Into the Blue

Most lightning flashes occur in the convective heart of thunderstorms. Every so often, however, flashes may in anvil or stratiform regions where there is little-to-no rain at the surface. In some cases, lightning can strike as "bolts from the blue" tens of kilometers from an active thunderstorm core. Here, we use the meteorological instrumentation on TRMM to quantify how often lightning can be found outside of convection.

Lightning is a natural hazard that is often associated with convective processes. Strong updrafts within the thunderstorm’s core provide a venue for different species of ice to collide and transfer electrons in the process. They also sort ice particles by mass, leading to charge separation and lightning production. Lightning can occur outside of the convective core, however. This study uses Tropical Rainfall Measuring Mission (TRMM) observations to identify lightning flashes in anvil and stratiform regions of thunderstorms across the tropics.

The Lightning Imaging Sensor (LIS) measures lightning by detecting changes in the optical scene at 777 nm that are associated with lightning. Each optical flash is associated with a TRMM Microwave Imager (TMI) and Precipitation Radar (PR) pixel and Radar Precipitation Feature (RPF) based on the reported location of the weighted flash center. We use this approach to distinguish between convective, anvil, and stratiform flashes and to discuss the properties of the parent thunderstorm.