Abstract:Four cumulus convection parameterization schemes, i.e., the KainFritsch (KF), BettsMillerJanjic (BMJ), GrellDevenyi (GD) and Simplified ArakawaSchubert (SAS) schemes in the weather research and forecasting modeling system (WRF V3.5.1 version) are respectively used to simulate the severe torrential rain event in Beijing during 21-22 July 2012, particularly focusing on spatiotemporal features of convection bursts, and the impact factors of precipitation forecast. The results show that the simulated rainfall location and intensity by the KF scheme agree well with the observation while the BMJ scheme exaggerates the scope and intensity of the severe rainfall. The GD and SAS schemes have poor simulation results. The initial burst states and evoluting process of convection in the four schemes are quite different, and the forecast time is also different. Generally speaking, KF scheme performs better in simulating convection burst and it can simulate a strong upward motion and abundant moisture during the severe torrential rain period. Meanwhile, the rainfall rates in the simulated deep convection area are relatively high with KF and BMJ schemes. However, the simulated precipitation by SAS scheme is dominated by the stratus cloud area and it is unable to work out the center of the severe rainfall.

Abstract:Based on the surface dense automatic station data, Doppler radar data and NCEP/NCAR reanalysis data, the strong convective weather occurring over Jiangsu and Anhui Provinces on April 28, 2015 under the background of cold vortex was analyzed. Moreover, the structure characteristics, formation and maintenance mechanism of the supercell storm with long life cycle, which led to the regional hail in this weather process, were also significantly studied. The results showed that the formation of the northerly jet at the back of cold vortex and cold advection which was carried to the south promoted the development of conditional unstable stratification and deep vertical wind shear, providing a favorable environment for the occurrence of severe convective weather. Surface mesoscale depression and the accompanied convergence line were one kind of the triggering mechanisms. Supercell storm with long life cycle occurred in the middle troposphere and had highly organized dynamic structure at its mature stage. The storm had the significant rotation characteristics, especially in middle layer. The middle and low layer of the storm corresponded with deep convergence zone, while the top of the storm presented obvious divergence feature. Such veritical distribution of divergence field enhanced the intensity of rising flow within the storm and the warm, humid flow in the low level of the storm, making the abundant water vapor in low level transported into the storm, so the convective storm increased vertically and developed intensively. The top height of the storm and the centroid height showed features of wave motion before and after the hail occurring. The hail happened at the rapid descending stage of the above two heights, and the centroid height had more obvious descending trend. The maintenance of supercell storm was related to the constant southerly cold advection in the middle troposphere, the strong vertical wind shear and rotation feature inside the storm.

Abstract:Based on the conventional observations, AWS, NCEP/NCAR (1°×1°, by 6 h) reanalysis and FY2C satellite data, this paper investigated the dynamic and thermal field structure characteristics throughout the three interaction stages between westerly trough and subtropical high (SH) in the rainstorm which occurred in Shandong from 15 to 18 August 2007. The results indicated that there are three stages sequentially throughout the whole process. Firstly, SH advanced westward accompanied with the shear line shifting westward at a snail’s pace; secondly, the transversal trough moved southward with the SH weakening; thirdly, the trough transformed from transversal into upright with SH southward retreating. The three stages share some features in common: There was a shear line and a θse frontal zone in the mid and low levels, and a low level jet (LLJ) at 700 hPa. Besides, the convective cloud cluster had the feature of backpropagating, causing the rainstorm to merge several times in its life. The difference of the three stages lies in that: (1) In the first stage, the slope of θse frontal zone was gentle and north tilted with shear line and frontal zone backward tilted, so it was typical warm front precipitation. With the saturation region extending broad and upward to 300 hPa, the rainstorm area got extensive and uniform distributed, wavering around the water vapor convergence center in the junction of θse frontal zone and the warm ridge at 850 hPa. So, the low cyclonic convergence, shear line convergence and frontal uplift are the dynamic mechanism of the rainstorm, while the LLJ is the enhancement mechanism. (2) In the second stage, the θse frontal zone was sharpsloped and intersectedgradient by leaning northward and southward in turn with height, and the colddry air invaded into the warm ridge from the low and mid layers respectively, thus creating typical severe convection precipitation and furious upward movement. Also, with the saturation region extending upward to 200 hPa and getting narrow, the distribution of the rainstorm area became nonuniform, the intensity was high and range got small, located around the θse warm ridge vertical axis. Hence, the main dynamic mechanism of the Xintai strong convection precipitation is frontal uplift, and the enhancement mechanism is the invasion of colddry air in the middle troposphere. (3) In the third stage, the θse frontal zone was sharpsloped and south tilted, having a forerake characteristics, which resulted in the typical upper trough precipitation. With the saturation region extending narrow and upward to 500 hPa, the rainstorm area became long, narrow, dispersive and in a low intensity, located at the 850 hPa shear line which also was an position near the frontal zone in the θse warm tongue. Thus, dynamic mechanism of the rainstorm is the shear line convergence, and the enhancement mechanism is the invasion of dry air in the middle troposphere.

