Lightning Activity And Precipitation Correlation Study

In order to improve the level of the application of the lightning data on the warning of severe weather processes and precipitation and the lightning warning and forecasting, kinds of observation data, including total lightning, cloud-to-ground (CG) lightning, radar, TRMM satellite, electric field mills, sounding and so on, are synthetically analyzed in this dissertation and the relationship between lightning activities and precipitation, the relationship between lightning activities and the hydrometeors in the cloud and the impact of the dynamical and microphysical processes on electric structure and lightning activities are discussed. The quantificational results will provide a reference for the applications of lightning data on the severe weathers warning and precipitation estimation. The level of lightning forecasting also will be advanced by assimilating the relationship between the hydrometeors and the lightning activities to the numerical prediction models. The analysis is beneficial to deeply understand the mechanism about the relationship among the aforesaid factors, extending the application field of the lightning data and promoting the development of"lightning meteorology". The main research contents and results are as follows.The first chapter introduces the research progress and furthermore the necessity, objective, significance and innovation of this dissertation.The research results in the second chapter indicates that the relationship between the lightning activities and the precipitation characterized by the lightning activities increases with the latitude increasing and the climate changing from humid to relative arid. In the area of Jiangxi and Fujian provinces, the correlation coefficients are respectively 0.56 for day variation, 0.73 for ten days variation and 0.74 for month variation. According to the same sequence, the correlation coefficients are respectively 0.46, 0.86 and 0.88 in Henan and Shaanxi provinces, 0.56, 0.89, and 0.97 in Beijing and its surrounding area, and 0.80, 0.92 and 0.99 in Heilongjiang province. The spatial linear relationship between the lightning activities and precipitation in these four areas also increase successively.In the third chapter, radar data and total lightning detected by SAFIR coming from 18 thunderstorms are used to research the relationship between the lightning activities and convectional rainfall (CR) and additional thunderstorms'characteristics. It is indicated that the convectional rainyield per flash (RPF) is 2.65×107kg for total lightning, 3.74×107kg for introcloud lightning and 11.32×107kg for CG lightning. The relationship between total lightning and CR is more stable than that between CG lightning and CR among different thunderstorms and during different development stage of the thunderstorms. Total lightning frequency (expressed by FTL with the time space being 6min) can be used to calculate the amount of CR (expressed by MCR with the unit being kg) with the equation MCR=1.574×107FTL+2.956×108 and calculate the area of the convetive region (expressed by ACR with the unit being km2) with ACR=4.267FTL+130.283. It is believed through spatial analysis that most lightning activities locate in the convective region of the thunderstorms with the average ratio being 58.96% for total lighting discharges and 66.53% for CG lightning discharges. In addition, the ratio value is the largest in the vigorous stage and the smallest in the decline stage of the thunderstorms. Most lighting activities locate in the regions where the compositive reflectivity (ZCR) is from 39 to 52dBZ, the horizontal gradient of the ZCR is from3.4 to 5.0dB/km, the Height of 35dBZ reflectivity (H35) is from 5.8 to 10.3km, the horizontal gradient of the H35 is from 0.3 to 0.6km/km, the vertically integrated liquid (VIL) is from 1.5 to 13.0kg/m2, the density of the VIL is from 0.3 to 1.1 g/m-3, and the rainfall intensity is from 5 to 48mm/h.In the fourth chapter, the relationships between the lightning activities and the hydrometeors in the cloud are synthetically analyzed by using the data from TRMM/TMI/LIS and SAFIR. It is found that good relationship between the lightning activities and the maximum rainfall intensity exists only when some threshold values are introduced. The power function relationship between total lightning density relative to the rainfall intensity threshold value of 30mm/h (expressed by DL with the unit of km-2min-1 and calculated through the area of the region where the rainfall intensity is more than 30mm/h being divided by the total lightning frequency for one minute) and the maximum rainfall intensity (expressed by Rmax with the unit of mm/h) is the best with the equation of Rmax=23.103×DL-0.183+11. Only under the condition of some threshold values, there are good relationships between the lighting activities and the area or mass of the hydrometeors whose vertically integrated content (VIC) are larger the threshold values. For example, the best threshold value for rainfall intensity is 10mm/h, and the equation is M=18408061.949FL+208884424.650. For the liquid water phase particles, the best threshold value is that the VIC of the water at whole heights is 3kg/m2, and the equation is FL=1.936×10-9M+4.296. For the ice phase particles, the best threshold value is that the VIC of the ice particles above -10℃is 3kg/m2 and the equation is FL=1.862×10-9M+7.872. In these equations, M express the mass of the precipitation or the hydrometers that are larger than the threshold values with the unit of kg and FL means lightning frequency with the unit of min-1. The stable relationships among different thunderstorms, among different regions of the thunderstorms and among different development stages of the thunderstorms are in favor of forecasting the lighting activities through the information of hydrometeors. Although the spatial quantitative relationships between the lightning activities and the rainfall intensity or the VIC of the hydrometeors are unobvious and complex, the power function relationship between them is more obvious than other function relationships for the density of the lightning as independent variable and the rainfall intensity as dependent variable and the exponential function relationship between them is more obvious than other function relationships for the VIC of the hydrometeors as independent variable and the density of the lightning as dependent variable.In the fifth chapter, a hailstorm case is analyzed to discuss the impact of the dynamical and microphysical processes on the electric characteristics and precipitation. The results indicate that it is possible for the electric structure of a thunderstorm to change in its life period. During the hail shooting stage of the hailstorm, the electric structure is inverted. After that, the electric structure is adjusted rapidly and then forms normal inclined tripole. The three