*3.1. Climatologies*

We evaluated in total about 48 million samples of TROWARA measurements from 2004 to 2016 (sampling rates are between 6 and 11 s). The number of samples of IWV or ILW is about 48 million. The number of samples with cloud occurrence (group CF4) is about 24 million. The number of samples of the group CF1 is about 7 million. The number of samples of CF2 is 6 million, and the number of samples of CF3 is about 10 million. The number of samples of rain (ILW ≥ 400 g/m2) is about 4 million. The number of samples of IWV, rain, CF1, CF2, CF3 and CF4 are shown in Figure 1 as a function of month. Most critical might be the statistics of thick supercooled liquid water clouds (CF2) in summer.

The climatologies of IWV, ILW, CF1, CF2, CF3 and CF4 above Bern from 2004 to 2016 are shown in Figure 2. Generally, there are strong seasonal variations in Figure 2. The error bars indicate the standard deviation of the monthly mean from year to year. Next, we use the climatological curves for computation of the diurnal cycles with respect to the monthly means. IWV varies from 8 kg/m2 in winter to 24 kg/m<sup>2</sup> in summer. This annual oscillation of IWV is due to the seasonal change in air temperature and the Clausius–Clapeyron equation. The seasonal cycle of ILW contains an annual and a semi-annual component where the latter is a bit stronger. Cloud fraction of thin liquid water clouds (CF1) is fairly constant during the year except during winter months when CF1 presents higher values. Thick supercooled liquid water clouds (CF2) almost disappear during the summer months when the air temperature is high. Thick warm liquid water clouds (CF3) are strongly reduced during the winter. Cloud fraction of all liquid water clouds (CF4) increases slightly during winter, and a semi-annual oscillation is present.

**Figure 1.** Number of samples of integrated water vapour (IWV), rain (ILW <sup>≥</sup> 400 g/m2) and cloud fraction (CF) of four cloud categories (defined in the text) as a function of month observed by the TROWARA radiometer in Bern from 2004 to 2016.

**Figure 2.** Climatologies of integrated water vapour (IWV), integrated liquid water (ILW) and cloud fraction (CF) of four cloud categories (defined in the text) observed by the TROWARA radiometer in Bern from 2004 to 2016. The error bars indicate the standard deviation of the monthly mean from year to year.
