Dust in the Planetary Boundary Layers of Mars and Earth
Mesospheric Atmospheric Gravity Wave Properties Derived From Rayleigh-Scatter Lidar Observations Above Logan, Utah
Approximately 900 nights of observations with a Rayleigh-scatter lidar at Utah State University's Atmospheric Lidar Observatory (41.7°N, 111.8°W), spanning the 11-year period from late 1993 through 2004, have been reduced to derive nighttime temperature and relative density profiles between 45 and 90 km, i.e., over the entire mesosphere. Of these, 150 profiles that extend to 90 km or above were used in this work, which is based mainly on relative density data with 3-km altitude resolution and 1-hour temporal resolution. This is, we believe, the first comprehensive study of monochromatic gravity waves using Rayleigh-scatter lidar observations extending through the entire mesosphere at mid-latitudes. The variations of relative density perturbations were used to identify the presence of monochromatic gravity waves. These waves have a clear downward phase progression (i.e. upward energy propagation) with the most prevalent vertical phase velocity (cz) of 0.6 ms-1 (2.2 km/hr). The most dominant vertical wavelength (λz) is 12 km. The values of the Brunt-Väisälä frequency, N(rad/sec), the maximum gravity wave frequency, were calculated by using seasonally averaged nightly temperature and temperature derivative profiles. Using the gravity wave dispersion relations and the values of cz, λz, and N, other gravity wave parameters such as wave period (τ), horizontal wavelength (λx), horizontal phase velocity (cx), and horizontal distance to the source region (X) were calculated. The most prevalent values of τ, λx, cx and are 6 hours, 550 km, and 35 ms-1 (125 km/hr), respectively. The most dominant values of X for 45-km and 90-km altitudes are 2500 km and 5000 km, respectively, which suggest that these large-scale gravity waves are generated from a very distant and very extended source region. There appears to be a seasonal dependence in cz, τ, λx, and X but not in λx and cx. The vertical phase velocities maximized in summer whereas the apparent periods, horizontal wavelengths, and horizontal distance to the source region maximized in winter. The magnitude of the relative density perturbations on average grew with altitude with an e- folding distance of 20 km, which is larger than the 2H = 14 km expected for undisturbed gravity wave propagation, where H is the scale height. This means that the amplitude of the observed fluctuations increases less rapidly with altitude than for the undisturbed situation, which also implies that significant gravity- wave energy dissipation occurs in this region.