Data collection:

The iWS consists of a custom-built weather station unit, assembled at the Institute of Marine and Atmospheric research Utrecht (IMAU). The unit consists of a 3D-printed plastic housing with an array of miniature solar panels on top. In the housing, there are sensors for air temperature, surface air pressure, relative humidity, as well as a gps, an acoustic snow height sensor, an ARGOS communication antenna, and three Lithium batteries that fuel the unit when solar radiation is absent.

The unit is complemented by a propeller-vane Young anemometer measuring wind direction and speed. Additionally, all radiation fluxes are measured with a Kipp and Zonen CNR4 radiometer.

Due to malfunctioning, no subsurface temperature measurements are available.

Data quality:

A number of corrections and adjustments to the raw data were applied for this dataset.

1) The temperature sensor is not artificially ventilated. This leads to a positive bias in temperature measurements under conditions of high insolation and low wind speed. Simultaneous observations from a thin-wire thermocouple provided a correction procedure, detailed in Smeets et al. (2017).

2) The relative humidity sensor is placed within the unit and experiences elevated temperature under sunny conditions. Internally-observed temperature of the sensor allows the calculation of a dew point, which gives a relative humidity for the observed air temperature. Next, relative humidity is corrected for observations over ice rather than over water. And finally, a well-known underestimation of RH-observations at low temperatures is corrected for by fitting a polynomial through the upper percentile of data and define that polynomial as a RH of 100%.

3) Longwave radiation observations are corrected for the internal instrument temperature, and for window heating under high insolation conditions.

4) Acoustic snow height observations are corrected for the dependency of sound propagation on air temperature.

5) A few small data 30- to 60-minute data gaps were filled by linearly interpolation.