Statistical Analysis Of Lightning And Typhoon Activities In The Northwest Pacific Regio

Based on WWLLN lightning data,tropical cyclone best track data,Fengyun-2 satellite data and ERA5 reanalysis data from 2011 to 2018,this paper studies the relationship between lightning and typhoon activities in the Northwest Pacific Ocean.The main contents include:The distribution characteristics of lightning in typhoon activity,the relationship between lightning and the change of brightness temperature in typhoon activity,and the relationship between lightning and vertical wind shear during typhoon evolution.The main conclusions are as follows:(1)Most typhoons in the northwest Pacific region reach their maximum intensity in the eastern sea area of the Philippines and Taiwan region of China,and most of them can reach the coastal areas of China.Lightning in typhoon system mostly occurs on the sea surface,and the maximum density ranges from 110 °E to 125 °E and from 10 °N to 25 °N.Compared with the winter half year,the lightning frequency in the summer half year is significantly enhanced,and the high density area has an obvious trend of deviation to the high latitude area.The lightning in the summer half year typhoon has a greater impact on the coastal area than that in the winter half year.(2)The lightning in the inner core,inner rain bands and outer rain bands in the northwest Pacific presents a three-circle distribution feature of "high-low-high" on the whole,but the lightning frequency decreases slightly in the range of 600-700 km from the typhoon center,and then increases obviously.If the radius is 1100 km,the radial distribution of lightning presents a five-circle pattern of "high-low-high-low-high".When the typhoon intensity is weak,the radial distribution characteristics of lightning in the typhoon are not obvious.With the increase of the typhoon intensity,the three-circle distribution characteristics of the inner core,inner rain bands and outer rain bands become more obvious.Lightning in typhoons in the Northwest Pacific region tends to be on the left side of the typhoon’s direction of advance.(3)Lightning in the outer rain bands is easy to occur in the area with low brightness temperature value and the area with relatively high brightness temperature value and large variation of brightness temperature gradient.When the typhoon does not reach the super typhoon level,lightning in the inner core mostly occurs in the clouds with low brightness temperature.When the typhoon reaching the super strong typhoon level,due to the appearance of the typhoon eye,a large number of lightning also appears in the high brightness temperature value area in the inner core.Lightning in typhoons tends to occur in areas where the brightness temperature value decreases.The brightness temperature is at the lowest value at the time of lightning occurrence.After lightning occurs,the brightness temperature in most areas where lightning occurs rises slowly.(4)The lightning in the outer rain bands is more likely to appear in the right side of the vertical wind shear direction.When the typhoon intensity is weak,the lightning in the inner core tends to appear in the direction of the reverse direction of vertical wind shear.With the increase of the typhoon intensity,the lightning in the inner core tends to move in the direction of vertical wind shear.Lightning in typhoons is easy to occur in the time period when vertical wind shear value decreases and the time period when vertical wind shear value is low.Some typhoons are affected by high sea temperature and a large amount of lightning occurs in the period of strong vertical wind shear.Other factors such as typhoon turning and landing process may also lead to lightning outbreak.