shows the time series of radiation budget, temperature, and wind speed and direction during the campaign. The periods of cloudy weather were determined from measurements of longwave and shortwave radiation (Figure 3
a), according to Marty and Philipona [42
]. Variations of the apparent emittance due to cloud cover significantly exceeded the variations of the clear sky emittance caused by variations of air humidity. We used the apparent emittance value as a criterion for determining cloudy periods. The threshold value of the emittance between clear sky and cloudy weather was chosen from the analysis of the time series of incoming shortwave radiation. In Figure 3
, the identified time periods of cloudy weather are shaded (grey). The yellow bars indicate the local daytime periods. The cloudy days (12, 17, and 19 June) were excluded from the statistics. Figure 3
b shows the time series of air temperature measured at the platform mast 15 m a.s.l., at the onshore mast 10 m a.g.l., and sea surface temperature (SST) obtained from radiometer measurements. Note that, during the entire experiment, the water temperature did not exceed the air temperature at 15 m a.s.l. Time series of the wind direction and speed from the data of sodar measurement and the onshore mast are given in Figure 3
c,d, respectively. A steady west wind was observed daily during the daytime, with speed values of up to 12 m s
at 50 m a.s.l. The night wind direction was less steady and generally ranged from the north-west to the east with typical speed values of about 2–3 m s
at 50 m a.s.l. A rapid change in wind direction in the morning and evening hours was observed daily. The values of geostrophic wind speed and direction are also presented in Figure 3
c,d, which were calculated from reanalysis data of sea level pressure by the United States National Center for Environmental Prediction (NCEP). During the experiment, the geostrophic wind direction was predominantly western and ranged from the northwest to the southeast. According to a quadrant classification (see, e.g., [43
]), the geostrophic wind direction was generally from quadrants Q1 and Q3. The diurnal behavior of the probability density of the wind speed and direction, as well as the mean wind speed, is presented in Figure 4
. The plots show a typical diurnal cycle of wind speed and direction, with dominant direction from the north for night hours (from 19:00 to 7:00 local time (+3 GMT)) and from the west (along the coast) for the daytime (from 7:00 to 19:00). The mean wind speed time course had two maxima: about 6 m s
at around 03:00 and about 2.5 m s
at around 15:00; and two minima: at 08:00 and at around midnight.
Wind roses from measurements at the platform and onshore masts for all days with fair weather are presented in Figure 5
. The wind roses were built for both the entire time and separately for day and night hours, in accordance with the daily change of wind mode. The prevailing wind directions near sea level were from the west (along the coast) and from the north (in the direction of the coastal slope). A north wind was typical at night, whereas a west wind was typical during the day. Wind from the open sea (from the east) was observed sporadically in the morning hours and sometimes at night. Wind from the south was rare. The distribution of wind speed and direction, according to the measurements at the onshore mast, qualitatively repeated the distribution of winds at the platform; however, a slight shift in the wind direction is observable, which can be associated with the orography of the area.