Variability of the Brunt–Väisälä frequency at the OH<sup>∗</sup>-airglow layer height at low and midlatitudes

Abstract

Abstract. Airglow spectrometers, as they are operated within the Network for the Detection of Mesospheric Change (NDMC; https://ndmc.dlr.de, last access: 1 November 2020), for example, allow the derivation of rotational temperatures which are equivalent to the kinetic temperature, local thermodynamic equilibrium provided. Temperature variations at the height of the airglow layer are, amongst others, caused by gravity waves. However, airglow spectrometers do not deliver vertically resolved temperature information. This is an obstacle for the calculation of the density of gravity wave potential energy from these measurements. As Wüst et al. (2016) showed, the density of wave potential energy can be estimated from data of OH∗-airglow spectrometers if co-located TIMED-SABER (Thermosphere Ionosphere Mesosphere Energetics Dynamics, Sounding of the Atmosphere using Broadband Emission Radiometry) measurements are available, since they allow the calculation of the Brunt–Väisälä frequency. If co-located measurements are not available, a climatology of the Brunt–Väisälä frequency is an alternative. Based on 17 years of TIMED-SABER temperature data (2002–2018), such a climatology is provided here for the OH∗-airglow layer height and for a latitudinal longitudinal grid of 10∘×20∘ at midlatitudes and low latitudes. Additionally, climatologies of height and thickness of the OH∗-airglow layer are calculated.

Gravity wave instability structures and turbulence from more than one and a half years of OH* airglow imager observations in Slovenia

“…The derived values of eddy diffusion coefficients are in the range around 10 − 10 m²s and agree mostly with earlier results from rocket and lidar measurements and simulations. Considering the respective values of the BV frequency as calculated by Wüst et al (2020) turbulence event. These have the same order of magnitude as the daily chemical heating rates as reported by Marsh (2011).…”

“…For both, gravity wave statistics (section 4.1) and the calculation of the energy dissipation rate (section 4.2) the BV frequency is required, which is adapted from the climatology presented by Wüst et al (2020)…”

“…We use an uncertainty of ± 5 % as according to Wüst et al (2020) 91 % of their data lie within this range around the harmonic approximation. The BV period is then referred to as = .…”

The OH (3-1) nightglow volume emission rate retrieved from OSIRIS measurements: 2001 to 2015

“…8, the SAO signature are evident in all three parameters especially at the lower latitudes. The SAO signature in peak height at low latitudes has maxima at solstices (minima at equinoxes), which is also shown by Sheese et al (2014), Gao et al (2010), Teiser and von Savigny (2017) and Wüst et al (2020). Figure 9 also shows the anti-correlation between the peak intensity and peak height which is well studied by, among others, Liu and Sheperd (2006);von Savigny et al (2012).…”

Vertical layering of OH line emission from X-shooter and SABER observations of a passing quasi-2-day wave

“…Rocket flights showed typical peak heights of about 87 km and layer widths of about 8 km (Baker & Stair, 1988). Moreover, OH emission profiles have frequently been observed by limbsounding instruments in space (e.g., Baker et al, 2007;Dodd et al, 1994;von Savigny et al, 2012;Wüst et al, 2020;Yee et al, 1997). Rare ground-based altitude measurements relied on the identification of the same emission features in imaging instruments at different sites (e.g., Kubota et al, 1999;Moreels et al, 2008).…”