Atmospheric gravity waves (GWs) are known to play key roles in a broad range of dynamical processes extending from Earth’s surface well into the Mesosphere and Lower Thermosphere (MLT) region (~80-100 km) and potentially to higher altitudes. Excited primarily in the lower atmosphere by strong convection, topography, and wind shears, these waves attain large amplitudes as they propagate upwards transporting copious amounts of energy and momentum. Remote sensing optical measurements of the naturally occurring airglow emissions provide an effective method for studying wave occurrence and properties in the MLT region, particularly small-scale, short period (<1 hour) waves which can propagate rapidly (a few hours) from their lower atmospheric sources into the MLT. These events typically exhibit horizontal wavelengths of only a few tens of km yet they can strongly perturb the MLT region due to the onset of wave instability and dissipation effects. In this study we summarize and compare recent measurements of short-period gravity waves observed at equatorial, mid- and polar latitudes focusing on their seasonal characteristics. We also investigate the potential for larger-scale waves, occasionally evident in these MLT image data, to propagate to higher altitudes well into the lower thermosphere and ionosphere, and compare their properties at different latitudes (where known). These results provide new insight into the “global” occurrence, variability and penetration of gravity waves into the upper reaches of the neutral atmosphere and ionosphere.

Sprites, halos, ELVEs and jets are all prominent members of an extraordinary family of Transient Luminous Events (TLEs) that were discovered and named in the 1990’s. Sprites are large vertically structured transient events (few 10s of ms) that can extend from the mesosphere down into the stratosphere (~85-40 km) and are sometimes capped, and briefly preceded (few ms), by a fainter horizontal disk-like halo. Sprites are almost exclusively generated by large positive cloud to ground (CG) lightning discharges whereas halos have been observed by satellite in association with both negative and positive lightning strokes. These types of TLEs are both caused by quasi-static electric fields that excite molecular nitrogen at mesospheric heights to produce N2 first positive band emissions. In contrast, an ELVE is a large (typically 300 km diameter) horizontal donut-shaped flash of light produced by the absorption of an electromagnetic pulse radiated by a powerful lightning discharge as it intersects the base of the nighttime ionosphere (~90-100 km). ELVEs are highly transient (few micro seconds) and are associated with both negative and positive lightning discharges. Jets are even more enigmatic: they originate in the cloud tops and propagate rapidly upwards to the lower ionosphere, branching on the way. Although jets have been imaged on a number of occasions their possible association with lightning events remains unclear. In this talk I will briefly summarize current knowledge on TLEs utilizing video and new high speed image data to exemplify their properties. Recent measurements of TLEs at visible and near infrared wavelengths, in association with both positive and negative lightning will be presented. Possible association of TLEs with powerful terrestrial gamma ray flashes (TGFs) will also be discussed.