Vol.29, NO.2, 2018

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ARTICLES
A Circulation Index of the Spring Persistent Rainfall in the South of the Yangtze and Its Synoptic Characteristics
Zhang Bo, Jin Ronghua, Zhao Bin, Li Yong
2018, 29(2): 129-140. DOI: 10.11898/1001-7313.20180201
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Abstract:
Using daily precipitation dataset of 2466 stations over China, daily and monthly reanalysis dataset from 1961 to 2016 by National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), a circulation index of spring persistent rainfall (ISPR) is defined based on latitudinal differences of zonal winds in lower troposphere over the region from East Asia to the western Pacific. Relationships of ISPR with spring persistent rainfall and general circulation is investigated. Results show that the westerly wind from the South of the Yangtze to South China and the easterly wind located in the region from Huanghuai to Jianghuai area in spring is beneficial to the spring persistent rainfall in the South of the Yangtze. Using this characteristic, the spring rainfall circulation index in the South of the Yangtze is defined. In high-index cases, rainfall increases in the South of the Yangtze; and in low-index cases, rainfall decreases. Meanwhile, the index defined not only reflect the annual variation of the spring persistent rainfall, but also can reflect the daily variation of the spring persistent rainfall. The index has good synoptic significance, and is positively correlated with the daily precipitation in the South of the Yangtze. A verification using data from 1961 to 2016 in the South of the Yangtze indicates that this definition of index can reflect the precipitation in most years in the South of the Yangtze in spring. Taking the year of 2016 as an example, results show that the index defined has a clear physical meaning. In high-index cases, the plateau trough and the southern branch of westerly trough are more active. The western Pacific high moves northward anomalously. Confluence of the southwesterly wind from the low trough, the western Pacific high and the cold air from the higher latitude occur from the South of the Yangtze to South China. Low level convergence and high level divergence provide dynamic uplifting conditions for spring persistent rainfall in the South of the Yangtze. In low-index cases, the western Pacific high moves southward anomalously, and anticyclone anomalies cover the mainland of China. The existence of weak divergence in the lower troposphere in the South of the Yangtze to South China goes against persistent rainfall.
Catastrophe Distinction Index of Oilseed Rape Vernal Waterlogging in Hunan
Fan Yuxian, Huo Zhiguo, Yang Hongyi, Shang Ying
2018, 29(2): 141-153. DOI: 10.11898/1001-7313.20180202
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Abstract:
Focusing on the oilseed rape waterlogging in Hunan, several waterlogging process samples are picked out from historical disaster information to build the impending hazard sample set and affected sample set. As disaster-causing factors in different status have significant difference, t-test is used to quantify the significance of precipitation factor difference in different attenuation coefficients and create effective accumulation preparation (PE). According to PE and continuous cloudy days (D), the critical line is derived from Fisher principle to build oilseed rape vernal waterlogging catastrophe distinction index which can distinguish the affected status day by day. The waterlogging catastrophe index is verified by inverting waterlogging process samples and calculating the value of independent samples. By calculating the affected frequency of waterlogging in each site, and the waterlogging catastrophe index, the relationship between the frequency of waterlogging damage and the relative meteorological yields is studied, and the waterlogging impact evaluation model is constructed. Results show that current precipitation and antecedent precipitation have significant effects on the formation of the waterlogging disaster in Hunan. When the influence attenuation coefficient is 0.899, the difference between PE of the impending hazard sample set and affected sample set is most significant. The oilseed rape vernal waterlogging catastrophe distinction index can be used to monitor the waterlogged catastrophe process on a daily basis, and indicate the catastrophe time and the intensity of the disaster, providing theoretical support for the dynamic monitoring of regional oilseed rape waterlogging process and a new idea for the real-time monitoring and early warning of the precipitation process. In the independent sample verification, the maximum value of waterlogging catastrophe index shows a similar distribution with disaster records, and can reflect the actual disaster situation. It can be a better scientific basis for regional disaster controlling and preventing. According to analysis results, the waterlogging-affected frequency of oilseed rape in Hunan shows an overall trend of high in the southeast and low in the northwest. The waterlogging-affected frequency is higher in flowering and fruiting period and lower in mature period. The waterlogging disaster in fruiting period has the most significant effects on the oilseed rape relative meteorological yields. Oilseed rape vernal waterlogged disaster influence index shows a trend of high in the southeast and low in the northwest. The rape yield is most affected by waterlogged disaster in the east of Changsha, central and north of Zhuzhou, Xiangtan, Yongzhou and the middle of Chenzhou.
