*Article* **Diurnal Cycle in Atmospheric Water over Switzerland**

**Klemens Hocke 1,2,\*,†, Francisco Navas-Guzmán 1, Lorena Moreira 1, Leonie Bernet 1,2 and Christian Mätzler 1,2**


Academic Editors: Yuei-An Liou, Jean-Pierre Barriot, Chung-Ru Ho, Yuriy Kuleshov, Chyi-Tyi Lee, Richard Müller and Prasad S. Thenkabail Received: 21 June 2017; Accepted: 30 August 2017; Published: 31 August 2017

**Abstract:** The TROpospheric WAter RAdiometer (TROWARA) is a ground-based microwave radiometer with an additional infrared channel observing atmospheric water parameters in Bern, Switzerland. TROWARA measures with nearly all-weather capability during day- and nighttime with a high temporal resolution (about 10 s). Using the almost complete data set from 2004 to 2016, we derive and discuss the diurnal cycles in cloud fraction (CF), integrated liquid water (ILW) and integrated water vapour (IWV) for different seasons and the annual mean. The amplitude of the mean diurnal cycle in IWV is 0.41 kg/m2. The sub-daily minimum of IWV is at 10:00 LT while the maximum of IWV occurs at 19:00 LT. The relative amplitudes of the diurnal cycle in ILW are up to 25% in October, November and January, which is possibly related to a breaking up of the cloud layer at 10:00 LT. The minimum of ILW occurs at 12:00 LT, which is due to cloud solar absorption. In case of cloud fraction of liquid water clouds, maximal values of +10% are reached at 07:00 LT and then a decrease starts towards the minimum of −10%, which is reached at 16:00 LT in autumn. This breakup of cloud layers in the late morning and early afternoon hours seems to be typical for the weather in Bern in autumn. Finally, the diurnal cycle in rain fraction is analysed, which shows an increase of a few percent in the late afternoon hours during summer.

**Keywords:** cloud fraction; integrated liquid water; integrated water vapour; diurnal cycle; microwave radiometer
