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This article presents the results of observations of selected fluxes of the radiation balance in north-western Spitsbergen in the years from 2010 to 2014. Measurements were taken in Ny-Ålesund and in the area of Kaffiøyra, on different surface types occurring in the Polar zone: moraine, tundra, snow and ice. Substantial differences in the radiation balance among the various types of surface were observed. The observations carried out in the summer seasons of 2010–2014 in the area of Kaffiøyra demonstrated that the considerable reflection of solar radiation on the Waldemar Glacier (albedo 55%) resulted in a smaller solar energy net income. During the polar day, a diurnal course of the components of the radiation balance was apparently related to the solar elevation angle. When the sun was low over the horizon, the radiation balance became negative, especially on the glacier. Diurnal, annual and multi-annual variations in the radiation balance have a significant influence on the functioning of the environment in polar conditions.

For the first time, the cloud radiative effect (CRE) has been characterized for the Arctic site Ny-Ålesund, Svalbard, Norway, including more than 2 years of data (June 2016–September 2018). The cloud radiative effect, that is, the difference between the all-sky and equivalent clear-sky net radiative fluxes, has been derived based on a combination of ground-based remote sensing observations of cloud properties and the application of broadband radiative transfer simulations. The simulated fluxes have been evaluated in terms of a radiative closure study. Good agreement with observed surface net shortwave (SW) and longwave (LW) fluxes has been found, with small biases for clear-sky (SW: 3.8 W m−2; LW: −4.9 W m−2) and all-sky (SW: −5.4 W m−2; LW: −0.2 W m−2) situations. For monthly averages, uncertainties in the CRE are estimated to be small (~2 W m−2). At Ny-Ålesund, the monthly net surface CRE is positive from September to April/May and negative in summer. The annual surface warming effect by clouds is 11.1 W m−2. The longwave surface CRE of liquid-containing cloud is mainly driven by liquid water path (LWP) with an asymptote value of 75 W m−2 for large LWP values. The shortwave surface CRE can largely be explained by LWP, solar zenith angle, and surface albedo. Liquid-containing clouds (LWP > 5 g m−2) clearly contribute most to the shortwave surface CRE (70%–98%) and, from late spring to autumn, also to the longwave surface CRE (up to 95%). Only in winter are ice clouds (IWP > 0 g m−2; LWP < 5 g m−2) equally important or even dominating the signal in the longwave surface CRE. [ABSTRACT FROM AUTHOR]

Here we evaluate five atmospheric reanalyses in an Arctic gateway during late summer. The reanalyses include ERA5, ERA‐Interim, Japanese 55 year Re‐Analysis (JRA‐55), Climate Forecasting System Reanalysis‐version 2 (CFSv2), and Modern Era Retrospective analysis for Research and Applications‐version 2 (MERRA‐2). We use observations from 50 radiosondes launched in the Fram Strait around 79‐80°N, between 25 August and 11 September 2017. Crucially, data from 27 radiosondes were not transmitted to the Global Telecommunications System and therefore not assimilated into any reanalysis. In most reanalyses, the magnitude of wind speed and humidity errors is similar for profiles with and without data assimilation. In cases without data assimilation, correlation coefficients (R) exceed 0.88 for temperature, wind speed, and specific humidity, in all reanalyses. Overall, the newly released ERA5 has higher correlation coefficients than any other reanalyses as well as smaller biases and root‐mean‐square errors, for all three variables. The largest improvements identified in ERA5 are in its representation of the wind field, and temperature profiles over warm water. Plain Language Summary: The Arctic is undergoing rapid and ongoing changes. However, due to the harsh environment, there are relatively few observations from this region. To understand the drivers of these changes, we rely heavily on atmospheric reanalyses. Reanalyses are our best guess at the state of the atmosphere at a given time. Reanalyses are generated by assimilating all available atmospheric observations into a weather forecast model. A key question within the scientific community is how accurate reanalyses are in the Arctic. One problem with answering this question is that most observations used to test the performance of reanalyses were ingested in to the model and are therefore not an independent data set. Here we present a new set of balloon‐borne atmospheric observations from the Fram Strait, between Svalbard and Greenland. Many of these data were not assimilated in to any reanalyses, providing a rare opportunity to evaluate their performance in this important Arctic gateway. We test five products, including the newly released ERA5 from the European Centre for Medium Ranged Weather Forecasting. All products simulate the temperature, humidity, and wind fields well, even without data assimilation. Overall, the newly released ERA5 performs best, with the largest improvements in the wind and temperature fields. Key Points: In situ Arctic observations: 27 atmospheric profiles from radiosondes in Fram Strait (August–Septmber 2017) were not transmitted to GTSERA5 simulates observed atmospheric profiles more accurately than ERA‐Interim, JRA‐55, CFSv2, and MERRA‐2Largest improvements are found in ERA5 for wind and temperature profiles over warmer eastern Fram Strait [ABSTRACT FROM AUTHOR]