Improving Parameters of Nonlinear Accumulated Temperature Model for Spring Maize in Northeast China
Li Rui, Guo Jianping
2018, 29(2): 154-164. DOI: 10.11898/1001-7313.20180203
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Abstract:
Heat condition is one of the most crucial factors that affect the growth and development of crops, which is also of great importance for Northeast China located in the middle and high latitudes. Accumulated temperature is the main factor affecting yield formation, and similarly, temperature plays a key role in determining the duration of growing seasons, yield and so on. Effects of temperature on growth and development of crops are investigated extensively and various kinds of accumulated temperature indexes are established. However, these accumulated temperature models are not always stable. Therefore, it is important to improve the indexes or models, making them convenient to calculate with great stability and applicable to different regions, environments and varieties. A relatively stable accumulated temperature model (NLM) proposed by Shen Guoquan is studied which is applicable to spring maize in northeast China. There are numerous maize varieties and significant differences in parameters determined by different varieties when applying NLM. Therefore, it is important to establish a general accumulated temperature model considering varietal attribute to improve the applicability. Four varieties with more observable years and stations are selected, which are Dongnong 248, Longdan 13, Sidan 19 and Danyu 13. The NLM is adopted based on observations of the growth and development of spring maize and meteorological data in-situ in Northeast China. Biological significance of parameters and the relationship between parameters and varieties or mature period are analyzed, and thus NLM is improved effectively and verified.Results show that, there are no invalid parameters in fitting equations of four maize varieties. The parameter P is determined as 0.5 based on the smallest variation coefficient of accumulated temperature. There is a significant correlation between parameter K and parameter Q, indicating that the parameter K may be only a statistical parameter with no clear biological significance. There is a significant difference of accumulated temperature among varieties. The relationship between the parameter Q and the mean value of effective accumulated temperature or active accumulated temperature during the whole growth period is found to be of good correlation, which indicates that Q is related to the mature period types of different maize varieties. Therefore, a general model applicable to different varieties is proposed whose parameters Q and K are represented by effective accumulated temperature or active accumulated temperature. The application capacity of the model has been significantly improved.
Effects of Climatic Change on Maize Varieties Distribution in the Future of Northeast China
Chu Zheng, Guo Jianping
2018, 29(2): 165-176. DOI: 10.11898/1001-7313.20180204
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Abstract:
Rising ground temperature as a part of climate change has a considerable influence on the climate and environment. Northeast China, as one major grain area ensuring the food security in China, suffers serious impacts of the climate change. Traditional cultivation ways cannot adapt the new situation, leading to an increasing instability of the agricultural system. The planting system, structure and layout cannot match the original climatic resources. The research adopts the RCPs situation instead of the original SRES scenarios data, to provide a reasonable variety selection, and a scientific basis for dealing with the climate change in the future. To explore effects of future climate change on maize varieties and climatic potential productivity in Northeast China, simulations are carried out with regional climate model, using two emission scenarios RCP4.5, RCP8.5 during 2011-2099, and daily observations of 91 stations during 1961-2010. A series of analysis are carried out on the temporal and spatial distribution of maize variety, climatic potential productivity, resource utilization ratio under the situation of climate change in the future. The result shows that in the baseline scenario (1961-2010), the late maturing varieties can be planted in smaller southern areas, while they cannot grow in northern areas. Under the condition of RCP4.5 and RCP8.5(2011-2099), suitable areas for late maturing varieties will expand, and in RCP8.5, the suitable areas are the largest. The climatic potential productivity in Northeast China is high in the south while low in the north. In the baseline scenario, the annual production is 10492.54 kg·hm-2, and in RCP4.5 it increases to 10697.16 kg·hm-2, while in RCP8.5 it drops to 9410.17 kg·hm-2. The maize potential productivity increases with this climate change trend in the whole area. In the baseline scenario, the radiation suitability is highest but the temperature suitability is lowest for maize production. With the climate change, the radiation suitability and temperature suitability both increase, but the water suitability will decrease to 0.63 and 0.48 in scenarios of RCP4.5 and RCP8.5, which will become a main factor that restricts the production of crop in Northeast China. In the baseline scenario, the resource utilization rate is 0.826, and its growth rate is 0.009/(10 a). In the situation of RCP4.5, RCP8.5, they are 0.804 and 0.647, and growth rates are 0.010/(10 a) and -0.002/(10 a). Suitable areas for late maturing varieties expand evidently, but the potential productivity of maize and resources utilization declines. It should also be noted that the regional climate model may bring uncertainties to results.
