Observation of a mesospheric front in a thermal-doppler duct over King George Island, Antarctica

Abstract

Abstract.A mesospheric front was observed with an allsky airglow imager on the night of 9-10 July 2007 at Ferraz Station (62 • S, 58 • W), located on King George island on the Antarctic Peninsula. The observed wave propagated from southwest to northeast with a well defined wave front and a series of crests behind the main front. The wave parameters were obtained via a 2-D Fourier transform of the imager data providing a horizontal wavelength of 33 km, an observed period of 6 min, and a horizontal phase speed of 92 m s −1 . Simultaneous mesospheric winds were measured with a medium frequency (MF) radar at Rothera Station (68 • S, 68 • W) and temperature profiles were obtained from the SABER instrument on the TIMED satellite. These wind and temperature profiles were used to estimate the propagation environment of the wave event. A wavelet technique was applied to the wind in the plane of wave propagation at the OH emission height spanning three days centered on the front event to define the dominant periodicities. Results revealed a dominance of near-inertial periods, and semi-diurnal and terdiurnal tides suggesting that the ducting structure enabling mesospheric front propagation occurred on large spatial scales. The observed tidal motions were used to reconstruct the winds employing a least-squares method, which were then compared to the observed ducting environment. Results suggest an important contribution of largescale winds to the ducting structure, but with buoyancy frequency variations in the vertical also expected to be important. These results allow us to conclude that the wave front event was supported by a duct including contributions from both winds and temperature.Correspondence to:

Mesospheric front observations by the OH airglow imager carried out at Ferraz Station on King George Island, Antarctic Peninsula, in 2011

“…The second mesospheric wave front event is quite similar to the event described by Bageston et al (2011b) in terms of its morphology, i.e., a remarkable wave front followed by a series of wave crests confined in a very well-defined duct, with the main contribution from the wind structure, but different from the present case, which showed a thermal duct condition for the front propagation. For this case, the potential source in the troposphere is shown in Fig.…”

“…9a. This kind of system is a potential wave source already identified and linked to gravity waves in the mesosphere near the Antarctic Peninsula (Bageston et al, 2018). The cyclones are commonly observed around the peninsula and have been reported by several authors (e.g., Heinemann, 1990;Carrasco et al, 2003).…”

“…Bageston et al (2009) in their observations at Ferraz Station, during 2007, observed more than 230 gravity wave events, but only two clear cases of mesospheric fronts were reported. The first one was a mesospheric wall (Bageston et al, 2011a) and the second one was a mesospheric bore (Bageston et al, 2011b). In both cases, the fronts were supported by stable ducts (the first one a thermal duct and the second one a thermal-Doppler duct).…”

An investigation of long-distance propagation of gravity waves under CAWSES India Phase II Programme

“…The ducts due to the variations in the mean wind field are called Doppler ducts, while those associated with strong discontinuities in the temperature field are called thermal ducts. And gravity waves trapped in these ducts can travel (without being considerably attenuated) to large horizontal distances before dissipating their energy and momentum to the background atmosphere; hence, these ducted waves are more likely to be detectable at large distance from their origin (Chimonas and Hines, 1986;Fritts and Yuan, 1989;Isler et al, 1997;Ding et al, 2003;Snively et al, 2007;Bageston et al, 2011). At low latitudes, such waves are more common in occurrence compared to those freely propagating (Isler et al, 1997).…”

Investigation of a mesospheric bore event over northern China

“…In contrast, bores with increased emission intensity behind the leading front have been reported by other observations Narayanan et al, 2009;Nielsen et al, 2006;Stockwell et al, 2006Stockwell et al, , 2011Fechine et al, 2009). In a recent paper, Bageston et al (2011a) reported a clear wave front followed by a series of wave crests. However, a clear step function was not observed.…”