Analysis on Lightning Activities and Its Disastrous Climate Characteristics in Shandong Province

By using the reported data of lightning disaster and the data of lightning monitoring network in Shandong Province since its establishment,the lightning activities and the disaster climate characteristics in Shandong Province were analyzed.The data were processed by lattice formulation,and the spatial and temporal distribution characteristics of positive and negative CG flashes were given.The parameter characteristics of positive and negative ground lightning and its relationship with the lightning disasters were analyzed.And the lightning parameter characteristics of lightning in major cities of Shandong Province were analyzed.

AHP Model-Based Risk Assessment of Lightning in Meizhou

Based on the cloud-to-ground（ CG） lightning flashes data and other related data from 1999 to 2016,the lightning risk zoning of Meizhou was conducted by using the analytic hierarchy process（ AHP） model. The model considered the natural conditions,social economic conditions and other factors,and the main assessment factors were selected,containing ＂ flash density,lightning current intensity,annual thunderstorm days,lightning disaster frequency,construction area per capita and GDP per capita＂,in order to establish the evaluation model,and divide the level of risk. The results showed that the lightning risk in Meizhou area roughly had the trend of ＂ center higher than all-around,the south higher than the north,the west higher than the east＂. High-risk area was in the most region of Meijiang District and central region of Meixian District,and Wuhua County was next high-risk area. Xingning City and Fengshun County were medium risk areas,most of the other were low risk area. The result of regionalization was consistent with the actual situation,and the evaluation method was scientific and effective. Through the analysis of the lightning risk zoning,this paper could provide a scientific basis for the lightning protection and disaster reduction in the region in the future.

Occurrence conditions of positive cloud-to-ground flashes in severe thunderstorms

The purpose of this study was to understand the reasons why frequent positive cloud-to-ground(+CG) flashes occur in severe thunderstorms. A three-dimensional dynamics-electrification coupled model was used to simulate a severe thunderstorm to permit analysis of the conditions that might easily cause +CG flashes. The results showed that strong updrafts play an important role in the occurrence of intracloud flashes. However, frequent +CG flashes require not only strong updrafts but also strong downdrafts in the lower cloud region, conditions that correspond to the later phase of the mature stage and the period of the heaviest solid precipitation of a thunderstorm. During this stage, strong updrafts elevated each charge area in the updraft region to a higher level, which resulted in an inverted tripole charge structure. A wide mid-level region of strong positive charge caused largely by positively charged graupel, presented in the middle of the updraft region because of a non-inductive ice-ice collisional charging mechanism. The charge structure in the downdraft region was consistently more complex and revealed several vertically stacked charge regions, alternating in polarity. Much of the graupel/hail outside the updrafts was lowered to cloud-base by strong downdrafts. In this area, the graupel/hail was charged negatively because of the transportation of negatively charged graupel/hail from higher regions of negative charge in the updrafts, and via the inductive charging mechanism of collisions between graupel/hail and cloud droplets at the bottom of the cloud. Consequently, a large region of negative charge formed near the ground. This meant that +CG flashes were initiated more easily in the lower inverted dipole, i.e., the middle region of positive charge and lower region of negative charge. Frequent +CG flashes began almost synchronously with dramatic increases in the storm updrafts, hail volume, and total flash rate. Therefore, the occurrence of +CG flashes appears a good indicator of storm intensification and it could have some use as a predictor of severe weather in the form of hail.

A Lightning Activity Forecast Scheme Developed for Summer Thunderstorms in South China

Based on the relationship between lightning flash density and radar echoes and a statistical analysis using satellite and radar observations,a scheme was introduced into the mesoscale model GRAPES（Global and Regional Assimilation and PrEdiction System）to forecast the cloud to ground（CC）flash activities.Because the relationship is a necessary but not sufficient condition for lightning,an additional constraint condition related to temperature of cloud top is added into the scheme to determine whether the lightning activity really occurs.Only if the lightning activity meets the criterion to occur,the CG flash density in a grid is considered to be valid.This was proved to be necessary for reducing the false prediction.Two cases that occurred on the edge of the subtropical high in coastal regions of South China were simulated to examine the efficiency of the scheme.The results showed that the scheme was capable of forecasting lightning activities in South China.The simulated lightning areas agreed with the CG flash observations,and the CG flash density forecast by the model was also consistent with observational results in magnitude.In consideration of the forecast aging of the explicit cloud microphysical scheme in GRAPES,lightning activities can now be forecast accurately within 6 h.