Locations and Radiation Strength of Narrow Bipolar Pulses in a Thunderstorm
Jiang Ruijiao, Dong Wansheng, Liu Hengyi, Yang Lei
2018, 29(2): 177-187. DOI: 10.11898/1001-7313.20180205
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Abstract:
Narrow bipolar pulses (NBE) are special flashes in thunderstorms which are different from regular in-cloud discharges and cloud-to-ground discharges. They can produce intense radiation in both VLF/LF and VHF bands. To explore the meteorological environment and discharge characteristics of NBE, locations and radiation strength of 608 positive NBE and 82 negative NBE detected in a thunderstorm day are analyzed using the dual band 3D lightning locating system in Chongqing. Results show that positive NBE occur at the altitude of 7-15 km, with the average altitude of 10.0 km. According to the radar reflectivity of positive NBE, they can be divided into three groups. 49 positive NBE, which occur in the thunderstorm cores (reflectivity), are categorized as Group Ⅰ. 350 NBE occurring in regions outside cores with the reflectivity higher than 5 dBZ are categorized as Group Ⅱ. The rest 209 positive NBE are Group Ⅲ. The radiation strength of these three groups are in descending order on both bands. The mean value of all positive NBE VLF/LF electric field change peaks normalized to 100 km is 13.4 V·m-1. The mean value of their VHF radiant powers is 73.5 kW. Negative NBE are generally produced in two regions in the thunderstorm. Among 82 negative NBE, 72 of them occur at the altitude of 16-20 km, and the average altitude is 18.0 km. They occur on or beside tops of thunderstorms with 30-35 dBZ echo heights higher than 18 km. The mean value of their VLF/LF electric field change peaks normalized to 100 km is 42.7 V·m-1. The mean value of the VHF radiant powers is 76.9 kW. 10 negative NBE occur at the altitude of 4-10 km, whose average altitude is 6.0 km. They all occur in thunderstorm cores. The mean value of VLF/LF electric field change peaks normalized to 100 km is 2.7 V·m-1. The mean value of VHF radiant powers is 18.2 kW. According to statistical results, the radiation strength of the upper negative NBE is mostly stronger than those of positive NBE and the lower negative NBE on VLF/LF band. In VHF band, values are similar, both of which are stronger than the lower negative NBE. The radiation strength of the lower negative NBE is weaker than that of positive NBE in both bands.
