A collaborative study on temperature diurnal tide in the midlatitude mesopause region (411N, 1051W) with Na lidar and TIMED/SABER observations Tao Yuan a,n , Chiao-Yao She a , David Krueger a , Steven C. Reising a , Xiaoli Zhang b , Jeffrey M. Forbes b a Utah State University, Logan, UT 84322-4415, USA b University of Colorado, Boulder, CO 80309-0429, USA article info Article history: Received 15 July 2009 Received in revised form 29 January 2010 Accepted 6 February 2010 Available online 11 February 2010 Keywords: Tide Mesopause Lidar abstract The na lidar-observed temperature diurnal tidal perturbations, based on full-diurnal-cycle observations from 2002 to 2008, are compared with tidal wave measurements by the TIMED/SABER instrument to elucidate the nature of diurnal tidal-period perturbations observed locally. The diurnal amplitude and phase profiles deduced by the two instruments are in very good agreement most of the year. However, the lidar-observed diurnal amplitudes during winter months and early spring are considerably larger than SABER observations, leading to the existence of a significant amplitude maximum of 12 K near 90 km in February and a different seasonal structure of temperature diurnal amplitude from the two instruments. The lidar-observed diurnal phase shows propagating wave characteristics during equinoctial months, but exhibit ‘‘evanescent wave’’ behavior in winter months, whereas SABER diurnal tidal phase exhibits propagating diurnal tidal character all year long with small seasonal variation. This anomalous tidal characteristic from the lidar observations repeats almost every winter. The exact mechanism behind this tidal feature is not fully understood, therefore further investigation and more experimental observations are necessary. & 2010 Elsevier Ltd. All rights reserved. 1. Introduction Solar thermal tidal waves are global scale waves that are harmonics of a solar day, consistently modulating the MLT (Mesosphere and Lower Thermosphere) region of the atmosphere with considerable amplitudes, and are one of the most important dynamic effects within the middle and upper atmosphere. Among them, the migrating tides, which are mostly generated due to solar energy absorption by water vapor in the troposphere and ozone in the stratosphere and, therefore, synchronized with the relative motion of sun, have been known as the dominant tidal component within most parts of the MLT region (Chapman and Lindzen, 1970, Forbes and Garrett, 1978). Its seasonal variations within this region are largely controlled by the combination of the variation in solar heating and zonal mean winds (McLandress, 2002). Hagan (1996) pointed out that the seasonal variations of the phase difference between IR (infrared by water vapor within troposphere) and UV (ultraviolet by ozone within stratosphere) forcing could also impact the seasonal change of tidal wave amplitudes. The nonmigrating (not sun synchronous) tides were also thought to be an important contributor to tidal variability in the MLT region (Forbes and Garrett, 1979; Kato, 1980; Forbes, 1984, 1995; Volland, 1988; Hagan, 2000). The invaluable satellite observations during the past decade (Talaat and Lieberman, 1999; Oberheide et al., 2006; Wu et al., 2008; Forbes and Wu, 2006; Forbes et al., 2008), provide signatures of nonmigrating tides, resulting in their intensive investigation giving insight to tidal wave modulations of the mean atmosphere. However, the tidal forcing for nonmigrating tides is complex. The latent heat released due to rain drop formation in the troposphere is long- known to be one major nonmigrating tidal source (Lindzen, 1978; Hong and Wang, 1980; Forbes et al., 1997; Hagan et al., 1997; Hagan and Forbes, 2002). In addition, nonlinear interactions of migrating tidal waves with global scale planetary waves (Miya- hara and Miyoshi, 1997; Hagan and Roble, 2001; Mclandress, 2001; Mayr et al., 2003; Lieberman et al., 2004) and with gravity waves (Mclandress and Ward, 1994; Walterscheid, 1981; Mayr et al., 2001) can also excite significant nonmigrating tidal components. From a single ground-based station (Tsuda et al., 1988; Vincent et al., 1989; Manson et al., 1989; Avery et al., 1989; Franke and Thorsen, 1993), one may easily observe local oscillations of atmospheric variables at sub-harmonics of the diurnal frequency but is unable to identify whether these oscillations are global ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jastp Journal of Atmospheric and Solar-Terrestrial Physics 1364-6826/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2010.02.007 n Corresponding author. Tel.: + 1 970 491 5646. E-mail address: titus@lamar.colostate.edu (T. Yuan). Journal of Atmospheric and Solar-Terrestrial Physics 72 (2010) 541–549