Concurrent OH imager and sodium temperature/wind lidar observation of localized ripples over northern Colorado

Abstract

[1] On 3 and 5 September 2002 the OH all-sky imager at Platteville, Colorado (40.2°N, 104.7°W), observed small-scale, wavelike patterns (known as ripples), with horizontal wavelengths of $9 km and $7 km and lifetimes of $9 min and $15 min, respectively. The Colorado State University sodium lidar at nearby Fort Collins, Colorado (40.6°N, 105°W), also made concurrent observations of temperature and zonal and meridional winds, which allowed us to determine the nature of the ripples observed. Our observations suggest that the 3 September ripple was induced by a convective instability located at 87.5 km and the 5 September ripple was induced by a dynamic instability at 88.5 km. The ripples clearly advected as packets with the background wind. Lidar measurements also allowed us to relate the directions of wind shear to the phase front alignments of both the ripples and the nearby short-period atmospheric gravity waves. These spatial relationships provided a meaningful comparison with previously observed ripples as well as with current theoretical models. Using the 16-hour continuous lidar data set for each case, we deduced that long-period waves created an unusually large temperature perturbation at the ripple times on 3 September and an unusually large wind shear perturbation on 5 September. These perturbations prepared the background atmosphere to be near the verge of local instability, but, as revealed again by lidar observation, it was the superposition of smaller-scale perturbations at the time of the ripples that helped to actually reach the conditions required for instability and generation of the ripples.

Variability of gravity wave occurrence frequency and propagation direction in the upper mesosphere observed by the OH imager in Northern Colorado

“…There were often 2 or more visible band structures present, we counted them separately. We also noted that in winter smaller scale features known as ripples occurred more frequently than those in summer; since these typically last for less than 10 min and are signature of atmopheric instability (Hecht, 2004;Li et al, 2005), we did not include them in the statistics. To determine the interannual variability of gravity wave propagation direction, we presented the seasonal plots for all the years separately.…”

Seasonal variation of mesopause region wind shears, convective and dynamic instabilities above Fort Collins, CO: A statistical study

“…Statistical study of convective and dynamic instabilities in the MLT has been rare. To our knowledge, there are only four papers in the literature at this point: three by the University of Illinois (UI) group (Gardner et al, 2002;Zhao et al, 2003;Li et al, 2005c) using data collected at the Starfire Optical Range (SOR), near Albuquerque, NM (351N, 106.51W), and those collected from Maui mesosphere and lower thermosphere (Maui MALT), over Maui Hawaii (20.71N, 156.31W) and one by the Colorado State University (CSU) group (Sherman et al, 2003) using data collected at the Fort Collins facility, Fort Collins, CO (411N, 1051W). Though with similar objectives, the measurement resolutions with which these studies were made are quite different.…”

Investigation of a mesospheric gravity wave ducting event using coordinated sodium lidar and Mesospheric Temperature Mapper measurements at ALOMAR, Norway (69°N)

“…These include estimates of MLT GW momentum fluxes employing various techniques [e.g., Vincent and Reid, 1983;Fritts and Vincent, 1987;Reid and Vincent, 1987;Reid et al, 1988;Meyer et al, 1989;Tsuda et al, 1990;Wang and Fritts, 1990;Hitchman et al, 1992;Murphy and Vincent, 1993;Nakamura et al, 1993;Swenson et al, 1999;Gavrilov et al, 2000;Espy et al, 2004Espy et al, , 2006Suzuki et al, 2007;Antonita et al, 2008;Fritts et al, 2010Fritts et al, , 2012. Other studies yielded direct evidence for local instabilities suggesting GW "breaking," dissipation, and energy and momentum deposition [e.g., Swenson and Mende, 1994;Hecht et al, 1997;Yamada et al, 2001;Xu et al, 2006;Li et al, 2005Li et al, , 2007. Evidence of GW ducting behavior in the MLT has also been obtained [e.g., Isler et al, 1997;Walterscheid et al, 1999;Simkhada et al, 2009], including large-amplitude events now recognized as mesospheric bores [Taylor et al, 1995a;Dewan et al, 1998;Dewan and Picard, 2001;Medeiros et al, 2001Medeiros et al, , 2005Smith et al, 2003Smith et al, , 2005Smith et al, , 2006She et al, 2004;Fechine et al, 2005;Nielsen et al, 2006;Stockwell et al, 2...…”