of other analogue TC characteristics, ensemble forecasting of TC precipitation, and the best scheme selection. There are two key technologies involved: the Objective Synoptic Analysis Technique (OSAT) for partitioning TC precipitation and the objective TC Track Similarity Area Index (TSAI). The application of LTP_DSEF model for 21 TCs with accumulated LTP ≥100 mm in South China during 2012-2016 reveals that the new method shows a better performance than the three NWP models (EC, GFS and T639) in predicting LTP. For ≥50 mm LTP forecasts, the threat score (TS) of LTP_DSEF models results are superior to those of the three NWP models. Analysis of the values of the LTP_DSEF models parameters for three best schemes shows that, the initial time designed to be the closest to the impact time, i.e., 1200 UTC on the previous day with precipitation on land and the ensemble parameter being the maximum are both beneficial to ideal forecasts.

Abstract:Conventional observation data, quantitative precipitation forecast (QPF) data of numerical weather prediction (NWP) models and NMC forecasters, and NCEP FNL analysis data are employed to verify the QPF and study the causes and forecast focus of the scattered rainstorm of Typhoon Soudelor on Day 2 after landing. On Day 2, rainstorm of Typhoon Soudelor was relatively scarred. QPF of NWP models all had obvious errors. Although 24 h QPF produced by NMC got many good corrections compared with numerical models, it still showed false heavy rainfall alarm or missed rainstorm in detail. Because of the forecasted location of rainstorm was more southerly than observation, there exited false alarm on the south side and missed rainstorm on the north side of the heavy rainfall. Impacted by environmental conditions and asymmetric structure of the typhoon, the favorable dynamical and water vapor conditions distributed in the north side of the typhoon and the eastern coastal areas. There were two strong convergence belts in lowlevel troposphere in northeast quadrant of typhoon. Between the two convergent belts, weak lowlevel divergence and downward motion were seen leading to much weaker rainfall in this area. Forecasters underestimated the asymmetry of typhoon structure and the inhomogeneity of wind field. So, for the weak rainfall area around the typhoon center and between two convergence belts, they obviously overestimated. Induced by topographic effect, heavy rainfall emerged continuously in Zhejiang coastal areas. And then the rainstrom evolved into a spiral rainband along tangential direction and extended northward. Forecasters omitted the tangential evolution and outward transportation of spiral rainband forced by terrain continuously, which resulted in the missing of rainstorm in the north of Zhejiang. The forecast key points of the Day 2 scattered rainstorm included typhoon’s asymmetric structure, nonhomogeneous distribution of wind, evolution of spiral rainband and terrain effect, etc. Largerscale heavy rainfall distributions were decided by the asymmetric structure of typhoon, while for refined locations of rainstorm, the evolution of spiral rainband influenced by nonhomogeneous lowlevel convergence and location of lowlevel jet was very important. Thus, terrain can not only amplify rainfall in local areas, but also have effects on downstream heavy rainfall.

Abstract:By using conventional meteorological data, satellite data, radar data and NCEP reanalysis data, the instability formation process of a torrential rainfall from Taiyuan to Shijiazhuang on 9 July 2013 is studied. The results show that the torrential rainfall near Taiyuan occurred after light stratiform precipitation existed for six hours. The convective precipitation with weak thunder and lightning was embedded in the stratiform and it was located behind the cold front, more than 120 km away from surface front. Such cold sector torrential rainfall is easy to be missed. From 08:00 BT to 14:00 BT, depth of planetary boundary layer (PBL) cold air was continuously deepening, the dry and cold air mass with low pseudoequivalent potential temperature extended from northeast to southwest, and the unstable atmosphere was situated over the stable boundary layer, so the torrential rain was caused by elevated convection. The northeast wind at 850 hPa and the southwest wind at 500 hPa were strengthened at the same time, baroclinicity of frontal zone got stronger, the atmospheric stratification was transformed from absolute stability, which was almost neutral, to potential instability by the dry advection in 400-500 hPa and was moistened at lower level by frontal lifting. The potential unstable layer changed to conditional unstable layer by the frontal lifting of warm and humid air layer. In the afternoon, the atmosphere was absolutely stable near Shijiazhuang.

