Comparative effects of migrating solar sources on tidal signatures in the middle and upper atmosphere

Abstract

A steady state two-dimensional linearized model that extends from the ground into the thermosphere and captures the salient features of migrating diurnal and semidiurnal tidal components is used to investigate the comparative importance of the principal sources of these waves. The results, which have previously gone unreported in the literature, demonstrate the nonnegligible effects of atmospheric absorption of solar radiation at infrared (in the troposphere) and ultraviolet (in the stratosphere) wavelengths on mesospheric and lower thermospheric semidiurnal and diurnal tidal fields, respectively. In addition, latent heat release associated with cloudiness or rainfall in the troposphere is shown to be another plausible source of semidiurnal variability in the upper atmosphere. The important effects of these sources on the dynamics of the mesosphere and lower thermosphere emphasize the need to include realistic parameterizations of migrating tides at the lower boundaries of middle and upper atmospheric general circulation models. The results of this investigation also suggest that updated parameterizations of tropospheric tidal forcing are needed to further current understanding of tidal variability in the upper atmosphere. IntroductionMigrating solar tides are global-scale atmospheric waves which propagate westward with the apparent motion of the Sun at periods that are harmonics of a solar day. These waves are forced by absorption of solar radiation throughout the Earth's atmosphere. Ground-based and satellite-borne wind and temperature measurements [e.g., Avery et al., 1989; Manson et al., 1989; Vincent et al., 1989; Clark and $alah, 1991; Morton et al., 1993; Fritts and Islet, 1994; Hays et al., 1993; McLandress et al., 1994] reveal that some of the strongest tidal signatures are found in the mesosphere and lower thermosphere (MLT, -,•80-120 km). The uninitiated find these MLT tidal signatures surprising. They expect small or negligible tides in the MLT, because the region spans the coldest place in the atmosphere where comparatively little solar radiation is absorbed [e.g., Hagan, 1995], so in situ thermotidal forcing is either absent or weak. However, even the earliest models of atmospheric tides established that these strong MLT signatures are manifestations of tidal components forced below the region, which grow in amplitude while propagating upward as neutral atmospheric density decreases [e.g., Chapman and Lindzen, 1970; Forbes and Garrett, 1979; Walterscheid et al., 1980; Aso et al., 1981]. Subsequent to the earliest theoretical and numerical investigations of atmospheric tides cited above, increasing complexities were systematically introduced to two-dimensional linearized steady-state numerical models. These improvements quantified the important effects of mean winds and horizontal temperature gradients [Lindzen and Hong, 1974], viscous dissipation [e.g., Walterscheid et al., 1980; Aso et al., 1981], and the turbulent diffusion of momentum [Vial, 1986; Forbes and Hagan, 1988] as well as heat [Forbes, ...

Tidal signatures in temperature data from CRISTA 1 mission

“…Instead, the temperature fields themselves are more useful since the temperature response in this region is a combination of the propagating mode associated with water vapor heating in the troposphere and trapped modes associated with local ozone heating in the stratosphere which are out of phase with the propagating mode [Hagan, 1996]. Above this height, where the adiabatic heating associated with the tidal motions dominates the tidal temperature signatures, the effects of the background profile should be taken into account.…”

Local heating/cooling of the mesosphere due to gravity wave and tidal coupling

“…GSWM also accounts for the effects of ion drag, molecular and eddy viscosity and conductivity, radiative damping, and gravity wave drag on the diurnal tide. The reader is referred to [Hagan, 1996] and [ [Liu, 1996] and ].…”

“…Molecular diffusion in the horizontal direction is also included in the equation, because when the flow becomes unstable, large wavenumber components may be generated in the $olov'eva [1992a, 1992b] is used in the mesopause region. GSWM migrating tidal forcing is attributable to the absorption of solar radiation throughout the atmosphere and is parameterized in GSWM [Hagan, 1996]. GSWM also accounts for the effects of ion drag, molecular and eddy viscosity and conductivity, radiative damping, and gravity wave drag on the diurnal tide.…”

Seasonal variations of the nighttime O(1S) and OH airglow emission rates at mid‐to‐high latitudes in the context of the large‐scale circulation

“…The model is set for a horizontal resolution of 5°Â 5°latitude/longitude, and a vertical resolution of 2 grid points per scale height, which for the altitude range of 80-100 km is of the order of 5 km. Diurnal and semidiurnal tides from the Global Scale Wave Model (GSWM) [Hagan, 1996] are specified at the lower boundary. The gravity wave effects in the TIME-GCM are parameterized according to the linear saturation theory proposed by Lindzen [1981].…”