Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. (2012)

We discuss the role of atmospheric gravity waves in modulating cloud radiative and dynamical properties over the southeast Pacific. Satellite imagery and satellite-retrieved cloud properties during October 2008 illustrate three distinct episodes of horizontal propagation of gravity wave trains across the large-scale stratocumulus (Sc) cloud deck capping the local marine boundary layer. In one period, 7–9 Octo-ber 2008, the waves modulated cloud-top-height by up to 400 m peak-to-trough, propagating perpendicular to the synoptic boundary layer flow with phase speed 15.3 m s−1, period ∼1 h and horizontal wavelength 55 km. The gravity waves were observed to be non-dispersive. These waves were first evident in the cloud deck near 30◦S, 85◦Wduring a 24 h period beginning at midday on 7 October 2008, and prop-agated northeastward toward the Peruvian coast for the following 48 h. During this time they induced both reversible and non-reversible changes in cloud-radiative and cloud-dynamic properties, such that areas of clear sky developed in the troughs of passing wave-fronts. These pockets of open cells persisted long after the passage of the gravity waves, advecting northwestward with the background wind. Using th