Two‐Day Wave Modulation of Gravity Wave Momentum Fluxes Observed Over South America

Abstract Planetary wave (PW) modulation of gravity wave (GW) dissipation has long been proposed as a source of longitudinal variability in the mesosphere and lower thermosphere. However, direct measurements of GW drag are rare. We identify 2‐day wave variations in GW momentum fluxes measured by the Southern Argentina Agile Meteor Radar (SAAMER) in Rio Grande, Tierra del Fuego, and a meteor radar at the Andes Lidar Observatory (ALO) in Cerro Pachon, Chile. Typical amplitudes range from 1 to 5 and are generally, though not always, out of phase with the horizontal wind consistent with wind‐induced dissipation of upward‐propagating GWs. The 2‐day wave‐modulated GW drag ranges between 20 and 140 m and can amplify, damp, and alter the phase of the 2‐day wave. These multiple relationships between the GW drag and the 2‐day wave suggest that in situ processes may influence GW drag, including secondary GWs excited from the breakdown of primary GW packets.