Spatiotemporal variability of solar radiation introduced by clouds over Arctic sea ice

Abstract

Abstract. The role of clouds in recent Arctic warming is not fully understood, including their effects on the solar radiation and the surface energy budget. To investigate relevant small-scale processes in detail, the intensive Physical feedbacks of Arctic planetary boundary layer, Sea ice, Cloud and AerosoL (PASCAL) drifting ice floe station field campaign was conducted during early summer in the central arctic. During this campaign, the small-scale spatiotemporal variability of global irradiance was observed for the first time on an ice floe with a dense network of autonomous pyranometers. A total of 15 stations were deployed covering an area of 0.83 km×1.59 km from 4–16 June 2017. This unique, open-access dataset is described here, and an analysis of the spatiotemporal variability deduced from this dataset is presented for different synoptic conditions. Based on additional observations, five typical sky conditions were identified and used to determine the values of the mean and variance of atmospheric global transmittance for these conditions. Overcast conditions were observed 39.6 % of the time predominantly during the first week, with an overall mean transmittance of 0.47. The second most frequent conditions corresponded to multilayer clouds (32.4 %), which prevailed in particular during the second week, with a mean transmittance of 0.43. Broken clouds had a mean transmittance of 0.61 and a frequency of occurrence of 22.1 %. Finally, the least frequent sky conditions were thin clouds and cloudless conditions, which both had a mean transmittance of 0.76 and occurrence frequencies of 3.5 % and 2.4 %, respectively. For overcast conditions, lower global irradiance was observed for stations closer to the ice edge, likely attributable to the low surface albedo of dark open water and a resulting reduction of multiple reflections between the surface and cloud base. Using a wavelet-based multi-resolution analysis, power spectra of the time series of atmospheric transmittance were compared for single-station and spatially averaged observations and for different sky conditions. It is shown that both the absolute magnitude and the scale dependence of variability contains characteristic features for the different sky conditions.

Application of the shipborne remote sensing supersite OCEANET for profiling of Arctic aerosols and clouds during <i>Polarstern</i> cruise PS106

“…Values range from 20 to 60 µm, with a peak at around 50 µm. This is consistent with other studies of ice effective radius (e.g., Blanchard et al, 2017).…”

Seasonal and interannual variations in the propagation of photosynthetically available radiation through the Arctic atmosphere

“…We did not compute E d (PAR, 0 þ ) when cloud fraction, cloud optical thickness, or surface albedo were not available, which generally occurred over land-dominated pixels or near the North Pole where satellite orbit inclination limits data availability. When cloud fraction, cloud optical thickness and surface albedo were available, but cloud top height, ozone, water vapor content or AOD were not, missing values of the latter were replaced by climatological values, as these geophysical variables are not the main drivers of variations in E d (PAR, 0 þ ) in the Arctic (Barrientos Velasco et al, 2020). We calculated the daily climatology on a pixel basis from all available values over the 17-year MODIS data set.…”

Lipidome Plasticity Enables Unusual Photosynthetic Flexibility in Arctic vs. Temperate Diatoms

“…The potential for variability in the light environment of marine diatoms, and thus the need for photoacclimative responses, is greater in polar regions due to the strong seasonality (i.e., polar day and night cycles), high frequency of cloud cover, presence of attenuating sea ice cover, as well as high solar zenith angle of downwelling [18,19]. As a result, numerous studies have demonstrated enhanced dark survival and low irradiance requirements of Arctic diatoms [20,21], in addition to niche-dependent nonphotochemical quenching strategies [22].…”