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Volume 17, issue 19 | Copyright
Atmos. Chem. Phys., 17, 12121-12131, 2017
https://doi.org/10.5194/acp-17-12121-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Oct 2017

Research article | 12 Oct 2017

Oscillations in atmospheric water above Switzerland

Klemens Hocke1,2, Francisco Navas-Guzmán1, Lorena Moreira1, Leonie Bernet1,2, and Christian Mätzler1,2 Klemens Hocke et al.
  • 1Institute of Applied Physics, University of Bern, Bern, Switzerland
  • 2Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Abstract. Cloud fraction (CF), integrated liquid water (ILW) and integrated water vapour (IWV) were continuously measured from 2004 to 2016 by the TROpospheric WAter RAdiometer (TROWARA) in Bern, Switzerland. There are indications for interannual variations of CF and ILW. A spectral analysis shows that IWV is dominated by an annual oscillation, leading to an IWV maximum of 24kgm−2 in July to August and a minimum of 8kgm−2 in February. The seasonal behaviour of CF and ILW is composed by both the annual and the semiannual oscillation. However, the annual oscillation of CF has a maximum in December while the annual oscillation of ILW has a maximum in July. The semiannual oscillations of CF and ILW are strong from 2010 to 2014. The normalized power spectra of ILW and CF show statistically significant spectral components with periods of 76, 85, 97 and 150 days. We find a similarity between the power spectra of ILW and CF with those of zonal wind at 830hPa (1.5km) above Bern. Particularly, the occurrence of higher harmonics in the CF and ILW spectra is possibly forced by the behaviour of the lower-tropospheric wind. The mean amplitude spectra of CF, ILW and IWV show increased short-term variability on timescales less than 40 days from spring to fall. We find a weekly cycle of CF and ILW from June to September with increased values on Saturday, Sunday and Monday.

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We derive the annual and semi-annual oscillations in cloud fraction (CF), integrated liquid water (ILW) and integrated water vapour (IWV) from the long-term measurements of the TROWARA radiometer in Bern, Switzerland. Further, we find a weekly cycle of CF and ILW from June to September with increased values on Saturday, Sunday and Monday.
We derive the annual and semi-annual oscillations in cloud fraction (CF), integrated liquid...
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