Global distribution and interannual variations of mesospheric and lower thermospheric neutral wind diurnal tide: 1. Migrating tide

Abstract

[1] Using the TIMED Doppler interferometer (TIDI) mesospheric and lower thermospheric neutral-wind multiyear data set (2002)(2003)(2004)(2005)(2006)(2007) and NCAR TIME General Circulation Models (GCM) 1.2 annual run results (2002)(2003)(2004)(2005) at the TIDI sampling points, we study the migrating diurnal tide's global distribution, interannual, and seasonal variations in connection with the mean zonal wind interannual variations. A strong quasi-biennial oscillation (QBO) effect on the diurnal tide was observed in the TIDI data and reproduced to a lesser degree in the TIME-GCM run. The migrating diurnal tide amplitude is larger during the eastward phase of the stratospheric QBO and weaker during the westward phase. Westward mesospheric equatorial mean zonal winds appeared during the eastward phase of the stratospheric QBO (in 2002, 2004, and 2006). The strongest QBO effect on both the migrating diurnal tide and mean zonal winds was observed during the March equinox. The stronger tides may be related to the weaker gravity wave filtering in the stratosphere during the eastward phase stratospheric QBO. The TIDI data also exhibit large interhemispheric asymmetry. The westward mean zonal winds in the mesosphere appeared to be associated with the enhanced diurnal tide. The TIME-GCM 1.2 diurnal tide amplitudes are in general smaller than those observed by the TIDI instrument. Limited vertical spatial resolution for the TIME-CGM 1.2 is suggested as the cause. Future improvements are expected with a higher spatial resolution in the model.

On the variability of the seasonal scale oscillations over Cachoeira Paulista (22.7°S, 45°W), Brazil

“…The present diurnal tide amplitude shows semiannual variability with maxima during equinoxes ( Figure 5). The amplitude peak observed during the March/April equinox is significantly higher than the spring maximum, which supports the findings of a number of past investigations (Vincent et al 1998;Wu et al 2008;Xu et al 2009). …”

“…It should be mentioned that the diurnal tide also shows amplitude maxima ( Figure 5) during March/April in the years 2002, 2004, 2006, and 2008, indicating a quasi-biennial modulation. Such quasi-biennial enhancement of the diurnal tide amplitude was also reported in the available literature (Vincent et al 1998;Wu et al 2008). Therefore, the diurnal tide as well as gravity waves are supposed to be responsible for such quasi-biennial modulation of the MAO in the present case since these waves are the dominant driver for large scale oscillations in the atmosphere.…”

The roles of vertical advection and eddy diffusion in the equatorial mesospheric semi-annual oscillation (MSAO)

“…Smith et al (2010) have also successfully simulated the significant diurnal tidal effects in the O observations made with SABER. Studies by Wu et al (2008) and John and Kumar (2011) provide further insight into the details of the tides. Again, when comparing observations made at different local times the tidal effect must be considered.…”

“…Diurnal tides, eddy diffusion and the prevailing background vertical winds make up the dynamic components included in the 1-D model. More detailed examples of such combined photochemical and dynamical model comparisons with observations are those of Marsh et al (2003), Smith and Marsh (2005) based on the ROSE model, Wu et al (2008) with the TIME-GCM model, and Dikty et al (2010) using the HAMMONIA model.…”

Global Dynamics of the MLT

“…A periodicity that appears in investigations of the interannual variability of the DW1 tide is a biennial or quasi-biennial oscillation (QBO) (Burrage et al 1995;Wu et al 2008;Xu et al 2009b). The amplitude of the DW1 tide varies in alternate years and appears to be related to the QBO in the zonal wind in the lower stratosphere.…”