The character of polar tidal signatures in the extended Canadian Middle Atmosphere Model

Abstract

The characteristics of the diurnal, semidiurnal, and terdiurnal tides (zonal wave numbers À5 to +5 in temperature and zonal wind) in the polar mesosphere and lower thermosphere region as simulated by the extended Canadian Middle Atmosphere Model are examined. The most significant diurnal, semidiurnal, and terdiurnal tides in the polar regions are Ds0, Dw1, and De1; Sw3, Sw2, Sw1, Ss0, Se1, and Se2; and Tw3, Ts0, and Tw1, respectively, and their latitudinal structures, seasonal variations, and hemispheric asymmetries noted. Of these components, Ds0, Tw1, Ts0, and Tw3 exhibit a seasonally symmetric variation with both hemispheres strengthening simultaneously. On the other hand, Dw1 strengthens asymmetrically so that when one hemisphere is strong, the other is weak. The remainder show no seasonal tendency but vacillate on shorter than seasonal time scales in a symmetric or antisymmetric manner at different times of the year. Global-scale correlations of the amplitudes of the migrating tides Dw1/Sw2 and the stationary planetary wave 1 and the assumed "child" nonmigrating tides are also examined. The results indicate that the correlations are highly time scale-dependent and the significant correlations seen with the original time series are mainly due to longer-term variations (>18 days). There are no consistent global correlations associated with the short-term variations (<18 days) among these waves.

Climatology of the diurnal tides from eCMAM30 (1979 to 2010) and its comparison with SABER

“…The magnitude of the two mid-latitude maxima is similar in eCMAM30, while the NH mid-latitude maximum tends to be stronger than the SH counterpart in SABER. Moreover, Dw1 exhibits an annual variation in the Polar Regions in eCMAM30, which has also been reported in Du et al (2014) from the free-running eCMAM.…”

“…As illustrated in Figure 2, 11 diurnal tidal components are included in the spectrum, but in practice, relatively few tidal components (such as Dw1, De3, Dw2, and Ds0) are found to dominate. These diurnal tidal components have also been identified in previous analyses of satellite and model data (Talaat and Lieberman 1999;Forbes et al 2003a, b;Forbes and Wu 2006;Zhang et al 2006;Huang and Reber 2004;Manson et al 2004;Du 2008;Du et al 2014) and are now well-accepted diurnal tides of importance in the MLT region.…”

“…The model includes realistic tidal forcing due to radiative heating, convective processes, and latent heat release (Scinocca and McFarlane 2004). These processes have been shown to provide the forcing necessary to generate the migrating and nonmigrating tides in the free-running eCMAM (McLandress 1998(McLandress , 2002aWard et al 2005;Du et al 2007;Du and Ward 2010;Du et al 2014).…”

On the Roles of Advection and Solar Heating in Seasonal Variation of the Migrating Diurnal Tide in the Stratosphere, Mesosphere, and Lower Thermosphere

“…These physical parameterizations mainly include: modified non-orographic gravity wave drag [44,45], molecular heat diffusion and viscosity, extreme ultraviolet radiation, chemical heating, and ion drag. The extended model has been demonstrated to generate the tidal oscillations reasonably well under the free-running mode [46][47][48].…”

Statistics on Nonmigrating Diurnal Tides Generated by Tide-Planetary Wave Interaction and Their Relationship to Sudden Stratospheric Warming

“…The model includes realistic tidal forcing due to radiative heating, convective processes, and latent heat release [37]. These processes have been shown to provide the forcing necessary to generate the migrating and nonmigrating tides [18,[38][39][40][41].…”