Observed and modelled cloud cover up to 6 km height at Station Nord in the high Arctic

Abstract

We present results from an analyses of cloud cover based on profiles of the attenuated backscatter coefficient from an 8-year-long data series (July 2011-April 2019). The observations are carried out in the high Arctic by a ceilometer with a maximum range setting of 7.7 km from the Villum Research Station at Station Nord, Greenland. Results show that the hourly cloud cover turned out to follow a U-shaped rather than Gaussian-like distribution. Annual and seasonal cloud cover variation is illustrated. The cloud cover is larger during the autumn and winter as compared to summer and spring. The cloud cover exhibits a substantial variation from year to year without a clear trend. The cloud cover during spring is low and decreasing between 2012 and 2017. The cloud cover during the autumn of 2016 is lowest compared to the other years. The observed cloud cover is compared to the cloud cover provided in the ERA5 reanalysis dataset. The cloud cover for low clouds and medium clouds are combined to represent a total height of 6 km. Both the observed and modelled cloud cover is larger during winter as compared to summertime cloud cover. The measured reduction in the cloud cover for the autumn of 2016 is present in the reanalysis data as well but the measured low cloud cover during spring is not apparent in the reanalysis data. Because the cloud cover distribution is U-shaped rather than of a Gaussian nature, standard metrics are not applicable. We apply a generalized skill score that is developed for contingency tables or joint histograms. Three skill scores were calculated. It was found that for all three methods, skills for the predictability of the cloud cover by the ERA5 modelling is better for winter than summer and is poor during the spring.

Observed aerosol‐layer depth at Station Nord in the high Arctic

“…To illustrate the observations further, a histogram of the depth of the aerosol layer, using the measurements during summer and winter in 2018, is shown in Figure 8. Here we apply definitions of the seasons at VRS following Gryning et al (2021), where the seasons are defined according to the sun's position relative to the horizon. Summer is defined as the period from 10 April to 3 September, where the sun is up all day and winter as the period 17 October–24 February where it is down all day.…”

“…Analysis presented here on the depth of the aerosol layer is based on hourly averaged profiles of attenuated backscatter from the ceilometer derived from the raw measurements. In order to exclude cases of low clouds, precipitation and fog from the analysis, only profiles where all values in the hourly averaged attenuated backscatter between 100 and 500 m are less than 2Á10 −5 sr −1 Ám −1 are considered (e.g., Gryning et al, 2021). Fulfilling this condition discards 15% of the profiles.…”

“…Towards east the isolated ice cap Flade Isblink reaches a height of approximately 700 m. The inland ice is more than 100 km south of the station. More details on the landscape are available in Goodsite et al (2014) and Gryning et al (2021).…”

“…One is the Vaisala CL51 laser diode ceilometer. While originally designed for detection of cloud base layers (e.g., Gryning et al, 2021), it is widely used for automatic monitoring of the height of the atmospheric boundary layer (Kotthaus et al, 2020). The other remote sensing instrument is a Wind Cube V2 Doppler wind lidar, which has obtained widespread use in the wind industry.…”

Ice Nucleating Particles in Northern Greenland: annual cycles, biological contribution and parameterizations

“…The atmospheric INP number concentration of the heated samples (N heated INP,air ) and its corresponding unheated samples (i.e. the full spectrum, see Appendix A1 for details of merging procedure) at each temperature were used to derive the bio-ratio N bioratio using the followoing equation: (Gryning et al, 2022).…”