Main Influencing Factors of Visibility in Beijing
Jiang Jiang, Zhang Guoping, Gao Jinbing
2018, 29(2): 188-199. DOI: 10.11898/1001-7313.20180206
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Abstract:
People's work, life and travel could be affected by the air visibility especially low visibility which has harmful effects on society and traffic safety.In recent years, the cause and variation of visibility become a very important topic in the field of atmosphere and environment research.In light of this, an analysis is carried out on the visibility in Beijing using all available observations.And two typical low visibility events are picked out to analyze in detail.As for Beijing, the most relevant elements of visibility are relative humidity, wind speed and PM2.5 concentration.PM2.5 concentration reduces visibility by extinction for light.Water vapor in the air causes the atmospheric aerosol particles increasing through moisture absorption and changes its characteristics, which brings down the visibility.And when the wind velocity is low, with poor air pollutant diffusion conditions and accumulating particles, the visibility decreases obviously.So it could be concluded that atmospheric visibility depends on both meteorological conditions and air pollution, which differs in different areas because of geographical locations, climatic conditions, and the composition of particulate matter.In brief, the correlation between visibility and wind speed is positive, which means that visibility increases with the increase of wind speed.And correlations among visibility, PM2.5 concentration and relative humidity are both negative, which means that visibility decreases with the increase of relative humidity and PM2.5 concentration.But it is important to point out that once relative humidity reaches a certain threshold (80%), the correlation between visibility and PM2.5 concentration declines, which results in the visibility mainly depending on relative humidity.Generally, the periodic variation of visibility is more consistent with the change of meteorological conditions, and the relationship between visibility and PM2.5 concentration is more complicated.In recent years, the result shows that the visibility in the northwest is obviously higher than that in the southeast including the city center.The annual spatial distribution of visibility turns out to decrease gradually from northwest to southeast.And the highest visibility in a year in Beijing happens in spring and the lowest is in summer.The maximum is in May and the minimum is in July.The lowest visibility in a day happens at about 0600 BT, which postpones in winter.The visibility peak happens at about 1600 BT, which advances in winter.Results show the probability of low visibility events is 62.14% in Beijing.Dry haze happens more frequently than wet haze.In addition, as for the case studies, it should be noted that, when the wet haze event occurs, visibility in Beijing deteriorates more obviously than that in the dry haze event.And PM2.5 concentration in the wet haze events is needed to drop more for improving visibility than that in the dry haze event.
Methods of Aircraft-based Precipitation Enhancement Operation for Convective-stratiform Mixed Clouds in Autumn in Hunan Province
Fan Zhichao, Zhou Sheng, Wang Ling, Zhou Changqing, Li Qiong, Peng Yue
2018, 29(2): 200-216. DOI: 10.11898/1001-7313.20180207
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Abstract:
Based on ground meteorological observations at Changsha of Hunan, and the aircraft artificial precipitation enhancement operation data in autumn of recent 10 years in Hunan, some statistical analysis results on the convective-stratiform mixed clouds systems are obtained, including the distribution of precipitation, structure characteristics and the seeding method of aircraft artificial precipitation enhancement operation.Physical characteristics of typical operation weather processes are analyzed by using Doppler radar data, the numerical model GRAPES_CAMS, and meso-scale meteorological data.Paired convective clouds and the echo tracking method based on TREC algorithm are used for effect evaluation.12 macro and micro parameters are picked out as indicators of artificial precipitation enhancement operation with convective-stratiform mixed clouds, including precipitation weather situation, the main cloud system, cloud-top height, cloud-top temperature, cloud thickness, seeding layer height, seeding layer temperature, seeding layer relative humidity, radar echo intensity, vertically integrated liquid, supercooled water content, rainfall situation and so on.The best seeding time, position and catalyst amount of the artificial precipitation enhancement operation using Yun-7 aircraft and AgI catalyst are discussed.For convective-stratiform mixed clouds including precipitus stratiform clouds and cumulus clouds, the most suitable area, seeding height and catalyst dosage of the operation are summarized.In supercooled -15 to -5℃ layer of altostratus cloud, seeding catalyst could make the artificial ice crystal concentration reach 30 L-1; in supercooled -15 to -7℃ layer of cumulus cloud, static seeding catalyst makes the concentration 30 L-1 while dynamic seeding catalyst makes it 100 L-1.These operation methods achieves good results in the practice of artificial precipitation enhancement.Among more than 40 times aircraft precipitation enhancement operation practice in recent 8 years, cold cloud catalyst seeding in precipitus stratiform clouds in convective-stratiform mixed clouds system usually leads to light rain (1-10 mm); cold cloud catalyst seeding in cumulus clouds in convective-stratiform mixed clouds system usually lead to small to moderate rain (5-17 mm); another 4 operations of warm cloud catalyst seeding in relatively stable stratiform warm clouds maintaining more than 12 h only bring slight enhancement of precipitation (0.1 mm).In the future, airborne meteorological equipment should be developed for cloud physics detection, especially for the detection and study of cumulus.Based on improved performance indicators of cumulus seeding, the cloud physics concept model of cumulus cloud artificial precipitation in southern China can be gradually established.