Abstract:Based on the high spatiotemporal resolution data of automatic weather stations,Doppler weather radar and wind profiler radar, we analyzed the development of the mesoscale convective systems during the heavy rainfall in Tianjin on 6 July 2017, and discussed the structural characteristics of easterly flow from the Bohai Sea and its influence on the local heavy rainfall. The results are as follows: The local heavy rainfall was caused by two warmzone mesoscale convective systems and a vortex shear line system. Among them, the second mesoscale convective system in warm area dominated the formation of local heavy rainfall, and it was closely related to the easterly flow in the boundary layer. The easterly flow during this heavy rainfall had warm and wet characteristics, which was conductive to the occurrence and development of heavy rainstorms. At the same time, the wind speed from the Bohai Sea to the inland showed obviously disturbance, leading to the convergence of water vapor in the boundary layer and the development of the ascending movement. Furthermore, the mesoscale disturbance of easterly flow below 0.6 km played an important role in the triggering and maintaining mechanism of the heavy rainfall. Under the convergence system caused by the wind speed disturbance, the updraft flow was forced, triggering the occurrence of the mesoγscale convection. On the other hand, the outflow of cold pool caused by the heavy rainfall and the increasing easterly inflow interacted each other and formed the convergence, and the mesoscale convective system was maintained stably, resulting in the strong precipitation echo above 40 dBz lasting nearly 3 h, with an average precipitation of 6.8 mm per 6 min. In addition, the change of rain intensity was closely related to the fluctuation of the easterly jet in the boundary layer. The establishment, development, weakening and disappearance of the jet corresponded to the four phases of steep increasing, peak, weakening and steep dropping of precipitation.

Abstract:Based on the assimilation of radar radial wind, radar retrieval wind and GPS water vapor data with the ensemble Kalman filtering (EnKF) method, the initial water vapor field of a squall line that occurred on 30 July 2014 in eastcentral Anhui was adjusted according to radar reflectivity data. Compared with the simulation results of EnKF, this method has improved the simulation of intensity, location, duration, precipitation and surface wind of the squall line. Simulation performance of ground convergence zone in the front of the squall line was improved after adjusting humidity field, leading to better simulation results of the intensity and location of the squall line. In addition, the squall line maintained for a shorter time without humidity adjustment and the intensity was weak. This can be explained by the fact that midlevel dry air entrainment was weak in the rear of the squall line, and the cold pool moved quickly away from the squall line, which was unfavorable for the maintenance of squall line. In contrast, after the humidity field was adjusted, dry air entrainment in the rear of the squall line was strong, and the resultant downdraft generated the cold pool, which was located in the rear of the squall line, favorable for the maintenance of squall line. The possible reason for dry air entrainment strengthening tends to be that atmospheric instability was increased with the moisturizing of midlow level (600-900 hPa) after the humidity field adjustment, and the development of convection results in the enhancement of lowvalue system. The westerly in the south of lowvalue system intensifies, strengthening the dry cold air entrainment in the rear of the squall line. This experiment reveals that the adjustment of the humidity leads to the adjustment of the dynamic field, which plays an important role in the development and organization of the convection system.

Abstract:Wind energy is originated from the movement of the atmosphere with great randomness and intermittency. Wind speed forecasting is the basis of wind power forecasting in wind power plant, and its accuracy is of great significance. For complex terrain conditions, wind speed forecasting has been the difficulty and focus of research in all countries. In order to improve the accuracy of shortterm wind speed forecasting of wind power plant, this paper uses different boundary layer parameterization schemes to forecast wind speed. The wind speed of each single boundary layer parameterization scheme prediction and the corresponding measured wind data are used to establish the forecast model by random forest algorithm to study the shortterm wind speed in wind power plant. The experimental results show that with the integrated forecasting method of wind speed, the wind speed prediction error is significantly smaller compared to the single boundary layer parameterization scheme. Also, it has a good simulation effect for wind speed and wind direction and other meteorological elements in the study area and can effectively improve the accuracy of wind speed forecasting.

