5:15 PM - 6:30 PM
[MIS07-P03] Estimation of the relation between electrical properties of lightning and tropical cyclone intensity in the western north Pacific.
Keywords:lightning , typhoon, ELF, charge moment change
Although the track prediction of tropical cyclones (TC) is improved year by year, the prediction of the TC intensities such as the minimum sea level pressure and the maximum wind speed is getting worse year by year and is an big issue to be solved. Previous studies indicate that the lightning activities in TCs can be a good proxy of the TC intensity development. In the previous studies, the relation between the lightning occurrence number and the TC intensity development were investigated. However, the relation of the electrical properties (EPs) of lightning discharges with the TC intensity development is poorly investigated. As there are some reports showing close relation between the lightning EPs and the thunderstorm activities causing severe weather, it’s important to clarify the relation between the lightning occurrence number, lightning EPs and the TC intensity development.
The purpose of this study is to clarify the relation between the lightning EPs and the TC intensity development and to verify whether the lightning EPs or the lightning occurrence number is a better proxy to predict the TC intensity development. For this purpose, we have (1) estimated the lightning occurrence number in the inner core and the rainband of TCs using the ground-based lightning detection network data, (2) identified the transient ELF waves detected by the ground-based ELF observation network and related to lightning discharge in the TC region, and (3) estimated the lightning EPs and analyzed relation between the lightning EPs and the TC intensity development. We used the best track data of TCs provided by Joint Typhoon Warning Center (JTWC), lightning data containing both time and location data provided by World Wide Lightning Location Network (WWLLN) and ELF magnetic field waveform data obtained at Syowa station in Antarctica and Kuju station in Japan, that are the two stations of Global ELF Observation Network (GEON). As the collection window of lightning discharges in TCs, we defined (i) the inner core as the region within the 100 km (200 km) distance from the TC center for normal (large) TCs, (ii) the rainband as the region of 100-500 km (200-1000 km) from the center for normal (large) TCs. Using ELF waveform data, we estimated the peak current (Ip), charge moment change (Qdl), and charge amount (Q) as the lightning EPs. Ip and Qdl were estimated from ELF data obtained at Syowa, while Q was estimated from ELF data obtained at Kuju. Using above methods and the estimated parameters, we conducted the cross-correlation analyses between the TC intensity development and the lightning EPs for 40 TCs occurred in the western north Pacific in 2013 and 2014.
First, we found that the median value of the lightning EPs in positive cloud-to-ground (+CG) discharges peaked at the generation stage in the 29 TCs. When multiple cumulonimbus are merged in the TC region, the cloud top of these cumulonimbus reaches near the tropopause, and the upper clouds will horizontally spread. Then +CG with long discharge length occur from the upper positive charge region overhanging or the developing stratiform region. Second, we found that total value and median value of the EPs of -CGs peaked during the development stage in the 11 super TCs (very strong typhoons and violent typhoons) out of the 12 super TCs analyzed. This is probably caused by the updraft intensification in the eyewall which tends to reduce the electrical breakdown voltage and transfer the negative charge to upper layer. As the EPs of -CG discharges during the development stage in the super TCs peaked 1-2 days before the TC intensity maximum, the EPs of -CG discharges as well as lightning occurrence number can be a good predictor of the TC intensity development.
The purpose of this study is to clarify the relation between the lightning EPs and the TC intensity development and to verify whether the lightning EPs or the lightning occurrence number is a better proxy to predict the TC intensity development. For this purpose, we have (1) estimated the lightning occurrence number in the inner core and the rainband of TCs using the ground-based lightning detection network data, (2) identified the transient ELF waves detected by the ground-based ELF observation network and related to lightning discharge in the TC region, and (3) estimated the lightning EPs and analyzed relation between the lightning EPs and the TC intensity development. We used the best track data of TCs provided by Joint Typhoon Warning Center (JTWC), lightning data containing both time and location data provided by World Wide Lightning Location Network (WWLLN) and ELF magnetic field waveform data obtained at Syowa station in Antarctica and Kuju station in Japan, that are the two stations of Global ELF Observation Network (GEON). As the collection window of lightning discharges in TCs, we defined (i) the inner core as the region within the 100 km (200 km) distance from the TC center for normal (large) TCs, (ii) the rainband as the region of 100-500 km (200-1000 km) from the center for normal (large) TCs. Using ELF waveform data, we estimated the peak current (Ip), charge moment change (Qdl), and charge amount (Q) as the lightning EPs. Ip and Qdl were estimated from ELF data obtained at Syowa, while Q was estimated from ELF data obtained at Kuju. Using above methods and the estimated parameters, we conducted the cross-correlation analyses between the TC intensity development and the lightning EPs for 40 TCs occurred in the western north Pacific in 2013 and 2014.
First, we found that the median value of the lightning EPs in positive cloud-to-ground (+CG) discharges peaked at the generation stage in the 29 TCs. When multiple cumulonimbus are merged in the TC region, the cloud top of these cumulonimbus reaches near the tropopause, and the upper clouds will horizontally spread. Then +CG with long discharge length occur from the upper positive charge region overhanging or the developing stratiform region. Second, we found that total value and median value of the EPs of -CGs peaked during the development stage in the 11 super TCs (very strong typhoons and violent typhoons) out of the 12 super TCs analyzed. This is probably caused by the updraft intensification in the eyewall which tends to reduce the electrical breakdown voltage and transfer the negative charge to upper layer. As the EPs of -CG discharges during the development stage in the super TCs peaked 1-2 days before the TC intensity maximum, the EPs of -CG discharges as well as lightning occurrence number can be a good predictor of the TC intensity development.