A Multi-scale Spatial-temporal Projection Method for Monthly and Seasonal Rainfall Prediction in Guangdong
Li Chunhui, Pan Weijuan, Wang Ting
2018, 29(2): 217-231. DOI: 10.11898/1001-7313.20180208
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Abstract:
Guangdong Province is located in low latitude areas and affected by both tropical weather systems and high latitude weather systems.A multi-scale spatial-temporal projection (MSTP) method is developed to predict the monthly and seasonal precipitation in Guangdong.Multi-factor and multi-scale forecasting method can be used to seek for the forecast factor by quantity scale separation through scale decomposition conforming to the physical meaning, thus it can reduce climate non-stationary time series and improve the prediction accuracy.The key feature of MSTP mothod is that it considers not only spatially but also temporally varying large-scale field connection between the predictor and predictand.Based on main modes of the empirical orthogonal function (EOF) analysis, periods are gained from the wavelet analysis and decomposed by Lanczos filtering.According to the correlation between the precipitation and Climate Forecast Systems datasets provided by National Centers for Environmental Prediction dynamic model data (CFSv2), significant influencing factors are selected to predict precipitation with MSTP method.Using the least square error correction method, Guangdong monthly and seasonal precipitation predictions are obtained based on inter-annual increment approach.The test of independent samples from 2006 to 2015 shows the correction can improve the performance of prediction, making PS score of operational test change smoothly.After correction PS scores are improved greatly during 6 years of the hindcast period, and the monthly and seasonal rainfall account for 68.8%.For 87.5% of total samples, the forecast average score is over 70.The prediction effect is closely related to period changes of the precipitation main mode.If the inter-annual period is priority to other period, the prediction effect after correction is significantly higher than that before the correction, otherwise it is poor.The root mean square error within 0.5-1 standard deviation rate after correction is higher than that before corrections.Within 0.5 standard deviations, the monthly and seasonal rainfalls, of which the root mean square error of probability is more than 40%, account for 81.3% after correction comparing to 31.3% before correction.Within 1 standard deviation, the monthly and seasonal rainfalls, of which the root mean square error of probability is more than 70%, account for 56.3% comparing to 50% before correction.It suggests that most of rainfall prediction errors are within 1 standard deviation.Therefore, the prediction from MSTP method can offer important reference to operational prediction of short-term climate prediction for monthly and seasonal prediction in Guangdong.