stages of the electric structures respectively correspond to the first active stage, the weak stage and the second active stage of the lightning discharges. There is stronger updraft and more plentiful big particles in the first active stage of the lightning discharges. The ratio of the CG lightning to the total lightning is low with the value of 6.16%. However, the ratio of the positive CG (PCG) lightning to the total CG lightning being 20.00% is larger than normal value. The PCG lightning discharges during the stage of the inverted electric structure are mainly produced by the middle positive charge region striking to the ground through the bottom negative charge region. During the stage of the normal inclined tripolar charge structure, the parts of the upper positive charge region and the middle negative charge region are exposed to the ground directly from the bottom positive charge region. In the edge of the main body of the hailstorm, the upper positive charge region strikes to the ground through the middle negative charge region, which is another reason for the PCG lightning discharges. Furthermore, during the life period of this hailstorm, the variation of the lightning frequency is consistent with the maximum height of the strong reflectivity, the maximum reflectivity, the area of the strong reflectivity at different heights and the volume of the strong reflectivity. The peak time of the lightning activities is prior to that of the hail shooting about 5min. In a rectangle region with the side length being 10km, the lightning frequency in this region can provide about 5-15min warning time for the maximum rainfall intensity observed by the automatic weather station (AWS) locating in the center of the region. At the same time, good relationships are also found between the variation of the lightning activities in these regions and some meteorological elements observed by the AWSs.The sixth chapter is about the relationships among dynamical and microphysical processes, electric characteristics and precipitation in a persistent rainstorm case. It is shown that there is a normal tripolar electric structure in the convetive region and dipolar electric structure with small height in the stratus region. In the convetive region, there are plenty of negative cloud-to-ground (NCG) lightning discharges which come from the middle negative charge region. The dispersedly distributed PCG lightning discharges in the stratus region come from the upper positive charge region. During the life period of the rainstorm system, CG lightning discharges are active. The ratio of the PCG lightning discharges is only 3.52% during the vigorous stage of the system and however 21.25% during the decaying stage. It is because that the NCG lightning activities in the convective region weaken with the decrease or disappear of the convective motion and the PCG lightning activities varies little with the status region being impacted little by the convective motion. The main positive charge region taking part in the discharges locates in the lower part of the largest-density ice crystal region and the main negative charge region taking part in the discharges is well consistent at the height with the largest density region of the graupel and hail. The relationship between the lighting activities and the precipitation in this persistent rainstorm case is of its own characteristics. Its convective precipitation and the area of the convective region are both smaller than general storms (e.g. the storms discussed in the third chapter). The CG lightning frequency (expressed by FCG with unit of 6min-1) can be used to calculate the area of the convective region (expressed by AC with the unit of km2) with the equation of AC=1.633FCG-55.688 and calculate the mass of the CR (expressed by MCR with the unit of kg) with the equation of MCR=3.507×106FCG-1.683×108. Under the condition of a certain threshold value, there are good linear relationships between CG lightning activities and the characteristics of the radar. For example, the relationship between CG lightning frequency and the area where the compositive reflectivity is larger than 45dBZ (expressed by A(Z>=45dBZ) with the unit of km2) is the best with the fitting equation being A(Z>=45dBZ)=2.824FCG-29.963. The threshold values at different height that obtain the best relationship between the CG lightning activities and the area of reflectivity decrease with the height increasing. The threshold value is 45dBZ at 3km, around 35dBZ at middle level and 20dBZ above 10km. In addition, the volume of the reflectivity larger than 40dBZ (expressed by V(Z>=40dBZ) with unit of km3) has the best relation with CG lightning activities with the fitting equation being V(Z>=40dBZ)=23.055FCG+1748.756. The significant relation makes it possible to use lightning information to infer the characteristics of the main body of the thunderstorms or to use radar observation to infer the characteristics of the lightning activities. Furthermore, compared with the most lightning discharge, the most active lightning discharges are related with larger rainfall intensity and contents of the hydrometeors. In decaying stage, the values of the rainfall intensity and contents of the hydrometeors corresponding with the location of the main lightning activities are nearer to their maximum values than other stages.In the seventh chapter, the dynamical and microphysical processes and the electric characteristics are compared between the hailstorm case and the rainstorm case. The results show that the updraft influences the water vapor transport, ice particles'growth and the water vapor consumption, and then in a great extent controls the magnitude of the liquid water content in the cloud which impacts the polarity of the charge carried by the graupel in the region where the temperature is lower than the inverted temperature. So, updraft is the key factor impacting the electric structure. It is difficult for the bottom charge region to strike to the ground directly. The polarity of the CG lightning may depend on the polarity of the charge region upon the bottom charge region which however is a necessary condition for the occurrence of the CG lightning discharge. Just through impacting the electric structure, the updraft impacts the lightning discharge indirectly. The reason why many severe thunderstorms are easy to be dominated by positive CG lightning is that the very strong updraft dominate the thunderstorms and help to inform inverted tripolar electric structure. The middle positive charge region discharge positive charge to the ground through the low negative charge region. The analysis shows that the difference of the polarity of the lighting and the temporal and spatial features among different style of weather processes can be used to indicate the intensity of the thunderstorms, the style of the precipitation and its location.The eighth chapter is about the summary and prospect.