Abstract:During 14:00-15:00 Beijing Time (BT) 23 June 2016, an extremely tornado with the EF4 scale hit the Funing County of Jiangsu Province, causing severe damages. Due to the topographic effect, 11 tornado events were recorded causing more than 10 deaths in nearby region in the past 50 years, and 6 occurred after 1979. By decomposing model initial variables and model predicted outputs into temporal climatic state and anomaly, this paper first analyzed the 6 tornado events using observation data, finding that these tornadoes were associated with lowlevel negative anomalous height trough axes and clashes of anomalous cold and warm air masses. Tornadoes always occur in the anomalous warm air mass. In the second half of the paper, the performances of ECMWF model and NCEP GFS on the tornado process on 23 June 2016 were evaluated using anomalous variables and indices. Analysis results at 14:00 BT illustrated that the tornado occurred at the intersection between a 925 hPa height anomaly trough and a maximum axis of moist vorticity anomaly and moist convergence anomaly at 850 hPa, respectively. The lowlevel moisture convergence and moist vorticity anomalies could well indicate the moisture and unstable condition for tornadogenesis. The ECMWF model well predicted the troughaxis feature for leading 42 h in advance while the NCEP GFS predicted for leading 18 h in advance, respectively. These anomalous variables and indices could help forecasters indicate a potential timespace domain of severe convective systems more quickly.

Abstract:The spatiotemporal distribution of shorttime heavy rainfall in Huangshan Mountain region was analyzed statistically by using the observations from 191 ground automatic observation stations in Huangshan Mountain region. Statistics revealed that the frequency of shorttime severe rainfall process increases significantly from afternoon to evening (14:00-18:00) period; shorttime severe rainfall occurs most often in Huangshan Mountain and the nearby area; the distribution of shortterm heavy rainfall frequency is highly correlated with mountain shape and terrain. Using three typical cases, the function of the enhancement of mountain terrain dynamic blocking and thermodynamics in shorttime severe rainfall is analyzed. The findings are concluded as follows: (1) The rainfall increases due to the lifting rate of mountain terrain on the windward slope, and the rainfall coulds reach 60% according to the diagnosis by the water vapor budget method. (2) When the frontal surface passes the mountain area, its vertical disturbance enhances frontogenesis, while in the leeward slope, the surface vortex, and ascending motion are enhanced, resulting in the increase in precipitation. (3) In the southwest region thermal low forms due to the difference of surface latent heat flux, making this area warmer and wetter and the atmospheric instability enhanced. Affected by cold advection, severe convective weather develops, thus increasing the precipitation in the mountain region.

