Climate change occurs more rapidly at high latitudes, making polar ecosystems highly vulnerable to environmental changes. Plants respond to these conditions by altering the fluxes of water vapor (H2O) and carbon dioxide (CO2). This study analyzed the seasonal variability of the Net Ecosystem Exchange (NEE) of CO2, as well as the sensible (H) and latent (LE) heat fluxes, in two ecosystems in north-central Siberia: a subarctic palsa mire near Igarka, and a mature larch forest near Tura. The flux responses to variations in atmospheric parameters were also assessed. Experimental data were collected from 2019 to 2023 using eddy covariance methods. The results showed that both permafrost ecosystems consistently served as net atmospheric CO2 sinks during the growing seasons, despite significant year-to-year meteorological variations. From 2019 to 2023, summer NEE ranged from -62.9 to -120.2 gC m-2 in the Igarka palsa mire and from -63.5 to -83.6 gC m-2 in the Tura larch forest. During summer periods characterized by prolonged insufficient soil moisture, higher air temperatures, and limited precipitation, the palsa mire exhibited reduced CO2 uptake (i.e., less negative NEE) and Gross Primary Production (GPP) compared to the larch forest. These results suggest that larch forests may be more resilient to climate change than palsa mires. This resilience is primarily linked to deep-rooted water access and conservative stomatal control in larch, whereas palsa mire vegetation depends strongly on surface moisture availability. H and LE fluxes exhibited significant interannual variations, primarily due to variations in incoming solar radiation and precipitation. No significant LE decrease occurred during periods of low precipitation in 2019 and 2020 when drought conditions were observed at both stations during the summer. Maximum H and LE flux rates occurred in June and July when net radiation values were at their maximum for both ecosystems. These findings underscore the urgent need for ecosystem-specific climate strategies, as differential resilience could significantly impact future carbon dynamics in the rapidly warming Arctic.

The impact of moderately absorbing aerosols on the energy budget over Central Europe is discussed, based on experimental observations and numerical simulations obtained for the summer of 2015. Aerosol events, defined as aerosol optical depth (AOD) at 500 nm greater than 0.15, especially in August, are mostly attributed to transport of biomass burning (BB) from Eastern Europe. Shortwave (SW) aerosol radiative forcings (ARF) at the surface and the top of the atmosphere (TOA) are estimated from ensembles of ten and eight observational and model-based approaches, respectively. Different measuring methods, including unmanned aviation system (UAS) and ground-based measurements, radiative transfer models, including MOTRAN and FuLiou, and parameterisations of aerosol optical properties regarding full vertical profiles, columnar and surface properties, are used in these approaches. The mean ARF is-15.9 +/- 2.1 W/ m2,-9.1 +/- 1.4 W/m2, and 7.0 +/- 1.0 W/m2, respectively, for the Earth's surface, TOA, and atmosphere under clear conditions for June-August 2015. During an aerosol event with AOD peak of about 0.6 at 500 nm, the daily mean surface, TOA, and atmosphere ARF are around-30,-18, and 13 W/m2, respectively. The mean ARF differences between all methods are about 4.0 W/m2 for the surface and about 2.3 W/m2 for the TOA, which correspond to 23% of ensemble means. Aerosols are also shown to have a significant impact on observed surface sensible and latent heat fluxes for the study period. Flux sensitivity to AOD for a solar zenith angle of 45? is-70 +/- 41 W/ m2/tau 500,-112 +/- 56 W/m2/tau 500, and-119 +/- 19 W/m2/tau 500, respectively, for sensible, latent, and net SW and longwave (LW) radiation flux. When averaged over day time, sensitivities of sensible heat, latent heat fluxes, and net radiation fluxes to AOD are reduced by about 50%, 20%, and 70%, respectively.

Global warming will bring about changes in surface energy balance of Arctic ecosystems, which will have implications for ecosystem structure and functioning, as well as for climate system feedback mechanisms. In this study, we present a unique, long-term (2000-2010) record of summer-time energy balance components (net radiation, R-n; sensible heat flux, H; latent heat flux, LE; and soil heat flux, G) from a high Arctic tundra heath in Zackenberg, Northeast Greenland. This area has been subjected to strong summer-time warming with increasing active layer depths (ALD) during the last decades. We observe high energy partitioning into H, low partitioning into LE and high Bowen ratio (beta = H/LE) compared with other Arctic sites, associated with local climatic conditions dominated by onshore winds, slender vegetation with low transpiration activity and relatively dry soils. Surface saturation vapour pressure deficit (D-s) was found to be an important variable controlling within-year surface energy partitioning. Throughout the study period, we observe increasing H/R-n and LE/R-n and decreasing G/R-n and beta, related to increasing ALD and decreasing soil wetness. Thus, changes in summer-time surface energy balance partitioning in Arctic ecosystems may be of importance for the climate system.