Airglow imager observations of atmospheric gravity waves at Alice Springs and Adelaide, Australia during the Darwin Area Wave Experiment (DAWEX)

Abstract

The Darwin Area Wave Experiment occurred in Australia from October to December 2001. An objective was to characterize the atmospheric gravity wave field produced from intense convective activity that is routinely observed around Darwin during November and December. Two airglow imagers were sited at Adelaide and at Alice Springs, each located over 1000 km south of Darwin. Waves were observed at the mesopause region propagating predominantly toward the southeast, with some going to the northwest but with none observed going from east to west. The lack of waves propagating toward the west suggests some wind filtering mechanism below 80 km altitude. Waves observed over Alice Springs were analyzed in detail on three nights. On 16 November they were seen propagating toward the northwest. It is proposed that they were generated by dynamical events associated with a cutoff low‐pressure system present over southwest Australia. On 17 and 19 November the observations are consistent with wave generation by convective activity present in the Darwin area. Thus as proposed by Walterscheid et al. [1999] and Hecht et al. [2001a], the ducting of waves from distant sources is shown to be a viable explanation for the quasi‐monochromatic waves frequently observed in airglow observations. Walterscheid et al. [1999] suggested that ducting of waves from the extensive region of deep cumulus convection over northern Australia explained the strong poleward directionality seen in the summer months. The present study suggests that propagation from northern Australia is selective, and ducted waves from this region may not be the primary source of waves over Adelaide when convection is occurring over central Australia.

Propagation of short-period gravity waves at high-latitudes during the MaCWAVE winter campaign

“…Waves can be ducted at maxima in the wind field in the plane of wave propagation, termed Doppler ducting (Chimonas and Hines, 1986;Wang and Tuan, 1988;Isler et al, 1997), by thermal ducts at sharp temperature inversions (Walterscheid et al, 1999), or by a combination of these processes (Fritts and Yuan, 1989b). Due to their relatively small scale sizes, short period gravity waves are considered prone to both forms of ducting and convincing evidence of ducted wave motions at MLT heights has been reported at mid-and low latitudes (Isler et al, 1997;Walterscheid et al, 1999;Hecht et al, 2001aHecht et al, , 2004bPautet et al, 2005).…”

“…However, the possibility also exists for horizontal wave propagation over much longer distances if the waves were ducted in nature (Walterscheid et al, 1999;Hecht et al, 2004b;Pautet et al, 2005). Waves can be ducted at maxima in the wind field in the plane of wave propagation, termed Doppler ducting (Chimonas and Hines, 1986;Wang and Tuan, 1988;Isler et al, 1997), by thermal ducts at sharp temperature inversions (Walterscheid et al, 1999), or by a combination of these processes (Fritts and Yuan, 1989b).…”

Convection: the likely source of the medium-scale gravity waves observed in the OH airglow layer near Brasilia, Brazil, during the SpreadFEx campaign

“…Jones, 1969;Marks and Eckermann, 1995;Cowling et al, 1971;Jones, 1984, 1987;Hung and Kuo, 1978;Hung and Smith, 1978;Lighthill, 1978;Gerrard et al, 2004;Hecht et al, 2004;Wrasse et al, 2009;Lin and Zhang, 2008). Although these past formalisms allowed for the propagation of GWs through varying 3-D winds and temperatures, they did not allow for the propagation of high-frequency GWs through a thermosphere containing realistic dissipation.…”

“…While many are clearly freely propagating, a significant number of the GWs are thought to be ducted (or evanescent) in nature, particularly those having short horizontal wavelengths (Isler et al, 1997;Walterscheid et al, 1999;Hecht et al, 2001Hecht et al, , 2004Pautet et al, 2005;Snively et al, 2007). These GWs may have been excited directly from tropospheric sources; however, they may also have been excited from wave-wave or wave-mean flow interactions accompanying the breaking of GWs from wind flow over mountains and convection (e.g.…”

“…Because of their uncertain origins, and because of their small phase speeds, it is more difficult to utilize them via reverse ray tracing studies for source identification and quantification if there are large uncertainties in the horizontal winds. However, one study did determine, via reverse ray trace studies, that the small-scale GWs observed in the OH layer were probably excited from deep convection (Hecht et al, 2004).…”