AGU: Geophysical Research Letters

 

Editors' Highlight

Upper atmosphere lightning: Studying the behavior of halos

Most lightning occurs between clouds and the ground when negative or positive charge in the cloud reequilibrates with opposite charge on the ground (called negative/positive cloud-to-ground lightning), forming a bolt of energy. However, lightning can also propagate upward from the cloud, forming transient luminous events (TLEs). To determine patterns in TLEs, Frey et al. (2007) analyzed data over Central America from the Imager for Sprites and Upper Atmospheric Lightning (ISUAL) aboard Taiwan's FORMOSAT 2 spacecraft. The authors specifically focused on halos, a class of TLE consisting of brief, diffuse flashes of light with diameters less then 100 km at about 70–90 km in altitude, which are conventionally thought to be residuals of positive cloud-to-ground lightning. Instead, results showed that all haloes were created by negative cloud-to-ground lightning that occurred almost exclusively over the open water; only three out of 31 observed events happened over land. The authors concluded that the Central American region seems to be a location that favors the generation of halos by negative cloud-to-ground lightning.

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