Ground-based measurements of the hemispherical-directional reflectance factor (HDRF) of windblown snow-covered Arctic tundra were measured at large solar zenith angles ( 79^\circ– 85^\circ ) for six sites near the international research base in Ny-Ålesund, Svalbard. Measurements were made with the Gonio RAdiometric Spectrometer System over the viewing angles 0^\circ– 50^\circ and the azimuth angles 0^\circ– 360^\circ , for the wavelength range 400–1700 nm. The HDRF measurements showed good consistency between sites for near-nadir and backward viewing angles, with a relative standard deviation of less than 10% between sites where the snowpack was smooth and the snow depth was greater than 40 cm. The averaged HDRF showed good symmetry with respect to the solar principal plane and exhibited a forward scattering peak that was strongly wavelength dependent, with greater than a factor of 2 increase in the ratio of maximum to minimum HDRF values for all viewing angles over the wavelength range 400–1300 nm. The angular effects on the HDRF had minimal influence for viewing angles less than 15^\circ in the backward viewing direction for the averaged sites and agreed well with another study of snow HDRF for infrared wavelengths, but showed differences of up to 0.24 in the HDRF for visible wavelengths owing to light-absorbing impurities measured in the snowpack. The site that had the largest roughness elements showed the strongest anisotropy in the HDRF, a large reduction in forward scattering, and a strong asymmetry with respect to the solar principal plane. [ABSTRACT FROM PUBLISHER]

Abstract: In this work, a closure experiment for tropospheric aerosol is presented. Aerosol size distributions and single scattering albedo from remote sensing data are compared to those measured in-situ. An aerosol pollution event on 4 April 2009 was observed by ground based and airborne lidar and photometer in and around Ny-Ålesund, Spitsbergen, as well as by DMPS, nephelometer and particle soot absorption photometer at the nearby Zeppelin Mountain Research Station. The presented measurements were conducted in an area of 40 × 20 km around Ny-Ålesund as part of the 2009 Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP). Aerosol mainly in the accumulation mode was found in the lower troposphere, however, enhanced backscattering was observed up to the tropopause altitude. A comparison of meteorological data available at different locations reveals a stable multi-layer-structure of the lower troposphere. It is followed by the retrieval of optical and microphysical aerosol parameters. Extinction values have been derived using two different methods, and it was found that extinction (especially in the UV) derived from Raman lidar data significantly surpasses the extinction derived from photometer AOD profiles. Airborne lidar data shows volume depolarization values to be less than 2.5% between 500 m and 2.5 km altitude, hence, particles in this range can be assumed to be of spherical shape. In-situ particle number concentrations measured at the Zeppelin Mountain Research Station at 474 m altitude peak at about 0.18 μm diameter, which was also found for the microphysical inversion calculations performed at 850 m and 1500 m altitude. Number concentrations depend on the assumed extinction values, and slightly decrease with altitude as well as the effective particle diameter. A low imaginary part in the derived refractive index suggests weakly absorbing aerosols, which is confirmed by low black carbon concentrations, measured at the Zeppelin Mountain as well as on board the Polar 5 aircraft. [Copyright &y& Elsevier]