Exploring Wave‐Wave Interactions in a General Circulation Model

Abstract

AbstractNonlinear interactions involving Kelvin waves with (periods, zonal wave numbers) = (3.7d, s =− 1) (UFKW1) and = (2.4d, s =− 1) (UFKW2) and s = 0 and s = 1 quasi 9 day waves (Q9DW) with diurnal tides DW1, DW2, DW3, DE2, and DE3 are explored within a National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) simulation driven at its ∼30 km lower boundary by interpolated 3‐hourly output from Modern‐Era Retrospective Analysis for Research and Applications (MERRA). The existence of nonlinear wave‐wave interactions between the above primary waves is determined by the presence of secondary waves (SWs) with frequencies and zonal wave numbers that are the sums and differences of those of the primary (interacting) waves. Focus is on 10–21 April 2009, when the nontidal dynamics in the mesosphere‐lower thermosphere (MLT) region is dominated by UFKW and when identification of SW is robust. Fifteen SWs are identified in all. An interesting triad is identified involving UFKW1, DE3, and a secondary UFKW4 = (1.5d, s =− 2): The UFKW1‐DE3 interaction produces UFKW4, the UFKW4‐DE3 interaction produces UFKW1, and the UFKW1 interaction with UFKW4 produces DE3. At 120 km the dynamic range of the reconstructed latitude‐longitude zonal wind field due to all of the SW is roughly half that of the primary waves, which produced them. This suggests that nonlinear wave‐wave interactions could significantly modify the way that the lower atmosphere couples with the ionosphere.