Seasonal variations of semidiurnal tidal perturbations in mesopause region temperature and zonal and meridional winds above Fort Collins, Colorado (40.6°N, 105.1°W)

Abstract

[1] On the basis of Colorado State University (CSU) Na lidar observations over full diurnal cycles from May 2002 to April 2006, a harmonic analysis was performed to extract semidiurnal perturbations in mesopause region temperature and zonal and meridional winds over Fort Collins, Colorado (40.6°N, 105.1°W). The observed monthly results are in good agreement with MF radar tidal climatology for Urbana, Illinois, and with predictions of the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), sampled at the CSU Na lidar coordinates. The observed semidiurnal tidal period perturbation within the mesopause region is found to be dominated by propagating modes in winter and equinoctial months with a combined vertical wavelength varying from 50 km to almost 90 km and by a mode with evanescent behavior and longer vertical wavelength (100-150 km) in summer months, most likely due to dominance of (2, 2) and (2, 3) tidal (Hough) modes. The observed semidiurnal tidal amplitude shows strong seasonal variation, with a large amplitude during the winter months, with a higher growth rate above $85-90 km, and minimal amplitudes during the summer months. Maximum tidal amplitudes over 50 m/s for wind and 12 K for temperature occur during fall equinox. A detailed comparison with HAMMONIA predictions shows excellent agreement in semidiurnal phases. HAMMONIA-predicted semidiurnal amplitudes generally agree well with observations; however, HOMMONIA underestimates temperature amplitudes in some of the nonsummer months as well as zonal wind and meridional wind amplitudes in April and September but overestimates them in February. To reveal the effects of the atmospheric background on vertical propagation of tidal modes and their relative importance in the composite semidiurnal tide during different seasons, we use the lidarobserved monthly mean temperature and zonal wind from the same data set as well as HAMMONIA output to calculate the vertical wave number seasonal variations of the major tidal modes of the migrating semidiurnal tide. This leads to a qualitative understanding of the lidar-observed and HAMMONIA-predicted seasonal variation of the semidiurnal tidal perturbation.

Comment on "Global structure, seasonal and interannual variability of the migrating semidiurnal tide seen in the SABER/TIMED temperatures (2002–2007)" by Pancheva et al. (2009)

“…A significant quantity of high quality ground-based observations at Colorado-USA (40/41 • N, Platteville and Fort Collins) have facilitated this present study (e.g. Yuan et al, 2008) and this Comment, as both temperature and windtides have been successfully observed there with good instruments. The tidal peaks are sufficiently broad in latitude to enable this.…”

Global structure, seasonal and interannual variability of the migrating semidiurnal tide seen in the SABER/TIMED temperatures (2002–2007)

“…Recently on the basis of Na lidar observations over full diurnal cycles from May 2002 to April 2006Yuan et al (2008 investigated the seasonal variations of the semidiurnal tidal characteristics over Fort Collins, Colorado (41 • N, 105 • W) in the altitude range between 80 and 100 km. The comparison with the results from this study for middle latitudes, 40 • N, reveals the follows: (i) the largest tidal amplitudes derived from the lidar and SABER temperatures have average magnitudes of 12 and ∼13 K (see upper right plot of Fig.…”

“…A major advantage of the ground-based methods is their ability to study in detail seasonal, intraseasonal and interannual variability of the tides in the MLT at various geographic points (Bernard, 1981;Avery et al, 1989;Manson et al, 1990Manson et al, , 1999Clark and Salah, 1991;Vincent et al, 1998;Jacobi et al, 1999;Pancheva et al, 2000Pancheva et al, , 2002, as well as their vertical structure including vertical wavelengths and direction of propagation She et al, 2004;Yuan et al, 2008). A disadvantage of the ground-based methods is their inability to distinguish between global and local signatures and to provide only coarse information on spatial (latitudinal and longitudinal) structures of the tides.…”

“…The meteor radar observations revealed also that the winter maximum of the semidiurnal tide is actually the main maximum in the MLT region Manson et al, 2004;). The winter maximum of the semidiurnal tide was documented by the lidar (Yuan et al, 2008) and satellite (Burrage et al, 1995) measurements as well. Observational studies of the semidiurnal tide have revealed a very high degree of variability in tidal characteristics occurring over a range of time scales including short-term (several days), seasonal and long-term (including interannual and solar-cycle) changes.…”

A climatology of the diurnal variations in stratospheric and mesospheric ozone over Bern, Switzerland

“…Beig et al (2012) studied diurnal variations of ozone and temperature in the equatorial mesosphere by analysing data from the HAMMONIA model and the satellite experiment UARS/HALOE. Analysis of the diurnal and semidiurnal tides in the mesosphere and lower thermosphere in simulation data of HAMMONIA shows that many observational results of tides are reproduced by the model (Achatz et al, 2008;Yuan et al, 2008).…”