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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Apr 2019

Research article | 15 Apr 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Diurnal cycle of short-term fluctuations of integrated water vapour above Switzerland

Klemens Hocke1, Leonie Bernet1, Jonas Hagen1, Axel Murk1, Matthias Renker2, and Christian Mätzler1 Klemens Hocke et al.
  • 1Institute of Applied Physics and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 2Armasuisse, Thun, Switzerland

Abstract. The TROpospheric WAter RAdiometer (TROWARA) continuously measures integrated water vapour (IWV) with a time resolution of 6 seconds at Bern in Switzerland. During summer, we often see that IWV has temporal fluctuations during daytime while the night-time data are without fluctuations. The data analysis is focused on the year 2010 where TROWARA has a good data quality without data gaps. We derive the spectrum of the IWV fluctuations in the period range from about 1 to 100 min. The FFT spectrum with a window size of 3 months leads to a serious underestimation of the spectral amplitudes of the fluctuations. Thus, we apply a band pass filtering method to derive the amplitudes as a function of period Tp. The amplitudes are proportional to Tp0.5. Another method is the computation of the moving standard deviation with time window lengths from about 1 to 100 min. Here, we get similar results as for the band pass filtering method. At all periods, the IWV fluctuations are strongest during summer while they are smallest during winter. We derive the diurnal variation of the short-term IWV fluctuations by applying a moving standard deviation with a window length of 10 min. The daily cycle is strongest during the summer season with standard deviations up to 0.22 mm at about 14:00 CET. The diurnal cycle disappears during winter time. Using the meteorological weather station at Bern, we derive the diurnal cycle of the short-term fluctuations of the specific kinetic energy ek. Since these data have a temporal resolution of 10 min, we apply a 20 min-moving standard deviation. The derived short-term ek fluctuations can be regarded as a proxy of turbulent kinetic energy (TKE). During summer time, the 20 min-moving standard deviation of ek increases during daytime and has a similar diurnal cycle like the short-term IWV fluctuations. Thus, we conclude that the diurnal cycle of the short-term IWV fluctuations is caused by turbulence associated with large convective heating during daytime in summer.

Klemens Hocke et al.
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Klemens Hocke et al.
Klemens Hocke et al.
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Short summary
The Tropospheric Water Radiometer (TROWARA) observed an enhanced intensity of short-term IWV fluctuations during daytime in summer. These IWV fluctuations are possibly related to thermal convective activity in the lower troposphere. The observed climatology and spectra of IWV fluctuations might be useful for modeling studies of water vapor convection in the atmospheric boundary layer at mid-latitudes.
The Tropospheric Water Radiometer (TROWARA) observed an enhanced intensity of short-term IWV...