Abstract:Based on meteorological data and JRA55 reanalysis data, the dominant interannual patterns of summer precipitation over Shandong Province and their circulation characteristics were investigated by using the EOF, correlation analysis and composite analysis methods. The results indicate that the spatial distributions of interannual summer precipitation over Shandong Province can be classified into ‘consistent distribution’, ‘northwestsoutheast seesaw distribution’ and ‘northeastsouthwest seesaw distribution’ modes. In the consistent more (less) precipitation year, there is a dipole anomaly pattern with high (low) pressure over the Sea of Japan and low (high) pressure over Mongolia Plateau; a meridional wavetrain resembles EAP teleconnection pattern is distributed as ‘-+-’ (‘+-+’) over East Asia; the Arabian Sea, the Bay of Bengal and the Philippine regions are characterized by anomalous low level anticyclones. In the years of more precipitation over northwest (southeast) and less precipitation over southeast (northwest) of Shandong, the activities of Ural blocking high and Okhotsk blocking high are enhanced (suppressed) and a wavetrain which is analogous to ‘Silk Road’ teleconnection pattern propagating eastward along the upper westerly jet stream. In the years of more precipitation over northeast (southwest) and less precipitation over southwest (northeast) of Shandong, a northeastsouthwest wavetrain is distributed as ‘-+-’ (‘+-+’) over western and central Eurasia and the tropical zone is characterized by anomalous east (west) wind. In addition, the ‘consistent distribution’ mode is mainly influenced by the latitude position of West Pacific subtropical high (WPSH) ridge while the ‘northwestsoutheast seesaw distribution’ mode is largely affected by the westward extending and eastward retreating of WPSH. As for the upper westerly jet stream, a dipole anomaly pattern is located in the south and north sides of jet axis over Shandong and its vicinal region in all of the three modes with position differences of the anomalous centers. These results would be helpful in further understanding anomalous summer precipitation and its atmospheric circulation to improve the predictability of summer precipitation over Shandong Province.

Abstract:In this paper, the method of QPE based on ZH and KDP[R（C ) ] method is improved, and Φ DP of Guangzhou Sband dual polarization radar during two squall lines and two typhoons in 2016 is filtered by wavelet analysis, and then KDP is estimated by Φ DP in 1.5-4.5 km resolution. The rainfall of the squall lines and typhoons is estimated by R（C） and R（ZH） methods, and the estimated result is compared with the hourly rainfall gauge. In addition, the evaluating results of R(C) and R（ZH） methods are compared to each other. The results show that （1） for squall lines, R（C） is better than R（Z H） when the rainfall rate is higher than 5 mm·h-1. The higher the rainfall rate is, the more obvious the advantage of R(C) will be. When the rainfall rate is higher than 20 mm·h-1, the average RE decreases by 17.2%, the average AE decreases by 1.89 mm, and the average RMSE decreases by 1.66 mm. (2) For typhoons, R(C) is better 〖JP2〗than R（ZH） when the rainfall rate is higher than 5 mm·h-1. When the rainfall rate is higher than 20 mm·h-1,〖JP〗 the average RE of R（C） is 33.1% lower than that of R（Z H）, the average AE is reduced by 3.95 mm, and the average RMSE is reduced by 4.05 mm. In general, R(C) could solve the underestimate problem existing in R（ZH） method. However, R(C) could also underestimate the precipitation when the rainfall rate is higher than 10 mm·h-1. The possible reason is the small value of the coefficient fitted by the raindrop spectrum data because of the observation error or the observation error caused by the radar hardware.

Abstract:The anomalous climate features in China during the summer (JJA) of 2018, corresponding atmospheric circulation anomalies in East Asia and possible impacts from the ocean are analyzed in this paper. The results show that in the summer (JJA) of 2018, the average precipitation in China is 9.6% more than average. The precipitation in North and South China is more than normal while the precipitation in the middle and lower reaches of Yangtze River Valley is less than average. The atmospheric circulation in summer exhibits a typical feature of strong East Asian summer monsoon. The East Asian subtropical jet and the Northwest Pacific subtropical high are both significantly more northward located than average. In the lower troposphere, a cyclonic circulation dominates the area near the Philippines. At the same time, the midhigh latitude atmospheric circulation over Eurasia mainly exhibits a zonal feature. Under the combined impacts of the subtropical and midhigh latitude circulation, the transportation of water vapor to North and Northwest China is strengthened and more precipitation is induced in these regions. The precipitation in South China is also increased because of the strengthened tropical convective activity near South China Sea. However, in the middle and lower reaches of Yangtze River Valley, anomalous divergence and subsidence is observed and less precipitation is caused. In addition, it is also revealed that the La Nina event from October 2017 to April 2018 exerted a significant impact on the East Asian summer monsoon circulation and the summer precipitation in China.

Abstract:The main characteristics of the general atmospheric circulation in October 2018 are as follows. Over the Northern Hemisphere, the polar vortex showed a dipole pattern. The circulation presented a fourwave pattern in middlehigh latitudes. The western Pacific subtropical high extented remarkably more westward than normal. The monthly mean precipitation amount was 28.1 mm, which is 21.6% less than normal (35.8 mm). The monthly mean temperature was 9.9℃, 0.4℃ lower than normal (10.3℃), ranking the lowest since 2002. There was no largerange heavy rainfall processes over China. There were five cold air processes, more than usual, and two fog and haze events in the region of BeijingTianjinHebei, which were also weaker than usual. There was no landfall typhoon in October 2018.