P1.3 Applications of Lightning Observations to Tropical Cyclone Intensity Forecasting

The next generation geostationary satellite system starting with GOES-R will include a geostationary lightning mapper (GLM). The GLM will provide nearly continuous times and locations of total lightning with an accuracy of about 10 km over most of the field of view of GOES-east and –west. This coverage will include nearly all of the regions where tropical cyclones occur in the Atlantic and north Eastern Pacific. This lightning data will provide information about the convective structure in tropical cyclones and their environments. Previous studies with ground-based lightning networks have revealed a number of interesting relationships between storm structure and the lightning distribution. Using data from the National Lightning Detection Network (NLDN) Molinari et al. (1999) have shown that the lightning density (strikes per unit area and time) tends to have a bi-modal structure as a function of radius from the storm center, with maxima near the eyewall region and in the rainband region (150300 km radius) and a minimum in between. Their study and more recent analysis with the Long-range Lighting Detection Network (LLDN) (Squires and Businger 2008) indicate that the lightning near the storm center tends to be much more transient than that in the rainband region. Corbosiero and Molinari (2002) showed a strong relationship between the environmental shear and the azimuthal distribution of lightning, with a maximum in strikes on the down shear side of the storm. Using the very simple argument that lightning is favored when the cloud updrafts are stronger (e.g., Black and Hallet 1999) it might be expected that increased lightning activity near the storm center would be correlated with short term intensification. However, previous studies with the NLDN and LLDN data have shown that this relationship is not straightforward, with peaks in lightning density occurring during the intensification, steady state and weakening stages of tropical cyclones. It is possible that the effect of vertical wind shear complicates the relationship with intensity changes. Also, Black and Hallet (1999) showed that the vertical electric fields in tropical cyclones are much weaker than those in continental convection suggesting that lightning outbreaks in the tropical cyclone inner core might be somewhat rare. _________________ * Corresponding author address: Mark DeMaria, NOAA/NESDIS/ORA, CIRA/Colorado State University, W. Laporte Avenue, Foothills Campus, Fort Collins, CO 80523-1375; e-mail: Mark. [email protected] In this study the relationship between lighting density and intensity changes will be investigated for a large sample of Atlantic tropical cyclone cases (20052007) using data from the World Wide Lightning Location Network (WWLLN). To help isolate the influences of vertical shear, the dataset is stratified into lowand high-shear regimes, where the shear is calculated from the NCEP global forecasting system (GFS) analysis fields.