The Arctic climate is influenced by the interaction of shortwave (SW) and longwave (LW) radiation with the atmosphere and the surface. The comprehensive evolution of the Surface Radiative Fluxes (SRF) on different time scales is of paramount importance to understanding the complex mechanisms governing the Arctic climate. However, only a few sites located in the Arctic region provide long-term time series of SRF allowing for capturing of the seasonality of atmospheric and surface parameters and for carrying out validation of satellite products and/or reanalyses. This paper presents the daily and monthly SRF record collected at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W), in North-Western Greenland. The downwelling components of the SW (DSI) and the LW (DLI) irradiances have been measured at THAAO since 2009, whereas the collection of the upwelling SW (USI) and LW (ULI) irradiance was started in 2016, together with additional measurements, such as meteorological parameters and column water vapour. The datasets of DSI (Meloni et al., 2022a; 10.13127/thaao/dsi), USI (Meloni et al., 2022b; 10.13127/thaao/usi), DLI (Meloni et al., 2022c; 10.13127/thaao/dli), ULI (Meloni et al., 2022d; 10.13127/thaao/uli), and near-surface air temperature (Muscari et al., 2018; 10.13127/thaao/met), can be accessed through the THAAO web site (https://www.thuleatmos-it.it/data, last access: 16 January 2024). The DSI is absent (solar zenith angle ≥90° ) from 29 October to 13 February, assuming maxima in June (monthly mean of 277.0Wm-2), when it is about half of the total incoming irradiance. The USI maximum occurs in May (132.4Wm-2) owing to the combination of moderately high DSI values and high albedo. The shortwave surface albedo (A) assumes an average of 0.16 during summer, when the surface is free of snow. Differently, during months of snow-covered surface, when solar radiation allows A to be estimated, its values are greater than 0.6. A large interannual variability is observed in May and September, months characterized by rapidly changing surface conditions, having a link with air temperature anomalies. The DLI and ULI maxima occur in July and August, and the minima in February and March. ULI is always larger than DLI and shows a wider annual cycle. ULI is well described by a fourth-order polynomial fit to the air temperature (R2>0.99 for monthly data and R2>0.97 for daily data). The Surface Radiation Budget (SRB) is positive from April to August, when absorption of solar radiation exceeds the infrared net cooling, with a maximum value of 153.2Wm-2 in June. From November to February, during the polar night, the LW net flux varies between -34.5 and -43.0Wm-2. In March and September, the negative LW net flux overcomes the positive SW contribution, producing a negative SRB. The THAAO measurements show clear evidence of the influence of several regional weather/climate events, that appear strongly linked with SRF anomalies. These anomalies were found, for example, during summer 2012, when a large ice melting event took place over Greenland, and during winter 2019-2020, which was extraordinarily cold in the Arctic region. © 2024 Daniela Meloni et al.

Export Date: 15 February 2024Correspondence Address: Meloni, D.; Italian National Agency for New Technologies, Italy; email: daniela.meloni@enea.itFunding details: National Science Foundation, NSFFunding details: Istituto Nazionale di Geofisica e Vulcanologia, INGVFunding details: Dipartimento di Matematica e Informatica, Università degli Studi di Catania, DMI, UNICTFunding text 1: The Thule High Arctic Atmospheric Observatory (THAAO, 76.5 N, 68.8 W, 220 m a.m.s.l.) was set up in the 1990s with a collaborative effort of Italian and Danish institutions: the Danish Meteorological Institute (DMI), the University of Rome “Sapienza”, and the Italian National Agency for New Technologies, Energy, and Sustainable Economic Development (ENEA). In 1999, the National Center for Atmospheric Research (NCAR) joined the collaboration followed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in 2009. The collaboration between DMI, at that time already involved with measures dedicated to the study of the Arctic climate at the Thule Air Base, and the Italian institutions started with the installation of an aerosol/Rayleigh lidar by the University of Rome in addition to the DMI instruments (ozonesondes and UV/visible spectrometer), to improve knowledge of the stratospheric ozone depletion phenomenon that was observed to be very intense over Antarctica and also anticipated to become important over the Arctic (Muscari et al., 2014). In 2017, DMI ceased its activities at THAAO, and the Observatory is now managed by the US National Science Foundation (NSF).Funding text 2: This research has been supported by the Italian Antarctic research program (PNRA) through the Clouds And Radiation in the Arctic and Antarctica (CLARA2) project, and by the Italian Arctic Research Programme (PRA) through the Effects of Changing Albedo and Precipitation on the Arctic Climate (ECAPAC) project. Both PNRA and PRA are directed by the Ministry of University and Research. The Italian activities at THAAO have been supported by the Istituto Nazionale di Geofisica e Vulcanologia (Environment Department) within the framework of the Multidisciplinary Analysis of Climate change indicators in the Mediterranean And Polar regions (MACMAP) project.Funding text 3: Authors acknowledge the United States Space Force and Pituffik Space Base for hosting THAAO. In particular, the collaboration of Charles Klinger, Jeffrey Villa, and Otto Lee in the management of the instruments at THAAO is greatly appreciated. We thank the National Science Foundation for providing services at THAAO and the Polar Field Services for the logistic support.Funding text 4: This research has been supported by the Italian Antarctic research program (PNRA) through the Clouds And Radiation in the Arctic and Antarctica (CLARA2) project, and by the Italian Arctic Research Programme (PRA) through the Effects of Changing Albedo and Precipitation on the Arctic Climate (ECAPAC) project. Both PNRA and PRA are directed by the Ministry of University and Research. The Italian activities at THAAO have been supported by the Istituto Nazionale di Geofisica e Vulcanologia (Environment Department) within the framework of the Multidisciplinary Analysis of Climate change indicators in the Mediterranean And Polar regions (MACMAP) project.