Meso-scale Characteristics of Typical Summer Short-time Strong Rainfall Events in Inner Mongolia
Chang Yu, Ma Suyan, Zhong Xia
2018, 29(2): 232-244. DOI: 10.11898/1001-7313.20180209
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Inner Mongolia Autonomous Region is in the northern frontier of China, where characteristics of short-time strong rainfall events(STSRE) are spatially small-scale and abrupt, and it is easy to cause urban waterlogging and local floods.Especially, the STSRE below 20 mm per hour could cause disaster in the west of Inner Mongolia.In the forecast operation, it's found that the combination of wind field data, sea-level pressure of automatic weather stations, and lighting data could capture meso-micro scale information that triggers the development of the mesoscale convective system(MCS).Meso-scale characteristics near ground layer over MCS is related to STSRE, such as meso-cyclone or medium low pressure.Using conventional observations, global analysis data by National Centers for Environment Prediction(NCEP), black body temperature(TBB) data of FY-2D, automatic weather station data and lighting data of Inner Mongolia, 37 STSRE are analyzed from 2012 to 2015 in summer over Inner Mongolia.In west region of Inner Mongolia, synoptic scale patterns that cause STSRE are low vortex or low trough at 500 hPa, which interact with Indian vortex(Plateau vortex, Sichuan vortex or northwest vortex) at 700 hPa, and the Western Pacific subtropical high or typhoon.But in the east region, synoptic scale patterns that cause STSRE are either low vortex or low trough, or the interaction of low vortex or low trough with the Western Pacific subtropical high or typhoon.These synoptic patterns could both affect central region of Inner Mongolia.MCS occurs in the rear of cold front cloud system, vortex cloud system and warm-wet shear cloud system, is the direct inducement systems of STSRE.STSRE occur when MCS is developing and matured, and they appear in high TBB gradient areas where MCS moves out and cold air intrudes in.Meso-cyclone, meso-scale depression, meso-small scale cyclonic convergence wind field and mesoscale shear line are observed by automatic weather station trigger the evolution of MCS.The developing MCSs above the meso-cyclone are elliptical, while MCSs induced by shear line are mostly band shaped, and most MCSs that develop in the synoptic scale vortex cloud system are banded or irregular.Cloud-to-ground(CG) lightning flashes density value reaches the maximum when MCS is developing and matured.The high value of CG lightning intensity is in accordance with the region of development and strengthening of MCS, too.In the western and central northern regions of Inner Mongolia, 3 hours before STSRE, the relative humidity is normally 60%-80% but in other regions it is 80%-90%.The cold air in the low troposphere is critical for the development of MCS.
Comparative Analysis of Two Strong Convections Triggered by Sea-breeze Front in Shandong Peninsula
Gao Xiaomei, Yu Xiaoding, Wang Lingjun, Wang Xinhong, Wang Shijie, Wang Xiaoli
2018, 29(2): 245-256. DOI: 10.11898/1001-7313.20180210
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Abstract:
Using surface and high conventional observations, radar echo data and automatic weather station data of Yantai and Qingdao, two strong convections triggered by sea-breeze front in Shandong Peninsula on 14 July 2014 and 29 June 2009 are analyzed.The convection on 14 July 2014 occurs under circulation patterns of forward-tilting trough in the back of cold vortex, where dry and cold air at middle and upper layer is strong, warm and humid air at low layer is weak, leading to obvious static instability stratification and moderate convective available potential energy.The vertical wind shear is from weak to moderate, therefore the duration of supercell is short, and the range of hail is small.The convection on 29 June 2009 appears under circulation patterns of a typical northeast cold vortex, and strong vertical wind shear is a principal factor in the maintenance of supercell.Sea-breeze front, gust front and convergence line of surface are triggering systems.The high convective available potential energy, temperature and pseudo equivalent potential temperature difference between 850 hPa and 500 hPa, average wind speed of storm bearing layer, wind indices, and potential downside indices are indicative to the intensity of convection.Both processes have supercell storms, showing similar echo characteristics, such as hanging strong echoes, weak echoes regions, echo pendency, hook echoes and mesocyclones.The difference is that there is a strong mesocyclone on 29 June 2009, while the mesocyclone on 14 July 2014 is much weaker, so the former has a larger convection range and stronger intensity.The collision process between sea-breeze front and gust front enhances the mesocyclone, and when one factor weakens the mesocyclone weakens too.Two hail processes appear in the decline phase of cell top and echo top, maximum period of a storm with maximum reflectivity.The strong radar echoes over 50 dBZ in both processes extend to much higher than the height of -20℃.Lower melting level, suitable height of 0℃, thick depth of negative temperature layer are important to large hails.In addition, the formation period of large hails are in the period of low base height, deep thickness, severe rotation intensity of mesocyclone and is simultaneous with the strong period of mesocyclone.Therefore, the size of hail is related to base height, thickness, and rotation intensity of mesocyclone.Supercell storms of two processes occur to storms of the sea-breeze front which is close to the mountains.The stronger uplift triggering caused by combination of terrain and sea-breeze front is critical to strengthen original convective storms and evolve into supercell storms.
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