Characteristics and sources of gravity waves observed in noctilucent cloud over Norway

Abstract

Abstract. Four years of noctilucent cloud (NLC) images from an automated digital camera in Trondheim and results from a ray-tracing model are used to extend the climatology of gravity waves to higher latitudes and to identify their sources during summertime. The climatology of the summertime gravity waves detected in NLC between 64 and 74 • N is similar to that observed between 60 and 64 • N by Pautet et al. (2011). The direction of propagation of gravity waves observed in the NLC north of 64 • N is a continuation of the north and northeast propagation as observed in south of 64 • N. However, a unique population of fast, short wavelength waves propagating towards the SW is observed in the NLC, which is consistent with transverse instabilities generated in situ by breaking gravity waves . The relative amplitude of the waves observed in the NLC Mie scatter have been combined with raytracing results to show that waves propagating from near the tropopause, rather than those resulting from secondary generation in the stratosphere or mesosphere, are more likely to be the sources of the prominent wave structures observed in the NLC. The coastal region of Norway along the latitude of 70 • N is identified as the primary source region of the waves generated near the tropopause.

Observation of Kelvin-Helmholtz Instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

“…Fritts et al (2014) and Baumgarten and Fritts (2014) analyzed two KHI events from a NLC camera network and inferred the background wind situation by tracing the ice clouds over a much larger field of view than the billows. They retrieved a horizontal wavelength of Comparing our results to previous optical observations from a NLC camera at Trondheim monitoring the MLT above Andenes 10 suggest slightly higher observed phase speeds and much shorter observed wave periods (Demissie et al, 2014). The horizontal wavelengths are comparable and had values between 20-40 km.…”

Unravelling the microphysics of polar mesospheric cloud formation

“…In this work we performed laboratory experiments using the MICE-TRAPS apparatus which was described earlier (Duft et al, 2015;Meinen et al, 2010;Nachbar et al, 2018bNachbar et al, , 2016. In brief, sub-4 nm iron silicate nanoparticles of adjustable elemental composition are produced in a microwave plasma particle source as MSP analogues (Nachbar et al, 2018a).…”

“…The saturation is usually varied by changing the particle temperature while keeping the water vapour density in MICE constant to facilitate comparison. In principle, water vapour density and particle temperature can be chosen independently within the limits of this experimental approach (Duft et al, 2015). Typical mass growth curves of iron oxide particles of initial radius r dry = 1.87 nm are shown in Fig.…”

“…In recent years NLCs have been intensely studied using ground-based (e.g. Demissie et al, 2014;Kaifler et al, 2013;Kirkwood et al, 2008) and space-borne (e.g. DeLand et al, 2007;Hervig et al, 2016;Rong et al, 2015) methods.…”

“…the ability of the material to serve as ice nuclei), the ice phase forming at mesopause conditions, and the effect the electrical charge of MSPs may have on the ice formation process. In order to improve our understanding of NLC formation we recently introduced an experimental set-up to study ice formation and growth processes on nanoparticles exposed to realistic mesopause conditions (Duft et al, 2015). We used this set-up in two previous studies to investigate ice growth rates on iron oxide and silica nanoparticles which served as analogues for MSPs (Nachbar et al, 2018b, c).…”