Abstract
Abstract. Mesospheric water vapour has been observed above ALOMAR in northern Norway (69° N 16° E) by our group since 1995 using a 22 GHz ground based microwave spectrometer. A new instrument with higher sensitivity, providing a much better time resolution especially in the upper mesosphere, was installed in May 2008. The time resolution is high enough to provide observations of daily variations in the water vapour mixing ratio. We present the first ground based detections of tidal behaviour in the polar middle atmospheric water vapour distribution. Diurnal and semidiurnal variations of water vapour have been observed and due to the long chemical lifetime of water they are assumed to be caused by changing wind patterns which transport water-rich or poor air into the observed region. The detected tidal behaviour does not follow any single other dynamical field but is instead assumed to be a result of the different wind components. Both the diurnal and semidiurnal amplitude and phase components are resolved. The former shows a stable seasonal behaviour consistent with earlier observations of wind fields and model calculations, whereas the latter appears more complex and no regular behaviour has so far been observed.
Highlights
The dynamical behaviour of the polar middle atmosphere is important for the global circulation and in order to correctly model it a comprehensive knowledge of all the involved processes is needed.Atmospheric tides are known to affect the gravity waves which are an important component for the dynamical behaviour in the middle atmosphere (Fritts and Vincent, 1987; Wang and Fritts, 1991)
It is of interest to understand all aspects of the tidal behaviour in the Mesosphere and Lower Thermosphere (MLT) region
Information about the water vapour above this level can only be understood as the total column depth which is projected onto the 80 km layer
Summary
The dynamical behaviour of the polar middle atmosphere is important for the global circulation and in order to correctly model it a comprehensive knowledge of all the involved processes is needed. Tidal behaviour in temperature and the different wind components in the polar regions are commonly observed by satellite (Forbes and Wu, 2006; Manson et al, 2002a) as well as by ground based instruments (Manson et al, 2002b; Lubken et al, 2011). Observations of tides in temperature was done with the UARS satellite (Forbes and Wu, 2006) and recently a ground based LIDAR was able to detect them (Lubken et al, 2011). Haefele et al (2008) report of daily variations in the WVMR measured with a ground based microwave spectrometer in the Alps They compare these variations to chemistry-climate models (SOCOL, MSDOL and LMDz) and conclude that the variations in the stratosphere are mainly induced by meridional advection and in the mesosphere by vertical advection. To the best of the authors knowledge this is the first time diurnal (and semidiurnal) variations of water vapour at a polar location have been observed and described
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