Global observations and modeling of nonmigrating diurnal tides generated by tide-planetary wave interactions

Abstract

Advective processes that couple planetary waves with tides have long been proposed as sources of nonmigrating diurnal tides. This paper reports observations of short-term variability in global observations of nonmigrating tides predicted to arise from the interaction of the migrating diurnal tide (DW1) with a quasi-stationary planetary wave number one (PW1). PW1 and tidal definitions are extracted from satellite temperatures and high-altitude meteorological analyses. During winter months, the evolution of westward traveling diurnal tides with zonal wave number 2 (DW2) generally tracks that of strong-amplitude stratospheric PW1. DW1 and PW1 spectra are used to compute nonlinear tidal forcing terms arising from advection. We then examine the response of a primitive equation model to the observation-based nonlinear forcing. The model experiments indicate that meridional advection of PW1 zonal momentum by DW1 is a significant source of lower thermospheric DW2. Modeled DW2 amplitudes are very consistent with observed DW2 amplitudes when stratospheric PW1 penetrates to equatorial latitudes. The model experiments also indicate that the interaction can imprint short-term variability associated with wintertime PW1 upon DW2 in the summer hemisphere and the lower thermosphere.