Abstract:In terms of mass water content, field capacity, wilting moisture, and bulk density at 247 agricultural meteorological observing stations during 1981-2010 in China, effective quality control method of these data is applied according to climatic characteristics and soil texture as well as the theory of extreme values and relationship in soil hydrological constants. Analysis and calibration of singular historical observation data of manual soil water are conducted through each station and are presented in this paper taking typical stations as examples. As the base detective conditions, mass water content ranging in 0-50% and varying less than 30% during every two depths, field capacity ranging from 10% to 40% and varying less than 20%, wilting moisture ranging from 1% to 13% and varying less than 10%, bulk density ranging from 0.8 g·cm-3 to 2.0 g·cm-3 and varying less than 0.5 g·cm-3 are considered as credible data. Through typical analysis, errors of soil hydrological constants can be divided into three categories including the error of manual record, reduplicative observation and yearly obvious variation. Similarly, errors of mass water content exceedes proper ranges with minimum value of air dried soil moisture content and maximum one of saturated water content. One effective observation series of manual soil water can be obtained through quality control and applied for better understanding and scientific researches.

Abstract:The melting process in the melting layer gives rise to the enhancement of radar reflectivity, which is known as the ‘bright band’. An automatic identification and correction algorithm of bright band is presented in this paper. This algorithm is developed from the characteristics of stratiform or blended precipitation based on WPR data in Fangshan, Beijing, from August to October 2014. A typical blended precipitation episode from 1 to 2 September 2014 is analyzed by using this algorithm. The identified bright band parameters are compared with sonde and Doppler radar data, which is verified to be reliable. After bright band correction, the high echo intensity areas are restrained, and the obvious curve of the vertical profile of echo intensity near bright band height disappears.

Abstract:The statistic characteristics of 127 PIREPs (pilot reports) including icing type, cloud classification, temperature and supercooled liquid water content are investigated based on the CloudSat data. The results indicate that most of the aircraft icing events happened in the environment with temperature above -20℃, only four appeared below -20℃. Clear ice mainly occurs between -5~0℃, rime ice between -20~-10℃, and mixed ice between -15~-5℃. Most aircraft icing happens in the stratocumulus (Sc), altostratus (As), and nimbostratus (Ns). The supercooled liquid water content and its distribution decrease with decreasing temperature. 2BCWCRO product can identify the supercooled liquid water in the Sc, As and Ns, but it can’t identify the supercooled liquid water in cirriform cloud and convective cloud when temperature is below -20℃.

Abstract:The clear channel scheme presented by McNally and Watts (2003) is used to detect cloud radiances in GRAPES3Dvar system measured by highspectralresolution infrared sounders. This scheme is based on the bias of simulated radiances and actual radiances, and the determination of bias is related to forecast model. Traditionally, we use subjective determination schemes to select threshold in cloud detection, such as image contrast analysis. This paper presents two new and objective schemes based on the subjective scheme. (1) Analysis of view field bias: observe the cloud top pressure under different thresholds to evaluate the rationality by analyzing the vertical distribution of bias between simulated observation and actual observation. (2) Evaluation of cloud detection index: establish a series of cloud evaluation indices to select appropriate thresholds. By combining the three methods mentioned above, we determine the IASI radiances cloud detection. The gradient threshold keeps the same value as that from European Center for it has a weak effect in cloud detection. The bias threshold is determined by a comprehensive analysis method, thus overcoming the visual error of the pure use of image. The results show that bias threshold selects 2.0 K, gradient threshold selects 0.4 K for window channels and 0.02 K for nonwindow channels. Finally, a monthlong experiment shows that the cloud detection bias threshold is effective by comparing the assimilation results.

Abstract:The effect of two rocket precipitation enhancement cases for convective cloud in Jiangxi Province is evaluated using the methods of historical regression analysis and timeseries comparison and analysis for cloud units, which are based on regional rainfall data and radar data, respectively. The results show that the consequences about the effect of the two cases are positive deviations, and both precipitation effects have passed the significance test. The reason for the precipitation enhancement effect difference between the daily precipitation data and hourly rainfall data may be that the gap of the two kinds of data is larger in spatial and temporal distribution, and the selected operation periods of the two kinds of rainfall data are not in the same length. Through comparing physical parameters between the seeded cloud units and the unseeded cloud units, which are similar to those seeded detected by radar before and after the operation, an obvious positive deviation is found. So, the radar detection evidence of precipitation enhancement is provided. The radar detection results are consistent with the regional historical regression results in the two cases. The variation trends of the two cases are consistent and both of the two cases have positive deviations.

