Resumen
The meteorological control of gravity wave activity through ?ltering by winds and generation by spontaneous adjustment of unbalanced ?ows is investigated. This investigation is based on a new analysis of Rayleigh LiDAR measurements of gravity wave activity in the upper stratosphere-lower mesosphere (USLM,40?50km)on 152 nights at Poker Flat Research Range (PFRR), Chatanika, Alaska (65? N, 147? W), over 13 years between 1998 and 2014. The LiDAR measurements resolve inertia-gravity waves with observed periods between 1 h and 4 h and vertical wavelengths between 2 km and 10 km. The meteorological conditions are de?ned by reanalysis data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA). The gravity wave activity shows large night-to-night variability, but a clear annual cycle with a maximum in winter,and systematic interannual variability associated with stratospheric sudden warming events. The USLM gravity wave activity is correlated with the MERRA winds and is controlled by the winds in the lower stratosphere through ?ltering by critical layer ?ltering. The USLM gravity wave activity is also correlated with MERRA unbalanced ?ow as characterized by the residual of the nonlinear balance equation. This correlation with unbalanced ?ow only appears when the wind conditions are taken into account, indicating that wind ?ltering is the primary control of the gravity wave activity.