Short-term variability in the migrating diurnal tide caused by interactions with the quasi 2 day wave

Abstract

[1] The migrating diurnal tide is one of the dominant dynamical features in the low latitudes of the Earth's mesosphere and lower thermosphere (MLT) region, representing the atmospheric response to the largest component of solar forcing. Ground-based observations of the tide have resolved short-term variations attributed to nonlinear interactions between the tide and planetary waves that are also in the region. Using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM), we simulate a quasi 2 day wave (QTDW) event under late-January conditions. In this case, sideband sum and difference child waves are resolved, indicating that a nonlinear interaction is occurring between the QTDW and the tide. The migrating diurnal tide in the MLT displays local amplitude decreases of 20-40%, as well as a shortening of vertical wavelength by roughly 4 km. Examining the physical mechanisms driving the interaction, nonlinear advection is found to result in amplification of the tide in some regions and damping in others, manifesting as increased smoothing of the tidal structure when the QTDW is present in the MLT. Additionally, the QTDW also enhances the easterly summer mean wind jet that can also account for changes in tidal amplitude and vertical wavelength. We find that QTDW-induced background atmosphere changes in TIME-GCM can drive tidal variability at levels greater than nonlinear advection, a possibility not previously considered.Citation: Chang, L. C., S. E. Palo, and H.-L. Liu (2011), Short-term variability in the migrating diurnal tide caused by interactions with the quasi 2 day wave,

Influence of the sudden stratospheric warming on quasi-2-day waves

“…The EP flux vectors in all the experimental runs show that the W3 propagates mainly southward from the northern hemispheric wave source region at lower altitudes and then propagates upward after reaching the Southern Hemisphere. These propagation features agree well with previous model simulations (Chang et al, 2011;Yue et al, 2012). The meridional and vertical components of the W3 EP flux (EPY and EPZ) are shown in Fig.…”

“…These speculations are further investigated by cal- culating the nonlinear advection tendency between W3 and SPW1. The nonlinear advection tendency terms in the momentum equations, which have been utilized by Chang et al (2011) in studying the nonlinear coupling between QTDW and tides, are of the following form:…”

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Global climatology of 2-, 5-, 10-and 16-day waves has been established by satellite measurements, e.g., Gu et al (2013), Moudden and Forbes (2014) for 2-day waves; Wu et al (1994) If the amplitude of the planetary waves is sufficiently large in the dynamo region, they will drive ionospheric currents and affect geomagnetic perturbations on the ground. Even if the planetary waves dissipate before they reach the dynamo region, they can still interact with tides and mean flow in the middle atmosphere, which will affect the upward propagation of tides to the dynamo region, and thus affect the ionospheric dynamo (e.g., Liu et al 2010;Chang et al 2011). Either case, the presence of the planetary waves would lead to oscillations of Sq and EEJ with periods similar to those of the waves.…”

Global Dynamics of the MLT

“…There are a large number of observations of tidal temperature and horizontal winds; in additions, observations show the impact of the tide on trace species (Marsh and Russell 2000;Smith et al 2010a) and interactions with other waves (Chang et al 2011). Figure 8 shows the temperature amplitude of the average diurnal tide near the March equinox derived from SABER observations.…”