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 $m^2{s}^{-2}$ 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 $s^{-1}{\text{day}}^{-1}$ 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.