A QBO-signal in mesospheric water vapor measurements at ALOMAR (69.29° N, 16.03° E) and in model calculations by LIMA over a solar cycle

Abstract. Microwave water vapor measurements between 40 and 80 km over a solar cycle (1996–2006) were carried out in high latitudes at ALOMAR (69.29° N, 16.03° E), Norway. Three larger interuptions in the winters of 1996/97 and 2005/06, and from spring 2001 to spring 2002, a few smaller interruptions of monitoring occurred during this period. The observed year-to-year variability is not directly related to the solar activity. The analysis of the observations by the Fast Fourier Transform (FFT) method revealed peaks close to two years, particularly in the upper monitoring domain. Model calculations by means of the real date model LIMA, Leibniz-Institute Middle Atmosphere model, reflect essential patterns of the water vapor variation. The FFT-analysis of the calculated water vapor mixing ratios also showed peaks of around two years. The real period of the QBO during the monitoring period ranged quite close to two years within the time interval considered, with the exception of the years 2001/02 when the period was essentially longer. Although the QBO is a phenomenon occurring in the zonal wind of the tropical stratosphere, we suppose an influence of the QBO on the water vapor distribution of the mesosphere of high latitudes controlled by transport processes. A possible link could be given by the planetary wave activity triggered by the QBO.