Showing papers by "National Waste & Recycling Association published in 1998"

Recent results with an MF radar at McMurdo, Antarctica : Characteristics and variability of motions near 12-hour period in the mesosphere

Abstract: We present an analysis of the first wind measurements obtained with an MF (medium frequency) radar installed at McMurdo Station, Antarctica in January 1996. The largest amplitude motions are the quasi-12-hr motions, with additional periodicities at 24 hr, ∼10 hr and 2 to 10 days. The quasi-12-hr motions occur at discrete periods distinct from 12 hr and exhibit pronounced amplitude and vertical wavenumber modulations at planetary wave periodicities. During the months analyzed in this report (mid-January through April 1996) the 12-hr wave is by far the dominant motion the mesosphere. The source of this wave is unknown, but our results provide additional support for the suggestion that such motions arise through nonlinear interactions involving the migrating semidiurnal tide and low-frequency planetary wave motions.

Kelvin twist waves in the transition to turbulence

Abstract: We present evidence for Kelvin twist waves on vortex tubes in a numerical simulation of the transition to turbulence in a breaking internal gravity wave. Specifically, m = 0, m = 1, and m = 2 twist waves are found and are compared to analytic versions of the waves. The observed twist waves are of a sufficiently large amplitude to break up the vortex tubes on which they reside, with the m = 0 waves fragmenting the vortex tubes along their length and the m = 2 waves unraveling the vortex tubes into pairs of helical tubes. Under the influence of these waves, the flow evolves from an organized collection of horseshoe vortices to a disorganized collection of vortex fragments.