scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Observations of the Phase-Locked Two day Wave Over the Australian Sector Using
Medium Frequency Radar and Airglow Data
Hecht James 1 , Walterscheid Richard 1 , Gelinas Lynette 1 , Vincent Robert 2 , Reid Iain 2 , Woithe
Jonathan 2
1 2
The Aerospace Corporation, Department of Physics and Mathematical Physics, University of
Adelaide
The quasi two day wave (QTDW), with a nominal mean period just above 50 hours, is a
significant feature of the 80 to 100 km altitude region in both hemispheres. It becomes
particularly prominent in the southern hemisphere summer at mid latitudes where, a short
time after summer solstice, its amplitude rapidly increases and its mean period is found to be
approximately 48 hours, producing an oscillation phase locked in local time. This lasts for a
few weeks. Presented here are observations of the meridional winds and airglow over two
sites in Australia, for four years during the austral summers of 2003 to 2006. We show that
during those times when the large-amplitude phase-locked two-day wave (PL-TDW) is
present the diurnal tide greatly decreases. This is consistent with the Walterscheid and
Vincent (1996) model in which the PL-TDW derives its energy from a parametric excitation
by the diurnal tide. These data also show that the diurnal tide is more suppressed, and the PL-
TDW amplitude is larger, in odd-numbered years, suggesting a biannual effect. The airglow
data indicated that, for the PL-TDW, the winds and temperature are close to out of phase.
When the PL-TDW is present airglow amplitudes can become quite large, a result dependent
on the local time of the PL-TDW maximum. The airglow intensity response was in general
much larger than what would be expected from the airglow temperature response suggesting
that the PL-TDW is causing a significant composition change possibly due to minor
constituent transport.
Walterscheid, R., and R. Vincent (1996), Tidal generation of the phase-locked 2-day wave in
the southern hemisphere summer by wave-wave interactions, J. Geophys. Res., 101(D21),
26567-26576.