Abstract
Abstract. Observations of oscillations in the abundance of middle-atmospheric trace gases can provide insight into the dynamics of the middle atmosphere. Long-term, high-temporal-resolution and continuous measurements of dynamical tracers within the strato- and mesosphere are rare but would facilitate better understanding of the impact of atmospheric waves on the middle atmosphere. Here we report on water vapor measurements from the ground-based microwave radiometer MIAWARA (MIddle Atmospheric WAter vapor RAdiometer) located close to Bern during two winter periods of 6 months from October to March. Oscillations with periods between 6 and 30 h are analyzed in the pressure range 0.02–2 hPa. Seven out of 12 months have the highest wave amplitudes between 15 and 21 h periods in the mesosphere above 0.1 hPa. The quasi 18 h wave signature in the water vapor tracer is studied in more detail by analyzing its temporal evolution in the mesosphere up to an altitude of 75 km. Eighteen-hour oscillations in midlatitude zonal wind observations from the microwave Doppler wind radiometer WIRA (WInd RAdiometer) could be identified within the pressure range 0.1–1 hPa during an ARISE (Atmospheric dynamics Research InfraStructure in Europe)-affiliated measurement campaign at the Observatoire de Haute-Provence (355 km from Bern) in France in 2013. The origin of the observed upper-mesospheric quasi 18 h oscillations is uncertain and could not be determined with our available data sets. Possible drivers could be low-frequency inertia-gravity waves or a nonlinear wave–wave interaction between the quasi 2-day wave and the diurnal tide.
Highlights
The dynamics of the middle atmosphere are controlled by a broad spectrum of waves
Within the subsequent section we investigate how often the 18 h wave packets have been observed in the MIAWARA water vapor time series
For the first time a dominant quasi 18 h wave in mesospheric water vapor has been reported from ground-based measurements
Summary
Knowledge about the wave characteristics and incidence is important, to better understand the elements of middle-atmospheric dynamics to improve predictions of weather (Hardiman et al, 2011) and climate (Orr et al, 2010) models. The latter are getting more important since the social impact of severe-weather events and climate change is increasing. A well-known class of planetary waves are Rossby waves (Salby, 1981b) Their periods range from 2 to approximately 18 days in the middle atmosphere, showing strong interannual variability (Jacobi et al, 1998). Characteristics of the 5-day wave were analyzed by Rosenlof and Thomas (1990), Wu et al (1994), Riggin et al (2006) and Belova et al (2008), and waves with even longer periods have been observed in the mesosphere and lower thermosphere (Forbes et al, 1995; McDonald et al, 2011; Scheiben et al, 2014; Rüfenacht et al, 2016)
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