Abstract:In 2000, the Automatic Surface Observation System (ASOS) was set up by China Meteorological Administration (CMA), and several surface meteorological parameters started to be automatically measured. Because of the difference between manual and automatic observations, the 2 min wind data from 2195 meteorological observation stations from 2000 to 2010 are compared to analyze the difference between the two observation methods. The discrepancy of frequency of calm condition between manual and automatic observations is calculated, and its reason is studied. Meanwhile, the application method of annual frequency of calm condition is explored. The results indicate that the national annual mean frequency of calm is 26.3% by manual observation and 10.0% by automatic observation. The greater the average wind speed, the lower the frequency of calm, the smaller the difference between the two kinds of observations. During the twoyear comparative observation period in Hubei, the annual mean frequency of calm by manual observation in the 1st and 2nd years is 29.1% and 28.8% separately. However, the frequency of calm by automatic observation in 1st and 2nd years is 18.1% and 12.4% lower than manual observation. The difference of instruments and observation methods both create the deviation. Manual observation takes the rounded to integer way, and only when the wind speed is less than 0.5 m·s-1, the manual observation records calm. But because of the automatic equipment has higher precision, calm condition would be recorded when the wind speed is less than or equal to 0.2 m·s-1. The calm difference between automatic and manual observation in the 2nd year in Hubei is assessed. According to the artificial observation rules, and by reprocessing the automatic observation data to a manual dataset, the revised annual mean frequency of calm is 22.8%, and its deviation from the average value by manual observation on the 2nd year is -6.0%, obviously smaller than the average data of original automatic observation.

Abstract:The midterm forecasting products of T639, ECMWF and Japan numerical models from September to November in 2016 are analyzed and tested. The results show that the three models have good performance on the adjustment and evolution of the Asian midhigh latitude circulation pattern, of which the ECMWF model does the best. Regarding the forecast of the subtropical high, the ECMWF model creates very small error to the position of the subtropical high ridge, while the T639 model predicts the position of the western ridge point of the subtropical high much better. The three models all have good forecasting ability for the 850 hPa temperature change trend, and they do better for the temperature in the South of China than for that in the North. In addition, the three models have different deviations for the center position and intensity of the severe Typhoon Moranti (No.1614) in the 120 h forecast, but the ECMWF model can predict the direction of typhoon track better in its later developing stage. The T639 model is superior to the ECMWF model in forecasting the surface high pressure of the cold wave.

Abstract:The main characteristics of the general atmospheric circulation in November 2016 are as follows. There were two polar vortex centers in the Northern Hemisphere. In the midhigh latitudes of Eurasian areas, there were a high pressure ridge over Ural Mountain and a strong transverse trough over West Siberian. The midhigh latitudes of China were under the control of negative geopotential height anomaly areas, and the zonal circulation was more straight. The northwestern Pacific subtropical high was stronger than normal, located more westward. The south branch trough was located around 90°E averagely. In November, precipitation was characterized by more rainy days and more rainfall amount in the South of the Yangtze River and Southern China. The monthly mean precipitation amount is 30.6 mm, which is 61% more than climatological mean (19 mm). There were four major severe precipitation processes. Extreme continuous precipitation day events occurred over 14 stations, and the daily rainfall amount of 71 stations exceeded the local maximum records in November. Meanwhile, the monthly mean temperature is 2.9℃, which is similar with the climatological mean. There were four main stronger cold air processes, which caused extreme drop in temperature events at 180 stations, among which the readings at 30 stations broke historical extremes. Meanwhile, there were four serious and wide foghaze weather processes. Besides, three typhoons were generated in the Northwest Pacific, South China Sea and Philippines, but their influence on China was little.